The sky’s the limit

Since first coming across the concept a couple of years ago, I’ve felt that air-launching rockets is a pretty cool idea. Put basically, you chuck a launch vehicle out of the back of an aircraft at high altitude.

This gives a number of benefits. For a start, the rocket is already partway to orbit. Also, should the engines not fire, for whatever reason, then out pops a parachute and the payload can safely return to earth. Not to mention the fact that the actual launch can take place anywhere the carrier aircraft can reach, and so is not constrained by local weather conditions or the orbits reachable from fixed launch sites. And should anything catastrophic occur during launch, then it all happens miles away from anyone.

Unfortunately, the system is constrained by the weight that can be lifted by the carrier aircraft. The Antonov An-225 Mriya is the world’s heaviest aircraft and can carry up to 250,000 kg of cargo. The Saturn 1B launch vehicle weighs more than that double that… without payload. The Ariane 5 rocket weighs 777,000 kg and the Soyuz-2 weighs 305,000 kg. Of course, any rocket designed for air launch would not need as many stages, and so would be somewhat lighter. But no one had ever gone as far as to actually design build such a rocket…

But now they might.

Paul G Allen of Microsoft fame and Burt Rutan of Scaled Composites have just announced a new venture, Stratolaunch Systems, which aims to do just that. They plan to build a huge carrier aircraft, powered by six Boeing 747 turbofans, which will be able to lift a a specially-designed SpaceX booster which will launch at high altitude.

Given the expense and difficulties of getting to orbit, a move into space in any kind of useful numbers is unlikely in the near to medium future. An orbital elevator would certainly make travel to orbit both cheaper and easier, but construction of one is well beyond our present capabilities – or companies’ abilities or willingness to invest. An air-launch system could be an excellent interim system. It might actually be the system that makes the commercial space transportation sector a very real alternative to national and transnational space agencies.

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2 Comments

Filed under space travel

2 responses to “The sky’s the limit

  1. You know, Ian, back in the 50s, there were any number of balloon-launched rockets, designed to get upper-atmosphere data. I wonder why the designers of the world never hybridized the concept: the dirigible-launched rocket. Build the dirigible large enough, and you can lift some amazing loads. They don’t have to be cigars, either. Why not build a dirigible in a flying wing shape and push it at 60mph? Or better yet, heat the helium to gain even more lift. Sure, you’re not going 500mph when the rocket gets cut loose, but that’s only a couple dozen seconds under full thrust.

    I of the firm belief that NASA should transition to become the FAA of space (for the US). Instead of building rockets themselves, merely police the would-be entrepreneurs so that Goddard’s rockets don’t crash into the neighbor’s gardens.

  2. Sam Kepfield

    Weird; I just penned a story that uses this very concept — take a probe to the edge of space with a balloon, release it, and send the probe on its way. The probe, by the way, is sent on an asteroid mission. It seems a pretty cheap way to get to space.

    And I think bill’s right on — maybe NASA will become an administrative agency overseeing commercial launches someday.

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