[ale] OT: Space Shuttle Columbia

[Chuck Huber]

On Wed, Feb 05, 2003 at 12:27:28AM -0500, tfreeman at intel.digichem.net wrote:
> On 4 Feb 2003, Jeff Hubbs wrote:
> > This is just wild idle thinking, but could there be such a thing as a
> > temp-limited re-entry?
> 
> Actually, the thinking of vaunBraun and the other thinkers of the '50s was 
> exactly that - a slower reentry even if it circled the planet almost 
> twice before touching down. (Also, that is a "if memory serves" item, take 
> it with a grain of salt). It might even work if the heat shield material 
> was intact enough to protect the aluminum underneath from somewhat lower 
> heat over a longer period. Of course, aluminum doesn't much care for red 
> heat in the presense of oxygen...

Good point.  It seems to me that it's only been in the past decade that
aerobraking has been refined enough to use.  One of the most noteable
missions that used aerobraking is the Galeleo mission to Jupiter.  It
used aerobraking to capture into orbit, then successive passes lowered
the apogee to the desired orbit.  JPL then boosted the velocity at
apogee to raise the perigee above the atmosphere.

As far as the mechanics go, a reduction in velocity at the perigee 
results in a lower altitude at the apogee.  This is why the orbiter
commits to landing when it's half-way around the earth.  The orbit is
changed by firing the OMS engines such that the perigee is 10nm high,
which is about 50,000'.  The apogee remains the same as the original
circular orbit - 100nm to 250nm.

If they were to raise the perigee such that the orbiter were to
encounter aerobraking, all it would do is lower the altitude of
the apogee.  Successive passes would continue to lower the apogee
until the orbit was circular at the altitude of the perigee.  Since
the perigee is already low enough to interface with the atmosphere,
the orbital velocity would continued to decrease until you're right
back in the same boat as our reentry profile now.

So, yes, it's possible, but I'm not sure how much cooler the reentry
would be.

Another scenario that is fuel prohibitive is to bring the orbital
velocity to near zero such that it falls straight down. If that were
done, interface with the atmosphere would take place at much, much
lower velocities when compared to the 13,000+ mph experienced by
Columbia.  The amount of fuel would be less than that used during
launch, but a whole lot more than what's presently carried.

Enjoy,
    - Chuck
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