April 24, 2019 – Jay McMahon has earned a NASA early career fellowship to help ensure future missions to Mars can land safely.
McMahon, an assistant professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder, has received a three year, $600,000 NASA Space Technology Research Early Career Faculty fellowship. The program provides outstanding researchers resources to advanced technology in NASA-designated high priority areas. McMahon’s work is in Entry Guidance Methods for Precision Planetary Lenders, particularly focusing on Mars.
While there have been nearly a dozen successful landings on the Red Planet, all have been with relatively light payloads. The heaviest, 2011‘s Curiosity Rover, tipped the scales at just 899 kg (1,982 pounds, roughly the weight of a classic Volkswagen Beetle. As we move toward manned missions to Mars, mass will increase dramatically, since astronauts need to bring food, water and living quarters with them.
That makes landing a problem.
A ship entering the Martian atmosphere will likely be traveling at speeds in excess of 21,000 kilometers per hour (13,000 mph). Because earlier Mars missions have had fairly low weights, they have been able to rely almost exclusively on passive technology to slow down – an ablative heat shield in the upper atmosphere and then parachutes or airbags closer to the ground.
“If we want to send larger payloads, we have to use rockets in the upper atmosphere to slow down enough to land safely,” McMahon said.
The challenge is it has never been done before. A few missions have used rockets, but only during the final few thousand feet before touchdown. That experience unfortunately will not translate well to firing rockets at high altitudes, as wind and other atmospheric conditions are very different compared to close to the ground.
“We know how to use propulsion; that’s not the problem. What we don’t know is if you’re at 100,000 feet and you thrust to the left, by the time you get closer to the ground, how far off course will that have sent you? Can you get back to where you need to be?” McMahon said.
His team is working to answer those questions by developing guidance algorithms for computers aboard future spacecraft. Their software will provide the system with the decision-making capabilities information it needs and determine robust solutions to reach the ground safely and accurately.
“We have to build algorithms that can account for uncertainty. Mars is not Earth. We don’t know exactly what the weather will be the day of the landing. The algorithm has to sense and adapt to that,” McMahon said. “It also has to be able to make predictions, so when it’s descending it can draw on previous knowledge — if the atmosphere has been like X so far, it will probably be like Y further down below.”
If it sounds complex, it is. Computers have always done heavy lifting during the entry, descent, and landing (EDL) phase of missions, even dating back to the Apollo era. There are simply too many variables for humans to make the necessary calculations in real time. Adding rockets only increases the complexity.
“There is such a time crunch during entry, descent and landing. When you’re still in space orbiting a planet, there are lots of situations where if something goes wrong you can recover. If that happens during EDL, you don’t get a second chance. It’s over,” he said.
McMahon’s team is one of three from across the country working on this issue for NASA. At the conclusion of the grant, NASA intends to bring all three teams together for side-by-side tests utilizing the space agency’s high fidelity simulator.
“The whole reason I’m an engineer versus a scientist or mathematician is I want to use my skills to solve real problems,” McMahon said. “We’re closer than we’ve ever been to a manned Mars mission. That’s what NASA is planning for, and these are the kinds of questions that have to be answered to get there.”