Commercial Rockets

PEGASUS (and STRATOLAUNCH) — USA, 1990

We now come to the first orbital launch rocket developed from scratch as a purely private commercial venture. Orbital Sciences Corporation was founded in 1982 and merged with Alliant Techsystems in 2006 to form Orbital ATK. Orbital is just one of many military and aerospace outfits borged by Alliant; they make lots of military gear, and were America’s leading manufacturer of bullets under numerous brand names, until they spun off their consumer-products branch as Vista Outdoor in 2015. Their run of acquisitions is at an end, though: they’ve now been absorbed by Northrop Grumman.

The important part is that one of these Alliant companies was Thiokol, which had long been America’s premier maker of big solid rocket boosters, and another was Hercules Aerospace. It was the latter which originally developed the small Orion rocket motors used to make the Pegasus. Orbital Sciences wanted to put up some satellites, and a partnership was born. And they soon got a lot of interest in a rocket that could replace the Scout — America’s best option for small cheap launches since 1961, which retired in 1994.

Orbital Sciences’ first satellite carrier was the Pegasus, a small torpedo-like device launched from under an airplane. It has three solid-fuel stages, and a fourth stage can be added for precise orbital insertion. This kick stage uses monopropellant: plain hydrazine, N2H4, which is broken down into gases by an iridium catalyst. This isn’t powerful, but it is simple and compact, making it popular for small thrusters, especially in situations where a satellite or probe has to retain a reserve capacity for several years.

The first stage steers using wings and a tail, while the second has vectorable thrust despite using solid fuel. They inject stuff on one side or another of the combustion chamber — extra oxidizer, I think — which steers the rocket by making its flame asymmetrical. It then coasts up to space before firing the third stage. In 1994 they lengthened it to raise performance, as the original Peg could lift only a quarter ton. The newer one is called the Pegasus XL. Launch prices have been offered as low as $6 million, but that’s for very barebones service — it’s the extra charges that get ya. And prices have gone up. Apparently it’s gotten rare to get away from the Pegasus dealership without spending $40 million or more.

A company called Stratolaunch Systems, which was owned by the late Paul Allen, has built a plane with the world’s widest wingspan, for the sole purpose of launching Pegasi from under it. The intent was to make a larger Pegasus model which would be able to launch a ton or more, but Orbital apparently backed out of that, so Stratolaunch was hoping to interest somebody else in making a heavier air-launched rocket. With small Pegasi, the plane can take up three of them at a time... but that’s a limitation of size, not weight: if a new rocket were designed for Stratolaunch, they say it could weigh up to 200 tons. Maybe then it’ll pay off; unfortunately, it turns out that running a big unique plane like that has costs that are comparable to those of using an expendable booster stages to get small rockets through the lower atmosphere. Below a certain size of rocket, it may not even break even. SpaceX was at one point going to build a suitable air-launched rocket with four Merlin engines, but they concluded that the airborne approach wasn’t worth the trouble, and pulled out. The Stratolaunch people have recently publicized some vague plans for a new midsized air-launched rocket that their plane will carry, but in early 2019 they gave up the idea, halting all in-house efforts to design a new rocket.

The Pegasus XL semi-retired in 2008. It came back in 2012, but only for very occasional use. Orbital insists that they are not retiring it, even if demand remains low because of the price increases... but given how many new small launchers are coming onto the market and promising far lower prices, it’s hard to imagine the Peg making any sort of comeback. Especially not now that the current owners of Stratolaunch just put the whole outfit up for sale, and Richard Branson offered $1 for the plane. Somebody bought it anonymously; it turned out to be a group led by billionaire Steve Feinberg. The plane has been called the spruce goose of our time.

Stratolaunch seemed dead, but new owners are now hiring. Their new long term plan is to build a small hypersonic rocket-plane to be carried by the big plane, and piggyback rockets on that — an idea that had been shelved by the old owners. (But they’ll start with a tiny payloadless hypersonic plane, to be called Talon-A, before building something bigger.) Boeing just gave up on the Phantom Xpress project as apparently not workable within a reasonable budget, but I think the basic idea of using a rocket-plane as a booster stage is still sound, so if they can get through the short term I think this might work well.

The one thing the Pegasus offered that other competitors did not was the ability to launch small satellites from the equator into orbits with zero inclination. But then SpaceX announced that they could do such orbits from Florida at a price no higher than the Pegasus; by putting a small sat onto a large second stage, they had enough delta-V to correct the orbital plane. This may indicate that SpaceX’s profit margins now have room for further cutting, should any of their competitors catch up on price. Then Virgin Orbit demonstrated that their cheaper air-launched rocket. This, according to industry observers, probably means the Pegasus is now dead, Stratolaunch or no Stratolaunch. But after they said that, the Peg did get one more military launch job in 2021. This was apparently done with a surplus rocket which had been built for Stratolaunch, and was discounted accordingly. One more surplus Peg is said to be available.

Respect where it’s due: the Pegasus may now be obsolete, but it was the first of a new breed. In fact, you could say it’s the first of two new breeds at once — one being air-launched orbital rockets, and the second being purely commercial rockets developed without any government funding. Like the Space Shuttle, it’s too expensive because it was ahead of its time.

Pegasus XL: mass 23.1 t, diam 1.3 m, thrust 560 kN, imp 2.8 km/s, type S, payload 0.44 t (1.9%), cost $25-$125M/t, record 41/0/4 (may be final).