[amsat-bb] Re: Discovery
nate at natetech.com
Mon Dec 11 09:17:43 PST 2006
John Magliacane wrote:
> Bob, N4HY wrote:
>> The simplest kind of approximation says they are attempting to enter a
>> certain orbit which has a certain well known orbital period. In order
>> to achieve this, the motors would have to be going long past the time
>> the shuttle would come above the horizon here. We know from experience
>> how long the motors burn.
> An interesting observation made by several of us who were able to view the
> Shuttle from the NJ/NY region was that the Shuttle's main engines were still
> plainly visible AFTER the Shuttle had confirmed MECO.
> Since I was listening to shuttle audio via our local ATV repeater, and the
> NASA-TV feed into the repeater is via an MPEG-2 satellite feed (the
> encode/decode process of which introduces some noticeable delay), I would have
> expected to see MECO occur BEFORE the delayed announcement was received. In
> fact, just the opposite occurred.
> Perhaps what we casual observers on the ground might define as main engine
> cutoff (the extinction of visible flame) isn't the true STS/NASA definition.
> I also observed the engines "sputter" for a while after MECO was announced.
> In past launches, I attributed that effect to the Shuttle possibly moving
> behind some clouds.
> But the skies on Saturday night were absolutely pristine.
> 73, de John, KD2BD
I'm no expert, just some casual layman's notes below, but did you watch
the replays on NASA TV, John? Some of what you saw could probably be
described from the video from the External Tank (ET) centerline camera
video. (Which is absolutely phenomenal by the way... if you haven't
seen it and you're reading this, find an outlet for the Flight Day 1
video and watch the launch videos. The lame press here in the States
doesn't ever play the good stuff.)
Just after MECO, there's a bunch of thruster, and (I think) OMS engine
firing to pull away (+Z) from the dropped ET. Plus I would assume the
main engine bells are probably still quite hot, possibly producing
visible light? That last part is just a guess.
The centerline camera images this time showed that the thruster and
other things firing during the ET drop, light up the tank and the
underside of the orbiter almost perfectly.
I think this might have been the "sputtering" you were seeing.
According the Flight Day 1 Press Conference, the planners at NASA had
cancelled the burn ("+X Flyby") that they do in daylight to "fly" the
Shuttle past the ET camera for inspection via the ET camera, because
they thought the orbiter would be in total darkness.
Turns out that there was PLENTY of light to do that "+X flyby" of the
camera on the ET, and they're now planning on re-adding it to the flight
plan on future night launches.
They even used the imagery to give a preliminary assessment of the
condition of the underside of Discovery long before the Flight Director
and management were expecting it. It was that bright. From what I saw,
The other really amazing thing about the ET camera shots both times I've
watched it is the plasma / "St. Elmo's Fire" effects on the wing leading
edges, especially during the above-mentioned +X flyby and even more-so
when they do the pitch-up and over maneuver to flip the Shuttle on its
back so crewmembers inside can photograph the ET. Absolutely gorgeous.
Additionally, seeing just how much friction is still happening the the
very beginnings of orbit is interesting. The RCS jet plumes seem to
flow backward just as if the Orbiter was in the atmosphere, even though
it's already outside of "most" of it at that point in the flight. That
surprised me. I know they're still in a very low Earth orbit at that
point, but still was a "hmm, never thought of that" type of surprise
when I first saw it.
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