Author Topic: The "I'm brand new to Shuttle, explain what an RCS thruster is and does etc" Q&A  (Read 20604 times)

Offline smith5se


Answering the obvious followup question in advance: there would be no point in starting to paint the ETs white again to keep foam from falling off the tank. Postflight data showed STS-1 and 2 had about as many debris impacts as subsequent flights with unpainted tanks.


Thanks for the answer, and the follow up answer; guessing that question has popped up a lot.

Now for, also wouldn't the paint make the foam slightly heavier which could result in more damage to the tiles if hit?
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Offline Lee Jay

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Answering the obvious followup question in advance: there would be no point in starting to paint the ETs white again to keep foam from falling off the tank. Postflight data showed STS-1 and 2 had about as many debris impacts as subsequent flights with unpainted tanks.


Thanks for the answer, and the follow up answer; guessing that question has popped up a lot.

Now for, also wouldn't the paint make the foam slightly heavier which could result in more damage to the tiles if hit?

Not really - it's pretty light compared to a chunk of foam capable of causing damage.

Offline Sesquipedalian

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Some launch questions:

1) What is OPS-3?

2) "OMS-1 not required" -- has OMS-1 ever been required?  (Excluding an ATO situation.)

3a) "Press to MECO" -- what does "press" mean in this context?

3b) One of my coworkers said that during the early part of the shuttle program, way back circa STS-1, it was originally "press two MECO", meaning you could get there on two engines.  Is this correct, and if so, why the change?

Offline Jorge

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Some launch questions:

1) What is OPS-3?

The entry software for the orbiter.

Quote
2) "OMS-1 not required" -- has OMS-1 ever been required?  (Excluding an ATO situation.)

Always required for Standard Insertion missions, the last of which was STS-30 in 1989.

For Direct Insertion missions, OMS-1 is only required in the event of an ascent underspeed. Hasn't happened (excluding ATO).


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3a) "Press to MECO" -- what does "press" mean in this context?

Means that the mission may proceed to a nominal MECO if one engine fails (as opposed to aborting ATO).

Quote
3b) One of my coworkers said that during the early part of the shuttle program, way back circa STS-1, it was originally "press two MECO", meaning you could get there on two engines.  Is this correct, and if so, why the change?

Your co-worker misheard. It has always been "to", never "two".
JRF

Offline Lee Jay

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For Direct Insertion missions, OMS-1 is only required in the event of an ascent underspeed. Hasn't happened (excluding ATO).

Well, I think STS-93 had an ascent underspeed (15fps, IIRC), just not enough under for an OMS-1 burn, correct?

Offline Sesquipedalian

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They definitely said "OMS-1 not required" on the STS-93 video.  I remember being surprised.

Quote
1) What is OPS-3?

The entry software for the orbiter.
K, let me be more specific. :)  What does it mean when, during launch, they say "Single-engine OPS-3"?
« Last Edit: 07/15/2009 11:51 PM by Sesquipedalian »

Offline psloss

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Well, I think STS-93 had an ascent underspeed (15fps, IIRC), just not enough under for an OMS-1 burn, correct?
Yes.  Not sure what the predicted/preflight vs. performed OMS-2 was, but that might have changed a little.
« Last Edit: 07/16/2009 12:58 AM by psloss »

Offline Jorge

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For Direct Insertion missions, OMS-1 is only required in the event of an ascent underspeed. Hasn't happened (excluding ATO).

Well, I think STS-93 had an ascent underspeed (15fps, IIRC), just not enough under for an OMS-1 burn, correct?

Right, I didn't mention that there was a threshold. Can't remember offhand what it is.
JRF

Offline Jorge

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They definitely said "OMS-1 not required" on the STS-93 video.  I remember being surprised.

Quote
1) What is OPS-3?

The entry software for the orbiter.
K, let me be more specific. :)  What does it mean when, during launch, they say "Single-engine OPS-3"?

Think Mark Kirkman answered that once - try searching the Q&A.
JRF

Offline psloss

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They definitely said "OMS-1 not required" on the STS-93 video.  I remember being surprised.

Quote
1) What is OPS-3?

The entry software for the orbiter.
K, let me be more specific. :)  What does it mean when, during launch, they say "Single-engine OPS-3"?

Think Mark Kirkman answered that once - try searching the Q&A.
Unfortunately, it's a bit technical and "filed" under the old call "droop 109":
http://forum.nasaspaceflight.com/index.php?topic=6156.msg144644#msg144644

If I find something more appropriate, I'll post the link.

Offline Sesquipedalian

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I tried searching using Google, instead of on the site, and found this:
Quote
"Shuttle, Houston, you are single engine OPS 3."  This cryptic call, not usually explained by the NASA commentator, means that the flight software needs to select an entry mode instead of an abort mode if two engines fail.  This is because the shuttle is going fast enough that a proper series of banking S-turns is required to slow the shuttle down safely.  If this were to have happened while that call was being made, youd likely be parachuting into Portugal or the ocean.

So if I understand correctly, this marks the point when Shuttle re-entry must include the S-turns, rather than dropping straight down.  Is that right?

Not sure what Portugal has to do with it though.
« Last Edit: 07/16/2009 03:37 AM by Sesquipedalian »

Offline Danny Dot

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snip
Quote
3a) "Press to MECO" -- what does "press" mean in this context?

Means that the mission may proceed to a nominal MECO if one engine fails (as opposed to aborting ATO).

snip

All of the abort boundary calls made by PAO are a little off.  Press to MECO isn't to nominal MECO, it is go uphill with one engine out and not be slower than "design underspeed" at MECO -- without doing a pre MECO OMS dump.  Design underspeed keeps the ET off of a populated land mass.  For low inclination missions, this is Matagasgar off the coast of Africa, for ISS flights I think it is Saudia Arabia.

I worked with PAO in about 1995 to come up with precise definitions, but we decieded they we too complex to make on NASA TV real time.

Danny Deger
Danny Deger

Offline Danny Dot

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They definitely said "OMS-1 not required" on the STS-93 video.  I remember being surprised.

Quote
1) What is OPS-3?

The entry software for the orbiter.
K, let me be more specific. :)  What does it mean when, during launch, they say "Single-engine OPS-3"?

It is the first point that if two engines fail, the remaining engine can be burned until either fuel depletion or a guided cut off to a TAL target.  Before this point the shuttle will droop into the atmosphere during powerd flight, and the ET might heat up and explode.  It gets its name because the entry will be done in OPS 3 (nominal entry software) vs. OPS 9 (RTLS and contingency entry software).  It in no way states the shuttle will make a landing site. Before this point if two engines fail, the oribter will get off the tank while there is still lots of prop in the tank and do a contingency entry to a bail out over the ocean.


Danny Deger
Danny Deger

Offline Danny Dot

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I tried searching using Google, instead of on the site, and found this:
Quote
"Shuttle, Houston, you are single engine OPS 3."  This cryptic call, not usually explained by the NASA commentator, means that the flight software needs to select an entry mode instead of an abort mode if two engines fail.  This is because the shuttle is going fast enough that a proper series of banking S-turns is required to slow the shuttle down safely.  If this were to have happened while that call was being made, youd likely be parachuting into Portugal or the ocean.

So if I understand correctly, this marks the point when Shuttle re-entry must include the S-turns, rather than dropping straight down.  Is that right?

Not sure what Portugal has to do with it though.

The shuttle does not do S-turns on entry to slow down, it does roll reverseals to keep the nose pointed at the landing site.  The turns do nothing to help the orbiter slow down.  Maybe Mark K. can get my Entry Guidance training manual posted here for all to read.

Danny Deger
Danny Deger

Offline smith5se

Quick question while I can't sleep; NASA tv just mentioned that the white specs seen in the shots are burnt out pixels not stars. How often are these cameras changed out, since they do sustain damage during launch and while in orbit, periodically or per-flight?


Seconly, and proably a stupid one, but can someone explain how the payload canister works (never realized it was a canister). Such as, is there a new canister every flight, or are they just a part of the shuttle that can come out and be put back in? Upon moving, how do they guarentee no contamination? When are they put into the shuttle (in the VAB I assume) but before or after mating to the ET and SRBs? (yeah sorry, noob question)
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Offline MKremer

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Seconly, and proably a stupid one, but can someone explain how the payload canister works (never realized it was a canister). Such as, is there a new canister every flight, or are they just a part of the shuttle that can come out and be put back in? Upon moving, how do they guarentee no contamination? When are they put into the shuttle (in the VAB I assume) but before or after mating to the ET and SRBs? (yeah sorry, noob question)

Similar question answered here:
http://forum.nasaspaceflight.com/index.php?topic=10600.msg412184#msg412184

Offline tva

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2.  5 crew became the standard, once SAS was understood.

What stands SAS for ?
« Last Edit: 07/19/2009 03:34 PM by tva »
Rocky enthusiast
after Christer Fuglesang's mission
on STS-116

Offline Jim

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space adaptation syndrome

Offline Mike_1179

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The shuttle does not do S-turns on entry to slow down, it does roll reverseals to keep the nose pointed at the landing site.  The turns do nothing to help the orbiter slow down.  Maybe Mark K. can get my Entry Guidance training manual posted here for all to read.

Danny Deger

Mark explained it beautifully once before, but I'm having trouble searching for his post. 

A simplified (an hopefully not entirely wrong paraphrasing) The orbiter does not fly like a regular airplane / glider.  In most aircraft, if you need to adjust your altitude, you can pitch the nose up or down.  The orbiter has a very narrow band of pitch angles (the angle of attack) where she can fly.

The lift of the orbiter is perpendicular to the plane of the wings, regardless of what orientation the orbiter is in.  To adjust how much lift the wings generate, since you can’t play with the pitch too much, the orbiter has to be rolled.  By rolling the orbiter to one side, the direction of that lift doesn’t point up as much – some of that lift now forces the orbiter to go to one side.  That’s great because now you can control your altitude but if you do this too long, the orbiter starts turning away from its destination.  To keep the nose pointed the right way, orbiter is rolled in the opposite direction (the roll is reversed) which now pulls the orbiter in the other direction. 

The end result of this is an S-shaped ground track, but its not used to “burn off speed”.  The S-shaped track is an effect of the roll reversals, which are used to keep orbiter pointed towards its landing site.  The reason you need to roll in the first place is to control lift from the wings.

Offline psloss

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Mark explained it beautifully once before, but I'm having trouble searching for his post. 
Search for posts by him with the phrase "bank angle" (there are probably other useful phrases to filter).

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