That’s like saying that guns don’t kill people, it’s the bullets that kill them. No, wait, it’s not the bullets, it’s the holes made by the bullets. Wait again, it’s not the holes, but the loss of blood that the holes allow. But then it’s not the blood loss itself, it’s the lack of oxygen to the brain…

Seriously, if the ram pressure causes the shockwave and the shock wave causes the heating, then the ram pressure does cause the heating.

Plus the “Viking funerals”, it seems, have Jedi and Time Lord – plus Star Trek (eg. Spock in movies II & III) – approval.

Heh, good point. Though I do wonder why they bothered to make Spock’s casket reentry-capable if they thought he was truly dead. If they wanted to interr him planetside, why not just beam the casket into a cave?

BTW. Sorry to hear about your (ex)job – that really sucks. I know having been through that myself. Sympathies and hope something good comes along for you soonest.

Thanks much! It’s nice to hear (er, well, you know) those words today.

http://www.spaceflightnow.com/station/exp29/111102p45pdock/

- Ben H.

@ 29. Joseph G : Am I the only one who thinks that this would be an absolutely epic way to go?

Not at all – I feel exactly the same way on that. Plus the “Viking funerals”, it seems, have Jedi and Time Lord – plus Star Trek (eg. Spock in movies II & III) – approval.

BTW. Sorry to hear about your (ex)job – that really sucks. I know having been through that myself. Sympathies and hope something good comes along for you soonest.

@ 25. Ben H. :

If the ISS Program management cannot be convinced of the safety of the rocket before mid-November we will be forced to bring the current ISS crew home before the new crew launches so there will be a period of time without astronauts in space (for the first time in 11 years). This is what is being referred to as “De-crew” and no one wants to do it! Hope that helps.
- Ben H. Mission Control, Houston, TX

Thanks for that & all the other info you’ve contributed here – much appreciated.

Really hoping we can keep the International Space Station occupied (albiet NOT in the protest sense of the word! ) continuously and avoid having to decrew. Any idea when we are likely to know more and have a decision confirmed & made public?

Haha. How about this: “You’re gonna eat energy and you’re gonna crap entropy!”

I hope they check carefully that no-ones inside the Progress craft before it departs for its “viking funeral” re-entry.

Am I the only one who thinks that this would be an absolutely epic way to go? Like if you had terminal cancer or something, and you were able to take the Slim Pickens way out (sans the nuclear holocaust of course)?

In all seriousness, the “Viking funeral” idea; would that not be a fantastic way for people to remember you? A capsule with your body is braked into a relatively steep re-entry (for predictability’s sake) Everyone gathers in the twilight on the beach to share a few things about you, and at the appointed time, a brilliant shooting star slowly scuds across the sky… That’s how I’d want to be remembered, if it were possible and I had the choice.
Plus it takes care of cremation and ash-scattering all in one shot.

Meh, pardon my morbidity today. I got fired, so everything is death and doom with me.

The Progress doesn’t have a reentry module (landing capsule): the Soyuz has. In the Progress design, the reentry module has been replaced by fuel tanks.

While I admire your persistence on the topic, I just don’t think your explanation and Phil’s are sufficiently different to justify confusing many readers with too much detail.

Well, I think Paul’s explanation is clear enough, but I eat entropy for breakfast*.

To quote Phil in the post, “As the pieces hit the air, they compress it violently, heating it up (it’s not actually friction that does the majority of heating, but this ram pressure that does it).”

As Paul points out, this is oversimplified to the point of wrong. IIUC, the ram pressure creates the shock wave and it’s the shock wave that does the heating.

If you can make your version this brief and clear to average readers then you may get him to change, but I doubt it can be done.

The compression of the atmosphere in front of the object creates a shock wave, and as air molecules pass through the shock wave, they heat up.

I am guessing, for example, that a majority of readers even here don’t have a clear understanding of entropy or its significance, and may have some serious misconceptions about supersonic shocks as well. Just getting people to understand that it’s not friction is victory enough

This is a very good point. Paul’s comment about entropy seems to be less an explanation of what actually happens and more an explanation of why Phil’s explanation is wrong. Even so, I agree that dispelling the friction myth is a victory, but if you are going to dispel one myth, why not replace it with the truth rather than another myth?

* Well, no, actually, I don’t. But the entropy of my breakfast cereal increases dramatically after I have eaten it.

@2. Ben H. :

Phil,You say “On October 29, 2011 — last Saturday — it undocked, empty.” You are correct that it would be empty of useful items.

I guess the important things is that it’s “empty” of astronauts!

I hope they check carefully that no-ones inside the Progress craft before it departs for its “viking funeral” re-entry.

Wonder if they have any contingency plans to do something about it if someone was accidentally caught aboard when the Progress leaves on its final flight? Is that something they’ve considered and simulated and would they be capable of using the Progress craft as a “lifeboat” Aquarius (Apoll0-13 LEM) style if the need arose?

The paragraph you refer to in Phil’s other post is:

“This means it looks like the Russians have indeed figured out what went wrong in the previous launch and fixed the issue. I’ll be happier with two successful launches rather than one — they may have gotten it right by accident — but still, I bet a lot of folks at NASA are breathing easier now, and this will ease discussion of de-crewing the ISS, which NASA was considering a few months ago.”

The last Progress supply vehicle that launched in August was lost during ascent. The Progress vehicles use the same launch vehicles as the manned Soyuz vehicles. If the ISS Program management cannot be convinced of the safety of the rocket before mid-November we will be forced to bring the current ISS crew home before the new crew launches so there will be a period of time without astronauts in space (for the first time in 11 years). This is what is being referred to as “De-crew” and no one wants to do it!

Hope that helps.
- Ben H.
Mission Contro, Houston, TX

To my understanding of mechanical physics and what Phil was saying, the burning up of the cargo ship was a result of drag, a sort of air frictional force. This drag was transformed into thermal energy (hence the flames), and this coupled with the kinetic energy of the falling ship were equal to the gravitational potential energy of the ship, which was likely very high.

@Phil and @Ben H.

I remember you mentioning “Great news: Russians successfully launch Soyuz rocket to ISS!” post and comments that while the ISS was receiving new supplies and was getting rid of waste, it was also “decrewing”. I just wanted to inquire about the meaning of this. Is it just a transfer of astronauts to and from the ISS? It seems like that is the case, seeing as you say more were coming in as some were leaving, and it does really make sense for NASA and other space agencies to empty the ISS and leave an unmanned space station in space.

Thanks for your response Nigel, I got some cooking to do and some reading/watching up to do all in that order and will get back later.

While I admire your persistence on the topic, I just don’t think your explanation and Phil’s are sufficiently different to justify confusing many readers with too much detail. To quote Phil in the post, “As the pieces hit the air, they compress it violently, heating it up (it’s not actually friction that does the majority of heating, but this ram pressure that does it).” If you can make your version this brief and clear to average readers then you may get him to change, but I doubt it can be done. I am guessing, for example, that a majority of readers even here don’t have a clear understanding of entropy or its significance, and may have some serious misconceptions about supersonic shocks as well. Just getting people to understand that it’s not friction is victory enough.

No, it’s not just semantics. I’ve corrected Phil on this before, to no avail, but let’s try one more time.

Ordinary adiabatic compression, as occurs in a bicycle pump, causes air to become hot. However, this process is isentropic: if we ignore transfer of heat from the air to the cylinder walls, the process is entirely reversible. No entropy is generated. If you reexpand the air, doing work on the piston, then when the air gets back to ambient pressure the temperature is the same as when you started.

This is NOT TRUE of what happens to air encountering a supersonic body. The air passes through a shock, and at the shock the properties of the air change over a very short distance (maybe ten mean free paths of the air molecules). Entropy, temperature, and pressure all increase. Kinetic energy is converted irreversibly into heat. You can think of what happens as a cushion of slower moving air building up in front of the body, and the incoming air runs into this cushion (and keeps it inflated).

If the air that has passed through a shock is reexpanded back to its initial pressure, it will not return to its initial temperature. Energy has been dissipated irreversibly.

We know the the chemical composition of the sun because by observing emmision lines of hydrogen, sodium, helium etc in it’s spectra??

Not really.

The main body of the sun is dense enough that it emits as a black body (more or less). However, the sun has an atmosphere of sorts, which contains highly rarefied gas, and absorbs some of the light from the surface of the sun. This makes dark absorbtion lines in the sun’s spectrum, from which we know the chemical composition of the sun.

The same technique allows us to analyse other stars, and other galaxies.

We can analyze reflected sunlight from the moon and tell the chemical composition of the surface of the moon by looking at the absorption lines in the moons spectra??

I am not so sure about this, but I believe this could be done in principle, provided that allowance is made for the sun’s absorption lines.

Can someone correct me please if I’m wrong, but if I were to analyze the entire spectrum of light that is being given off by this cargo ship burning up on re-entry, would I expect to see black absorption lines in specific parts of the spectrum that correlate with specific elements on the periodic table?

Well, leaving aside the emission / absorption lines question, which seems already to have been addressed, no.

Low-density gases give sharply-defined emission or absorption lines (depending largely on the temperature of the gas and whether electrons have been excited by some other form of emission such as UV). However, as density increases, the lines tend to blur out. A gas of sufficiently high density emits like a black body. Sodium vapour street lamps illustrate this point fairly well. Low-pressure sodium lamps issue a monochromatic (well, OK, there are two sodium emission lines that look orangey-yellow to us) light; medium pressure sodium lamps produce a pinky-white light that is broader in the range of wavelnegths it includes; and high-pressure sodium lamps produce a white light.

And from that I could determine what elements – Iron, Silicon, chromium etc.. – the object is made from? Is that how it works?

Finally, if my understanding above is correct, is this exactly the same process we use to determine the elemental composition of stars and planets/atmospheres over vast distances? Is my understanding of all this correct?

In principle, yes. IIUC, however, the plasma produced when a space vehicle enters the atmosphere is too dense for this technique to work.

http://www.amazon.com/Packing-Mars-Curious-Science-Life/dp/0393339912/ref=sr_1_1?ie=UTF8&qid=1320076735&sr=8-1

- Ben H.
Mission Control, Houston, TX

As a serious enquiery aside from my toilet humour, would there be metabolic changes as a result of living in zero g and if so would these changes be detectable in the solid waste of the astronauts. Like increased or decreased levels of certain chemical compounds? A strange line of enquiery I understand, but interesting nontheless

- Ben H.
Mission Control, Houston, TX