THE PEGASUS FAMILY

Pegasus: (1990) Privately-funded, air-launched winged light satellite launcher.
Pegasus HAPS: (1991) Pegasus launcher with optional HAPS stage 4.
Pegasus XL: (1994) Uprated version of Pegasus air-launched winged light satellite launcher.
Taurus: (1994) Pad-launched launch vehicle using Pegasus upper stages and Castor-120 first stage. First launch used slightly larger Peacekeeper ICBM first stage instead of Castor-120.

PEGASUS SPECIFICATIONS

First launch: 5-Apr-1990
Number launched: 10 through Mar-1996
Launch sites: now hosted by L-1011 operating out of Vandeberg AFB, NASA Wallops and Cape Canaveral (Spain's Minisat will be from Torrejon AB near Madrid)
Principal uses: small payload to LEO
Vehicle success rate: 80.0%
Performance:
LEO (463 km equatorial): 3-stage typically 288 kg (XL: 382 kg); payload fraction 2.2%
Polar (463 km): 200 kg (XL: 279 kg)
GTO: 165 kg capacity projected with XL + stage 4
Availability: 1 flight/45 days projected
Cost: $53,000/kg or $12 million for 227 kg payload
Number of stages: 3
Overall length: 15.51 m; XL: 16.8 m
Principal diameter: 1.27 m (wingspan 6.71 m)
Launch mass: 18,518 kg; XL: 22,583 kg
Guidance: autonomous autopilot forward of stage 3, with Oettle & Reicher's 68430-based flight computer containing mission-specific mission data load (MDL). Inertial/attitude data are provided from Litton LR-81 Inertial Measurement Unit (IMU). Flight #2 demonstrated a Trimble GPS receiver for navigation. It is now standard; IMU is retained for attitude data. XL carries upgraded avionics for increased payload mass/dynamic volume

PEGASUS STAGE 1
Stage 1 incorporates a Scaled Composites Inc graphite composite wing with 45^o sweptback leading edge and 6.71 m span. Subsonic L/D is 4.0. The airfoil is a double wedge with 2.5 cm radius leading edge. The wing thickness is truncated to 20.3 cm, with upper/lower parallel surfaces facilitating attachment to the motor case wing saddle.
Motor: Alliant Techsystems Orion 50S (stretched 137 cm for XL); fixed nozzle
Length: 9.39 m; XL: 10.76 m
Diameter: 1.27 m
Mass at ignition: 14,020 kg; XL: 17,157 kg
Propellant: HTPB solid
Propellant mass: 12,152 kg; XL: 15,051 kg
Thrust: 486.7 kN vac average, 583.7 kN vac max; XL: 619.9 kN vac average
Total impulse: 35.05 MNs; XL: 39.9 MNs
Burn time: 72.3 s; XL: 64.3 s
Attitude control: control during stage 1 burn is provided by three active aft fins as part of an aluminum assembly attached to the motor's skirt extension. Control is augmented at end of stage 1 burn by firing small fin-mounted motors
Separation: the forward skirt, which also serves as interstage adapter, incorporates two linear-shaped charges
Burn sequence: vehicle is released from L-1011, activating sequencer and autopilot. At 2 s, the arming sequence begins for stage 1 arming/ignition at 3/5 s, respectively. Burnout occurs at 76-84 s

PEGASUS STAGE 2
Motor: Alliant Techsystems Orion 50 (stretched 45 cm for XL)
Length: 3.84 m; XL: 4.29 m
Diameter: 1.27 m
Mass at ignition: 3,370 kg; XL: 4,314 kg
Propellant: solid
Propellant mass: 3,024 kg; XL: 3,919 kg
Thrust: 113.9 kN vac avg, 131.7 kN vac max; XL: 160.1 kN vac avg, 195.3 kN vac max
Total impulse: 8.67 MNs; XL: 11.22 MNs
Burn time: 75.9 s; XL: 70.1 s
Attitude control: motor nozzle flexing provides pitch/yaw control during powered flight; roll control and 3-axis control during coast provided by six N₂ thrusters on stage 3

PEGASUS STAGE 3
Motor: Alliant Techsystems Orion 38 (XL uses same stage 3 as standard Pegasus)
Length: 2.08 m
Diameter: 0.965 m
Mass at ignition: 893 kg
Propellant: solid
Propellant mass: 771 kg
Thrust: 34.31 kN vac average, 38.69 kN vac max
Total impulse: 2.18 MNs
Burn time: 63.8 s
Attitude control: motor nozzle flexing provides pitch/yaw control during powered flight; roll control and 3-axis control during coast provided by six N₂ thrusters in two modules

PEGASUS STAGE 4
The HAPS Hydrazine Auxiliary Propulsion System is an optional stage carried to improve injection accuracy and performance by about 36 kg for 720 km, 82^o. It occupies the payload adapter interior, replacing the N₂ tank of the 3-stage version. The attitude jets are supplied instead from two high pressure (395 atm) N₂ tanks on the adapter's outer surface.
Thrusters: three fixed blowdown monopropellant Olin Aerospace MR-107s
Propellant: hydrazine
Propellant mass: 72.6 kg
Thrust: each 222 N vac
Burn time: typically 2 burns of 131 + 110 s
Attitude control: nitrogen jets + differential firing of main thrusters

FAIRING/PAYLOAD ACCOMODATION
127 kg 2-piece composite fairing, which also covers stage 3 and the avionics packages (and stage 4 when carried), is jettisoned during stage 2 burn. The payload may remain attached to stage 3 or separated by clamp, following pointing to ±2^o accuracy or spin-up. On the ground, air-conditioning maintains 21 ±5^oC.
Payload volume: 1.17 m diameter, 2.13 m long for 3-stage; 1.76 m or 1.79 m long when HAPS carried
Acceleration load: 8 g longitudinal maximum at end of stage 1 burn (lighter payloads can exceed 8 g during stage 3 burn)