Night driving for MSL? |
Night driving for MSL? |
Guest_Actionman_* |
Aug 28 2014, 11:11 AM
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#1
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Guests |
Driving at night might be better.
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Aug 28 2014, 12:42 PM
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#2
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
How would you conduct hazard avoidance in the dark? How much extra energy would you be spending heating the mobility system to allowable temperatures before moving?
And moreover....why might it be better at night anyway? I've attempted to drive across the sand in 40degF heat and 105degF heat....didn't change a thing. |
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Guest_Actionman_* |
Aug 28 2014, 09:23 PM
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#3
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Guests |
How would you conduct hazard avoidance in the dark? How much extra energy would you be spending heating the mobility system to allowable temperatures before moving? And moreover....why might it be better at night anyway? I've attempted to drive across the sand in 40degF heat and 105degF heat....didn't change a thing. You would use infrared time exposers with real time overhead data link. Or just do a short test and compare wheel slippage with the daylight data which you could after the fact.. |
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Aug 28 2014, 10:04 PM
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#4
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
You would use infrared time exposers with real time overhead data link. The Haz and Navcam's are not IR cameras. They can not see in the dark. https://www-robotics.jpl.nasa.gov/publicati...ne/fulltext.pdf Their sensitivity is between 600 and 800nm. Thermal IR starts at 3,500nm What is a 'realtime overhead data link'? Are you talking about returning data from MRO? That only happens for about a 15 minute period, twice a day, and the one-way light time is usually more than the duration of an MRO pass. |
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Guest_Actionman_* |
Aug 28 2014, 10:54 PM
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#5
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Guests |
Their sensitivity is between 600 and 800nm. Thermal IR starts at 3,500nm What is a 'realtime overhead data link'? Are you talking about returning data from MRO? That only happens for about a 15 minute period, twice a day, and the one-way light time is usually more than the duration of an MRO pass. 1035nm MastCam with starlight is good for dune driving. With just one peak form MRO it would be a short drive But it could be worth it if the dune dust is more cohesive after it's cooled down.. say some time after midnight. |
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Aug 28 2014, 11:14 PM
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#6
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Senior Member Group: Members Posts: 2085 Joined: 13-February 10 From: Ontario Member No.: 5221 |
If there was any advantage to driving at night at all, it would have been done at least once some time in the last two years, so let's give the planners the benefit of the doubt. They're pretty good at this sort of thing, after all.
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Aug 28 2014, 11:39 PM
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#7
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
1035nm MastCam with starlight is good for dune driving. MastCam can not be used for AutoNav. MastCam will not see anything in 'starlight' Moreover -The MRO pass would not be long enough for an in-the-loop driving decision process. -Earth may well not be visible during a night time MRO pass at Gale. -The energy required to warm the mobility system to do this would be huge (if not entirely insurmountable) -What evidence is there that 'cool' sand dunes offer more traction? |
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Aug 29 2014, 02:36 AM
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#8
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Senior Member Group: Members Posts: 1044 Joined: 17-February 09 Member No.: 4605 |
The silt, sand and dust that makes up the ripples seem to be mechanically locked. The surface is absolutely desiccated and empirical measurements suggest that there is no transfer of the miniscule atmospheric H2O to the regolith overnight other than very minor surface frost so there would be no ice cementing if that is what you are positing. Any minor contraction due to temperature drop would in fact reduce the effectiveness of mechanical locking such as it is. The only potential gain is that aluminium would have a marginal increase in tensile and yield strength at the very low overnight temperatures but hardly sufficient to provide mitigation for wheel damage. IMHO it would be pretty senseless to take the risk of night drives when there is no payoff.
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Guest_Actionman_* |
Aug 29 2014, 10:59 AM
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#9
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Guests |
It will be imperative to cross dune at some point with or with out confidence. I don't see any reason to think a dune walk at night is any more dangers then at day. That should be a one move operation none stop crossing.
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Aug 29 2014, 12:00 PM
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#10
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Senior Member Group: Members Posts: 2346 Joined: 7-December 12 Member No.: 6780 |
It's more dangerous, because the ratio of slip versus wheel rotation cannot be monitored in the dark by VisualOdometry.
Hence excessive slip above a previously defined trigger level may not be detected in time. This increases the risk to get stuck. Early detection of excessive slip allows tracking back and choosing alternative routes, until a successful crossing is accomplished, if crossing the dune turns out to be necessary at all. South of the entry point there are gaps between the large dunes. On the way to the entry point, there is no need to drive away more than 10m from solid ground or shallow sand. |
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Aug 29 2014, 12:54 PM
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#11
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Member Group: Admin Posts: 976 Joined: 29-September 06 From: Pasadena, CA - USA Member No.: 1200 |
Driving at night would be quite expensive due to the amount of heating necessary to keep the actuators warm and cozy. But mostly we could not use VO or autonav. We could just drive blind and use other parts of safety mechanisms to detect embedding but these would be very, very short drives, 10-20 meters at most. And so far I haven't heard anyone suggest that sand on Mars is more cohesive in cold temperatures. If it was, we would have seen differences in driving Spirit and Oppy, besides Curry, in Winter vs Summer.
Paolo -------------------- Disclaimer: all opinions, ideas and information included here are my own,and should not be intended to represent opinion or policy of my employer.
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Aug 29 2014, 02:45 PM
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#12
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Founder Group: Chairman Posts: 14432 Joined: 8-February 04 Member No.: 1 |
It will be imperative to cross dune at some point with or with out confidence. It is imperative to not do something that is likely to get the rover permanently stuck. Driving into areas with questionable traction without autonav & visual odometry etc is significantly more likely to result in a permanent embedding event that would bring the mission to a premature end. QUOTE I don't see any reason to think a dune walk at night is any more dangers then at day. Just because you don't see them doesn't mean they don't exist. It's been explained why driving in the dark would present an entirely unnecessary risk to the vehicle |
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Guest_Actionman_* |
Aug 29 2014, 06:16 PM
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#13
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Just because you don't see them doesn't mean they don't exist. It's been explained why driving in the dark would present an entirely unnecessary risk to the vehicle A night test is not so far fetched. The electrostatic continuity of the subsoil will be enhanced in a sub -40 degree night environment, compared to the heat of the day... implying the possibility of a increase of cohesiveness in the soil. |
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Aug 29 2014, 06:33 PM
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#14
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Solar System Cartographer Group: Members Posts: 10161 Joined: 5-April 05 From: Canada Member No.: 227 |
No energy for actuator heating at night, no light for visodom, slip checks etc. Give it up! The best engineers on Planet Earth are already on the job.
Phil -------------------- ... because the Solar System ain't gonna map itself.
Also to be found posting similar content on https://mastodon.social/@PhilStooke Maps for download (free PD: https://upload.wikimedia.org/wikipedia/comm...Cartography.pdf NOTE: everything created by me which I post on UMSF is considered to be in the public domain (NOT CC, public domain) |
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Aug 29 2014, 07:12 PM
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#15
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Senior Member Group: Members Posts: 2516 Joined: 13-September 05 Member No.: 497 |
MastCam can not be used for AutoNav. I'm not 100% sure this is true, as it was discussed as a backup in case of Navcam failure during development. But it's certainly not assured; Mastcam is not even allowed to be powered on during driving at present. As has been pointed out, there seems to be some confusion about how night vision works. I know of three flavors: image intensification of ambient light ("starlight scopes"), near-IR with active illumination in the near-IR (seen in some security cameras, baby monitors, etc.) and thermal IR. We can't do any of those with anything on MSL and the longest exposures we could take would be unlikely to even detect the ground. Near-IR works no better than visible for ambient light -- worse, because the sensitivity of Mastcam in the near IR is quite low compared to the visible. The best we could do is use the MAHLI LEDs for illumination, but the arm can't be deployed while driving and in the stowed position the LEDs aren't pointed in a useful direction, and they're not all that bright anyway. It's an interesting idea that slip properties might change as a function of temperature, but I don't think there's any evidence that this might be true, and I don't think there are any known examples of it for terrestrial analogs. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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