Commercial Rockets

ANTARES — USA, 2013

Orbital ATK finally got out of the solid-fuel ghetto by building a kerosene burning twin-engine first stage... except not really, because they subcontracted that part to the Ukrainian company Yuzhnoye/Yuzhmash, who are basically building them a shortened Zenit variant. It uses two RD-181 engines, which are loosely of the same high-performance kerosene burning family as the Zenit’s 171 and the Atlas’s 180, but with single nozzles. The pair is about as powerful as a single 180. The earliest Antareses used old Kuznetsov NK-33 engines which were bought by Aerojet Rocketdyne, refurbished, and sold as the AJ26, but these were not reliable. They were originally built for the N-1, the rocket which was supposed to land cosmonauts on the Moon, but which kept breaking up after launch. In their day they were the best engines in the world, but that was long ago. Orbital ditched them after a turbine failure made an Antares fall back onto its pad and explode. The rockets with the new engines are designated as the “200 series”, with the originals being the “100 series”. The RD-181s are actually overpowered for the size of the rocket, and have to be throttled down to not overstrain the airframe. They hope in the future to strengthen it so they can use the extra 340 kilonewtons of available thrust. (But first they’d better hope for this rocket to have any future at all.)

There’s been some talk of maybe replacing the RD-181 engines with a single Blue Origin BE-4, because it doesn’t look much better for Orbital to be buying Russian engines than for ULA to be doing so. The BE-4 should have about 30% more thrust than the RD-181 pair, but it’s not clear how they would compare in cost. A Raptor would probably be a better fit for size, but SpaceX hasn’t yet shown any willingness to sell engines to third parties. They managed to continue Antares flights into 2021 despite the Yuzhmash plant being more or less shut down since the Crimea invasion... whether they can put any more together is an open question.

They still use solid fuel for the second stage — it’s based on the Minotaur’s first stage, but shortened. It’s called the Castor 30, or in the latest re-embiggened version, 30XL. This is skinnier than the booster, so the interstage goes around it rather than under it. They don’t light it up until both the interstage and the fairing are well clear.

The fairing has recently been upgraded with a feature called a “pop top”, which allows the tip of the nose cone to be removed and replaced very easily. This allows perishables to be put into the Cygnus after the rocket is already at the pad, just 24 hours before launch. Using this involves lowering the rocket back to horizontal after it’s been raised for checkout, which means the fuel tanks probably have to be empty.

They have a choice of optional third stages: two sizes of solid motor for high but imprecise orbits, and a little monopropellant one for tuning lower orbits accurately. (They used to have a hypergolic one in this role.) But no customer has yet taken any of these options. The rocket’s only use has been to deliver cargo flights to the space station in their Cygnus freight capsule (though these missions do allow other satellites to piggyback as ride shares). This doesn’t need a third stage because the Cygnus has a service module with its own propulsion. They recently signed up with NASA for a second batch of Cygnus flights to the space station, and this time they say the price they asked is lower than SpaceX’s... though I don’t see anybody showing any numbers to back this up. As yet, nobody else has paid for an Antares flight, which would be very strange if the price were really that affordable.

During times of hiatus, three Cygnus canisters ended up being launched on Atlases, which probably made them more expensive. These did have a higher weight capacity, but they are now doing heavier loads on the Antares itself.

The rocket was originally called the Taurus II, but that name got some bad branding juju thanks to launch failures, so the II became the Antares and the original Taurus became the Minotaur-C.

Antares-230: mass 298 t, diam 3.9 m, thrust 3850 kN, imp 3.3 km/s, type ZOk, payload 6.1 t (2.0%), cost $13M/t?, record 13/1/1.
Stage name Antares (200+) Castor 30XL OAM * Star 48BV Orion 38
Role (pos) count core (1) upper (2) kick (3), opt kick (3), opt kick (3), opt
Diameter (m)   3.90   3.90   1.24   0.97
Liftoff mass (t) 261    26.4  2.2  0.9
Empty mass (t) 20.3  1.5  0.2  0.1
Fuel mass (t) ~67    ~7.5  1.2 ~0.6 ~0.2
Oxidizer mass (t) ~174     ~17.4  ~1.4 ~0.6
Fuel type kerosene HTPB+aluminum hydrazine * HTPB+aluminum HTPB+aluminum
Engine Energomash
RD-181 ×2
Castor 30XL REA ×8 * Star 48BV Orion 38
Power cycle staged (ZO) solid pressure-fed solid solid
Chamber pres. (bar) 258   
Ox./fuel ratio   2.60
Thrust, vac max (kN) 2085     533     1.6 78   36.9
Thrust, SL initial (kN) 1922    
Spec. imp, vac (km/s)   3.30   2.90  2.1?   2.82   2.82
Total imp, vac (t·km/s) 8801    72   ~2.5  5.8  2.1