PDA

View Full Version : Can a shuttle pull itself out of reentry & back into orbit?



Yul
2003-Feb-12, 10:41 PM
In light of this, if they would've been apprised in time of their parlous state, would it have been possible for the shuttle to have pulled itself out of reentry and back into orbit to await a rescue, in theory? Is a shuttle capable of such a manoeuvre, with or without using its rockets?
http://story.news.yahoo.com/news?tmpl=story2&cid=68&ncid=716&e=17&u=/nyt/20030212/ts_nyt/tapes_of_shuttle_s_descent_show_dawning_of_disaste r

Kizarvexis
2003-Feb-12, 10:58 PM
Nope. As I understand it, the deorbit burn procedures use up the rest of the fuel.

Kizarvexis

daver
2003-Feb-12, 11:06 PM
On 2003-02-12 17:41, Yul wrote:
In light of this, if they would've been apprised in time of their parlous state, would it have been possible for the shuttle to have pulled itself out of reentry and back into orbit to await a rescue, in theory? Is a shuttle capable of such a manoeuvre, with or without using its rockets?
http://story.news.yahoo.com/news?tmpl=story2&cid=68&ncid=716&e=17&u=/nyt/20030212/ts_nyt/tapes_of_shuttle_s_descent_show_dawning_of_disaste r


I don't know. It depends on the mission. Total OMS delta V is about 1000 feet/sec; deorbit burns are maybe 250 feet/sec. So if 250 feet/sec were used to establish the shuttle in orbit and another 250 feet/sec to deorbit the shuttle, you still have some left to change your mind, provided you do it soon enough (before you've encountered the sensible atmosphere).

The warnings in the article came much too late to do anything about.

<font size=-1>[ This Message was edited by: daver on 2003-02-12 18:10 ]</font>

Cloudy
2003-Feb-13, 08:28 AM
But that 250 m/sec must be used at a precise point determined by what landing site you want. To do it at an arbitrary point would require allot more delta V.

And when you think about it, thats what you would have to do in order to reverse the process. You can't choose when to abort. Even if you havn't touched the atmosphere yet, you would probably not be in a position where a reversing burn would be effective.

Once you actually enter the atmosphere, you lose delta-v very fast. Well before you start pulling G's, you have lost far more than an OMS burn could regain for you even if it were done from an optimal position allong your orbit.

I'm no expert, but I'd put some money on a guess that once the OMS burn is done - you are commited for reentry.

daver
2003-Feb-13, 06:54 PM
On 2003-02-13 03:28, Cloudy wrote:
But that 250 m/sec must be used at a precise point determined by what landing site you want. To do it at an arbitrary point would require allot more delta V.

And when you think about it, thats what you would have to do in order to reverse the process. You can't choose when to abort. Even if you havn't touched the atmosphere yet, you would probably not be in a position where a reversing burn would be effective.

Once you actually enter the atmosphere, you lose delta-v very fast. Well before you start pulling G's, you have lost far more than an OMS burn could regain for you even if it were done from an optimal position allong your orbit.

I'm no expert, but I'd put some money on a guess that once the OMS burn is done - you are commited for reentry.


I don't know the details of the OMS burns. It could be that after the deorbit burn they vent most of the remaining propellant--if so, there's not an awful lot that you can do. If not, and if you haven't hit enough of the atmosphere to bleed off your speed, you should be able to reattain a low orbit.

Going with the numbers i posted, a mission might use 25% of the OMS delta V attaining orbit, and another 25% leaving orbit. That should leave roughly half your total delta V to play with. Any time before hitting enough of the atmosphere to start bleeding off speed, you should be able to make another burn--say using 40% of the original delta V. Use the rest at apogee to lift your perigee a bit. The orbit won't last too long, but that's ok, you don't have that many supplies.

Irishman
2003-Feb-14, 10:34 AM
Gah! I hate long links messing the screen width. Yul, next time abbreviate the link.

like this (http://story.news.yahoo.com/news?tmpl=story2&cid=68&ncid=716&e=17&u=/nyt/20030212/ts_nyt/tapes_of_shuttle_s_descent_show_dawning_of_disaste r)

(You might try editing your post.)

And daver, did you have to quote the already too long link? Sheesh!

I don't think the situation is as simple as you make it sound. For starters, OMS are used for on-orbit operations as well. True, the RCS is used for station-keeping and attitude hold, but OMS is also for in-flight maneuvering. How much is actually left at the time of the deorbit burn varies each flight, but it's not just 50% of total supply.

Second, I believe the remaining fuel is vented. I'm not certain, but I think that's the policy, because they really don't want to return with a lot of hydrazine in the tanks.

Third, someone with a better grasp of orbital dynamics will have to tackle the question of just how long after the deorbit burn they could conceivably reverse course back to orbit. I don't think it's as simple as an equal reverse burn. The deorbit burn is just enough thrust to slow them enough to start getting drag from the atmosphere. Once that happens, it's one way downhill. A counter burn before the drag increases too much might put you into a lower orbit, one that wouldn't last very long.

By the time they hit the S curves, it's definitely too late.

David Hall
2003-Feb-14, 11:10 AM
On 2003-02-14 05:34, Irishman wrote:

Gah! I hate long links messing the screen width. Yul, next time abbreviate the link.


He probably doesn't notice any problem. I've just tested it, and both IE and Opera automatically word-wrap the link to keep it from going off the screen. Of the big ones, only Mozilla-based browsers seem to be unable to handle it.

Kaptain K
2003-Feb-14, 12:19 PM
David,
My problem is screen resolution. This computer (my back-up) has a maximum resolution of 800x640. Long URLs and big pictures require scrolling. My main computer has a maximum resolution of 1024x768 and does not cause this problem nearly as often. It was terminally virused and is in the back room waiting for parts. I hope to have it back up soon.

daver
2003-Feb-14, 06:37 PM
I don't think the situation is as simple as you make it sound. For starters, OMS are used for on-orbit operations as well. True, the RCS is used for station-keeping and attitude hold, but OMS is also for in-flight maneuvering. How much is actually left at the time of the deorbit burn varies each flight, but it's not just 50% of total supply.


Obviously the amount used will depend on the mission. It seems that the vast majority of the OMS burns are going to be in achieving orbit and getting out of orbit; i can imagine situations where you'd need to use a bunch of delta V for other matters, but i'd think they'd be fairly rare.



Second, I believe the remaining fuel is vented. I'm not certain, but I think that's the policy, because they really don't want to return with a lot of hydrazine in the tanks.

I imagine that would be the case, but i don't know when you'd want to vent it. I'd think you'd wait until fairly far into the atmosphere, just to keep your options open. Someone could go to sci.space.shuttle to find out for sure.

I saw a fairly impressive fireball in one of the shots of Columbia--i don't know if that was RCS fuel or OMS fuel.


Third, someone with a better grasp of orbital dynamics will have to tackle the question of just how long after the deorbit burn they could conceivably reverse course back to orbit. I don't think it's as simple as an equal reverse burn. The deorbit burn is just enough thrust to slow them enough to start getting drag from the atmosphere. Once that happens, it's one way downhill. A counter burn before the drag increases too much might put you into a lower orbit, one that wouldn't last very long.


Once you've hit the atmosphere, it's all over. There will be a point of no return that's a function of how much OMS fuel you have left and how long your new orbit will need to last. Say you make a burn that changes you from a 200 mile circular orbit to a 200x60 mile elliptical orbit, and halfway along that ellipse (130 miles up) you change your mind. You've got sufficient energy to maintain a circular orbit at that height, but you're heading in the wrong direction. If i've drawn my ellipses right (actually, i know i haven't, but i think they're close enough) that's going to take about a 400 foot/second burn to circularize. That's pretty close to all your remaining fuel.

If you change your mind at a higher point, you need less fuel to circularize.



By the time they hit the S curves, it's definitely too late.

Oh, yes. Depending on what your reserves look like, you might have 20 minutes or so after the deorbit burn to change your mind. And of course, if they do vent the OMS fuel, any time after that you're committed.

Anyway, my original reply was wrong--thanks for making me work through the geometry. Even with half your original OMS fuel in reserve, there's going to be a point of no return.

<font size=-1>[ This Message was edited by: daver on 2003-02-14 13:40 ]</font>