Minotaur IV

Minotaur IV was developed by Orbital Sciences — now part of Northrop Grumman — under the US Air Force's Orbital Suborbital Program. The starting point was the LGM-118 Peacekeeper, an intercontinental ballistic missile deployed from 1985 until 2005 whose solid motors became available once the weapon was withdrawn. The launcher's first three stages are literally those motors: the SR-118 delivers 2,224 kN over 56.6 seconds, the SR-119 provides 1,223 kN for 61 seconds, and the SR-120 burns for 72 seconds at an average thrust of 289 kN. All three have thrust vector control, and the second and third also feature extendable nozzles.

Several variants branch off that common trunk. The standard Minotaur IV adds an Orion 38 fourth stage — the same motor used on Pegasus, Minotaur I and Minotaur-C — which performs final orbital insertion. Minotaur IV+ replaces it with a Star 48BV carrying more propellant and offering thrust vectoring, uncommon in that motor series. Minotaur IV Lite drops the fourth stage and flies suborbital trajectories. The same trunk also yielded Minotaur V, with an extra Star 37FM stage for high-energy trajectories, and the Minotaur VI and VI+ concepts, which have never flown.

The first lift-off took place on 22 April 2010 from SLC-8 at Vandenberg, in IV Lite configuration carrying the HTV-2a hypersonic vehicle: the launch itself worked, though the payload failed. The first orbital flight followed on 26 September 2010 with the Space Based Space Surveillance satellite for the Air Force. The STP-S26 mission of 20 November 2010, flown from Kodiak, deployed eight payloads and debuted the Hydrazine Auxiliary Propulsion System, which raised its orbit from 650 to 1,200 kilometres. For the ORS-5 mission in 2017 the rocket exceptionally flew with five stages, adding a second Orion 38 to reach an equatorial orbit. To date it has accumulated nine launches and nine successes, the most recent on 7 April 2026 with the STP-S29A mission from Vandenberg.