textfiles/bbs/KEELYNET/GRAVITY/sat2.asc

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                                  August 3, 1990

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       FLTSATCOM LAUNCH
       KSC 81-89
                                                               September   
       1989

                                    FLTSATCOM-8

       VERSATILE UHF/EHF MILITARY SATELLITE COMMUNICATIONS SYSTEM SHARED BY
       THE U.S. NAVY, AIR FORCE, AND DEPARTMENT OF DEFENSE

       PROVIDES RELIABLE, SECURE COMMUNICATIONS FOR SHIPS AND SUBMARINES AT
       SEA, PLANES IN THE AIR, AND MILITARY GROUND UNITS THROUGHOUT THE
       WORLD

       PROVIDES INSTANT COMMUNICATIONS BETWEEN PRESIDENT AND COMMANDING
       OFFICERS IN THE UNITED STATES AND REMOTE UNITS ANYWHERE IN THE WORLD

       FLTSATCOM (pronounced FleetSatCom, for Fleet Satellite
       Communications) is a versatile, high-capacity worldwide military
       communications system operated by the United States. NASA previously
       launched seven of these spacecraft for the military services, all on
       Atlas/Centaur vehicles. With FLTSATCOM-8, the last to be launched
       under NASA auspices,  there  will   be   six   FLTSATCOM  satellites
       operating in orbit.

       FLTSATCOM provides instant communications between the President and
       commanding officers in the United States and remote units stationed
       anywhere in the world. FLTSATCOM-1, operating since February 1978,
       provides service from Southeast Asia across the Pacific to the West
       Coast of the  United  States.  FLTSATCOM-2, launched  in  May  1979,
       covers the Indian   Ocean  area  from  Africa  to  the  Phillipines.
       FLTSATCOM-3, launched in January  1980,  provides  service  from the
       middle of the   United   States   across   the  Atlantic   and   the
       Mediterranean. FLTSATCOM-4, launched  in October 1980, is co-located
       with FLTSATCOM-1 and provides coverage  over the Pacific. FLTSATCOM-
       5, launched in August 1981, was damaged during launch, and was never
       declared operational.

       FLTSATCOM-7, launched in  December  1986, was placed  in  orbit  co-
       located with FLTSATCOM-1. It now provides service over the United
       States. The most recent, FLTSATCOM-6, was lost after being struck by
       lightning shortly after launch in March 1987.

       In addition to the Ultra High Frequency (UHF) capability of the
       earlier satellites in this series, FLTSATCOMs 7 and 8 carry an
       Extremely High Frequency (EHF) communications package. This package
       serves as a test bed for the new MILSTAR terminals.





       FLTSATCOMS are launched on Atlas/Centaurs from Launch Complex 36 on
       the Cape Canaveral  Air  Force  Station  in Florida. The Atlas stage
       will complete its burn and fall into  the  ocean.  The first burn of
       the Centaur injects  the  spacecraft  into  a parking  orbit,  at  a
       perigee altitude of  about  92  statute  miles  (148 kilometers) and
       apogee of approximately 229 statute  miles (369 kilometers). After a
       coast period of about 14 minutes, the Centaur engines  ignite  again
       and place the spacecraft into a highly elliptical, or egg-shaped,
       "transfer orbit" with an apogee of about 22,362 miles (35,988
       kilometers).

       The Centaur releases  the spacecraft and, as its final act, performs
       a retromaneuver which takes it safely  out  of  the flight path. The
       U.S.  Air Force Space Systems Division (SSD) then assumes  charge of
       the satellite, operating through its Consolidated Space Test Center
       (CSTC) at Onizuka Air Force Base, Sunnyvale, CA. NASA tracking
       stations throughout the world, together with the Air Force Satellite
       Control Network Remote Tracking Stations, provide range and
       range-rate measurement support to assist the CSTC controllers in
       bringing the satellite on station.

       The elliptical transfer orbit is designed so that the satellite will
       reach its apogee  while  over the equator. To convert the orbit from
       an elliptical to a circular one, and change the angle of inclination
       so that the flight path will be more nearly above the equator,  CSTC
       operators will correctly aim the  spacecraft  and  fire  an  onboard
       solid propellant motor  at  a  selected  apogee.  This   final  burn
       "transfers" the satellite  into  a circular "drift" orbit, almost at
       synchronous altitude and with the  angle of inclination reduced to 5
       degrees. The FLTSATCOM  then  drifts to its assigned  place  in  the
       global network, where  the CSTC controllers fire the small thrusters
       of the onboard hydrazine reaction  control  system to stop the drift
       motion.

       When a satellite is located above and in line with the equator at an
       altitude of about 22,238 miles (35,789 kilometers), and given a
       velocity of 6,879 miles (11,071 kilometers) per hour, its movement
       becomes "synchronized" with that of the Earth below. It appears to
       remain stationary in the sky, while actually completing one orbit
       every 24 hours. All fully geosynchronous satellites, including those
       for  commercial communications, weather observation, and military
       communications, are stationed  above  the  equator   at   the   same
       altitude, spaced around   a  circle  about  165,000  miles  (266,000
       kilometers) in circumference.  They   are   carefully  separated  by
       distance or by  assigned  radio frequencies to prevent  interference
       between their individual communications systems.

       Since FLTSATCOM-8, like its predecessors, will initially be inclined
       to the equator, it will appear from the ground to be moving back and
       forth from north to south. At the same time, it will appear to move
       slightly east and west from the centerpoint, and so trace a constant
       figure "8" across the equator in the sky.

       The Navy portion   of   the   FLTSATCOM   shared   system   provides
       communications between naval aircraft, ships, submarines, and ground
       stations.  The Air Force portion of each satellite is part of the
       USAF Satellite Communications System (AFSATCOM).  AFSATCOM links the
       National Command Authority with Strategic Air Command units, and
       other arms of the Air Force. A FLTSATCOM provides 23 UHF channels.

       FLTSATCOM-8, with an 81-pound (37-kilogram)  adapter  for connection
       to the vehicle, weighs about 5,061 pounds (2,296 kilograms) on the




       ground, and has a mass of about 2,696 pounds (1,223 kilograms) in
       space after burning  up  the  apogee  motor propellants. It measures
       43.4 feet (13.2 meters) from tip to tip of the fully extended solar
       panels. The main body is 7.5 feet (2.3 meters) wide, and 21.6 feet
       (6.6 meters) high from the bottom of the body to the tip of the
       offset spiral antenna mast. Both the spiral antenna and the solar
       panels are in a retracted configuration for launch, as is the
       16-foot-(4.9-meter) diameter, silver-filled stainless steel mesh UHF
       antenna.

       The main body consists of three attached  hexagonal  modules  called
       the payload module, the spacecraft module, and the  EHF  module,  or
       FEP.  The solar arrays extend from the spacecraft module, which also
       contains the hydrazine-fueled reaction control system thrusters and
       tanks, Sun and Earth sensors, a reaction wheel which spins to hold
       the spacecraft steady in its operating attitude, and the other
       systems needed for control and operation of the spacecraft. The
       payload module contains the three antenna systems, the transponders
       for the 23 channels, and all the associated electronics required to
       support the communications functions. The offset mast is the UHF
       transmit antenna. A small, separate conical helix antenna atop the
       central mast serves as the S-band Tracking, Telemetry and Control
       antenna, used to command and monitor the spacecraft. The superhigh
       frequency antenna horn protrudes through a hole cut into the UHF
       antenna mesh.

       The FEP contains   the   Extremely   High  Frequency  communications
       package, with its  30  (maximum) voice  channels.  The  package  was
       designed and built  by  the  MIT  Lincoln Laboratory  in  Lexington,
       Massachusetts. The EHF  antenna,  consisting of a 5 degree steerable
       spot beam and an Earth coverage aperture,  look  through  cutouts in
       the center portion of the UHF transmitting antenna.

       In operation, the momentum wheel provides a means to control the
       spacecraft attitude so that the antennas are always aimed at the
       Earth. The two solar arrays rotate on their extended arms so that
       they constantly face the Sun. These two arrays contain three panels
       each, with a total of 23,000 solar cells, each 0.79  by  1.57 inches
       (2 by 4  centimeters)  in size, which will produce about 2,200 watts
       at the beginning of their orbital life. Three 24-cell nickel-cadmium
       batteries provide power when the spacecraft must operate in the
       Earth's shadow; 2,150 of the solar cells are reserved for battery
       charging.

       FLTSATCOMs 1 through 4 and 7 have accumulated some 40 years of
       on-orbit service. Four of the five orbiting satellites already have
       lasted longer than their five-year design life. The current estimate
       of the expected life of the UHF communications capability is in
       excess of 10 years. The Extremely High Frequency package on
       FLTSATCOM-8 is expected to last more than two years.

       The spacecraft are built by TRW Space & Technology Group, Redondo
       Beach, CA. The U.S. Navy manages the overall program, and the U.S.
       Air Force Space Systems Division is the contracting agency for the
       space segment. The military agencies reimburse NASA for the cost of
       the Atlas/Centaur launch vehicle and associated launch services.


       ATLAS/CENTAUR

       137.6 FEET (41.9 METERS) TALL; 10 FEET (3 METERS) IN DIAMETER





       WITH PAYLOAD, WEIGHS    APPROXIMATELY    360,856   POUNDS   (163,684
       KILOGRAMS) AT LIFTOFF

       ATLAS THRUST 438,416 POUNDS (1,950,074 NEWTONS) AT LIFTOFF

       CENTAUR THRUST 33,000 POUNDS (146,784 NEWTONS) IN A VACUUM FOR 7 1/2
       MINUTES


       Atlas/Centaur vehicles are built by General Dynamics/Space Systems
       Division (GDSS). FLTSATCOM-8 and its launch vehicle will be launched
       by a team from NASA, GDSS and the U.S. Air Force. This will be the
       last Atlas/Centaur launch by NASA. In the future, NASA will contract
       with either the  U.S.  Air Force  or  the  vehicle  manufacturer  to
       procure Expendable Launch Vehicles (ELVs) such as the Atlas/Centaur,
       and related launch    services.    NASA   will   retain    oversight
       responsibilities for those vehicles which carry NASA payloads.

       The two-stage, liquid-fueled Atlas/Centaur has been used to launch a
       variety of scientific and technological spacecraft. These have
       included Surveyors to the moon, Mariners to Venus, Mercury and Mars,
       and Pioneers to Jupiter and Saturn. It has placed Applications
       Technology Satellites, and COMSTAR, INTELSAT, and FLTSATCOM
       communications satellites into geosynchronous transfer orbits. In
       1984, it was upgraded by lengthening the Atlas stage to provide
       larger propellant tanks. The Centaur stage has been improved by
       substituting attitude control  thrusters  powered by hydrazine (used
       as a monopropellant) for ones powered by hydrogen peroxide, and
       replacing the oxygen and hydrogen propellant pumps by pressure-fed
       systems.

       The 76.3-foot (23.3-meter) long first stage is an uprated version of
       the flight-proven Atlas vehicle used in the national space program
       since 1959. The Rockwell International/Rocketdyne MA-5 engine system
       burns RP-1, a highly refined kerosene, and liquid oxygen. The MA-5
       uses two main engines, a 377,500-pound (1,679,120-newton) thrust
       booster engine with two thrust chambers,  and  a  smaller  sustainer
       with a single  thrust  chamber  that  produces approximately  60,000
       pounds (266,900 newtons)  of thrust. The sustainer nozzle is located
       between the two larger ones of the booster engine. Two small vernier
       engines which help control the vehicle in flight also are burning at
       liftoff, for a total thrust of 438,416  pounds  (1,950,074 newtons).
       Total weight at liftoff is about 360,856 pounds (163,684 kilograms).

       An unusual feature of the Atlas vehicle is its "stage-and-a-half"
       construction. All five thrust chambers are burning at liftoff. After
       more than 2 1/2 minutes of flight, the booster engine cuts off. This
       engine and its  supporting  structures  are jettisoned,  deleting  a
       large portion of  the structural weight of this stage. The sustainer
       and vernier engines continue to burn until the propellants are gone,
       at about 4 1/2 minutes. This means  an  Atlas  retains  most  of the
       weight reduction advantage gained by jettisoning  a  used-up  stage,
       but does not  have  to  ignite  its engines in flight, as a separate
       stage must.

       The only radio frequency system on the Atlas is a range safety
       command system, consisting of two receivers, a power control unit,
       and a destruct unit. The Atlas can be destroyed in flight by ground
       control if necessary, but otherwise receives all its control
       directions from the Centaur stage.

       The Centaur stage sits above the Atlas on a barrel-shaped interstage




       adapter. The Atlas and Centaur separate two or three seconds after
       the Atlas burns out. Eight small retrorockets near the bottom of the
       Atlas fuel tank then back this stage away from the Centaur.

       The Centaur stage is 30 feet (9.1 meters) in length without the
       fairing on top. Exclusive of payload, it weighs about 39,000 pounds
       (17,700 kilograms) when loaded with propellants. The main propulsion
       system consists of two Pratt & Whitney engines burning liquid oxygen
       and liquid hydrogen,   producing  33,000  pounds  (146,784  newtons)
       thrust in the vacuum of space in which they are designed to operate.
       These engines can be stopped and restarted,  allowing the Centaur to
       coast to the  best point from which to achieve its final  trajectory
       before igniting for  another  burn.  While  coasting,  the  stage is
       controlled by 12 small thruster engines, powered by hydrazine. These
       hold the stage steady and provide  a  small  constant thrust to keep
       the propellants settled  in the bottom of their tanks,  a  necessity
       for a second or third burn.

       A cylindrical nose  fairing  with  a conical top sits on the Centaur
       and protects the spacecraft. Total  vehicle  height  is  137.6  feet
       (41.9 meters). Both stages are 10 feet (3 meters) in diameter.

       The Centaur electronic packages are mounted in a circle around a
       conical equipment module, located above the upper tank.  An  adapter
       on top of  this module connects to the payload adapter on the bottom
       of the spacecraft. These electronic packages provide an integrated
       flight control system  which  performs   the  navigation,  guidance,
       autopilot, attitude control, sequence of events, and telemetry and
       data management functions for both the Atlas and Centaur stages. The
       heart of this system is a Digital Computer Unit (DCU), built by
       Teledyne. The DCU sends commands to control most planned actions,
       including all but  items  one,  two,  and five in the  table,  shown
       below.  The DCU  receives guidance information from a combination of
       sensors called the Inertial Measurement  Group,  built by Honeywell,
       and sends steering  commands to all Atlas and Centaur  engines.  The
       Centaur also has a ground-controlled destruct system similar to that
       on the Atlas, in case the vehicle must be destroyed in flight.

       The Centaur uses the most powerful propellant combination available,
       has a lightweight structure, and an engine burn time of up to 7 1/2
       minutes, the longest  of  any upper stage now in service. This gives
       it the most total energy for its size of any stage yet built.


       The following table provides a list of the major events that will
       occur during the flight.

       Event              Time After                   Distance
                   Liftoff    Altitude     Downrange      Velocity
                          MIN:SEC    MI/KM MI/KM        MPH/KPH



       Liftoff            T+0          --/--        --/--        --/--



       Atlas Booster
       Engine Cutoff      2:35            37/60        55/89
       5,703/9,178






       Jettison Atlas
       Booster Engine     2:38            39/63        60/97
       5,764/9,276



       Jettison Centaur
       Insulation Panels  3:0             51/82        93/150
       6,124/9,856



       Jettison Nose
       Fairing            3:43            71/114       169/272
       7,055/11,354



       Atlas Sustainer/
       Vernier Engines
       Cutoff            4:30             89/143       266/428
       8,466/13,625



       Atlas/Centaur
       Separation        4:32             89/143       271/436
       8,469/13,630





       First Centaur Main
       Engines Start     4:43             97/156       295/475
       8,441/13,584



       Centaur Main
       Engines Cutoff    9:55                  102/164          1,294/2,082
       16,652/26,799



       Second Centaur Main
       Engines Start    23:56                  101/163          5,103/8,212
       16,686/26,854


       Second Centaur Main
       Engines Cutoff   25:32                 110/177           5,600/9,012
       22,013/35,426



       Centaur/Spacecraft
       Separation       27:47             179/288              6,391/10,285
       21,791/35,069







       These numbers may vary, depending on exact launch date, launch time,
       and spacecraft weight.

       NOTE: The final  velocity  of  22,013  miles (35,426 kilometers) per
       hour places the spacecraft in a transfer  orbit,  with  an apogee of
       22,362 miles (35,988 kilometers) and a perigee of 104 miles (167
       kilometers). The U.S. Air Force then assumes control of the
       spacecraft. At an  apogee  chosen  by  Air  Force  controllers,  the
       onboard apogee motor  will  be fired to make the orbit more circular
       at geosynchronous altitude, about  22,238  miles (35,789 kilometers)
       above the equator. It will then be "drifted" to its  assigned  place
       in the FLTSATCOM  global  network.  The spacecraft will have a final
       velocity of about 6,879 miles (11,071  kilometers) per hour. It will
       complete one orbit every 24 hours, and so move back  and forth above
       the same area on both sides of the equator.

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       If you have comments or other information relating to such topics as
       this paper covers,  please upload to KeelyNet or send to the Vangard
       Sciences address as listed on the  first  page.   Thank you for your
       consideration, interest and support.

           Jerry W. Decker.........Ron Barker...........Chuck Henderson
                             Vangard Sciences/KeelyNet

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