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Space Forum / Shuttle / July 2005Query for Jorge - OMS burn on ascent?
This is a question for Jorge (or really, anyone who has specific knowledge of ascent flight ops). I was watching streaming video of the launch and the PAO voice-over guy indicated at one point in the launch after SRB sep that the OMS engines were burning; he said something like "to assist Discovery's climb to orbit." Is that true? Are OMS burns done during ascent while the SSME's are firing? That seems to me to be a bit unnecessary - surely the SSME's provide plenty of delta-V during second stage ascent such that the few percent additional from the OMS wouldn't be particularly necessary, I wouldn't think. Any corrections would be welcomed. Anyway, this is the first launch I've watched since probably the mid/late 90's - I LOVE the ET cam view; I'd love to see a replay of launch showing launch and then SRB sep from that vantage point, as well as some of the in-cabin video (like I mentioned seeing from a Russian Soyuz launch about six months ago).  Signature"Fame may be fleeting but obscurity is forever." ~Anonymous "I believe as little as possible and know as much as I can." ~Todd Stuart Phillips <www.angryherb.net> >This is a question for Jorge (or really, anyone who has specific >knowledge of ascent flight ops). I was watching streaming video of the >launch and the PAO voice-over guy indicated at one point in the launch >after SRB sep that the OMS engines were burning; he said something like >"to assist Discovery's climb to orbit." Is that true? The "OMS Assist" burn was introduced for Space Station missions. Basically, they fill the OMS tanks more than necessary for the baseline flight and burn off the excess with a firing after SRB separation to buy a few more pounds of payload. Brian I'm not Jorge, but I'll take a shot at it. They call it "OMS Assist". It's something they do now on most trips to the Station. If they use the OMS engines during launch (after SRB separation and before MECO) they can loft another 250 pounds or so of cargo weight. That's not much in the way of construction equipment, but it's a shitload of cheese sandwiches. > This is a question for Jorge (or really, anyone who has specific > knowledge of ascent flight ops). I was watching streaming video of the [quoted text clipped - 12 lines] > as some of the in-cabin video (like I mentioned seeing from a Russian > Soyuz launch about six months ago). > I'm not Jorge, but I'll take a shot at it. > [quoted text clipped - 20 lines] >> well as some of the in-cabin video (like I mentioned seeing from a >> Russian Soyuz launch about six months ago). Not much to add, except to quantify a bit: it takes about 20 lbs of OMS Assist prop to add one lb of payload. Not terribly efficient, but like Henry said, on ISS flights every little bit counts. SignatureJRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. >...the PAO voice-over guy indicated at one point in the launch >after SRB sep that the OMS engines were burning; he said something like >"to assist Discovery's climb to orbit." Is that true? Are OMS burns >done during ascent while the SSME's are firing? Yes, sometimes. When the mission (including reserves) doesn't require the full capacity of the OMS tanks, you can get a small payload gain by starting with full OMS tanks, and burning off the excess during ascent. The advantage isn't large, but every bit counts on ISS flights especially. Signature"Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | henry@spsystems.net >I was watching streaming video of the >launch and the PAO voice-over guy indicated at one point in the launch [quoted text clipped - 5 lines] >wouldn't be particularly necessary, I wouldn't think. Any corrections >would be welcomed. (AIUI) The OMS tanks have to be full at launch to cover RTLS contingencies - so they burn off the excess during launch to add delta-V. Not having to carry the extra fuel to or on orbit adds a few hundred extra pounds of cargo capacity. D. SignatureTouch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL > (AIUI) The OMS tanks have to be full at launch to cover RTLS > contingencies - so they burn off the excess during launch to add > delta-V. Actually, no. During an RTLS the majority of the OMS propellant is dumped and having a larger OMS load simply means you dump for a longer period of time. The only OMS that could potentially be used during an RTLS abort would be the propellant expended if two main engines were to fail and the RCS jets took over roll control of the stack from the SSMEs using OMS propellant, Single Engine Roll Control (SERC). The RTLS OMS dump (and pre-MECO TAL dump for that matter) is designed to hold back enough propellant for this contingency should it be required, but other than that the OMS propellant is largely just dead weight for an abort. SignatureDean Lenort | You really need a dual GHz G4 to fully harness dean.lenort | the power of cowsay. -- Matt McIrvin @att.net | Anybody notice that the OMS ignition appears on the rocketcam as a bief flare of flame from the side of the Orbiter body, about ten sec after SRB sep? Scared the sh.t out of some of us. Lucky the camera only shows us waist up. Jim >Anybody notice that the OMS ignition appears on the rocketcam >as a bief flare of flame from the side of the Orbiter body, >about ten sec after SRB sep? Scared the sh.t out of some of us. >Lucky the camera only shows us waist up. I had on NASA TV at work and a few people were watching the monitor and when I saw that I think I said "Oh sh*t" the they announced it. Totally forgot that that is now the normal way to fly. George ===[George R. Kasica]=== +1 262 677 0766 President +1 206 374 6482 FAX Netwrx Consulting Inc. Jackson, WI USA http://www.netwrx1.com georgek@netwrx1.com ICQ #12862186 >>Anybody notice that the OMS ignition appears on the rocketcam >>as a bief flare of flame from the side of the Orbiter body, [quoted text clipped - 4 lines] > and when I saw that I think I said "Oh sh*t" the they announced it. > Totally forgot that that is now the normal way to fly. It looked normal to me, based on having seen earlier footage taken from the shuttle sft windows of OMS burns, and the wide though rather diffuse plume that that caused, and that was just visible enough. So, when I saw that same sort of diffuse pluming right after ET sep, thats what I figured it was; a OMS or thruster firing to move Discovery away from the dropped tank. Bearing in mind that we've never had this aspect view before. Andre -- " I'm a man... But, I can change... If I have to... I guess. " The Man Prayer, Red Green. |
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