SpaceShipOne and reentry heat

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LRW

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Jun 21, 2004, 11:40:08 AM6/21/04
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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

Gary Coffman

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Jun 21, 2004, 1:08:20 PM6/21/04
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On 21 Jun 2004 08:40:08 -0700, de...@celticbear.com (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

Harald Kucharek

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Jun 21, 2004, 1:32:20 PM6/21/04
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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.

Henry Spencer

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Jun 21, 2004, 2:35:25 PM6/21/04
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In article <3a1d1813.04062...@posting.google.com>,

LRW <de...@celticbear.com> wrote:
>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. =)

Mostly, because it didn't go very high and wasn't in orbit, so it
reentered at quite low speed.

To reach an altitude of 100km, which SS1 (just barely) did, it needed a
speed of 1.5-2km/s (depending on how steep the ascent was), and it would
have come back down at around the same speed. Orbital velocity, on the
other hand, is 8km/s, and return from the Moon brings you in at 11km/s.

Moreover, a lot of the reentry issues scale with kinetic energy, which is
proportional to the *square* of velocity, so 8km/s is not four times as
bad as 2km/s, it's more like sixteen times as bad.

Between the low speed and the clever design of SS1, the reentry was quite
a mild one. The designers couldn't quite ignore the heating issue, but
they didn't have to do anything very elaborate about it.

If SS1 had gone two or three times as high, reentry heating would have
needed more attention. If SS1 had been moving fast enough horizontally to
be in orbit, reentry heating would have needed a *lot* more attention.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert | he...@spsystems.net

Ian Stirling

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Jun 21, 2004, 1:33:17 PM6/21/04
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In article <3a1d1813.04062...@posting.google.com> you wrote:
<snip>

> 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. =)

Basically, as it's going much, much slower.
Craft reentering from low-earth orbit come in at around mach 30.
The SS1 reenters at mach 3 (?).
Heating is more or less proportional to the cube of speed, so the
heating will be around a thousandth of that coming in from orbit.
The RS-71 flew at mach 3, and was fine with just a titanium skin.
If you tried to put a titanium skin on a craft coming in at orbital
velocities, you get little more than a bright shower of sparks
as it atomises.

MSu1049321

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Jun 21, 2004, 12:50:53 PM6/21/04
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<< Doesn't it also need the
observe the same careful considerations for reentry?
If not, why? In simple "Physics for English Majors" language. =)
>>


Not going nearly as ast, mach 3 instead of mach 25, and from lower/deeper in
the atmosphere. And when it activates it's novel "shuttlecock" drag system, it
slows the craft down in a place where the air is very very thin, by the time it
hits thicker air, it has already slowed considerably. There IS reentry heating,
but orders of magnitude below what a capsule or shuttle sees. The goofs who
talk about the same craft becomeing orbital don't "get it" about the SS-1: it
was designed for a very narrow mission, which it obviously performs well. To
make the leap to orbit, will require a redesign that takes into account the
much much more difficult factors involved. The system may look similar, in the
way a forumula one race car has four wheels like your family commuter. But
really it's a different breed of cat altogether.

Michael K. Heney

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Jun 21, 2004, 1:57:05 PM6/21/04
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It's all a matter of speed. Vehicles returning from the moon (Apollo)
are doing about Mach 35; Orbital vehicles are doing about Mach 25;
SpaceShip 1 did about Mach 3.5 today. Reentering vehicles are using
the atmosphere to absorb their kinetic energy (velocity) and slow them
down to touchdown speed at ground level - and that's what generates the
re-entry heat. The faster you're going, the more energy there is to
dissapate, the more heat is produced.

So SS1 has to deal with some heating, true - but it's not the same
level of heating as a shuttle or Apollo spacecraft. And since it's
on a ballistic (suborbital) trajectory, it can't "skip" off the
atmosphere - it's not going fast enough or heading in the right
direction to do that. SS1 does have to pay attention to it's re-enty
profile and make sure it can handle the heat and ends up back at the
runway - but the constraints are milder than shuttle or Apollo dealt
with.

Derek Lyons

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Jun 21, 2004, 2:15:05 PM6/21/04
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de...@celticbear.com (LRW) wrote:
>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 flies much lower and *MUCH* slower than orbital craft (SS1 is
sub-orbital), and thus does not require the same considerations and
protection.

D.
--
Touch-twice life. Eat. Drink. Laugh.

David Pugh

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Jun 21, 2004, 2:26:39 PM6/21/04
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"LRW" <de...@celticbear.com> wrote in message
news:3a1d1813.04062...@posting.google.com...

> 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. =)

Basically, SpaceShipOne was not moving all that fast when it left the
atmosphere. If something is in orbit, it is moving around Mach 25 (compared
with SSO's top speed of less than Mach 3).


Alcore

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Jun 21, 2004, 2:45:21 PM6/21/04
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On 21 Jun 2004, LRW wrote:

[snip]


>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.

[snip]


>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?

Airplanes don't superheat.

Baseballs and Skydivers don't either.

It's all about air friction.

If you are moving through the air, you have to push it aside to get
through. The faster and more energetically you do this the more you will
heat it (and it will heat you).

Spacecraft in orbit superheat on return because they are moving VERY fast
as they enter the upper atmosphere.

Spaceship one is using a trajactory that just barely rises above the
atmosphere... and has no "ground speed" at all.

So instead of smashing into the upper atmosphere at 5 or 6 miles per
second (22,000 miles per hour) like a space-shuttle, Spaceship One hits
the upper atmosphere at around 1,200 miles per hour. The energy that it's
hull must absorb/shed is therefore only about 5% as much. This is easy to
handle with normal aircraft materials.

The numbers I've just given are really rough. But they're not completely
wrong.

I hope this helps.

Gene Pharr
New Orleans, LA

--
Alcore Nilth - The Mad Alchemist of Gevbeck
alc...@uurth.com


Earl Colby Pottinger

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Jun 21, 2004, 3:47:58 PM6/21/04
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de...@celticbear.com (LRW) :

The simple answer is that while it is going almost as high as some orbital
craft did in the past, it is not going as fast as a true orbital craft so it
does not see as much heat. That is why you will see it refered to as an
sub-orbital spaceship.

Earl Colby Pottinger

--
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the time? http://webhome.idirect.com/~earlcp

Jake McGuire

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Jun 21, 2004, 6:07:06 PM6/21/04
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de...@celticbear.com (LRW) wrote in message news:<3a1d1813.04062...@posting.google.com>...

> 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. =)

Objects reentering from orbit come screaming into the atmosphere going
sideways at 20,000 miles per hour. SpaceShipOne sort of plopped in at
a couple thousand. It's the difference between jumping off of a 3m
diving board (if you don't enter the water carefully, you're going to
be uncomfortable), and getting shot horizontally from a cannon at 200
mph ("ouch" is a serious understatement).

-jake

Rodney Kelp

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Jun 21, 2004, 7:28:59 PM6/21/04
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They never reached orbital speed (24,000 mph). All they did was throw a rock
high in the air and let it fall. The shuttle would not have a reentry heat
problem either if it could slow down to mach 1 with it's engines before
reentry but there isn't enough fuel hanging around up there. They use the
atmosphere to slow the bath tub down.

"LRW" <de...@celticbear.com> wrote in message
news:3a1d1813.04062...@posting.google.com...


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quasarstrider

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Jun 21, 2004, 8:18:51 PM6/21/04
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> 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.

I am not a Physics major either, however I had college level Physics. But
that was a long time ago. :-)

> 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.

This is correct. Friction of the aircraft against the 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.

Because that way you minimize the time of exposure of the spacecraft
to the high-temperatures caused by friction. A quick burn instead of a
long roast.

> 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 has less energy to bleed off than, for example, the Space Shuttle
on reentry. Hence it experiences less friction.
It has less energy because it neither gets as high, nor as fast as the Shuttle.

Tony Rusi

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Jun 24, 2004, 12:18:51 PM6/24/04
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> 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.

Daniel Walker

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Jun 24, 2004, 12:23:40 PM6/24/04
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Reading these postings about SS1's re-entry and from what we've heard
recently regarding the space shuttle's TPS and its problems, why have
spacecraft tended not to use engine-based deceleration to reduce the
thermal effect of re-entry? If the orbital velocity is a major factor in
re-entry speed, why not take this off and just drop in? Dropping in from
400km would give you a nominal speed of ~2.8km/s if you reached the
Earth's surface (assuming I've done my sums right!).

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?

Dan

David Given

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Jun 25, 2004, 8:00:09 AM6/25/04
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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
| d...@cowlark.com | moon where the principal form of recreation was
| (d...@tao-group.com) | juggling geese. Baby geese. Goslings. They were
+- www.cowlark.com --+ juggled." --- Firefly, _Our Mrs. Reynolds_

Henry Spencer

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Jun 25, 2004, 10:54:32 AM6/25/04
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In article <Pine.LNX.4.60.04...@hermes-1.csi.cam.ac.uk>,
Daniel Walker <dw...@hermes.cam.ac.uk> wrote:
>...why have
>spacecraft tended not to use engine-based deceleration to reduce the
>thermal effect of re-entry?

Because making even a modest difference requires vast amounts of fuel, far
more than can reasonably be made available.

>...so at what point (what altitude) does the

>weight of thermal protection tiles beat the extra fuel needed for an
>orbital craft?

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.

Henry Spencer

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Jun 25, 2004, 10:56:21 AM6/25/04
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In article <889ef2b7.04062...@posting.google.com>,

Tony Rusi <marsb...@yahoo.com> 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.

Mike Miller

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Jun 25, 2004, 9:16:07 PM6/25/04
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Daniel Walker <dw...@hermes.cam.ac.uk> wrote in message news:<Pine.LNX.4.60.04...@hermes-1.csi.cam.ac.uk>...

> 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.

Equal and opposite reactions: getting out of orbit would require a
similar amount of fuel. The 100 ton shuttle needs 2000 tons of fuel
(give or take) to get into orbit; it would need 2000 tons to get out
of orbit. Of course, to put 2000 tons of fuel into orbit, you need
40,000 tons to put it in orbit...

In comparison, a well-designed heat shield is about 5% of the
re-entering vehicle's weight. A 100-ton vehicle needs about 5 tons,
maybe 10, of heat shielding to re-enter when using ablative or
reusable heat shields.

So: 10 tons of heat shield or 2000 tons of fuel to brake a 100-ton
spacecraft out of orbit.

Even if you just use a little fuel, you'll have a hard time beating
the efficiency of heat shields.

Mike Miller

Mike Miller

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Jun 25, 2004, 9:17:55 PM6/25/04
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"Rodney Kelp" <Rodney...@hotmail.com> wrote in message news:<gPqdnYFIGeS...@adelphia.com>...

> They never reached orbital speed (24,000 mph).

That's closer to escape velocity. Orbital velocity for a low earth
orbit is 17500mph. Escape velocity is 25000mph

Scott Lowther

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Jun 26, 2004, 2:07:30 PM6/26/04
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Henry Spencer wrote:
>
> In article <Pine.LNX.4.60.04...@hermes-1.csi.cam.ac.uk>,
> Daniel Walker <dw...@hermes.cam.ac.uk> wrote:
> >...why have
> >spacecraft tended not to use engine-based deceleration to reduce the
> >thermal effect of re-entry?
>
> Because making even a modest difference requires vast amounts of fuel, far
> more than can reasonably be made available.

Good rule of thumb: you'll need about the same detla-v to deorbit as to
get into orbit in the first place, if you wish to dispense with TPS.
This means either refueling on orbit, or extraordinary mass fractions.

--
Scott Lowther, Engineer
Remove the obvious (capitalized) anti-spam
gibberish from the reply-to e-mail address

Hephaestus

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Jun 26, 2004, 2:57:25 PM6/26/04
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Daniel Walker <dw...@hermes.cam.ac.uk> wrote in message news:<Pine.LNX.4.60.04...@hermes-1.csi.cam.ac.uk>...

When you see a rocket launch, the vast majority of it (about 95%) is just
there to get the other 5% into orbit. That includes the fuel, engines, and
so on required to get the payload to the required velocity. Conveniently,
zeroing out the velocity like you propose takes exactly the same amount of
work, so if you have a full size rocket in orbit, it can return the payload
to earth via your mechanism.

Unfortunately, since the payload fraction is 1/20th, you've just increased
the amount of weight that must be launched by a factor of twenty! For example,
for a one ton payload, instead of a 20 ton rocket to launch it into orbit, you
now need a 400 ton rocket to launch the payload plus 20 ton return rocket into
orbit. It's easier to build a TPS, no matter how exotic, than to eat a 20-fold
increase in rocket size.

Joann Evans

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Jun 26, 2004, 3:38:05 PM6/26/04
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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....

Christopher M. Jones

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Jun 28, 2004, 2:11:13 AM6/28/04
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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.

Henry Spencer

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Jun 28, 2004, 11:58:22 AM6/28/04
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In article <pan.2004.06.25....@cowlark.com>,

David Given <d...@cowlark.com> 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.

Allen Thomson

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Jun 29, 2004, 2:04:20 PM6/29/04
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he...@spsystems.net (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.

Kieran A. Carroll

unread,
Jun 29, 2004, 4:14:35 PM6/29/04
to sci-spa...@moderators.isc.org
he...@spsystems.net (Henry Spencer) wrote in message news:<I010D...@spsystems.net>...

> In article <pan.2004.06.25....@cowlark.com>,
> David Given <d...@cowlark.com> 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?

Jorge R. Frank

unread,
Jul 2, 2004, 12:17:52 AM7/2/04
to sci-spa...@moderators.isc.org
k...@dynacon.ca (Kieran A. Carroll) wrote in
news:d87d73a5.04062...@posting.google.com:

> he...@spsystems.net (Henry Spencer) wrote in message
> news:<I010D...@spsystems.net>...
>> In article <pan.2004.06.25....@cowlark.com>,
>> David Given <d...@cowlark.com> 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 here:

> 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

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Jake

unread,
Jul 2, 2004, 1:11:23 PM7/2/04
to sci-spa...@moderators.isc.org
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.

Ian Stirling

unread,
Jul 2, 2004, 1:20:06 PM7/2/04
to
Mike Miller <cra...@hotmail.com> wrote:
> Daniel Walker <dw...@hermes.cam.ac.uk> wrote in message news:<Pine.LNX.4.60.04...@hermes-1.csi.cam.ac.uk>...
>> 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.

Henry Spencer

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Jul 4, 2004, 12:46:59 PM7/4/04
to
In article <40E5973B...@NOSPAMhobonet.com>,
From he...@spsystems.net Sun Jul 04 12:30:32 2004
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Newsgroups: sci.space.tech
Path: henry
From: he...@spsystems.net (Henry Spencer)
Subject: Re: What does it make sense to bring back?
Organization: SP Systems, Toronto, Canada
Message-ID: <I0CC7...@spsystems.net>
References: <375b1119.04062...@posting.google.com>
Date: Sun, 4 Jul 2004 18:47:33 GMT

In article <375b1119.04062...@posting.google.com>,
Hephaestus <hepha...@phreaker.net> wrote:
>Basically, once you decide not to go 100% reusable, you have the ability to
>decide certain components (tanks, structure, etc) just aren't cost effective
>to reuse. Right?

Correct. There have been a number of proposals for semi-reusable
launchers that would return engines and electronics but sacrifice the
tanks, either leaving them in orbit or expending them in some other way.

It's not a ridiculous idea, but it's also not one that gives you as much
gain as you might think. The subsystem mass for reentry and landing --
heatshield etc. -- scales very strongly with the mass of the object and
only rather weakly with its size, and tanks just don't weigh very much.
An engine pod is much smaller than the whole vehicle, but it's also much
denser and makes a much harsher reentry, so the heatshield mass isn't
reduced much.

A lot depends on details, but it's not obvious that you really benefit
greatly from bringing "just the essentials" down. There are advantages,
like greater configuration flexibility. There are also disadvantages,
such as potentially lower reliability due to being unable to flight-test
the expendable components. (This is probably a more important issue than
the actual *cost* of the expendable bits.)

Whether it's an attractive approach will depend on what your priorities
are and how you prefer to tackle certain issues.

Paul F. Dietz

unread,
Jul 4, 2004, 3:56:07 AM7/4/04
to sci-spa...@moderators.isc.org
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

Bruce Hoult

unread,
Jul 4, 2004, 4:03:25 AM7/4/04
to sci-spa...@moderators.isc.org
In article <aPgFc.1663$Fc7.3...@stones.force9.net>,
Ian Stirling <ro...@mauve.demon.co.uk> 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

Henry Spencer

unread,
Jul 4, 2004, 4:48:08 PM7/4/04
to
(Oddly, two of my submissions to s.s.t seem to have gotten smushed
together somehow in transit... Here's a resend of the first. --HS)

In article <40E5973B...@NOSPAMhobonet.com>,


Jake <jak...@NOSPAMhobonet.com.retro.com> wrote:
>The dirty little secret is that 100 km as "the edge of space" is a
>complete fiction.

No, it is an arbitrary boundary for formal and legal purposes.

>Earth's atmosphere extends upwards for hundreds of kilometers.

Tens of thousands, actually. The only real "end" to it is at the edge of
the magnetosphere, where it meets the solar wind.

>SpaceShipOne didn't reenter the atmosphere, it never left!

If you're being pedantic about it, neither does the shuttle or Soyuz; by
that definition, the Apollo lunar missions and their Russian unmanned
counterparts are the only spacecraft which have ever reentered. However,
"reentry" is normally given a less pedantic and more practical definition,
involving ascent to a region where aerodynamic forces are insignificant
and return involving noticeable heating. SpaceShip One did that.

>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.

True but irrelevant. This is *not* why 100km is taken as the boundary of
space. It's taken as the boundary because it's a nice round number that
is in the right general vicinity.

>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.

Reentry heating calculations start at whatever point is deemed convenient
by the people doing the calculation. 150km is definitely too high to be
the edge of space -- it's possible to orbit at that altitude, although not
for long. (Later Apollo lunar flights used parking orbits at 160-170km.)

>One last thing: the heating isn't caused by "friction".

Again, pedantically correct. Friction drag (and friction heating)
technically occur only when air slides over a surface more or less
parallel to the air flow. This *does* contribute to the heating, but
not very much.

However, the looser use of the term to encompass all forms of aerodynamic
drag and heating is common.

>If that was the case, skydivers would burn.

No, numbers matter. Skydivers wouldn't burn in any case, because they
simply don't move very fast.

>The heating is caused by hypersonic objects
>supercompressing the air before it could move out of the way.

Basically correct (although the term normally used is just "compressing").

>The supercompression heats up the air and the heat is transferred to the
>object via radiation.

No, sorry, wrong. Most of the heat transfer is simply by conduction --
hot air in contact with the object heats it. The emissivity of hot air is
quite low; it doesn't radiate heat easily. Heat transfer by radiation
doesn't become significant for spacecraft until you're talking about lunar
reentries, and it doesn't dominate the situation until you're looking at
deep-space reentries coming in substantially faster than escape velocity.
The only spacecraft (re)entry to date in which radiation heating was the
main issue was the Galileo atmosphere probe hitting Jupiter's atmosphere
at nearly 50km/s.

Andrew Gray

unread,
Jul 6, 2004, 2:17:59 PM7/6/04
to sci-spa...@moderators.isc.org
On 2004-07-04, Henry Spencer <he...@spsystems.net> wrote:

>>SpaceShipOne didn't reenter the atmosphere, it never left!
>
> If you're being pedantic about it, neither does the shuttle or Soyuz; by
> that definition, the Apollo lunar missions and their Russian unmanned
> counterparts are the only spacecraft which have ever reentered. However,

Equally pedantic response: on that defintion Cassini also re-entered the
atmosphere... and headed on out again... as did Galileo.
--
-Andrew Gray
andre...@dunelm.org.uk

Michael Smith

unread,
Jul 7, 2004, 9:10:29 AM7/7/04
to sci-spa...@moderators.isc.org
Jake <jak...@NOSPAMhobonet.com.retro.com> wrote in message

> 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.

By definition heat is related to the kinetic energy of moving
molecules, so the air is hot because it has a high speed relative to
the spacecraft.

Henry Spencer

unread,
Jul 6, 2004, 5:06:32 PM7/6/04
to
In article <slrncelr6n.6h...@compsoc.dur.ac.uk>,

Andrew Gray <andre...@dunelm.org.uk> wrote:
>> If you're being pedantic about it, neither does the shuttle or Soyuz; by
>> that definition, the Apollo lunar missions and their Russian unmanned
>> counterparts are the only spacecraft which have ever reentered. However,
>
>Equally pedantic response: on that defintion Cassini also re-entered the
>atmosphere... and headed on out again... as did Galileo.

Also several other spacecraft that have done gravity assists, like NEAR
and Giotto.

Keith F. Lynch

unread,
Jul 7, 2004, 9:51:12 PM7/7/04
to sci-spa...@moderators.isc.org
Henry Spencer <he...@spsystems.net> wrote:
> ... 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.)

How difficult would it be to mount lots of lights inside the wings,
and paint the inside white, so that any hole in the wing can easily
be detected from a great distance?
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

Jorge R. Frank

unread,
Jul 12, 2004, 9:59:15 AM7/12/04
to sci-spa...@moderators.isc.org
"Keith F. Lynch" <k...@KeithLynch.net> wrote in
news:cci9ag$j69$1...@panix3.panix.com:

> Henry Spencer <he...@spsystems.net> wrote:
>> ... 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.)
>
> How difficult would it be to mount lots of lights inside the wings,
> and paint the inside white, so that any hole in the wing can easily
> be detected from a great distance?

How great a distance? That's potentially going to take a *lot* of
electrical power.

And in the end, it *won't* *save* *you*. Post-Columbia RCC tests have shown
that even cracks or quarter-inch pits that don't completely penetrate the
RCC can be fatal.

Much more practical would be to instrument the inside of the wing leading
edge with accelerometers and other sensors so that any impact to the
leading edge can be detected and localized early in the flight after it
happens. And that is, in fact, exactly what NASA is doing.

Henry Spencer

unread,
Jul 12, 2004, 11:32:37 AM7/12/04
to
In article <cci9ag$j69$1...@panix3.panix.com>,
Keith F. Lynch <k...@KeithLynch.net> wrote:
>> ...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.)
>
>How difficult would it be to mount lots of lights inside the wings,
>and paint the inside white, so that any hole in the wing can easily
>be detected from a great distance?

A lot of work if you want to get them into every nook and cranny, plus the
question of whether structural damage might also happen to cut the wiring.
And detection from a great distance requires a lot of light...

Much better, on the whole, to improve close-up inspection technology by
using things like lidar imaging.

Message has been deleted

Cameron Dorrough

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Jul 13, 2004, 11:24:41 PM7/13/04
to sci-spa...@moderators.isc.org
"Henry Spencer" <he...@spsystems.net> wrote in message
news:I0qwI...@spsystems.net...

> In article <cci9ag$j69$1...@panix3.panix.com>,
> Keith F. Lynch <k...@KeithLynch.net> wrote:
> >
> >How difficult would it be to mount lots of lights inside the wings,
> >and paint the inside white, so that any hole in the wing can easily
> >be detected from a great distance?
>
> A lot of work if you want to get them into every nook and cranny, plus the
> question of whether structural damage might also happen to cut the wiring.
> And detection from a great distance requires a lot of light...
>
> Much better, on the whole, to improve close-up inspection technology by
> using things like lidar imaging.

I know that I've asked this before a long time ago, on an NG far, far away,
but what about using a robotic camera to do this - something like
AERCam/Sprint??

IIRC, the main concern seemed to be if a thruster failed on and caused a
collision, but surely materials technology is good enough now to allow the
thing to be padded heavily in sponge rubber and you wouldn't want to fly it
too fast anyway..

Cameron:-)


Jorge R. Frank

unread,
Jul 14, 2004, 2:07:30 AM7/14/04
to sci-spa...@moderators.isc.org
he...@spsystems.net (Henry Spencer) wrote in
news:I0qwI...@spsystems.net:

> In article <cci9ag$j69$1...@panix3.panix.com>,
> Keith F. Lynch <k...@KeithLynch.net> wrote:
>>> ...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.)
>>
>>How difficult would it be to mount lots of lights inside the wings,
>>and paint the inside white, so that any hole in the wing can easily
>>be detected from a great distance?
>
> A lot of work if you want to get them into every nook and cranny, plus
> the question of whether structural damage might also happen to cut the
> wiring. And detection from a great distance requires a lot of light...
>
> Much better, on the whole, to improve close-up inspection technology
> by using things like lidar imaging.

Yup. The boom system the Canadians are building (OBSS) will accommodate two
lidars: Sandia's LDRI and the Neptec LCS.

Henry Spencer

unread,
Jul 15, 2004, 11:00:16 AM7/15/04
to
In article <cd291r$ovi$1...@perki.connect.com.au>,

Cameron Dorrough <cdor...@nortonconsultants.com> wrote:
>> Much better, on the whole, to improve close-up inspection technology by
>> using things like lidar imaging.
>
>I know that I've asked this before a long time ago, on an NG far, far away,
>but what about using a robotic camera to do this - something like
>AERCam/Sprint??

It's an option, but the current idea of an extension boom for the arm is
probably better. There are some concerns about adequate stability, I
understand, but it lets you take your time, not worry about running out of
thruster gas, and carry relatively heavy sensors if that's useful.

Jorge R. Frank

unread,
Jul 14, 2004, 6:54:44 PM7/14/04
to sci-spa...@moderators.isc.org
"Cameron Dorrough" <cdor...@nortonconsultants.com> wrote in
news:cd291r$ovi$1...@perki.connect.com.au:

> "Henry Spencer" <he...@spsystems.net> wrote in message
> news:I0qwI...@spsystems.net...
>> In article <cci9ag$j69$1...@panix3.panix.com>,
>> Keith F. Lynch <k...@KeithLynch.net> wrote:
>> >
>> >How difficult would it be to mount lots of lights inside the wings,
>> >and paint the inside white, so that any hole in the wing can easily
>> >be detected from a great distance?
>>
>> A lot of work if you want to get them into every nook and cranny,
>> plus the question of whether structural damage might also happen to
>> cut the wiring. And detection from a great distance requires a lot of
>> light...
>>
>> Much better, on the whole, to improve close-up inspection technology
>> by using things like lidar imaging.
>
> I know that I've asked this before a long time ago, on an NG far, far
> away, but what about using a robotic camera to do this - something
> like AERCam/Sprint??

It's been discussed ad nauseam over on s.s.shuttle. Here is the most recent
word on it:

<http://www.google.com/groups?selm=Xns951054C2BFC8jrfrank%40204.52.135.40>

(watch URL word wrap)

Jan Vorbrüggen

unread,
Jul 16, 2004, 4:50:48 AM7/16/04
to sci-spa...@moderators.isc.org
> And in the end, it *won't* *save* *you*. Post-Columbia RCC tests have shown
> that even cracks or quarter-inch pits that don't completely penetrate the
> RCC can be fatal.

Is there a press release or somesuch available somewhere that summarizes
these experiments?

If your conclusion above is correct, then it seems to me that previous
flights have been lucky in that, for instance, those paint flecks made
their pits in the windows and not some piece of RCC.

Jan

Jorge R. Frank

unread,
Jul 16, 2004, 10:07:34 PM7/16/04
to sci-spa...@moderators.isc.org
Jan Vorbrüggen <jvorbrue...@mediasec.de> wrote in
news:2lpj79F...@uni-berlin.de:

>> And in the end, it *won't* *save* *you*. Post-Columbia RCC tests have
>> shown that even cracks or quarter-inch pits that don't completely
>> penetrate the RCC can be fatal.
>
> Is there a press release or somesuch available somewhere that
> summarizes these experiments?

Not directly, alas. The Implementation Plan for Return To Flight has the
implications of the results:

http://www.nasa.gov/pdf/58541main_RTF_rev2.pdf

See Figure 6.4-1-1 on p. 1-23 (p. 55 of the PDF), which summarizes the
resolution requirements for TPS damage inspection. Note that the resolution
requirement on the lower surface of the wing leading edge RCC panels is
0.25 inch.

What the report *doesn't* say is that this requirement is the result of RCC
tests at the NASA/JSC arcjet facility that show that a 0.25 inch pit (or a
1.5 by 0.03 inch crack) on those panels results in burnthrough of the panel
during entry.

(Incidentally, these tests also provide the final nail in the coffin for
the theory that in-flight repair of STS-107's wing damage could have saved
the crew. If Columbia's panel was cracked or delaminated anything like the
test panel in Figures 3.8-9 and 3.8-10 of the CAIB report, the burnthrough
would have quickly propagated along those cracks and delaminated areas.)

> If your conclusion above is correct, then it seems to me that previous
> flights have been lucky in that, for instance, those paint flecks made
> their pits in the windows and not some piece of RCC.

Indeed.

Cameron Dorrough

unread,
Jul 18, 2004, 10:19:05 PM7/18/04
to sci-spa...@moderators.isc.org
"Jorge R. Frank" <jrf...@ibm-pc.borg.retro.com> wrote in message
news:Xns9526B635...@204.52.135.40...

> "Cameron Dorrough" <cdor...@nortonconsultants.com> wrote in
> news:cd291r$ovi$1...@perki.connect.com.au:
>
> > "Henry Spencer" <he...@spsystems.net> wrote in message
> > news:I0qwI...@spsystems.net...
> >> In article <cci9ag$j69$1...@panix3.panix.com>,
> >> Keith F. Lynch <k...@KeithLynch.net> wrote:
> >> >
> >> >How difficult would it be to mount lots of lights inside the wings,
> >> >and paint the inside white, so that any hole in the wing can easily
> >> >be detected from a great distance?
> >>
> >> A lot of work if you want to get them into every nook and cranny,
> >> plus the question of whether structural damage might also happen to
> >> cut the wiring. And detection from a great distance requires a lot of
> >> light...
> >>
> >> Much better, on the whole, to improve close-up inspection technology
> >> by using things like lidar imaging.
> >
> > I know that I've asked this before a long time ago, on an NG far, far
> > away, but what about using a robotic camera to do this - something
> > like AERCam/Sprint??
>
> It's been discussed ad nauseam over on s.s.shuttle. Here is the most
recent
> word on it:
>
> <http://www.google.com/groups?selm=Xns951054C2BFC8jrfrank%40204.52.135.40>
>
> (watch URL word wrap)

Thanks, Jorge (and Henry). I concur with Adrian. :-)

Cameron:-)


Jan Vorbrüggen

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Jul 19, 2004, 2:58:11 AM7/19/04
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> What the report *doesn't* say is that this requirement is the result of RCC
> tests at the NASA/JSC arcjet facility that show that a 0.25 inch pit (or a
> 1.5 by 0.03 inch crack) on those panels results in burnthrough of the panel
> during entry.

Thanks for the background information. Pretty bad situation - I'd call that
an TPS design problem, wouldn't you? However, it's not clear to me from the
above whether the burnthrough from a ~6 mm pit would necessarily translate
into LOV, or just a scary descent and landing.

Jan

David Harper

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Jul 21, 2004, 2:12:11 PM7/21/04
to sci-spa...@moderators.isc.org
Jake <jak...@NOSPAMhobonet.com.retro.com> wrote in message news:<40E5973B...@NOSPAMhobonet.com>...

> 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.

Not so much radiation as convection. Not until you hit really high
velocities does radiation become a significant factor. Radiation
transfer is a function of T^4. Furthermore, objects travelling around
Mach 2 or 3 experience only a few hundred degrees delta-T from
ambient. Radiation at these temperatures is pretty low by comparison.

Dave

Andrew Gray

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Jul 21, 2004, 3:23:57 PM7/21/04
to sci-spa...@moderators.isc.org
[copied to .shuttle, followups set]

On 2004-07-17, Jorge R. Frank <jrf...@ibm-pc.borg.retro.com> wrote:
>
>> If your conclusion above is correct, then it seems to me that previous
>> flights have been lucky in that, for instance, those paint flecks made
>> their pits in the windows and not some piece of RCC.
>
> Indeed.

A related query:

In a study of orbital debris I have at home, it shows a graph of the
statistically expected number of window replacements - due to impact
pitting, I believe - against the orbital attitude of the Orbiter.
(tail-first getting less damage than nose-first, for example). It
comments that flight rules require that, all other factors (mission
requirements, say) considered, the attitude should be planned to
minimise window damage.

Is there plans to develop a similar rule regarding RCC "exposure", or is
the expected flux low enough that attitude isn't a significant factor?

(I suppose this is a lot less relevant now that most on-orbit time will
be docked to ISS, where attitude is pretty much mandated by the station,
but...)

--
-Andrew Gray
andre...@dunelm.org.uk

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