Sea Launch User's Guide

Purge air quality
during ground
processing
After encapsulation, the payload fairing air purge defines the spacecraft
environment. This is HEPA filtered and delivered at a nominal cleanliness
of class 1,000 (per FED-STD-209E). Purge air is provided from the
time the payload unit leaves the payload processing facility through liftoff
or launch abort, described in section 5.
The purge air quality is monitored with an airborne particle counter near
the payload fairing inlet. Monitoring is discontinued only during the hoist
of the integrated launch vehicle from the assembly and command ship to
the launch platform, and after erection of the integrated launch vehicle on
the launch pad.
Helium exposure
during ground
processing
Helium concentration in the spacecraft environment is a concern to some
customers. The primary source of helium in the Sea Launch system is
venting and leakage from the Block DM-SL, with the highest concentration
occurring prior to Block DM-SL liquid oxygen load on the launch
pad. Payload fairing positive pressure, provided by the purge airflow
through the payload structure one-way vent valves, is an effective barrier
to helium leakage from the Block DM-SL cavity.
Spacecraft access
at sea during
ground processing
If access to the spacecraft is required on the launch platform, a temporary
air lock can be installed around the payload fairing access door to provide
a clean zone for working and to shield the payload fairing opening from
debris. Purge air from the payload fairing will provide a clean air environment
within the air lock.
Contamination
during flight
The potential for spacecraft contamination during liftoff, ascent, and
transfer orbit phases is minimized by proper hardware design and flight
design. Flight hardware design considerations include cleanability, selection
of low-outgassing materials, venting design, and containment of pyrotechnics.
Flight design considerations include minimization of thruster
plume impingement and exposure to materials outgassing during separation
maneuvers.
Payload unit materials
outgassing
The payload unit is constructed from low-outgassing materials, screened
using the ASTM E595 outgassing test method. Small amounts of critical
materials may not meet the screening requirement but are accepted based
on other factors, such as moderate flight temperature, small surface area,
or short duration use. A full list of payload accommodation nonmetallic
materials is provided in the generic contamination analysis.
REV B D688-10009-1 5-27