Re-entry methods

[bdewoody]

Other than the space elevator does anyone have any ideas for a method to return from orbit that would not involved the need for extensive heat shielding and the vehicle resembling a falling asteroid or comet.<br /><br />My reason for asking is I find it doubtful that the average passenger would be willing to place him/her self in such a situation.<br /><br />To me anti-gravity if it is possible could be a way to avoid a firey re-entry. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[jimfromnsf]

Yes, a rocket as large as the one that put the spacecraft into orbit. If the earth had no atmosphere like the moon, then the only way to land would be like the Apollo Lunar Module. Due to earth's higher gravity. The same amount of fuel would be needed to land. Therefore the same size rocket is needed to reduce the energy of the orbit. <br /><br />Current spacecraft returning from orbit use the atmosphere to reduce the speed and dissipate the orbital energy. This actually is a very efficent method and the weight of the heat shield is small compared to the propellant needed.<br /> <br />The average passenger is going to have to handle reentry for the next few decades.

 

[MannyPim]

The only one that occurs to me off hand is the Airship TO Orbit (ATO) technology being developed by JP Aerospace.<br /><br />Link: http://www.jpaerospace.com/<br /><br />However, this approach requires about 5 days to achieve orbit, which I presume means about the same amount of time to de-orbit. <div class="Discussion_UserSignature"> <font size="2" color="#0000ff"><em>The only way to know what is possible is to attempt the impossible.</em></font> </div>

 

[j05h]

<i>> Other than the space elevator does anyone have any ideas for a method to return from orbit that would not involved the need for extensive heat shielding and the vehicle resembling a falling asteroid or comet. </i><br /><br />Heatshields are here to stay for a while, space elevators and anti-Grav are not really on the horizon. Whether capsule or putative space plane, some kind of thermal protection is needed. How to improve the experience? One option for reusability is transparational cooling and metal or ceramic heatshield. For lowering crew G-loading there has been research (ARD, etc) into ballutes and hypersonic drogue shoots. <br /><br />There is nothing wrong with a base-first capsule, indeed plenty of safety and reliability are their forte'. The real question for passenger space travel is how comfortable, functional and how good the view is from your capsule. Except for SpaceDev's DreamChaser, all orbital craft on the drawing boards now are base-first capsules.<br /><br />What we need, product-wise are spacecraft that are simple for passengers (especially training time), have simple ground/landing procedures and multiple uses on-orbit (LEO, L1, Lunar, etc). Anyone rich/determined enough to get to orbit will put up with 2.5 - 4 Gs during reentry - there is already a proven market for similar Soyuz flights.<br /><br />Anti-gravity may not be possible, but there are other options. Laser-launch has been tested and could be used for supporting deorbit theoretically. Micromachined surfaces could eventually function as both heatshield and engine, using nanochanneling and various propellants. It would require loading some propellant on orbit, but would allow a DC-X type burn for landing.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[kelvinzero]

Cheaper fuel in orbit is probably the most obvious option, so that you can deaccelerate using engines rather than air. This could come from<li>a cheaper launch method<li>luna resources especially oxygen<li>That orbital atmosphere gatherer idea we were kicking around a while ago.<br /><br />Another more extravagant one that I like is an orbital ring that could accelerate or deacellerate craft to orbital velocity. That cant happen until we have a truely massive space industry though.</li></li></li>

 

[spacefire]

ballute reentry!<br /><br /><br />http://www.andrews-space.com/content-main.php?subsection=MTA0 <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[docm]

Beat me to it!<br /><br />GMTA <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> </div>

 

[thereiwas]

Bill Stone in his TED talk proposed using something like this to decelerate fuel tankers coming back from the moon to LEO speed. The drawing he showed did not look like this ballute, but more like an inverted umbrella.

 

[j05h]

Spacefire's link is a 'full body' ballute. Biggest advantage, IMHO, is it allows a very small cross-section for the main heatshield. Potentially it allows an all-fabric heatshield. <br /><br />The "inverted umbrella" is probably a hypersonic drogue chute. Did it trail behind the returning craft? <br /><br />How about this for low-G, weird reentry: a trailing drogue deployed in space that has a power-generating function (it spins?) that powers a plasma sheath around the craft. The Russians experimented with using plasma to reduce drag on aircraft, could it be charged the other way to generate more drag? Something like this might make spaceplanes more feasible since the main reentry hardware could be an antenna on one end and drogue on other. Then there is the massive power exchanger... and a million other details. <br /><br />Focusing on making reentry safe, comfortable and routine is more important than pursuing entirely new methods of spaceflight. If there is a breakthrough (quantum teleportation or space elevator or whatever) then that's golden. In the mean time making next-gen capsules work is very important.<br /><br />It could go opposite to what the original post suggested: go with modern, sharp-edge high-temperature ceramics and "knife" through the atmosphere. This would mean higher-Gs for much shorter periods and probably is not something for passengers. <br /><br />I don't understand his fear of reentry? Both Shuttle and Soyuz are safe enough and there is no indication of anything less safe on the horizon.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[thereiwas]

No it wasn't trailing behind. It was in front, curved side forward. It was *very* much larger than the cargo, which was in tanks in the center. The curved aeroshell was drawn with stiffening ribs inside, very much like an umbrella.<br /><br />He wasn't trying to do a reentry with it - just kill off enough lunar-return velocity to get the cargo into LEO to resupply the orbiting fuel depot.

 

[thereiwas]

I grabbed a shot from the TED video.

 

[tomnackid]

Assumming we don't have nuclear powered spacecraft taking off and landing slowly on their tails anytime soon (Although I wouldn't completely discount that. The Air Force was doing some pretty heavy research on antimatter propulsion before it went black.) the only viable alternative for a manned re-entry vehicle is probably a wave rider type design. A wave rider generates lift at hypersonic speeds by compressing its own shockwave. The shuttle uses some principles of the wave rider durring reentry. The Valkerie supersonic bomber was designed to make use of this principle as well. Theoretically a wave rider could fly from orbital velocity all the way to subsonic speeds and not ever have to drop like a brick the way the shuttle does. Heat sheilding is still a problem. It would probably require super heat resistant ceramics that are still light or an active cooling system.

 

[spacefire]

I always was intrigued by the idea of using the charge of a plasma field around the reentrering craft to reduce heat load by charging the skin of the ship with the same polarity... <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[jimfromnsf]

Plasma has no net charge. Unworkable

 

[kelvinzero]

Ive got no idea if that is workable, but I just wanted to comment that while plasma may have no charge, Im guessing it is the positive ions that carry most of the momentum, so a positive charge could push against that.<br /><br />Also, a magnetic field could be useful at least in principle because the plasma is moving in a fairly uniform direction. You could compare this to the magnetic sail principle, or alternatively an MHD generator that generates electricity from the plasma streaming past, thus also generating drag. This power could be used to shunt the plasma around the craft to begin with, either magnetically or with an air spike

 

[j05h]

That "Umbrella" is really interesting. It looks kind of heavy if those are metal arms holding it open. The net effect is that same as "torus" or donut shaped ballutes. Should be workable one way or another. The idea of using it to aerobrake into LEO is very smart. <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[thereiwas]

The circular ribs might be inflated, with only the radial arms being rigid metal. The larger it is, the lighter it can be (per square meter of surface). Hard to tell what the scale is.

 

[vulture2]

It's entirely possible that large-area low-thermal-load heatshields may prove to be the best approach, but this wil require some actual test flights. <br /><br />The first and simplest way of keeping the heat away from an entry vehicle is a very blunt leading surface that produces a strong but completely detached shockwave that remains ahead of the vehicle and carries away much of the kinetic energy before it reaches the skin. This was the genius of the Mercury designers; after decades of always striving to reduce drag, the capsule was designed to re-enter backwards, blunt end first. Except for the Shuttle, which needed higher lift, almost all entry vehicles have used this method since. The Apollo capsules entered at 11km/sec, considerably faster than the Shuttle, with a heatshield of simple ceramic-filled honeycomb construction.

 

[thereiwas]

The counterintuitive discovery that a blunt shape worked best was made in 1952 by by H. Julian Allen and A. J. Eggers of NACA.<br /><br /><font color="yellow">From simple engineering principles, Allen and Eggers showed that the heat load experienced by an entry vehicle was inversely proportional to the drag coefficient, i.e. the greater the drag, the less the heat load. Through making the reentry vehicle blunt, the shock wave and heated shock layer were pushed forward, away from the vehicle's outer wall. Since most of the hot gases were not in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere.</font> <br /><br />The umbrella just takes this to an extreme.

 

[louiswu]

A variant on the space elevator is the rotating tether. This has a number of advantages over an elevator in that it is shorter, doesn't have to contend with the atmosphere and gets payload to orbital velocity quickly because it uses momentum exchange rather than requiring the payload to crawl up the cable.<br />Many articles on the subject refer to electric propulsion for enabling the system to regain the energy lost when accelerating payloads to orbit, but by using the system in reverse, any vehicle wishing to de-orbit would usefully transfer its unwanted momentum back to the tether. The decelerated vehicle would then be able to free-fall the rest of the way to the atmosphere resulting in a re-entry speed of around Mach 3.

 

[MeteorWayne]

Not sure what you mean by a rotating tether. Can you explain it? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bitbanger]

This site does a good job of explaining the concept.<br /><br />http://www.tethers.com/OrbitToOrbit.html

 

[MeteorWayne]

Thanx. Interesting concept. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>