Tag Archives: MIT

Riding the Phantom Zephyr

1.  Background

When charged molecules in the air are subjected to an electric field, they are accelerated. When these charged molecules collide with neutral ones, they transfer part of their momentum, leading to air movement known as an “ionic wind.”  This basic process is shown in the following diagram, which depicts a strong electric field between a discharge electrode (left) and a ground electrode (right), and the motion of negative ions toward the ground electrode where they are collected.  The neutral molecules pass through the ground electrode and generate the thrust called the ionic wind.

This post summarizes work that has been done to develop ionic wind propulsion systems for aircraft.  The particular projects summarized are the following:

  • Major Alexander de Seversky’s Ionocraft vertical lifter (1964)
  • The Festo b-IONIC Airfish airship (2005)
  • NASA ionic wind study (2009)
  • The MIT electroaerodynamic (EAD) heaver-than-air, fixed wing aircraft (2018)

2.  Scale model of ion-propelled Ionocraft vertical takeoff lifter flew in 1964

Major Alexander de Seversky developed the design concept for a novel aircraft concept called the “Ionocraft,” which was capable of hovering or moving in any direction at high altitudes by means of ionic discharge. His design for the Ionocraft is described in US Patent 3,130,945, “Ionocraft,” dated 28 April 1964.  You can read this patent here: https://patents.google.com/patent/US3130945A/en

The operating principle of de Seversky’s Ionocraft propulsion system is depicted in the following graphic.

Ion propulsion scheme implemented in the de Seversky Ionocraft. 
Source: Popular Mechanics, August 1964

In 1964, de Seversky built a two-ounce (57 gram) Ionocraft scale model and demonstrated its ability to fly while powered from an external 90 watt power conversion system (30,000 volts at 3 mA), significantly higher that conventional aircraft and helicopters.  This translated into a power-to-weight ratio of about 0.96 hp/pound.  You can watch a short 1964 video of a scale model Ionocraft test flight here: 

Screenshot showing Ionocraft scale model in flight
Screenshot showing ionic wind downdraft under an Ionocraft scale model in flight

De Seversky’s Ionocraft and its test program are described in an article in the August 1964 Popular Mechanics magazine, which is available at the following link:  https://books.google.com/books?id=ROMDAAAAMBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Alexander de Seversky’s one-man Ionocraft concept.
Source: Popular Mechanics Archive, August 1964
Alexander de Seversky’s Ionocraft commuter concept.
Source: Popular Mechanics Archive, August 1964
1960s Soviet concept for a passenger carrying Ionocraft.
The Museum of Unnatural Mystery, http://www.unmuseum.org/

In the 1960s, engineers found that Ionocraft technology did not scale up well and they were unable to build a vehicle that could generate enough lift to carry the equipment needed to produce the electricity needed to drive it.

3.  The first free-flying ion-propelled aircraft flew in 2005: the Festo b-IONIC Airfish

The Festo b-IONIC Airfish airship was developed at the Technical University of Berlinwith guidance of the firm Festo AG & Co. KG.  This small, non-rigid airship is notable because, in 2005, it became the first aircraft to fly with a solid state propulsion system.  The neutrally-buoyant Airfish only flew indoors, in a controlled environment, at a very slow speed, but it flew.

Airfish. Source:  Festo AG & Co. KG

Some of the technical characteristics of the Airfish are listed below:

  • Length:  7.5 meters (24.6 ft)
  • Span: 3.0 meters (9.8 ft)
  • Shell diameter: 1.83 meters (6 ft)
  • Helium volume:  9.0 m3(318 ft3)
  • Total weight:  9.04 kg (19.9 lb)
  • Power source in tail: 12 x 1,500 mAh lithium-ion polymer cells (18 Ah total)
  • Power source per wing (two wings): 9 x 3,200 mAh lithium-ion polymer cells (28.8 Ah total)
  • High voltage: 20,000 to 30,000 volts
  • Buoyancy:  9.0 – 9.3 kg (19.8 – 20.5 lb)
  • Total thrust:  8 – 10 grams (0.018 – 0.022 pounds) 
  • Maximum velocity: 0.7 meters/sec (2.5 kph; 1.6 mph)

The b-IONIC Airfish employed two solid state propulsion systems, an electrostatic ionic jet and a plasma ray, which Festo describes as follows:

  • Electrostatic ionic jet:  “At the tail end Airfish uses the classic principle of an electrostatic ionic jet propulsion engine. High-voltage DC-fields (20-30 kV) along thin copper wires tear electrons away from air molecules. The positive ions thus created are then accelerated towards the negatively charged counter electrodes (ring-shaped aluminum foils) at high speeds (300-400 m/s), pulling along additional neutral air molecules. This creates an effective ion stream with speeds of up to 10 m/s.”
  • Plasma-ray:  “The side wings of Airfish are equipped with a new bionic plasma-ray propulsion system, which mimics the wing based stroke principle used by birds, such as penguins, without actually applying movable mechanical parts. As is the case with the natural role model, the plasma-ray system accelerates air in a wavelike pattern while it is moving across the wings.”
Airfish.  Source: Festo AG & Co. KG
Airfish.  Source: Festo AG & Co

The Festo b-IONIC Airfish demonstrated that a solid state propulsion system was possible.  The tests also demonstrated that the solid state propulsion systems also reduced drag, raising the intriguing possibility that it may be possible to significantly reduce drag if an entire vessel could be enclosed in a ionized plasma bubble.You’ll find more information on the Festo b-IONIC Airfish, its solid state propulsion system and implications for drag reduction in the the Festo brochure here: https://www.festo.com/net/SupportPortal/Files/344798/b_IONIC_Airfish_en.pdf

You can watch a 2005 short video on the Festo b-IONIC Airfish flight here:

4.  NASA ionic wind study – 2009

A corona discharge device generates an ionic wind, and thrust, when a high voltage corona discharge is struck between sharply pointed electrodes and larger radius ground electrodes.

In 2009, National Aeronautics & Space Administration (NASA) researchers Jack Wilson, Hugh Perkins and William Thompson conducted a study to examine whether the thrust of corona discharge systems could be scaled to values of interest for aircraft propulsion.  Their results are reported in report NASA/TM-2009-215822, which you’ll find at the following link: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100000021.pdf

Key points of the study included:

  • Different types of high voltage electrodes were tried, including wires, knife-edges, and arrays of pins. A pin array was found to be optimum. 
  • Parametric experiments, and theory, showed that the thrust per unit power could be raised from early values of 5 N/kW to values approaching 50 N/kW, but only by lowering the thrust produced, and raising the voltage applied. 
  • In addition to using DC voltage, pulsed excitation, with and without a DC bias, was examined. The results were inconclusive as to whether this was advantageous. 
  • It was concluded that the use of a corona discharge for aircraft propulsion did not seem very practical.”

5.  The first heavier-than-air, fixed-wing, ion-propelled aircraft flew in 2018

On 21 November 2018, MIT researchers reported successfully flying the world’s first heavier-than-air, fixed-wing, ion-propelled (electroaerodynamic, EAD) aircraft.  You can read the paper by Haofeng Xu, et al., “Flight of an aeroplane with solid-state propulsion,” on the Nature website here: https://www.nature.com/articles/s41586-018-0707-9

The design of the MIT EAD aircraft is shown below:

a, Computer-generated rendering of the EAD airplane. 
b, Photograph of actual EAD airplane (after multiple flight trials).

Some of the technical characteristics of this MIT aircraft are listed below:

  • Wingspan: 4.9 meters (16 ft)
  • Total weight: 2.45 kg (5.4 lb)
  • Power source: powered by 54 x 3.7 volt 150 mAh lithium-ion polymer cells (8.1 Ah total)
  • High voltage: 40,000 volts (+ 20,000 volts / – 20,000 volts)
  • Total thrust: 3.2 N, 326 grams (0.718 pounds) 
  • Maximum velocity: 4.8 meters/sec (17.3 kph; 10.7 mph)

In their paper, the MIT researchers reported:

  • “We performed ten flights with the full-scale experimental aircraft at the MIT Johnson Indoor Track…. Owing to the limited length of the indoor space (60 m), we used a bungeed launch system to accelerate the aircraft from stationary to a steady flight velocity of 5 meters/sec within 5 meters, and performed free flight in the remaining 55 meters of flight space. We also performed ten unpowered glides with the thrusters turned off, in which the airplane flew for less than 10 meters. We used cameras and a computer vision algorithm to track the aircraft position and determine the flight trajectory.”
  • “All flights gained height over the 8–9 second segment of steady flight, which covered a distance of 40–45 meters…. The average physical height gain of all flights was 0.47 meters…. However, for some of the flights, the aircraft velocity decreased during the flight. An adjustment for this loss of kinetic energy…. results in an energy equivalent height gain, which is the height gain that would have been achieved had the velocity remained constant. This was positive for seven of the ten flights, showing that better than steady-level flight had been achieved in those cases.”
  • “In this proof of concept for this method of propulsion, the realized thrust-to-power ratio was 5 N/kW1, which is of the order of conventional airplane propulsion methods such as the jet engine.”  Overall efficiency was estimated to be 2.56%.

The propulsion principles of the MIT EAD aircraft are explained in relation to the following diagram in the November 2018 article by Franck Plouraboué, “Flying With Ionic Wind,” which you can read on the Nature website at the following link:  https://www.nature.com/articles/d41586-018-07411-z

The following diagram and explanatory text are reproduced from that article.

  • In Figure a, above: …an electric field (not shown) is applied to the region surrounding a fine wire called the emitter (shown in cross-section). The field induces electron cascades, whereby free electrons collide with air molecules (not shown in the cascades) and consequently free up more electrons. This process produces charged air molecules in the vicinity of the emitter — a corona discharge. Depending on the electric field, negatively or positively charged molecules drift away (red arrows) from the emitter. These molecules collide with neutral air molecules, generating an ionic wind (black arrows). 
  • In Figure b, above: The aircraft uses a series of emitters and devices called collectors, the longitudinal directions of which are perpendicular to the ionic wind. The flow of charged air molecules occurs mainly along the directions (red arrows) joining emitters and collectors. Consequently, the ionic wind is accelerated (black arrows) predominantly in these regions. 

You can view a short video of the MIT EAD aircraft test flights here:  

6.  The future of ionic propulsion for aerospace applications.

If it can be successfully developed to much larger scales, ionic propulsion offers the potential for aircraft to fly in the atmosphere on a variety of practical missions using only ionized air for propulsion.  Using other ionized fluid media, ionic propulsion could develop into a means to fly directly from the surface of the earth into the vacuum of space and then operate in that environment.In 2006, the Technical University of Berlin’s Airfish project manager, Berkant Göksel, founded the firm Electrofluidsystems Ltd., which in 2012 was rebranded as IB Göksel Electrofluidsystems.  This firm presently is developing a new third generation of plasma-driven airships with highly reduced ozone and nitrogen oxide (NOx) emissions, magneto-plasma actuators for plasma flow control, and the company’s own blended wing type flying wing products.  You’ll find their website here:  https://www.electrofluidsystems.com

Source: Electrofluidsystems TU Berlin
Advanced plasma-driven aircraft concept. Source:  Electrofluidsystems TU Berlin

MIT researchers are developing designs for high-performance aircraft using ionic propulsion.  Theoretically, efficiency improves with speed, with an efficiency of 50% possible at a speed of about 1,000 kph (621 mph).  You can watch a short video on MIT work to develop a Star Trek-like ion drive aircraft here:  

7.  More reading on electrodynamic propulsion for aircraft

General

MIT electroaerodynamic aircraft

Ionocraft lifters

Standby for a New Round of Gravitational Wave Detection

Since late August 2017, the US LIGO 0bservatories in Washington and Louisiana and the European Gravitational Observatory (EGO), Virgo, in Italy, have been off-line for updating and testing.  These gravitational wave observatories were set to start Observing Run 3 (O3) on 1 April 2019 and conduct continuous observations for one year.  All three of these gravitational wave observatories have improved sensitivities and are capable of “seeing” a larger volume of the universe than in Observing Run 2 (O2).

Later in 2019, the Japanese gravitational wave observatory, KAGRA, is expected to come online for the first time and join O3.  By 2024, a new gravitational wave observatory in India is expected to join the worldwide network.

On the advent of this next gravitational wave detection cycle, here’s is a brief summary of the status of worldwide gravitational wave observatories.

Advanced LIGO 

The following upgrades were implemented at the two LIGO observatories since Observing Run 2 (O2) concluded in 2017:

  • Laser power has been doubled, increasing the detectors’ sensitivity to gravitational waves.
  • Upgrades were made to LIGO’s mirrors at both locations, with five of eight mirrors being swapped out for better-performing versions.
  • Upgrades have been implemented to reduce levels of quantum noise. Quantum noise occurs due to random fluctuations of photons, which can lead to uncertainty in the measurements and can mask faint gravitational wave signals. By employing a technique called quantum “squeezing” (vacuum squeezing), researchers can shift the uncertainty in the laser light photons around, making their amplitudes less certain and their phases, or timing, more certain. The timing of photons is what is crucial for LIGO’s ability to detect gravitational waves.  This technique initially was developed for gravitational wave detectors at the Australian National University, and matured and routinely used since 2010 at the GEO600 gravitational wave detector in Hannover, Germany,

In comparison to its capabilities in 2017 during O2, the twin LIGO detectors have a combined increase in sensitivity of about 40%, more than doubling the volume of the observable universe.

You’ll find more news and information on the LIGO website at the following link:

https://www.ligo.caltech.edu/news

GEO600 

GEO600 is a modest-size laser interferometric gravitational wave detector (600 meter / 1,969 foot arms) located near Hannover, Germany. It was designed and is operated by the Max Planck Institute for Gravitational Physics, along with partners in the United Kingdom.

In mid-2010, GEO600 became the first gravitational wave detector to employ quantum “squeezing” (vacuum squeezing) and has since been testing it under operating conditions using two lasers: its standard laser, and a “squeezed-light” laser that just adds a few entangled photons per second but significantly improves the sensitivity of GEO600.  In a May 2013 paper entitled, “First Long-Term Application of Squeezed States of Light in a Gravitational Wave Observatory,” researchers reported the following results of operational tests in 2011 and 2012.

“During this time, squeezed vacuum was applied for 90.2% (205.2 days total) of the time that science-quality data were acquired with GEO600. A sensitivity increase from squeezed vacuum application was observed broadband above 400 Hz. The time average of gain in sensitivity was 26% (2.0 dB), determined in the frequency band from 3.7 to 4.0 kHz. This corresponds to a factor of 2 increase in the observed volume of the Universe for sources in the kHz region (e.g., supernovae, magnetars).”

The installed GEO600 squeezer (in the foreground) inside the GEO600 clean room together with the vacuum tanks (in the background).  
Source: http://www.geo600.org/15581/1-High-Tech

While GEO600 has conducted observations in coordination with LIGO and Virgo, GEO600 has not reported detecting gravitational waves. At high frequencies GEO600 sensitivity is limited by the available laser power. At the low frequency end, the sensitivity is limited by seismic ground motion.

You’ll find more information on GEO600 at the following link:

http://www.geo600.org/3020/About-GEO600

Advanced Virgo, the European Gravitational Observatory (EGO)

At Virgo, the following upgrades were implemented since Observing Run 2 (O2) concluded in 2017:

  • The steel wires used during O2 observation campaign to suspend the four main mirrors of the interferometer have been replaced.  The 42 kg (92.6 pound) mirrors now are suspended with thin fused-silica (glass) fibers, which are expected to increase the sensitivity in the low-medium frequency region.  The mirrors in Advanced LIGO have been suspended by similar fused-silica fibers since those two observatories went online in 2015.
  • A more powerful laser source has been installed, which should improve sensitivity at high frequencies. 
  • Quantum “squeezing” has been implemented in collaboration with the Albert Einstein Institute in Hannover, Germany.  This should improve the sensitivity at high frequencies.
Virgo mirror suspension with fused-silica fibers.  
Source: EGO/Virgo Collaboration/Perciballi

In comparison to its capabilities in 2017 during O2, Virgo sensitivity has been improved by a factor of about 2, increasing the volume of the observable universe by a factor of about 8.

You’ll find more information on Virgo at the following link:

http://www.virgo-gw.eu

Japan’s KAGRA 

KAGRA is a cryogenically-cooled laser interferometer gravitational wave detector that is sited in a deep underground cavern in Kamioka, Japan.  This gravitational wave observatory is being developed by the Institute for Cosmic Ray Research (ICRR) of the University of Tokyo.  The project website is at the following link:

https://gwcenter.icrr.u-tokyo.ac.jp/en/

One leg of the KAGRA interferometer.  
Source: ICRR, University of Tokyo

The cryogenic mirror cooling system is intended to cool the mirror surfaces to about 20° Kelvin (–253° Celsius) to minimize the motion of molecules (jitter) on the mirror surface and improve measurement sensitivity.   KAGRA’s deep underground site is expected to be “quieter” than the LIGO and VIRGO sites, which are on the surface and have experienced effects from nearby vehicles, weather and some animals.

The focus of work in 2018 was on pre-operational testing and commissioning of various systems and equipment at the KAGRA observatory. In December 2018, the KAGRA Scientific Congress reported that, “If our schedule is kept, we expect to join (LIGO and VIRGO in) the latter half of O3…”   You can follow the latest news from the KAGRA team here:

https://gwcenter.icrr.u-tokyo.ac.jp/en/category/latestnews

LIGO-India

IndIGO, the Indian Initiative in Gravitational-wave Observations, describes itself as an initiative to set up advanced experimental facilities, with appropriate theoretical and computational support, for a multi-institutional Indian national project in gravitational wave astronomy.  The IndIGO website provides a good overview of the status of efforts to deploy a gravitational wave detector in India.  Here’s the link:

http://www.gw-indigo.org/tiki-index.php?page=Welcome

On 22 January 2019, T. V. Padma reported on the Naturewebsite that India’s government had given “in-principle” approval for a LIGO gravitational wave observatory to be built in the western India state of Maharashtra. 

“India’s Department of Atomic Energy and its Department of Science and Technology signed a memorandum of understanding with the US National Science Foundation for the LIGO project in March 2016. Under the agreement, the LIGO Laboratory — which is operated by the California Institute of Technology (Caltech) in Pasadena and the Massachusetts Institute of Technology (MIT) in Cambridge — will provide the hardware for a complete LIGO interferometer in India, technical data on its design, as well as training and assistance with installation and commissioning for the supporting infrastructure. India will provide the site, the vacuum system and other infrastructure required to house and operate the interferometer — as well as all labor, materials and supplies for installation.”

India’s LIGO observatory is expected to cost about US$177 million.  Full funding is expected in 2020 and the observatory currently is planned for completion in 2024.  India’s Inter-University Centre for Astronomy and Astrophysics (IUCAA), also in Maharashtra  state, will lead the project’s gravitational-wave science and the new detector’s data analysis.

For T. V. Padma’s complete article, refer to: 

https://www.nature.com/articles/d41586-019-00184-z.

Spatial resolution of gravitational wave events

Using only the two US LIGO detectors, it is not possible to localize the source of gravitational waves beyond a broad sweep through the sky.  On 1 August 2017, Virgo joined LIGO during the second Observation Run, O2. While the LIGO-Virgo three-detector network was operational for only three-and-a-half weeks, five gravitational wave events were observed.  As shown in the following figure, the spatial resolution of the source was greatly improved when a triple detection was made by the two LIGO observatories and Virgo. These events are labeled with the suffix “HLV”.  

Source:  http://www.virgo-gw.eu, 3 December 2018

The greatly reduced areas of the triple event localizations demonstrate the capabilities of the current global gravitational wave observatory network to resolve the source of a gravitational-wave detection.  The LIGO and Virgo Collaboration reports that it can send Open Public Alerts within five minutes of a gravitational wave detection.

With timely notification and more precise source location information, other land-based and space observatories can collaborate more rapidly and develop a comprehensive, multi-spectral (“multi-messenger”) view of the source of the gravitational waves.

When KAGRA and LIGO-India join the worldwide gravitational wave detection network, it is expected that source localizations will become 5 to 10 times more accurate than can be accomplished with just the LIGO and Virgo detectors.

For more background information on gravitational-wave detection, see the following Lyncean posts:

DARPA Maximum Mobility & Manipulation (M3) Program is Showing Impressive New Results with the Boston Dynamics / MIT Cheetah

The two primary goals of the M3 program are:

  • Create a significantly improved scientific framework for the rapid design and fabrication of robot systems and greatly enhance robot mobility and manipulation in natural environments.
  • Significantly improve robot capabilities through fundamentally new approaches to the engineering of better design tools and fabrication methods.

More details on the M3 program are presented on the following DARPA website:

http://www.darpa.mil/our_work/dso/programs/maximum_mobility_and_manipulation_(m3).aspx

In September 2012, the DARPA / Boston Dynamics / MIT Cheetah 4-legged robot, being developed under the M3 program, reached a top speed of over 29 mph in a tethered test on a treadmill, exceeding the fastest speed ever run by a human, Usain Bolt, at 27.78 mph in a 20-meter sprint. You can see a video of this tethered test of the Cheetah at the following link:

https://www.youtube.com/watch?v=YqpO58x7vuE

In May 2015, the Cheetah demonstrated it’s ability to hurdle obstacles up to 18”tall in both tethered treadmill and untethered indoor track tests while running at an average speed of about 5 mph.

MIT-Jumping-Cheetah-1  Source: MIT

You can read the article and see a video of this test at the following link:

https://newsoffice.mit.edu/2015/cheetah-robot-lands-running-jump-0529

As described in this article:

“To get a running jump, the robot plans out its path, much like a human runner: As it detects an approaching obstacle, it estimates that object’s height and distance. The robot gauges the best position from which to jump, and adjusts its stride to land just short of the obstacle, before exerting enough force to push up and over. Based on the obstacle’s height, the robot then applies a certain amount of force to land safely, before resuming its initial pace.”

 On the treadmill, the Cheetah only had about a meter in which to detect the obstacle and then plan and execute the jump. Nonetheless, the Cheetah cleared the obstacles about 70% of the time. I can only imagine that a human runner on that same treadmill might not have performed much better. In the untethered tests on an indoor track, the Cheetah cleared the obstacles about 90% of the time. Future tests will explore the ability of the Cheetah to clear hurdles on softer terrain.

You can see more high-mobility robots being developed by Boston Dynamics at the following link:

http://www.bostondynamics.com/index.html

These robots include:

  • Atlas: a high mobility, humanoid (bipedal) robot designed to negotiate outdoor, rough terrain. Atlas will be one of the competitors in the DARPA Robotics Challenge (DRC) Finals that will take place on 5 – 6 June 2015 at Fairplex in Pomona, California. See my 23 March 2015 post for more information on the DRC Finals.
  • LS3: a rough-terrain quadruped robot designed to go anywhere soldiers go on foot, helping carry their load.
  • PETMAN: an anthropomorphic (bipedal) robot designed for testing chemical protection clothing.
  • BigDog: a rough-terrain quadruped robot that walks, runs, climbs and carries heavy loads.
  • Sand Flea: a small robot that drives like an remote-controlled car on flat terrain, but can jump 30 ft. into the air to overcome obstacles
  • RHex: a six-legged, high mobility robot designed to climb in rock fields, mud, sand, vegetation, fallen telephone poles, railroad tracks, and up slopes and stairways.
  • RiSE: a robot that uses micro-claws to climb vertical terrain such as walls, trees and fences.
  • LittleDog: a quadruped robot designed for research on learning locomotion.