Site Map Employee Directory. Re-entry is a particularly dangerous time for the shuttle, a time during which the shuttle experiences tremendous stress and high temperatures. There are actually two different phenomena at work to heat the shuttle, compressive heating and friction. Perhaps you have noticed when you use a bicycle pump that the fitting at the end of the pump gets very hot, very quickly. That heat comes primarily from the action of your muscles pushing on a plunger and compressing the air in the pump.
When air or any gas, for that matter is compressed it heats up; conversely when it expands it cools. Now consider the re-entry of the space shuttle or the fall of a meteor through our atmosphere. Initially, the shuttle moves around Earth in the emptiness of space at a tremendous speed. You need around 0. This is why it was such a major gaffe for the Gravity film when it showed all the orbital debris orbiting Earth from East to West, as Neil deGrasse Tyson tweeted.
But you can achieve a much gentler re-entry using a ballute - a cross between a balloon and a parachute. It works like an aeroshell but decelerates much higher in the atmosphere. It combines some of the approaches of the previous ideas. The space engineers in the early s explored many other such ideas detailed here: Rescue. Some seem rather hair-raising, including the Paracone —the astronaut just sits in a seat, with their back towards the Earth, and aims towards the center of a large continent, as its margin of error is kilometers.
When it re-enters, then a large inflatable aeroshell deploys with a crushable cone. There is no parachute—it relies on the aeroshell crushing during landing to protect the astronaut. The astronaut has an inflatable aeroshell stowed away in the seat. During re-entry this deploys.
Unlike the Paracone, you do have a parachute as well, for the landing. This is another idea originally developed for Gemini in the early s. For a while, before they settled on the familiar parachutes, the engineers thought that after the fiery stage of re-entry, the capsules would glide down to Earth beneath a parasail or paraglider.
Those tests were quite promising, though they ran into many issues; for instance, getting the glider to unfold. Eventually this line of research ended in when they changed to the parachutes as used by Apollo. The Russians also used parachutes for the Soyuz flights. For details of the paraglider research, see: Coming Home. Anyway, at around the same time in , the engineers came up with the idea of using the same paraglider approach to go all the way from orbit right down to the surface, without an aeroshell.
It could be folded up into a small cylindrical package that would be kept docked to a space station, much as our modern Soyuz TMA is. In an emergency, the crew enter this cylinder, and separate. The paraglider then inflates and deploys.
It would re-enter at an angle of 1 degree, with the paraglider angle of attack of 70 degrees. It would approach the speed of sound at 43 km altitude, and from there it would be able to glide km horizontally before eventually landing. The Spaceship-One uses a different idea for re-entry. This is only for a sub-orbital hop at present. The first demonstration of the feather system was in The Virgin Galactica crash in was a result of the pilot accidentally unlocking the feathering system too soon.
It then deployed by itself and changed the shape of the rocket far too early, when it still needed to be streamlined. What about returning a final stage? That also is low mass and it presents a large cross section if you fly it backwards, rocket motors first, with supersonic retropropulsion. First, some background. Every time a spaceship goes into orbit, it needs a final stage, a thin container full of fuel which is burnt right at the end, to get it to orbital velocity.
It has to do that, because the spaceship itself is far too small to have enough fuel to get to orbit by itself, even with the help of the first and sometimes second stage.
It then discards the final stage, which normally orbits Earth a few times and finally falls back to Earth apart from interplanetary missions and missions to the Moon, which often use a more powerful final stage, for instance nearly every mission to Mars also sends a final stage in the general direction of Mars too.
So, could a final stage be returned to Earth in the same way that SpaceX have returned the Falcon first stage? Well, when SpaceX returns the first stage of the Falcon 9, it slows down partly through friction in the upper atmosphere.
The landing legs alone reduce its terminal velocity by a factor of two. It also has a burn in orbit and another burn just before it reaches the barge.
You can see the first stage at the beginning and end of this movie most of it is for the second stage. That may seem rather similar, but it only has to shed one kilometer per second of delta v, and much of that is done with the two burns. So, we're really going very far out.
These are high delta-velocity missions, so to try to get something back from that is really difficult. The basic idea of all these designs is that the lighter it is, or the greater the cross sectional area it presents to the atmosphere, then the higher it is when it slows down, and so the lower the temperature of its skin during re-entry.
What matters is the mass per cross sectional area - or more precisely, the ballistic coefficient which is complex to calculate.
If the spaceship can use a glide to stay high in the atmosphere, this also helps. It also helps if it can use retropropulsion to reduce its velocity before it enters the atmosphere, and as it descends. Then, if it can radiate or absorb heat or ablate, for instance with an aeroshell, or use active cooling perhaps in the future , this also helps.
Another way around it is to use a space elevator. You can also use a skyhook. You could then just fly up to the bottom end of the skyhook, and if you fly fast enough you could keep pace with it in our atmosphere, and attach yourself to it. If we had an extra moon close to Earth it might be very useful. The idea is, if you build a 6, km long skyhook-type tether outwards from Deimos then it can throw objects out with escape velocity and also catch incoming spacecraft from elsewhere in the solar system to a gentle rendezvous that only needs docking thrusters, like docking with the ISS.
Then if you build a 2, km long skyhook tether inwards from Deimos and a km tether outwards from Phobos, then it turns out that if you drop a spaceship off the Deimos tether, then it is traveling at just the right velocity to send you in a transfer orbit to the Phobos tether.
Your transfer vehicle ends up stationary next to the Phobos tether when it gets there, with plenty of time to dock, much as spacecraft do with the ISS. Then you can just go down that tether to Phobos. All this requires no acceleration and no rocket fuel, apart from maneuvering thrusters for the docking itself. Once you are on Phobos, a 1, km tether extended downwards towards Mars can be used to drop materials down to an elliptical orbit which reaches down to Low Mars Orbit at a height of km when closest to Mars.
Hop David found that slightly longer kilometer long tether could put it into an atmosphere grazing orbit so that you can use the Mars atmosphere for aerobraking to circularize its orbit. The total mass for all these tethers if made from Kevlar is not that great considering what it does. You need between 5, and 90, tons if designed to handle a payload of 20, tons. You could also bypass Deimos and just have a single tether from Phobos upwards to reach escape velocity right away.
The mass of Deimos and Phobos is so great that you could run this system for decades with no noticeable effects on their orbits. Hop David has explored Phobos tethers in a lot more detail. He finds that a much shorter 7 km tether extending from Phobos towards Mars would let spacecraft dock with its L1 position where the gravity of Phobos is balanced with the gravity of Mars. Then, a very long 1, km tether grazing the Mars atmosphere would mean you only need meters per second delta v to land on Mars.
See Lower Phobos Tether and his General template for space elevators. This spins in such a way that the end closest to the Earth moves backwards relative to its orbit around Earth. In the other direction, you could use the same approach to lift a payload, for instance, attached to a balloon, and attach it to the bottom of the space tether when stationary relative to Earth, and the tether would boost it into orbit, or send it to the Moon or in a transfer orbit to GEO all in one go.
You could have a shorter tether which spins more rapidly, in an orbit closer to Earth. That makes it a less massive construction. It also means you get into orbit quickly. With the space elevator, it could take quite a while to get there. At mph it would take seven and a half days to go up all the way to GEO, and at 2, mph it would take nearly 18 hours. Can helicopters fly upside down? How does a jet engine work? Would it be feasible to dump nuclear waste on the Moon? How does an airplane stop on a runway after landing?
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