Re: SpaceShipOne and reentry heat

From: Michael K. Heney (mheney_at_mach-25.com)
Date: 06/21/04 

Date: Mon, 21 Jun 2004 17:57:05 -0000

In article <3a1d1813.0406210740.467d250d@posting.google.com>, 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

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.

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