2009 Or 2011 ?, 1 or 2 ? |
2009 Or 2011 ?, 1 or 2 ? |
May 3 2005, 11:11 AM
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#1
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Member Group: Members Posts: 290 Joined: 26-March 04 From: Edam, The Netherlands Member No.: 65 |
Does anybody know when and how many MSL will go, or when the decision on this will be made ?
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Guest_BruceMoomaw_* |
May 4 2005, 07:57 PM
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#2
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Guests |
[quote=Marcel,May 4 2005, 06:48 AM]
[[/quote] Why don't they use semi flexible booms, (say 3 or 4, to prevent twisting)extendable from the crane down, like telescopic fishing rods ? It will definately damp out unwanted movement of the rover with respect to the crane during the critical (final) stage before landing. I don't mean rigid, i don't mean rope like.....something in between. [/quote] ___________________________ No. That kind of semi-flexibility would be extremely difficult to program the descent rocket autopilot to compensate for, even after extensive ground testing. That, after all, is precisely how we got those self-reinforcing resonances in the Mariner 10 magnetometer boom, and the problem in this case would be far worse. Now, I myself did seriously consider the possibility of a COMPLETELY rigid attachment between the rover and the descent stge, or at least as rigid as we could make it -- using either a pyramid of 3 or 4 cables fastened from the corners of the lander to the corners of the rover, or else a lightweight telescoping metal boom made out of a flat metal strip that curled its edges into a tube as soon as it was unrolled from the descent stage (a technique that's often used for spacecraft booms, including the sampling arm on the Vikings). I thought that this, by eliminating any swinging or twisting by the rover as it's being lowered, would simplify the problem -- but Nick Hoffman heaped scorn and wrath on my head, and then MSL engineer Pete Theisinger himself confirmed at the Mars Roadmap meeting that it causes more trouble than it solves. Such a rigid linkage makes the descent stage itself tilt back and forth, and apparently the control difficulties of cancelling this out with its descent engines are actually harder than having the descent stage keep itself hovering stable while lowering the rover on a loose cable (or, in reality, 3 cables fastened to corners of the rover but converging at a single point on the descent stage to allow swinging and twisting). Not being an engineer, I bow to their judgment -- apparently the only valid choices are a free-dangling Skycrane or no Skycrane at all. |
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