Vacuum Ablation?

[Megidolaon]

I'm reading The Night's Dawn Trilogy and Haimlton mentions this pretty often.

The rest of the story is full of proper scientific concepts, but the only references I found about vacuum ablation say it's nonsense.

 

Certainly, the idea that materials would "boil away" in empty space doesn't sound very convincing.

 

Is vacuum ablation real? At what pace would a spaceshuttle hull ablate?

And what is it that really causes the ablation? Radiation? The cosmic microwave background?

 

[Greg H.]

See Ablation: Spaceflight on Wikipedia for current uses in a vacuum. Basically it's a controlled burn of solid materials to radiate excess heat away from the ship so that you don't cook the occupants, but we (AFAIK) don't call it vacuum ablation specifically. I disremember what context PH uses for it in the NDT, since it's been a couple years since I read it, so I don't know if this matches his supposed use or not.

[swansont]

Solids do have a vapor pressure, so the effect of ablating something owing to it being present in a vacuum is real, though for most materials this wouldn't be an issue except in the ultra-long-term. For a spaceship, collisions with the background gas of space would be a real issue, especially if the ship got to relativistic speeds. You'd turn the hull into a sputtering source.

[Megidolaon]

Hmm, maybe he means that.

In the Night's Dawn trilogy they use wormholes for spaceflight and fusion drives for short distance which don't get even close to lightspeed, but I suppose they are exposed to space for a long time, not being capapble of entering an atmosphere.

 

But considering it takes place at the beginning of the 27th century, I suppose the spaceships are not even around long enough for ultra long term (as in millions or billions of years?).

Could the Interstellar medium cause the ablation even without relativistic speed?

 

Apparently it's an issue and they are about trade with some aliens for a technology to prevent ablation efficiently.

[Enthalpy]

Sublimation depends on the material. Cadmium and zinc for instance are not used on a spacecraft because they sublimate too quickly. That's a serious worry because both are useful coatings on steel, and are commonly used on terrestrial parts, which therefore can't serve in space.

 

Besides sublimation, some polymers (PVC especially) lose water in vacuum and shrink then, up to 3% in each dimension, so that parts wouldn't function any more. PVC is excluded from spacecraft - one more common material found in many terrestrial components, like electrical wires.

 

Erosion by residual atmosphere is a real concern on low-Earth orbit, like 200km to 400km altitude. It won't punch a hole through a metal wall, but it does change the colour of the outer surfaces, which are essential to define the spacecraft's temperature.

 

Other materials fail quickly in space because of UV light or ionizing radiation, rather than vacuum.

[Megidolaon]

Thanks.

So it really a concern.

[Greg H.]

Thanks.

So it really a concern.

It's an engineering/design issue, yes.