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Within the months since we flew for the primary time, we now have realized an ideal deal about working a helicopter on Mars. We’ve explored Ingenuity’s strengths and limitations intimately, leveraging the previous and dealing across the latter to operationalize it as a extremely succesful reconnaissance platform.
With the advantage of the data acquired, conducting flights on Mars has in most methods turn into simpler than it was on the outset. However in a single essential manner it’s truly getting tougher day-after-day: I’m speaking concerning the atmospheric density, which was already extraordinarily low and is now dropping additional as a result of differences due to the season on Mars.
Once we designed and examined Ingenuity on Earth, we anticipated Ingenuity’s five-flight mission to be accomplished inside the first few months after Perseverance’s touchdown in February 2021. We due to this fact ready for flights at atmospheric densities between 0.0145 and 0.0185 kg/m3, which is equal to 1.2-1.5% of Earth’s atmospheric density at sea stage. With Ingenuity in its sixth month of operation, nevertheless, we now have entered a season the place the densities in Jezero Crater are dropping to even decrease ranges. Within the coming months we might even see densities as little as 0.012 kg/m3 (1.0% of Earth’s density) through the afternoon hours which are preferable for flight.
The distinction could seem small, but it surely has a major influence on Ingenuity’s capability to fly. At our decrease design restrict for atmospheric density (0.0145 kg/m3), we all know that Ingenuity has a thrust margin of at the least 30%. Thrust margin refers back to the extra thrust that Ingenuity can produce above and past what’s required to hover. That extra thrust is required on takeoffs and climbs, throughout maneuvers, and in addition when monitoring terrain with various peak. But when the atmospheric density have been to drop to 0.012 kg/m3 within the coming months, our helicopter’s thrust margin might drop to as little as 8%, which signifies that Ingenuity can be working near aerodynamic stall (a situation the place additional will increase within the blade’s angle of assault doesn’t produce extra carry, solely extra drag).
Fortunately, there’s a strategy to deal with this situation – but it surely includes spinning the rotors even quicker than we now have been doing so far. In reality, they must spin quicker than we now have ever tried with Ingenuity or any of our check helicopters on Earth. This isn’t one thing we take evenly, which is why our subsequent operations on Mars can be centered on fastidiously testing out greater rotor speeds in preparation for future flights.
We are going to start by performing a high-speed spin of the rotor with out leaving the bottom, reaching a peak rotor velocity of two,800 rpm (greater than a ten% improve relative to our prior Mars expertise of two,537 rpm). If all goes nicely, we are going to comply with this with a brief check flight at a barely decrease rotor velocity of two,700 rpm. This is able to be our 14th flight and (hopefully) a comparatively boring one in comparison with any of our newer flights, the place we flew lengthy distances to amass pictures of curiosity for the Perseverance rover staff. Occurring no sooner than Friday, Sept. 17 (with information coming down no sooner than Saturday morning), the quick hop would have Ingenuity take off, climb to 16 ft (5 meters), carry out a small translation (sideways transfer), after which land once more. And whereas the outcomes from a Flight 14 needs to be lower than riveting, the numerous improve in obtainable rpms (from 2,537 to 2,700) for future helicopter operations will present us the choice to carry out scouting missions for Perseverance at decrease atmospheric densities. It additionally leaves some wiggle room if we determine a further rpm improve is required later.
A velocity improve like this comes with a variety of potential points. One in every of these has to do with aerodynamics: A rotor velocity of two,800 rpm, together with wind and helicopter movement, might trigger the information of the rotor blades to come across the air at practically 0.8 Mach – that’s, 80% of the velocity of sound on Mars. (The velocity of sound on Mars is considerably decrease than we’re used to – about ¾ the velocity of sound on Earth.) If the blade ideas get sufficiently near the velocity of sound, they’ll expertise a really massive improve in aerodynamic drag that may be prohibitive for flight. For Ingenuity’s rotor we don’t count on to come across this phenomenon till even greater Mach numbers, however this has by no means been confirmed in testing on Earth.
One other potential situation is unknown resonances within the helicopter construction. Like all mechanical programs, Ingenuity has resonances that may result in massive vibrations when excited at explicit frequencies. You will need to be sure that there aren’t any vital resonances on the rotor velocity used for flight, as this might trigger harm to {hardware} and result in a deterioration in sensor readings wanted by the flight management system.
Further calls for can even be placed on a number of parts of Ingenuity’s design: The motors might want to spin quicker, {the electrical} system might want to ship extra energy, and the whole rotor system might want to face up to the upper hundreds that include elevated rotor speeds. All of it provides as much as a major problem, however by approaching the problem slowly and methodically, we hope to totally try the system at greater rotor speeds and allow Ingenuity to maintain flying within the months forward. Keep tuned for updates.
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