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Beagle 2 in HiRISE, Possible Targets
djellison
post Dec 17 2008, 09:16 PM
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Two things have always put an entry-phase burn-up top of my list of Beagle 2 failure modes. Firstly, the lack of any parachute visible in MOC imagery (which would be very very visible) - and secondly - the fact that the B2 shape was Huygens like rather than Viking like.

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rlorenz
post Dec 18 2008, 02:19 PM
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QUOTE (djellison @ Dec 17 2008, 04:16 PM) *
Two things have always put an entry-phase burn-up top of my list of Beagle 2 failure modes. Firstly, the lack of any parachute visible in MOC imagery (which would be very very visible) - and secondly - the fact that the B2 shape was Huygens like rather than Viking like.


Eh? Huygens worked - not sure I follow.

Havent read this new australian paper yet ; I always liked the ammonia-leaked-out theory
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mchan
post Dec 18 2008, 04:32 PM
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It could be that a shape designed for the thicker Titan atmosphere may not work as well for thinner Mars atmosphere as a shape designed for thinner Mars atmosphere.
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djellison
post Dec 18 2008, 04:51 PM
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QUOTE (rlorenz @ Dec 18 2008, 02:19 PM) *
Eh? Huygens worked - not sure I follow.


.01 bar CO2 vs 1.5 bar N2 - there was a chap over at The Habitable Zone who was fairly convinced that Beagle looking more like a small Huygens than a small MPF was a recipe for high mach number problems.
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ugordan
post Dec 18 2008, 05:52 PM
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In all fairness, you can't compare surface conditions to entry conditions both probes experienced. Huygens entered at what, 6 km/s and isn't that a typical Mars entry velocity, too?

The bigger difference could have been entry angle, but even then if you had two identical probes on the outside and their centers of mass were located differently, they could behave entirely differently. A Huygens-lookalike probably isn't a bad thing by itself.


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dvandorn
post Dec 18 2008, 06:34 PM
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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


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Doc
post Dec 18 2008, 07:22 PM
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Perfectly Doug! But the question now is what the hell persuaded the B2 team to install the Huygens shield? Honestly this is one of the reasons why someone should come with a standard issue book titled 'How to land on different worlds for idiots!'


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mcaplinger
post Dec 18 2008, 07:24 PM
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QUOTE (dvandorn @ Dec 18 2008, 10:34 AM) *
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.


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Guest_Enceladus75_*
post Dec 18 2008, 08:27 PM
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So the evidence from new analysis is pointing to an atmospheric burning up for the ill fated Beagle 2. If that truly was the fate of B2, then there can't be any chance of HiRISE finding anything on the Martian surface at Isidis.

It's a darn shame...why was the Huygens aeroshell selected? Did the engineers not realise that the atmospheric dynamics at Mars would be completely different to that of Titan? This appears to be almost as bad a gaffe as the Mars Climate Orbiter mix up of metric and imperial units. Again, I suspect penny pinching and keeping costs cut to the bone was the main problem - Beagle 2 was underfunded - too fast and too cheap! sad.gif
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mcaplinger
post Dec 18 2008, 08:45 PM
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QUOTE (Enceladus75 @ Dec 18 2008, 12:27 PM) *
Did the engineers not realise that the atmospheric dynamics at Mars would be completely different to that of Titan?

Did you read my last post? You guys are way too eager to jump to conclusions without much knowledge of the engineering realities involved. I haven't seen a detailed analysis of the Beagle aeroshell design, but certainly the independent JPL review said nothing about this, so if it was an error, it was a subtle one, not a stupid and obvious one.


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Guest_Enceladus75_*
post Dec 18 2008, 08:57 PM
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QUOTE (mcaplinger @ Dec 18 2008, 08:45 PM) *
Did you read my last post? You guys are way too eager to jump to conclusions without much knowledge of the engineering realities involved. I haven't seen a detailed analysis of the Beagle aeroshell design, but certainly the independent JPL review said nothing about this, so if it was an error, it was a subtle one, not a stupid and obvious one.


OK I take your point, mcplinger...but please, no need to jump down the throats of us lesser mortals who are not aerospace engineers. sad.gif

I do still hold to my belief that a very limited budget and limited resources to the B2 team was what ultimately contributed to Beagle 2's demise on Mars. As I've heard the saying, you can have two of the three ..."faster, better, cheaper" ... any two, but not all three.
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climber
post Dec 18 2008, 08:58 PM
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A bit OT but anyway, do you know if Phoenix EDL reconstruction help assuming MPL's "ED" must have been nominal so we can assume only "L" failed?


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Stu
post Dec 18 2008, 09:02 PM
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QUOTE (Doc @ Dec 18 2008, 07:22 PM) *
Honestly this is one of the reasons why someone should come with a standard issue book titled 'How to land on different worlds for idiots!'


As the Phoenix team went to great pains to point out as we crept towards EDL, landing on Mars is hard... incredibly hard... teeth-gnashingly, hair-pulling-out hard. I don't think we know what went wrong with Beagle yet, this is just another New Best Guess.

And as the Beagle team had to fight their way through ten different levels of Hell to even get the probe built and taken to Mars, and the probe they designed and built with little support from any Big Money, was a marvel of engineering, "as elegant as a pocket watch" it has been said. If it had worked they'd have been praised to the skies for "exploring Mars on a shoestring" and "upstaging NASA for a hundredth of the money"... Hindsight is always 20/20, and yes, mistakes were probably made, but denouncing them as 'idiots' is very unfair I think.

I spent that fateful Christmas Day going online every twenty minutes, desperate for updates. I had a horrible, sick feeling in my gut all day waiting for news, with hope gradually ebbing away... and if I was that bad, what nightmares the Beagle team experienced I don't like to imagine.

Idiots? Never. I'm still proud of them for even trying. smile.gif


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mcaplinger
post Dec 18 2008, 09:36 PM
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Here's the Casani report for people who feel like reading it. Note section 6.2.2 in particular.

http://www.bnsc.gov.uk/5278.aspx


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Doc
post Dec 18 2008, 09:41 PM
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Don't you worry Stu, I vented my anger a long time ago on the UK gov't who were supposed to nurture the mission if you will. The B2 team are alright. (seeing that you are british I hope I didn't offend you wink.gif )


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