General Question Space Shuttle Orbital/OMS procedures.

[Slaintemaith]

The shuttle launches. The SRBs drop away a couple minutes later. The main engines cut off roughly six minutes after that.

I know that it's not in orbit after MECO. I know that there's an OMS burn(s) afterward to make it so. My question is: (At least with regards to an ISS mission) what happens next from an orbital height standpoint?

Does the shuttle make its first OMS burn to put it at the apogee/perigee of the ISS, or just circularize its own orbit? Or something in between?

I've searched both the forums and The Web At Large for this info and come up with bupkis. (And I'd be willing to bet there's a mission-by-mission breakdown around somewhere!)

 

[garyw]

Post launch the shuttle performs an OMS-2 burn. That buts it into orbit but still below the ISS. From there are a series of burns (NC-1, NC-2 and others) which slowly raise the orbit to the ISS.

This might give you a better explanation -> http://www.shuttlepresskit.com/sts-93/ref85.htm

 

[redneck]

Post launch the shuttle performs an OMS-2 burn. That buts it into orbit but still below the ISS. From there are a series of burns (NC-1, NC-2 and others) which slowly raise the orbit to the ISS.

This might give you a better explanation -> http://www.shuttlepresskit.com/sts-93/ref85.htm

To bad we don't have a mfd that does all those burns automaticaly. Hopefully SSU will have something like that.

 

[zerofay32]

SSU woun't do the burns automaticaly. For some missions it is planned to have all the burns in a flight plan so you know when to make the burns but even then you'll still have to set up the DAP and enter the right figures into the GPC's burn software. For user created missions you'll have to figure out the burns on your own just as you do now. All OMS burns are controled by the GPC's but the time, duration, and direction all have to inputed manually by the crew. If anything OMS burns are easier to perform now (all you have to do is point in the right direction and press + ) but you can't do that in the real shuttle and you woun't be able to do that in SSU.

 

[Capt_hensley]

If anything OMS burns are easier to perform now (all you have to do is point in the right direction and press + ) but you can't do that in the real shuttle and you woun't be able to do that in SSU.

Why not build in the option? Ultra implies "the best" and this is after all "a sim". I think it could be a great learning tool to have something show you all the automated stuff, then you could learn how to do it manually as you go along.

Or would a well planed and recorded scenario file do it?

 

[redneck]

Why not build in the option? Ultra implies "the best" and this is after all "a sim". I think it could be a great learning tool to have something show you all the automated stuff, then you could learn how to do it manually as you go along.

Or would a well planed and recorded scenario file do it?

I like the recorded scenario idea. I didn't think of that. That would be easier I guess then making a autopilot type MFD. How far along is SSU reguarding a release?

 

[Donamy]

it's released now, well sort of. You just need to download the files from sourceforge and load the newest modeles.

 

[Urwumpe]

How far along is SSU reguarding a release?

About 2,747 manhours from release. Will be reached on a Tuesday.

Why not build in the option? Ultra implies "the best" and this is after all "a sim". I think it could be a great learning tool to have something show you all the automated stuff, then you could learn how to do it manually as you go along.

Ultra means Ultra-realistic, not Ultra-Easy. For Ultra-Easy, you have already Shuttle Fleet, and we don't dare getting rivals in that part of education. Ultra also means no switch throwing simulation, but simulating on a subsystem level.

Seriously: Ultra isn't really selected because it means one extreme, we just needed a good word for improving "Deluxe". Ultra is some sort of a trademark for the SSU project and other work developed based on it, but there is currently no "Ultra" quality standard that you can comply to. Ultra just means, the original checklists work, we can follow realistic flight plans and are within reasonable distance of the historic flights.

Its just a game. But they say the same about DCS.

SSU won't do the burns automatically.

Correction: The ascent and abort OMS burns will be pretty much automated by using "Initial Loads" or "I-Loads", which the crew just needs to confirm.

But all others will be classic programming of the on-board computers. It is planned to permit getting the OMS burn pads from a simplified mission control simulation, or a gang of VSA buddies via Internet, but that is currently not high-priority.

---------- Post added at 06:24 PM ---------- Previous post was at 06:17 PM ----------

Does the shuttle make its first OMS burn to put it at the apogee/perigee of the ISS, or just circularize its own orbit? Or something in between?

Below the orbit of the ISS, in a catch-up orbit. The initial orbital parameters that you get after OMS-2 (OMS-1 is omitted usually) are just coarsely chosen since you can't get perfect accuracy that early in flight. After a few radar measurements, the Shuttle does a small phasing burn, that sets the orbit period of the Shuttle so, that it is in the right distance of the ISS after two days to intercept it by the final rendezvous maneuvers.

If you use the so-called standard ascent profile, you have one OMS-1 to leave the suborbital trajectory that it had after MECO, raising your apogee to the target orbit (eg, the catch-up orbit), and then have OMS-2 to circularize it.

 

[zerofay32]

Correction: The ascent and abort OMS burns will be pretty much automated by using "Initial Loads" or "I-Loads", which the crew just needs to confirm.

I was referring to on-orbit type burns, but your right. Thanks for clarifying for me.

 

[ky]

How long do the burns take?

 

[C3PO]

How long do the burns take?

That, my friend, is rocket science.

Time to start researching.

 

[Urwumpe]

How long do the burns take?

Can be quite long, 300 ft/s velocity change mean ~50 seconds burn time with two engines.

 

[Slaintemaith]

Thanks for your answers, all.


[Off Topic] Urwumpe--I just want you to know that -I- caught your Pratchett reference (Pax Morporkia) in another thread--no one else did. Made me a little sad, actually.[/Off Topic]

 

[David413]

Some real-world state vectors

Attached is the original (before the slight pause at T-31 seconds) state vectors for STS-135. At the beginning of the file you can see the predicted OMS burns, starting with OMS2, (at an MET of +00:38:21.738) which was predicted to be a 1 minute, 6.417 second dual-OMS burn. Next is NC1, a 1 minute, 42.762 second burn, and so on. I leave it as an exercise for the student to determine the other listed burns (hint: check the original flight plan...).

Dave

Incidentally, the OMS2 burn was a total increase of velocity of 98.1 feet/sec, over 66 seconds. It was mostly an in-plane burn (the DVx is almost the total burn...)

 

[Donamy]

What attitudes are the burns ?

 

[David413]

What attitudes are the burns ?

Depends on what values are required for each axis at the time of the burn. Also, are you talking inertial, or LVLH relative? Each of the entries gives those numbers along the principle axis. The more minor "tweak burns" are using the RCS instead of the OMS, and some of the OMS burns are a single engine burn. It also depends on whether the burn is an altitude adjust burn (only) or a plane-change (alignment burn) or a combination of both (such as an NCC burn).

 

[mode1bravo]

Depends on what values are required for each axis at the time of the burn. Also, are you talking inertial, or LVLH relative? Each of the entries gives those numbers along the principle axis. The more minor "tweak burns" are using the RCS instead of the OMS, and some of the OMS burns are a single engine burn. It also depends on whether the burn is an altitude adjust burn (only) or a plane-change (alignment burn) or a combination of both (such as an NCC burn).

Hey David413, I was wondering doesn't the shuttle pitch up like 07 degress off LVLH to offset the slight misalignment of the OMS engines on the vehicle to not impart downward thrust, just forward prograde OMS2? Any yaw component in this would be to cancel out Rinc right?

Thanks for Shuttle Fleet!

 

[David413]

Hey David413, I was wondering doesn't the shuttle pitch up like 07 degress off LVLH to offset the slight misalignment of the OMS engines on the vehicle to not impart downward thrust, just forward prograde OMS2? Any yaw component in this would be to cancel out Rinc right?

Thanks for Shuttle Fleet!

The engines do have some gimbaling ability, however the vehicle may also pitch and yaw in order to get the correct Dv on the required axis. Sometimes the deorbit burn will be significantly out-of-plane in order to "waste" prop in order to get the weight and balance correct for the entry.

So, the simple answer to your question is, it ain't so simple (sometimes!).

 

[Tommy]

[Off Topic] Urwumpe--I just want you to know that -I- caught your Pratchett reference (Pax Morporkia) in another thread--no one else did. Made me a little sad, actually.[/Off Topic]

Don't worry, quite a few of us caught the reference, just didn't bother to post about it.

We also catch his references to "Moon is a Harsh Mistress" (TANSTAAFL) and "Stranger in a Strange Land" (grok).

 

[C3PO]

The engines do have some gimbaling ability, however the vehicle may also pitch and yaw in order to get the correct Dv on the required axis.

I always thought the OMS gimbal was to point the resulting force at the CoG to avoid torque. Isn't that the case?