Jon Berndt wrote:

"Adam Darren" wrote in message

Ok, lets say that there was a problem with tiles and that they decided to
attempt a very different re-entry profile to protect the damaged side (at
the
expense of other areas).

I don't believe there's really much of a predictable capability to do
this; the black side of the orbiter gets hot - the grey areas get really
hot, and
the white areas aren't supposed to get very hot. ;-) Aerodynamics,
control, and thermal constraints dictate the attitude the orbiter flies at
during entry. "Protecting" a damaged area - even if theoretically possible
- would likely involve flying in an un-trimmed state and require constant
jet firings and also possibly put other areas of the vehicle over their
allowable design temperatures and creating more (and possibly worse)
problems.

Could the re-entry program be modified with a new
re-entry profile while the shuttle is in orbit ?

There are three parameters that are very important at EI (entry
interface): energy (altitude and speed), REI (range at entry interface),
and the angle at EI. REI and the angle at EI have to be within a specific
range and are
dependent on many things including vehicle weight, etc. The shuttle's
entry conditions have been adjusted over the years, as I recall, to result
in the
most benign entry possible. There has been some discussion about
decresing the angle at EI *slightly* and increasing the REI *slightly* in
order to provide a lower *peak* temperature, but that would result in
greater tile
backface temperatures - there's always a tradeoff. I have seen other
papers that purport to lower the temps even further, but they are only
theoretical and have not been tested or evaluated in any way.



They could reduce the EI flight path angle further and pick a little extra
payload by changing the initial roll at EI to 180 degrees. Essentially,
grabbing a hold of the atmosphere and pulling themselves deeper into it.
Payload would be slightly increased because the deorbit burn delta-V
requirements would be reduced.

Additionally, if they had realtime heating sensors in the wing, there is
probably a small window where the Orbiter could abort the entry. Too much
heat in the wing, roll to heads up, raise perigee slightly and apply a
patch to the Orbiter and try again. Although this might come at the cost of
a little payload, as more OMS/RCS FPR would be required.

Craig Fink