NASA has been flying the Ingenuity Mars Helicopter on the Red Planet for several months. Mission operators have learned a lot about operating a helicopter on another planet and gained more information on the strengths and weaknesses of the Ingenuity platform. Significant amounts of work have been put into leveraging the strengths of the helicopter’s design while mitigating its weaknesses.
Operating the helicopter has become easier as NASA has learned more about Ingenuity’s strengths and weaknesses, but one aspect is getting difficult. According to NASA, the changing seasons on Mars is resulting in decreasing atmospheric density. Atmospheric density was already a concern because it’s low on Mars at all times, which was one of the reasons NASA wasn’t sure if they’d even be able to fly Ingenuity at all.
As seasons change on Mars, the atmospheric density is decreasing even further. NASA prepared for flights with atmospheric densities in the area of 1.2 to 1.5 percent of the atmospheric density on earth at sea level. That works out to a density of between 0.0145 and 0.0185 kg/m3.
However, with the changing seasons, NASA expects to see densities as low as 0.012 kg/m, which would be about 1.0 percent of the atmospheric density on earth. It expects to see those reduced numbers during the afternoon hours when helicopter typically flies. While those percentages are very close together, the lower densities have a significant impact on the ability of Ingenuity to take to the Martian sky.
The lower design limit for atmospheric density was 0.0145 kg/m3, but NASA says the helicopter has thrust of at least 30 percent higher than what is required to fly at that density. With the changing atmospheric density in the coming months, a reduction to 0.012 kg/m3 would mean extra thrust margin could decline to as little as eight percent. That would mean the helicopter would operate very near stall conditions.
The fix is that NASA plans to spin the rotors faster at a rate of 2800 RPM, which is more than ten percent faster than the rotors currently spin at. Spinning the rotors faster could lead to vibrations that introduce other problems and will increase wear on the helicopter. NASA plans to test new approaches to keep the helicopter flying as long as possible in the coming days.