MSL FAQ - The pool of questions |
MSL FAQ - The pool of questions |
Jun 1 2007, 03:11 PM
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#1
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
Rob Manning and I swopped emails last night - and we think it might make sense to pool all the questions people have about MSL (and specifically MSL's EDL ) into one thread - and then answer as many as make sense either via a Q'n'A in the style of the previous ones I've done with Steve and Jim - or via Rob's typing fingers.
It'll be a few weeks till we sort this out - but submit-away until then Doug |
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Jun 4 2007, 05:22 PM
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#2
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
Here's a few that I've received by email. The first two are variations on a theme:
What kind of AI, if any, is built into the descent stage in terms of selecting an exact point to set the rover down? In other words, does the sky crane "look around" for a suitable spot as it descends, or does it just go straight down regardless? Is it the rover or the descent stage that decides when the rover is safe on the ground? I'm guessing they both need to know when touch-down occurs because, from the video, it looks like the rover releases the cables and the descent stage flies clear of the rover. So do they both detect it? Or does one detect it and communicate to the other? How is detection done? Radar? Touch sensor? Why is the "skycrane" concept better than just lowering the rover to the ground with retrorockets (as if using zero-length cables)? Are the cables used for cushioning? Wouldn't it be better for the "skycrane" to hover in one place and lower the rover by unwinding the cables very slowly till the rover touches down, rather than descending with the cables fully extended, as in the video? -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Jun 4 2007, 10:30 PM
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#3
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Member Group: Members Posts: 321 Joined: 6-April 06 From: Cape Canaveral Member No.: 734 |
1. Why is the "skycrane" concept better than just lowering the rover to the ground with retrorockets (as if using zero-length cables)? Are the cables used for cushioning? Wouldn't it be better for the "skycrane" to hover in one place and lower the rover by unwinding the cables very slowly till the rover touches down, rather than descending with the cables fully extended, as in the video? Skycrane concept eliminates thruster plumes and dust on the rover The mobility system (wheels etc) absorb the shock no, extended hover is harder to maintain |
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Jun 5 2007, 01:44 PM
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#4
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Member Group: Members Posts: 153 Joined: 11-December 04 Member No.: 120 |
Skycrane concept eliminates thruster plumes and dust on the rover Would that be a problem when there is no solar panel up there? I believe the big advantage of the skycrane is that it minimizes the mass that actually lands. And by doing so it reduces the stress and loads caused by touchdown. The mobility system (wheels etc) absorb the shock I don't think a rocker-bogie system does much shock absorbing as it is completely rigid. This simply means the vertical speed at touch down must be very small. BTW, I'm much more concerned about horizontal speed at landing than about vertical speed, which is much more easy to control. I'm afraid the suspension system will not have much tolerance for horizontal speed at touchdown and any swinging motion of the rover must be dampened by the skycrane. Or does the rover have any reaction control system of its own? (I don't think so, as it doesn't carry any fuel tanks). This will be a pretty tough control job in the windy Martian atmosphere and coming from a huge horizontal entry speed. |
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Jun 5 2007, 04:31 PM
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#5
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Member Group: Members Posts: 321 Joined: 6-April 06 From: Cape Canaveral Member No.: 734 |
Would that be a problem when there is no solar panel up there? I believe the big advantage of the skycrane is that it minimizes the mass that actually lands. And by doing so it reduces the stress and loads caused by touchdown. I don't think a rocker-bogie system does much shock absorbing as it is completely rigid. This simply means the vertical speed at touch down must be very small. BTW, I'm much more concerned about horizontal speed at landing than about vertical speed, which is much more easy to control. I'm afraid the suspension system will not have much tolerance for horizontal speed at touchdown and any swinging motion of the rover must be dampened by the skycrane. Or does the rover have any reaction control system of its own? (I don't think so, as it doesn't carry any fuel tanks). This will be a pretty tough control job in the windy Martian atmosphere and coming from a huge horizontal entry speed. The dust and the effluents from the thrusters would contaminate the rover there is no "huge" horizontal velocity, it is coming vertical by the time the rover is repelling |
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