Orbital Pegasus - Manual (Page 20)

Release 7.0 Apr 2010 9
Pegasus User’s Guide
3.2. Performance Capability
Performance capabilities to various orbits for the
Pegasus XL are illustrated in Figure 3-3 and
Figure 3-4 (HAPS configuration). These
performance data were generated using the
Program to Optimize Simulated Trajectories
(POST), which is described below. Precise
performance capabilities to specific orbits are
typically provided per the documentation schedule
shown in Section 8.0.
3.3. Trajectory Design Optimization
Orbital designs a unique mission trajectory for
each Pegasus flight to maximize payload
performance while complying with any applicable
payload and launch vehicle constraints. In this
process, a 3DOF simulation is developed using
the current Pegasus mass properties,
aerodynamic models, and motor ballistics data,
and the desired target orbit and any applicable
trajectory constraints are specified. POST then uses a set of specified control parameters to
iterate on the trajectory design until an optimal
solution is identified which maximizes performance
to the desired target orbit subject to the specified
constraints. Typically, these constraints may
include limitations on the angle of attack profile,
dynamic loading constraints, payload
environmental constraints such as heat rate, and
Range-imposed constraints on the launch azimuth
and spent stage impact locations. After POST has
been used to determine the optimal trajectory
design, a high-fidelity, Pegasus-specific, 6DOF
simulation is then developed to conduct detailed
trajectory analyses to verify the acceptability of the
trajectory design and to verify robust control
system stability margins.
3.4. Orbit Insertion Accuracy
The estimated orbit insertion errors for Pegasus
vary from mission to mission and are influenced by
a variety of factors including the target orbit,
Figure 3-1. Pegasus XL Mission Profile to 741 km (400nmi) Circular, Polar Orbit with a 227 kg
(501 lbm) Payload