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The Mars Helicopter Is Online and Getting Ready to Fly

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Re: The Mars Helicopter Is Online and Getting Ready to Fly

#131

Post by bryananderson »

ilamont wrote: post #18

One of the most significant obstacles for landing on Mars will continue to present problems for our heroic helicopter now that it is safely on the surface. The atmospheric pressure on the surface of Mars is only about 1% that of Earth. Does this also limit the use of parachutes on Mars, or require bigger canopies? I know that Perseverance had a parachute for part of the descent, but not the final landing sequence. II…

Yes indeed. Mars entry, descent, and landing (EDL) is hard. On Earth it’s easy: we can use the thick atmosphere to decelerate to a gentle drop into the ocean. On the Moon it’s easy: the minimal gravity makes powered descent feasible. On Mars it’s hard: too much gravity for an easy powered descent, too little atmosphere for an easy aerobraked descent. Larger spacecraft such as Curiosity and Perseverance (sky crane) and Spirit and Opportunity (bouncing air bags) have to get creative.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#132

Post by tus89 »

contravariant wrote: post #127
tus89 wrote: post #123

Earlier quoted context omitted.

If we understand "flight" as being the use of a wing to generate lift in an atmosphere, then I think we can safely say this is the first time we have flown on another planet. I assume this little helicopter actually has rotary wings rather than fans.

If we're splitting hairs then the lack of control seems like a better criterion to distinguish the two. If you ask me there's no reason a zeppelin would be inherently less 'flighty' than a helicopter.

I think they are more "floaty" that "flighty" :P

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#133

Post by Asraelite »

MayeulC wrote: post #92
Robotbeat wrote: post #50

Earlier quoted context omitted.

They work better primarily because they had previously invested in the tooling to rad-harden them and it’s really expensive to do that again one time for each mission; cheaper to rely on already-rad-hardened designs.

Not necessarily; physical size matters a lot. Just an example: consider you were to add some extra electrical charge to the gate of a transistor (from an electron or ion beam, I don't know). A larger transistor has a higher gate capacitance, it is therefore quite immune against a few extra charges. On smaller transistors, though, it could dramatically increase the voltage, leading to a bit error, or destroying the tr…

This raises the question, why not simply continue to make larger circuits today for this purpose?

Surely we could still make a chip today with the same transistor size as one from 2001, but better in other ways.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#134

Post by rriepe »

dal wrote: post #105
alpaca128 wrote: post #100

Earlier quoted context omitted.

> ...arguably the first _powered_ flights were done by the sky cranes of Opportunity and Perseverance Not the Apollo 11 lunar module? In contrast to the sky cranes it actually lifted off again.

The moon is not a planet.

I'd argue Mars is still the most impressive. Rockets in no atmosphere is easy. Floating on Venus is easy because it has more atmo than any other rocky planet.

Figuring out something that works well in Mars' thin (but still there) atmosphere, especially a helicopter, is really impressive. The celestial body classification is just a cherry on top.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#135

Post by newsbinator »

mhh__ wrote: post #113
tomerico wrote: post #94

Earlier quoted context omitted.

The problem is that NASA is designed around long term and expensive projects. At one point, a fast iterating company like space-x will surpass their achievements.

Why would SpaceX bother doing science, though? If you imagine a project like Voyager, you might think they just dump the data and "go home" (not quite, obviously) but to analyse the data and to know what to look for they had to hire geologists and meteorologists (for example) along with the planetary scientists and co. NASA should be about long term and expensive projects, SpaceX is just a tool to achieve that goal w…

SpaceX will do any science that’s profitable in the near/mid term

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#136

Post by dotancohen »

dal wrote: post #105
alpaca128 wrote: post #100

Earlier quoted context omitted.

> ...arguably the first _powered_ flights were done by the sky cranes of Opportunity and Perseverance Not the Apollo 11 lunar module? In contrast to the sky cranes it actually lifted off again.

The moon is not a planet.

By many definitions the Earth-Moon system is a dual planetary system. The moon has more that 1% the mass of the Earth, which is by far the largest primary-secondary "not a planet" system in the solar system. Only not-a-planet Pluto and Charon exceed it.

Also, Isaac Asimov considered the system a dual-planet system as the Moon's path around the sun is at no point convex nor retrograde.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#137

Post by jhayward »

kabdib wrote: post #115
jjoonathan wrote: post #68

Earlier quoted context omitted.

Reminds me of Apollo 11, where the computer kept resetting on the way down to the lunar surface but still got Neil Armstrong and Buzz Aldrin to the moon with the whole world watching.

It wasn't resetting, it was ditching lower priority tasks that it didn't have (real) time to accomplish. Notably, the computer was still doing important work (ahem, flying the LM :-) ), and the tasks it didn't have time to do were not critical. The team had recently seen similar failures in simulation, and was able to quickly decide it was okay to proceed.

> Notably, the computer was still doing important work (ahem, flying the LM :-) ), and the tasks it didn't have time to do were not critical.

I believe this is incorrect. From an earlier HN discussion:

"The 1202s were also a lot less benign than is often reported. They occurred because of the fixed two-second guidance cycle in the landing software. That is, once every two seconds, a job called the SERVICER would start. SERVICER had many tasks during the landing. In order: navigation, guidance, commanding throttle, commanding attitude, and updating displays. With an excessive load as caused by the CDU, new SERVICERs were starting before old ones could finish. Eventually there would be two many old SERVICERs hanging around, and when the time came to start a new one, there would be no slots for new jobs available. When this happened, the EXECUTIVE (job scheduler) would issue a 1201 or 1202 alarm and cause a soft restart of the computer. Every job and task was flushed, and the computer started up fresh, resuming from its last checkpoint. It was essentially a full-on crash and restart, rather than a graceful cancellation of a few jobs. And unlike is often said, the computer wasn't dropping low-priority things; it was failing to complete the most critical job of the landing, the SERVICER.

Luckily, the load was light enough that of the SERVICER's duties, the old SERVICER was usually in the final display updating code when it got preempted by a new SERVICER. This caused times in the descent when the display stopped updating entirely, but the flight proceeded mostly as usual. However, with slightly more load, it was fully possible that the SERVICER could have been preempted in the attitude control portion of the code, or worse yet, the throttle control portion. Since each SERVICER shared the same memory location as the last one (since there was only ever supposed to be one running at a time), this could lead to violent attitude or throttle excursions, which would have certainly called for an abort. Luckily, this didn't happen -- and the flight controllers didn't abort the mission not because 1202s were always safe, but because they didn't understand just how bad it could be, were the load just a tiny bit higher."

[1] https://news.ycombinator.com/item?id=20791307

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#138

Post by alexvoda »

ericbarrett wrote: post #89
Robotbeat wrote: post #51

Earlier quoted context omitted.

It’s less about longevity and more about reducing errors. Interestingly, Ingenuity has some sort of watchdog that can reset the Snapdragon in-flight fast enough to recover if there is an error.

A consumer chip is a lot more likely to be permanently damaged by a "silver bullet" cosmic ray, though. Rad-hard chips don't just have shielding, they can also have redundant circuits and modifications to the foundry process. That said, I'm sure Ingenuity's processor is fit to purpose.

It's a bit of a shame that radiation hardened chips are stuck so far in the past.

I believe the volume is so low it does not warrant the investment to make radiation hardened versions more often.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#139

Post by azernik »

dmurray wrote: post #102
madaxe_again wrote: post #95

Earlier quoted context omitted.

Between the two. 30 µSv per hour on the surface of Mars on average compared to 60 µSv on the Moon - compared to 5 µSv on a jet. Not friendly, but not too awful.

Or 0.5 per hour on Earth at sea level. That's only 2 orders of magnitude difference. Given that we don't expect radiation damage to be a major source of failures in Earthbound consumer or commercial electronics, it's a bit surprising it's such a big deal in space.

The composition of that radiation is important - Earth's atmosphere preferentially filters out a lot of the higher-energy particles that are likely to permanently damage electronics. The sievert as a unit is weighted based on damage to biological systems, not electronics.

Re: The Mars Helicopter Is Online and Getting Ready to Fly

#140

Post by azernik »

emteycz wrote: post #54
rwmj wrote: post #6

Wikipedia page about the Ingenuity helicopter: https://en.wikipedia.org/wiki/Ingenuity_(helicopter) I didn't realise it was so large (1.8 kg, 1.2 m diameter rotors). I suppose it has to have the large rotors to be able to generate lift in the thin atmosphere, 1/160th of the density [edit: pressure, not density - thanks Robotbeat] of the earth's atmosphere at sea level according to the article.

Wow, I never realized it might be 160 times harder to get off the ground on Mars. Perhaps lower gravity helps on the other hand, though the difference definitely seems way lower (please correct me if my physics is wrong).

Yup - lower gravity helps, but by much less than the orders of magnitude by which the thin atmosphere hinders.
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