# Spaceplanes unworkable? **URL:** \ **Category:** Factual Questions\ **Created:** [June 3, 2002, 3:15am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071 "2002-06-03T03:15:19Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [June 3, 2002, 3:15am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/1 "2002-06-03T03:15:19Z")
Can someone clear this up for me? I have read any number of proposals for building transatmospheric aircraft, or “spaceplanes”. These would be air breathing craft capable of hypersonic flight to the fringe of the atmosphere. They would then use pure rocket engines to complete the jump into orbit. Now currently the technology isn’t there to actually build one, since it would require engines with hypersonic airflow. But what about the thermal problem? An aircraft flying at the fringe of the atmosphere at near-orbital velocity would be doing a fair imitation of a meteorite, and not just for the few minutes typical of reentry. Note that I’m not talking about vertical takeoff/horizontal landing winged craft like the Shuttle, but planes that would have to overcome prolonged thermal stress as they accellerate to suborbital speed. Do engineers really think that they can build an airframe that can take this? ---
**Author:** ![Tranquilis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tranquilis/32/3639_2.png) [@Tranquilis](https://boards.straightdope.com/u/Tranquilis)\ **Post date:** [June 3, 2002, 5:26am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/2 "2002-06-03T05:26:39Z")
I’m thinking the issue is more one of money, and hence, practicality, than any insurmountable _physical_ barriers. ---
**Author:** ![Sam\_Stone](https://avatars.discourse-cdn.com/v4/letter/s/ecccb3/32.png) [@Sam\_Stone](https://boards.straightdope.com/u/Sam_Stone)\ **Post date:** [June 3, 2002, 5:36am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/3 "2002-06-03T05:36:20Z")
I don’t believe any of the ‘space plane’ proposals involved actually attaining orbit. The NASP was hypersonic, but just flew a parabolic arc to its destination. Planes like the X-33 were ‘space planes’ in the sense that they went up and came down in one piece, but they went up like a rocket and down like a shuttle. ---
**Author:** ![SPOOFE](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)\ **Post date:** [June 3, 2002, 9:27am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/4 "2002-06-03T09:27:50Z")
Lumpy, are you referring to the recently publicized scramjet system? If I recall correctly, they’re designing it to ultimately attain Mach 7… I think that’s something like 1.5 miles per second. Escape velocity for Earth (and, I’m assuming, the speed at which the Space Shuttle and such fly around Earth after attaining orbit) is about 7 miles per second. So the Scramjet is still a little bit off in that regard. Still, that’s a good deal of friction, but not an inordinate amount for some tough, high-temperature materials to deal with. On the other hand, I may be remembering my numbers wrong. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 3, 2002, 9:41am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/5 "2002-06-03T09:41:41Z")
Nitpick: escape speed is the speed you need to get away from earth completely. You don’t want to do that with your spaceplane. You want just enough speed to get into and stay in orbit, i.e. orbital speed, or 7 km per second (about 4.5 miles per second). About 25 times the speed of sound in air. (I don’t think you can call it Mach 25 since you can’t define sound speed in vacuum) By the way, one of the stated goals of the National Aerospace Plane (NASP, aka X-30) project was to develop a launch vehicle. Actually it was a broad group of projects to develop the necessary technology for hypersonic flight, which can be applied to anything from hypersonic airliners to launch vehicles. The project was terminated in 1994. There have been other “space plane” projects, like the X-33 and HOTOL, which used conventional rocket engines. (Or tried to - none of the projects actually produced a spaceworthy vehicle.) ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 3, 2002, 2:10pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/6 "2002-06-03T14:10:56Z")
> [@](#): > > \*Originally posted by Tranquilis \* > \*\*I’m thinking the issue is more one of money, and hence, practicality, than any insurmountable _physical_ barriers. \*\* I think this is correct. I believe if we _really_ wanted to we could probably build a spaceplane today. What is stopping them is the economics. No one is going to bother with the hideously expensive development costs unless they see the spaceplane as being in any way practical. BTW, I remeber recently hearing about some spaceplane design that didn’t use rocket engines at all. Instead it used it scramjets to loft itself into orbit where they’d be turned off. The plane would eventually descend back into the atmosphere where the scramjets would restart and give another boost back into space. The plane would bascially skip along the upper atmosphere in this fashion till it wanted to come down (IIRC a flight from New York to Tokyo would require 7 such skips). The up side to this whole plan is you don’t need the additional expensive, heavy and complex rocket engines carried with you (not to mention the highly volatile fuel they use). The downside might be that it’d make for a rough ride that passengers wouldn’t enjoy. Anyone have any idea what I’m talking about or did I dream it? ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [June 3, 2002, 3:11pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/7 "2002-06-03T15:11:24Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\*Nitpick: escape speed is the speed you need to get away from earth completely. You don’t want to do that with your spaceplane. You want just enough speed to get into and stay in orbit, i.e. orbital speed, or 7 km per second (about 4.5 miles per second). About 25 times the speed of sound in air. (I don’t think you can call it Mach 25 since you can’t define sound speed in vacuum) > \*\* [hijack] I remember on my old Commodore 64 I had some space-shuttle “sim” and it actually had velocity given in Mach… I seem to recall orbiting at about Mach 24 or something like that. [/hijack] ---
**Author:** ![micco](https://avatars.discourse-cdn.com/v4/letter/m/5f8ce5/32.png) [@micco](https://boards.straightdope.com/u/micco)\ **Post date:** [June 3, 2002, 4:58pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/8 "2002-06-03T16:58:29Z")
The thermal problems with hypersonic flight are solvable with current technology. IIRC, the NASP project used a hydrogen slush fuel which was piped through the wing and nacelle leading edges to provide cooling for the craft and preheat for the fuel. As an interesting side note, the problems with high-speed commercial flight are neither technical or economic. The problem is public perception. The “Tokyo Express” high-speed commercial airliner was intended to be a Mach 7 transport but the marketting department decided there were two problems: there was no way to convince Joe Sixpack that the wings were supposed to glow red, and no one wanted to fly from LA to Tokyo so fast they didn’t get an inflight meal. The goal was changed to Mach 3, and the project eventually died on the vine. I don’t have a cite for this, but it comes directly from some consultants who worked on the project so I consider it fairly reliable trivia. ---
**Author:** ![Tranquilis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tranquilis/32/3639_2.png) [@Tranquilis](https://boards.straightdope.com/u/Tranquilis)\ **Post date:** [June 3, 2002, 6:52pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/9 "2002-06-03T18:52:56Z")
[You’re not dreaming](http://www.geocities.com/pentagon/bunker/3351/germweps/sanger.html), **Whack-a-Mole**. It just wasn’t a _transport_… Check the flight profile chart about a third of the way down [this page](http://www.ufx.org/german/antiplofer.html), left-hand side. > [@](#): > > As the aircraft accelerated and descended under the pull of gravity, it would then hit the denser air at about 40 km (25 miles) and ‘skip’ back up, just like a stone thrown on a lake. The skips would gradually decrease until the aircraft would glide back to a normal landing using its tricycle landing gear, after covering approximately 23500 km (14594 miles). ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 3, 2002, 7:41pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/10 "2002-06-03T19:41:01Z")
> [@](#): > > \*Originally posted by Tranquilis \* > \*\*[You’re not dreaming](http://www.geocities.com/pentagon/bunker/3351/germweps/sanger.html), **Whack-a-Mole**. It just wasn’t a _transport_… Check the flight profile chart about a third of the way down [this page](http://www.ufx.org/german/antiplofer.html), left-hand side. > \*\* That’s pretty cool. I vaguely remember the name Amerika Bomber but I didn’t know it was to be an atmosphere skipper nor did I realize how far along the Germans actually got on that thing. Of course, it seems that plane would be ludicrously expensive to operate and not be much more than a terror weapon. One 8,000 pound bomb isn’t going to seriously cripple any military or economy but the Germans seemed to go in for wild, bleeding edge stuff as well as more down-to-earth (no pun intended) designs. Still, the plane I am thinking of is to be a modern transport complete with scramjets and sans any rocket motors. I’ll see if I can find a cite. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 3, 2002, 9:15pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/11 "2002-06-03T21:15:42Z")
> [@](#): > > One 8,000 pound bomb isn’t going to seriously cripple any military or economy Remember, the Germans also intended to build an atomic bomb, which would presumably have been the payload for such a beastie. Funny, how chasing all of your best scientists out of the country and into your biggest opponent will slow down R&D a tad… ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [June 3, 2002, 9:30pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/12 "2002-06-03T21:30:04Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*Still, the plane I am thinking of is to be a modern transport complete with scramjets and sans any rocket motors. I’ll see if I can find a cite. \*\* Found it! It’s called Hypersoar. Here’s a little piece about it and a link (I did get one thing wrong…they say in the article that a flight from the Midwest to Japan would require 25 ‘skips’). > [@](#): > > [U.S. engineers propose new ``hypersonic’’ aircraft](http://www.beachbrowser.com/Archives/Science-and-Health/June-99/hypersonic.htm#DoE%20Announces%20New%20Hypersonic%20Design) > > The key to HyperSoar is the skipping motion of its flight along the edge of Earth’s atmosphere – much like a rock skipped across water. A HyperSoar aircraft would ascend to approximately 130,000 feet – lofting outside the Earth’s atmosphere – then turn off its engines and coast back to the surface of the atmosphere. There, it would again fire its air-breathing engines and skip back into space. The craft would repeat this process until it reached its destination. > > A commercial flight from the midwestern United States to Japan would require approximately 25 such skips to complete the one-and-a-half-hour journey. The aircraft’s angles of descent and ascent during the skips would only be 5 degrees. Passengers would feel 1.5 times the force of gravity at the bottom of each skip and weightlessness while in space. (1.5 Gs is comparable to the effect felt on a child’s swing, though HyperSoar’s motion would be 100 times slower.) ---
**Author:** ![Tranquilis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tranquilis/32/3639_2.png) [@Tranquilis](https://boards.straightdope.com/u/Tranquilis)\ **Post date:** [June 3, 2002, 9:33pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/13 "2002-06-03T21:33:45Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > **One 8,000 pound bomb isn’t going to seriously cripple any military or economy but the Germans seemed to go in for wild, bleeding edge stuff as well as more down-to-earth (no pun intended) designs.** Remember that the “one bomb” would’ve been landing at _extremely_ high speed. Kinda like a big rock from space… Check the estimated bomb damage plot from the second site I linked to. Even if the Germans were overestimating by 50%, one bomb would’ve done _huge_ damage at the speeds we’re talking about. > [@](#): > > \*\*Still, the plane I am thinking of is to be a modern transport complete with scramjets and sans any rocket motors. I’ll see if I can find a cite. \*\* Probably there was one. I just can’t remember any details at this time… ---
**Author:** ![bernse](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bernse](https://boards.straightdope.com/u/bernse)\ **Post date:** [June 4, 2002, 8:28pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/14 "2002-06-04T20:28:26Z")
> [@](#): > > That’s pretty cool. I vaguely remember the name Amerika Bomber but I didn’t know it was to be an atmosphere skipper They actually built a 6 or 8 engine prop bomber that supposidly made it to less than 10 miles from New York City, called the **Amerika Bomber**. I don’t know of an online cite, but I know it is in a book I have at home on German Wonder-Weapons. I can get the title if anyone is curious. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [June 4, 2002, 10:47pm UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/15 "2002-06-04T22:47:52Z")
> [@](#): > > \*Originally posted by scr4 \* > I don’t think you can call it Mach 25 since you can’t define sound speed in vacuum IIRC Mach 1 is the speed of sound at sea level. it doesn’t matter if there is actually sound to go faster than. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [June 5, 2002, 3:15am UTC](https://boards.straightdope.com/t/spaceplanes-unworkable/112071/16 "2002-06-05T03:15:16Z")
Mach number is measured relative to the speed of sound in the surrounding medium. It’s not just a fancy unit of speed, it’s a useful ratio to know. If you hear a plane is travelling at 700 mph, it could be a sub-sonic flight at high altitude or supersonic flight at low altitude. But if someone tells you the plane is doing Mach 1.1, you know it’s supersonic. Such “dimentionless numbers” (measurements expressed as a ratio to some physical quantity) are often more useful than the actual number. Relative humidity is one exampe.