Orbital Reentry shield/landing system?

lou writes:

The real purpose of the TPS is to convert orbital velocity to heat
energy and transport it to somwhere that isn't the crew compartment.

....And also pretty much _any_ structurally important component of the
spacecraft...

From an operational standpoint, wouldn't it make more sense to haul up
enough delta-v to perform a larger retro burn? Not enough to bring the
orbiter to a full stop relative to the surface, but enough so that a
titanium hull like the X-15 or the SR-71 could withstand the rest.

....Not if all that propellant would mass significantly more than a TPS would.
(All else being equal, every kilogram of propellant you haul up is one kilogram
of cargo that you =CAN'T= haul up!)


Also, is there any way on a winged orbiter to do a phased reentry to
control temperatures (stall and fall till heat rises, then straight an
level till heat drops, repeat till on or underneat ground)

The lift-to-drag ratio of just about =ANY= a hypersonic vehicle
pretty much sucks, and high lift entry profiles tend to imply
=VERY= high heat loads on the leading edges of the wings.
(Even the shuttle enters with an angle of attack that is so high
that it is more "belly first" rather than nose first --- i.e.,
more like a "capsule" than an aircraft...


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article Fwseb.643725$Ho3.133875@sccrnsc03,
lou wrote:
From an operational standpoint, wouldn't it make more sense to haul up
enough delta-v to perform a larger retro burn?

No. The required delta-V is horrendous, grossly impractical for chemical
rockets.

Not enough to bring the
orbiter to a full stop relative to the surface, but enough so that a
titanium hull like the X-15 or the SR-71 could withstand the rest.

That is, for all practical purposes, the same thing. Neither titanium
(SR-71) nor Inconel (X-15) can take more than a rather small fraction of
orbital velocity (respectively about Mach 3 and Mach 6; orbit is Mach 25).

Also, is there any way on a winged orbiter to do a phased reentry to
control temperatures (stall and fall till heat rises, then straight an
level till heat drops, repeat till on or underneat ground)

Not if by "control temperatures", you mean controlling them to the level
that TPS would not be needed. Limiting temperatures is just a matter of
staying up at sufficiently high altitude... but there is no way to do it
that well, not for a winged orbiter having any reasonable density.
Aerodynamic lift just isn't enough.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
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Henry Spencer wrote:

Limiting temperatures is just a matter of staying up at sufficiently
high altitude... but there is no way to do it that well, not for a
winged orbiter having any reasonable density.

How about some sort of a very-low-pressure balloon, deployed in orbit,
that dramatically increases the cross-section of the orbiter?

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Michael J Wise writes:

Henry Spencer wrote:

Limiting temperatures is just a matter of staying up at sufficiently
high altitude... but there is no way to do it that well, not for a
winged orbiter having any reasonable density.

How about some sort of a very-low-pressure balloon, deployed in orbit,
that dramatically increases the cross-section of the orbiter?


No, because once you slow down even a little bit, you won't be in
orbit any more, and so won't be staying up at a sufficiently high
altitude for much longer.

Barring antigravity or the like, the bit where you decelerate below
7 km/s and the bit where you descend into air thick enough for your
wings (if any) to bite, are going to come within minutes of each other.
And air thick enough for your wings to bite, coming at you at 7 km/s,
makes a blast furnace look temperate by comparison.

This is why TPS is not a trivial matter.


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In Henry Spencer wrote:
lou wrote:
Also, is there any way on a winged orbiter to do a phased reentry to
control temperatures (stall and fall till heat rises, then straight an
level till heat drops, repeat till on or underneat ground)

Not if by "control temperatures", you mean controlling them to the
level that TPS would not be needed. Limiting temperatures is just a
matter of staying up at sufficiently high altitude... but there is no
way to do it that well, not for a winged orbiter having any reasonable
density. Aerodynamic lift just isn't enough.

I've seen some (paper) concepts using "skip" reentries that do this:
drop into the atmosphere, use lift to pop out temporarily and radiate
away heat, drop back down, repeat...

--
Geoffrey A. Landis
http://www.sff.net/people/geoffrey.landis