Vertiflite May/June 2021

MiMi Aung, Ingenuity project manager at JPL.

Aung and team celebrate Ingenuity’s first flight during the wee hours of the morning on April 19.

performed, Ingenuity was expected to achieve a maximum altitude of about 16.4 ft (5 m). Horizontal translational velocity of up to 4.5 mph (2 m/s) was planned; accounting for the harsh Mars winds, its true airspeed was limited to 22.4 mph (10 m/s). If those tests are successful, there is a possibility that Ingenuity could be pushed beyond initial goals, possibly on the final flight. Engineering Ingenuity Ingenuity was started in August 2013 but was only formally added to the Mars mission in May 2018. Several design criteria had to be met before Ingenuity could be part of the Mars mission. Maximum gross weight had to be light enough to be carried into space and to fly in the thin Mars atmosphere. In addition, the rotors had to be large enough to generate sufficient lift, according to Balaram. Mars’ atmosphere is around 100 times thinner than Earth’s, with over 95% carbon dioxide and 2.7% nitrogen, though gravity is only one-third that of our home planet. Several hours of testing a one-third-scale model in a 25-ft (7.6-m) diameter chamber filled primarily with carbon dioxide to simulate theMars atmosphere supported the hypothesis that Ingenuity could sustain flight on the Red Planet. The model used twin, counter- rotating blades to whip through the thin Martian atmosphere at 2,500-3,000 revolutions per minute, which which produces a tip Mach number near 0.65-0.7, similar to manned helicopters on Earth. Before the first flight, Balaram said: “We will be looking at engineering performance. We hope that Ingenuity will help expand our aerial mobility on Mars.” Dr. Farah Alibay, JPL’s Perseverance integration lead for Ingenuity, smiling after the rover successfully touched down on Feb. 18.

of air density to its viscosity. In the case of Ingenuity, the Re is the product of the density, the rotor blade chord and the velocity over the blade, divided by dynamic viscosity. The Re for Ingenuity is nominally around 11,000, compared to about 5 million for a conventional helicopter on Earth. “The engineering challenge is to have enough blade area and chord Reynolds number to generate lift in the thin Mars atmosphere at minimal size,” said Dr. Anubhav Datta, associate professor at the University of Maryland. “The two-rotor, two blades per rotor design is the most compact configuration to meet those needs.” Datta helped JPL and AeroVironment carry out dynamic stress analysis during the Ingenuity design phase. Early in the program, tests revealed that sustained flight of Ingenuity could not be achieved with a desktop pilot using a joystick, due to the long delays between transmission signals. Ingenuity had to be autonomous, obeying general commands that transmitted from JPL to a Mars Reconnaissance Orbiter, down to Perseverance, and over to Ingenuity. Controlled and sustained flight could be achieved with the help of onboard sensors and high-speed computers. Ingenuity is designed to execute the flight maneuvers autonomously. Future Flights As this article was being completed, NASA’s JPL was reviewing the data prior to additional flight tests. If the overall mission is successful, rotorcraft drones could become valuable assets for future missions in mapping the surface of Mars, scouting routes for rovers and exploring sources of life and water — the key ingredient to maintaining a long-term presence on the planet. Ingenuity carried a tiny piece of muslin from the Wright Flyer that made the first controlled, powered flight on Earth, at Kitty Hawk, North Carolina, on Dec. 17, 1903. That flight lasted only 12 seconds and only reached an altitude of about 8 ft (2.4 m).

May / June 2021

Maintaining flight above Mars with a low Reynolds number (Re) is one of several areas to be examined. The Re is the ratio

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