On Aug. 2, 2023, at 00:31 UTC, an Antares 230+ took off from the launch facility of Wallops Island. It transported the Cygnus cargo spacecraft to low Earth orbit intended to supply the International Space Station.
This is the 18th mission of the Antares launcher, the last of the 230+ versions equipped with the two Russian-made first-stage engines RD-181.
Due to the sanctions imposed after the outbreak of the conflict in Ukraine, the supply of these engines by NPO Energomash has been suspended and those that flew last August 2, were the previous two specimens left.
Liftoff of @NorthropGrumman's #Cygnus cargo craft to replenish the Exp 69 crew with over 8,200 pounds of science and supplies. The space delivery is scheduled for 5:55am ET on Friday. More… https://t.co/oY5WbuB8wh pic.twitter.com/HrKqa6y6p8— International Space Station (@Space_Station) August 2, 2023
The engine that came in from the cold
The story of the Antares medium launcher begins in the early 2000s as an evolution of the project Taurus-II, a study of a launcher capable of carrying 8,000 Kg. into low orbit to resupply the ISS with the Euro-American cargo spacecraft Cygnus.
The first version of the Antares, the 100, was equipped with two closed circuit engines Aerojet AJ-26 whose history is linked to the failure of the Soviet lunar program.
They are nothing but the Kuznetsov NK-33 engines, intended for the final version of the Soviet lunar mega-launcher N-1 which should have been destroyed after the cancellation of the program, but which were daringly saved from destruction.
At the fall of the USSR, a group of engineers from the Kuznetsov design bureau, founded a Joint Venture with US investors called Aerojet.
Those engines, rebadged AJ-26, provided the backbone of the nascent Antares launcher.
In the second stage, however, the Antares uses a solid-fuel Castor 30XL engine derived from ICBM Minotaur.
For the third stage, three different solutions are envisaged, depending on the load: the first using a bi-propellant (BTS) engine, and the others with two different solid fuel rockets: Star-48 and Orion-38.
The engine of the Buran
But the link between the former USSR and the Antares didn’t end there.
Following the failure to launch in October 2014, caused by corrosion and material fatigue phenomena of the remaining AJ-26 engines, it was decided to sign an agreement with the NPO Energomash for the supply of the most modern and powerful (440 kN more than the AJ-26) engine RD-181.
The single-camera version of the closed loop engine RD-170 equipped the launcher Energia famous for bringing the Soviet shuttle Buran into orbit in its all-automatic flight in November 1988. With these new engines, we passed from the 100 series to the 200 and 200+ series.
Unfortunately, the outbreak of the conflict in Ukraine and the consequent sanctions imposed by the US government on Russia caused the import of these engines to stop. Over the years, stocks of these have gradually decreased: the last two RD-181s flew on Aug. 2, 2023.
For the future, a new engine is being developed in cooperation with Firefly Aerospace: Miranda.
This new engine, still in the testing phase, will ensure greater launch power with a thrust of 7,200 kN. However, it is still not possible to predict the date by which the first Antares 300 will be able to be tested in flight.
At present, this determines the halt of the Cygnus program and the loss, albeit temporary, of a valid refueling and additional propulsion system for Progress.
Cygnus cargo ship
The pressurized supply pod Cygnus it’s a Euro-US collaboration made under the Commercial Resupply Services a series of qualified flights from NASA for the replenishment of the International Space Station, which also includes the Dragon and, in the future, the reusable shuttle Dream Chaser.
It consists of a service module, made by Northrop Grumman based on the system GEOStar, and a pressurized section of a 31 m2 based on the ISS module PMM, made by the Italian Thales Alenia.
Equipped with maneuvering motors, Cygnus has demonstrated the ability to use it also to change the altitude and the orientation of ISS effectively becoming an additional instrument to the Russian cargo ship Progress.
The stop of the Antares flights effectively leaves the ISS without an alternative to the supply flights of the Progress and Dragons.