The Complete Book of Spaceflight: From Apollo 1 to Zero Gravity

318 Pegasus (spacecraft)
Pegasus (launch vehicle) The
Pegasus space booster attached
to the wing pylon of NASA’s
B-52 launch aircraft. NASA
burns HTPB solid fuel and can boost the payload onto
an Earth-escape trajectory. The Pegasus XL uses a standard
payload fairing, 2.1 m long with a diameter of 1.1 m,
which can accommodate one payload in a dedicated
launch configuration or two payloads in a shared launch.
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 isn’t fired until five seconds later at an altitude
of 11,470 m. The rocket has an inertial guidance system
to pitch it upward after first stage ignition. The first
stage burns out 77 seconds after launch and is jettisoned.
The second stage kicks in 95 seconds after launch and
burns out 73 seconds later, at which point the second and
third stage combination begin an unpowered coast. During
this coast period, the second stage stays attached to
provide aerodynamic stability. Ultimately, the spent second
stage is jettisoned and the third stage is fired 592 seconds
after launch, burns out 65 seconds later, and is
jettisoned from the payload, having successfully inserted
it into orbit. (See table, “Pegasus XL Specifications.”)
Pegasus (spacecraft)
A series of spacecraft that over a three-year period investigated
the extent of the micrometeroid threat to the
manned Apollo missions. Each was launched with a boilerplate
Apollo capsule and, when in orbit, extended two
large “wings,” each measuring 4.3 by 14.6 m, mounted
with detector panels. The fewer-than-expected number of
impacting particles enabled about 450 kg of shielding to
be trimmed from the operational Apollo vehicles. (See
table, “Pegasus Missions.”)
Launch:
Vehicle: Saturn I
Site: Cape Canaveral
Mass: approx. 10,500 kg
Pegasus Missions
Spacecraft Launch Date Orbit
Pegasus 1 Feb. 16, 1965 510 × 726 km × 31.7°
Pegasus 2 May 25, 1965 502 × 740 km × 31.7°
Pegasus 3 Jul. 30, 1965 441 × 449 km × 28.9°
penetration probe
A device that, by impact, tunneling, or melting, penetrates
the surface of a planet, moon, asteroid, or comet,
to investigate the subsurface environment. Data is typically
transmitted to a mother craft for re-transmission to
Earth. Among missions being designed or developed that
will deploy penetration probes are the Deep Impact and
the Europa Ocean Explorer. The first intended penetration
probes, carried by the Mars Polar Lander, failed
along with the rest of the mission.
periapsis
The point in an orbit closest to the body being orbited.
perigee
For a satellite in an elliptical Earth orbit, the point in the
orbit that is nearest to Earth. Compare with apogee and
perihelion.