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Guest_Oersted_*
post Jul 4 2011, 03:54 PM
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QUOTE (Oersted @ Jun 27 2011, 02:47 AM) *
I remember discussing the fate of the skycrane with MarsEngineer on this forum a good while ago, and to my recollection he said something like that, sure, if they had time for it they might try to program a soft landing into it... Not a priority though, and since it doesn't really serve a purpose, apart from pollution mitigation, it probably wont happen. Would be neat if they tried though.


BTW, I found what MarsEngineer said about this subject... (partial quote, from the "Skycrane" thread):

QUOTE (MarsEngineer @ Dec 15 2008, 10:03 AM) *
...
I will respond to Oersted's questions by italicizing his questions
...
...It would be neat if the lander/skycrane itself could fly off and make a soft landing with its remaining fuel. There will now be to years extra for coding, so maybe a little proggie can be made for the skycrane computer that could try to effect that? Why would it be interesting to land softly? Maybe to scour some trenches that the rover could visit... Then again, a crashing lander should make a nice big hole on its own. smile.gif


hmmm.... you are not the first to suggest that we try for a soft descent stage landing, Oersted. While that would not be impossible to consider, it would be a lot of work and as you know (and MSL folks know all too well) time is money. However I will be more than happy to tease my friend Jeff about it (he's one of the main developers of the code that controls the "flyaway" mode of the descent stage).
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monty python
post Nov 21 2011, 07:57 AM
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Sorry to resurrect an old thread here but after looking at the MSL EDL awesome video for the 10th time or so, it dawned on me- do we know what direction the "skycrane" section of the landing system will fly after landing?

Could it fly directly into our path towards gale crater?

I would really like to see the reck.
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nprev
post Nov 21 2011, 09:04 AM
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Not a bad question, but I don't think it will be an issue. My understanding is that after a nominal touchdown the descent stage will have enough fuel to depart in whatever random direction for quite some distance...and, frankly, MSL doesn't want to be anywhere near it, wherever it happens to crash.

The descent stage will undoubtedly have all kinds of highly volatile material--mostly hydrazine--present regardless of its end state (unless by some miracle it blows itself into literal smithereens.) Nobody wants that stuff anywhere near the geochemical science payload. Hell, I don't even want it near the optics.

Bottom line is that "ooo! cool!" would probably be the most reward we'd get for imaging the wreckage of the descent stage. The risks to MSL's mission success incurred by approaching that crap would be far greater...easy math to do.



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MahFL
post Nov 21 2011, 11:09 AM
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I think I read somewhere the Skycrane would head off at 270 degrees. Also that they definately won't be going anywhere near the wrecked skycrane.....well at least not for the first 10 years tongue.gif.
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MahFL
post Nov 21 2011, 12:45 PM
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QUOTE (monty python @ Nov 21 2011, 08:57 AM) *
...
Could it fly directly into our path towards gale crater?...


Curiosity is of course landing inside Gale Crater, I think you meant the central mound, right ?
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ElkGroveDan
post Nov 21 2011, 03:24 PM
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QUOTE (nprev @ Nov 21 2011, 01:04 AM) *
The descent stage will undoubtedly have all kinds of highly volatile material--mostly hydrazine--present regardless of its end state (unless by some miracle it blows itself into literal smithereens.) Nobody wants that stuff anywhere near the geochemical science payload. Hell, I don't even want it near the optics.


As I recall (but forget where I heard it) even Opportunity approaching the heat-shield turned out to not be such a good idea. Again from memory, during that stop there was some kind of chemical or particulate residue that accumulated on the hazcam lenses. In this low-pressure, sterile environment, anything from earth that comes to a violent end on Mars is going to be coughing up all kinds of polymers, residues, and other non-propellent volatiles that were never intended to be part of a rover or lander.


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Guest_Oersted_*
post Nov 22 2011, 11:13 PM
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Well, they had two extra years to enter some extra code into the Skycrane, so as MarsEngineer teasingly said, maybe they've tried to see if it can be made to soft-land, given that enough fuel remains... - Would be very cool (and environmentally responsible! smile.gif )
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nprev
post Nov 22 2011, 11:27 PM
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I think that adding a new requirement (and new software, and system-level testing, and, and) for the descent stage to soft-land would incur a tremendous amount of mission success risk for VERY limited potential gain.

Believe that we already established the fact (via Dan's post) that there's no valid scientific (or even a priority engineering) reason to approach the descent stage due to the risk of contamination. It could severely screw up the science instruments, and as far as post-game engineering analysis...hey, either it works or it don't. If MSL survives the descent, then it worked.

I think the "Skycrane" is gonna fly off once its job is done & go boom. But it will be fondly remembered. smile.gif


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MarsEngineer
post Nov 23 2011, 01:27 AM
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Hi all,

It has been a long time since I have posted. MSL has been keeping me swamped.

In answer to the question about the descent stage direction of flight after flyaway, unlike Phoenix, we have no specific requirement on the rover's compass heading upon landing. While we could have dedicated some fuel and timeline to orienting the "powered descent vehicle" configuration into a desired orientation prior the start of the skycrane phase (near the ground) we decided that the rover had enough to do in EDL so we don't bother. Once the rover lands the descent stage will either fly away from the front or away to the back of the rover (the RTG side). We can a priori select which of these two options to use by command that will be sent in the days leading up to EDL. We do not want the descent stage to bank or twist in such a way that the canted rocket engines impinge on the rover so those two are the only options. Once it tips away and heads out it essentially accelerate in a fixed attitude for a fixed duration or it runs out of fuel.

In summary we can not say today which direction the descent stage will be from the rover in advance. We will certainly know the day of landing from the data the rover sends during EDL on the UHF radio link to the orbiters. We also know that it will be around a half kilometer away (either behind or in front) of the rover.

In any case we will not drive the rover to the descent stage nor to the heatshield. We want to keep the rover clean and the descent stage has stuff that we do not want near the rover's sensitive equipment. Indeed there was a lot of concern when we drove Opportunity to its heatshield after landing (at my and my team's behest). We wanted to learn more about the heatshield performance (we learned a lot!).

Unfortunately, while the rover was near the heatshield, apparently wind picked up some particulates that got onto the rear Hazcam lenses. It may have been a coincidence and it was only Mars dust but more probably it was char from the heatshield that the wind blew onto the lenses.

We are ready! The team is working on the post-launch list of things to do (finally).

-Rob Manning
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nprev
post Nov 23 2011, 01:37 AM
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You heard the man, people. (And thanks for posting this, sir!)


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MarsEngineer
post Nov 23 2011, 01:40 AM
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QUOTE (Oersted @ Nov 22 2011, 04:13 PM) *
Well, they had two extra years to enter some extra code into the Skycrane, so as MarsEngineer teasingly said, maybe they've tried to see if it can be made to soft-land, given that enough fuel remains... - Would be very cool (and environmentally responsible! smile.gif )



Hi Oersted,

Indeed I was teasing! It is not impossible, but it is really hard. Perhaps the next time? wink.gif
Regardless we could never do a "soft" landing with those engines. It will have to stop and drop.

-Rob
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MarsEngineer
post Nov 23 2011, 01:42 AM
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QUOTE (nprev @ Nov 22 2011, 06:37 PM) *
You heard the man, people. (And thanks for posting this, sir!)



You are welcome nprev! Good to see you still at it!

Yes the descent stage will be fondly remembered! (imagine the cruise stage fans!).

-Rob
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nprev
post Nov 23 2011, 01:56 AM
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rolleyes.gif ...meh, I'm sometimes unpleasantly persistent. tongue.gif

But glad you came to visit, man. Please keep on doing so when time permits....we VERY much appreciate your insight!!!


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monty python
post Nov 23 2011, 07:02 AM
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I love this place!!
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ElkGroveDan
post Nov 23 2011, 07:14 AM
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QUOTE (MarsEngineer @ Nov 22 2011, 05:27 PM) *
We wanted to learn more about the heatshield performance (we learned a lot!).

Ditto Rob, in the thanks-for-dropping-by parade.

On the subject of the heat-shield recon, has there been any kind of paper, journal interview, or other public summary of what was learned? Even in a very general sense? Or is that data all still proprietary?


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