Beagle 2 in HiRISE, Possible Targets |
Beagle 2 in HiRISE, Possible Targets |
Feb 14 2007, 05:04 PM
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Administrator Group: Admin Posts: 5172 Joined: 4-August 05 From: Pasadena, CA, USA, Earth Member No.: 454 |
EDIT: Moved these posts from the Feb 14 HiRISE Release thread to here to collect all Beagle 2 search related stuff in one place.
I'm downloading them now too -- guess I can't blog about them until I've examined them very carefully! For a bit of history on the search, Here's a blog entry I wrote about this spot a while ago Here's the MOC team's take on that spot And here's the BBC page with the Beagle 2 team's take on it EDIT: and here's my updated blog entry with links to the Beagle 2 landing ellipse images split up into 40-MB chunks. --Emily -------------------- My website - My Patreon - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Dec 18 2008, 06:34 PM
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Senior Member Group: Members Posts: 3419 Joined: 9-February 04 From: Minneapolis, MN, USA Member No.: 15 |
As I understand it, though, what's now being speculated is that Beagle 2 failed to successfully cross transition boundaries, not that the heat shield failed during the heat pulse. The shape of the entry vehicle is critical to how the vehicle maintains stability through hypersonic to supersonic velocities, and there are a lot of factors, including the actual atmospheric deceleration rate, that affect how the shape and the regime interact.
Huygens continued to decelerate at a faster and faster rate as it dug into Titan's thicker atmosphere. Beagle 2 continued moving faster for longer after it hit its maximum deceleration (which would have been less decel than Huygens saw, since Mars' atmosphere doesn't thicken with depth to the extent that Titan's does). I would be extremely surprised if Huygens and Beagle 2 were traveling at similar airspeed velocities a minute after the end of peak heating. You would have to plug in speed, deceleration rate and air density throughout the descent profile for each probe to determine the differences in transition boundaries between the two events. I guess what I'm thinking is that Huygens was slowed more quickly and effectively, and thus plowed through the transition boundaries very quickly, with very little time for the vehicle to become unstable (and, as I recall, there *are* some indications that Huygens tumbled briefly at some points during its descent). Because of the thinner air, Beagle 2 slowed more slowly and spent more time passing through transition boundaries than Huygens did, thus increasing the possibility that both its spin rate and any inherent instability in the aerodynamics of the vehicle's shape would cause the craft to tumble while still in a fairly challenging heating regime. Make sense? -the other Doug -------------------- “The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
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Dec 18 2008, 07:24 PM
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Senior Member Group: Members Posts: 2547 Joined: 13-September 05 Member No.: 497 |
You would have to plug in speed, deceleration rate and air density throughout the descent profile... I believe it's a lot more involved than that, since we are talking about fluid dynamic regimes where gas properties are far from ideal, etc, etc. Designing these things is still a black art (literally; I think many aspects of RV design are still classified.) That said, the Beagle entry design was done by engineers at EADS, and one presumes they had some basis to think it would work. It's not as if they picked the Huygens shape with no justification. My limited understanding is that the RV shape is at least partly a matter of tradition and heritage, not strongly engineering-driven. -------------------- Disclaimer: This post is based on public information only. Any opinions are my own.
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