SpaceShipOne and reentry heat

I'm just an average person with an English degree, so I'm unfamiliar
with the science and physics and space craft reentry, so this is
likely a very stupid question.

But it's my uneducated understanding that returning space craft, like
all objects entering our atmosphere, super-heat from the friction of
falling through our atmosphere.
Which is why all crafts from Apollo to the space shuttles must have
carefully crafted heat shields and enter at a VERY narrow angle to
prevent either burn-up or "skipping" off the atmosphere.

Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne
reach the very edge of the atmosphere? Doesn't it also need the
observe the same careful considerations for reentry?
If not, why? In simple "Physics for English Majors" language. =)

Thanks!
Liam

On 21 Jun 2004 08:40:08 -0700, (LRW) wrote:
But it's my uneducated understanding that returning space craft, like
all objects entering our atmosphere, super-heat from the friction of
falling through our atmosphere.
Which is why all crafts from Apollo to the space shuttles must have
carefully crafted heat shields and enter at a VERY narrow angle to
prevent either burn-up or "skipping" off the atmosphere.

Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne
reach the very edge of the atmosphere? Doesn't it also need the
observe the same careful considerations for reentry?
If not, why? In simple "Physics for English Majors" language. =)

It was going very much slower than a re-entering orbital craft.
Top speed was Mach 3.

In other words, it was at relative rest with respect to the Earth at
the top of its arc while a re-entering orbital craft would be moving
5 miles per second or faster at that point.

Gary

LRW wrote:
I'm just an average person with an English degree, so I'm unfamiliar
with the science and physics and space craft reentry, so this is
likely a very stupid question.

But it's my uneducated understanding that returning space craft, like
all objects entering our atmosphere, super-heat from the friction of
falling through our atmosphere.
Which is why all crafts from Apollo to the space shuttles must have
carefully crafted heat shields and enter at a VERY narrow angle to
prevent either burn-up or "skipping" off the atmosphere.

Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne
reach the very edge of the atmosphere? Doesn't it also need the
observe the same careful considerations for reentry?
If not, why? In simple "Physics for English Majors" language. =)


SpaceShipOne dropped down from a height of 100km, while a shuttle drops
down from a height of some 400km AND has additionally a horizontal
velocity of some 8km/s. And an Apollo spacecraft dropped down from some
400000km. That's in both cases a *LOT* of kinetic energy more to kill
than SSO had to.

SpaceShipOne dropped down from a height of 100km, while a shuttle drops
down from a height of some 400km AND has additionally a horizontal
velocity of some 8km/s. And an Apollo spacecraft dropped down from some
400000km. That's in both cases a *LOT* of kinetic energy more to kill
than SSO had to.

Interesting, for any spacecraft, if more fuel were used on orbit to
bring the (actually tangental) velocity component closer to zero, then
reentry heating shielding requirements are minimal like SS1. Maybe a
heat tile damaged spaceshuttle could re-enter the same way? Maybe this
last crew could have been saved with more fuel and/or less space
shuttle mass and momentum. Maybe they could have taken an engine and
tank off, performed a slowing burn, got into their emergency transfer
beach balls and parachuted from 200k? Iknow probably not enough fuel,
no way to pull an engine and tank off, no transfer beach balls on
board, etc. etc.

On Thu, 24 Jun 2004 09:18:51 -0700, Tony Rusi wrote:
[...]
Interesting, for any spacecraft, if more fuel were used on orbit to
bring the (actually tangental) velocity component closer to zero, then
reentry heating shielding requirements are minimal like SS1. Maybe a
heat tile damaged spaceshuttle could re-enter the same way? Maybe this
last crew could have been saved with more fuel and/or less space shuttle
mass and momentum. Maybe they could have taken an engine and tank off,
performed a slowing burn, got into their emergency transfer beach balls
and parachuted from 200k? Iknow probably not enough fuel, no way to pull
an engine and tank off, no transfer beach balls on board, etc. etc.

There are people here with more technical knowledge than I, but I do know
that the shuttle's main engines aren't restartable. (Do they even have
on-board fuel tanks?) On-orbit, the shuttle manouvers using a completely
different set of engines, the OMS, that has a very small dV capacity. IIRC
it's about the most the OMS can do just to get the shuttle onto a reentry
trajectory.

*However*, it suddenly occurs to me that surviving reentry is actually
pretty simple in the appropriately designed vehicle: passive capsules like
the Soyuz and Apollo return vehicles are old, reliable technology.
(They're aerodynamically stable, and because they're only going to be used
once you can use ablative shielding rather than the TPS tiles.) They're
also small, in mass and volume.

How about fitting the shuttle out with a lifeboat? Stick it somewhere in
the cargo bay. If a shuttle gets sufficiently damaged that it can't
reenter, you use the capsule to get the crew down.

Depending on whether the capsule had its own thruster system, you would
get the choice of putting the shuttle onto a reentry trajectory and then
bailing out, or leaving the shuttle on orbit and just returning in the
capsule. The first option would almost certainly lose the shuttle, but if
you have to use the capsule the shuttle's probably not going to survive
reentry anyway. The second option would leave the shuttle intact in orbit,
where it could (possibly) be repaired, but would require the capsule to
have a fairly decent dV capacity. You'd also have to outfit the shuttle
with an automated station-keeping facility using the OMS; you wouldn't
want it to accidentally fall on someone.

(What's the lightest-weight way of getting a single human down from orbit?
Could you build something like an orbital parachute? If so, would that be
more appropriate than a combined capsule?)

--
+- David Given --McQ-+ "Every planet is weird. I spent six weeks on a
| | moon where the principal form of recreation was
| ) | juggling geese. Baby geese. Goslings. They were
+- www.cowlark.com --+ juggled." --- Firefly, _Our Mrs. Reynolds_

David Given wrote:

How about fitting the shuttle out with a lifeboat? Stick it somewhere in
the cargo bay. If a shuttle gets sufficiently damaged that it can't
reenter, you use the capsule to get the crew down.

Ships usually (certainly not always) take some time to sink. In a
Columbia-type scenario, you don't know you have a serious problem until
it hits hard and fast. Even if it could survive having the orbiter come
apart around it, you need at least enough time to get to such capsules.

Something like this is why the B-58 and B-70 bombers had enclosable
ejection capsules for the crew, which were also their normal seats. And
even in the B-70 that went down after a mid-air collision, one of the
crew still didn't make it out.

And, of course, a 'lifeboat' capsule takes weight/volume away from
possible payloads....

--

You know what to remove, to reply....

In article ,
David Given wrote:
There are people here with more technical knowledge than I, but I do know
that the shuttle's main engines aren't restartable. (Do they even have
on-board fuel tanks?)

Not for the main engines. Which, as you note, are not restartable.
(There is no fundamental reason why they couldn't be, but there is no
requirement for it, and so various details of setup for engine start are
handled with the help of ground equipment.)

How about fitting the shuttle out with a lifeboat? Stick it somewhere in
the cargo bay. If a shuttle gets sufficiently damaged that it can't
reenter, you use the capsule to get the crew down.

It's been proposed many times. It presents some problems of physical
layout, its mass puts a considerable dent in the payload capacity... and
note that it wouldn't have saved Columbia's crew, since they didn't know
something was badly wrong until too late. (Nor is there any plausible
scenario where they would have. Suspicions about TPS damage were focused
on the tiles, not the RCC leading edge, and no plausible imaging -- from
the ground or from elsewhere in space -- would have been at all likely to
notice a small dark hole in a black surface.)

Depending on whether the capsule had its own thruster system, you would
get the choice of putting the shuttle onto a reentry trajectory and then
bailing out, or leaving the shuttle on orbit and just returning in the
capsule.

You'd want the capsule to do its own maneuvering, partly so that entering
it and separating wouldn't be time-critical operations, partly to cover
cases like the orbiter being unable to do its own deorbit burn. This
isn't that big a deal; a deorbit burn isn't large.

...You'd also have to outfit the shuttle
with an automated station-keeping facility using the OMS; you wouldn't
want it to accidentally fall on someone.

The orbiter will be dead and uncontrolled within days anyway: when its
fuel cells run out of reactants, it loses power.

(What's the lightest-weight way of getting a single human down from orbit?
Could you build something like an orbital parachute? If so, would that be
more appropriate than a combined capsule?)

There have been various proposals for "orbital bailout" kits. But a shared
capsule is probably better: it keeps the crew together, it can serve as
shelter or boat, it simplifies providing sizable amounts of survival gear
and electronics, it greatly simplifies cases where someone is injured.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote

no plausible imaging -- from the ground or from elsewhere
in space -- would have been at all likely to notice a small
dark hole in a black surface.

I'm not entirely persuaded of that -- it would be interesting
to see a detailed study of the possibilities, which include ground-
and space-based visual and IR imagery and at least ground-based
radar imagery. Resolution isn't the whole tale when it comes to
detecting features, witness the fact that we can see stars and
orbital tethers that are way below the diffraction limit. Radar,
somewhat analogously, can "see" features such as holes, cracks
and roughness at scales below the nominal (I)SAR resolution.

Also, if the damage were suspected, it wouldn't be a matter of
noticing it, but of finding it as a result of detailed inspection.
Among other things the orbiter could have actively cooperated in
inspection efforts by orienting itself to present the most
favorable aspects to the sensors, heating the leading edge in the
sun to increase IR contrast, etc.

(Henry Spencer) wrote in message ...
In article ,
David Given wrote:

How about fitting the shuttle out with a lifeboat? Stick it somewhere in
the cargo bay. If a shuttle gets sufficiently damaged that it can't
reenter, you use the capsule to get the crew down.

It's been proposed many times. It presents some problems of physical
layout, its mass puts a considerable dent in the payload capacity... and
note that it wouldn't have saved Columbia's crew, since they didn't know
something was badly wrong until too late. (Nor is there any plausible
scenario where they would have. Suspicions about TPS damage were focused
on the tiles, not the RCC leading edge, and no plausible imaging -- from
the ground or from elsewhere in space -- would have been at all likely to
notice a small dark hole in a black surface.)

However, for *future* Shuttle flights, the plan is for the entire TPS
to be scrutinized, using a high-resolution 3D laser ranging imager system
(being developed by Ottawa's Neptec), which will be maneuvered around on
the end of an extension boom (being developed by MDRobotics in Brampton),
mounted on the end of the Canadarm.

NASA's current plan for what to do, in case a TPS failure is discovered
once on-orbit, seems to be a combination of patching it (if it's small
enough to be patched using the in-development-now patch kit), and decamping
to the ISS to await a rescue flight (if the TPS failure is not amenable
to a field repair). Hence the decision to fly future Shuttle missions
only to ISS (presumably inspection would also be easier using vantage
points from ISS). Having a lifeboat capability could conceivably allow
non-ISS missions to once again be flown...if you tructed the lifeboat
sufficiently...

Hmm...this line of thinking makes me wonder: is NASA generalizing their
criteria for return-to-flight beyond inspecting for TPS-related failures?
Are there any other Criticality One failures that could/should be inspected
for on-orbit, given the ISS-as-a-safe-haven option?

In article ,
Tony Rusi wrote:
Interesting, for any spacecraft, if more fuel were used on orbit to
bring the (actually tangental) velocity component closer to zero, then
reentry heating shielding requirements are minimal like SS1. Maybe a
heat tile damaged spaceshuttle could re-enter the same way?

Nope. The amount of fuel available is insufficient to make any real
difference. It's not just a little short, but a couple of orders of
magnitude short.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |