On Thu, 19 Dec 2002, Ian Woollard wrote:
> Does anyone know any rules of thumb for a reentry shield? (I'm trying
> to design a reusable vehicle.)
*What sort* of reusable vehicle? TPS requirements vary enormously with
your approach to the problem; in particular, semiballistic capsules and
winged vehicles are completely different. (Capsules make short sharp
reentries, for which expendable coolants like the Apollo ablative TPS or
Roton's water cooling are perfect. Winged vehicles make long slow
reentries with low heating rates but high total heat loads, so insulating
TPS must be used instead, as on the shuttle.)
This is a complex problem, and gentle introductions to it fill whole books.
> The only thing I've found so far is a reference that Apollo used a
> shield mass of 15 pounds per square foot(!); but I'm unclear how to
> scale this. [presumably more area = less loading = less shield per
> square foot]
Lower loading changes the trajectory, particularly for a lifting semi-
ballistic reentry, so the scaling is not simple.
Henry Spencer
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