h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hello. Can Pinniped explain the Physics of re-entry for Spaceship One, the ship that won the Ansari X-Prize.

Pinniped. In your article you say that Plasma starts forming at 135 km high and Athmospheric drag starts at 85km high. Well SpaceshipOne lifted to around 100km, within the range of Plasma formation, and it slowed down using a unique swing wing system where the wing acted as an atmospheric brake.

My main point of enquiry is, why did the Plasma effect not destroy SpaceshipOne in the Range 100km to 85kn high? As far as I know this craft did not make use of ceramic tiles or ablative material.

Did the swing wing have any effective braking action in the Plasma region?

Most importantly, could the swing wing configuration or similar design work to slow down a Space craft from a much higher altitude LOE 400km high? If so, then surely the problm of re-entry is solved.

Hi keep-it-simple

It's about speed.

To be truthful, I don't know too much about Spaceship One, but it was a ballistic mission and so it fell to zero speed at the highest point of its trajectory (around 111 km). At all times in the mission its speed would be well below the hypersonic re-entry condition that the Shuttle endures.

The plasma is induced by the passage of the craft through a sufficiently-dense atmosphere at sufficiently high speed. The 135 km altitude that's characteristic for the Shuttle is thus a result of its very high speed, and Spaceship One and ballistic craft like it won't (I'm fairly sure) be going fast enough to generate a plasma shroud.

The plasma problem is one for craft that come from a stable earth orbit, and that lack the rocket energy for a controlled (power-decelerated) descent.

Swing-wings (or anything much in the way of wings at all) are a liability under plasma conditions. The high surface curvature turns them into hot-spots, and they're not aerodynamically useful until lower down where there's sufficient air to produce lift..

Thankyou Pinniped,

Its interesting that the NASA Shuttle replacement, orignally known as the CEV (Crew Exploration Vehicle) but officially named the Orion spacecraft in August 2006, is being designed to use simple ablative shielding to slow it down and deal with the high tempertures of re-entry. For now NASA is going for a simple reliable option.

I've been reading about the CEV, and its an interesting concept. Apparently NASA will use the same basic spacecraft for International spacestation missions, Moon Missions and Mars Missions. It will look and be smilar to the old Apollo re-entry module, but it will be more capable and larger (5m diameter to Apollo's 3.6m). It will have a different configuration for each mission and the heat shield will change for each mission, because the re-entry speeds differ for each mission. The Moon missions will generate a plasma cloud 3000 degrees hotter than ITT missions, and the Mars missions will have an even higher re-entry speed.

I guess, barring a dramatic inprovement in materials, we are stuck with ablative re-entry for the near future.