Rockets of Today


Orbital ATK wants to play with the big boys, promising a rocket in a size class comparable to a Falcon or Vulcan... with a solid booster. They plan to start with a shorter first stage and then make a taller “XL” version. The booster motor would be called a Castor 600, and the later version could use a Castor 1200, which would be about double the length. (The number of a Castor motor roughly indicates its weight in thousands of pounds.) These are based on the old Space Shuttle solid boosters, but with modernized materials — a development which comes out of the NASA SLS program, which needs these giant motors as side boosters for its hydrogen-burning core stage, just as the shuttle did. The 1200 is a full-sized remake of the Shuttle booster, and the 600 is similar but with about half the length. What I don’t know is whether it has half the thrust, or full thrust for half the time, or something in between — they haven’t released the specs.

Speaking of side boosters, when extra lift is needed this rocket would use the same “GEM” strap-ons that Orbital sells to ULA for the Atlas and Delta. The last plans they’ve announced are to use a minimum of two and a maximum of six GEMs. I would think that using none ought to be perfectly feasible, but for some reason that’s not being included as an option. Maybe the 600 needs them but the 1200 won’t, I don’t know.

Ares I and V

Actually this came not from the SLS program, but from the Ares/Constellation program which preceded it. That program called not just for a big Ares V (which was cheapened down a bit to become the SLS), but also a midsized Ares I, which would use the V’s big strap-on as the first stage. Atop this solid booster they planned to perch a comically oversized hydrogen-burning second stage, which would have essentially been a revival of the S-IVB third stage of the Apollo, with a remade “J-2X” version of the old engine. This stage was almost twice the diameter of the booster they planned to put under it. The name “Potato Masher” has been heard among those working on this idea.

The Ares I was intended for carrying Orion crew capsules! The big solid booster housing was meant to be reusable, as the Shuttle’s had been. This advanced far enough for a prototype to take a low altitude test flight in 2009, with a dummy second stage. This version of the solid booster was taller than the original Shuttle version — it would be a Castor 1500 in the modern nomenclature, but it had the old segmented steel body instead of the single piece carbon fiber casing they want to use now. They are also changing the binding agent from the polybutadiene acrylonitrile (PBAN) used by the shuttle to the cheaper HTPB urethane that’s used in most other solid rockets. (Both versions include aluminum powder in the fuel mix.)

The Ares I program got into increasing difficulty as people started to notice how dangerous it was to put a crew capsule on top of a solid rocket. People working on the capsule escape tower ended up concluding that during at least some parts of the flight, no possible escape rocket could get the capsule away from an exploding booster — they’d be riddled with flaming wreckage before they could get away, unless they used lethal acceleration. I guess they originally figured that if it was good enough for the Space Shuttle it would be good enough for Ares, but in terms of safety, the Shuttle is certainly not a system to emulate, as it has killed more people than all other crewed spacecraft combined. Not only that, but the solid rocket produced such severe vibration that they had to add heavy springs to the upper stage.

The whole Ares/Constellation program turned out to be an expensive boondoggle. It came out of the same Bush/Cheney administration that killed the VentureStar, which would have been far more cost-effective for low orbit work, and far more innovative, if we had just stuck to it and worked through the many technical challenges, some of which have since been solved in other contexts.

this test did not end well

When Ares I was cancelled, Orbital (or Alliant, as it was known before the merger) proposed a private version of it which they dubbed the Liberty (though internally they just called it “the stick”), with the core stage of an Ariane 5 now being used as the second stage. NASA twice declined to help fund this, so Orbital “moved on” and focused on the Antares. But the design came back to life, though reduced in height... because after all, their manufacturing facility for these giant motors is just sitting there largely unused. They got some backing from the Air Force this time. So they’ve replaced the single large solid booster with two smaller ones, the second being a Castor 300, for some extra push to compensate for the initial Castor 600 first stage being so much shorter than the Liberty’s. The XL version will perch the 300 on top of a Castor 1200. They’ve dropped all ideas of reuse, as the new lightweight carbon fiber casing can’t recover from the heat as well as the old metal could.

The hydrogen stage will now come third, and be much reduced in size. They originally said it would use a Blue Origin BE-3U engine, but when they finalized the rocket’s name (which has a stylized A and is often capitalized as “OmegA”), they also announced that they’re now going with dual Aerojet Rocketdyne RL10C engines, as used in the high-thrust version of ULA’s Centaur. It would still be wider than the stages under it, as the Liberty’s second stage would have been, but it will now fit inside the large fairing.

The acceleration looks like it could be fairly fierce, if the thrust is similar to what it was on the shuttle. As for the rocket’s overall payload capacity, they’ve announced a target for geostationary orbits but not for low orbit. At least they’re not talking about putting crew capsules on it.

I thought this all sounded like fairly safe conservative technology that wouldn’t need much development, but apparently they have work left to do: in 2019 they test-fired an Omega-labeled Castor 600 booster, and its nozzle ruptured. (Apparently this incident is not seen as reflecting on the older style SLS booster.)

There’s one other question they left unanswered at this point: how they expect this dinosaur to ever be able to compete with reusable rockets. I was not entirely surprised at Orbital losing its independence and being bought out by Northrop Grumman, who might have been interested mainly in their military munitions products. It has since come out that some Orbital/Northrop insiders were telling people that they knew it would never fly.

Northrop did try, submitting the Omega for Air Force contracts against ULA and SpaceX. They (and Blue Origin) were awarded 0% of the launch mission pie. After thinking this over, they concluded that the project would not be financially viable without a government customer, and cancelled it.

OmegA with minimal strap-ons: mass ~450 t?, diam 3.7 m, thrust ~12000 kN?, imp 2.7 km/s?, type S, payload ~10 t?, cost unknown.