Orbital Pegasus - Manual (Page 19)

Release 7.0 Apr 2010 8
Pegasus User’s Guide
The OCA also has the capability to ferry Pegasus
across the United States or across the ocean
(depending on landing site) to support ferry and
campaign missions.
3. GENERAL PERFORMANCE CAPABILITY
This section describes the orbital performance
capabilities of the Pegasus XL vehicle with and
without the optional HAPS described in Section
10. Together these configurations can deliver
payloads to a wide variety of circular and elliptical
orbits and trajectories, and attain a complete
range of prograde and retrograde inclinations
through a suitable choice of launch points and
azimuths. In general, the optional HAPS will
provide additional performance at higher altitudes,
as well as providing a more accurate insertion
orbit capability.
From the WR, Pegasus can achieve inclinations
between 70° and 130°. A broader range of
inclinations may be achievable, subject to
additional analyses and coordination with Range
authorities. Additionally, lower inclinations can be
achieved through dog-leg trajectories, with a
commensurate reduction in performance. Some
specific inclinations within this range may be
limited by stage impact point or other restrictions.
Other inclinations can be supported through use of
Wallops Flight Facility (WFF), Eastern Range
(ER), Reagan Test Site (RTS) Kwajalein, or other
remote TT&C sites. Pegasus requirements for
remote sites are listed in Appendix D.
3.1. Mission Profiles
This section describes circular low earth orbit
mission profiles. Performance quotes for non-
circular orbits will be provided on a mission-
specific basis.
Profiles of typical missions performed by Pegasus
XL with and without HAPS are illustrated in
Figure 3-1 and Figure 3-2. The depicted profile
begins after the OCA has reached the launch point, and continues through orbit insertion. The
time, altitude, and velocity for the major ignition,
separation, and burnout events are shown for a
typical trajectory that achieves a 741 km (400 nm)
circular, polar (90° inclination) orbit after launch
from the WR. These events will vary based on
mission requirements.
The typical launch sequence begins with release
of Pegasus from the carrier aircraft at an altitude
of approximately 11,900 m (39,000 ft) and a speed
of Mach 0.82. Approximately 5 seconds after
drop, when Pegasus has cleared the aircraft,
Stage 1 ignition occurs. The vehicle quickly
accelerates to supersonic speed while beginning a
pull up maneuver. Maximum dynamic pressure is
experienced approximately 30 seconds after
ignition. At approximately 15-20 seconds, a
maneuver is initiated to depress the trajectory and
the vehicle transitions to progressively lower
angles of attack.
Stage 2 ignition occurs shortly after Stage 1
burnout, and the payload fairing is jettisoned
during Stage 2 burn as quickly as fairing dynamic
pressure and payload aerodynamic heating
limitations will allow, approximately 112,000 m
(366,000 ft) and 121 seconds after drop. Stage 2
burnout is followed by a long coast, during which
the payload and Stage 3 achieve orbital altitude.
For a non-HAPS Pegasus configuration, Stage 3
then provides the additional velocity necessary to
circularize the orbit. Stage 3 burnout typically
occurs approximately 10 minutes after launch and
2,200 km (1,200 nm) downrange of the launch
point.
An FAS, in conjunction with three aerodynamic
fins, provides attitude control from drop through
Stage 1 separation. Pitch and yaw attitude control
during Stage 2 and Stage 3 powered flight is
provided by the motor TVC system while roll
attitude is controlled by the nitrogen cold gas RCS.
The RCS also provides three-axis control during
coast phases of the trajectory.