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Fact Sheet: February, 1999
The Inertial Upper Stage: Space
Workhorse To Boost Chandra X-ray Observatory
The Inertial Upper Stage is a two-stage, solid rocket
used to place spacecraft into a high-Earth orbit or
boost them away from the Earth on interplanetary
missions. The Inertial Upper Stage is launched from
Earth aboard either the NASA Space Shuttle or with a
one-use launch vehicle, such as the Air Force's Titan
rocket. Once in space, the Inertial Upper Stage is
deployed from the Shuttle or Titan and ignites to
propel its attached spacecraft to the proper point in
space.
In 1999, the Inertial Upper Stage will help propel the
newest of NASA's Great Observatories - the Chandra
X-ray Observatory - from low Earth orbit into an
elliptical orbit reaching one-third of the way to the
Moon. The upper stage and the attached Chandra X-ray
Observatory will be deployed from the Space Shuttle
Columbia on its sixth or seventh orbit after launch.
The Inertial Upper Stage then will fire its first stage
solid rocket motor for about two minutes, then coast
through space for about two minutes more. The first
stage will then separate, and the second stage will
fire for another minute-and-a-half.
About one hour later, the Chandra observatory's solar
panels will be deployed. Then, having done its job, the
remains of the Inertial Upper Stage will separate from
the Chandra observatory and use small thruster motors
to maneuver away from Chandra. This will clear the way
for Chandra's own propulsion system to boost it the
rest of the way to its working orbit.
Background
Since its first use by NASA in 1983, the Inertial
Upper Stage has supported a variety of important
missions. The Inertial Upper Stage has boosted all of
NASA's Tracking and Data Relay Satellites from
low-Earth orbit to geosynchronous orbit. The Inertial
Upper Stage also has helped send the Galileo spacecraft
on a journey to explore Jupiter, the Magellan
spacecraft to study and map Venus, and the Ulysses
spacecraft toward a polar orbit of the Sun. Marshall
Space Flight Center in Huntsville, Ala., manages the
NASA Inertial Upper Stage Program.
The Inertial Upper Stage, originally called the
Interim Upper Stage, was designed as a temporary
reusable space tug. The word "Inertial" - signifying
the guidance technology - replaced "Interim" when it
was determined that the Interim Upper Stage would be
needed through the 1990s.
The Inertial Upper Stage was developed and built by
the Boeing Aerospace Co., at Seattle, Wash., under
contract to the Air Force Materiel Command's Space and
Missile Systems Center. The Space and Missile Systems
Center is the executive agent for all Department of
Defense activities pertaining to the Space Shuttle
system and, for all NASA missions prior to Chandra,
provided the Inertial Upper Stage for Space Shuttle
use. The Inertial Upper Stage for the Chandra mission
has been procured and provided by the Marshall Space
Flight Center. Marshall is working cooperatively with
the United States Air Force 3rd Space Launch
Squadron for prelaunch integration and launch support
for the Chandra mission and with the United States Air
Force 5th Space Operations Squadron for
orbital operations support for the Chandra
mission.
NASA's most recent use of the Inertial Upper Stage was
on the STS-70 mission of the Space Shuttle in July
1995. The Inertial Upper Stage successfully transported
Tracking Data Relay Satellite "G" to geosynchronous
orbit, 22,300 miles from Earth.
Specifications
The Inertial Upper Stage is a two stage, inertially
guided, three axis stabilized, solid rocket vehicle. It
is approximately 17 feet long and 9.25 feet in
diameter, with an overall weight of approximately
32,500 pounds. The Inertial Upper Stage first stage is
comprised of a solid rocket motor and an interstage.
The first stage solid rocket motor normally contains a
maximum 21,580 pounds of propellant and generates an
average of 44,000 pounds of thrust. The large first
stage motor when first flown, with the capability to
burn as long as 150 seconds, was the longest burning
solid rocket motor ever developed for space
application. For the Chandra mission, the first stage
solid rocket motor propellant weight will be only
19,621 pounds due to weight constraints for the
Shuttle, but by adjusting the exhaust nozzle on the
motor the average thrust will be increased to 46,198
pounds and the burn time will be 125 seconds.
The second stage consists of an equipment support
section and a solid rocket motor. The second stage
solid rocket motor has a normal maximum load of 6,000
pounds of propellant generating an average thrust of
about 18,200 pounds. The Chandra mission will carry an
additional 16 pounds of propellant at a reduced average
thrust of 16,350 pounds.
The equipment support section houses the avionics
systems of the Inertial Upper Stage. These systems
provide guidance, navigation, control, telemetry,
command and data management, reaction control and
electrical power. All vital components of the avionics
system, along with thrust vector actuators, reaction
control thrusters, motor igniter and pyrotechnic stage
separation equipment have backup systems to provide
reliability of better than 98 percent. Once deployed
from the Shuttle, the Inertial Upper Stage's computers
will send commands to the Chandra X-ray Observatory.
Until spacecraft separation, these commands will assist
Chandra in controlling power, safety systems,
recorders, propulsion and heaters.
The Inertial Upper Stage uses airborne support
equipment installed in the Shuttle to operate and
deploy into space. The Airborne Support Equipment
consists of the mechanical, avionics and structural
equipment located in the orbiter. The structural and
mechanical equipment attaches the Inertial Upper Stage
and the payload to the orbiter payload bay and provides
the mechanisms to elevate the Inertial Upper Stage and
the payload and deploy it from the Shuttle. The
Airborne Support Equipment avionics provides command
and information transfer between the Upper Stage and
the Shuttle during payload checkout.
FS-1999-02-08-MSFC
February 1999
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For More Info on the Chandra X-ray Observatory:
http://chandra.nasa.gov
http://chandra.harvard.edu
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