Minotaur 4 is a four-stage solid fuel expendable launch vehicle. It uses three retired MX (Peacekeeper) ICBM stages and is topped by a commercial Orion 38 fourth stage. Orion 38, originally developed for Orbital’s air launched Pegasus rocket, also serves as the fourth stage for Orbital’s Taurus launch vehicle.
A 2.34 meter diameter Taurus payload fairing tops the rocket. Minotaur 4’s avionics are derived from Orbital’s Pegasus and Taurus systems,
Orbital developed Minotaur 4 under the U.S. Air Force Orbital Suborbital Program 2 (OSP-2). Minotaur 4 is one of three Peacekeeper-based launch vehicles to be created under the program.
The others include Minotaur 3, a suborbital version that uses a monopropellant fourth stage in place of an Orion 38, and Minotaur 5, an more powerful orbital launcher that replaces the Orion 38 with a Star 48V fourth stage and adds a Star 37FM fifth stage.
Like its Minuteman-based Minotaur cousin, Minotaur 4 is launched from a basic pedestal platform with a fallback umbilical using minimal support equipment.
Planned launch sites include Vandenberg AFB SLC 8 and Kodiak Island, Alaska. East coast launches are also plausible from Wallops Island, Virginia and Cape Canaveral, Florida.
Development of the LSG-118 MX missile, the most powerful U.S. ICBM of its time, began in 1979. The first of 51 MX test launches took place in 1983. 50 MX missiles were deployed in underground missile silos from 1988 until 2005, when the system was retired to meet post Cold-War treaty requirements.
Also read: Minotaur Data Sheet
First Minotaur Orbital Launch
Minotaur 4 first flew on April 22, 2010 as a three stage “lite” variant, using only the three MX stages but controlled by Orbital avionics. The inaugural launch launched DARPA’s Hypersonic Test Vehicle (HTTV)-2a from Vandenberg AFB SLC 8.
The launch was successful, but HTV-2a, meant to glide through upper atmosphere at up to Mach 20 toward Kwajalein, disappeared about 9 minutes after liftoff as it reentered the upper atmosphere.
Minotaur 4 performed its first orbital launch on September 26, 2010 from Vandenberg AFB Space Launch Complex 8. The four stage solid fuel rocket orbited SBSS, the 1.03 tonne Space Based Space Surveilance satellite, for the U.S. Strategic Command. SBSS was designed to track objects in orbit using an on-board gimbaled optical sensor.
Minotaur 4 lifted off at 04:41 UTC. Its first three, MX missile based stages burned in succession during the first 3 minutes 27 seconds of the flight, lifting the vehicle to a 192 km altitude and propelling it 580 km downrange. The fourth stage then coasted for about eight minutes before its Orion 38 motor ignited for a 67 second burn to inject SBSS into a 541 x 538 km x 98 deg orbit. Spacecraft separation occured about 15 minutes after liftoff.
Vehicle Configurations
| LEO Payload (metric tons) 650 km x 98 deg | Configuration | LIftoff Height (meters) | Liftoff Mass (metric tons) | ||
| Minotaur 4 | 1.8 tonnes | SR118 + SR119 + SR120 + Orion38 | 23.88 m | 88.3 t |
Vehicle Components
| Stg 1 (SR118) | Stg 2 (SR119) | Stg 3 (SR120) | Stg 4 (Orion38) | Payload Fairing | |
| Diameter (m) | 2.34 m | 2.34 m | 2.34 m | 0.97 m | 2.34 m |
| Length (m) | 8.39 m | 7.88 m | 2.33 m | 2.08 m | 6.38 m |
| Propellant Mass (tonnes) | 45.37 t | 24.49 t | 7.07 t | 0.77 t | |
| Empty Mass (tonnes) | 3.62 t | 3.18 t | 0.64 t | 0.41 t | |
| Total Mass (tonnes) | 48.99 t | 27.67 t | 7.71 t | 1.18 t | ~0.4 t |
| Engine | SR118 | SR119 | SR120 | Orion38 | |
| Engine Mfgr | Thiokol | Aerojet | Hercules | ATK | – |
| Propellant | HTPB | HTPB | NEPE | HTPB | – |
| Thrust (SL tons) | 209 t | – | – | – | – |
| Thrust (avg tons) | 226.8 t | 124.7 t | 29.48 t | 3.525 t | – |
| ISP (SL sec) | 229 s | – | – | – | – |
| ISP (Vac sec) | 282 s | 309 s | 300 s | 293 s | – |
| Burn Time (sec) | 56.4 s | 60.7 s | 72 s | 65 s | – |
| No. Engines | 1 | 1 | 1 | 1 | – |
MX (Peacekeeper) Variants ======================================================================= Name Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 ------------------------------------------------------------------------- Peacekeeper SR-118 SR-119 SR-120 PBM Athena I Castor 120 Orbus 21D OAM Athena II Castor 120 Castor 120 Orbus 21D OAM Taurus 1XXX SR-118 Orion 50S Orion 50 Orion 38 Taurus 2XXX Castor 120 Orion 50SG Orion 50 Orion 38 Taurus 3XXX Castor 120 Orion 50SXL Orion 50XL Orion 38 Minotaur 3 SR-118 SR-119 SR-120 SuperHAPS Minotaur 4 SR-118 SR-119 SR-120 Orion 38 Minotaur 5 SR-118 SR-119 SR-120 Star 48V Star 37FM ========================================================================
