Minotaur 4 Suborbital Launch

Minotaur 4 Suborbital Launch

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 Suborbital 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
 ConfigurationLIftoff
Height
(meters)
Liftoff
Mass
(metric tons)
Minotaur 41.8 tonnes SR118 + SR119 + SR120 + Orion3823.88 m88.3 t

Vehicle Components

 Stg 1
(SR118)
Stg 2
(SR119)
Stg 3
(SR120)
Stg 4
(Orion38)
Payload
Fairing
Diameter (m)2.34 m2.34 m2.34 m0.97 m2.34 m
Length (m)8.39 m7.88 m2.33 m2.08 m6.38 m
Propellant Mass (tonnes)45.37 t24.49 t7.07 t0.77 t 
Empty Mass (tonnes)3.62 t3.18 t0.64 t0.41 t 
Total Mass (tonnes)48.99 t27.67 t7.71 t1.18 t~0.4 t
EngineSR118SR119SR120Orion38 
Engine MfgrThiokolAerojetHerculesATK
PropellantHTPBHTPBNEPEHTPB
Thrust
(SL tons)
209 t
Thrust
(avg tons)
226.8 t124.7 t29.48 t3.525 t
ISP (SL sec)229 s
ISP (Vac sec)282 s309 s300 s293 s
Burn Time (sec)56.4 s60.7 s72 s65 s
No. Engines1111
MX (Peacekeeper) Variants
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Name          Stage 1      Stage 2     Stage 3     Stage 4     Stage 5
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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
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