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Gut feeling...
djellison
post May 23 2008, 01:26 PM
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5mph they keep saying - 2.5ish m/sec

2.5 m/sec to a standstill in, say, .25 seconds - 1G.

Atmospheric entry and the chute-deployment snap will be much higher than that, 6, 7, 8, 9 G sort of figures.

Doug
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Stu
post May 23 2008, 01:32 PM
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To be honest I can't even bring myself to think of a figure; a little part of me thinks that doing so would jinx the mission, so sorry, no percentage from me. I do, though, think that it's quite unlikely Phoenix will land on perfectly flat ground, having seen the latest HiRISE images. There are so many mounds, trenches and ridges that I'm pretty confident that our first images of the landscape will show the horizon at an angle.

I just finished work for the long Bank Holiday weekend, and I'm not in again until Tuesday afternoon. Strange to think that the next time I walk through the door at work we'll either have a new probe on Mars, sending back new pictures and data, or we'll all be spectators to another Beagle- or MPL-like interplanetary post-mortem...

My "gut feeling" isn't a percentage, it's a word: sick... huh.gif


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djellison
post May 23 2008, 02:11 PM
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I am genuinely beginning to get a physical reaction to the tension of the whole thing. Phoenix is making me physically nervous already. Quite what I'll be like on Sunday I don't know.

Doug
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nprev
post May 23 2008, 02:23 PM
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Be chilly, you guys, keep an even keel...really, it's gonna be alright. Don't know why I know it, but I know it. smile.gif


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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jamescanvin
post May 23 2008, 02:29 PM
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Me too, I've already got that nervous-butterfly's-in-stomach feeling., I'm going to be wreck come Sunday night!

Made the decision today to take Tuesday and Wednesday off work next week, in addition to the Bank Holiday Monday, to recover and work full time on Phoenix data*. smile.gif

* That in the spirit of this thread I'm 90% sure we'll have by then.

James


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Guest_Zvezdichko_*
post May 23 2008, 02:41 PM
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Same here. I woke up early with a stomach pain smile.gif

We all know everything will be all right, but I don't know why I'm worried
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tim53
post May 23 2008, 02:42 PM
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QUOTE (kwan3217 @ May 22 2008, 10:28 PM) *
Quotes removed. Better use the "add reply" button at the bottom of the page when replying to the previous post. Tesheiner

Both MERs are travelling from west to east, so both of them are long, A is only a little bit long, B is a lot long.

But surely by the mere fact of flying the MERs, we understand the aerodynamics of the shell better, and since Phoenix's shell is almost identical, if there is some systematic factor which made the MERs go long, it must be understood and modelled out of Phoenix's ellipse.


I just realized that MPF also "went long", as the trajectory was from NE to SW.

This may be nothing more than a coincidence, though. Different years, different atmospheric models.

Beagle II may likely have gone downrange from the center of the landing ellipse, since it "landed" near in time to the MER landings. This should aid our search, somewhat.

-Tim.
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nprev
post May 23 2008, 02:56 PM
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What's weird is that I sweated blood before both of the MERs, and I'm actually...serene?!...for Phoenix. Now I'm worried about the fact that I ain't worried!

EDIT: Ahh, got it. After watching V1 & V2 as a kid (to say nothing of the Apollos), I trust powered landings, and am confident that Phoenix has learned all relevant lessons from MPL.


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djellison
post May 23 2008, 03:22 PM
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QUOTE (tim53 @ May 23 2008, 03:42 PM) *
I just realized that MPF also "went long", as the trajectory was from NE to SW.


I thought that was the case (with the landing at night) but I wasn't sure enough to say anything smile.gif

Doug
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tanjent
post May 23 2008, 03:31 PM
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This is what markets are good for. We can all exchange our best guesses, and we all feel a great emotional stake in the outcome. But a pecuniary stake tends to weed out the casual guessers and weight those remaining according to their confidence in a) the quality of their information and cool.gif their having the experience and judgment to apply it effectively.

An outfit called Intrade has a similar market for the probability of the Google Lunar X prize being won by 2012.

http://www.intrade.com

It's probably not the only one. I think Lloyd's used to quote odds on a whole range of possible binary events.

It's too late to do anything about Phoenix over the weekend, but maybe we should encourage the Intrade people to float a similar issue based on the successful landing of MSL. If it seems crass to think about monetary payoffs when the really important value is something like "raising the consciousness of humankind" then pledge your future proceeds to the Planetary Society!

I think I'll be on the sidelines though, because my expertise is pretty much on the level of keeping my fingers crossed. Accordingly, if pressed, my best guess would have to be 50-50 with no apologies to either side. Anyway, it's just our left brains that feel compelled to quote odds about the probabilities. There is complete unanimity with respect to our hopes. 100% probability on that.

tanjent
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Decepticon
post May 23 2008, 03:47 PM
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QUOTE (Zvezdichko @ May 23 2008, 03:38 AM) *
With regards to your opinion, the powered descent phase is just 40 seconds, not 5 minutes.


Whoa! I put 5 Mins!

I should of put 5 seconds.




Im so worried. unsure.gif
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centsworth_II
post May 23 2008, 03:56 PM
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QUOTE (Decepticon @ May 23 2008, 11:47 AM) *
Im so worried. unsure.gif

Ok, but 5%? Even the most pessimistic outlook should have it at no lower than 50%. All this worry about the powered landing has me wondering how TWO Vikings ever made it to the ground in one piece, not to mention countless (by me anyway) Lunar landers -- including manned! I think powered landings are a pretty well explored territory. Heck, that last 30 seconds could well be the most sure part of the EDL sequence! I've got myself convinced anyway. smile.gif
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Guest_Zvezdichko_*
post May 23 2008, 03:59 PM
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You are right, of course, but this technology hasn't been used for decades! A lot of people working on the projects have already retired. That's a lot of experience to lose!

Also, the pulsed thrusters. I have some worries on how they keep the spacecraft stable.
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centsworth_II
post May 23 2008, 04:03 PM
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QUOTE (Zvezdichko @ May 23 2008, 11:59 AM) *
I have some worries on how they keep the spacecraft stable.

I guess they proved themselves in all the testing... or they wouldn't be flying.
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ugordan
post May 23 2008, 04:19 PM
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QUOTE (centsworth_II @ May 23 2008, 06:03 PM) *
I guess they proved themselves in all the testing... or they wouldn't be flying.

For some reason this reminds me of the story of Saturn V J-2 engines that were undoubtedly tested and tested again on the ground and proved themselves robust. Then came Apollo 6 and a mysterious failure of 2 of those engines. Turns out they weren't actually tested in an environment they were meant to operate in - effectively pure vacuum and there was a design failure that only showed up in actual vacuum operation. I'm not implying something similar will happen on Phoenix, not by a long shot. It's merely an anecdote how unknown variables can always be in the hiding somewhere.

There's no such thing as the ultimate test, for that you'd have to be there, fly the exact same profile as in the real thing many times and see whether any problems crop up. Everything else is just an approximation and modeling. The devil's always in the details. That said, I'm sure the Phoenix testing was quite adequate, the thing I worry the most is the actual touchdown.


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