Helo on Mars? Not Unless NASA Is Wrong About Air Pressure.

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Mars Helicopter
JPL Figrure 1: The Mars Helicopter, a small, autonomous rotorcraft, will travel with NASA's Mars 2020 rover, currently scheduled to launch in July 2020, to demonstrate the viability and potential of heavier-than-air vehicles on the Red Planet. Image credit: NASA/JPL-Caltech
› Larger view.

       The problem with their Figure 1 is that it only shows three blades with no obvious way to prevent torque, however the movie clip that follows in the JPL article shows two rotors (four blades) - one rotating in one direction and the other in the opposite direction. This makes sense, but air density remains a concern. The two rotors are shown operating is this film clip:


JPL continues:

NASA is sending a helicopter to Mars.

The Mars Helicopter, a small, autonomous rotorcraft, will travel with the agency's Mars 2020 rover mission, currently scheduled to launch in July 2020, to demonstrate the viability and potential of heavier-than-air vehicles on the Red Planet.

"NASA has a proud history of firsts," said NASA Administrator Jim Bridenstine. "The idea of a helicopter flying the skies of another planet is thrilling. The Mars Helicopter holds much promise for our future science, discovery, and exploration missions to Mars."

The Mars Helicopter is a technology demonstration that will travel to the Red Planet with the Mars 2020 rover. It will attempt controlled flight in Mars' thin atmosphere, which may enable more ambitious missions in the future.

U.S. Rep. John Culberson of Texas echoed Bridenstine's appreciation of the impact of American firsts on the future of exploration and discovery.

"It's fitting that the United States of America is the first nation in history to fly the first heavier-than-air craft on another world," Culberson said. "This exciting and visionary achievement will inspire young people all over the United States to become scientists and engineers, paving the way for even greater discoveries in the future."

Started in August 2013 as a technology development project at NASA's Jet Propulsion Laboratory, the Mars Helicopter had to prove that big things could come in small packages. The result of the team's four years of design, testing and redesign weighs in at little under four pounds (1.8 kilograms). Its fuselage is about the size of a softball, and its twin, counter-rotating blades will bite into the thin Martian atmosphere at almost 3,000 rpm - (revolutions per minute) - about 10 times the rate of a helicopter on Earth.

Actually, we find the last statement to be misleading. While it is true that many helicopters on Earth operate at around 300 rpm, for small RC (radio controlled) helicopters, some in fact do operate at about 3,000 rpm. Comparing  a drone on Mars with a large helicopter on Earth is like comparing oranges with watermelons. So let's pause here and look at the rpm figures for rotary aircraft on Earth.

Full size helicopters main rotor spins between 250 and 600 rpm. The larger the rotor the slower it turns. The tip speed of the blade is the limiting factor.

Model helicopters on Earth operate at up to 3,000 rpm.  Since the envisioned helicopter for Mars is about 1.8 kg (under 4 pounds on Earth - under 1.508 pounds on Mars) the model figure pertains to it on Earth, and on Mars.  Here are some rpms and blade lengths of RC devises and for helicopters that can carry  people:

450 RC: 110 m/s (3000 rpm, 0.35 m tip radius)
500 RC: 126 m/s (2500 rpm, 0.48 m)
600 RC: 133 m/s (1900 rpm, 0.67 m)
700 RC: 155 m/s (1900 rpm, 0.78 m)
Hughes MD530F: 213 m/s (490 rpm, 4.15 m)
Bell 206: 210 m/s (394 rpm, 5.08 m)
Sikorsky UH-60L: 221 m/s (258 rpm, 8.18 m)

 JPL continues:

"Exploring the Red Planet with NASA's Mars Helicopter exemplifies a successful marriage of science and technology innovation and is a unique opportunity to advance Mars exploration for the future," said Thomas Zurbuchen, Associate Administrator for NASA's Science Mission Directorate at the agency headquarters in Washington. "After the Wright Brothers proved 117 years ago that powered, sustained, and controlled flight was possible here on Earth, another group of American pioneers may prove the same can be done on another world."

The helicopter also contains built-in capabilities needed for operation at Mars, including solar cells to charge its lithium-ion batteries, and a heating mechanism to keep it warm through the cold Martian nights. But before the helicopter can fly at Mars it has to get there. It will do so attached to the belly pan of the Mars 2020 rover.

"The altitude record for a helicopter flying here on Earth is about 40,000 feet. The atmosphere of Mars is only one percent that of Earth, so when our helicopter is on the Martian surface, it's already at the Earth equivalent of 100,000 feet up," said Mimi Aung, Mars Helicopter project manager at JPL. "To make it fly at that low atmospheric density, we had to scrutinize everything, make it as light as possible while being as strong and as powerful as it can possibly be."

OUR COMMENT: Again, we find the information provided to be less than straightforward. The record altitude for a full sized heliicopter on Earth was set at 40,820 feet on June 21, 1972.  Jean Boulet of France flew a single-turboshaft Aerospatiale SA 315B Lama, which had been stripped of all unnecessary equipment to reduce weight. He could have possibly gone higher, but the Lama's engine flamed out, which necessitated an autorotation to the ground and an unintentional additional record: the longest successful autorotation. However we have not seen small, RC helicopters get to anywhere near that alttitude.

In 2012 a record altitude was achieved for an RC plane at 4,930 meters/16,177 feet - nowhere near the 100,000 feet NASA is talking about. See 4931m 16177ft RC plane altitude record at https://www.youtube.com/watch?v=AKZj-7fCoMk. However, that's for a fixed wing aircraft. However, an initial search online for a record altitude for an RC helicopter did not come up with anything concrete.  A concern was seen with worries about losing sight of the hello, and having it fall on people or property below (not problems for the envisioned Mars test flight). The starting altitude was often mentioned, but it did not appear to be a major problem (at least up to altitudes of about 11,000 feet).

We will need to do more research to calculate an answer here.

 JPL continues:

Once the rover is on the planet's surface, a suitable location will be found to deploy the helicopter down from the vehicle and place it onto the ground. The rover then will be driven away from the helicopter to a safe distance from which it will relay commands. After its batteries are charged and a myriad of tests are performed, controllers on Earth will command the Mars Helicopter to take its first autonomous flight into history.

"We don't have a pilot and Earth will be several light minutes away, so there is no way to joystick this mission in real time," said Aung. "Instead, we have an autonomous capability that will be able to receive and interpret commands from the ground, and then fly the mission on its own."

The full 30-day flight test campaign will include up to five flights of incrementally farther flight distances, up to a few hundred meters, and longer durations as long as 90 seconds, over a period. On its first flight, the helicopter will make a short vertical climb to 10 feet (3 meters), where it will hover for about 30 seconds.

OUR COMMENT: There are three altitudes of interest in earth. The first is hover ceiling out of ground effect (OGE). This is the point at which power available equals power required to hoever at a given gross weight. Second is the hover ceiling in ground effect (IGE). Because ground effect reduces the induced power required, the IGE is much higher than the OGE ceiling. It sounds like NASA is counting on IGE to help them achieve flight above Mars. The third ceiling of interest is the maximum ceiling. This is the altitude in forward flight at the speed of minimum power. 

As a technology demonstration, the Mars Helicopter is considered a high-risk, high-reward project. If it does not work, the Mars 2020 mission will not be impacted. If it does work, helicopters may have a real future as low-flying scouts and aerial vehicles to access locations not reachable by ground travel.

"The ability to see clearly what lies beyond the next hill is crucial for future explorers," said Zurbuchen. "We already have great views of Mars from the surface as well as from orbit. With the added dimension of a bird's-eye view from a 'marscopter,' we can only imagine what future missions will achieve."

Mars 2020 will launch on a United Launch Alliance (ULA) Atlas V rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida, and is expected to reach Mars in February 2021.

The rover will conduct geological assessments of its landing site on Mars, determine the habitability of the environment, search for signs of ancient Martian life, and assess natural resources and hazards for future human explorers. Scientists will use the instruments aboard the rover to identify and collect samples of rock and soil, encase them in sealed tubes, and leave them on the planet's surface for potential return to Earth on a future Mars mission.

The Mars 2020 Project at JPL in Pasadena, California, manages rover development for the Science Mission Directorate at NASA Headquarters in Washington. NASA's Launch Services Program, based at the agency's Kennedy Space Center in Florida, is responsible for launch management.

For more information about NASA's Mars missions, go to:


DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown / JoAnna Wendel
NASA Headquarters, Washington
202-358-1726 / 202-358-1003
dwayne.c.brown@nasa.gov / joanna.r.wendel@nasa.gov


OUR GENERAL COMMENTS. The information provided above is largely for public relations purposes. It is our experience that Public Relations (PR) at JPL and NASA often get quote facts that are very wrong or incomplete. As we note in Section 1 of our report, Mars Correct: Critique of All NASA Mars Weather Data, for Mars Science Laboratory (MSL) PR folks published totally wrong, never changing for wind direction and speed for 9 months, and likewise never changing sunrise and sunset time for a similar period of time until we contacted Guy Webster at JPL and convinced him to alter the wind data to N/A and to alter sunrise sunset times to within one minute of our calculations. We would like  to see the reports for projects like the helo attempt written by technians who both understand their projects complete and who can write the overview given to the public. These overviews should not be dumbed down to the level of an 8th grader. Fortunately, we found what we needed at https://rotorcraft.arc.nasa.gov/Publications/files/Balaram_AIAA2018_0023.pdf with the article entitled Mars Helicopter Technology Demonstrator by J. (Bob) Balaram et. al (2018).

GRAVITY. In trying to understand how the weak gravity on Mars (3:71 m/s2 vs. 9.81 m/s2) might help get the marscopter off the ground, we searched in vain fior an answer in the JOL announcement but found it in the Balaram article. They note:

The mass of this first prototype was approximately 0.75 kg allowing free-flight under Earth gravity conditions. For the Mars Technology demonstrator EDM at approximately 1.7 kg, free-flight is not possible without the lower gravity of Mars partially compensating for its thinner atmosphere by requiring less lift to fly a vehicle than would be required on Earth. To test fly a vehicle on Earth that was designed for Mars, a gravity offload system must be used to effectively reduce the weight lifted by the rotors. The offload system consists of a constant force motor (implemented by closed-loop sensing of line tension) and a reel fitted with Dyneema filament.

THE MARSCOPTER TEST FLIGHT vs. THE AMES TEST FACILITY TESTING FOR DUST DEVIL SIMULATION. The JPL article didn't really tell us anything about the Mars Helicopter test flight, but the article by Balaram et. al (2018) was more convincing. The device was flown in a JPL 25-foot Space Simulator Chamber shown in JPL Figure 2. The primary reason that we have to doubt what it and the video clip shown earlier has to do with what happened when NASA Ames tried to replicate dust devils on Mars with a space simulator at Ames in Mountain View, California. They failed with a fan.

JPL Figure 2 - The 25-ft space simulator with Mars helicopter test equipment shown inside and the Mars Helicopter in flight..

NASA Ames Test of Martian Pressures and Dust Devils 

An effort was made at the Ames facility to simulate Martian dust devils at a pressure of 10 mbar.  NASA (2005 article)1states that, “The high-pressure air draws thin air through the tunnel like a vacuum cleaner sucks air. Scientists also compare this process to a person sucking water through a straw. The resulting simulated Mars wind moves at about 230 feet per second (70 m/s).”  Actual recorded dust devil wind speeds seen on Mars by Pathfinder and Phoenix were about 6 m/s.24 Seventy m/s is 252 kilometers per hour, nearly the strength of a category 5 hurricane.  NASA Ames was unable to replicate a dust devil with a fan spinning at the 10 mbar pressure level. They state that “the simulated (10 mbar) Martian atmosphere in the wind tunnel is so tenuous that a fan would have to spin at too high a speed to blow thin wind through the test section.” As such, it becomes harder to accept that dust devils can occur in such low pressures. The problem becomes more severe when we see Martian dust devils operating at even lower speeds, or on Arsia Mons where pressure is ~1 mbar.

Figure 3 - NASA Ames was unable to form a dust devil by using a fan.

Is it fair to compare fan blades that could not lift dust at Ames with blades on a helicopter that must lift a helicopter at similar low pressures? First let's look at the issue of particle size with respect to dust devils on Mars. The following is taken from Section 1.7 of our Report, Mars Correct: Critique of All NASA Mars Weather.

1.1.7 Dust Particle Size – The Problem of Martian Dust <2 Microns and Wind Speeds

Balme and Greeley3 also state, “The Martian atmosphere is thinner than Earth’s… so much higher wind speeds are required to pick up sand or dust on Mars.  Wind tunnel studies have shown that, like Earth, particles with diameter 80-100 μm (fine sand) are the easiest to move, having the lowest static threshold friction velocity, and that larger and smaller particles require stronger winds to entrain them into the flow.  However, much of Mars’ atmospheric dust load is very small, and the boundary layer wind speeds required to entrain such fine material are in excess of those measured at the surface (Magalhaes et al., 1999).4 Nevertheless, fine dust is somehow being injected into the atmosphere to support… haze and … local… and global… dust storms.”

The problem of dust particle size is more serious than indicated above.  Optimum particle size for direct lifting by the wind (with the lowest threshold velocity) is around 90 μm. This requires a wind at 5 meters altitude to be around 30-40 m/s. For smaller particles like the 1 μm size dust typically suspended in the air over Mars, the threshold velocity is extremely high, requiring enormous wind speeds (>500 m/s) at 5 m altitude which would never occur.  It is thus argued that saltation must be crucial to the lifting of very small particles into the air (Read and Lewis, 2004, 190).5

Saltation occurs when large particles are briefly lifted into air by surface winds, and then soon fall out by sedimentation.21 On impact with the surface, they may dislodge smaller particles and lift them into the air.  Read and Lewis indicate that the velocity that fine sand (~ 100 μm) would have on impact is only about 50 to 80 cm per second (1.8 to 2.88 kph).5

       Everywhere we look the weather plainly seen on Mars does not match what would be expected with an average pressure of 6.1 mbar/hPa at areoid (the Martian equivalent of sea level). No wonder Ames could not replicate dust devils if they used the correct particle size, expected pressure, and typical or even the most extreme winds seen on Mars.

       Dust particles are held together by static attractions. When the particles are as small as those on Mars, they may be hard to pull apart, especially if we accept the standard air pressure published by NASA (which we do not). There is no need to overcome this force to fly a small helicopter. The essential question that we will explore over the next week is how much force must be required to produce the necessary lift in the low gravity Martian environment.

THE MARS HELICOPTER AND FLIGHT IN SUCH THIN AIR. When we first heard about this project we wre tempted to dimiss it as likely impossible in the air density that NASA claims is true. We actually think that air density and pressure are about two orders of magnitude than what they tell us. It's not just because Ames couldn't replicate dust devils at 10 mbar, but because rapidly filled MER Spirit tracks required wind speeds of 80 mph at the assumed low pressures. These winds were never recorded on Mars. Nor could NASA explain drifting Barchan sand dunes. There are dust devils on Arsia Mons to altitudes of 17 km above areoid, spiral storms with 10 km eye-walls above Arsia Mons and similar storms above Olympus Mons (over 21 km high). Other reasons include extreme dust storm opacity, snow at Phoenix and elsewhere that descends 1 to 2 km in only 5 or 10 minutes, excessive aero braking, liquid water running on the surface in numerous locations at Recurring Slope Lineae (RSL) and stratus clouds 13 km above areoid.  For these reasons we argue for an average pressure at areoid of ~511 mbar rather than the accepted 6.1 mbar.  But, for the moment, let's suppose that we're wrong. Returning to the Balaram article. They wrote:

The mass of this first prototype was approximately 0.75 kg allowing free-flight under Earth gravity conditions. For the Mars Technology demonstrator EDM at approximately 1.7 kg, free-flight is not possible without the lower gravity of Mars partially compensating for its thinner atmosphere by requiring less lift to fly a vehicle than would be required on Earth.

       What the above statement tells us is that the truth here is not a matter of intuition. It's a matter of math, and this is what we will be examining as soon as we can gather together all the appropriate equations. One matter that is disturbing centers around the three potential landing sites for the 2020 mission.  We have already been to Columbia Hills (Gusev Crater) which is home to the Spirit Rover. While the Mars Helicopter is not considered to be mission critical, we would rather see a landing spot in a much lower area, one associated with running water (at the recurring slope lineae - RSL) and one where there is clearing enough air density to allow for flight of the helicopter - someplace like the Hellas Crater or in the Valles Marinaris.

These three places on Mars are potential landing sites under consideration as the destination for the Mars 2020 rover mission.

Final Three Landing Sites



1Dunbar, Brian. "NASA Simulates Small Martian 'Dust Devils' and Wind in Vacuum Tower." NASA. NASA, 03 Mar. 2005. Web. 10 Feb. 2015. http://www.nasa.gov/centers/ames/research/exploringtheuniverse/vaccumchamber.html

2Ellehoj, M.D., Gunnlaugsson H.P., Taylor  P.A.,Gheynani, B.T ., Whiteway, J., Lemmon , M.T., Bean,  K.M., Tamppari, L.K., Drube1, L., Von Holstein-Rathlou, C., Madsen, M.B., Fisher ,D, & Smith, P. (2009). Dust Devils and Vortices at the Phoenix landing site on Mars.  40th Planetary and Lunar Conference. Retrieved from http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1558.pdf

3 Balme, M., Greeley R. (2006), Dust devils on Earth and Mars, Review Geophysics., 44, RG3003,doi:10.1029/2005RG000188. 

4 Magalhaes, J.A., Schofield, J.T., & Seiff, A. (1999). 

         Results of the Mars Pathfinder atmospheric structure investigation, J. Physics. Res., 104, 8943-8955


5 Read, P. L., & Lewis, S. R. (2004). The Martian Climate Revisited, Atmosphere and Environment of a Desert Planet, Chichester, UK: Praxis.

6 Bagnold, R. A. (1954). The Physics of Blown Sand and Desert Dunes. London, Methuen.