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RafaelAustin
2003-Feb-03, 08:46 AM
EDIT: What changes would you make to any future shuttle design if we stay with the lifting body concept?


A friend tonight was asking what kind of heat shield was used on the Apollo capsules and why can't we use that on the shuttle. I assume it's because of the weight, but I don't know exactly what was used before. Anyone here know?

Also, since weight is currently a primary concern, how much lifting capability would you be willing to sacrifice for added safety features? 1 ton? 5 tons?

<font size=-1>[ This Message was edited by: RafaelAustin on 2003-02-03 09:50 ]</font>

Lexx_Luthor
2003-Feb-03, 09:19 AM
http://www.wikipedia.org/wiki/Ablative_heat_shield

Weight--I think. The early heat shields used epoxy like materials that evaporated or burned off under the friction. They traded thickness for time--literally. By the time parachutes opened, little was left on the sheild and it was designed to do that.

I think the Mercury capsule and I think alot of missile warheads used copper "heatsinks." They, well, I don't know how they worked. Word search around for it (heatshield, etc..).

Also, Apollo had to re~enter at 1.5 times faster than anyother manned spacecraft. If anyone here knows, what did the Galileo atmosphere probe use in its "entry" into Jupiter's atmosphere at about 50,000 mph. (yikes)

No changes to the shuttle--please. I have read they plan to use it until 2020 (and probably beyond that). Now, how will they do that if they don't build more? And how are they going to build more? Inquiring minds would like to know. Who is making money from running the shuttle ops?

The problem with the shuttle is that there is alot of surface area for the payload volume inside. The Russians may have the right idea...spherical re~entry vehicles....or shall we say the Russians have the balls. The old lifting body theme would be better for volume/surface-area but...I don't know. /phpBB/images/smiles/icon_biggrin.gif Just some thoughts tacked on in editing.

Great thread. There has been some looking into recovering the lower stages of traditional *style* launch vehicles. I'd love to see a Saturn V *type* of booster with recoverable lower stage to launch heavy payloads. Smaller boosters could launch people or supplies.


_________________
Stanly is a moron, kai is a walking dead beet, Xev just want sex.

<font size=-1>[ This Message was edited by: Lexx_Luthor on 2003-02-03 04:35 ]</font>

Eric McLoughlin
2003-Feb-03, 12:56 PM
The heat shields used on the Mercury, Gemini, Apollo, Vostok, Voshkod and Soyuz spacecraft were/are of the "ablative" kind. They dissipate heat by boiling, melting and burning away. Each time the heat shield is used, it is damaged neyond repair.This is obviously not a problem when the spacecraft is never going to be used again. The Shuttle, being re-usable, cannot use an ablative type shield. That is why the tile/blanket system was developed in the 70s for Shuttle use as, in theory, the heat shield can be used over and over again. In reality, the tiles are fragile and some tile damage is always incurred during the course of the flight. Sometimes at launch and often by debris, stones etc thrown up by the landing gear on touchdown. Despite almost thirty years elapsing since the tile sytem was decided on, a practical alternative has still not been invented.

ToSeek
2003-Feb-03, 03:28 PM
If money were no object:

- Get rid of the SRBs and use a manned "booster" component that gets the shuttle to high altitude and then lands like a plan. (This was originally considered but discarded due to the cost.)

- Replace the shuttle tiles with a more continuous material that requires less maintenance and has less risk of component failure.

That would be a start, though perhaps the ideal approach would be to look at entirely new approaches for low-cost entry to orbit.

daver
2003-Feb-03, 08:55 PM
On 2003-02-03 07:56, Eric McLoughlin wrote:
The heat shields used on the Mercury, Gemini, Apollo, Vostok, Voshkod and Soyuz spacecraft were/are of the "ablative" kind. They dissipate heat by boiling, melting and burning away. Each time the heat shield is used, it is damaged neyond repair.


That may be an exaggeration. I don't know of any that have been reused, but reusing them was considered at one time.



This is obviously not a problem when the spacecraft is never going to be used again. The Shuttle, being re-usable, cannot use an ablative type shield. That is why the tile/blanket system was developed in the 70s for Shuttle use as, in theory, the heat shield can be used over and over again. In reality, the tiles are fragile and some tile damage is always incurred during the course of the flight. Sometimes at launch and often by debris, stones etc thrown up by the landing gear on touchdown. Despite almost thirty years elapsing since the tile sytem was decided on, a practical alternative has still not been invented.


There was talk about some metallic foam heat shield materials on some of the alternate shuttle designs; they weren't as good as the ceramic tiles eventually used for the shuttle, but would (probably) have done for a smaller shuttle.

It sounds as if there will not be a replacement orbiter built this time around (we got lucky after Challenger--they still had some spares for major sections of the orbiter). My guess is that after the next one is destroyed (and if they fly again, they will eventually lose another) that they will have to shut down the shuttle system.

This makes it fairly important to bring another man-rated system on line. I'd think the best thing to do would be to start two parallel programs--one for an ELV launched mini-shuttle (no main engines, RCS, maybe OMS), either semi-ballistic or winged recovery, as reusable as possible given the timeline) and another for a full-fledged replacement. The ELV-based orbiter should be undertaken with the idea of being ready to fly within five years, the other could take longer--maybe up to 15 years.

NASA has a tendency to design stuff somewhat past the bleeding edge; this should be avoided as much as possible (particularly for the ELV design).

As for the replacement orbiter--if it's going to fly in 15 years it pretty much has to use known technology. Rockets, not scramjets or LACE or what have you. I like aerospikes, but they seem to be too far out for this timeline. Single-stage would be nice, but that, too, seems too difficult. Cargo capacity probably quite a bit smaller than the existing orbiter (use an expendable and rendezvous on orbit if you need more). That loses the ability to fly and return big payloads (satellite rescue and refurbish, Space Lab). Don't try to be the single-source answer to all of the planet's space needs.