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 in this film clip:
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. The actual anticipated rpm for the Mars helicopter is 2,800 rpm. In the helicopter lift formula (Lift = CL ½ρV2S) discussed later, V is the rpm. Since it's squared, it's not a good to overstate it by 200 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 spin 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. The rotor diameter for the Mars Helicopter is 1.21 m (that is, its tip radius is 0.605 m). Here are some rpms and blade lengths (radii) 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)
"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. 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 helo, 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).
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 hover 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:
Jet Propulsion Laboratory, Pasadena, Calif.
Dwayne Brown / JoAnna Wendel
NASA Headquarters, Washington
202-358-1726 / 202-358-1003
firstname.lastname@example.org / email@example.com
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 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 technicians who both understand their projects completely 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 much of 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 on Earth) might help get the marscopter off the ground, we searched in vain for an answer in the JPL 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.
What is Dyneema filament? Dyneema and Spectra are lightweight high-strength oriented-strand gel spun through a spinneret. They have yield strengths as high as 240 kg/mm2 or 350,000 psi and density as low as 0.97 g/cm3 (for Dyneema SK75). High-strength steels have comparable yield strengths, and low-carbon steels have yield strengths much lower (around 0.5 GPa). Since steel has a specific gravity of roughly 7.8, these materials have a strength-to-weight ratios eight times that of high-strength steels. Dyneema was invented by Albert Pennings in 1963 but made commercially available by DSM in 1990.
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 2A. The primary reason that we have to doubt JPL is what happened when NASA Ames tried to replicate dust devils on Mars with a fan in a space simulator at Ames in Mountain View, California. Ames failed. But we need more information about the fan blades and lifting dust is not the same as lifting a small toy-like helicopter in a low gravity environment. Frankly, if we are right about Martian air pressure being so much higher than NASA asserts (511 mbar at areoid vs. 6.1 mbar at areoid) , we might be able to get a helicopter to fly there that could carry people.