Tag Archives: European Space Agency

Reusable Space Launch Vehicles are Becoming a Reality

In my 12 April 2016 post, “Landing a Reusable Booster Rocket on a Dime,” I discussed the first successful flights and recoveries of the SpaceX Falcon 9 orbital booster rocket and Blue Origin’s New Shepard suborbital booster rocket. In the past year, both SpaceX and Blue Origin have successfully launched and recovered several rockets. In addition, SpaceX and Blue Origin both have reused one or more booster rockets that were flown on previous missions.

Here’s a quick look at the SpaceX and Blue Origin track records and their future plans for even more ambitious recoverable launch vehicles. We’ll also take a brief look at what competitors are doing with their existing and planned launch vehicles.

SpaceX reusable booster rockets: Falcon 9 v1.2, Falcon Heavy, and Interplanetary Transport System

The Falcon 9 v1.2 is the current, operational version of this commercial, medium-lift, two-stage family of launch vehicles. This booster has a length of 230 ft (70 m) with the payload fairing and a booster diameter of 12 ft (3.66 m). The first stage generates 1.7 million pounds of thrust from seven Merlin engines burning liquid oxygen (LOX) and RP-1 kerosene. The second stage uses a single Merlin engine optimized for vacuum conditions. The Falcon 9 v1.2 specified payload mass is:

  • 50,265 pounds (22.8 metric tons, 22,800 kg) to Low Earth Orbit (LEO),
  • 18,298 pounds (8.3 metric tons, 8,300 kg) to Geosynchronous Transfer Orbit (GTO), or
  • 8,862 pounds (4.02 metric tons, 4,020 kg) to escape velocity.

Falcon Heavy is an advanced heavy-lift, two-stage launch vehicle with a first stage comprised of three Falcon 9 booster rockets. The first stage generates 5.1 million pounds of thrust from 21 Merlin engines. The Falcon Heavy specified payload mass is:

  • 119,931 pounds (54.4 metric tons, 54,400 kg) to LEO,
  • 48,942 pounds (22.2 metric tons, 22,200 kg) to GTO, or
  • 29,983 pounds (13.6 metric tons, 13,600) kg to escape velocity.

The first Falcon Heavy is expected to be launched in late 2017.

The Falcon 9 v1.2 family and the Falcon Heavy launch vehicles are shown in the following diagram. The scale-up from Falcon 9 V1.2 to Falcon Heavy is relatively straightforward. Versions designed for recovering the first stage include four extendable landing legs near the base of the rocket. In the diagram below, you can see that one version of the Falcon 9 does not include the landing legs, sacrificing booster recovery for greater booster performance.

  Source: SpaceX   

SpaceX describes their Falcon 9 booster recovery process as follows:

“After being jettisoned, the first stage (autonomously) initiates a flip maneuver and begins a powered return back to Earth. Using a combination of reaction control thrusters, forward-mounted grid fins, and thrust from one to three of the main engines, the first stage flies either to a remotely-operated ship in the Atlantic (or Pacific) Ocean, or to land. Upon arrival, the vehicle deploys a set of landing legs and sets itself down upright.”

In practice, SpaceX expects to recover about 1/3 of its boosters on land, back near the launch site. Boosters for most of the remaining missions (primarily the higher-energy missions) will be recovered on a downrange drone ship. You can watch a short video explaining these two mission profiles at the following link:


A recovered Falcon 9 first stage booster rocket is very large:

  • overall length of about 151 ft (46 m) in landing configuration,
  • dry mass is about 50,706 pounds (23,000 kg), and
  • estimated total mass is 94,578 pounds (42,900 kg) with 5% residual fuel after landing.

The large scale of the Falcon 9 booster is apparent in the following photo taken after a landing on the stationary drone ship.

Source: SpaceXSource: Ken Kremer/kenkremer.com

You can see a video of the January 2017 Falcon 9 v1.2 launch and booster recovery at the following link:


The SpaceX mission on 30 March 2017 marked two important milestones:

  • The first reuse of a Falcon 9 booster stage, which was recovered on the drone barge and will be available again for reuse.
  • The first recovery of the costly (about $6 million) payload fairing, which was jettisoned during ascent and returned under parachute for an ocean splashdown.  The payload fairing will be reused.

As of 3 April 2017, the SpaceX Falcon 9 scorecard is:

  • Thirteen booster recoveries attempted
  • Three successful recoveries on land; first in December 2015
  • Six successful recoveries on a drone ship at sea, first in April 2016
  • Four drone ship recovery failures
  • One booster stage reused

The number of times a Falcon 9 first stage can be re-flown is not clearly specified. However, Elon Musk placed that number at 10 – 20 additional missions, and, with minor refurbishment, up to 100 missions.

Falcon Heavy missions will involve considerably more complex, simultaneous, autonomous booster recovery operations. The port and starboard Falcon 9 boosters will separate first and fly to designated recovery points, likely on land. The core booster will burn longer before separating from the second stage, which will take the payload into orbit. After separation, the core Falcon 9 booster also will fly to a designated recovery point, likely on a downrange drone ship. After a Falcon Heavy launch, it literally will be raining Falcon 9 boosters. This will be a spectacular demonstration of autonomous flight control and range safety.

You’ll find a list of Falcon 9 and Falcon Heavy launches, booster recovery status, and future missions at the following link:


SpaceX has been developing the recoverable Dragon space capsule as a family of spacecraft to be launched by the Falcon booster to conduct a variety of orbital and interplanetary missions. Like the recoverable Falcon booster, the Dragon capsule uses aerodynamic forces to slow its descent into the atmosphere and rocket propulsion for the final landing phase.

  • Dragon CRS: Since October 2012, this unmanned cargo version of the Dragon space capsule has been conducting Commercial Resupply Service (CRS) missions to the International Space Station (ISS) and returning cargo to Earth.
  • Dragon CRS “free-flyer”: The Dragon capsule also can operate independently in Earth orbit carrying a variety of payloads and returning them to Earth.
  • Dragon 2: This is a human-rated version of the Dragon space capsule. The first manned orbital flight in expected 2018.
  • Red Dragon: This is an unmanned version of Dragon 2 adapted for a mission to Mars and launched by a Falcon Heavy. Red Dragon is designed to make a propulsive landing on Mars’ surface with a 2,200 pound (1,000 kg) payload. The first launch of a Red Dragon mission could occur as early as 2018. Thereafter, SpaceX plans to conduct “regular “ (as suitable launch windows occur) Red Dragon missions to Mars.

The SpaceX Interplanetary Transport System (ITS) is a concept for an enormous launch vehicle, a manned interplanetary spacecraft, and a tanker spacecraft for refueling the interplanetary spacecraft in Earth orbit before starting the interplanetary phase of the mission. ITS will enable transportation of a large crew and equipment to Mars starting in the late 2020s. Later, when propellant plants have been established on distant bodies in the solar system, the ITS interplanetary spacecraft will be able to refuel in deep space and journey beyond Mars. The ITS is “conceptualized to be fully reusable with 1,000 uses per booster, 100 uses per tanker and 12 round trips to Mars with one spacecraft over a period of over 25 years.”

As shown in the following diagram, the ITS booster rocket carrying the interplanetary spacecraft is much larger than the National Aeronautics and Space Administration’s (NASA) Saturn V used in the 1960s and 1970s on the Apollo lunar missions. At launch, the ITS will be 400 ft (122 m) tall and 39.4 ft (12 m) in diameter.

  ITS & Saturn V. Source: SpaceX

 With 42 Raptor sub-cooled liquid methane / liquid oxygen engines, the first stage will have a liftoff thrust of about 26 million pounds, which is more than three times the thrust of Saturn V. This engine configuration is reminiscent of the Soviet N-1 moon rocket, (circa late 1960s), which clustered 30 engines in a similar configuration.

  ITS 1st stage Raptor engines. Source: SpaceX

The ITS specified payload mass is:

  • 1 million pounds (500 metric tons, 500,000 kg) to LEO with a fully expendable booster, or
  • 661,000 pounds (300 metric tons, 300,000 kg) to LEO with a reusable booster

ITS can lift ten times the payload of the Falcon Heavy booster.

The first stage of the ITS launch vehicle will be designed to fly back to the launch site for rapid servicing and reuse (i.e., to launch the refueling tanker spacecraft). In landing configuration, the ITS booster stage will be about 254 ft (77.5 m) long with a dry mass of about 275 tons (25 metric tons, 250,000 kg).

You can watch Elon Musk’s briefing on the ITS concept, including a short video of the ITS launch and interplanetary mission profile, at the following link.


Can you spell A M B I T I O U S? The SpaceX ITS concept certainly is ambitious, but it offers a much more compelling vision of future manned spaceflight than anything NASA has offered over the past decade.

Blue Origin reusable booster rockets: New Shepard and New Glenn

New Shepard is a small, single stage, suborbital rocket intended for research and commercial passenger service to the fringe of space, above the Karman line at 62 miles (330,000 ft, 100 km) above the Earth. New Shepard is named for Project Mercury astronaut Alan Shepard, who, on 5 May 1961, made the first U.S. suborbital flight in the Freedom 7 capsule launched from Cape Canaveral by a Redstone rocket. The New Shepard, in launch and recovery configurations, is shown in the following figure.

Source: https://www.stlfinder.com/3dmodels/Besos

You can see a short video showing the June 2016 fourth launch and recovery of the New Shepard booster and capsule at the following link:


As of 3 April 2017, the New Shepard scorecard is:

  • Six booster recoveries attempted
  • Five successful recoveries on land; first in November 2015
  • One booster recovery failure
  • One booster stage recovered and used five times

In all of these New Shepard unmanned test flights, the passenger capsule was recovered.

Blue Origin expects to conduct the first manned tests of New Shepard in late 2017. Commercial passenger flights, with up to six people in the space capsule, could begin in 2018.  Blue Origin has stated that they may be able to conduct as many as 50 New Shepard flights per year.

You’ll find a list of New Shepard launches and booster recovery status, at the following link:


On 29 March 2017, the National Aeronautic Association (NAA) announced that it selected Blue Origin New Shepard to receive the prestigious 2016 Robert J. Collier Trophy. The award reads:

“… for successfully demonstrating rocket booster reusability with the New Shepard human spaceflight vehicle through five successful test flights of a single booster and engine, all of which performed powered vertical landings on Earth.”

You can read the complete NAA press release at the following link:


On 12 September 2016, Jeff Bezos announced Blue Origin’s plans to develop New Glenn, which is a very large, heavy-lift, 2- or 3-stage reusable launch vehicle. New Glenn is named for Project Mercury astronaut John Glenn, who, on 20 February 1962, became the first U.S. astronaut to reach orbit. John Glenn flew in the Friendship 7 capsule launched from Cape Canaveral by an Atlas rocket.

The size of New Glenn is apparent n the following diagram. The two-stage version will be 270 ft (82 m) tall, and the three-stage version will be 313 ft (95 m) tall, approaching the size of NASA’s Saturn V.

Source: Blue Origin

 The New Glenn first stage is powered by seven BE-4 methane / LOX engines rated at a combined 3.85 million pounds of thrust (about ½ of the Saturn V), the second stage is powered by a single BE-4 engine optimized for vacuum conditions and rated at 550,000 pounds of thrust, and the third stage is powered by one BE-3 liquid hydrogen / LOX engine rated at 110,000 pounds thrust. The BE-4 engines in the reusable first stage are designed with a 100-flight lifetime.

A more detailed size comparison between New Shepard, Falcon 9 and New Glenn is shown in the following diagram.

  Source: zisadesign I /u/zisa

The scale-up from New Shepard, which is not yet operational, to New Glenn is tremendous. The specified payload mass for the two-stage version of New Glenn is:

  • 99,000 pounds (45 metric tons, 45,000 kg) to LEO,
  • 29,000 pounds (13 metric tons, 13,000 kg) to GTO

The three-stage New Glenn will carry heavier payloads.

The first stage of the New Glenn booster is being designed to fly to a designated landing site to be recovered. Aerodynamic surfaces on the first stage will give New Glenn more aerodynamic maneuvering capability than the SpaceX Falcon during the descent to landing. On 7 March 2017, Jeff Bezos gave the following details on the recovery of the first stage.

“Those aerodynamic surfaces allow us to operate with very high availability in very high wind conditions……..We don’t want to constrain the availability of launch based on the availability of the landing of the reusable booster. We put a lot of effort into letting the vehicle fly back with aerodynamic surface control instead of with propulsion.”

Of course, rocket propulsion is needed for the final phase of landing on a large, moving platform at sea. The first stage has six extendable landing legs, and can land safely if only five deploy.

New Glenn landing. Source: Blue Origin

You’ll find a short animated video showing the launch and recovery process for New Glenn at the following link:


New Glenn flights are expected to start in 2020, about three years after the first SpaceX Falcon Heavy flight.

What are other launch vehicle competitors doing?

No other operational or planned launch vehicles offer the extent of reusability found in the SpaceX Falcon and ITS and the Blue Origin New Shepard and New Glenn. The following launch vehicles will offer only partial reusability.

NASA: partially-reusable Space Launch System (SLS)

 NASA is developing the SLS to launch heavy payloads into Earth orbit and to launch the Orion manned spacecraft on a variety of near-Earth and deep space missions. As shown in the following diagram,  the SLS booster rocket has a large, liquid-fueled, two-stage core flanked by two large solid rocket boosters manufactured by Orbital ATK.

SLS is designed to put 150,000 to 290,000 pounds (70,000 to 130,000 kg) into LEO.

SLS launch vehicle: Source: NASA

As with the NASA Space Shuttle, the solid rocket boosters are designed to be recovered and reused. However, the liquid-fueled first stage booster is expendable; not designed for reuse.

United Launch Alliance (ULA): partially-reusable Vulcan

ULA currently provides medium- and heavy-lift launch with the expendable Atlas V, Delta III and Delta IV boosters. In April 2015, ULA announced that they were developing Vulcan as their Next-Generation Launch System (NGLS) to support a wide variety of Earth-orbital and interplanetary missions. In August 2016, ULA announced plans to qualify Vulcan for manned space missions.

As shown in the following diagram, Vulcan is comprised of a liquid-fueled, two-stage core rocket that can be augmented with up to six solid rocket boosters as needed for the specific mission. This basic architecture is quite similar to ULA’s current Delta III booster, but on a larger scale.

Vulcan launch vehicle. Source: ULA

Vulcan’s maximum payload capacity is expected to fall between ULA’s current Atlas V and Delta IV boosters. ULA expects that “bare bones” Vulcan launch services will sell for half the price of an Atlas V, which is less costly to fly than the Delta IV.

The Vulcan first stage is not designed to be recovered as a unit and reused like the SpaceX Falcon. Instead, ULA is planning a future version that will be partially reusable. In this version, the engines will be designed to detach from the booster after engine cutoff, descend through the atmosphere inside a heat shield, and deploy a parachute for final descent and recovery.

European Space Agency (ESA): expendable Ariane 5 & partially-reusable Ariane 6

ESA’s current Ariane 5 medium- to heavy-lift booster has a two-stage, liquid-fueled core rocket flanked by two large solid rocket boosters. The basic configuration of Ariane 5 is shown in the following diagram. Ariane V is an expendable booster, not designed for reuse.

Ariane 5. Source: Arianespace

Ariane 5 first flew in June 1996 and has been employed on a wide variety of Earth orbital and interplanetary missions. Versions of Ariane 5 can deliver a payload of more than 44,000 pounds (20,000 kg) to LEO or 23,100 pounds (10,735 kg) to GTO.

In 2014, ESA announced the basic configuration of the Ariane 6 launch vehicle. Like Ariane 5, Arian 6 will have a two-stage, liquid-fueled core rocket flanked by solid rocket boosters.

Ariane 6.  Source: adapted from BBC

Two versions are being developed:

  • Ariane 62, with two solid rocket boosters capable of launching about 11,000 pounds (5,000 kg) to GTO
  • Ariane 64, with four solid rocket boosters capable of launching about 24,000 pounds (11,000 kg) to GTO

Ariane 62 and 64 are expendable boosters, not designed for reuse.

In 2015, Airbus Defense and Space announced plans to develop a partially reusable first stage named Adeline that could enter service on a future version of Ariane 6 in the 2025 – 2030 time frame. Like ULA’s plans for Vulcan, only the Ariane 6 first stage high-value parts (i.e., the engine) would be recovered for reuse.

Stratolaunch Systems: giant aircraft plus potentially reusable, air-launched rocket booster

Paul Allen’s firm Stratolaunch Systems is building what will become the world’s largest aircraft, for use as an airborne launch platform for a variety of booster rockets that will take small-to-medium payloads into Earth orbit. The Stratolaunch Carrier will have two fuselages, six jet engines, a length of 238 feet (72 m), and a wingspan of 385 feet (117 m). The giant plane is designed to carry a rocket and payload with a combined weight of up to 550,000 pounds (250,000 kg) to a launch altitude of about 30,000 ft (9,144 m). Payloads up to 13,500 pounds (6,136 kg) can be delivered to LEO. The Stratolaunch Carrier can fly more than 1,000 miles to reach the launch point, giving it unprecedented operational flexibility for delivering payloads to orbit. An example mission profile is shown in the following figure.

Source: Stratolaunch

In 2014, Sierra Nevada Corporation (SNC) announced that it planned to use Stratolaunch as the launch platform for a scaled version of its Dream Chaser reusable spacecraft, initially for unmanned missions and later for manned missions with up to three astronauts. As shown in the following concept drawing, Dream Chaser appears to mounted on a winged, recoverable booster rocket.  For more information on the Dream Chaser reusable spacecraft, visit the SNC website at the following link:


Stratolauncher Carrier with Dream Chaser. Source: Sierra Nevada

In 2014, a planned partnership between Stratolaunch Systems and SpaceX for an air-dropped version of the Falcon booster failed to materialize. In October 2016, Stratolaunch announced a partnership with Orbital ATK, which will provide Pegasus XL expendable boosters for use in launching small satellites into Earth orbit from the Stratolaunch aircraft.

The Stratolaunch Carrier was reported to be 76% complete in 2016. Stratolaunch Systems expects the aircraft to be operational by the end of this decade. You’ll find more information on Stratolaunch here:


Other launch systems

You’ll find a list of worldwide orbital launch systems at the following link.  Most of these are expendable launch systems.


A comparison of these orbital launch systems is available here:


Not included in the above list is the new Next Generation Launch (NGL) System announced by Orbital ATK on 6 April 2017. Two versions of this new, expendable, three-stage booster will be developed to handle medium-to-large payloads, roughly comparable to the payload capability of the SpaceX Falcon 9 reusable booster. The first two stages of the NGL System will be solid fueled.   First flight is planned for 2021. You’ll find a fact sheet on the NGL system at the following link:


In conclusion

In the highly competitive launch vehicle market, booster reusability should yield a significant economic advantage. In the long run, demonstrating better launch service economies will determine the success or failure of reusable launch vehicles.

While SpaceX and Blue Origin have demonstrated the technical ability to recover and reuse the first stage of a launch vehicle, they have not yet demonstrated the long-term economic value of that capability. In 2017, SpaceX plans to re-fly about six Falcon 9 v1.2 boosters, with even more recycled boosters to be launched in 2018. Blue Origin will likely start New Shepard passenger flights in 2018.

I’m betting that SpaceX and Blue Origin will be successful and reusable boosters will find a permanent role in reducing the price for delivering cargo and people into space.




Grand Finale of the Cassini Mission to Saturn

The National Aeronautics and Space Administration’s (NASA’s) Cassini spacecraft was launched on 15 October 1997 and cruised through interplanetary space for seven years before arriving at Saturn on 30 June 2004. The Cassini spacecraft carried the European Space Agency’s (ESA’s) Huygens probe, which landed on Saturn’s largest moon, Titan, on 14 January 2005. Since then, Cassini has been performing a series of missions in orbit around Saturn, returning spectacular images and collecting scientific data on the ringed planet and its many moons.

In 2017, Cassini is performing its Grand Finale in a highly elliptical polar orbit around Saturn. The geometry for this orbital flight path is shown in the following diagram.

Cassini_20161205cSource: NASA/JPL-Caltech

In the first phase of the Grand Finale (grey orbits in the above diagram), which is underway now, Cassini’s orbit crosses the plane of Saturn’s equatorial ring system just outside the F-ring (there are just two rings outside of the F-ring: G and E). Later in 2017, Cassini’s polar orbit will be adjusted to cross the plane of the ring system insider the innermost D-ring (blue orbits). From there the spacecraft will gradually descend toward Saturn in a region that has never before been explored. The mission will end when Cassini is destroyed somewhere in Saturn’s atmosphere (orange orbit). This is scheduled to occur on September 15, 2017 at 5:07 a.m. PDT.

NASA’s Cassini mission website is at the following link:


You’ll find a NASA fact sheet on the Grand Finale here:


You can follow the countdown to the final plunge into Saturn’s atmosphere and also review the entire mission timeline and other resources here:


A few Grand Finale images taken during recent ring-grazing orbits past the F-ring are shown below.  The source of these three images and captions are: NASA/JPL-Caltech/Space Science Institute

Cassini_pia21056_deblurred cropThe above image, taken 16 January 2017, shows Saturn’s moon Daphnis (5 miles, 8 kilometers across), which orbits within the 26 mile (42 km) wide Keeler Gap (between the F and A rings). The gap appears foreshortened because of the viewing angle. The little moon’s gravity raises waves in the edges of the gap in both the horizontal and vertical directions.

Cassini_pia20511-1041Waves created by Daphnis are visible in this wider-angle view of the ring system. The F-ring is the bright, narrow ring crossing the center of the image. Since the moon moves in and out of the ring-plane, and closer to and farther from the rings’ edges as it orbits, the waves it makes change over time.

Cassini_pia21055-1041This image, taken on 18 December 2016, is one of the highest-resolution views ever taken of Saturn’s moon Pandora (52 miles, 84 kilometers across), which orbits just outside the F-ring.

13 April 2017 Update – Cassini’s close-up view of Saturn’s moon Pan

In early March, Cassini imaged Pan, which is one of Saturn’s innermost moons. As you can see in the following photos, this small moon (diameter of 221.7 miles, 35 km) has a most unusual shape. It isn’t known if the ridge circling the moon is solid, or a loose aggregation of particles with a very steep slope enabled by the moons weak gravity.

Source: NASA/JPL-Caltech/Space Science Institute

The NASA announcement and more photos of Pan are at the following link:



NuSTAR Provides a High-Resolution X-ray View of our Universe

In my 6 March 2016 post, “Remarkable Multispectral View of Our Milky Way Galaxy,” I briefly discussed several of the space-based observatories that are helping to develop a deeper understanding of our galaxy and the universe. One space-based observatory not mentioned in that post is the National Aeronautics and Space Administration (NASA) Nuclear Spectroscopic Telescope Array (NuSTAR) X-Ray observatory, which was launched on 13 June 2012 into a near equatorial, low Earth orbit. NASA describes the NuSTAR mission as follows:

“The NuSTAR mission has deployed the first orbiting telescopes to focus light in the high energy X-ray (6 – 79 keV) region of the electromagnetic spectrum. Our view of the universe in this spectral window has been limited because previous orbiting telescopes have not employed true focusing optics, but rather have used coded apertures that have intrinsically high backgrounds and limited sensitivity.

During a two-year primary mission phase, NuSTAR will map selected regions of the sky in order to:

1.  Take a census of collapsed stars and black holes of different sizes by surveying regions surrounding the center of own Milky Way Galaxy and performing deep observations of the extragalactic sky;

2.  Map recently-synthesized material in young supernova remnants to understand how stars explode and how elements are created; and

3.  Understand what powers relativistic jets of particles from the most extreme active galaxies hosting supermassive black holes.”

 The NuSTAR spacecraft is relatively small, with a payload mass of only 171 kg (377 lb). In it’s stowed configuration, this compact satellite was launched by an Orbital ATK Pegasus XL booster, which was carried aloft by the Stargazer L-1011 aircraft to approximately 40,000 feet over open ocean, where the booster was released and carried the small payload into orbit.

Orbital ATK L-1011 StargazerStargazer L-1011 dropping a Pegasus XL booster. Source: Orbital ATK

In orbit, the solar-powered NuSTAR extended to a total length of 10.9 meters (35.8 feet) in the orbital configuration shown below. The extended spacecraft gives the X-ray telescope a 10 meter (32.8 foot) focal length.

NuSTAR satelliteNuSTAR orbital configuration. Source: NASA / JPL – Caltech

NASA describes the NuSTAR X-Ray telescope as follows:

“The NuSTAR instrument consists of two co-aligned grazing incidence X-Ray telescopes (Wolter type I) with specially coated optics and newly developed detectors that extend sensitivity to higher energies as compared to previous missions such as NASA’a Chandra X-Ray Observatory launched in 1999 and the European Space Agency’s (ESA) XMM-Newton (aka High-throughput X-Ray Spectrometry Mission), also launched in 1999…….. The observatory will provide a combination of sensitivity, spatial, and spectral resolution factors of 10 to 100 improved over previous missions that have operated at these X-ray energies.”

The NASA NuSTAR mission website is at the following link:


Some examples of NuSTAR findings posted on this website are summarized below.

X-ray emitting structures of galaxies identified

In the following composite image of Galaxy 1068, high-energy X-rays (shown in magenta) captured by NuSTAR are overlaid on visible-light images from both NASA’s Hubble Space Telescope and the Sloan Digital Sky Survey.

Galaxy 1068Galaxy 1068. Source: NASA/JPL-Caltech/Roma Tre Univ

Below is a more detailed X-ray view of portion of the Andromeda galaxy (aka M31), which is the galaxy nearest to our Milky Way. On 5 January 2017, NASA reported:

“The space mission has observed 40 ‘X-ray binaries’ — intense sources of X-rays comprised of a black hole or neutron star that feeds off a stellar companion.

Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own.”

In the following image, the portion of the Andromeda galaxy surveyed by NuSTAR is in the smaller outlined area. The larger outlined area toward the top of this image is the corresponding X-ray view of the surveyed area.

Andromeda galaxyAndromeda galaxy.  Source: NASA/JPL-Caltech/GSFC

NASA describes the following mechanism for X-ray binaries to generate the observed intense X-ray emissions:

“In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can “spill over” its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays.”

You can read more on this NuStar discovery at the following link:


Composition of supernova remnants determined

Cassiopeia A is within our Milky Way, about 11,000 light-years from Earth. The following NASA three-panel chart shows Cassiopeia A originally as an iron-core star. After going supernova, Cassiopeia A scattered its outer layers, which have distributed into the diffuse structure we see today, known as the supernova remnant. The image in the right-hand panel is a composite X-ray image of the supernova remnant from both the Chandra X-ray Observatory and NuStar.

Cassiopeia ASource: NASA/CXC/SAO/JPL-Caltech

In the following three-panel chart, the composite image (above, right) is unfolded into its components. Red shows iron and green shows both silicon and magnesium, as seen by the Chandra X-ray Observatory. Blue shows radioactive titanium-44, as mapped by NuSTAR.

 Cassiopeia A componentsSource: NASA/JPL-Caltech/CXC/SAO

Supernova 1987A is about 168,000 light-years from Earth in the Large Magellanic Cloud. As shown below, NuSTAR also observed titanium in this supernova remnant.

SN 1987A titaniumSource: NASA/JPL-Caltech/UC Berkeley

These observations are providing new insights into how massive stars explode into supernovae.


There’s Increased Worldwide Interest in Asteroid and Moon Mining Missions

In my 31 December 2015 post, “Legal Basis Established for U.S. Commercial Space Launch Industry Self-regulation and Commercial Asteroid Mining,” I commented on the likely impact of the “U.S. Commercial Space Launch Competitiveness Act,” (2015 Space Act) which was signed into law on 25 November 2016. A lot has happened since then.

Planetary Resources building technology base for commercial asteroid prospecting

The firm Planetary Resources (Redmond, Washington) has a roadmap for developing a working space-based prospecting system built on the following technologies:

  • Space-based observation systems: miniaturization of hyperspectral sensors and mid-wavelength infrared sensors.
  • Low-cost avionics software: tiered and modular spacecraft avionics with a distributed set of commercially-available, low-level hardened elements each handling local control of a specific spacecraft function.
  • Attitude determination and control systems: distributed system, as above
  • Space communications: laser communications
  • High delta V small satellite propulsion systems: “Oberth maneuver” (powered flyby) provides most efficient use of fuel to escape Earth’s gravity well

Check out their short video, “Why Asteroids Fuel Human Expansion,” at the following link:


 Planetary Resources videoSource: Planetary Resources

For more information, visit the Planetary Resources home page at the following link:


Luxembourg SpaceResources.lu Initiative and collaboration with Planetary Resources

On 3 November 2016, Planetary Resources announced funding and a target date for their first asteroid mining mission:

“Planetary Resources, Inc. …. announced today that it has finalized a 25 million euro agreement that includes direct capital investment of 12 million euros and grants of 13 million euros from the Government of the Grand Duchy of Luxembourg and the banking institution Société Nationale de Crédit et d’Investissement (SNCI). The funding will accelerate the company’s technical advancements with the aim of launching the first commercial asteroid prospecting mission by 2020. This milestone fulfilled the intent of the Memorandum of Understanding with the Grand Duchy and its SpaceResources.lu initiative that was agreed upon this past June.”

The homepage for Luxembourg’s SpaceResources.lu Initiative is at the following link:


Here the Grand-Duchy announced its intent to position Luxembourg as a European hub in the exploration and use of space resources.

“Luxembourg is the first European country to set out a formal legal framework which ensures that private operators working in space can be confident about their rights to the resources they extract, i.e. valuable resources from asteroids. Such a legal framework will be worked out in full consideration of international law. The Grand-Duchy aims to participate with other nations in all relevant fora in order to agree on a mutually beneficial international framework.”

Remember the book, “The Mouse that Roared?” Well, here’s Luxembourg leading the European Union (EU) into the business of asteroid mining.

European Space Agency (ESA) cancels Asteroid Impact Mission (AIM)

ESA’s Asteroid Impact Mission (AIM) was planning to send a small spacecraft to a pair of co-orbital asteroids, Didymoon and Didymos, in 2022. Among other goals, this ESA mission was intended to observe the NASA’s Double Asteroid Redirection Test when it impacts Didymoon at high speed. ESA mission profile for AIM is described at the following link:


On 2 Dec 2016, ESA announced that AIM did not win enough support from member governments and will be cancelled. Perhaps the plans for an earlier commercial asteroid mission marginalized the value of the ESA investment in AIM.

Japanese Aerospace Exploration Agency (JAXA) announces collaboration for lunar resource prospecting, production and delivery

On 16 December 2016, JAXA announced that it will collaborate with the private lunar exploration firm, ispace, Inc. to prospect for lunar resources and then eventually build production and resource delivery facilities on the Moon.

ispace is a member of Japan’s Team Hakuto, which is competing for the Google Lunar XPrize. Team Hakuto describes their mission as follows:

“In addition to the Grand Prize, Hakuto will be attempting to win the Range Bonus. Furthermore, Hakuto’s ultimate target is to explore holes that are thought to be caves or “skylights” into underlying lava tubes, for the first time in human history.  These lava tubes could prove to be very important scientifically, as they could help explain the moon’s volcanic past. They could also become candidate sites for long-term habitats, able to shield humans from the moon’s hostile environment.”

Hakuto is facing the challenges of the Google Lunar XPRIZE and skylight exploration with its unique ‘Dual Rover’ system, consisting of two-wheeled ‘Tetris’ and four-wheeled ‘Moonraker.’ The two rovers are linked by a tether, so that Tetris can be lowered into a suspected skylight.”

Hakuto rover-with-tail

Team Hakuto dual rover. Source: ispace, Inc.

So far, the team has won one Milestone Prize worth $500,000 and must complete its lunar mission by the end of 2017 in order to be eligible for the final prizes. You can read more about Team Hakuto and their rover on the Google Lunar XPrize website at the following link:


Building on this experience, and apparently using the XPrize rover, ispace has proposed the following roadmap to the moon (click on the graphic to enlarge).

ispace lunar roadmapSource: ispace, Inc.

This ambitious roadmap offers an initial lunar resource utilization capability by 2030. Ice will be the primary resource sought on the Moon. Ispace reports:

“According to recent studies, the Moon houses an abundance of precious minerals on its surface, and an estimated 6 billion tons of water ice at its poles. In particular, water can be broken down into oxygen and hydrogen to produce efficient rocket fuel. With a fuel station established in space, the world will witness a revolution in the space transportation system.”

The ispace website is at the following link:




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:


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:


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:


A subscription is required for access to the full paper.

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

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:


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:


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.”


The Universe is Isotropic

The concepts of up and down appear to be relatively local conventions that can be applied at the levels of subatomic particles, planets and galaxies. However, the universe as a whole apparently does not have a preferred direction that would allow the concepts of up and down to be applied at such a grand scale.

A 7 September 2016 article entitled, “It’s official: You’re lost in a directionless universe,” by Adrian Cho, provides an overview of research that demonstrates, with a high level of confidence, that the universe is isotropic. The research was based on data from the Planck space observatory. In this article, Cho notes:

“Now, one team of cosmologists has used the oldest radiation there is, the afterglow of the big bang, or the cosmic microwave background (CMB), to show that the universe is “isotropic,” or the same no matter which way you look: There is no spin axis or any other special direction in space. In fact, they estimate that there is only a one-in-121,000 chance of a preferred direction—the best evidence yet for an isotropic universe. That finding should provide some comfort for cosmologists, whose standard model of the evolution of the universe rests on an assumption of such uniformity.”

The European Space Agency (ESA) developed the Planck space observatory to map the CMB in microwave and infrared frequencies at unprecedented levels of detail. Planck was launched on 14 May 2009 and was placed in a Lissajous orbit around the L2 Lagrange point, which is 1,500,000 km (930,000 miles) directly behind the Earth. L2 is a quiet place, with the Earth shielding Planck from noise from the Sun. The approximate geometry of the Earth-Moon-Sun system and a representative spacecraft trajectory (not Planck, specifically) to the L2 Lagrange point is shown in the following figure.

Lissajous orbit L2Source: Abestrobi / Wikimedia Commons

The Planck space observatory entered service on 3 July 2009. At the end of its service life, Planck departed its valuable position at L2, was placed in a heliocentric orbit, and was deactivated on 23 October 2013. During more than four years in service, Planck performed its CBM mapping mission with much greater resolution than NASA’s Wilkinson Microwave Anisotropy Probe, which operated from 2001 to 2010.

One key result of the Planck mission is the all-sky survey shown below.

Planck_CMB_black_background_fullwidthPlanck all-sky survey. Source; ESA / Planck Collaboration

ESA characterizes this map as follows:

“The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today.”

The researchers who reported that the universe was isotropic noted that an anisotropic universe would leave telltale patterns in the CMB. However, these researchers found that the actual CMB shows only random noise and no signs of such patterns.

You’ll find more details on the Planck mission and scientific results on the ESA’s website at the following link:


You can read Adrian Cho’s article on the Science magazine website at the following link:


The original research paper, “How Isotropic is the Universe?” by Saadeh, D., et al., was published on 21 September 2016. It is available on the Physical Review Letters website, if you have a subscription, at the following link:




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:



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:


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:



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:


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.

So, when will eLISA be launched? The eLISA website currently suggests a launch in 2028. See Science Context 2028 on the eLISA website at the following link:


In the 6 June 2016 LISA Pathfinder briefing, LPF and ESA officials raised the possibility of a somewhat later launch date (2029 – 2032 time frame). Whenever it happens, eLISA will be a remarkable collaborative technical achievement and a new window to our universe.

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:


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:


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:


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:




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:


and the ASU website at the following link:


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:




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:


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:


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:


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:


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:


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.