Antares (rocket)

Antares (), known during early development as Taurus II, is an American expendable medium-lift launch vehicle developed by Orbital Sciences Corporation with financial support from NASA under the Commercial Orbital Transportation Services (COTS) program awarded in February 2008. It was developed alongside Orbital's automated cargo spacecraft, Cygnus, which also received COTS funding. Like other Orbital launch vehicles, Antares leveraged lower-cost, off-the-shelf parts and designs. Since 2018, the rocket has been manufactured by Northrop Grumman.

The first stage is liquid fueled, burning RP-1 (kerosene) and liquid oxygen (LOX). As Orbital had limited experience with large liquid stages, construction was subcontracted for all versions of Antares. The 100 and 200 series were built by the Ukrainian companies Pivdenne and Pivdenmash, using refurbished NK-33 engines from the Soviet N1 program on the 100 series and newly built Russian RD-181 engines on the 200 series after the loss of an Antares 130 vehicle in 2014. After Russia's 2022 invasion of Ukraine ended access to these suppliers, Northrop Grumman announced the 300 series, with a first stage developed by Firefly Aerospace based on the company's MLV rocket using composite structures and seven Miranda engines to increase payload capacity.

The second stage is a solid-fuel motor from the Castor 30 family, derived from the Castor 120 used on the Minotaur-C (the original Taurus I) and ultimately from the Peacekeeper ICBM first stage. While an optional third stage is offered, it has never been used, as the Cygnus spacecraft incorporates its own service module for orbital maneuvers.

Antares made its first flight on April 21, 2013, launching the Antares A-ONE mission from Launch Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) with a Cygnus mass simulator. On September 18, 2013, it successfully launched Orb-D1, the first Cygnus mission to rendezvous with the International Space Station (ISS). After completing the two COTS demonstration flights, Antares and Cygnus were awarded two Commercial Resupply Services contracts covering 25 ISS cargo missions.

The COTS program also supported the development of SpaceX's Dragon spacecraft and Falcon 9 rocket, intended to foster a competitive commercial spaceflight industry. Unlike Falcon 9, which has secured a broad commercial launch market, Antares has been used exclusively for NASA cargo missions, with Cygnus as its sole payload.