The Pegasus XL attached to the L-1011 | Photo: NASA Kennedy, CC BY-SA 2.0
Back on December 15, Orbital ATK launched eight small satellites for NASA. But the way they did it — while not new — is still pretty unusual, so I thought I’d take a moment to (re)introduce you to the Pegasus XL.
One of the big problems of getting things into orbit is mass — the mass of the satellites, yes, but also of the rockets to carry them and the fuel to lift them (not to mention the fuel to send them sideways so fast they miss the Earth when they fall). So for decades scientists and engineers thought of ways to lower that mass, and one of them is called “air launch to orbit.”
The idea is simple (even if the technology is not): launch a big plane to carry your rocket as high as it can go before launching. That way you ditch the fuel requirements for (if you’re lucky) the first 40,000 feet (roughly 7.5 miles) of vertical lift, and the fuel requirements to lift the fuel required to get up those 40,000 feet. It also gives you some forward momentum, so you spend at least a little less fuel getting up to that “miss the Earth” sideways speed.
That’s exactly what Orbital ATK’s Pegasus XL does, and has done since 1990. A plane that looks like a jumbo jet, called the Stargazer L-1011, carries the three-stage Pegasus rocket up as high as it can go, and then drops it. Five seconds later its rocket kicks in and its forward momentum (along with a small delta wing) lift it up into low Earth orbit, just like it did on December 15 of this year.
Now this used to be the most economical way to get small satellites into orbit — the total payload is a little smaller than your average orbital rocket because of the weight constraints of the L-1011 — but that’s starting to change. The Pegasus can take 443kg (977 lbs) to LEO for $56.3 million per launch. SpaceX’s Falcon 9 is currently $62 million per launch, and can carry 22,800kg (50,300 lbs) to LEO. To top it off, that SpaceX price is soon to go down: with full reusability of just the first stage, apparently SpaceX officials are on the record as hoping they can get the price down to around $18 million per launch.
That doesn’t mean air launch is going away anytime soon. Virgin Galactic’s White Knight Two / SpaceShipTwo (including VSS Unity) combo is an air launch system, though they don’t go to orbit, only to the edge of space and back. But the cost-to-orbit of the Pegasus XL may make it less feasible once reusability becomes a serious factor in orbital launch pricing schemes.
In the meantime, though, it’s a pretty cool thing to watch.
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Richard Ford Burley is a human, writer, and doctoral candidate at Boston College, as well as Deputy Managing Editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and futurism here at This Week In Tomorrow.