Compression burns

[Fatleaf]

I was just injecting through the corona of a star after injecting through the atmosphere of a planet and wondered why you heat up amazingly fast in the planetary atmosphere but don't heat up at all due to friction in the corona of a star!

Is this an oversight?

EDIT: Renamed thread from an erroneous statement to a correct one. (Thanks )

[Disembodied]

A star's corona is much less dense than a planet's atmosphere, so there shouldn't be much in the way of friction. It's the very uppermost layer: you probably wouldn't notice any friction* in the same (roughly analogous) layer of a planet's atmosphere.

*Well, you would, if you were going at 35% of the speed of light. But what's a little physics here and there?

[Fatleaf]

*Well, you would, if you were going at 35% of the speed of light. But what's a little physics here and there?

He said the 'P' word in here! Burn the heretic

[Cody]

A star's corona is much less dense than a planet's atmosphere, so there shouldn't be much in the way of friction. It's the very uppermost layer: you probably wouldn't notice any friction* in the same (roughly analogous) layer of a planet's atmosphere.

*Well, you would, if you were going at 35% of the speed of light. But what's a little physics here and there?

<chortles> Does Light Mach equate to the speed of light now?

[Disembodied]

Does Light Mach equate to the speed of light now?

Mibbes aye, mibbes naw, as we say in the Snort ... your mach may vary. Whatever your opinion, a Cobra III does, I think we can agree, go at a fair old clip.

[aegidian]

Phys*cally, it's always important to remember that it's not friction that causes air to heat around a very fast object, but the compression of the gas ahead of the object.

I seem to recall coding for atmospheric heating when going fast at low altitude when I first introduced fuel injectors as a piece of equipment, but I'm probably mistaken.

[Diziet Sma]

I seem to recall coding for atmospheric heating when going fast at low altitude when I first introduced fuel injectors as a piece of equipment, but I'm probably mistaken.

That would tend to explain why I heated up so fast the time I did an injector-assisted powerdive into atmosphere to escape a bunch of folks intent upon my death..

[Commander McLane]

Indeed, using your injectors close to a planet's surface is dangerous. But I think the same is true when very close to a star (not yet in the outer layers of the corona).

[Fatleaf]

Indeed, using your injectors close to a planet's surface is dangerous. But I think the same is true when very close to a star (not yet in the outer layers of the corona).

Yeah, you heat up amazingly fast when in the atmosphere but I am yet to notice any extra heating (apart from the usual heating by being in close proximity to a star) due to injecting no matter how close I get.

[JensAyton]

For reference, the “surface” of the sun (the upper photosphere) is about 1/6000 the density of air under standard conditions. (For larger stars, it’s much lower.) By my calculations, this is about the same as the atmosphere at 38 km. Reentering spacecraft experience maximum drag at altitudes more than twice as high (i.e., pressures another 6000 or more times lower).

[Disembodied]

According to NASA*, though, the sun's corona "has a density about 0.0000000001 times that of the Earth's sea-level atmosphere" (about one-ten billionth, if I've counted the zeros correctly). Between the corona and the photosphere is about 2500 kilometres of chromosphere, which ranges in temperature from 4500°K at the bottom to 10,000°K at the top ... that said, the temperature of the corona is apparently measured in millions of degrees, so atmospheric compression is probably not too much of a concern. The ship's shields must keep the charged particles away from the ship's hull, with some sort of filtering process allowing quirium to bleed in through the scoops. But presumably, in a planetary atmosphere, the shields can't keep the gases away and so you get direct heating of the hull.


* I had to go to NASA's junior school site before I found something I could understand ...

[JensAyton]

I knew I was missing a step…

The chromosphere, which is what you’d be in if you were just above the “surface”, is 1/10000 the density of the upper photosphere… which puts it at similar density to the region where boring old Earthican spaceships get glowy.

On the other hand, at Oolite scale the chromosphere is a few mm thick.

[cim]

On the other hand, at Oolite scale the chromosphere is a few mm thick.

...and if you run into it your ship experiences extreme thermal heating.

[Wyvern Mommy]

...which puts it at similar density to the region where boring old Earthican spaceships get glowy.

but then, those boring ships had a speed of about 7000 m/s when they got glowy. the orbital speed just above the sun's photosphere is about 500 km/s.

[JensAyton]

but then, those boring ships had a speed of about 7000 m/s when they got glowy. the orbital speed just above the sun's photosphere is about 500 km/s.

Regardless of one’s interpretation of the scale issues, I don’t think there’s anything to suggest Oolite ships normally travel anywhere near as slowly as orbital speeds. :-)