Category Archives: Spacecraft and Missions

Strange Things are Happening Underground

In the last month, there have been reports of some very unexpected things happening under the surface of the earth. I’m talking about subduction plates that maintain their structure as they dive toward the Earth’s core and “jet streams” in the Earth’s core itself. Let’s take a look at these interesting phenomena.

What happens to subduction plates?

Oceanic tectonic plates are formed as magma wells up along mid-ocean ridges, forming new lithospheric rock that spread away from both sides of the ridge, building two different tectonic plates. This is known as a divergent plate boundary.

As tectonic plates move slowly across the Earth’s surface, each one moves differently than the adjacent plates. In simple terms, this relative motion at the plate interfaces is either a slipping, side-by-side (transform) motion, or a head-to-head (convergent) motion.

A map of the Earth showing the tectonic plates and the nature of the relative motion at the plate interfaces is shown below (click on the image to enlarge).

ESRT Page5

Source: http://www.regentsearth.com/

When two tectonic plate converge, one will sink under (subduct) the other. In the case of an oceanic plate converging with a continental plate, the heavier oceanic plate always sinks under the continental plate and may cause mountain building along the edge of the continental plate. When two oceanic plates converge, one will subduct the other, creating a deep mid-ocean trench (i.e., Mariana trench) and possibly forming an arc of islands on the overriding plate (i.e., Aleutian Islands and south Pacific island chains). In the diagram above, you can see that some subduction zones are quite long.

subd_zoneSource: http://www.columbia.edu/~vjd1/subd_zone_basic.htm

The above diagram shows the subducting material from an oceanic plate descending deep into the Earth beneath the overriding continental plate.  New research indicates that the subducting plates maintain their structure to a considerable depth below the surface of the Earth.

On 22 November 2016, an article by Paul Voosen, “’Atlas of the Underworld’ reveals oceans and mountains lost to Earth’s history,” was posted on the sciencemag.org website. The author reports:

“A team of Dutch scientists will announce a catalog of 100 subducted plates, with information about their age, size, and related surface rock records, based on their own tomographic model and cross-checks with other published studies.”

“…geoscientists have begun ….peering into the mantel itself, using earthquake waves that pass through Earth’s interior to generate images resembling computerized tomography (CT) scans. In the past few years, improvements in these tomographic techniques have revealed many of these cold, thick slabs as they free fall in slow motion to their ultimate graveyard—heaps of rock sitting just above Earth’s molten core, 2900 kilometers below.”

The following concept drawing illustrates how a CT scan of the whole Earth might look, with curtains of subducting material surrounding the molten core.

Atlas_1121_1280x720Source: Science / Fabio Crameri

The author notes that research teams around the world are using more than 20 different models to interpret similar tomographic data. As you might expect, results differ. However, a few points are consistent:

  • The subducting slabs in the upper mantle appear to be stiff, straight curtains of lithospheric rock
  • These slabs may flex but they don’t crumble.
  • These two features make it possible to “unwind” the geologic history of individual tectonic slabs and develop a better understanding of the route each slab took to its present location.
  • The geologic history in subducting slabs only stretches back about 250 million years, which is the time it takes for subducting material to fall from the surface to the bottom of the mantle and be fully recycled.

You can read the fill article by Paul Voosen at the following link:

http://www.sciencemag.org/news/2016/11/atlas-underworld-reveals-oceans-and-mountains-lost-earths-history

Hopefully, the “Atlas of the Underworld” will help focus the dialogue among international research teams toward collaborative efforts to improve and standardize the processes and models for building an integrated CT model of our Earth.

A “jet stream” in the Earth’s core

The European Space Agency (ESA) developed the Swarm satellites to make highly accurate and frequent measurements of Earth’s continuously changing magnetic field, with the goal of developing new insights into our planet’s formation, dynamics and environment. The three-satellite Swarm mission was launched on 22 November 2013.

3 satellite SWARMSwarm satellites separating from Russian booster. Source: ESA

ESA’s website for the Swarm mission is at the following link:

http://www.esa.int/Our_Activities/Observing_the_Earth/Swarm/From_core_to_crust

Here ESA explains the value of the measurements made by the Swarm satellites.

“One of the very few ways of probing Earth’s liquid core is to measure the magnetic field it creates and how it changes over time. Since variations in the field directly reflect the flow of fluid in the outermost core, new information from Swarm will further our understanding of the physics and dynamics of Earth’s stormy heart.

The continuous changes in the core field that result in motion of the magnetic poles and reversals are important for the study of Earth’s lithosphere, also known as the ‘crustal’ field, which has induced and remnant magnetized parts. The latter depend on the magnetic properties of the sub-surface rock and the history of Earth’s core field.

We can therefore learn more about the history of the magnetic field and geological activity by studying magnetism in Earth’s crust. As new oceanic crust is created through volcanic activity, iron-rich minerals in the upwelling magma are oriented to magnetic north at the time.

These magnetic stripes are evidence of pole reversals so analyzing the magnetic imprints of the ocean floor allows past core field changes to be reconstructed and also helps to investigate tectonic plate motion.”

Data from the Swarm satellites indicates that the liquid iron part of the Earth’s core has an internal, 420 km (261 miles) wide “jet stream” circling the core at high latitude at a current speed of about 40 km/year (25 miles/year) and accelerating. In geologic terms, this “jet stream” is significantly faster than typical large scale flows in the core. The basic geometry of this “jet stream” is shown in the following diagram.

jet-stream-earth-core-ESA-e1482190909115Source: ESA

These results were published on 19 December 2016 in the article, An accelerating high-latitude jet in Earth’s core,” on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2859.html

A subscription is required for access to the full paper.

The Swarm mission is ongoing. Watch the ESA’s mission website for more news.

The Vision for Manned Exploration and Colonization of Mars is Alive Again

On 25 May 1961, President John F. Kennedy made an important speech to a joint session of Congress in which he stated:

“I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth.”

This was a very bold statement considering the state-of-the-art of U.S. aerospace technology in mid-1961. Yuri Gagarin became the first man to orbit the Earth on 12 April 1961 in a Soviet Vostok spacecraft and Alan Shepard completed the first Project Mercury suborbital flight on 5 May 1961. No American had yet flown in orbit. It wasn’t until 20 February 1962 that the first Project Mercury capsule flew into Earth orbit with astronaut John Glenn. The Soviets had hit the Moon with Luna 2 and returned photos from the backside of the moon with Luna 3. The U.S had only made one distant lunar flyby with the tiny Pioneer 4 spacecraft. The Apollo manned lunar program was underway, but still in the concept definition phase. The first U.S. heavy booster rocket designed to support the Apollo program, the Saturn 1, didn’t fly until 27 October 1961.

President Kennedy concluded this part of his 25 May 1961 speech with the following admonition:

“This decision (to proceed with the manned lunar program) demands a major national commitment of scientific and technical manpower, materiel and facilities, and the possibility of their diversion from other important activities where they are already thinly spread. It means a degree of dedication, organization and discipline, which have not always characterized our research and development efforts. It means we cannot afford undue work stoppages, inflated costs of material or talent, wasteful interagency rivalries, or a high turnover of key personnel.

New objectives and new money cannot solve these problems. They could in fact, aggravate them further–unless every scientist, every engineer, every serviceman, every technician, contractor, and civil servant gives his personal pledge that this nation will move forward, with the full speed of freedom, in the exciting adventure of space.”

This was the spirit that lead to the great success of the Apollo program, which landed the first men on the Moon, astronauts Neil Armstrong and Ed Aldrin, on 20 July 1969; a little more than 8 years after President Kennedy’s speech.

NASA’s plans for manned Mars exploration

By 1964, exciting concepts for manned Mars exploration vehicles were being developed under National Aeronautics and Space Administration (NASA) contract by several firms. One example is a Mars lander design shown below from Aeronutronic (then a division of Philco Corp). A Mars Excursion Module (MEM) would descend to the surface of Mars from a larger Mars Mission Module (MMM) that remained in orbit. The MEM was designed for landing a crew of three on Mars, spending 40 days on the Martian surface, and then returning the crew back to Mars orbit and rendezvousing with the MMM for the journey back to Earth.

1963 Aeronutronic Mars lander conceptSource: NASA / Aviation Week 24Feb64

This and other concepts developed in the 1960s are described in detail in Chapters 3 – 5 of NASA’s Monograph in Aerospace History #21, “Humans to Mars – Fifty Years of Mission Planning, 1950 – 2000,” which you can download at the following link:

http://www.nss.org/settlement/mars/2001-HumansToMars-FiftyYearsOfMissionPlanning.pdf

In the 1960’s the U.S. nuclear thermal rocket development program led to the development of the very promising NERVA nuclear engine for use in an upper stage or an interplanetary spacecraft. NASA and the Space Nuclear Propulsion Office (SNPO) felt that tests had “confirmed that a nuclear rocket engine was suitable for space flight application.”

In 1969, Marshall Space Flight Director Wernher von Braun propose sending 12 men to Mars aboard two rockets, each propelled by three NERVA engines. This spacecraft would have measured 270 feet long and 100 feet wide across the three nuclear engine modules, with a mass of 800 tons, including 600 tons of liquid hydrogen propellant for the NERVA engines. The two outboard nuclear engine modules only would be used to inject the spacecraft onto its trans-Mars trajectory, after which they would separate from the spacecraft. The central nuclear engine module would continue with the manned spacecraft and be used to enter and leave Mars orbit and enter Earth orbit at the end of the mission. The mission would launch in November 1981 and land on Mars in August 1982.

Marshall 1969 NERVA mars missionNERVA-powered Mars spacecraft. Source: NASA / Monograph #21

NASA’s momentum for conducting a manned Mars mission by the 1980s was short-lived. Development of the super heavy lift Nova booster, which was intended to place about 250 tons to low Earth orbit (LEO), was never funded. Congress reduced NASA’s funding in the FY-69 budget, resulting in NASA ending production of the Saturn 5 heavy-lift booster rocket (about 100 tons to LEO) and cancelling Apollo missions after Apollo 17. This left NASA without the heavy-lift booster rocket needed to carry NERVA and/or assembled interplanetary spacecraft into orbit.

NASA persevered with chemical rocket powered Mars mission concepts until 1971. The final NASA concept vehicle from that era, looking much like von Braun’s 1969 nuclear-powered spacecraft, is shown below.

NASA 1971 mars concept

Source: NASA / Monograph #21

The 24-foot diameter modules would have required six Shuttle-derived launch vehicles (essentially the large center tank and the strap-in solid boosters, without the Space Shuttle itself) to deliver the various modules for assembly in orbit.

While no longer a factor in Mars mission planning, the nuclear rocket program was canceled in 1972. You can read a history of the U.S. nuclear thermal rocket program at the following links:

http://www.lanl.gov/science/NSS/issue1_2011/story4full.shtml

and,

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19910017902.pdf

NASA budget realities in subsequent years, dictated largely by the cost of Space Shuttle and International Space Station development and operation, reduced NASA’s manned Mars efforts to a series of design studies, as described in the Monograph #21.

Science Applications International Corporation (SAIC) conducted manned Mars mission studies for NASA in 1984 and 1987. The latter mission design study was conducted in collaboration with astronaut Sally Ride’s August 1987 report, Leadership and America’s Future in Space. You can read this report at the following link.

http://history.nasa.gov/riderep/cover.htm

Details on the 1987 SAIC mission study are included in Chapter 8 of the Monograph #21. SAIC’s mission concept employed two chemically-fueled Mars spacecraft in “split/sprint” roles. An automated cargo-carrying spacecraft would be first to depart Earth. It would fly an energy-saving trajectory and enter Mars orbit carrying the fuel needed by the future manned spacecraft for its return to Earth. After the cargo spacecraft was in Mars orbit, the manned spacecraft would be launched on a faster “sprint” trajectory, taking about six months to get to Mars. With one month allocated for exploration of the Martian surface, total mission time would be on the order of 12 – 14 months.

President Obama’s FY-11 budget redirected NASA’s focus away from manned missions to the Moon and Mars. The result is that there are no current programs with near-term goals to establish a continuous U.S. presence on the Moon or conduct the first manned mission to Mars. Instead, NASA is engaged in developing hardware that will be used initially for a relatively near-Earth (but further out than astronauts have gone before) “asteroid re-direct mission.” NASA’s current vision for getting to Mars is summarized below.

  • In the 2020s, NASA will send astronauts on a year-long mission into (relatively near-Earth) deep space, verifying spacecraft habitation and testing our readiness for a Mars mission.
  • In the 2030s, NASA will send astronauts first to low-Mars orbit. This phase will test the entry, descent and landing techniques needed to get to the Martian surface and study what’s needed for in-situ resource utilization.
  • Eventually, NASA will land humans on Mars.

You can read NASA’s Journey to Mars Overview at the following link:

https://www.nasa.gov/content/journey-to-mars-overview

NASA’s current plans for getting to Mars don’t really sound like much of a plan to me. Think back to President Kennedy’s speech that outlined the national commitment needed to accomplish a lunar landing within the decade of the 1960s. There is no real sense of timeliness in NASA plans for getting to Mars.

Thinking back to the title of NASA’s Monograph #21, “Humans to Mars – Fifty Years of Mission Planning, 1950 – 2000,” I’d say that NASA is quite good at manned Mars mission planning, but woefully short on execution. I recognize that NASA’s ability to execute anything is driven by its budget. However, in 1969, Wernher von Braun thought the U.S. was about 12 years from being able to launch a nuclear-powered manned Mars mission in 1981. Now it seems we’re almost 20 years away, with no real concept for the spacecraft that will get our astronauts there and back.

Commercial plans for manned Mars exploration

Fortunately, the U.S. commercial aerospace sector seems more committed to conducting manned Mars missions than NASA. The leading U.S. contenders are Bigelow Aerospace and SpaceX. Let’s look at their plans.

Bigelow Aerospace

Bigelow is developing expandable structures that can be used to house various types of occupied spaces on manned Earth orbital platforms or on spacecraft destined for lunar orbital missions or long interplanetary missions. Versions of these expandable structures also can be used for habitats on the surface of the Moon, Mars, or elsewhere.

The first operational use of this type of expandable structure in space occurred on 26 May 2016, when the BEAM (Bigelow Expandable Activity Module) was deployed to its full size on the International Space Station (ISS). BEAM was expanded by air pressure from the ISS.

Bigelow BEAMBEAM installed in the ISS. Source: Bigelow Aerospace

You can view a NASA time-lapse video of BEAM deployment at the following link:

https://www.youtube.com/watch?v=QxzCCrj5ssE

A large, complex space vehicle can be built with a combination of relatively conventional structures and Bigelow inflatable modules, as shown in the following concept drawing.

Bigelow spacecraft conceptSource: Bigelow Aerospace

A 2011 NASA concept named Nautilus-X, also making extensive use of inflatable structures, is shown in the following concept drawing. Nautilus is an acronym for Non-Atmospheric Universal Transport Intended for Lengthy United States Exploration.

NASA Nautilus-X-space-exploration-vehicle-concept-1

Source: NASA / NASA Technology Applications Assessment Team

SpaceX

SpaceX announced that it plans to send its first Red Dragon capsule to Mars in 2018 to demonstrate the ability to land heavy loads using a combination of aero braking with the capsule’s ablative heat shield and propulsive braking using rocket engines for the final phase of landing.

Red Dragon landing on MarsSource: SpaceX

More details on the Red Dragon spacecraft are in a 2012 paper by Karcs, J. et al., entitled, “Red Dragon: Low-cost Access to the Surface of Mars Using Commercial Capabilities,” which you’ll find at the following link:

https://www.nas.nasa.gov/assets/pdf/staff/Aftosmis_M_RED_DRAGON_Low-Cost_Access_to_the_Surface_of_Mars_Using_Commercial_Capabilities.pdf

NASA is collaborating with SpaceX to gain experience with this landing technique, which NASA expects to employ in its own future Mars missions.

On 27 September 2016, SpaceX CEO Elon Musk unveiled his grand vision for colonizing Mars at the 67th International Astronautical Congress in Guadalajara, Mexico. You’ll find an excellent summary in the 29 September 2016 article by Dave Mosher entitled, “Elon Musk’s complete, sweeping vision on colonizing Mars to save humanity,” which you can read on the Business Insider website at the following link:

http://www.businessinsider.com/elon-musk-mars-speech-transcript-2016-9

The system architecture for the SpaceX colonizing flights is shown in the following diagram. Significant features include:

  • 100 passengers on a one-way trip to Mars
  • Booster and spacecraft are reusable
  • No spacecraft assembly in orbit required.
  • The manned interplanetary vehicle is fueled with methane in Earth orbit from a tanker spacecraft.
  • The entire manned interplanetary vehicle lands on Mars. There is no part of the vehicle left orbiting Mars.
  • The 100 passengers disembark to colonize Mars
  • Methane fuel for the return voyage to Earth is manufactured on the surface of Mars.
  • The spacecraft returns to Earth for reuse on another mission.
  • Price per person for Mars colonists could be in the $100,000 to $200,000 range.

The Mars launcher for this mission would have a gross lift-off mass of 10,500 tons; 3.5 times the mass of NASA’s Saturn 5 booster for the Apollo Moon landing program.

SpaceX colonist architectureSource: SpaceX

 Terraforming Mars

Colonizing Mars will require terraforming to transform the planet so it can sustain human life. Terraforming the hostile environment of another planet has never been done before. While there are theories about how to accomplish Martian terraforming, there currently is no clear roadmap. However, there is a new board game named, “Terraforming Mars,” that will test your skills at using limited resources wisely to terraform Mars.

Nate Anderson provides a detailed introduction to this board game in his 1 October 2016 article entitled, “Terraforming Mars review: Turn the ‘Red Planet’ green with this amazing board game,” which you can read at the following link:

http://arstechnica.com/gaming/2016/10/terraforming-mars-review/?utm_source=howtogeek&utm_medium=email&utm_campaign=newsletter

71RW5ZM0bBL._SL1000_Source: Stronghold GamesTerraforming Mars gameboardSource: Nate Anderson / arsTECHNICA

Nate Anderson described the game as follows:

“In Terraforming Mars, you play one of several competing corporations seeking to terraform the Red Planet into a livable—indeed, hospitable—place filled with cows, dogs, fish, lichen, bacteria, grasslands, atmosphere, and oceans. That goal is achieved when three things happen: atmospheric oxygen rises to 14 percent, planetary temperature rises to 8°C, and all nine of the game’s ocean tiles are placed.

Real science rests behind each of these numbers. The ocean tiles each represent one percent coverage of the Martian surface; once nine percent of the planet is covered with water, Mars should develop its own sustainable hydrologic cycle. An atmosphere of 14 percent oxygen is breathable by humans (though it feels like a 3,000 m elevation on Earth). And at 8°C, water will remain liquid in the Martian equatorial zone.

Once all three milestones have been achieved, Mars has been successfully terraformed, the game ends, and scores are calculated.”

The players are competing corporations, each with limited resources. The game play evolves based how each player (corporation) chooses to spend their resources to build their terraforming engines (constrained by some rules of precedence), and the opportunities dealt to them in each round.

You can buy the game Terraforming Mars on Amazon.

So, before you sign up with SpaceX to become a Martian colonist, practice your skills at terraforming Mars. You’ll be in high demand as an expert terraformer when you get to Mars on a SpaceX colonist ship in the late 2020s.

 

 

 

 

 

Rosetta Spacecraft Lands on Comet 67P, Completing its 12-Year Mission

The European Space Agency (ESA) launched the Rosetta mission in 2004. After its long journey from Earth, followed by 786 days in orbit around comet 67P / Churyumov–Gerasimenko, the Rosetta spacecraft managers maneuvered the spacecraft out of its orbit and directed it to a “hard” landing on the “head” (the smaller lobe) of the comet.

Comet_67P_15_April_2015Comet 67P. Source: ESA – European Space Agency

The descent path, which started from an altitude of 19 km (11.8 miles), was designed to bring Rosetta down in the vicinity of active pits that had been observed from higher altitude earlier in the mission. ESA noted:

  • The descent gave Rosetta the opportunity to study the comet’s gas, dust and plasma environment very close to its surface, as well as take very high-resolution images.
  • Pits are of particular interest because they play an important role in the comet’s activity (i.e., venting gases to space).

The spacecraft impacted at a speed of about 90 cm/sec (about 2 mph) at 11:19 AM GMT (4:19 AM PDT) on 30 September 2016. I stayed up in California to watch the ESA’s live stream of the end of this important mission. I have to say that the live stream was not designed as a media event. As the landing approached, only a few close-up photos of the surface were shown, including the following photo taken from an altitude of about 5.7 km (3.5 miles).

Comet 67P 30Sep2016Source: ESA – European Space Agency

At the appointed moment, touchdown was marked by the loss of the telemetry signal from Rosetta. ESA said that the Rosetta spacecraft contained a message in many languages for some future visitor to 67P to find.

You can read the ESA’s press release on the end of the Rosetta mission at the following link:

http://www.esa.int/For_Media/Press_Releases/Mission_complete_Rosetta_s_journey_ends_in_daring_descent_to_comet

Some of the key Rosetta mission findings reported by ESA include:

  • Comet 67P likely was “born” in a very cold region of the protoplanetary nebula when the Solar System was still forming more than 4.5 billion years ago.
  • The comet’s two lobes probably formed independently, joining in a low-speed collision in the early days of the Solar System.
  • The comet’s shape influences its “seasons,” which are characterized by variations in dust moving across its surface and variations in the density and composition of the coma, the comet’s ‘atmosphere’.
  • Gases streaming from the comet’s nucleus include molecular oxygen and nitrogen, and water with a different ‘flavor’ than water in Earth’s oceans.
    • 67P’s water contains about three times more deuterium (a heavy form of hydrogen) than water on Earth.
    • This suggests that comets like Rosetta’s may not have delivered as much of Earth’s water as previously believed.
  • Numerous inorganic chemicals and organic compounds were detected by Rosetta (from orbit) and the Philae lander (on the surface). These include the amino acid glycine, which is commonly found in proteins, and phosphorus, a key component of DNA and cell membranes.

Analysis of data from the Rosetta mission will continue for several years. It will be interesting to see how our understanding of comet 67P and similar comets evolve in the years ahead.

For more information on the Rosetta mission, visit the ESA’s Rosetta website at the following link:

http://sci.esa.int/rosetta/

Also see my following postings: 24 August 2016, “Exploring Microgravity Worlds,” and 6 September 2016, “Philae Found in a Rocky Ditch on Comet 67P/Churyumov-Gerasimenko.”

 

Space-based Gravity Wave Detection System to be Deployed by ESA

The first detection of gravitational waves occurred on 14 September 2015 at the land-based Laser Interferometer Gravitational-Wave Observatory (LIGO). Using optical folding techniques, LIGO has an effective baseline of 1,600 km (994 miles). See my 16 December 2015 and 11 February 2016 posts for more information on LIGO and other land-based gravitational wave detectors.

Significantly longer baselines, and theoretically greater sensitivity can be achieved with gravitational wave detectors in space. Generically, such a space-based detector has become known as a Laser Interferometer Space Antenna (LISA). Three projects associated with space-based gravitational wave detection are:

  • LISA (the project name predated the current generic usage of LISA)
  • LISA Pathfinder (a space-based gravitational wave detection technology demonstrator, not a detector)
  • Evolved LISA (eLISA)

These projects are discussed below.

The science being addressed by space-based gravitational wave detectors is discussed in the eLISA white paper, “The Gravitational Universe.” You can download this whitepaper, a 1-page summary, and related gravitational wave science material at the following link:

https://www.elisascience.org/whitepaper/

LISA

The LISA project originally was planned as a joint European Space Agency (ESA) and National Aeronautics & Space Administration (NASA) project to detect gravitational waves using a very long baseline, triangular interferometric array of three spacecraft.

Each spacecraft was to contain a gravitational wave detector sensitive at frequencies between 0.03 mHz and 0.1 Hz and have the capability to precisely measure its distances to the other two spacecraft forming the array. The equilateral triangular array, which was to measure about 5 million km (3.1 million miles) on a side, was expected to be capable of measuring gravitational-wave induced strains in space-time by precisely measuring changes of the separation distance between pairs of test masses in the three spacecraft. In 2011, NASA dropped out of this project because of funding constraints.

LISA Pathfinder

The LISA Pathfinder (LPF) is a single spacecraft intended to validate key technologies for space-based gravitational wave detection. It does not have the capability to detect gravity waves.

This mission was launched by ESA on 3 December 2015 and the spacecraft took station in a Lissajous orbit around the Sun-Earth L1 Lagrange point on 22 January 2016. L1 is directly between the Earth and the Sun, about 1.5 million km (932,000 miles) from Earth. An important characteristic of a Lissajous orbit is that the spacecraft will follow the L1 point without requiring any propulsion. This is important for minimizing external forces on the LISA Pathfinder experiment package. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft (not LPF, specifically) stationed at the L1 Lagrange point is shown in the following figure.

L1 Lagrange pointSource: Wikimedia Commons

The LISA Pathfinder’s mission is to validate the technologies used to shield two free-floating metal cubes (test masses), which form the core of the experiment package, from all internal and external forces that could contribute to noise in the gravitational wave measurement instruments. The on-board measurement instruments (inertial sensors and a laser interferometer) are designed to measure the relative position and orientation of the test masses, which are 38 cm (15 inches) apart, to an accuracy of less than 0.01 nanometers (10e-11 meters). This measurement accuracy is believed to be adequate for detecting gravitational waves using this technology on ESA’s follow-on mission, eLISA.

The first diagram below is an artist’s impression of the LISA Pathfinder technology package, showing the inertial sensors housing the test masses (gold) and the laser interferometer (middle platform). The second diagram provides a clearer view of the test masses and the laser interferometer.

LPF technology package 1

Source: ESA/ATG medialab, August 2015LPF technology package 2Source: ESA LISA Pathfinder briefing, 7 June 2016

You’ll find more general information in an ESA LISA Pathfinder overview, which you can download from NASA’s LISA website at the following link:

http://lisa.nasa.gov/Documentation/LISA-LPF-RP-0001_v1.1.pdf

LISA Pathfinder was commissioned and ready for scientific work on 1 March 2016. In a 7 June 2016 briefing, ESA reported very favorable performance results from LISA Pathfinder:

  • LPF successfully validated the technologies used in the local (in-spacecraft) instrument package (test masses, inertial sensors and interferometer).
  • LPF interferometer noise was a factor of 100 less than on the ground.
  • The measurement instruments can see femtometer motion of the test masses (LPF goal was picometer).
  • Performance is essentially at the level needed for the follow-on eLISA mission

You can watch this full (1+ hour) ESA briefing at the following link:

http://www.esa.int/Our_Activities/Space_Science/Watch_LISA_Pathfinder_briefing

eLISA

Evolved LISA, or eLISA, is ESA’s modern incarnation of the original LISA program described previously. ESA’s eLISA website home page is at the following link:

https://www.elisascience.org

As shown in the following diagrams, three eLISA spacecraft will form a very long baseline interferometric array that is expected to directly observe gravitational waves from sources anywhere in the universe. In essence, this array will be a low frequency microphone listening for the sounds of gravitational waves as they pass through the array.

eLISA constellation 1Source: ESAeLISA constellation 2Source: ESA

As discussed previously, gravity wave detection depends on the ability to very precisely measure the distance between test masses that are isolated from their environment but subject to the influence of passing gravitational waves. Measuring the relative motion of a pair of test masses is considerably more complex for eLISA than it was for LPF. The relative motion measurements needed for a single leg of the eLISA triangular array are:

  • Test mass 1 to Spacecraft 1
  • Spacecraft 1 to Spacecraft 2
  • Spacecraft 2 to Test Mass 2

This needs to be done for each of the three legs of the array.

LPF validated the technology for making the test mass to spacecraft measurement. Significant development work remains to be done on the spacecraft-to-spacecraft laser system that must take precise measurements at very long distances (5 million km, 3.1 million miles) of the relative motion between each pair of spacecraft.

In the 6 June 2016 LISA Pathfinder briefing, LPF and ESA officials indicated that an eLisa launch date is expected in the 2029 – 2032 time frame. Then it reaches its assigned position in a trailing heliocentric orbit, eLISA will be a remarkable collaborative technical achievement and a new window to our universe.

Breakthrough Starshot: Crashing Through Interstellar Dust and Gas Clouds at 0.2c

Yuri and Julia Milner founded the Breakthrough Initiatives in 2015 to explore the universe, seek scientific evidence of life beyond Earth, and encourage public debate from a planetary perspective. You’ll find an introduction to Breakthrough Initiatives at the following link:

https://breakthroughinitiatives.org/About

There are three initiatives described on this website:

Breakthrough Listen: This is a $100 million program of astronomical observations in search of evidence of intelligent life beyond Earth. It is by far the most comprehensive, intensive and sensitive search ever undertaken for artificial radio and optical signals. It includes a complete survey of the 1 million nearest stars, the plane and center of our galaxy, and the 100 nearest galaxies. All data will be open to the public.

Breakthrough Message: This is a $1 million competition to design a message representing Earth, life and humanity that could potentially be understood by another civilization.

Breakthrough Starshot: Yuri Milner and physicist Stephen Hawking announced the Breakthrough Starshot initiative on 12 April 2016. This is a $100 million research and engineering program with the goal of demonstrating proof-of-concept for a new technology: using laser light to accelerate ultra-light, unmanned, light sail spacecraft to 20% of the speed of light (0.2 c; 1.34 e+8 mph; 6.0e+7 meters/sec); and thereby enable a flyby mission to the nearest star system, Alpha Centauri, within a generation.

Breakthrough Starshot involves particularly intriguing engineering challenges. This initiative plans to launch many lightweight, light sail spacecraft from Earth and then individually accelerate each spacecraft to about 0.2 c using powerful terrestrial lasers. These lightweight spacecraft are expected to accelerate to about 0.2 c within a few minutes after laser propulsion begins. When the target speed has been reached, laser propulsion would be discontinued and the spacecraft will coast the rest of the way to its destination.

Solar sailing spacecraftThe Breakthrough Starshot light sail spacecraft after initial deployment, before the start of laser propulsion. Source: Breakthrough Starshot Initiative

Terrestrial laser power sourceThe terrestrial laser power source for the Breakthrough Starshot spacecraft. Source: Breakthrough Starshot Initiative

Breakthrough Starshot propelled by lasersBreakthrough Starshot light sail spacecraft being propelled by the terrestrial lasers. Source: Breakthrough Starshot Initiative

Spacecraft underwat toward deep spaceBreakthrough Starshot light sail spacecraft under power, heading for deep space. Source: Breakthrough Starshot Initiative

You can watch a short video on the Breakthrough Starshot spacecraft at the following link:

https://www.youtube.com/watch?v=wMkWGN1G6Kg

A detailed video (1hr 16 min) on this initiative, with discussions by Stephen Hawking and Freeman Dyson, is at the following link:

https://www.youtube.com/watch?v=0cVQwDdYF4w

While the concept of a terrestrial laser-powered, ultra-light, light sail spacecraft is intriguing, the reality of flying through interstellar space at a speed of 0.2 c relative to low-density cosmic dust and gas along the route may raise daunting engineering challenges related to spacecraft survivability. The approach being taken by the Breakthrough Starshot initiative will be to launch many light sail spacecraft to provide redundancy and improve the likelihood of mission success.

How much damage could a grain of space dust inflict on a spacecraft? The worst case would be for the spacecraft to absorb all the kinetic energy from the collision.

Wikipedia reports that cosmic dust falling to Earth has been studied and found to be composed of grains with masses between 10−16 kg and 10−4 kg.

The classical Newtonian equation for kinetic energy (Ek) will yield an adequate approximation of the kinetic energy transferred in an impact at a speed of 0.2 c:

Ek = ½ mv2

where m is the mass of the projectile, and v2 is the square of the velocity of the projectile.

The maximum kinetic energy deposited by a cosmic dust particle with an “average” mass, 10−10 kg, is estimated to be:

Ek = 0.5 (1e-10 kg)(3.6e+15 m2/sec2) = 1.8e+5 kg-m2/sec2 = 180,000 Joules

This is about 40 times the maximum kinetic energy of a projectile fired from a 12-gauge shotgun. That would be quite damaging, so hopefully there is a very low probability of encountering cosmic dust of this mass. In this case, that v2 term in the equation has a very bad effect on kinetic energy.

In comparison, the maximum kinetic energy deposited by a cosmic dust particle at the low end of the mass range, 10−16 kg, is estimated to be:

Ek = 0.5 (1e-16 kg)(3.6e+15 m2/sec2) = 1.8e-1 kg-m2/sec2 = 0.18 Joules

This is in the approximate kinetic energy range of a small projectile fired from an airsoft (paintball) type gun. If the spacecraft isn’t damaged, the momentum transfer, even from smaller impacts such as this, may be sufficient to alter the course of the spacecraft. As you can see, cosmic dust can be quite hazardous to fast moving spacecraft.

You can read more about the Breakthrough Starshot initiative at the following links:

arsTECHNICA, 23 August 2016: “Just how dangerous is it to travel at 20% the speed of light?

http://arstechnica.com/science/2016/08/could-breakthrough-starshots-ships-survive-the-trip/

National Geographic, 13 April 2016: “Is the New $100 Million ‘Starshot’ for Real?”

http://news.nationalgeographic.com/2016/04/160413-fast-facts-stephen-hawking-starshot-space/

 

 

Philae Found in a Rocky Ditch on Comet 67P/Churyumov-Gerasimenko

In my 24 August 2016 post, “Exploring Microgravity Worlds,” I described the European Space Agency’s (ESA’s) Rosetta mission to comet 67P and the Philae lander, which was intended to make a soft landing on 67P and attach itself to the surface. However, the securing devices (a pair of harpoons and screws on each leg) failed to work upon touching the surface the first time. In the microgravity environment of 67P, Philae rebounded and eventually came to rest adjacent to a rocky outcropping seen in a post-landing photo.

Rosetta_Auto52Main components of the Philae lander. Source: Philae teamPhilae as it was intended to land.Philae as it was intended to look after landing. Source: MEDIALAB/AFP/Getty ImagesPhilae landing photoView from Philae’s actual landing site. Source: ESA

On 2 September 2016, the ESA team managing the Rosetta mission found Philae in photographs taken from the Rosetta spacecraft at an altitude of about 2.7 km (1.7 miles) above the surface of 67P. The photos show that Philae, which is about the size of a washing machine, is lying on its side, wedged among large rocks. Knowing Philae’s actual orientation and environment is expected to help ESA reevaluate the data Philae transmitted from its resting place.

Philae is the “poster child” for the hazards of landing on microgravity worlds.

Philae_close-up_node_full_image_2Philae’s final resting place on comet 67P. Source: ESAPhilae_close-up_labelled_node_full_image_2Annotated Philae photo. Source: ESA

Meanwhile, Rosetta is being maneuvered into ever-closer orbits around 67P, with the goal be taking measurements of the comet’s “atmosphere” very close to the surface. The Rosetta mission is expected to come to an end in September 2016 with the spacecraft colliding with 67P.

 

 

Exploring Microgravity Worlds

1.  Background:

We’re all familiar with scenes of the Apollo astronauts bounding across the lunar surface in the low gravity on the Moon, where gravity (g) is 0.17 of the gravity on the Earth’s surface. Driving the Apollo lunar rover kicked up some dust, but otherwise proved to be a practical means of transportation on the Moon’s surface. While the Moon’s gravity is low relative to Earth, techniques for achieving lunar orbit have been demonstrated by many spacecraft, many soft landings have been made, locomotion on the Moon’s surface with wheeled vehicles has worked well, and there is no risk of flying off into space by accidentally exceeding the Moon’s escape velocity.

There are many small bodies in the Solar System (i.e., dwarf planets, asteroids, comets) where gravity is so low that it creates unique problems for visiting spacecraft and future astronauts: For example:

  • Spacecraft require efficient propulsion systems and precise navigation along complex trajectories to rendezvous with the small body and then move into a station-keeping position or establish a stable orbit around the body.
  • Landers require precise navigation to avoid hazards on the surface of the body (i.e., craters, boulders, steep slopes), land gently in a specific safe area, and not rebound back into space after touching down.
  • Rovers require a locomotion system that is adapted to the specific terrain and microgravity conditions of the body and allows the rover vehicle to move across the surface of the body without risk of being launched back into space by reaction forces.
  • Many asteroids and comets are irregularly shaped bodies, so the surface gravity vector will vary significantly depending on where you are relative to the center of mass of the body.

You will find a long list of known objects in the Solar System, including many with diameters less than 1 km (0.62 mile), at the following link:

https://en.wikipedia.org/wiki/List_of_Solar_System_objects_by_size

You can determine the gravity on the surface of a body in the Solar System using the following equation:

Equation for g

where (using metric):

g = acceleration due to gravity on the surface of the body (m/sec2)

G = universal gravitational constant = 6.672 x 10-11 m3/kg/sec2

M = mass of the body (kg)

r = radius of the body (which is assumed to be spherical) (m)

You can determine the escape velocity from a body using the following equation:

Equation - Escape velocity

Applying these equations to the Earth and several smaller bodies in in the Solar System yields the following results:

g and escape velocity table

Note how weak the gravity is on the small bodies in this table. These are very different conditions than on the surface of the Moon or Mars where the low gravity still allows relatively conventional locomotion.

As noted in my 31 December 2015 post, the “U.S. Commercial Space Launch Competitiveness Act,” which was signed into law on 25 November 2015, opens the way for U.S. commercial exploitation of space, including commercial missions to asteroids and comets.  Let’s take a look at missions to these microgravity worlds and some of the unique issues associated with visiting a microgravity world.

2.  Recent and Current Missions to Asteroids and Comets

There have been several spacecraft that have made a successful rendezvous with one or more small bodies in the Solar System. Several have been fly-by missions. Four spacecraft have flown in close formation with or entered orbit around low-gravity bodies. Three of these missions included landing on (or at least touching) the body, and one returned very small samples to Earth. These missions are:

  • National Aeronautics and Space Administration’s (NASA) NEAR-Shoemaker
  • Japan Aerospace Exploration Agency’s (JAXA) Hayabusa
  • European Space Agency’s (ESA) Rosetta
  • NASA’s Dawn

In addition, China’s Chang’e 2 mission demonstrated its ability to navigate to an asteroid intercept after completing its primary mission in lunar orbit. JAXA’s Hayabusa 2 mission currently is enroute to asteroid rendezvous.

Following is a short synopsis of each of these missions.

NASA’s NEAR-Shoemaker Mission (1996 – 2001): This mission was launched 17 February 1996 and on 27 June 1997 flew by the asteroid 253 Mathilde at a distance of about 1,200 km (746 miles).   On 14 February 2000, the spacecraft reached its destination and entered a near-circular orbit around the asteroid 433 Eros, which is about the size of Manhattan. After completing its survey of Eros, the NEAR spacecraft was maneuvered close to the surface and it touched down on 12 February 2001, after a four-hour descent, during which it transmitted 69 close-up images of the surface. Transmissions continued for a short time after landing. NEAR-Shoemaker was the first man-made object to soft-land on an asteroid.

Asteroid Eros                Asteroid EROS. Source: NASA/JPL/JHUAPL

JAXA’s Hayabusa Mission (2003 – 2010): The Hayabusa spacecraft was launched in May 2003. This solar-powered, ion-driven spacecraft rendezvoused with near-Earth asteroid 25143 Itokawa in mid-September 2005.

Asteroid Itokawa           Asteroid Itokawa. Source: JAXA

Hayabusa carried the solar-powered MINERVA (Micro/Nano Experimental Robot Vehicle for Asteroid) mini-lander, which was designed to be released close to the asteroid, land softly, and move across the surface using an internal flywheel and braking system to generate the momentum needed to hop in microgravity. However, MINERVA was not captured by the asteroid’s gravity after being released and was lost in deep space.

In November 2005, Hayabusa moved in from its station-keeping position and briefly touched the asteroid to collect surface samples in the form of tiny grains of asteroid material.

Hayabusa taking a sampleHayabusa in position to obtain samples. Source: JAXA

The spacecraft then backed off and navigated back to Earth using its failing ion thrusters. Hayabusa returned to Earth on 13 June 2010 and the sample-return capsule, with about 1,500 grains of asteroid material, was recovered after landing in the Woomera Test Range in the western Australian desert.

You’ll find a JAXA mission summary briefing at the following link:

https://www.nasa.gov/pdf/474206main_Kuninaka_HayabusaStatus_ExploreNOW.pdf

ESA’s Rosetta Mission (2004 – present): The Rosetta spacecraft was launched in March 2004 and in August 2014 rendezvoused with and achieved orbit around irregularly shaped comet 67P/Churyumov-Gerasimenko. This comet orbits the Sun outside of Earth’s orbit, between 1.24 and 5.68 AU (astronomical units; 1 AU = average distance from Earth’s orbit to the Sun). The size of 67P/Churyumov-Gerasimenko is compared to downtown Los Angeles in the following figure.

ESA Attempts To Land Probe On CometSource: ESA

Currently, Rosetta remains in orbit around this comet. The lander, Philae, is on the surface after a dramatic rebounding landing on 12 November 2014. Anchoring devices failed to secure Philae after its initial touchdown. The lander bounced twice and finally came to rest in an unfavorable position after contacting the surface a third time, about two hours after the initial touchdown. Philae was the first vehicle to land on a comet and it briefly transmitted data back from the surface of the comet in November 2014 and again in June – July 2015.

NASA’s Dawn Mission (2007 – present): Dawn was launched on 27 September 2007 and used its ion engine to fly a complex flight path to a 2009 gravitational assist flyby of Mars and then a rendezvous with the large asteroid Vesta (2011 – 2012) in the main asteroid belt.

NASA_Dawn_spacecraft_near_Ceres   Dawn approaches Vesta. Source: NASA / JPL Caltech

Dawn spent 14 months in orbit surveying Vesta before departing to its next destination, the dwarf planet Ceres, which also is in the main asteroid belt. On 6 March 2015 Dawn was captured by Ceres’ gravity and entered its initial orbit following the complex trajectory shown in the following diagram.

Dawn navigation to Ceres orbit   Dawn captured by Ceres gravity. Source: NASA / JPL Caltech

Dawn is continuing its mapping mission in a circular orbit at an altitude of 385 km (240 miles), circling Ceres every 5.4 hours at an orbital velocity of about 983 kph (611 mph). The Dawn mission does not include a lander.

See my 20 March 2015 and 13 Sep 2015 posts for more information on the Dawn mission.

CNSA’s Chang’e 2 extended mission (2010 – present): The China National Space Agency’s (CNSA) Chang’e 2 spacecraft was launched in October 2010 and placed into a 100 km lunar orbit with the primary objective of mapping the lunar surface. After completing this objective in 2011, Chang’e 2 navigated to the Earth-Sun L2 Lagrange point, which is a million miles from Earth in the opposite direction of the Sun. In April 2012, Chang’e 2 departed L2 for an extended mission to asteroid 4179 Toutatis, which it flew by in December 2012.

Toutatis_from_Chang'e_2Asteroid Toutatis. Source: CHSA

JAXA’s Hayabusa 2 Mission (2014 – 2020): The JAXA Hayabusa 2 spacecraft was launched on 3 December 2014. This ion-propelled spacecraft is very similar to the first Hayabusa spacecraft. Its planned arrival date at the target asteroid, 1999 JU3 (Ryugu), is in mid-2018.   As you can see in the following diagram, 1999 JU3 is a substantially larger asteroid than Itokawa.

Hayabusa 1-2 target comparisonSource: JAXA

The spacecraft will spend about a year mapping the asteroid using Near Infrared Spectrometer (NIRS3) and Thermal Infrared Imager (TIR) instruments.

Hayabusa 2 includes three solar-powered MINERVA-II mini-landers and one battery-powered MASCOT (Mobile Asteroid Surface Scout) small lander. All landers will be deployed to the asteroid surface from an altitude of about 100 meters (328 feet) so they can be captured by the asteroid’s very weak gravity. The 1.6 – 2.5 kg (3.5 – 5.5 pounds) MINERVA-II landers will deliver imagery and temperature measurements. The 10 kg (22 pound) MASCOT will make measurements of surface composition and properties using a camera, magnetometer, radiometer, and infrared microscope. All landers are expected to make several hops to take measurements at different locations on the asteroid’s surface.

Three MINERVA landers

 

Three MINERVA mini-landers. Source: JAXA

MASCOT lander         MASCOT small lander. Source: JAXA

For sample collection, Hayabusa 2 will descend to the surface to capture samples of the surface material. A device called a Small Carry-on Impactor (SCI) will be deployed and should impact the surface at about 2 km/sec, creating a small crater to expose material beneath the asteroid’s surface. Hayabusa 2 will attempt to gather a sample of the exposed material. More information about SCI is available at the following link:

http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1904.pdf

At the end of 2019, Hayabusa 2 is scheduled to depart asteroid 1999 JU3 (Ryugu) and return to Earth in 2020 with the collected samples. You will find more information on the Hayabusa 2 mission at the JAXA website at the following links:

http://global.jaxa.jp/projects/sat/hayabusa2/

and,

http://www.lpi.usra.edu/sbag/meetings/jan2013/presentations/sbag8_presentations/TUES_0900_Hayabusa-2.pdf

3.  Future Missions:

NASA OSIRIS-REx: This NASA’s mission is expected to launch in September 2016, travel to the near-Earth asteroid 101955 Bennu, map the surface, harvest a sample of surface material, and return the samples to Earth for study. After arriving at Bennu in 2018, the solar-powered OSIRIS-Rex spacecraft will map the asteroid surface from a station-keeping distance of about 5 km (3.1 miles) using two primary mapping instruments: the OVIRS Visible and Infrared Spectrometer and the OTRS Thermal Emission Spectrometer. Together, these instruments are expected to develop a comprehensive map of Bennu’s mineralogical and molecular components and enable mission planners to target the specific site(s) to be sampled. In 2019, a robotic arm on OSIRIS-REx will collect surface samples during one or more very close approaches, without landing. These samples (60 grams minimum) will be loaded into a small capsule that is scheduled to return to Earth in 2023.

OSIRIS-REx SpacecraftOSIRIS-REx spacecraft. Source: NASA / ASU

For more information on OSIRIS-REx, visit the NASA website at the following link:

http://sservi.nasa.gov/articles/nasas-asteroid-sample-return-mission-moves-into-development/

and the ASU website at the following link:

http://www.asteroidmission.org/objectives/

NASA Asteroid Redirect Mission (ARM): This mission will involve rendezvousing with a near-Earth asteroid, mapping the surface for about a year, and locating a suitable bolder to be captured [maximum diameter about 4 meters (13.1 feet)]. The ARM spacecraft will land and capture the intended bolder, lift off and deliver the bolder into a stable lunar orbit during the first half of the next decade. The current reference target is known as asteroid 2008 EV5.

ARM asteroid-capture      ARM lander gripping a bolder on an asteroid. Source: NASA

You can find more information on the NASA Asteroid Redirect Mission at the following links:

https://www.nasa.gov/content/what-is-nasa-s-asteroid-redirect-mission

and

https://www.nasa.gov/pdf/756122main_Asteroid%20Redirect%20Mission%20Reference%20Concept%20Description.pdf

4. Locomotion in Microgravity

OK, you’ve landed on a small asteroid, your spacecraft has anchored itself to the surface and now you want to go out and explore the surface. If this is asteroid 2008 EV5, the local gravity is about 1.79 E-05 that of Earth (less than 2/100,000 the gravity of Earth) and the escape velocity is about 0.6 mph (1 kph). Just how are you going to move about on the surface and not launch yourself on an escape trajectory into deep space?

There is a good article on the problems of locomotion in microgravity in a 7 March 2015 article entitled, “A Lightness of Being,” in the Economist magazine. You can find this article on the Economist website at the following link:

http://www.economist.com/news/technology-quarterly/21645508-space-vehicles-can-operate-ultra-low-gravity-asteroids-and-comets-are

In this article, it is noted that:

“Wheeled and tracked rovers could probably be made to work in gravity as low as a hundredth of that on Earth……But in the far weaker microgravity of small bodies like asteroids and comets, they would fail to get a grip in fine regolith. Wheels also might hover above the ground, spinning hopelessly and using up power. So an entirely different system of locomotion is needed for rovers operating in a microgravity.”

Novel concepts for locomotion in microgravity include:

  • Hoppers / tumblers
  • Structurally compliant rollers
  • Grippers

Hoppers / tumblers: Hoppers are designed to move across a surface using a moving internal mass that can be controlled to transfer momentum to the body of the rover to cause it to tumble or to generate a more dramatic hop, which is a short ballistic trajectory in microgravity. The magnitude of the hop must be controlled so the lander does not exceed escape velocity during a hop. JAXA’s MINERVA-II and MASCOT asteroid landers both are hoppers.

JAXA described the MINERVA-II hopping mechanism as follows:

“MINERVA can hop from one location to another using two DC motors – the first serving as a torquer, rotating an internal mass that leads to a resulting force, sufficient to make the rover hop for several meters. The second motor rotates the table on which the torquer is placed in order to control the direction of the hop. The rover reaches a top speed of 9 centimeters per second, allowing it to hop a considerable distance.”

JAXA MINERVA hopperMINERVA torque & turntable. Source: JAXA

The MASCOT hopper operates on a different principle:

“With a mass of not even half a gram in the gravitational field of the asteroid, the (MASCOT) lander can easily withstand its initial contact with the surface and several bounces that are expected upon landing. It also means that only small forces are needed to move the lander from point to point. MASCOT’s Mobility System essentially consists of an off-centered mass installed on an eccentric arm that moves that mass to generate momentum that is sufficient to either rotate the lander to face the surface with its instruments or initiate a hop of up to 70 meters to get to the next sampling site.”

MASCOT Mobility SystemMASCOT mobility mechanism. Source: JAXA

You will find a good animation of MASCOT and its Mobility System at the following link:

http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-18664/#/gallery/23722

NASA is examining a class of microgravity rovers called “hedgehogs” that are designed to hop and tumble on microgravity surfaces by spinning and braking a set of three internal flywheels. Cushions or spikes at the corners of the cubic body of a hedgehog protect the body from the terrain and act as feet while hopping and tumbling.

NASA Hedgehog                               NASA Hedgehog prototype. Source: NASA

Read more on the NASA hedgehog rovers at the following link:

http://www.jpl.nasa.gov/news/news.php?feature=4712

Structurally compliant rollers: One means of “rolling” across a microgravity surface is with a deformable structure that allows the location of the center of mass to be controlled in a way that causes the rover to tip over in the desired direction of motion. NASA is exploring the use of a class of rolling rovers called Super Ball Bots, which are terrestrial rovers based on a R. Buckminster Fuller’s tensegrity toy. NASA explains:

“The Super Ball Bot has a sphere-like matrix of cables and joints that could withstand being dropped from a spacecraft high above a planetary surface and hit the ground with a bounce. Once on the planet, the joints could adjust to roll the bot in any direction while housing a data collecting device within its core.”

NASA Super Ball Bot                    Source: http://www.nasa.gov/content/super-ball-bot

You’ll find a detailed description of the principles behind tensegrity (tensional integrity) in a 1961 R. Buckminster Fuller paper at the following link:

http://www.rwgrayprojects.com/rbfnotes/fpapers/tensegrity/tenseg01.html

Grippers: Without having a grip on a microgravity body, a rover cannot use sampling tools that generate a reaction force on the rover (i.e., drills, grinders, chippers). For such operations to be successful a rover needs an anchoring system to secure the rover and transfer the reaction loads into the microgravity body.

An approach being developed by Jet Propulsion Laboratory (JPL) involves articulated feet with microspine grippers that have a large number of small claws that can grip irregular rocky surfaces.

JPL microspine gripper           Microspine gripper. Source: NASA / JPL

Such a gripper could be used to hold a rover in place during mechanical sampling activities or to allow a rover to climb across an irregular surface like a spider.  See more about the operation of the NASA / JPL microspine gripper at the following link:

https://www-robotics.jpl.nasa.gov/tasks/taskVideo.cfm?TaskID=206&tdaID=700015&Video=147

5. Conclusions

Missions to small bodies in our Solar System are very complex undertakings that require very advanced technologies in many areas, including: propulsion, navigation, autonomous controls, remote sensing, and locomotion in microgravity. The ambitious current and planned future missions will greatly expand our knowledge of these small bodies and the engineering required to operate spacecraft in their vicinity and on their surface.

While commercial exploitation of dwarf planets, asteroids and comets still may sound like science fiction, the technical foundation for such activities is being developed now. It’s hard to guess how much progress will be made in the next decades. However, I’m convinced that the “U.S. Commercial Space Launch Competitiveness Act,” will encourage commercial investments in space exploration and exploitation and lead to much greater progress than if we depended on NASA alone.

The technologies being developed also may lead, in the long term, to effective techniques for redirecting an asteroid or comet that poses a threat to Earth. Such a development would give our Planetary Defense Officer (see my 21 January 2016 post) an actual tool for defending the planet.

Lunar Lander XCHALLENGE and Lunar XPrize are Paving the way for Commercial Lunar Missions

Lunar Lander XCHALLENGE and Lunar XPrize are two competitions promoting the development of technologies, vehicles and systems by private firms for landing unmanned vehicles on the Moon and demonstrating functional capabilities that can support future lunar exploration missions. The legal and regulatory framework for U.S. commercial space activities was greatly simplified in November 2015, when the Commercial Space Launch Competitiveness Act was signed into law. See my 31 December 2015 post for details on this Act.

On 3 August 2016, Lunar XPrize competitor Moon Express became the first private enterprise to be licensed by the U.S. Government (the Federal Aviation Administration) to conduct a mission to the lunar surface. Other Lunar XPrize competitors also are seeking similar approvals in preparation for lunar missions before the end of 2017.

Let’s take a look at how the private sector got this far.

Northrop Grumman / NASA Lunar Lander XCHALLENGE

In October 2007, XPrize and Northrop Grumman, in partnership with NASA’s Centennial Challenges program, launched the $2 million Lunar Lander XCHALLENGE, in which competing teams designed small rocket vehicles capable of routine and safe vertical takeoff and landing for lunar exploration and other applications. You’ll find details on the Lunar Lander XChallenge at the following link and an overview in the following text:

http://lunarlander.xprize.org

Lunar Lander XCHALLENGE badge   Source: XPrize

The XCHALLENGE was divided into two levels.

Level 1:

  • Required a rocket to take off from a designated launch area; climb to a low, fixed altitude of about 50 meters (164 feet); and fly for at least 90 seconds while translating horizontally to a precise landing point on a different landing pad 100 meters (328 feet) from the launch point. The flight must be repeated in reverse within a two and a half hour period.
  • Armadillo Aerospace, of Mesquite, TX won the $350K Level 1 first prize in October 2008. Masten Space Systems of Mojave, CA won the $150K Level 1 second place prize on 7 October 2009 when their Xombie rocket completed its flight with an average landing accuracy of 6.3 inches (16 cm).
  • You can watch a short video on the 2008 Level 1 competition and Armadillo Aerospace’s winning Level 1 flight at the following link:

https://www.youtube.com/watch?v=IhnY5tT4YeE

Armadillo Level 1 winner Armadillo Aerospace Level 1 winner. Source: NASA

Level 2:

  • Similar to the Level 1 flight profile, but required the rocket to fly for 180 seconds before landing precisely on a simulated lunar surface constructed with craters and boulders 100 meters (328 feet) from the launch point. The minimum flight time was calculated so that the Level 2 mission closely simulated the power needed to perform a real descent from lunar orbit down to the surface of the Moon.

XCHALLENGE lunar landing siteLevel 2 landing site. Source: NASA

  • Masten Space Systems won the $1M Level 2 first prize with the flight of their Xoie rocket on 30 October 2009. Xoie completed its Level 2 flight with an average landing accuracy of about 7.5 inches (19 cm). Armadillo Aerospace took second place and a $500K prize with the 12 September 2009 flight of their Scorpius (Super-mod) rocket, which had an average landing accuracy of about 34 inches (89 cm). These prizes were awarded on 5 November 2009 in Washington D.C.

Xoie winning Level 2 flightMasten Aerospace Xoie: Level 2 winner. Source: NASA.

  • You can watch a short video summary on the XCHALLENGE results, including the winning flight by Xoie at the following link:

https://www.youtube.com/watch?v=MAvZxa1VXKI

Armadillo Scorpius Level 2Armadillo Aerospace’s Scorpius: Level 2 second place. Source: NASA

  • You can watch a short video on the Scorpius 2009 flight at the following link:

https://www.youtube.com/watch?v=ALKvai4p7OE

The other XCHALLENGE competitors, TrueZer0 and Unreasonable Rockets, failed to qualify for Level 1 or 2.

Google Lunar XPrize

The Google Lunar XPrize was created in 2007, overlapping with the Northrop Grumman / NASA Lunar Lander XCHALLENGE. The Lunar XPrize is intended to actually deliver payloads to the Moon and “incentivize space entrepreneurs to create a new era of affordable access to the Moon and beyond.” The motto for the Google XPrize is: “Back to the Moon for good.”

The basic mission requirements are:

  • Land a privately funded rover on the Moon at a site announced in advance.
  • Travel at least 500 meters along a deliberate path on the lunar surface.
  • Transmit two “Mooncasts” from the surface of the Moon, including specified types of videos and still images.
  • Receive specified data uplinks from Earth and re-transmit the data back to Earth.
  • Deliver a small payload provided by XPrize (not to exceed 500 grams).
  • Private funding for 90% of the total mission cost. No more than 10% government funding, including the value of in-kind support.
  • Launch contract in place by the end of 2016 and mission completion by the end of 2017.

The primary incentives are large financial award to the first and second teams that accomplish all of the mission requirements: $20 million Grand Prize and $5 million for second place. In addition, there are several other financial prizes that add up to total awards of more than $40 million. Of course, the winner will have bragging rights for a long time to come.

  • Milestone prizes: $5.25 million already has been awarded to teams that demonstrated robust hardware in three categories: landing, mobility, and imaging. The following Milestone prize winners have been announced:

Milestone prize winnersSource: XPrize

  • Bonus prizes: Up to $4 million for successfully completing additional scientific and technical tasks not in the mission requirements
  • Apollo Heritage Bonus Prize: $4 million for making an Apollo Heritage Mooncast from the site of an Apollo moon landing.
  • Heritage Bonus Prize: $1 million for making a Mooncast from another site of interest to XPrize.
  • Range Bonus Prize: $2 million for a rover that can traverse five kilometers on the Moon’s surface.
  • Survival Bonus Prize: $2 million for successfully operating on two separate lunar days.
  • Water Detection Bonus Prize: $4 million for producing scientifically conclusive proof of the presence of water on the Moon.

The Google Lunar XPrize home page is at the following link, where you can navigate to many details on this competition and sign up for an XPrize newsletter:

http://lunar.xprize.org

The Google Lunar XPrize began with 29 teams and now 16 remain. As noted above, five teams already have won Milestone prizes.

The three teams that competed in the landing milestone competition are taking different approaches. Astrobotics is using a lunar lander developed by Masten Aerospace. Indus and Moon Express are developing their own lunar landers.

So far, only two teams have launch contracts:

  • On 7 October 2015, the Israeli team SpaceIL became the first Lunar XPrize team to sign a launch contract. They signed a launch services contract with Spaceflight Industries for launch on a SpaceX Falcon 9 launcher in the second half of 2017.
  • On 8 December 2017, XPrize verified the Moon Express launch contract with Rocket Lab USA. Moon Express contracted for three launches using an Electron booster, which, as of mid-2016, is still being developed.

By the end of 2016, all competitors that intend to continue into the finals must have a launch contract in place.

So far, only three nations have made a soft landing on the Moon: USA, Russia and China. In 2017, a privately funded team may be added to that list.  That would be a paradigm shift for lunar exploration, opening the door for private teams and commercial firms to have regular, relatively low cost access to the Moon.

Update 23 December 2016: Google Lunar XPrize Status

On 22 December 2016, author Daniel Clery posted an article, “Here’s who could win the $20 million XPrize for roving on the moon—but will any science get done?” The author reports that six teams claim to have booked flights to the moon for their lunar landers / rovers. The following chart provides a summary for five of the competitors. The small (4 kg) rover for the sixth competitor, Japan’s Team Hakuto, will be delivered to the moon on the same lander as India’s Team Indus.

LunarXPrixe competitors Dec 2016

Click on the graphic above to enlarge. Source: G. Grullón/Science

As I noted previously, all competitors that intend to continue into the Lunar XPrize finals must have a launch contract in place by the end of 2016, and the mission to the moon must be completed by the end of 2017.

You can read Daniel Clery’s complete article on the Sciencemag.org website, at the following link:

http://www.sciencemag.org/news/2016/12/heres-who-could-win-20-million-xprize-roving-moon-will-any-science-get-done?utm_campaign=news_daily_2016-12-22&et_rid=215579562&et_cid=1068715

Update 23 January 2018: Google Lunar XPrize Competion Cancelled

After concluding that none of the remaining competitors could meet the extended 31 March 2018 deadline for landing on the Moon, this competition came to a close, with the $30M in prizes remaining unclaimed.

 

 

Where Earth-orbiting Satellites go to Die

For satellites large enough to generate reentry debris that can reach the surface of the Earth, there are four choices: Manitowoc, WI, the Spacecraft Cemetery, a Graveyard Orbit, or the Space Garbage Truck. Let’s look at these alternatives.

Korabi-Sputnik 1 (aka Sputnik 4) was launched by the Soviet Union on 15 May 1960 and was reported to be a test of an orbital spacecraft with a recoverable, pressurized capsule capable of carrying a cosmonaut. At the time of its launch, Sputnik 4 was the largest satellite placed in orbit, with a weight of at least 5 tons.

Koralb_sputnikSource: pics-about-space.com

Sputnik 4 appears to have been a prototype of the Soviet Vostok spacecraft that carried the first human, Yuri Gagarin, into orbit on 12 April 1961.

Vostok_diagram Source: Space.com, graphics by Karl Tate

Due to a failure in the control or reentry system, the Sputnik 4 capsule did not return to Earth as planned, but instead, remained in orbit until 5 September 1962. On that day, Sputnik 4 reentered the Earth’s atmosphere and broke up, with fragments landing in Lake Michigan and in downtown Manitowoc, WI. The following diagram from the 3 December 1962 issue of Aviation Week magazine shows the paths for Sputnik 4 fragments that landed on the main street of Manitowoc, Wisconsin.

Sputnik 4 reentry over Manitowoc_5

On a recent trip, I visited the site in Manitowoc where a large, hot fragment landed and embedded itself into the asphalt pavement of a main street. That site is commemorated by a brass ring in the street and a granite plaque on the sidewalk.

Sputnik 4 landed hereSource: Author’s photos 

The Sputnik 4 debris was analyzed by the U.S. and then returned to the Soviet Union. The following photos from the 3 December 1962 issue of Aviation Week magazine show details of the largest fragment.

Sputnik 4 fragment photo 1

Sputnik 4 fragment photo 2

The Smithsonian Institution made two reproductions of this large fragment. Today, both reproductions normally are in Manitowoc; one at the Rahr-West Art Museum (on loan to a Green Bay museum on the day of my visit) and the other at the Manitowoc Visitor’s Center. Here’s a photo of the reproduction at the Visitor’s Center.

Sputnik 4 fragment DSC03294Source: Author’s photo

You can read more about Sputnik 4 in the article, “Sputnik Crashed Here,” at the following link:

http://www.roadsideamerica.com/story/12959

Many small satellites have reentered the Earth’s atmosphere at end-of-life and burned up completely, without debris reaching the Earth’s surface. No special end-of-life procedures are needed to manage the retirement of such small satellites.

Today, there is a systematic process for de-orbiting larger satellites in low Earth orbit that can produce reentry debris capable of reaching the Earth’s surface. NASA reports:

“There is a solution—spacecraft operators can plan for the final destination of their old satellites to make sure that any debris falls into a remote area. This place even has a nickname—the Spacecraft Cemetery! It’s in the Pacific Ocean and is pretty much the farthest place from any human civilization you can find.”

Spacecraft-cemeterySource: NASA

NASA has developed plans for de-orbiting the >500 ton International Space Station (ISS) at the end of its operational life, which is expected to last until at least 2028. There also is a plan to de-orbit the ISS if it must be evacuated in an emergency and cannot be recovered. You’ll find more information on NASA’s plans at the following link:

https://www.nasaspaceflight.com/2013/08/bringing-down-iss-plans-stations-demise-updated/

When the time comes, ISS reentry will be targeted for the Spacecraft Cemetery.

Spacecraft in higher orbits, including geosynchronous orbit, commonly are maneuvered into “graveyard orbits” where they are retired, outside the orbits of other active satellites. Here they will remain for a very long time without significant risk of interfering with active satellites or de-orbiting in an uncontrolled reentry.

A new option is under development by the European Space Agency (ESA), which launched the Clean Space Initiative in 2013 to address the great amount of debris and dead satellites in Earth orbit.  ESA reported:

“Scientists estimate the total number of space debris objects in orbit to be around 29 000 for sizes larger than 10 cm, 670 000 larger than 1 cm, and more than 170 million larger than 1 mm.

Any of these objects can cause harm to an operational satellite. For example, a collision with a 10 cm object would entail a catastrophic fragmentation of a typical satellite, a 1 cm object will most likely disable a spacecraft and penetrate the International Space Station shields, and a 1 mm object could destroy subsystems. Scientists generally agree that, for typical satellites, a collision with an energy-to-mass ratio exceeding 40 J/g would be catastrophic.”

The ESA’s warning signs posted in orbit proved to be ineffective.

No littering in orbit  Source:  How-to Geek Newsletter

Therefore, ESA is planning a more ambitious mission called e.DeOrbit for removing space debris.  For its demonstration mission, the ESA e.DeOrbit spacecraft is being designed to capture debris in polar orbit between 800 – 1,000 km (497 – 621 miles) altitude. Various concepts are being considered to capture the intended orbital target, including nets, arms, and tentacles. Once captured, the e.DeOrbit spacecraft will maneuver the combined satellite (target + e.DeOrbit) into a controlled reentry. The first launch of an e.DeOrbit garbage truck is expected to be in the 2023 time frame.

ESA eDeOrbit nete.DeOrbit capture using a net. Source: ESA

ESA eDeOrbit armse.DeOrbit capture using arms. Source: ESA

You can read more on the ESA Clean Space Initiative and the e.DeOrbit mission at the following links:

http://www.esa.int/Our_Activities/Space_Engineering_Technology/Clean_Space/How_to_catch_a_satellite

and

http://iaassconference2013.space-safety.org/wp-content/uploads/sites/28/2013/06/1200_Biesbroek_Innocenti.pdf

 

 

NASA’s Valkyrie (R5) Humanoid Robot is Being Groomed to Support Future Space Exploration Missions

The design of National Aeronautics and Space Administration’s (NASA’s) humanoid robot R5, commonly known as Valkyrie, started in October 2012 and it was unveiled in December 2013.

NASA Valkyrie robot  Source: NASA

Valkyrie was developed by a team from NASA’s Johnson Space Center (JSC) in Houston, in partnership with the University of Texas and Texas A&M and with funding from the state of Texas to compete in the Defense Advanced Projects Research Agency’s (DARPA) Robotics Challenge (DRC).  You’ll find a technical description of Valkyrie on the IEEE Spectrum website at the following link:

http://spectrum.ieee.org/automaton/robotics/military-robots/nasa-jsc-unveils-valkyrie-drc-robot

In the 2013 DRC Trials Valkyrie was a Track A entry, but it failed to score any points, largely due to unforeseen data communications problems.  An assessment of the developmental and operational problems encountered during the 2013 DRC Trials and another assessment of Valkyrie by the Florida Institute for Human & Machine Cognition (IHMC) is reported on the IEEE Spectrum website at the following link:

http://spectrum.ieee.org/automaton/robotics/humanoids/update-nasa-valkyrie-robot

Valkyrie did not compete in the 5 – 6 June 2015 DRC Finals. Instead, NASA brought two Valkyrie robots to the DRC Finals for display and demonstration and to help promote NASA’s Space Robotics Challenge (SRC), which was announced in March 2015.

NASA describes the SRC as follows:

“The Space Robotics Challenge is currently contemplated as a dual level, two-track challenge. The Level I challenge would involve a virtual challenge competition in software simulation and the Level II demonstration challenge would involve use of software to control a robot to perform sequences of tasks. Both Levels of the challenge would have a Track A and Track B option. A competitor would pick only one track in which to compete. Track A would utilize the Robonaut 2 platform and focus on simulated in-space tasks such as spacecraft maintenance and operations in transit to Mars, while Track B would utilize the R5 platform robot to perform simulated tasks on planetary surfaces, such as precursor habitat deployment on Mars, or disaster relief in an industrial setting on Earth.”

The highest scoring teams from the Level I (simulation) challenge will be given access to NASA-provided robots to prepare for the Level II (physical) challenge.

You can download a NASA Fact Sheet on SRC at the following link:

https://www.nasa.gov/sites/default/files/atoms/files/fs_space_robotics_150908.pdf

As part of SRC, NASA awarded Valkyrie robots to two university groups that competed in the DRC Finals. The winners announced in November 2015 were:

  • A team at MIT under the leadership of Russ Tedrake. Team MIT placed 6th in the 2015 DRC Finals with an Atlas robot built by Boston Dynamics
  • A team at Northeastern University under the leadership of Taskin Padir, who formerly was Co-PI of the Worcester Polytechnic Institute (WPI) – Carnegie Mellon University (CMU) team that placed 7th in the DRC Finals with an upgraded Atlas robot known as Warner.

Each team has possession of a Valkyrie robot for two years; receives up to $250,000; and has access to onsite and virtual technical support from NASA. NASA stated that, “The robots will have walking, balancing and manipulating capabilities so that future research may focus on the development of complex behaviors that would advance autonomy for bipedal humanoid robots.” These two teams will not compete in the SRC Level I challenge, but will be eligible to compete in the Level II challenge.

An assessment of Valkyrie’s potential roles in future missions to Mars was published in 23 June 2015 on the IEEE Spectrum website. You can read this article at the following link:

http://spectrum.ieee.org/automaton/robotics/humanoids/nasa-wants-help-training-valkyrie-robot-to-go-to-mars

The types of activities a humanoid robot might perform on a Mars mission are expected to become tasks to be demonstrated by each team choosing Track B in the SRC.

In the time between the DRC Finals and the SRC Level II competitions, I’m sure we’ll see substantial improvements in humanoid robot performance.