Orbital Pegasus - Manual (Page 27)

Release 7.0 Apr 2010 16
Pegasus User’s Guide
was used to create this overall envelope that
encompasses all phases of Pegasus launch
operation including OCA takeoff, captive carry,
and powered flight.
A +6 dB factor should be added to this spectrum
for 75 seconds for payload standard acoustic
testing to account for fatigue duration effects to
encompass at least two launch attempts and
powered flight.
4.8. Pressure Profile
Due to the low pressure decay rate associated
with OCA ascent and low initial static pressure at
drop, the depressurization rates for the Pegasus
payload fairing are less than 0.3 psi/sec. The
internal pressure at fairing jettison is well below
0.1 psia. Representative pressure profiles for
captive carry and powered flight are provided in
Figures 4-10 and 4-11.
4.9. Payload Thermal Environment
The payload thermal environment is maintained
during all phases of integrated operations
including payload processing, fairing
encapsulation, transportation of the launch
vehicle, ground operations at the flight line and
launch operations.
4.9.1. Payload Processing
During payload processing, the temperature and
humidity of the spacecraft processing areas within
Building 1555 are maintained within a range of 18
to 29 ºC (64.4 to 84.2 ºF) and ≤55%, respectively.
Following encapsulation of the payload, but prior
to transportation of the Pegasus vehicle to the Hot
Pad, the fairing is continuously purged with filtered
air. The temperature and humidity limits are the
same as listed above. The flowrate of air through
the fairing is maintained between 50 and 200 cfm.
The air flow enters the fairing forward of the
payload and exits aft of the payload. There are
baffles on the inlet that minimize the impingement
velocity of the air on the payload.
4.9.2. Transportation
During transportation of the Pegasus vehicle to the
Hot Pad, the fairing is continuously purged with
filtered and dried ambient air. The air temperature
is not actively controlled; however, transportation
operations are performed only when the ambient
temperature ensures that the air supplied to the
fairing will be between 2 to 29 ºC (35.6 to 84.2 ºF).
The relative humidity of the air supplied to the
Figure 4-3. Pegasus Design Limit Load Factors