Cosmonauts landing on land

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God, I just love picking nits. Today’s Classic Straight Dope Article, http://www.straightdope.com/classics/a940617a.html, contains two statements I’d like to pick apart.

The first was this:

Both U.S. and Russian spacecraft slow themselves with
retrorockets to start their descent, then open parachutes once they reach the atmosphere.

Now technically, the retrorockets do slow the spacecraft down slightly, but that is not the reason they are fired. A retro-directed rocket burn has the effect of lowering your perigee altitude. Burn the retrorockets long enough and hard enough, and your perigee altitude will get so low that you will intersect the atmosphere. This is called a deorbit burn. Ironically, by the time you hit the atmosphere, you’ve fallen enough that you’re going faster than when you were up in a circular orbit. (Typical circular low Earth orbital speed is 17,500 miles per hour.)

In addition, the parachutes are not opened when the spacecraft first hits the atmosphere. Doing so would burn the parachutes to a crisp. Instead, the spacecraft is oriented so that its heatshield is pointing “straight into the wind”, so to speak. It is the drag on the spacecraft caused by the air slamming into and screaming past its heatshield that causes most of the braking on the way down. Only when the spacecraft has slowed enough that it’s going subsonic (less than about 750 miles per hour) is it safe to let out the parachutes.

The second quote was this:

The two fatal accidents known to have occurred during the Soviet space program both happened during re-entry, but neither was attributable to touchdown on land. One involved loss of oxygen following improper detonation of explosive devices separating the capsule from its orbiter and the other a tangled parachute.

If touchdown on land isn’t affected by a tangled parachute, I’ll be a chimpanzee’s uncle!

[Kyberneticist]

Would a touchdown on water have been any more survivable with a tangled parachute?

Somehow I doubt it…

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Kyberneticist wrote:

Would a touchdown on water have been any more survivable with a tangled parachute?

No. It wouldn’t. Without a parachute, an average sized space capsule (say, the Apollo Command Module, for example) would hit the deck at about 300 miles per hour. At that speed, water basically behaves like concrete. It was the 200 mile-per-hour impact of the Space Shuttle Challenger’s crew cabin with the Atlantic ocean that killed its occupants.

Although the Cosmonaut whose parachute got tangled up after re-entry would have turned into a bloody pancake whether he’d smacked down in Siberia or the Pacific ocean, it happened to be a touchdown on land that actually killed him.

[Fiver]

tracer:

Although the Cosmonaut whose parachute got tangled up after re-entry would have turned into a bloody pancake whether he’d smacked down in Siberia or the Pacific ocean, it happened to be a touchdown on land that actually killed him.

True, but I think Cecil’s point was that a tangled parachute is not a unique hazard of a touchdown on land. Land or sea, you’d die either way.

[Jonas_Marainen]

*Originally posted by tracer *
It was the 200 mile-per-hour impact of the Space Shuttle Challenger’s crew cabin with the Atlantic ocean that killed its occupants.

I’m nitpicking, but we have no way of knowing whether this is true or not. The crew may have been dead long before then. Cecil talked about this here.

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Sigh. Yeah, you’re right, Jonas, the Challenger’s occupants could’ve all been dead before they hit the water.

But if any of them had survived up until that point, the water impact would certainly have finished them off.

By the way, I think “Deorbit Burn” would make a great title for a science fiction story.

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Or a rock band, for that matter.

[Irishman]

tracer, regarding your OP:

The first was this:

quote:
*
Both U.S. and Russian spacecraft slow themselves with retrorockets to start their descent, then open parachutes once they reach the atmosphere.*
Now technically, the retrorockets do slow the spacecraft down slightly, but that is not the reason they are fired. A retro-directed rocket burn has the effect of lowering your perigee altitude. Burn the retrorockets long enough and hard enough, and your perigee altitude will get so low that you will intersect the atmosphere. This is called a deorbit burn. Ironically, by the time you hit the atmosphere, you’ve fallen enough that you’re going faster than when you were up in a circular orbit. (Typical circular low Earth orbital speed is 17,500 miles per hour.)

In addition, the parachutes are not opened when the spacecraft first hits the atmosphere. Doing so would burn the parachutes to a crisp. Instead, the spacecraft is oriented so that its heatshield is pointing “straight into the wind”, so to speak. It is the drag on the spacecraft caused by the air slamming into and screaming past its heatshield that causes most of the braking on the way down. Only when the spacecraft has slowed enough that it’s going subsonic (less than about 750 miles per hour) is it safe to let out the parachutes.

While you add some interesting detail that clarifies the answer, nothing Cecil said is technically wrong. They use a retrorocket burn to deorbit, and after they are in the atmosphere they use parachutes. Cecil just left out the technical parts about how the dorbit burn works, about the heat shielding and drag, etc.

I’m glad you didn’t title your thread “Cecil was Wrong!”

[JRDelirious]

Also, to pick even further nits, the Apollo reentry modules were designed with some “lifting body” properties so that once they got to denser parts of the atmosphere, the airflow around the capsule would help some to the braking (the bulk being provided, still, by sheer blunt heat-conversion) and to keep the vehicle in a proper attitude.

[sineater]

To pick even further nits, the Soviet-designed capsules have additional retrorockets (touchdown rockets, actually) that fire just before touchdown to soften the landing. See http://www.rocketry.com/mwade/spaceflt.htm for everything you will ever need to know about Soviet