Friction is a force that resists relative motion between solids or fluids.

“Air Friction” is more correctly known as “Drag” which comes in three forms: Parasitic, Lift-induced and Wave drag.

And wave drag is the result of, you guessed it, compression shock

So IT IS friction… unless you are in this case referring to a specific form of friction that I am unfamiliar with

http://en.wikipedia.org/wiki/North_Sentinel_Island

As for spy satellites tracking ROSAT’s descent, I’d expect most of them would be focused on other things and that wouldn’t exactly be top priority for them as they’d be looking elsewhere?

PS. Yeah, I always have been a lousy typer. Mea culpa. What’s “center” in deutsch anyhow?

I know it is their satellite and all that, but I really think they just copied SSC’s report with very little own input.

I am not a native English speaker but I can very easily understand what Tara Li said. I’ll ty to re-phrase it for you, as you got her statemets completely wrong:

TL: “There’s enough of the bloody spy sats, …”

= “There are plenty of US owned military reconnaissance / early warning satellites in orbit that were able to trace the heat signature of the re-entering ROSAT…”

TL: “…and the signature of a significant re-entry is going to be so different from a missile launch, they could post when & where with no real impact on security.”

= “…so the USG knew withing almost real-time when and where ROSAT re-entered but refuses to let the rest of the world know as they are paranoid about disclosing their capabilities – which everybody already knows they have”

By the way, it’s officially the “German Aerospace Center”, not “Centre” I worked there for 10 years.

You’re welcome

George

Burial at sea in the Indian ocean I presume?

@4. Chris : “But were any fish hit? No one ever cares about the fish.”

Unlikely any fish were hit unless they were especially unlucky flying fish!

Once ROSAT hit the ocean it’s momentum would, I’d expect, have been much slower and gentler as it sank and the fish would probably have been easily able to move out the way.

Jellyfish aside.

@7. Tara Li :

There’s enough of the bloody spy sats, …

For Your Information, ROSAT (short name for ROentgen SATellite) was an astronomical scientific research satellite not a spy satellite. It was a mission designed and run by the German Aerospace Centre to study the sky in X-rays, a space telescope. Click on my name for a link to their website.

…and the signature of a significant re-entry is going to be so different from a missile launch, they could post when & where with no real impact on security.

Please can you rephrase, expand upon or otherwise clarify that last part of your sentence there because I honestly can’t understand what you are trying to say or what point you are presumably trying to make. You are not making sense there – to me at least – at all.

In rarefied air the drag coefficient is variable also.

Actually, the drag of an object is not related to its mass. It’s the resulting deceleration that is a function of mass.

Actually, it’s due to passage of gas through a shock. This compresses the gas, but most of the heat is from dissipation of kinetic energy at the shock, not from compression. Compression (as in a bicycle pump) is a reversible process (one that does not produce entropy). Passage of gas through a shock, on the other hand, is inherently dissipative and causes an increase in entropy.

http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kintem.html
The science
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/kintem.html#c4
The calculation. Air is 29 amu

Incoming sees gas at (most probable speed) 72,000 C!!! Now add shock compression.