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#740
by
Jorge
on 26 Oct, 2009 19:14
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wrong entry angle. Too shallow
What happens if you enter at too shallow an angle? Do you then descend too fast and burn up? I remember from playing with Orbiter that counterintuitively, if you are descending too fast you have to dive.
In case my previous post was too subtle...
Shuttle orbits are high enough that they will not decay naturally within the lifetime of the crew. Therefore this approach is not viable (literally!) and the discussion is moot.
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#741
by
mmeijeri
on 26 Oct, 2009 19:16
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Shuttle orbits are high enough that they will not decay naturally within the lifetime of the crew. Therefore this approach is not viable (literally!) and the discussion is moot.
I know, but I'm just curious. You've explained it would take too long, which seems understandable enough. Jim said the reentry angle would be too shallow and I don't understand what's wrong with that and I'd like to know. Feel free not to answer!
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#742
by
Sesquipedalian
on 27 Oct, 2009 00:51
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I know, but I'm just curious. You've explained it would take too long, which seems understandable enough. Jim said the reentry angle would be too shallow and I don't understand what's wrong with that and I'd like to know. Feel free not to answer!
I'm assuming it takes too long
because the entry angle is too shallow; at that altitude it takes a long time for atmospheric resistance to significantly affect your velocity. By descending more steeply, you reach the denser part of the atmosphere more quickly.
Of course, Jim might have had something else in mind. I wish he would give more verbose answers.
EDIT: On the other hand, you have to be mindful that the heat shield is on the
bottom of the shuttle, not the nose.
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#743
by
rdale
on 27 Oct, 2009 00:53
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It's pretty simple - if you don't have something to put brakes on the shuttle, it will stay up there for a LONG LONG time. I'm not sure what's confusing?
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#744
by
mmeijeri
on 27 Oct, 2009 00:55
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I did some googling and it turns out there is something called an entry corridor which determines the range of angles suitable for reentry. Too steep and you burn up, too shallow and you skip out of the atmosphere again. I don't know if this applies to return from LEO as well as lunar returns, but I suppose it does. So what happens once you skip out? Since you would have lost some energy your orbit would still be decaying. How steep would the next angle be? Could it be that the angle gets progressively steeper with every skip until finally you burn up?
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#745
by
mmeijeri
on 27 Oct, 2009 00:59
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It's pretty simple - if you don't have something to put brakes on the shuttle, it will stay up there for a LONG LONG time. I'm not sure what's confusing?
That part was clear. I know this is not a viable way to return - and I knew you could use the RCS for a deorbit burn before I asked the question since this has been discussed before.
I wondered if changing the attitude of the Shuttle could increase drag by enough to deorbit and I now know the answer is no. I wondered if the shallow reentry would be a problem and I now know it would be. What I don't understand is the details of what the correct angle for reentry is.
Again, feel free not to answer, I'm grateful for the answers I've received so far.
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#746
by
Antares
on 27 Oct, 2009 01:56
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So what happens once you skip out?
On a low eccentricity orbit, such as the subject hypothesis, there would be no skip. It would be a continuous aerodynamic decay.
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#747
by
elmarko
on 27 Oct, 2009 10:15
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Changing your attitude so that there's more of a cross section pointing in the direction of the velocity vector SHOULD increase drag, but probably not enough to do anything significant.
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#748
by
mdo
on 27 Oct, 2009 20:42
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What happens if you enter at too shallow an angle?
In all likelihood it will not reach an airport due to the increased uncertainty of the trajectory.
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#749
by
mmeijeri
on 27 Oct, 2009 21:05
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On a vaguely related note, is there anything an Orbiter with a damaged heatshield can do to make reentry safer in the sense that it would get down low enough and slow enough for the crew to bail out?
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#750
by
rdale
on 27 Oct, 2009 21:21
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Only if they bail in orbit. But then they have other issues.
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#751
by
kneecaps
on 28 Oct, 2009 10:57
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In the unlikely event that the Shuttle lost both OMS thrusters could the Shuttle reenter simply by letting its orbit decay? I imagine this depends very strongly on its altitude and orientation. How soon would the Shuttle's orbit decay if it presented the maximum possible area normal to its velocity vector? Could it survive such a reentry, provided it reoriented itself in time? Could it keep the crew alive for long enough to do this?
No but it could use its RCS thrusters
Yep. The +X RCS jets.
Doesn't have to be just the +X jets, fast flip and prebank can also contribute to getting the needed delta V. This topic has been covered a lot here so a search might find you some more detailed answers.
Mark Kirkman
For those on L2 there are some fab documents that cover prebank and fast flip.
Also when it comes to OMS ENGINE failures (assuming you have good prop) you can feed the aft RCS jets with the OMS tanks.
The Orbiter has many options available for a safe deorbit burn.
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#752
by
Hop_David
on 28 Oct, 2009 14:43
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I did some googling and it turns out there is something called an entry corridor which determines the range of angles suitable for reentry. Too steep and you burn up, too shallow and you skip out of the atmosphere again. I don't know if this applies to return from LEO as well as lunar returns, but I suppose it does. So what happens once you skip out? Since you would have lost some energy your orbit would still be decaying. How steep would the next angle be? Could it be that the angle gets progressively steeper with every skip until finally you burn up?
It seems to me angle of incidence would equal angle of reflection. Like a pool ball bouncing off the edge of a table or a photon bouncing off a mirror.
And since the spherical earth and elliptic orbit have a symmetry I would expect re-entry at the same angle that the craft bounced from.
Of course the ship's interaction with the atmosphere might change the bounce angle.
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#753
by
Antares
on 29 Oct, 2009 02:39
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I'm assuming you're talking about the atmosphere there, rather than on the orbiter itself. I just searched for an ESTEC standard that I ran across somewhere several years ago, but I can't find it now. Maybe you can come up with more creative Google terms than me.
Basically, the individual atoms or molecules are really hot (>1000K), but they are so far apart that it would "feel" really cold (<100K).
Edit: here's a ton of models
http://ccmc.gsfc.nasa.gov/modelweb/
I'd like to know what are temperatures on that altitude the space shuttle fly?
Mind like a steel trap, or maybe I stumbled across it while looking for the answer to someone else's Isp question.
http://www.spenvis.oma.be/spenvis/ecss/ecss07/ecss07.htmlYour answer is 699 Kelvin.
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#754
by
mmeijeri
on 29 Oct, 2009 09:52
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Great link! I thought SPENVIS only modeled the radiation environment in the van Allen belts, but it's much more extensive than that.
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#755
by
C5C6
on 29 Oct, 2009 15:01
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I recently saw some footage of slow motion MLP cameras during launch and I could see some kind of dirt covering up the cameras. I understand that is SRB exhaust. Does this 'dirt' contaminates the ocean when the SRBs fly over it??
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#756
by
ChrisGebhardt
on 29 Oct, 2009 23:05
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I recently saw some footage of slow motion MLP cameras during launch and I could see some kind of dirt covering up the cameras. I understand that is SRB exhaust. Does this 'dirt' contaminates the ocean when the SRBs fly over it??
SRBs do not pollute the ocean.
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#757
by
C5C6
on 30 Oct, 2009 23:07
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I recently saw some footage of slow motion MLP cameras during launch and I could see some kind of dirt covering up the cameras. I understand that is SRB exhaust. Does this 'dirt' contaminates the ocean when the SRBs fly over it??
SRBs do not pollute the ocean.
could you please explain it up??
is that 'dirt' covering the cameras not part of SRB exhaust?? in case they are part of it, does it fall into the ocean?? in case they fall into the ocean, is it toxic??
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#758
by
AlexInOklahoma
on 31 Oct, 2009 14:04
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is that 'dirt' covering the cameras not part of SRB exhaust?? in case they are part of it, does it fall into the ocean?? in case they fall into the ocean, is it toxic??
I could not find any quick/easy references for you, but, going from memory only, the exhaust is *not* a ~credible bio-hazard or such (imho) I think the 'particles' are aluminum-based and not a concern at all. Gritty and abrasive, but not 'reactive' biologically speaking The 'worst part' of the exhaust (IMHO) is that it can cause some pH 'shifting' of the air in the area (??), but it is so very (very, very, very....) slight that it is not of any practical concern whatsoever. It would be bad to pump out the exhaust for hours on end for months and months continuously, but at usual rates, non-issue
The perchlorate(s) (look *that* part up for more info, plz) formed are present but trivial overall (!!!) I am not explaining this any deeper as I forget the actual details and don't want to mislead by intention, but it is a non-issue environmentally speaking. Could be debatable, but IMHO, that is calling a tiny molehill a huge mountain...
Make sense? There is no effect from the exhaust that is meaningful. After all, there is a 'Refuge' surrounding the launch complex there
Gebhardt just put it a lot more succinctly as it can sometimes be stretched into something it is not
More here ->
http://forum.nasaspaceflight.com/index.php?topic=18447.0and here ->
http://www.epa.gov/OGWDW/contaminants/unregulated/perchlorate.htmlHTH,
Alex
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#759
by
Jim
on 31 Oct, 2009 14:21
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The exhaust products are aluminum oxide and hydrochloric acid.
Gebhardt just put it a lot more succinctly as it can sometimes be stretched into something it is not