The question concerns "orbital reentry", so the answer is "yes". With a space elevator the orbital mass is in a geosync orbit. The question for deep space return then is to slow down enough to enter geosync orbit and dock with this mass station.
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It's probably a (big) stretch, but could this be done magnetically? I saw experiments back in college where electrical feedback could bring a rotating shaft from several thousand rpm to dead stop in a matter of seconds, without all the heat. Just a 'back of the napkin' idea...
If one brought an orbiter in initially using an approach counter to Earth's rotation, and properly magnetized the hull in a pulsing manner, it might be possible to use the planet's magnetic field to slow it down considerably. The effect could be controlled for different approach profiles, delta-v requirements and crew safety / comfort concerns. It would be simlar to an electrical motor working in reverse.
Once enough energy is shed, the orbiter could maneuver into a more conventional rotation-matching reentry profile. I imagine with enough thought, some of the energy could even be recovered some way and utilized.
If one brought an orbiter in initially using an approach counter to Earth's rotation, and properly magnetized the hull in a pulsing manner, it might be possible to use the planet's magnetic field to slow it down considerably. The effect could be controlled for different approach profiles, delta-v requirements and crew safety / comfort concerns. It would be simlar to an electrical motor working in reverse.
Once enough energy is shed, the orbiter could maneuver into a more conventional rotation-matching reentry profile. I imagine with enough thought, some of the energy could even be recovered some way and utilized.
rcsplinters":1xsf42e4 said:
I completely agree with this. The general public has too much influence from Star Trek, Star Wars, Independence Day, or any other movie/show that involves space travel. For the sake of the show, they dont make it scientifically accurate. I recently completed my masters in space systems, and although many ideas sound great, making them happen is nigh impossible.
On your note of climbing a hill....Assume Earth is the bottom of the hill, and LEO is the top of the hill. You get on your bike and pedal your heart out to reach the top. (Lets assume a 8% grade, semi steep mountain pass). Now do the whole thing in 10min, thats a lot of energy to expend. Switching rolls....assume your at the top of the hill, and I push you down the road...oh, and the bike doesnt have brakes (they cost to much). How are you going to stop at the bottom??? Hopefully you brought a parachute to get some drag built up.
So it is with space travel. We make big rockets to get us up the hill quickly, and parachute/aerobrake to land.
Didn't the commercial Space Ship one achieve that? It came strait down and popped open parachutes. It was made out of wood too!
"Yes.
As slowly as possible."
I'd add "from the top".....
One of the reasons that re-entry vehicles aren't as streamlined as one might expect (besides the formation of the protective shockwave) is that few materials will withstand the heating without the insulating effect of the plasma. There have been advances in high-temperature materials, but not yet to the point where it is possible to build a vehicle.
However: with a sufficiently streamlined vehicle skinned in this magic "unobtanium" material, could an orbit be allowed to decay into the upper atmosphere? At first, the upper air would provide drag only, but at some point, a lifting body could begin to delay the descent - the longer the vehicle could stay higher, the slower the deceleration, but the lower the heating rate, at the expense of duration At some point, the orbit would become a really long glide. Instead of what? 8 minutes? of deceleration, could it be stretched out to an hour or so? I'm just guessing here, but I suspect that anyone who has "gone for the ride" really isn't in a hurry to come down, anyway....
SJQ
As slowly as possible."
I'd add "from the top".....
One of the reasons that re-entry vehicles aren't as streamlined as one might expect (besides the formation of the protective shockwave) is that few materials will withstand the heating without the insulating effect of the plasma. There have been advances in high-temperature materials, but not yet to the point where it is possible to build a vehicle.
However: with a sufficiently streamlined vehicle skinned in this magic "unobtanium" material, could an orbit be allowed to decay into the upper atmosphere? At first, the upper air would provide drag only, but at some point, a lifting body could begin to delay the descent - the longer the vehicle could stay higher, the slower the deceleration, but the lower the heating rate, at the expense of duration At some point, the orbit would become a really long glide. Instead of what? 8 minutes? of deceleration, could it be stretched out to an hour or so? I'm just guessing here, but I suspect that anyone who has "gone for the ride" really isn't in a hurry to come down, anyway....
SJQ
,Bugstomper2":147s0k4n said:
Space ship one came down as a glider no engines, did not pop parachutes, maybe after landing.
Low earth orbit also, speed maybe 2170 mphs.
Space Ship One never achieved orbit. It just went up and then straight back down. It never was going the approximate 17.000 mph needed to orbit so it had no energy other than that created by it's fall to dissipate. SS1 is a long way from being an orbital vehicle and if people are comparing it to the space shuttle they are sadly mistaken.Bugstomper2":3cyt51nz said:
I got to wondering about this topic many years ago and came up with a scheme. Imagine for example on old mercury style craft ( am I dating myself ) with a large leading edge surface. Instead of an ablative shield it would have a series of conduits connected to jets all over its surface through which water would be pumped into the region behind the shock wave. I am guessing that the water would absorb the heat from the shock and would vaporize carrying away much of the heat and in doing so perhaps even provide some thrust. The water might best be dyed as dark as possible to best absorb heat. The fluid flowing through the network of pipes would help to cool the leading edge of the craft. As I have no background in physics or engineering I am unable to evaluate this crackpot idea.
Turn on the zero-point-energy thrusters, slow to Mach 6 or so, fly leisurely to the spaceport, land. Or just slow to [LE] orbital speed (equiv. to Mach 23.5), park/orbit the craft, and beam down.
ulao":2p8108da said:
Unfortunately, a really bad idea. Water is VERY heavy, it would cost a fortune to carry enough with you.
MaxWithershins":32jrit3z said:
It is not a stupid Question. Just because you're some self righteous, high and mighty know-it-all, doesnt mean that someone else in this world might want to further their own knowledge.
Get over yourself.
Mod Hat On***
Let's cut out the sniping and stick to the subject please.
Mod Hat Off ***
Meteor Wayne
Let's cut out the sniping and stick to the subject please.
Mod Hat Off ***
Meteor Wayne
Buzz_Leapyear":1vi5wix5 said:
Not a stretch at all. As a matter of fact there have already been some tests with satellites that deploy a long wire to generate induced current from the Earth's magnetic field, which sets up a magnetic field around the wire. They are experimenting with this to deorbit old satellites and maybe even manned ships. Currently, the idea is to just slow the orbital velocity enough to bring it out of orbit into a conventional reentry. But, if the technique could slow the vehicle down fast enough it might work. I'd suspect there would be quite a bit of g-load on the vehicle.
Eddie_42":2ijzhnyw said:
Yes, I agree. This kind of response only stifles imagination, creativity and innovation.
This is how this forum views question about stupid questions :
"The Unexplained" Should be re-named "The Entertained"
and here is another (great) forum thread, perhaps closer to the topic :
Landing on other planets/moons
"The Unexplained" Should be re-named "The Entertained"
and here is another (great) forum thread, perhaps closer to the topic :
Landing on other planets/moons
Obviously getting into the atmosphere is a big part of the question.
The next is: how do we impart the delta vee to slow things down for reentry? And that question has not really been discussed.
Tether technology allows us the potential putting a "big arm" into earth orbit that can serve as both a launching point to the solar system as well as a "catcher's mitt" to slow down incoming payloads, direct their reentry, and preserve some of the energy that would otherwise be wasted.
It's also very efficient in that the momentum can be "built up" at the rotating arm and then used for either task. I can imagine that the satillite would resemble a rotating tower with extendable tethers on winches and ion-thrusters located at either end. The middle could be equipped with solar cells and power storage for the winches and thrusters as well as other zero-g items.
Each extendable tether would be tipped with a capture target. When it was desired to transfer a payload to geosynchronous orbit, the Lagrange points, the moon or mars, wherever, the tether could be "spun up" using cheap solar energy and ion thrusters. The satillite would rendezvous with the capture target and then the arm would transfer angular momentum (and the momentum of the whole structure) to the satellite. By combining changes in the length of the tether with timing of the capture and release, a predetermined quantity of delta vee (as well as change in direction) could be applied to each target.
Similar, a fast moving incoming payload could meet a capture target and it's straight line momentum transferred to angular momentum for the tether satillite. The payload could the been released as the appropriate time to reenter the atmsophere. If additional speed needed to be shed, then the satillite thrusters could be allowed to operate. There is also the potential for the use of gyroscopes to absorb the angular momentum and preserve it for future use.
Kind of cool, huh?
The next is: how do we impart the delta vee to slow things down for reentry? And that question has not really been discussed.
Tether technology allows us the potential putting a "big arm" into earth orbit that can serve as both a launching point to the solar system as well as a "catcher's mitt" to slow down incoming payloads, direct their reentry, and preserve some of the energy that would otherwise be wasted.
It's also very efficient in that the momentum can be "built up" at the rotating arm and then used for either task. I can imagine that the satillite would resemble a rotating tower with extendable tethers on winches and ion-thrusters located at either end. The middle could be equipped with solar cells and power storage for the winches and thrusters as well as other zero-g items.
Each extendable tether would be tipped with a capture target. When it was desired to transfer a payload to geosynchronous orbit, the Lagrange points, the moon or mars, wherever, the tether could be "spun up" using cheap solar energy and ion thrusters. The satillite would rendezvous with the capture target and then the arm would transfer angular momentum (and the momentum of the whole structure) to the satellite. By combining changes in the length of the tether with timing of the capture and release, a predetermined quantity of delta vee (as well as change in direction) could be applied to each target.
Similar, a fast moving incoming payload could meet a capture target and it's straight line momentum transferred to angular momentum for the tether satillite. The payload could the been released as the appropriate time to reenter the atmsophere. If additional speed needed to be shed, then the satillite thrusters could be allowed to operate. There is also the potential for the use of gyroscopes to absorb the angular momentum and preserve it for future use.
Kind of cool, huh?
The only place one magnet repells another is directly at the poles. So how about this for a wild idea. If we perfect super cooled magnets and could basically magnetize the entire skin of a vehicle, one just used to deliver to and retrieve from orbit crew, could we do it magnetically over either of the earth's magnetic poles? Something like the space elevator just without the cable. The vehicle could have supplimental thrusters to keep balance and for final approach.
Unfortunately, a really bad idea. Water is VERY heavy, it would cost a fortune to carry enough with you.
Thanks Meteor, After your kind remarks I did a little research. It can,t be that bad an idea, someone looked at a similar proposal back in the 60s.
"Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed to employ heat shields made from temperature-resistant metal alloys that incorporated a refrigerant or cryogenic fuel circulating through them. Such a TPS concept was proposed for the X-30 National Aerospace Plane (NASP). The NASP was supposed to have been a scramjet powered hypersonic aircraft but failed in development.
In the early 1960s various TPS systems were proposed to use water or other cooling liquid sprayed into the shock layer, or passed through channels in the heat shield. Advantages included the possibility of more all-metal designs which would be cheaper to develop, more rugged, and eliminating the need for classified technology. The disadvantage is increased weight and complexity, and lower reliability. The concept has never been flown, but a similar technology (the plug nozzle[22]) did undergo extensive ground testing." http://en.wikipedia.org/wiki/Atmospheric_reentry
The heat of vaporization for water is about 2.76 Mj/kg. Reentry from escape velocity produces about 60.5 Mj/kg. Assuming atmospheric drag contributes the lions share of the deceleration and the heat soak spans say 300 sec it is certainly not that far off. Yes there is a weight penalty but the other schemes have drawbacks too.
Can't be much lower reliability than shuttle tiles though.
Thanks Meteor, After your kind remarks I did a little research. It can,t be that bad an idea, someone looked at a similar proposal back in the 60s.
"Various advanced reusable spacecraft and hypersonic aircraft designs have been proposed to employ heat shields made from temperature-resistant metal alloys that incorporated a refrigerant or cryogenic fuel circulating through them. Such a TPS concept was proposed for the X-30 National Aerospace Plane (NASP). The NASP was supposed to have been a scramjet powered hypersonic aircraft but failed in development.
In the early 1960s various TPS systems were proposed to use water or other cooling liquid sprayed into the shock layer, or passed through channels in the heat shield. Advantages included the possibility of more all-metal designs which would be cheaper to develop, more rugged, and eliminating the need for classified technology. The disadvantage is increased weight and complexity, and lower reliability. The concept has never been flown, but a similar technology (the plug nozzle[22]) did undergo extensive ground testing." http://en.wikipedia.org/wiki/Atmospheric_reentry
The heat of vaporization for water is about 2.76 Mj/kg. Reentry from escape velocity produces about 60.5 Mj/kg. Assuming atmospheric drag contributes the lions share of the deceleration and the heat soak spans say 300 sec it is certainly not that far off. Yes there is a weight penalty but the other schemes have drawbacks too.
Can't be much lower reliability than shuttle tiles though.
Buzz_Leapyear":z8lgc3by said:
Although you may not have observed anything getting warm, I'll bet something did. You can't just make energy go away, it has to be dissipated somehow. Probably that spinning shaft got real toasty when it was slowed down.
ulao":srf92k2y said:
Why do you think that the shuttle tiles are unreliable? The loss of Columbia had nothing to do with a failure of the Thermal Protection System. The TPS was compromised at launch by an impact with an object moving fast. If I puncture one of your tires with a rifle as you are driving by at 90 miles per hour, are you going to blame the resulting crash on the design of the vehicle? If you ran the family car in a NASCAR race, would you blame the design if it blew up?
BOTH SHUTTLE LOSSES WERE THE RESULT OF MANAGEMENT DECISIONS, NOT OF DEFECTS IN THE DESIGN! Challenger was launched during extremely cold weather, and many engineers fully expected what happened. But NASA management had been told by somebody with a lot of power that it was going to fly that day. Or else.
NASA management was also aware that foam strikes were a potentially fatal problem. Endeavor came back with a good sized hole in one wing leading edge, and analysis of launch footage identified the culprit as foam coming off the External Tank. Management refused to stop launching until the problem was worked out, which resulted in the Columbia being lost.
As long as the vehicle is operated within parameters, it has been reliable and safe.
halman":3s40cjjr said:
I agree that poor management was the cause of both losses. But... can anyone tell my why the shuttles do not carry one or two peices of tile material plus a method for cutting them into the necessary shape? Along with a tube of adhesive or apoxy so that a damaged tile can be replaced prior tor rentry. I think this lack of what seems to be a simple safety precaution is what doomed Columbia.
Yes, I realize that adhesives can loose thier abilities to adhere in space, but then again it doesn't have to hold forever. Just long enough for re-entry. EVA and replace the bad tile just before retro burn. Then it only has to hold long enough to get the ship down thru the upper atmosphere.
And there may be other ways to replace a damaged or missing tile.
I like the idea of matching Earth's solar orbit speed then entering the atmosphere at a relatively low speed compared to the Earth. Once deep within the atmosphere, you would have a considerable amount of speed to shed or the planet will give you a truly rude greeting at 30 kps!
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