Advanced Re-Entry Vehicle

[Horwood Beer-Master]

Europe has taken the first step towards building its own manned spaceship.

[Horwood Beer-Master]

[klr]

... maybe not the best "bump" illustration given the thread matter.

[mistermack]

Two things I don't understand about re-entry :

Firstly, why do they re-enter so fast, that the temperatures become so intense?
Is it not possible to control re-entry so that it goes on for a lot longer, at lower temperatures?

Secondly, why not have a form of drag vehicle, attached by a cable to the human accommodation capsule, that can get as hot as it likes, and can be released when the speeds have dropped sufficiently.

I expect these strategies have been looked at, or tried, but I'd be interested to know what's wrong with them.

[Gawdzilla Sama]

They basically fall out of orbit, so they have to enter at an angle that prevents them from skipping off the atmosphere or coming in so fast that they burn up despite shielding. This means a certain speed is required. Too slow and they don't come down, too fast and they burn up.

As for the drag vehicle, it would be behind the capsule, so the capsule would be in denser air first, heating up marginally faster than the drag vehicle.

[mistermack]

They basically fall out of orbit, so they have to enter at an angle that prevents them from skipping off the atmosphere or coming in so fast that they burn up despite shielding. This means a certain speed is required. Too slow and they don't come down, too fast and they burn up.

As for the drag vehicle, it would be behind the capsule, so the capsule would be in denser air first, heating up marginally faster than the drag vehicle.

Yes but the shuttle could be flown, so it could obviously be controlled so that it neither skipped nor descended too fast. You could fly it, just like any plane.

And the capsule could be much more streamlined than the drag vehicle, so that the cable is kept taut, and the cabin doesn't heat so much.
The drag vehicle could have remotely controlled drag surfaces, which keep a steady tension in the cable. It's basically a sophisticated metal parachute.

[Gawdzilla Sama]

They basically fall out of orbit, so they have to enter at an angle that prevents them from skipping off the atmosphere or coming in so fast that they burn up despite shielding. This means a certain speed is required. Too slow and they don't come down, too fast and they burn up.

As for the drag vehicle, it would be behind the capsule, so the capsule would be in denser air first, heating up marginally faster than the drag vehicle.

Yes but the shuttle could be flown, so it could obviously be controlled so that it neither skipped nor descended too fast. You could fly it, just like any plane.

And the best re-entry path is still pretty damn hot. Whether the flying is done by humans with computer assist or programmed in on the ground, it is still a free fall from a hundred miles up or so.

And the capsule could be much more streamlined than the drag vehicle, so that the cable is kept taut, and the cabin doesn't heat so much.
The drag vehicle could have remotely controlled drag surfaces, which keep a steady tension in the cable. It's basically a sophisticated metal parachute.

Having two objects connected by a "string" as they're traveling hundreds of miles an hour would be a fun thing.

[mistermack]

It's not exactly a free fall.
The real problem is the huge quantity of energy that is put into the craft on launching, to get it to orbit. You have to shed this kinetic energy to re-enter.
A 100 mile fall wouldn't in itself be much of a problem. It's the 17,000 mph orbital speed that's the problem.

A cable could be practical, if the tension could be controlled.
If not, you could have a cylindrical metal connection, with all the heat being generated in the rear drag section.

All you are doing is turning kinetic energy into heat. I don't see why it has to be so uncontrolled. A plane can shed speed slowly, before landing. Why not a re-entry vehicle?

[Gawdzilla Sama]

It is a free fall, the re-entry engines simply slow the vehicle enough that it no longer remains in orbit. The earlier US capsules and the Soyus ships were simply rocks falling from the sky. The shuttles have some slight control, but they are going down only.

As for the cable, turbulence would be an issue, even very high. Any slack at all would result in yo-yoing, something the passengers wouldn't find fun at all.

And re-entry starts somewhere around Mach 5, so low-level, thick air aerodynamics are moot at that speed and air density.

[mistermack]

It is a free fall, the re-entry engines simply slow the vehicle enough that it no longer remains in orbit. The earlier US capsules and the Soyus ships were simply rocks falling from the sky. The shuttles have some slight control, but they are going down only.

What I meant was that it's a free fall, but of something that is travelling laterally at 17,000 mph, initially. So it's not going straight down, it's travelling nearly horizontally most of the time.

As for the cable, turbulence would be an issue, even very high. Any slack at all would result in yo-yoing, something the passengers wouldn't find fun at all.

That might be true, but if the drag surfaces could be electronically adjusted hundreds of times per second, a simple computer could probably keep the tension in the cable pretty constant. Constant tension means no yo-yo effect.

And re-entry starts somewhere around Mach 5, so low-level, thick air aerodynamics are moot at that speed and air density.

More like Mach 20, I would have thought, if the space station orbits at 17,000 mph.
Yes the aerodynamics would be different, but not necessarily impossible to design for.

The objective is to land safely. I don't see much advantage of landing like the space shuttle. It must have added hugelely to the payload to be able to do that.
I would say that a parachute landing like the Apollo missions was much more efficient.

[Gawdzilla Sama]

They have to slow down to drop out of orbit, but if 20 Mach is closer I'm okay with that.

The point of the shuttle was to have controlled landings. The Sovs have a much bigger dryland target to aim at, so they don't worry about water landings. But a much bigger vehicle with a much larger payload capacity required, in NASA thinking, the ability to land where they wanted it to go. The shuttles land at either the Cape or Edwards AFB in California. They're on the runway and near to the facilities that will get them ready for the next flight (or for a piggy back to that facility). The Mercury-Gemini-Apollo landings were impressive if they came down within sight of the recovery team.

[mistermack]

They have to slow down to drop out of orbit, but if 20 Mach is closer I'm okay with that.

The point of the shuttle was to have controlled landings. The Sovs have a much bigger dryland target to aim at, so they don't worry about water landings. But a much bigger vehicle with a much larger payload capacity required, in NASA thinking, the ability to land where they wanted it to go. The shuttles land at either the Cape or Edwards AFB in California. They're on the runway and near to the facilities that will get them ready for the next flight (or for a piggy back to that facility). The Mercury-Gemini-Apollo landings were impressive if they came down within sight of the recovery team.

I know. The shuttle was a fantastic bit of kit, and it did fantastic work, there's no doubt about it.
But it was designed in a time when energy was much cheaper, so it was viable at the time.
But today, every gram of weight costs a huge amount to get into the space-station orbit, so in today's climate, it's making instruments tiny and lightweight, that counts.
And that applies to the vehicles as well.
As it costs so much to get material up there, it's logical to keep it up there, and only bring down the absolute minimum needed for safety.
Anything that becomes useless should be kept up there, because one day, it will be practical to recycle stuff in space.

If I was designing a re-entry vehicle, it would be absolute minimum size, just to get humans down in the safest way possible. With today's computer technology, it could be done much more accurately than the Apollo mission.

[Gawdzilla Sama]

If I was designing a re-entry vehicle, it would be absolute minimum size, just to get humans down in the safest way possible. With today's computer technology, it could be done much more accurately than the Apollo mission.

The point of the shuttle was to get bigger payload into orbit. Hubble, for instance. And to get into space more often. Each Apollo and Soyuz is a one-time use vehicle. The shuttles were originally planned to fly every two weeks in rotation.

[Cormac]

If I was designing a re-entry vehicle, it would be absolute minimum size, just to get humans down in the safest way possible. With today's computer technology, it could be done much more accurately than the Apollo mission.

The point of the shuttle was to get bigger payload into orbit. Hubble, for instance. And to get into space more often. Each Apollo and Soyuz is a one-time use vehicle. The shuttles were originally planned to fly every two weeks in rotation.

I hate seeing this iconic vehicle put out to pasture, especially without being replaced by something even more fantastic.

Even though it didn't achieve the re-usability as originally hoped, it was still a brilliant brilliant machine.

The world is a little less bright today.

[mistermack]

If I was designing a re-entry vehicle, it would be absolute minimum size, just to get humans down in the safest way possible. With today's computer technology, it could be done much more accurately than the Apollo mission.

The point of the shuttle was to get bigger payload into orbit. Hubble, for instance. And to get into space more often. Each Apollo and Soyuz is a one-time use vehicle. The shuttles were originally planned to fly every two weeks in rotation.

I've just been reading Wiki on the shuttle re-entry, it's fascinating reading:

http://en.wikipedia.org/wiki/Space_Shut ... nd_landing

The re-entry speed is given as about Mach 25, and it performs sideways s shaped courses to avoid skipping upwards.
The Shuttle itself weighs about 2,000 tons, for a payload of 24 tons max.

You can see what I'm getting at. That ratio is just impractical today.
There have been 135 launches, so they have launched 270,000 tons into orbit, for a payload total of about 2,000 tons. In other words, they have put about 250,000 tons or more of material up into orbit, just to bring it back down again.

If you use an absolutely minimal re-entry vehicle, nearly all of that material could be still up there in space, available for use and re-use.