NASA believes it understands why Ingenuity crashed on Mars
arstechnica.com
arstechnica.com
For example, solar panels for the rovers are overbuilt because you can't clean them if a chance dust storm is a bit too dusty. But that overbuilding also means that as long as the panels stay reasonably free of dust, the rover will last a long time.
The design spec is something like “95% probability of completing 5 flights” - that is, the minimum threshold to be successful.
That leaves a lot of extra margin to keep going well past it - 90% for 10 flights; 80% for 20; etc.
(made up numbers)
You also get the “bathtub curve” in most mechanical systems. Once you get past the early design defect failures, things tend to last a long time, until they start wearing out.
Ingenuity funding was not actually included in the original Mars 2020 program and there was huge internal opposition to it, due to potentially infringing on the science goals of the mission.
Identifying this as the likely failure mode strikes me as pretty valuable for informing future designs, at least compared to the alternative of it just never being heard from again one day.
I'm a little surprised there isn't something more accurate than a camera for this.
I think the best approach would probably be to equip the "base station" / lander with an RF beacon. Ideally, you could drop some RF beacons throughout the environment as you went, but even a single beacon with some directional receivers on the drone should work pretty well (here, the featureless environment becomes a benefit as you have to contend much less with radio reflections).
100% agree on the RF beacons. You might not even need the directional antennas. Using things like RSSI might be enough to augment the local sensors. Alternatively having a digitally-controlled phased array could probably result in quite excellent positioning.
I think the system on Ingenuity just used feature detection based 2D optical flow rather than a more full-scale 3D environment-reconstruction type SLAM setup. Which is fine since neither would work in a blank environment like that.
They just aren't GPS satellites. At some point we'll likely get some there, but it's a) a good amount of payload and b) not something we've really needed there so far.
Every NASA science mission to Mars orbit for over 20 years has had a communications relay on it, for relaying messages from rovers back to Earth, but the one in the best orbit for communications (Mars Odyssey) is also the oldest and most likely to fail. The other NASA science orbiters (MRO, ME (ESA), MAVEN) all also have relays, but the orbits all leave something to be desired for communications purposes (they are in the right orbits for answering their scientific questions, e.g. MAVEN is in a highly elliptical orbit for studying the Martian atmosphere).
There was a proposed Mars Telecommunications Orbiter- a satellite whose primary mission would have been beaming back information from rovers on the surface- proposed back around 2005, but it was canceled in a budget crunch, when actual science producing satellites were prioritized. That would have been in the right orbit.
Building a positioning satellite network around another body is going to be significantly harder, incidentally. Even something like TRANSIT (aka NAVSAT) (1) is going to be significantly harder on another body because we haven't mapped their gravity fields due to density fluctuations as well, the upper atmosphere is not as well studied for drag effects, and we don't have fixed locations that can determine orbital parameters very precisely by either visual or radar observations after every orbital maintenance burn. Small uncertainty in orbital position lead to gigantic uncertainty in your position, and none of the techniques we use here on earth to remove that uncertainty would work around Mars.
1: Instead of the "see multiple atomic clocks and use triangulation and the speed of light to determine distance to each of them, then our location from their known locations" which is how all modern satnav systems work, TRANSIT used a single satellite passing nicely overhead every so often. When it was right above you, you could listen to the Doppler shift and know when it reached exactly the zenith above you. If you knew it's orbit very precisely you could tell where it was in space when it reached that zenith, and therefore where you were.
Not necessarily. Starlink can be used for positioning – not with the same accuracy as GPS can, but it definitely can be used. According to [0] a research group was involved with discussions with SpaceX about officially using Starlink as a positioning system, but the discussions were terminated because Musk didn't like the idea. And then the researchers went ahead and did it anyway – even without the ability to decrypt the signal, the unencrypted synchronisation data embedded in it is sufficient to get a position fix to within 30 metres. If SpaceX was actually cooperating and using data in the encrypted signal for this purpose, it could likely be made even more accurate. I suppose Musk's point is that however accurate it is, GPS is going to be even more accurate, and having Starlink offer a "just like GPS but less accurate" service has minimal commercial value and great potential for bad PR ("look how inaccurate SpaceX's GPS alternative is!")
SpaceX is proposing to build a "Marslink" constellation around Mars [1]. Likely SpaceX wouldn't have the same opposition to using it for positioning as they do for Earth Starlink, given there is no existing GPS to compete with.
> because we haven't mapped their gravity fields due to density fluctuations as well, the upper atmosphere is not as well studied for drag effects, and we don't have fixed locations that can determine orbital parameters very precisely by either visual or radar observations after every orbital maintenance burn. Small uncertainty in orbital position lead to gigantic uncertainty in your position, and none of the techniques we use here on earth to remove that uncertainty would work around Mars.
This is all true, but anything is better than nothing – a Martian GPS with significantly less accuracy than Earth GPS will still be superior to no Martian GPS. And it will be a step towards building the necessary research infrastructure to answer many of those questions about variations in Martian gravity and atmospheric drag. So the accuracy of the system is likely to improve over time.
[0] https://www.technologyreview.com/2022/10/21/1062001/spacex-s...
[1] https://www.pcmag.com/news/spacex-pitches-nasa-on-marslink-a...
The only approach that you can do is a Doppler based NAVSAT approach (since the Starlink satellites don't have their own atomic clock for distance calculations), which can't really handle movement by the ground station well in the first place, and to account for the uncertainty in orbits you end up needing to wait for several to pass overhead without moving and trust that with enough passes the uncertainties cancel out. NAVSAT was never designed for real-time tracking, it was designed to zero the huge mechanical gyro's on the inertial frame for nuclear ballistic missile submarines.
This approach wouldn't help a helicopter here on Earth- because it needs multiple zeniths without moving for the uncertainties to cancel out, this system would not provide much help for systems that are moving. It definitely would not provide much help for a helicopter on Mars. If you build a system for other reasons and can piggyback this off of that, sure, do it (I know that other spacecraft at least have the ability to measure Doppler shifts and so could use this system) but it isn't ever going to solve the original problem of the helicopter not able to tell what its horizontal velocity was, and it is always going to be very very rough.
And of course SpaceX will want to pitch a Starlink for Mars. Quite honestly, I suspect that upgrading the DSN sites here on Earth would be far more bang for the buck, more of the 34m BWG's would go a long way, since they are already a limiting factor and if Artemis is really going to happen we're going to see dramatically more data produced that the DSN is going to need to listen for.
But why isn't it practical?
Also, can't the inter-satellite laser links provide an additional source of information in measuring their orbital parameters?
> since the Starlink satellites don't have their own atomic clock
They might get them at some point. And even if the Earth constellation doesn't, maybe the Mars one will.
The atomic clocks used in GPS satellites are fiendishly expensive, but the gap between them and much cheaper chip-scale atomic clocks [0] is likely to continue to narrow.
For the MEO GNSS satellites, the last correction factor that I needed to implement in order to meet the system requirements ended up being Solar Radiation Pressure. Since the accuracy of a GNSS system depends on knowing the precise positions of the SVs at precise times, any error in the orbital position calculation is a direct error on the position; SRP, as it turned out, was enough to knock the real orbit off by about 1m over a… surprisingly short period of time (I don’t remember the exact period, somewhere around 30min to 6h).
Down in LEO you’ve got way less predicable correction factors with significantly larger magnitudes. Even at 300km there is still a little bit of atmosphere and your satellite experiences drag. Factoring in the huge number of SVs in the Starlink constellation and it’s going to be a nightmare to model their orbits accurately enough to do decent positioning.
But as I was writing that, a fun thought came to mind. All of the end-user GTs could be used as tracking stations. If the Dishys have a GPS receiver and can assume it is in a fixed static position (accelerometer to cross-check?), it can self-survey its own position on the ground probably to 1-2mm accuracy over time (higher-end consumer grade parts like the UBlox F9P can do this) and use the antenna phasing to get a good idea of the SV relative to the GT. Collect all of those high-resolution coordinates and the ranging data from all of the end-user GTs, set it up as a huge linear algebra problem, and throw it at some GPUs. It might work?
Basically, because of drag MEO will always be >>> than LEO for navigation purposes. That's why all the dedicated navsats are there! It is possibly to piggy-back and get a large enough scale to compensate for the loss of accuracy. Eyeballing satellitemap.space for my location (roughly 35N), it looks like you'd get a zenith every minute or two from Starlink. Again, fine for stationary, not sure about moving, given the need for multiple zeniths to correct uncertainty.
As for the laser link SpaceX is very tight-lipped about that as far as I can tell, and that is one where the precision is all going to be measured operationally. Something like LAGEOS shows that it is possible to do things incredibly precisely with light, but the question is, does Starlink have the mass, energy, and compute budget to actually do it in practice.
However I assume that would require special radio software, and they were using commercial Zigbee modules. In addition, I guess perhaps the helicopter and potentially rover wouldn't have accurate enough oscillators for this to be viable in any case.
The problem is this case was that there was nothing to reflect off of, except for a planar field of sand. You can't know how fast you're moving over a bare plane, without a feature being on that plane, that you can observe.
Another thing to keep in mind is that the helicopter was made using off-the-shelves parts[1], including for avionics, to see how well they held up on Mars.
As such I think it did amazingly well.
[1]: https://en.wikipedia.org/wiki/Ingenuity_(helicopter)#Design
So it never had a goal to last as long as possible, it had a goal to see how long it lasts when you don't sink 100 million into every screw.
I thought anyway.
My speculation is that the next one will have a host of sensors, given how much more likely double digit missions of greater length now seems.
A great example of how hard INS navigation is would be the SR-71 celestial INS navigation system R2-D2. The SR-71 would use astronomical observation in order to update it's INS navigation periodically, similar to a sailing ship at sea. Modern laser gyros are aligned automatically using GPS. However, on military aircraft, alignment can still be achieved using manual input or datalink.
https://theaviationgeekclub.com/the-sr-71-astroinertial-navi...
Hopefully it will eventually be deployed [0]
> Assuming a dish antenna with 1-m diameter, for a downward-looking antenna the total noise temperature is about the same as the Earth’s for all frequency bands of interest, with ±15 percent deviations. For an upward-looking antenna, the noise temperature is less than half that of Earth. [1]
[1] https://ipnpr.jpl.nasa.gov/2000-2009/progress_report/42-149/...
Although the thing that bothers me is that basing stuff on AI isn't really standing on the shoulders of giants. One big thing that held back human flight was that the published tables for lift were wrong so everybody that was using them couldn't fly even when they "should've" been able to (according to the wrong data). The Wright brothers had a good idea to re-compute the table and came up with different answers and were able to build a working plane.