Pegasus (launch vehicle)
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Pegasus XL
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An air-launched space launch vehicle, developed by Orbital
Sciences Corporation, that works in a similar way to an air-launched
ballistic missile (ALBM). Like an ALBM, Pegasus is dropped from an aircraft
and fires its rocket seconds later. But instead of completing a ballistic
trajectory to carry a weapons payload to its target, Pegasus carries a payload
into space.
The original vehicle, now referred to as the Pegasus Standard, has been
superceded by the Pegasus XL which is available in three- or four-stage
versions. There are two fourth-stage options. The Hydrazine Auxiliary Propulsion
System (HAPS), which burns hydrazine liquid
fuel, provides precision orbital insertion capability for the payload. Alternatively,
the fourth stage can be powered by a Thiokol Star 27 solid rocket motor,
which burns HTPB solid fuel and can provide Earth-escape trajectory capability
for the payload. The Pegasus XL employs a standard payload fairing, 2.1
m long with a diameter of 1.1 m. This fairing is able to accommodate one
payload in a dedicated launch configuration or two payloads in a shared
launch configuration.
Pegasus "firsts"
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World's first privately developed space launch vehicle
- Maiden 1990 mission marked the first all-new, unmanned space
launch vehicle developed in the U.S. in more than 20 years
- First winged vehicle to accelerate to eight times the speed
of sound
- First air-launched rocket to place satellites into orbit, using
its carrier aircraft as an "air breathing reusable first stage"
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In a typical mission profile without a fourth stage, the Pegasus XL is dropped
over open water from a customized L-1011 aircraft flying at an altitude
of 11,600 m. The drop is considered to be the actual launch, although the
first stage is not fired until five seconds later at an altitude of 11,470
m. The rocket employs an inertial guidance system to pitch
it upward after first stage ignition. The first stage burns out 77 sec after
launch, and is jettisoned. The second stage is fired 95 sec after launch,
followed by separation of the payload fairing at 111 sec after launch. The
second stage burns out 168 sec after launch, at which time the second and
third stage combination begin an unpowered coast period. During this coast
period, the second stage remains attached to provide aerodynamic stability.
Ultimately, the spent second stage is jettisoned and the third stage is
fired 592 sec after launch. The third stage burns out 657 sec after launch
and is jettisoned from the payload, having successfully inserted it into
orbit. The Pegasus XL can deliver a payload of 450 kg to low Earth orbit,
or place 125 kg on an Earth-escape trajectory.
| stages (Pegasus XL) |
first |
second |
third |
| engine designation |
Orion 50SXL |
Orion 50XL |
Orion 38 |
| length (m) |
10.3 |
3.1 |
1.3 |
| diameter (m) |
1.3 |
1.3 |
0.97 |
| fuel |
HTPB |
HTPB |
HTPB |
| thrust (N) |
726,000 |
153,000 |
32,000 |
Related category
• ROCKETS,
MISSILES, AND LAUNCH VEHICLES
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