Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!texbell!nuchat!steve From: steve@nuchat.UUCP (Steve Nuchia) Newsgroups: sci.space.shuttle Subject: Re: Shuttle Status for 09/25/89 (Forwarded) Keywords: firex Message-ID: <15054@nuchat.UUCP> Date: 28 Sep 89 07:07:48 GMT References: <32507@ames.arc.nasa.gov> <238@tness7.UUCP> <15035@nuchat.UUCP> <5442@hplabsb.HP.COM> Reply-To: steve@nuchat.UUCP (Steve Nuchia) Organization: Houston Public Access Lines: 34 In article <5442@hplabsb.HP.COM> dsmith@hplabsb.UUCP (David Smith) writes: >I had presumed that there would be concern that if water soaked into >the tiles, and didn't fully evaporate before re-entry, that flash >evaporation could break tiles. I had read of such concerns before >with respect to the shuttle sitting out in the rain. Is this truly >a concern, or am I all wet? :-) My understanding of it is that the tiles, officially called the Thermal Protection System (in NASAese, if it doesn't have three words in its name you have to add "system") are designed to deal with rain as long as they are intact. There is concern about raindrops encountered aloft, either during atmospheric ascent or descent or ferry operations, causing pitting of the tile surface. The tiles are not homogenous by the way -- they consist of a non-porous ceramic "glaze" layer encapsulating a very porous ceramic inside. The tiles are laid over a backing that is basically a felt of some kind. Excess water in the felt could lead to steam explosions damaging tiles, as could steam explosions in individual tiles. Fortunately the whole system gets a good soaking in hard vacuum on a normal mission, which should make any water in it sublimate harmlessly. I don't know the numbers but without running the calculations carefully I'd be concerned that an abort during the first few orbits (or partial orbit) might carry a steam explosion risk. Such an abort could occur if the orbiter fails to achieve a safe orbit or for a medical emergency, for instance. I'd guess that the forces involved in flash evaporation of water at ordinary temperatures in vacuum would not be great enough to damage an otherwise nominal tile. -- Steve Nuchia South Coast Computing Services uunet!nuchat!steve POB 270249 Houston, Texas 77277 (713) 964 2462 Consultation & Systems, Support for PD Software.