Nasa chooses Orion heat shield

"OM" wrote in message
...

...Alan? What crawled up your ass and died? You've been a colossal
jerk the past few weeks. What's the deal?

And you're hardly the one to talk about how anyone else responds.

Bluuuue Rajah wrote:

3 Is there a cost advantage to ablator over re-useable TPS?


Shuttle tile must be a lot more expensive than ablator.


Yes and no...the actual material used to make the shuttle tiles is
pretty cheap, it's the fact that each one has to be individually
manufactured to a very precise set of dimensions is what makes them
expensive.
With the honeycomb ablative heatshield of the Apollo, the goo that went
into the honeycomb wasn't all that expensive either, what was expensive
and very time consuming was making sure that every single cell in the
honeycomb was completly filled with no bubbles or air gaps at its
corners...as those could lead to uneven ablation during reentry.
Each individual cell was meticulously hand-filled by some very skilled
and patient people.

Pat

Jeff Findley wrote:
The velocity of a vehicle reentering coming from the moon is *a lot* higher
than the velocity of a vehicle reentering coming from low earth orbit.
Given the shape and density of the Orion (similar to Apollo CM), I've got to
believe that the shuttle TPS materials simply aren't good enough.


If you did a multi-skip lifting reentry RCC might have worked.

Pat

"Pat Flannery" wrote in message
dakotatelephone...


Jeff Findley wrote:
The velocity of a vehicle reentering coming from the moon is *a lot*
higher than the velocity of a vehicle reentering coming from low earth
orbit. Given the shape and density of the Orion (similar to Apollo CM),
I've got to believe that the shuttle TPS materials simply aren't good
enough.


If you did a multi-skip lifting reentry RCC might have worked.

Possibly, but I doubt it. A multi-skip reentry doesn't give you a lot of
time when you're out of the atmosphere to get rid of the heat from each
skip. Not getting rid of the heat is a problem.

Jeff
--
"Many things that were acceptable in 1958 are no longer acceptable today.
My own standards have changed too." -- Freeman Dyson

Jeff Findley wrote:


"Pat Flannery" wrote in message
dakotatelephone...


Jeff Findley wrote:
The velocity of a vehicle reentering coming from the moon is *a lot*
higher than the velocity of a vehicle reentering coming from low earth
orbit. Given the shape and density of the Orion (similar to Apollo CM),
I've got to believe that the shuttle TPS materials simply aren't good
enough.


If you did a multi-skip lifting reentry RCC might have worked.

Possibly, but I doubt it. A multi-skip reentry doesn't give you a lot of
time when you're out of the atmosphere to get rid of the heat from each
skip. Not getting rid of the heat is a problem.

Not only that, but you aren't developing enough lift to pull up until you
are well past teh peak heating region.
Pat, I've told you before - there is no "skip". You only get that when
there's a sharp and large change of density - like the surface of a pond,
when you're skipping a rock, or a concrete driveway when you're skipping a
Frisbee. That's not present in the upper atmosphere.
What you do is dive into the atmosphere until the dynamic pressure is high
enough to generate more lift than the aerospacecraft weighs, then pull up
like a regular airplane. With anything with a reasonably high lift, like,
say, a Shuttle Orbiter, by the time you reach that point, you're already
through the worst of the heating. For example, Columbia was through the
peak heating region, and was almost able to sustain 1G (Wings level) flight
when she broke up.
(I'm now going to stick pins into my Eugene Sanger doll (And that of his
translators) for using that whole silly skip terminology - it has poisoned
the minds of generations.)

--
Pete Stickney
The better the Four Wheel Drive, the further out you get stuck.

Peter Stickney wrote:
Not only that, but you aren't developing enough lift to pull up until you
are well past teh peak heating region.
Pat, I've told you before - there is no "skip". You only get that when
there's a sharp and large change of density - like the surface of a pond,
when you're skipping a rock, or a concrete driveway when you're skipping a
Frisbee. That's not present in the upper atmosphere.

You might want to look at the Zond reentry profile, in which the
returning capsule came into the atmosphere over Antarctica, then skipped
back out of it to finally descend in the Indian Ocean. This was
primarily to reduce G loads on the capsule so as not to injure the
returning cosmonauts of the planned lunar loop missions by getting rid
of the velocity in two separate reentry maneuvers
Originally, the Apollo CM was going to perform a similar maneuver, but
as planning advanced, they decided to go with a long lifting reentry
rather than a exo-atmospheric skip.

like a regular airplane. With anything with a reasonably high lift, like,
say, a Shuttle Orbiter, by the time you reach that point, you're already
through the worst of the heating.

But in this case we are talking about a capsule returning from the Moon,
not a aerodynamic spacecraft returning from Earth Orbit.
And according to this, Orion will use a skip reentry when returning from
the Moon: http://en.wikipedia.org/wiki/Skip_reentry

Pat

Meanwhile, mighty Zond 8 photo of Earth and Moon laughs at paltry little
"photo of century" made by hooligan Lunar Orbiter:
http://www.cmnh.org/site/Img/AboutUs.../MoonEarth.jpg
Why, what is that we see down in Texas?
Is it LBJ hiding under bed to escape light of Communist Moon?

Patsky

Jeff Findley wrote:
"Bluuuue Rajah" Bluuuuue@Rajah. wrote in message
. 17.102...
http://spacefellowship.com/News/?p=8617

As Apollo did, Orion will use an Avcoat heat-shield, which is made of
"silica fibers with an epoxy-novalic resin filled in a fiberglass-phenolic
honeycomb." Damn fools, shuttle tile is the good stuff. It shouldn't
take
three years to learn that they did it right the last time. :P~

The velocity of a vehicle reentering coming from the moon is *a lot* higher
than the velocity of a vehicle reentering coming from low earth orbit.
Given the shape and density of the Orion (similar to Apollo CM), I've got to
believe that the shuttle TPS materials simply aren't good enough.

Jeff

One of the reasons NASA is getting rid of the Shuttles is that the
Shuttle TPS is not good enough for the Shuttle.

Andrew Swallow

"Andrew Swallow" wrote in message
...
One of the reasons NASA is getting rid of the Shuttles is that the
Shuttle TPS is not good enough for the Shuttle.

Arguably the TPS works just fine, it's the ET shedding foam and ice that
impacts the TPS that is the horrible problem.

Jeff
--
"Many things that were acceptable in 1958 are no longer acceptable today.
My own standards have changed too." -- Freeman Dyson

"Jeff Findley" wrote in message
...
Arguably the TPS works just fine, it's the ET shedding foam and ice that
impacts the TPS that is the horrible problem.

Yes, but MTBF (mean time between failures) is an inverse function of the
number of possible failed parts, and the TPS has a lot of parts and a lot of
possible failure modes. NASA has learned a lot, and has improved that
system a lot over the lifetime of the shuttle program, but they still have
issues that do not seem to have anything to do with the ET (like the spacers
coming out in flight) and the loss of one tile could cause the loss of a
vehicle.

That said, an Orion heat shield would seem to be far simpler than the
shuttle system, and would clearly use far less tiles and far fewer unique
tiles.

Vaughn

On Apr 12, 2:40*pm, "vaughn"
wrote:
"Jeff Findley" wrote in message

...

Arguably the TPS works just fine, it's the ET shedding foam and ice that
impacts the TPS that is the horrible problem.

* *Yes, but MTBF (mean time between failures) is an inverse function of the
number of possible failed parts, and the TPS has a lot of parts and a lot of
possible failure modes. *NASA has learned a lot, and has improved that
system a lot over the lifetime of the shuttle program, but they still have
issues that do not seem to have anything to do with the ET (like the spacers
coming out in flight) and the loss of one tile could cause the loss of a
vehicle.

* *That said, an Orion heat shield would seem to be far simpler than the
shuttle system, and would clearly use far less tiles and far fewer unique
tiles.

Vaughn

They have a space repair kit, not really proven but better than
nothing.

O'Ryan is a different ball of wax.
http://www.floridatoday.com/apps/pbc...4090308&Ref=AR