Russian Manned Space Vehicle May Land With Rockets

The Narrative Fallacy writes "Russia's next-generation manned space vehicle may be equipped with thrusters to perform a precision landing on its return to Earth. Previous manned missions have landed on Earth using a parachute or, in the case of space shuttles, a pair of wings. Combined with retractable landing legs and a re-usable thermal protection system, the new system promises to enable not only a safe return to Earth, but also the possibility of performing multiple space missions with the same crew capsule. The spacecraft will fire its engines at an altitude of just 600-800m, as the capsule is streaking toward Earth after re-entering the atmosphere at the end of its mission. After a vertical descent, the precision landing would be initiated at the altitude of 30m above the surface. Last July, Korolev-based RKK Energia released the first drawings of a multi-purpose transport ship, known as the Advanced Crew Transportation System (ACTS), which, at the time, Russia had hoped to develop in co-operation with Europe. 'It was explained to us how it was supposed to work and, I think, from the technical point of view, there is no doubt that this concept would work,' says Christian Bank, the leading designer of manned space systems at EADS-Astrium in Bremen, Germany. However, the design of the spacecraft's crew capsule had raised eyebrows in some quarters, as it lacked a parachute — instead sporting a cluster of 12 soft-landing rockets, burning solid propellant. Inside Russia, the idea apparently has many detractors. During the formal defense of the project, one high-ranking official skeptical of the rocket-cushioned approach to landing reportedly used an unprintable expletive to describe what was going to happen to crew members unlucky enough to encounter a rocket engine failure a few seconds before touchdown."

Comments

Seems Pretty Inefficient

[Kozar_The_Malignant]

It seems pretty inefficient to carry the fuel mass for the retro rocket braking all the way up out of the gravity well into orbit and then back down into the gravity well so you can use it in the last kilometer of the flight. There doesn't seem any way to stop at a gas station on the way down, but maybe they are planning on lifting the fuel to orbit on non-reusable tankers, which also seems inefficient. In something like this, inefficient equates to really fucking expensive.

Re:Seems Pretty Inefficient

[evanbd]

Your choices are rockets, parachutes, wings and landing gear, or a variety of weird and exotic options (like deploying helicopter blades; see the Roton concepts). There are a variety of reasons to prefer rockets to parachutes (and vice versa). The rockets are likely somewhat heavier than the parachutes and their deployment system, but I suspect the weight difference is small enough that the decision would likely be made on the basis of operational advantages (like being able to do a landing on solid ground instead of the ocean easily).

The American space program seems to be of the opinion that everything should be as light weight and efficient as possible, without regard to other criteria. The Russians, on the other hand, have a long history of being willing to build larger, heavier, less efficient rockets in order to make operations easier. Personally, I think the Russian approach is better -- the correct figure of merit to optimize is not liftoff weight, but cost. If you can develop, build, and/or operate more cheaply by spending more weight on the problem, that's a win in my book.

Re:Weight problems?

[Red Flayer]

Yes, but how heavy were the parachute, parachute deployment system, and parachute shielding system that they were able to remove?

Re:Unprintable expletive?

[mea37]

You must be new here.

It's not a question of "what's unprintable on slashdot".

It's a question of "from whence was the summary text plagiarized, and what is considered unprintable there".

A precision landing with solid rockets?

[roystgnr]

Don't get me wrong, I'm all in favor of spaceships landing on a tail of fire, "the way God and Robert Heinlein intended!" But rocket-powered landings on Earth are a questionable engineering decision even when you get to reuse some of the liquid-fueled rocket engines that you already needed for liftoff and already wanted to recover intact. If you instead have to add extra weight to your upper stage for single-purpose solid rockets of lower ISP, it seems even more dubious.

And that's before you get into the issue of "solid rockets" and "precision". Even designing a liquid-fueled rocket with adequate throttle control for a gentle landing isn't easy. (It's like brain surgery! Or possibly like some other appropriate metaphor!) But at least throttling liquid fuel consumption rates is possible. Solid rockets basically have just three settings: "off", "on", and "kaboom".

Re:High-G landing?

[Waffle Iron]

Capsules don't just plummet vertically through the atmosphere. They spend most of the reentry going almost horizontally bleeding off speed. Most of them also angle the heat shield so that they get a good deal of lift, and they "fly" for a more gentle reentry.

In any case, a capsule must slow down to less than hypersonic speeds before deploying a parachute. Otherwise the parachute would burn up and/or be ripped to shreds.

Once a capsule is going slowly enough to put out a chute, it doesn't have all that much kinetic energy. Small retrorockets would be sufficient to stop it instead.

Re:High-G landing?

[shutdown -p now]

Something is amiss here. The energy to stop a falling box of people is APPROXIMATELY* the same energy is takes to get it up to where it fell FROM.

If this could REALLY work as described, we wouldn't need a whole stinking stage to get the box o'humans UP into space. Email me when this works. If it doesn't, I'll hear about it.

You missed one crucial factor here: terminal velocity. An object falling down to Earth does not accelerate indefinitely, but only until the force of air resistance (which, naturally, grows as speed increases) becomes large enough to offset the gravity completely - at that point, the speed is constant. So you only need to be able to brake from that to whatever is safe for touchdown.

I've no idea what the terminal velocity of this thing would be (it depends on both its mass and profile), but to give some idea of how it works: for a human, that velocity is ~200 km/h. Note that this is no matter how high you jump down from - it will still be the same figure as you approach the surface. It will certainly be higher for the module, but I wonder how much higher...