Intelsat VI F-3 Recovery


Editor’s Note:  I have combed my files and found some very interesting items on the Intelsat VI F-3 recovery.  The first piece is a Satellite Fact Sheet from the Boeing website, however I’m sure that it was originated by Hughes.  The other three items are NASA originated as indicated.  These convey much information about this recovery operation, however, the repsonsible Hughes engineers are not mentioned at all.  Anyone who has notes or recollections about our people that were involved in this operation are encouraged to comment on this post.

The most complex satellite rescue mission yet attempted was undertaken with the Intelsat VI F-3 reboost mission in 1992. It involved the first dual active rendezvous between a satellite and a space shuttle and the first in-orbit attachment of a solid propellant rocket motor.

As part of its maiden voyage, the space shuttle Endeavour rendezvoused with Intelsat VI  F-3, which was in a low Earth orbit since March 1990.  Astronauts maneuvered in space to capture the satellite, bring it into the shuttle bay, install the new motor, and then release it again into space. When Endeavour was moved a safe distance away, the new motor was fired to boost Intelsat VI F-3 into the geosynchronous orbit for which it was intended.


Intelsat VI F-3, one of five Hughes-built spacecraft in the Intelsat VI series, was launched on March 14, 1990. Because of a malfunction in the Titan 3 launch vehicle separation system, the second stage did not separate and prevented the satellite from continuing its ascent to its intended 22,300-mile geosynchronous orbit.

To prevent re-entry, satellite controllers had to react quickly to move the satellite to a safe orbit. Engineers in the INTELSAT Launch Control Center, working with telemetry, tracking, and command stations around the world, commanded the satellite to separate from its unused perigee kick motor (PKM), which took with it the burned-out Titan stage. Additional maneuvers, using the onboard liquid propellant, raised the orbit to 299 by 309 nautical miles to reduce the damaging effects of atomic oxygen on the silver solar cell interconnects that are integral to the spacecraft’s solar power generators. There the satellite remained, in a stable thermal and power state and in a safe but useless orbit, while engineers considered how best to raise F-3 to its appropriate orbit.

Hughes Aircraft Company’s Space and Communications Group built the spacecraft for the International Telecommunications Satellite Organization. The Intelsat VI series encompasses five satellites used to provide domestic and transoceanic voice, television, and data services to Earth stations in 180 countries. After the reboost mission, the F-3 spacecraft was positioned over the Atlantic Ocean to provide services between and among countries in North America, South America, Europe, and Africa.

Each Intelsat VI spacecraft has a capacity for three TV channels and 120,000 simultaneous two-way telephone circuits, using digital circuit multiplication equipment. Each also carries 48 active transponders, 38 at C-band and 10 at Ku-band.

 Mission Preparation

After studying several options, INTELSAT decided that it was more cost-effective and safer to bring a new motor to the satellite in space and reboost it from there, than to retrieve it, return it to ground, attach a new motor, and relaunch the satellite. Hughes was awarded a $43 million contract for special hardware, a new PKM, and mission support; and National Aeronautics and Space Administration (NASA) received a contract for a shuttle mission.

The new motor, built by United Technologies Corp. Chemical Systems Division, was an Orbus 21S solid rocket motor weighing 10,430 kilograms (23,000 pounds). It is called a PKM because the motor boosts the satellite from perigee (or lowest point in its elliptical orbit).

INTELSAT worked closely with Hughes and NASA in planning the recovery mission. Hughes built special hardware for the extravehicular activity and provided a specially designed cradle located in the aft payload bay to support the PKM and associated equipment during ascent in the shuttle.

Hughes also designed and built a docking adapter assembly. Astronauts will latch the adapter’s manually operated mounting clamps in space. The adapter will be released by pyrotechnically actuated bolt cutters by command from the ground after the motor is fired.

In providing mission support, Hughes engineers worked 25 feet underwater side by side with the astronauts who will walk in space to perform the reboost. Training was conducted underwater to simulate the effects of zero gravity, using NASA’s weightlessness environmental training facility in Houston, Texas.

 Operational Maneuvers

Rendezvous of Intelsat VI F-3 and the Endeavour involved intricate coordination of maneuvers of the two spacecraft. Immediately after shuttle launch, engineers in the INTELSAT Launch Control Center in Washington, D.C., and at stations around the world began sending a complex set of commands to the satellite to lower it from its 300-mile orbit. This was the first time that two spacecraft maneuvered simultaneously to achieve a rendezvous.

Intelsat VI F-3 and Endeavour rendezvoused within a “control box” volume that was defined by NASA approximately five hours after Endeavour’s takeoff. The control box extended over 6 degrees of arc in a roughly 200-nautical-mile circular orbit with an inclination of 28.35 degrees. Intelsat VI F-3 had to be in the control box within 46 hours after shuttle liftoff, and Endeavour completing the rendezvous 24 hours later.

About six hours before Endeavour’s approach, the satellite spun down via ground commands to its on-board thrusters and attitude control electronics. The spin speed was reduced to approximately 0.65 revolutions per minute. After the spindown was completed, the satellite was commanded into a safe configuration for rendezvous.

Endeavor, commanded by astronaut Dan Brandenstein, approached the satellite on flight day 4. Once the satellite and orbiter rendezvoused, Endeavour astronauts went outside the shuttle to capture the satellite, bring it into the shuttle bay, and attach the new perigee kick motor. The astronauts were expected to complete the tasks in 4.5 to 6 hours.

Extravehicular Activity

Approximately 90 minutes before the satellite was captured, two astronauts entered the payload bay. One astronaut was positioned on the manipulator foot restraint, which was attached to the remote manipulator system (RMS). After the RMS positioned the astronaut near the aft end of the satellite, he attached the capture bar to the satellite. Any satellite rotation was halted by the astronaut using a “steering wheel” in the center of the capture bar.

The astronauts then used the capture bar to dock the satellite to the shuttle. After the satellite was brought into the cargo bay, the two astronauts were positioned on diagonally opposite sides of the cradle. One attached an extension to the opposite end of the capture bar to help position the satellite within special alignment guides on the cradle and the docking adapter. These guides placed the satellite within range of the docking adapter clamps. The astronauts then latched the clamps.

Once the new motor was attached, the crew activated the power and the timer switches on each of the two staging and boost electronic units. The crew members then moved into the airlock prior to spacecraft deployment, which occurred at a time determined by INTELSAT. The shuttle crew in the cabin then fired the Super Zip to release the bay’s hold on the satellite. INTELSAT controllers established a command link with the satellite 35 minutes later, after it had reached a safe distance from the shuttle. The satellite’s control electronics were commanded on, its spin rate was increased, and it was placed in the proper attitude and prepared for motor ignition. The PKM was fired using a variable time delay that was commanded by the INTELSAT Launch Control Center.

The PKM thrusted the satellite into a supersynchronous elliptical transfer orbit with an apogee (or highest) altitude of about 45,000 miles (twice that of synchronous orbit). The higher transfer orbit altitude allowed a more efficient use of the PKM and reduced the amount of liquid propellant required to rotate the satellite’s orbital inclination toward Earth’s equatorial plane. By this means, the useful orbital lifetime of the satellite had been extended approximately 1.2 years to an estimated 10.8 years.

Over a period of several days, the controllers sent a series of commands to the satellite to take it to geostationary orbit. Once geostationary orbit was achieved, the controllers sent another series of commands to deploy the satellite’s solar drums and communications antennas.

After in-orbit testing, the satellite was expected to be in service over the Atlantic Ocean region by mid-1992.

NASA Press Release Sarah Loff May 13, 2015

On May 13, 1992, following the successful capture of the Intelsat VI satellite, three astronauts continue moving the 4.5 ton communications satellite into the space shuttle Endeavor’s cargo bay. A fellow crew member recorded this 70mm still frame from inside Endeavor’s cabin. Left to right, astronauts Richard J. Hieb, Thomas D. Akers and Pierre J. Thuot, cooperate on the effort to attach a specially designed grapple bar underneath the satellite. Thuot stands on the end of the Remote Manipulator System’s (RMS) arm while Hieb and Akers are on Portable Foot Restraints (PFR) affixed to Endeavor’s port side and the Multiple Support Structure (MPESS), respectively. The sections of Earth which form the backdrop for the scene are blanketed with thousands of square miles of clouds.EndeavorMissionThe Intelsat satellite, stranded in an unusable orbit since its launch aboard a Titan vehicle in March 1990, was equipped with a new perigee kick motor. The satellite was subsequently released into orbit and the new motor fired to put the spacecraft into geosynchronous orbit for operational use. The capture required three spacewalks: a planned one by astronaut Pierre J. Thuot and Richard J. Hieb who were unable to attach a capture bar to the satellite from a position on the RMS; a second unscheduled but identical attempt the following day; and finally an unscheduled but successful hand capture by Pierre J. Thuot and fellow crewmen Richard J. Hieb and Thomas D. Akers and Commander Daniel C. Brandenstein delicately maneuvered the orbiter to within a few feet of the 4.5 ton communications satellite.

The STS-49 mission, the first flight of shuttle Endeavor, set records for the first (and only, to date) spacewalk involving three astronauts; first shuttle mission to feature four spacewalks; first shuttle mission requiring three rendezvous with an orbiting spacecraft: first attachment of a live rocket motor to an orbiting satellite and first use of a drag chute during a shuttle landing.

NASA Photo Release 13 May 1992 Johnson Space Center

STS-49 ONBOARD SCENE—Florida’s Atlantic Coast and the Cape Canaveral area form the backdrop for this 70mm scene of Intelsat VI’s approach to the Space Shuttle Endeavor. Later, the seven-member crew was successful in capturikng the satellite and adding a perigee phase. The new motor allowed the needed boost for Intelsat, once the crewmembers had released it into space.IntelsatKSCNASA Photo Release 13 May 1992 Johnson Space Center

 STS-49 ONBOARD SCENE—This scene of Intelsat VI floating over a blue and white Earth greeted the STS-49 crewmembers as they prepared for their successful capture of the errant satellite. Within hours of this 35mm shot, three astronauts grabbed the satellite, moved it into the Endeavor’s cargo by, attached a perigee stage and released it into space. Later, a motor firing sent the vehicle on its way to a higher, geosynchronous orbit.IntelsatVIEarth

The following comment was provided by Dick (CR) Johnson:

Note that the failure of Intelsat VI F-3 to separate from the Titan L/V was due to a wiring error (not really a “malfunction”) in the separation system. The Titan P/L interface was configured to accommodate either a single passenger (lower P/L position) or dual passengers (lower and upper P/L positions) for injection and separation into a low earth orbit (LEO). The P/L separation system incorporated two sets of separation signal wiring – one for the upper P/L position and a second for the lower P/L position. It appears that a L/V technician connected the separation signal to the upper P/L position instead of the lower where VI F-3 was located. The physical separation interface was configured to separate the S/C, including the perigee kick motor (PKM), at the PKM interface. The only way to free the S/C from the spent Titan stage was to command PKM – S/C separation leaving the Intelsat VI F-3 in LEO with no PKM (not technically the L/V “second stage”) to inject it into Geosynchronous Transfer Orbit (GTO). (I believe that Intelsat brought legal action against Martin to recover the financial loss attributable to this wiring error.)

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About Jack Fisher

Jack was a systems engineer at Hughes from 1961 to 1992. He contributed to various programs including Surveyor, Pioneer Venus, Galileo, Intelsat VI and innumerable proposals. He was the manager of of the Spacecraft Systems Engineering Lab until his retirement. Upon retirement Jack taught systems engineering at a number of national and international venues.