Sue Wheatley wrote:
>
> What does OMS-2 mean? All the internet sites seem happy to use the term,
> but I can't find its meaning. Where can I get a good abbreviation
> dictionary that covers satellite observing terms?
> ---sue
Here are some exerpts from the STS Plus program documentation which
should make it clear.
> STSPLUS can generate launch simulation for Space Shuttle launches from
> Cape Canaveral, Florida. Prior to Version 9509, STSPLUS used only 2-Line
> Elements ("TLEs") and assumed that whatever satellite was being displayed
> "had always been in orbit" and that the current position could be
> accurately calculated from the TLEs, not quite in line with the typical
> situation for a Space Shuttle launch! Many STSPLUS viewers were confused by
> the fact that prior to launch, the orbiter appeared to be off the coast of
> Baja California rather than sitting quietly on Pad 39A or 39B at Cape
> Canaveral. The STSPLUS simulation did not catch up with the true orbit
> until approximately the OMS-2 burn (Orbital Maneuvering System, Burn #2)
> which typically occurs about 35 to 45 minutes after launch. The OMS-1 burn
> is not required for a nominal ascent trajectory but its place and number
> are reserved in the STS Timeline regardless of whether or not it takes
> place. I am always relieved by the CapCom call "OMS-1 NOT REQUIRED" because
> that means that the Solid Rocket Boosters (SRBs) and the Main Engines
> (SSMEs) did their job correctly.
> ....
> Estimated pre-launch TLEs are usually prepared well in advance of a
> flight by Gil Carman or others at the NASA Johnson Space Center, Flight
> Dynamics, in Houston, Texas. These TLEs represent the planned orbit for the
> Space Shuttle for a nominal launch and are calculated for a time (the
> "Epoch" of the TLEs) following the OMS-2 burn. It is the OMS-2 burn which
> circularizes the orbit at the intended altitude; prior to OMS-2, the
> orbiter is in a highly elliptical orbit whose perigee (low point,
> technically the minimum orbital distance from the center of the Earth) is
> some tens of miles above the surface and whose apogee (high point) is at or
> near the planned altitude. The OMS-2 burn occurs at apogee and in effect
> raises the perigee to the planned altitude. With apogee and perigee both at
> approximately the same altitude, a nearly circular orbit is the result.
> Without the OMS-2 burn the orbit is not sustainable, dipping too far into
> the Earth's atmosphere, and the orbiter would have to make a landing
> immediately.
In other words, the OMS-2 burn happens at the high point about half an
orbit after launch - probably somewhere over the Indian ocean.
I think that Shuttle operations have changed a bit since David Ransom
wrote this in that now the OMS is, I understand, used during the ascent.
It's called OMS Assist and is used to help get heavy loads into the
relatively high inclination orbit of the ISS. I might be confused
here though as it is possible that OMS Assist refers to the use of
the OMS-2 burn.
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This archive was generated by hypermail 2b29 : Wed May 29 2002 - 12:12:33 EDT