Minotaur IV
Minotaur IV
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Minotaur IV

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Minotaur IV

Minotaur IV, also known as Peacekeeper SLV and OSP-2 PK is an active expendable launch system derived from the retired LGM-118 Peacekeeper ICBM. It is operated by Northrop Grumman Space Systems, and made its maiden flight on 22 April 2010 carrying the HTV-2a Hypersonic Test Vehicle. The first orbital launch occurred on 26 September 2010 with the SBSS satellite for the United States Air Force.

The Minotaur IV vehicle consists of four stages and is capable of placing 1,591 kilograms (3,508 lb) of payload into a low Earth orbit (LEO). The first three stages are decommissioned Peacekeeper missile motors. On the baseline Minotaur IV, the fourth stage is an Orion 38. The higher-performance Minotaur IV+ variant instead replaces the Orion motor with a Star 48BV fourth stage. A three-stage configuration (no Orion 38 or Star 48), designated the Minotaur IV Lite, is available for suborbital trajectories. A five-stage derivative, the Minotaur V, made its maiden flight on 7 September 2013.

Minotaur IV launches are conducted from SLC-8 at Vandenberg Space Force Base, LP-0B at the Mid-Atlantic Regional Spaceport, SLC-46 at Cape Canaveral Space Force Station, and Pad 1 of the Pacific Spaceport Complex – Alaska (PSCA).

The Minotaur IV was developed by Orbital Sciences (now owned by Northrop Grumman) as part of the United States Air Force's Orbital Suborbital Program. There are three variants available: Minotaur IV, IV+, and IV Lite. Minotaur IV and IV+ are used for low Earth orbit missions, while Minotaur IV Lite is intended for suborbital launches, such as testing prototype hypersonic vehicles. The separate Minotaur V and Minotaur VI variants are also available, with the former optimized for high-energy trajectories such as geostationary transfer orbit or trans-lunar injection, and the latter intended for heavier low Earth orbit missions.

The Minotaur IV family is derived from the LGM-118 Peacekeeper Intercontinental ballistic missile (ICBM), deployed from 1985 until 2005. The Minotaur IV family utilizes decommissioned Peacekeeper solid rocket motors, which compose the first three stages in all Minotaur IV rockets and derivatives. This relatively simple architecture allows Minotaur to be launched from essentially anywhere in the United States through the use of mobile launch facilities, although this capability has never been needed. Because of its use of decommissioned ICBM components, Minotaur IV can only be used to launch US government missions.

The standard Minotaur IV rocket is composed of four stages. The first stage SR118 motor provides 2,224 kilonewtons (500,000 lbf) of thrust during its 56.6-second burn, followed immediately after by stage separation and second-stage ignition. The second stage, powered by an SR119 motor, burns for 61 seconds and provides an average thrust of 1,223 kilonewtons (275,000 lbf). The third stage then burns for 72 seconds, with an average thrust of 289 kilonewtons (65,000 lbf). The initial three stages all have thrust vector control, allowing them to steer the rocket downrange by gimballing the motor nozzles. The second and third stages also feature extendable nozzles, allowing for improved performance in the upper portions of Earth's atmosphere as well as the vacuum of space.

The fourth stage of the Minotaur IV is the Orion 38 motor, which is also used in the Minotaur-C, Minotaur I, Pegasus, and Ground-Based Interceptor rockets. This motor performs the final orbital insertion burn for the payload. Like the first three stages, the Orion 38 also features thrust vectoring, with a 5-degree range of motion.

The first 3 stages make up the majority of the rocket's body, while the smaller fourth stage is housed in a hollow cylindrical structure referred to as the "Guidance and Control Assembly skirt" (GCA skirt). The payload then mounts to the fourth stage via a structural adaptor.

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