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Valkyrie B-70

That's B-70 Valkyrie carrying the X-15. What private space is trying to accomplish, was done in the 60's. In fact, The X-15 remains the fastest and highest flying manned aircraft ever flown.

What happened? Both were cancelled, but data from tests made by the X-15 were used for the shuttle, while the ones from the B-70 helped to bridge the gap between supersonic and hypersonic travel.

Was this approach capable of reaching orbital flight? was the project cancelled because of technical hurdles, or simply it was deemed to expensive, compared to rockets?

More info about X-15: http://www.aerospaceweb.org/aircraft/research/x15/ More info about B-70 Valkyrie: http://www.aerospaceweb.org/aircraft/research/xb70/

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    $\begingroup$ That's an amazing picture. Was the X-15 ever launched from a B-70? If so, was a supersonic release ever contemplated/attempted? $\endgroup$ – Anthony X Nov 18 '14 at 0:59
  • $\begingroup$ Lurscher - I was under the impression that the Valkyrie wasn't used much in the X-15 program, but that the X-15 was more often dropped from, say, a B-52. $\endgroup$ – HDE 226868 Nov 18 '14 at 1:06
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    $\begingroup$ The B-70 never launched the X-15. They studied it but it went no further. That picture (although cool) is computer graphics. $\endgroup$ – GdD Nov 18 '14 at 9:08
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    $\begingroup$ And given what happened with the M-21/D-21 project, that looks like a good way to lose another B-70. $\endgroup$ – Russell Borogove Nov 18 '14 at 14:33
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    $\begingroup$ That picture also shows a never-flown delta wing config of the X-15. $\endgroup$ – Organic Marble Aug 22 '17 at 14:15
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Mach 6 buys you roughly 1.8 km/s at those altitudes. OK, let's say that X-15 reached 2 km/s for good measure. But at that speed, Newton still works against you and you're not going to perpetually miss the Earth because of carrying so much momentum in the velocity vector that you're effectively free-falling in a circle around it. To achieve orbital speed you need to go roughly 7.5 km/s (about Mach 25).

But at the altitude that you still gain any aerodynamic lift, and where such a lifting body design still comes useful, your orbit is also going to decay rather fast, and need I say your airframe is probably melting by now if you're still in denser, lower atmosphere below the Kármán line (100 km or 62 mi). So you also have to climb fast and then circularize, at which point aerodynamics don't do anything for it any more, but relatively large aerodynamic surfaces of your lifting body will increase the surface area exposed to atmospheric heating on reentry that you need to somehow protect with a heat shield, if you want to also return from orbit.

That's how these experimental airplanes helped the development of Space Shuttle Orbiter (SSO) - the reusable, lifting body part of the Space Transportation System (STS). They helped establish limitations of then on the cusp materials science and propulsion technologies, dynamic pressure on the body at rapid acceleration through lower atmosphere, and so on, and some of those findings were used to design the SSO while also helped dismiss failed, infeasible ideas so it ended up being relatively safe and reliable.

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  • $\begingroup$ Although the X-15 was not capable of achieving orbit, wasn't the X-15 program conceived as part of a longer-term runway-to-orbit goal? Seems to me I read somewhere (or saw on some documentary program) some factoid that when the X-15 was conceived, the long-term goal was to get to space from a runway. While the X-15 wasn't designed or expected to meet this goal itself, the idea was that an eventual successor would. The space race forced NASA to "get there quicker", so the path X-15 was on was shelved in favor of rocketry which was demonstrating faster progress. $\endgroup$ – Anthony X Jul 7 '19 at 14:30
  • $\begingroup$ To put my above comment another way, it was my understanding that the X-15 was part of an overall effort to get to space via aviation rather than rocketry, and it was only when rocketry was already putting things (and people) in orbit that the aviation effort was shelved as being too slow and expensive to meet the challenges of the space race. The X-15 program provided a wealth of data put to good use elsewhere, but the program's primary motivation was about getting to space via aviation. $\endgroup$ – Anthony X Jul 7 '19 at 16:00
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Was the X-15 capable of reaching orbit? Not on its own (it only carried enough fuel to reach 4500 mph), but with extra fuel tanks or a booster rocket, it could.

Was the X-15 capable of returning from orbit? Unambiguously not. The X-15 required an ablative heat-shield coating to reach the aforementioned 4500 mph; given the materials science of the time, there was no way of shielding an aircraft of its shape against the heat of re-entry.

(Incidentally, your picture is probably a CG render or other artist's conception: the carried aircraft is emphatically not an X-15. The wings are entirely wrong.)

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    $\begingroup$ "...but with extra fuel tanks or a booster rocket, it could." Do you mean all it needed was extra fuel tanks, and it could reach orbital velocity? It would be carrying these tanks the whole time? $\endgroup$ – uhoh Aug 22 '17 at 12:59
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    $\begingroup$ It's a proposed follow-on X-15 variant, but yeah, never built or flown. $\endgroup$ – Organic Marble Aug 22 '17 at 14:16
  • $\begingroup$ It is not a matter of more fuel and extra tanks, to reach a true orbit, two stages are needed. $\endgroup$ – Uwe Aug 23 '17 at 10:20
  • $\begingroup$ @Uwe, staging is only required for efficiency. I suspect you're thinking of the fact that you need two burns to reach orbit: the initial burn to raise your apogee out of the atmosphere, and an apogee burn to raise your perigee, but you can do that with just a single re-startable engine. $\endgroup$ – Mark Aug 29 '17 at 0:43
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As @TildalWave notes, the X-15 had nothing close to orbital capability, and wasn't intended to. There was some early consideration of putting an X-15 on top of a SM-64 Navaho missile, but NASA went with Project Mercury instead.

X-15's big successes were in developing the technology and techniques for transition between aerodynamic control and reaction control and back. In this, it was very successful, and lessons learned on the X-15 were applied most directly to the Space Shuttle.

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There was a program called the X15B that would launch using a Titan Booster to make one orbit in 1959.

From Wikipedia's North American X-15; Operational history:

Before 1958, United States Air Force (USAF) and NACA officials discussed an orbital X-15 spaceplane, the X-15B that would launch into outer space from atop an SM-64 Navaho missile. This was canceled when the NACA became NASA and adopted Project Mercury instead.

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  • $\begingroup$ Hi @AnthonyCipoletta and Welcome to Space! If you would like to take a minute to expand a bit on this, possibly include another supporting link (I've added one already), then that would be great. Have a look at astronautix.com/x/x-15b.html for example. $\endgroup$ – uhoh Jul 7 '19 at 14:13

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