"Survives first freezing night" == Is this just sensationalism? Should NASA not have a good estimate of what the chances of survival are? Maybe it is the media, maybe it is the need to fill columns (like the old days) but I would probably make a list of milestones and track "time to first flight" or something similar.
I find the order of milestones a little surprising.
Why didn't they test the survival of the freezing cold after testing the rotor blades, lift-off and perhaps a short flight in the vicinity of the rover?
I bet they'd move faster if they could. I'm guessing for takeoff there's a good amount of analysis to do beforehand. Terrain, weather, system checks, whatever.
I don't know the actual list, but it's not hard to guess why they couldn't do everything, including ejecting it from the main rover and getting the main rover out of the way, in the ~12-14 hours a day that they have to do stuff.
They fully expect it to survive the night - it'll have survived identical conditions in pre-launch testing - and thus there's no need to rush through the other steps.
But I prefer to hear it directly from the engineers involved:
> "What was it like seeing that first image of Ingenuity on mars?"
> "Oh it was a dream come true. To see the culmination of the entire team's hard work really pay off. Being dropped - that's one huge milestone, but the massive one for us over the last few days has been realising not only did we drop, but we actually survived the first night. That is huge. That was one of the huge huge achievements that we've been looking forward to and now we can look forward to the rest of the mission. But being able to drop under our own energy, sustain ourselves, keep ourselves warm through the whole night and then wake up and talk with Perseverance and say "yep we're here alive and healthy" the team couldn't be happier."
This is a technology demonstration of a novel robotics system build using many off-the-shelf parts, on a planet with night-time temperatures as low as -130F [1].
Ingenuity survived, literally, a first freezing night. That is an accomplishment by itself, and is hardly sensationalist.
2/3rds of Ingenuity's stored energy goes towards keeping its batteries and critical components warm each night. Only 1/3rd is available for powered flight. It literally takes more energy for this helicopter to survive the night than it takes to fly on mars.
Does it take a ton of power to heat. Or does it take very little power to fly?
I'd assume there is a ton of effort put into passive insulation? Since my non intuitive gut seem like it should be able to better insulate heat loss. I can't help but feel like there is probably a ton of effort and science to insulate. And this is even only possible because of that work. But is it just a much harder problem than I probably realize?
-130F/-90C is VERY cold, and this system is VERY weight-sensitive. Presumably adding more insulation that always needed to be carried was more weight than adding power capacity that can serve a dual-use.
The power capacity metric isn't necessarily concurrent; one could imagine the chopper using its power to fly (which will generate heat as a byproduct) for a third of the sunlight time, and then using the rest of the day to charge for the night-time cold.
Mars is very cold, things like the battery can't handle these temperatures. It's been thoroughly analysed, here is a quote from the white paper [0]:
"""H. Thermal System
The helicopter must survive the cold of the night on Mars where temperatures can drop to -100 C or lower. The most critical component is the battery which is kept above -15 C through the night as it powers Kapton film heaters attached to the battery cells. The avionics boards in the ECM surround the battery and are also kept at an elevated temperature by virtue of their proximity to the warm battery assembly. Insulation around the avionics boards is provided by a carbon-dioxide gap of 3 cm width. Additional insulation can be provided by replacing the carbon-dioxide gas with an Aerogel formulation. The outermost fuselage thermal coating is from Sheldahl with Solar absorptivity α = 0.8 and infra-red (IR) emissivity = 0.1.
In addition to thermal losses through the gas gap (or aerogel), additional losses occur due to conduction in the mast as well as through the copper wiring that penetrate the ECM from the mast. To minimize the latter, the wire gauges are selected to be of the thinnest gauges that can still support the current draw during operations without overheating. Prior to flight, under the control of the FPGA, the thermal system powers on heaters in the motor control boards that have been exposed to the ambient temperatures. The internal battery temperature is brought up to 5 C to allow hi-power energy extraction from the cells. During operation the ECM and battery warm up as a result of avionics operations and battery self-heating. However, the thermal inertia of the elements is such that for the short flights of the helicopter, there is no overheating."""
EDIT: some detail on the battery capacity from section G:
"A de-rated end-of-life battery capacity of 35.75 Wh is available for use. Of this capacity, 10.73 Wh (30%) is kept as reserve, night-time survival energy usage is estimated at 21 Wh for typical operation in the northern latitudes in the spring season, and approximately 10 Wh is available for flight. Assuming that 20% of the power is at the peak load of 510 W and 80% is at a continuous load of 360 W, approximately 90 sec of flight is possible. These energy projections represent conservative worst-case end-of-mission battery performance at 0 C initial temperature. More moderate power loads will extend the flight time."
On top of what others have said, we need advancement it batteries that can withstand low temperatures. Lithium ion batteries generally need to be kept above freezing temps. There have been some advances in capacitors that operate down to -100C, but their energy density makes them a non-ideal option for weight limited applications.
On the aerodynamic side, this aircraft has a mass of 1.8 kg / 4 lbs, which is an equivalent weight of 0.7 kg / 1.5 lbs on Mars. That is also the force required to maintain altitude. Imagine picking up four or five apples; that's what we're talking about as a minimum to stay in the air. For comparison, a DJI Phantom weighs 3 lbs, and a Mavic comes in at 2 lbs.
I can't find numbers on the power system or materials so I can't speak to the thermal side or how much flight time that affords.
EDIT: Apparently there's enough energy to fly for 90 seconds (!) per sol.
That's pretty interesting. Maybe the next rover needs an excavator tool so we can build an underground hidey-hole for storing sensitive equipment at night.
