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Are there any intercept jets (that can zoom climb like 1961 April 28 113,891ft Ye-66A Mig-21 Turbojet) built for heavy lift? I see the Stargazer and Stratolaunch as really slow heavy lift vehicles that cannot zoom climb. I saw one article about using an F15E as a rocket lifter. Is it silly to dream of a purpose-built large jet that could carry a large payload (like a Pegasus rocket) and zoom climb to a high altitude (100,000ft) before releasing its heavy rocket payload?

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Zoom climb of the carrier is useless. The rocket can do it alone after release with the same effect and is slightly more aerodynamic as it does not have the large wings of the carrier.

The rocket starts with certain amount of energy upon release. Part of this energy is kinetic, given by speed of the carrier, and part of this energy is potential, given by altitude. Now a zoom climb means exchanging kinetic energy from going fast for potential energy to climb higher. But the total amount of energy does not change. And since the rocket still needs to increase both it's kinetic and it's potential energy (accelerate and climb) it does not really care which form of energy it gets.

Now the orbital vehicle needs energy corresponding to 7.9 km/s and a launch aircraft like the Stargazer can give it perhaps 0.57 km/s (of which only ~0.24 km/s will be speed, the rest is the ~12 km altitude). This is a tiny fraction of what it needs, but:

  • It helps significantly that the rocket does not have to penetrate the thick low atmosphere. At 12 km the pressure is 19% of what it is at sea level. Going higher is not going to help all that much.
  • Due to the rocket equation (the amount of fuel needed is exponential) it can still make significant difference to payload fraction.

What we are likely to see is carriers that can give the orbital vehicle more initial energy. By going faster (like the F-15), by going higher (like the Stratolaunch) or both (using scramjets it to gain some higher hypersonic speed at altitude perhaps 30 km). But they won't do zoom climb, because that does not add any energy and adds complication.

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  • $\begingroup$ Maybe it is not totally useless, if it helps to cut the flying time at high density by shifting the acceleration to higher altitude. The launch profile would be similar to that of a rocket, but now the first stage is airbreathing. $\endgroup$ Dec 8, 2014 at 7:35
  • $\begingroup$ @PeterKämpf: But I don't see any difference between the launcher zooming and the rocket zooming alone just after release from the highest point where the launcher can still sustain flight. The energies involved are the same and the rocket alone should have lower drag (because it can do with smaller wings). $\endgroup$
    – Jan Hudec
    Dec 8, 2014 at 13:03

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