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SpaceShipOne and reentry heat



 
 
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  #21  
Old June 26th 04, 08:38 PM
Joann Evans
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Default SpaceShipOne and reentry heat

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....
  #22  
Old June 28th 04, 07:11 AM
Christopher M. Jones
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Default SpaceShipOne and reentry heat

Henry Spencer wrote:
The fast answer is that there is no crossover point: aerodynamic braking
is *always* a lot cheaper in mass than doing the same braking with rocket
fuel. That's not quite 100% true when you start examining specialized
situations, but for normal reentry from orbit you can take it as given.


That depends very heavily on the ratio between
delta V and rocket exhaust velocity, as you know.
Currently rocket exhaust velocities are so much
lower than useful delta vees that this ratio is
almost always greater than 1, which is definitely
the wrong side of that exponential to be on.
But in the long term, if we have rockets with
very high exhaust velocities then this ratio could
be much lower, and the behavior would be more
linear with respect to delta V and mass ratio.
High performance gas core nuclear thermal rockets
can just about reach the performance levels to do
multiples of Earth-to-LEO delta V, NSWR or Orion
would certainly have that capability with
reasonable mass ratios.
  #23  
Old June 28th 04, 04:58 PM
Henry Spencer
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Default SpaceShipOne and reentry heat

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 |
  #25  
Old June 29th 04, 09:14 PM
Kieran A. Carroll
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Default Shuttle lifeboat, on-orbit inspection for Criticaility One failures

(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?
  #26  
Old July 2nd 04, 05:17 AM
Jorge R. Frank
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Default Shuttle lifeboat, on-orbit inspection for Criticaility One failures

(Kieran A. Carroll) wrote in
om:

(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.)


Hmm... some corrections he

However, for *future* Shuttle flights, the plan is for the entire TPS


Correction: just the wing leading edge will be inspected by the boom/laser.
And even that will be fully inspected only on the first few flights. Impact
sensors installed behind the RCC panels will be used to "target"
inspections to specific spots after that.

to be scrutinized, using a high-resolution 3D laser ranging imager
system (being developed by Ottawa's Neptec),


Correction: the boom is being baselined with only Sandia's LDRI laser for
return to flight. The Neptec will only be added when it's ready, which is
not likely for the first flight.

(The *original* plan was to have both lasers for return-to-flight, but
Neptec has since had some schedule delays.)

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).


Correct. The acreage tiles on the underside will be inspected by flipping
the orbiter over at a range of 600 ft below ISS and having the ISS crew
photograph it. The resolution and depth measurement requirements are much
more lax for the acreage tiles than for the wing leading edge.

--
JRF

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check "Organization" (I am not assimilated) and
think one step ahead of IBM.
  #27  
Old July 2nd 04, 06:11 PM
Jake
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Default SpaceShipOne and reentry heat

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. =)

Thanks!
Liam


The dirty little secret is that 100 km as "the edge of space" is a
complete fiction. Earth's atmosphere extends upwards for hundreds of
kilometers. SpaceShipOne didn't reenter the atmosphere, it never left!
The significance of 100 km is that it taken as the division between the
homosphere, where the main composition of the air is a constant, and the
heterosphere, where the composition changes with altitude.

If reentry heating calculations begin at 150 km
(http://www.ucsusa.org/documents/CM_apF-J.pdf), then that should be
considered the real edge of space for reentry purposes.

One last thing: the heating isn't caused by "friction". If that was the
case, skydivers would burn. The heating is caused by hypersonic objects
supercompressing the air before it could move out of the way. The
supercompression heats up the air and the heat is transferred to the
object via radiation.
  #28  
Old July 2nd 04, 06:20 PM
Ian Stirling
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Default SpaceShipOne and reentry heat

Mike Miller wrote:
Daniel Walker wrote in message ...
I imagine the answers will involve the excess fuel needed, manoeuvring,
restartable engines, etc., so at what point (what altitude) does the
weight of thermal protection tiles beat the extra fuel needed for an
orbital craft? I know there's lots of variables involved, but wondered if
anyone had considered this?


Yes, it's been considered.

Getting to orbit typically requires about 90-95% of the vehicle to be
fuel. In other words, for every kilogram put in orbit, 9 to 19
kilograms (or more) of fuel are required to put that kilogram into
orbit.


Hmm.
200Kg payload to 100Km. (SS1).
Assume an ISP of 250.
Should be good for a few kilos to LEO, with a three/four stage solid
of modest performance.
  #29  
Old July 4th 04, 08:56 AM
Paul F. Dietz
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Default SpaceShipOne and reentry heat

Jake wrote:

One last thing: the heating isn't caused by "friction". If that was the
case, skydivers would burn. The heating is caused by hypersonic objects
supercompressing the air before it could move out of the way. The
supercompression heats up the air and the heat is transferred to the
object via radiation.



It's caused by the gas going through a shock, not (just) by the gas being
compressed. As the mach number increases, the density jump across
a shock does not increase unboundedly, but approaches some finite limit.
The *temperature* increases without limit, however. (There is also some
heating from turbulence.)

Entropy increases across a shock; it's an non-isoentropic process, unlike
compression of gas in an apparatus where the motion of the gas is very
subsonic, like your typical air compressor. In this sense a shock is
like friction, which is also an entropy-creating process.

Paul
  #30  
Old July 4th 04, 09:03 AM
Bruce Hoult
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Default SpaceShipOne and reentry heat

In article ,
Ian Stirling wrote:

Hmm.
200Kg payload to 100Km. (SS1).
Assume an ISP of 250.
Should be good for a few kilos to LEO, with a three/four stage solid
of modest performance.


According to XCOR's site, one use for the Xerus (as well as taking a
pilot and single paying passenger to 100 km) is to launch approx an 10
kg satellite.

-- Bruce
 




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