TACSAT–Dick Brandes

After the early successes of commercial communications satellites in the 1960’s with the formation of Intelsat and the deployments of Intelsats I & II, the US Air Force saw the need to rapidly explore the utility of communications satellites for tactical military purposes. To that end, the TACSAT program was initiated. It called for the expedited construction of a satellite carrying UHF and SHF repeaters using proven technology to the maximum extent possible, and to deliver the flight model within 18 months on a fixed price basis.

The Hughes Space Division management saw this program has a high priority target. It would provide for an early orbital demonstration of our patented gyrostat concept, that was planned to be proposed for future Intelsat and government programs. And it would undoubtedly evolve into follow-on operational satellites. Thus, we accepted the considerable schedule and financial risks, and put forth a major proposal effort that was ultimately successful. The contract was awarded in January 1967.

The resultant design, designated as HS-308, is shown in Figure 1 with Dick Johnson, systems analysis manager, Dick Brandes, Systems Engineering and Analysis Manager, and Louie Fermelia, systems engineer for telemetry and command. The spacecraft was huge by contemporary satellite standards, about 25 feet tall and 9 1/4 feet in diameter. It weighed about 1600 lbs in orbit. The spinning solar arrays generated almost a kilowatt of power. The size of TACSAT required the construction of a 3-story Hi-Bay assembly and test building. This iconic building (still in use) became the system level assembly/test area for virtually all future Hughes (and Boeing) spacecraft.

Figure 1.  TACSAT flight model with Dick Johnson, Dick Brandes, and Louie Fermelia.

Figure 1. TACSAT flight model with Dick Johnson, Dick Brandes, and Louie Fermelia.

TACSAT was to be launched by the new Titan IIIC booster that would directly insert it into synchronous orbit. With no apogee motor requirement, the simplest interface to the booster was the lower solar panel that became part of the primary load structure. The so-called bellyband separating the upper and lower solar panels was the base for a structural cone that rose upward nearly to the top of the upper solar panel At its apex was the bearing and power transfer assembly (BAPTA), that despun a platform mounting the communications equipment, ancillary equipment, and the nutation damper necessary for spacecraft stability. A slip ring assembly transferred power and signals across the rotating interface. As proposed, the platform itself was an annular ring about midway between the BAPTA and the bellyband, supported by a conical structure attached to the BAPTA.

Mounted on the spinning cone were the spinup and station-keeping fuel systems, the power control and battery systems, and the despin control electronics that achieved a pointing accuracy of 0.1 degree using earth and sun sensors. Attitude control and station-keeping were accomplished through ground commands similar to previous Hughes comsats.

The communications system was enormously powerful and complex.  The UHF peak output was over 40 db EIRP including an antenna gain of about 17 db. The corresponding SHF values were 33-db EIRP and 19-db antenna gain. UHF power was provided by 16 solid state amplifiers inputting a unique power summer that allowed any number to be operated depending on available spacecraft power. Normally, that meant 13 amplifiers with the others providing redundancy. SHF power came from three 20-watt traveling wave tubes (TWTs) paralleled in a three for two redundancy scheme. However challenging these transmitters were, the rest of the system was not far behind. The repeaters were operated in both straight through, e.g. UHF TO UHF, and in crossover modes, e.g. UHF to SHF. There were 8 different modes, variously having bandwidths of 50 KHz, 100 KHz, 425 KHz, 1 MHz, and 10 MHz. The UHF diplexer required over 175-db isolation between transmit and receive frequencies. This design would never have come together without the inspired leadership of Clint Lew, the Communications Labs system engineer.

Our proposal had, of course, touted the extent of proven technology in the design. And we had some. The spinup and propulsion systems were space proven technologies, as were the sun sensors, earth sensors, nutation damper, solar cells, and telemetry and command (T&C) antenna. After that, the list got very short. Besides the basically all new communications system, we had to develop solar panel substrates doubling as spacecraft structure, a machined beryllium BAPTA, extruded beryllium support tubes for the helical UHF antenna, and a slip ring assembly for transferring T&C signals and power across the spin/despin interface. The T&C system itself was a new all PCM design, which had to be compatible with customer furnished encryption/decryption units. The thermal design was novel, an open rear end cavity to radiate excess thermal energy to space. The spacecraft structural integrity would be demonstrated not by the traditional vibration test, but by low force tests to verify that the structure’s modes and frequencies agreed with the analytic values used to determine loads. We were also guinea pigs for Martin-Marietta’s first integration contract on the Titan IIIC. (Thank you Lee Groner for running interference for two years). Oh yes, then there was that stabilization system.


Most development programs encounter development problems, and we had our share. The initial fabrication of the lower load-bearing substrate resulted in ”mechanical property deficiencies” according to an Aerospace report. In other words, it failed its loads test. A significant research project ensued, which ultimately solved the problem. The beryllium BAPTA development went well, but the first extruded beryllium antenna support tubes had unacceptable surface qualities and excessive bow, triggering another successful research project. The slip ring assembly failed its life test; the brush slip ring interface created excessive debris thath shorted out electrical signals. More research!

The spacecraft thermal design was compromised by growth in platform equipment footprint. A few months into development, it became clear that the annular platform didn’t have enough area for all the units. So the ring level was raised closer to the BAPTA, enlarging it. Within a short time even more area was needed. The proposal to crank the platform up a little more was vetoed by Program Manager Dick Bentley. He said to take it to the top, i.e. the BAPTA level. “That’s all the room there is. We’ll have to make it work.” Making it work required a major redesign of the thermal control system. But thermal system manager, George Wolodkin, and his troops were up to the task. Gone was the open rear cavity, replaced by a thermal barrier to maintain proper temperature in the spinning compartment. Excess payload heat was radiated forward by a high emissivity/ high reflectivity sun shield. The new design aced the thermal model test.

Many developments went relatively smoothly. The T&C and power subsystems produced few headaches. The structural analysis team under Paul Bernstein produced a coupled loads analysis that was thoroughly confirmed in the modal testing. The complex communications system had a variety of hiccups, but no crises until we began system test at the spacecraft level. There, we found the UHF receiver flooded with spurious inputs. I joined Brian Rose, the UHF project leader, on the test floor to examine the data. I couldn’t contribute much. But I’ll never forget Brian staring at the data displays like Rodin’s statue of the Thinker. After what seemed like forever, he opined “It has to be the diplexer.” The unit was removed and sent to the vendor where an internal mechanical connection was identified as a suspect. After a welding rework, the unit was returned to spacecraft test and the problem disappeared. Whew!

Probably the most disturbing development for me occurred the day Dick Johnson and one of his analysts, John Velman, appeared in my office many months into the program. John had been creating a complex and complete digital simulation of the spacecraft dynamics including the damper and the despin control system. He ruefully announced that he had gotten his first complete runs back, and unfortunately the spacecraft was unstable; it would tumble in orbit. Oops!

John had traced the problem to the fact that TACSAT’s despun platform was not balanced; it had cross- products of inertia. When the despin control system applied rotational torque to the platform, a tipping torque was induced by the asymmetrical mass properties. The phasing of this torque was such that it would augment any nutation. We had a positive feedback loop producing instability.

Balancing the platform meant starting over. And we quickly determined we didn’t have to. Bob McElvain’s despin control system engineers suggested they could increase the servo lead to change the phase of the torque and eliminate positive feedback. A meeting was convened a few days later to hear their results. It was well attended by customer and Aerospace personnel. Bob’s design engineer gave a nice presentation for over half an hour, describing the design changes and their effect on stabilizing the spacecraft. Then he observed that while the spacecraft would be stable, the despin servo would not. The fix he’d described at length wouldn’t work. How embarrassing!

Fortunately, another of Bob’s guys had a plan B; to wit, increase the lag in the system to accomplish the same end. This was a more difficult implementation, but they worked it out, and Velman confirmed its success. In fact, the control system now acted as an active nutation damper. We had turned a vice into a virtue. We momentarily thought of chucking the damper, but wisely thought better of it.


TACSAT was delivered to the customer in December 1968, 23 months after start. We hadn’t achieved the 18-month objective, but still considered it a major accomplishment. Launch was scheduled for February 8. The system engineering team deployed to the Air Force Sunnyvale spacecraft control center anxious but confident. A one-day postponement of the launch resulted in an enlightening experience. The team decided to kill the day by visiting San Francisco for a little sightseeing. The sightseeing included a tour of Haight-Asbury where, like country bumpkins visiting a big city for the first time, we gawked in amazement at the surrounding scene. Our astonishment drove home how out of touch we were after spending two years holed up in our cubicles 50 to 60 hours a week.

The next day the launch was a go. The booster performance was spot on, and the spacecraft was deposited in synchronous orbit. After spinup, unlocking the despun platform, and activating the despin control system, we focused on the small nutation angle that had been induced by these maneuvers. To feelings somewhere between consternation and panic, we watched the angle slowly grow instead of diminish. Then it stopped and stayed at .8 degrees. After several hours of monitoring with no change, we believed we had a stable situation, but we were baffled.

We returned home to participate in a tiger team to revue every possible energy-dissipating element on the rotor to see if we had overlooked or miscalculated anything. Meanwhile the nutation angle displayed erratic behavior. It would spontaneously disappear and reappear, stabilizing between .6 deg. and 1.2 deg. After a few weeks we seemed at a dead end. All our calculations continued to show the damper alone had two orders of magnitude of stabilizing margin. Bob Telle, Controls Laboratory Manager, then posited that the problem had to be in the BAPTA. A sophisticated test was arranged on the qualification model BAPTA and did in fact show dissipative forces on the spinning side larger than the damper for small angles. The source was believed to be an oil filled gap between the spinning shaft and the inner bearing race. Modification of the unit to eliminate this feature and retest verified that we had found the culprit, to the relief of our other spacecraft programs utilizing gyrostat stabilization.


In-orbit testing showed all other spacecraft systems performing as expected. The small nutation had no significant effect on the earth coverage communications system. Then, some five months after launch, another mystery arose. The UHF EIRP dropped about 3db and started to vary erratically over a 2-db range. Within the time span this occurred, the spacecraft experienced a change in spin speed of .3 RPM and an attitude change of .09 degrees. Testing of the antenna pattern showed significant deviation from initial orbital tests. One first sidelobe had been subsumed into the main beam and the boresight had shifted. Ground testing on a scale model antenna found possibilities for the behavior involving damage to one of the outer helices. Some postulated that a meteorite had struck the antenna, accounting for the dynamic changes noted. While this notion was decried as highly improbable, I have never heard of another explanation.

TACSAT was used extensively for R&D and operational testing by many military communications agencies. It served as a test bed for its advanced design technologies. It supported recovery operations for Apollo. Most importantly for Hughes, it validated the gyrostat concept, which was used in our spacecraft designs for decades. As Fred Adler, Space Division Manager, noted maybe the little stabilization “wrinkle” was a not a bad thing. Unfortunately, there was no direct follow-on spacecraft. Hughes would have to wait for the LEASAT program to once again provide tactical communications.


TACSAT would not have happened without the dedication and personal sacrifice of scores of individuals, many of whom were collocated in one of our airport buildings. I’ve mentioned some of them, and time has fogged over the names of others who were equally critical. But certainly the leadership of Program Manager Dick Bentley and his assistants Roger Clapp and Tom Mattis bear noting. I was privileged to be part of that team.


Summary of Aeronautical Satellite Development, 1963-1972—Roland Boucher

My involvement began in late 1963 when I was assigned to a team at Hughes Aircraft which had been given the task of developing satellite communications applications.  Syncom 2 was in orbit and the age of satellite communication had begun.  As the junior member of the team, I was assigned mobile applications.  A brief study of the problem indicated that for truly mobile communications the user should be able to make use of a simple dipole antenna (or aircraft blade antenna) and that the optimum frequency would be in the 150 mhz to 450 mhz range. The telemetry and command system of Syncom 2 operated in the VHF band at 136 mhz and 148 mhz. this led to a proposal to use this spacecraft to demonstrate satellite-aircraft communications. The efforts of personnel at Hughes, NASA, Air Transport Association, Bendix, Pan-Am as well as the FAA and the US Weather Bureau are described herein.

Significant early contributors were Frank White (ATA); William Pulford and Harry Betsill (Bendix); Meredith Eick, Lou Greenbaum, and Roland Boucher (Hughes); Ben McLeod, Bob Bohanon and Waldo Lynch (Pan Am); Pat Corrigan and Bob Darcy (NASA Goddard) and members of the antenna department at Boeing.  Many other organizations were to become involved over the next nine years.

Receiving Tests with Syncom 2, 1963-64

This period began with a reception test on a satellite simulator in the lab followed by the reception of satellite signals on a dipole antenna and finally reception on a Pan AM 707. Potential degradation of reception due to Faraday rotation and both galactic and man-made noise were also examined. The first year also demonstrated the possibility of using the Syncom 2 command-enable audio tone for teletype communications. This was first demonstrated in the laboratory with a satellite simulator; then with a simple ground station simulating expected aircraft performance.  Ground to air communications was demonstrated on 21 November from the NASA /Hughes ground station at Camp Roberts, California to Bendix equipment and engineers aboard a Pan Am flight en route from San Francisco to Honolulu.

Two Way Communications Syncom 2 and  ATS -1 VHF Experiment, 1965

This year saw the first the two-way air-ground satellite communications. It took place on January 27, 1965 between NASA/Hughes station at Camp Roberts, California and the Bendix equipment aboard a Pan Am flight out of Hong Kong. Further tests were conducted during the year.

Within weeks of the test of January 27 NASA asked Hughes to develop a VHF repeater experiment for the NASA/Hughes Advanced Technology Satellite ATS-1. This experiment was managed at different times by Roland Boucher and Bill Penprase of Hughes and Pat Corrigan of NASA Goddard. I am sorry that I am quite fuzzy about events at this time. When returning home January 28, I was told that my father had contacted meningitis; he died after a brief illness. The next event that I really remember was the solution to an antenna temperature problem.

The antenna for the VHF experiment had been proposed to be mounted on the microwave end of the spacecraft; NASA repositioned it to the apogee motor end. The antenna now had to withstand the heat and blast forces from the rocket exhaust.  I proposed to manufacture the dipole elements from beryllium to absorb the terrific heat without failure; NASA agreed and also decided to flame coat the completed antenna with a ceramic material to provide additional protection. Shortly after this I was named acting program manager for the VHF Experiment on ATS-1.  This program is described in the  quarterly reports (two in 1965, two in 1966, and the final report in 1966).

ATS-1 Launched:  Air-Ground Voice Communications Demonstrated, 1966

The year was spent in the development of the VHF experiment and its new eight-element beryllium deployable antenna and planning for the involvement of the airline industry to be ready for aircraft tests with ATS-1 that was to be launched in December. I presented a paper to the aviation community In July titled “Satellites for VHF Aeronautical Communications – Present and Future.” Executives from nearly a dozen major airlines from all over the world came to visit Hughes to see the progress for themselves.  When ATS-1 was launched on December 7, 1966, aircraft from all over the world were equipped with satellite compatible communication sets. As I remember Pan Am was joined by TWA, United, Quantas, and other foreign airlines.  All reported that the signal was loud and clear except for a small amount of antenna spin modulation (walking feet).  This was most apparent at the edges of coverage. It was all but eliminated in a later test on a Pan Am flight from New York to Brazil when the satellite antenna beam was pointed to the center of the flight path.

Roland Boucher and "Gus" Gustavson With the ATS Prototype.

Roland Boucher and “Gus” Gustafson With the ATS Prototype.

More ATS-1 Tests, VHF Experiment on ATS-3, Circular Polarization, 1967

In early January I decided to see if it was possible to receive FM music transmissions from ATS-1.  The FM modulation (bandwidth) was increased 10 db and the aircraft blade antenna replaced with a simple three-element Yaggi. I modified an inexpensive Sony FM portable radio and tried it . It worked. The inexpensive Sony portable had an IF bandwidth of nearly 500 khz yet it received music transmitted from ATS -1.

The year saw many airlines participate in successful communications through ATS-1. The U.S. Coast Guard became involved with communication tests on the Klamath, the Staten island, and the USCGC Glacier. Hughes authorized me set up a VHF terminal in my home which became known as ARINC Los Angeles. A large number of audio tapes of the communications test were made of both aircraft and shipboard communications.

In May I presented a paper on VHF Satellites for maritime mobile communications before the Radio Technical Commission for Maritime Services. It was well received.

The VHF Experiment on ATS-3 used linear RF amplifiers in place of the Class C amplifiers on ATS-1. Linearity was important because it greatly reduced the intermodulation distortion inherent in multi-channel transmitters. This causes users at microwave frequencies to operate their spacecraft transmitters well below peak power (transmitter back-off). The VHF transmitters were solid state and used a class A/B final stage, The DC power required was reduced 0.5 db for every 1 db of back off.  This was a very important discovery since power is a very expensive commodity on any spacecraft.

At low elevation angles multi-path can cause a significant loss in signal for short periods of time as the reflected signal alternately cancels and adds to the direct signal. Circular polarization can eliminate this problem when used by both receiver and transmitter, (field tests with Tacsat verified this in 1969) Hughes designed and tested circular polarized replacements for the dipole antenna elements on ATS-3.  Unfortunately NASA did not approve their use. Meanwhile Boeing designed a circular polarized flush mounted VHF antenna for the 747.

C. A. Petry at ARINC worked with the airlines and FAA to produce ARINC Specification No. 546.  This specification described the performance and installation properties of a new spacecraft compatible aircraft radio set. When the first Boeing 747 was delivered to Pan Am, it was equipped with and ARINC 546 communication transceiver and a circular polarized antenna. This aircraft was equipped for satellite to aircraft communications. ATS-3 was launched successfully on November 5, 1967.

Hughes designed a small inexpensive VHF terminal for the US Coast Guard which was installed on the icebreaker, USCGC Glacier. This ship was used to resupply the Antarctic base. That winter,1967/1968, sun spot activity a was great and HF radio was unusable for long periods of time. The $4000 Hughes satellite terminal got through every time.

Working with Comsat and the International Community, Bogota Caper 1968

Hughes supported Comsat, NASA, ARIC, and the ATA as well as members of the international community to promote air-ground satellite communications. In September Hughes submitted a proposal to Comsat for a VHF Aeronautical Satellite.

NASA contracted with Philco Ford and General Electric /Hughes for a study program to define future ATS spacecraft models (F and G). The Philco-Ford design concept was chosen for development.

In the spring Hughes was asked if it were possible to broadcast ,through satellite, the up-coming visit of the Pope Paul VI to Bogota, Columbia scheduled in August. The Early Bird satellites operated by Comsat were designed to operate with an 85 foot ground antenna . Time and cost precluded using this approach. I suggested to the group that ATS-3 could be used and that a 15 foot diameter antenna would be sufficient if the prototype 10,000 watt transmitter recently completed at Hughes Fullerton could be made available. I also suggested that the Pope’s terminal contain a VHF communication set in case the telephone service from Bogota to Hughes CA prove unsuitable. NASA agreed to make ATS-3 available, and one month before the expected arrival of the Pope in Columbia we were given the go ahead. Time was short, so I approved the purchase for immediate delivery of a 15-foot antenna from Gabriel’s Horns in New Hampshire.

We ordered immediate delivery of a modified tilt up box from a garbage truck manufacture to be used serve as the terminal structure to house the Fullerton transmitter and other equipment. The FM video modulator was a borrowed prototype of the spacecraft unit used to transmit Spin Scan Camera Video. The FM voice subcarrier was generated by a Boonton signal generator. A VHF terminal similar to the one on the Glacier was installed and a 3 element Yaggi used for transmit and receive. The station was flown to Bogota in a USAF C-130 and set up in less than one week.

At first glance one might think that we were forced to transmit blind since we could not possibly receive video on a 15 foot antenna. Fortunately the video signal has a very large amount of energy in the blanking pulse and is transmitted at the 30 hz frame rate. We tracked the ATS-3 using this narrow band signal and plotted optimum antenna pointing angles with two carpenters tape measures mounted to the antenna gimbals. Later we used the VHF link to talk directly with the NASA ground stations to verify signal saturation levels in the spacecraft. After the successful transmission of the Pope’s Bogota visit by this first mobile satellite transmitting station it went to Iran to transmit the 2500th anniversary of the Persian Empire to the world, then on February 5, 1972 a C-130 flew it to China for the historic visit by President Nixon.

Comsat Plan, CCIR Conference in Geneva, 1969

Hughes provided technical assisted to Comsat and others as requested throughout the year to support its proposal for a VHF Aeronautical Satellite. We prepared a brochure titled “ Aerosat Commercial VHF Communications via Satellite.”

That fall I was selected as a representative of the State Department to the CCIR conference on satellite communications. Thanks to the efforts of Captain Charles Dorian and others we were able to convince the group to authorize VHF aircraft communications by satellite. France led the opposition and unfortunately they played politics better than we did. As I understand it, they got NASA to oppose Aerosat by agreeing to support the Space Shuttle. In any case I received a phone call in Geneva from Hughes saying its all over as NASA pulled the plug.


Flight tests continued, presentations were made all the way up to the office of the President (Nixon). I was offered a position in the Office of The President but declined. I had spent nearly almost 10 years in the pursuit of a VHF Aeronautical Satellite to no avail. Completely independent of my employment with Hughes, I had developed the concept of an electrical powered battlefield surveillance drone and a solar-powered high altitude spy plane. It was time to accept the offer to join the Office of the President or to start a new company to pursue this new field. I left Hughes Aircraft in January 1973. The prototype electric powered battlefield drone flew that year and a proof of concept model of the spy plane flew on solar power alone in 1974

30th Anniversary Celebration Aeronautical Satellite Communications, 1995

On September 29, 1995 Ben McLeod and Bob Bohanan (both from Pan American) organized a 30th anniversary celebration in Washington DC. Personnel from ATA, ARINC, Bendix, Comsat, FAA, FCC, Hughes, NASA and or course Pan Am were in attendance. We all were all thrilled that the aging Frank White was able to attend and were sad that other important contributors from Comsat, Collins Radio, and the US Coast Guard were unavailable or deceased.

This brief description of events almost 50 yeas ago are correct to the best of my recollection.

On the Gyrostat Road—John Neer

When Explorer 1 was launched in the 50’s, it “fell over” into a flat spin. After learning this physics lesson (“flat spin” is the lowest energy state for a prolate spinner), Syncom was designed as an oblate spinner and, therefore, stable. Ball, about the same time, introduced an oblate dual spin design for the first series of OSO satellites. Soon power and aperture growth were overly constrained by the oblate design “rule”. Along came Tony and the Gyrostat, a dual spin prolate design, to open up the design space for much higher power systems with despun platforms carrying large and multiple payloads.

In 1967 I had the good fortune to hook up with Tony Iorillo and was in charge of his laboratory dynamic model of a notional gyrostat. With the great help of John Thomas and Bernie Burns we constructed an air bearing model in Bob Telle’s lab in Building 366 (El Segundo). Here is Tony with that model:Tony

As the more astute reviewer will note, this is actually a “tri-spin” design with a doubly despun platform configuration. The solar array was unfolded and despun on the “south side” of the rotator. As the astute reviewer will also recall, this design was never implemented as 3-axis designs evolved in the 80’s to dominate the high power satellite design world.

The cut away of the lab model looked like this:Lab Model

The model was rather sophisticated and very representative of the gyrostat’s potential design flexibility. As in the case with Syncom, the Gyrostat was patented and the model was critical in demonstrating a reduction to practice criteria.

HS-308, TacSat, was the first Gyrostat and it paved the way for HS-318, HS-312, SDS and others that were developed and put into operation throughout the 70’s. TacSat’s “nutational anomaly” stirred a number of exhaustive pursuits into the mechanisms and sources of “rotor” energy dissipation. One such pursuit I personally got deeply involved with was the “fuel slosh” in the new “conispherical” tanks. That activity involved Jerry Salvatore and a scaled air bearing model set up in Culver City. Thinking that there was a “simple linear” energy dissipation formula, we set out to validate the formula’s prediction. However, when we put a closed circuit camera on the plastic tank with confetti in the liquid, reality struck. What we observed was total nonlinear flow and “churning”. From that point on we engaged in an extensive parametric test program to determine the energy dissipation rate and searched for resonances in fraction filled along with some limited inertia ratio changes. As a result of these early tests, we added an additional nutation damper to Intelsat IV before launch. While the tests were hard to conduct accurately in a 1-G field, it would be valuable to conduct an on orbit experiment validation.

HS-312, Intelsat IV, was a significant “step up” from Intelsat II and III. Here is Harold Rosen with the Intelsat IV mockup:Hal

Al Owens was the Intelsat IV program manager and led the program successfully through 8 satellite launches with one lost to a LV failure. In charge of “systems analysis” I supported the 8 launches back at the ComSat control center in DC. That was a great experience with Marty Votaw and Gene Jilg in charge of the program and operation for Intelsat’s side.

One “untold story” during the first launch: Gene Jilg and I were on “graveyard” ops shift duty and nothing was happening as we were waiting to get into the apogee motor firing orbit and position. Gene came over and asked what we might do to do something. I suggested why not perform a fuel slosh test to see how divergent the spacecraft really was in orbit and “real” 0-G. He was interested and wanted to know what we needed to do. I said we have to turn off the despun control electronics, DCE, disable the active nutational control (ANC) electronics, and let the platform spin up to centrifugally “pin” the eddy current dampers against the stops. Next we would need to pulse an axial jet to increase nutation to a measurable level via the fm accelerometer. I said we needed about one time constant to get an accurate measurement. That meant we would monitor the accelerometer and when we got to ~ ½ degree nutation, we’d send the DCE on command and enable the ANC. Gene thought a moment and said that sounds interesting and “fun”(my word)….and we did it! Those were the days when people were trusted over the process which now tries to control them (my words).

Bottomline: Divergence was faster than the scaled slosh tests predicted so we added another nutation damper on subsequent builds. The result of the test made it clear that the ground tests were not good when scaling to inertia ratio since our test was with the apogee motor and in the transfer orbit mass/inertia state. This led to much more parametric ground testing to better map the fraction filled condition against the inertia ratio. In the end this became a very important finding from a test on orbit that was unplanned and probably not one that would have been approved prior to launch.

As a historical note of some more importance of using an Intelsat IV to conduct a fuel slosh test, Intelsat IV was used to carry the video from Beijing when President Nixon unexpectedly visited there in February 1972. Our colleague, Bernie Burns, went over to China to help set up the ground terminal needed for the relay back to CONUS.

Many of our colleagues realize how rapidly we did things is design, developing and deploying satellite systems which today take 2-3+ times as long yet whose mission success is not significantly improved over what we did in 3-5 years back then. We were fortunate to be at the right place at the right time-a view from the NeerSide…

Thanks to all the colleagues and associates who helped invent the future in the 60’s and 70’s.


The Surveyor Proposal Team—Jack Fisher

When I wrote the post, “Surveyor: Study, Proposal, and Program Initiation,” I tried very hard to find out who was on the study and proposal team consulting a number of sources.  However, it’s been more than 50 years since Hughes captured this program and memories have faded.  I was very pleased to find this article from the Hughes News on February 3, 1961 that provided some information on the Surveyor team.

Hard Work, Long Hours Earn Pact

Outstanding individual efforts by nearly a score of Hughesites earned HAC the key role in the development of the Surveyor spacecraft, one of the nation’s “most meaningful” space programs.

The program has been termed “most meaningful” because Surveyor will answer questions about the moon that have been on men’s minds since the beginning of time.

For the first time we’ll know what the moon’s landscape really looks like. We’ll get an analysis of the soil; a determination of its “atmosphere” and its geophysical characteristics.

The Surveyor program was one of the most sought-after space programs. A total of 38 of the nation’s leading aircraft and electronic firms were in the initial competition vying for one of the four five-month contracts. Hughes was one of the four selected.

Enormous Effort

“ Each of these four companies put forth an enormous effort, not only because of the money involved, but because of the prestige factor,” said Dr. Leo Stoolman, HAC’s Surveyor project manager.

HAC’s effort was prodigious. The men assigned to the project worked 12 hours a day six days a week for seven months, and at one period worked 28 straight days.

Heading this technical team were Dr. Stoolman, R. E. Sears, assistant project manager, and R. K. Roney, technical director, R&D Laboratories, who provided technical direction for our entire Surveyor program.

Individuals Cited

Other key personnel involved were: P. G. Ackerman, scientific instruments; J. M. Bozajian, thermal control and flight mechanisms; J. D. Cloud, systems analysis; R. G. Colbert, vehicle design; T. F. Coleman, vehicle design; J. S. Green, missions operations; R. C. Hamilton, electrical power system; W. F. Hummel, guidance and control; L. G. Ludwig, missions operations; D. A. Mahaffy, propulsion; Max Mason, systems analysis; H. K. Redd, scientific instrument integration; S. C. Shallon, telecommunications; E. E. St. John, telecommunications; C. R. Telle, mechanisms; and A. T. Vall, reliability assurance and test.


Slicing the Bologna and Other Comsat Design Initiatives—Dick (CR) Johnson

The following is an abbreviated history of Hughes’ communication satellite design evolution during the latter part of the twentieth century. Hughes1 was the leading supplier of communication satellites from the mid 1960’s through the end of the twentieth century. This marketplace dominance was earned through the innovation, insight and timely responses of Hughes’ technical and management leadership coupled with outstanding execution by a staff of extraordinarily capable employees. For those on the Hughes space team fortunate enough to have lived through these heady times, it was truly a unique and exhilarating career experience.


 The advent of Syncom in the early 1960’s formed the spacecraft design foundation for the extraordinarily successful family of Hughes spin-stabilized communications satellites which endured for more than 40 years. This 80 pound, spin-stabilized spacecraft is a true masterpiece of design innovation. Syncom is a beautifully integrated design, elegant in its simplicity and efficiency. (See “The Syncom Story” by Harold Rosen.)  Syncom was, in short the perfect, and probably the only practical, spacecraft design solution capable of initiating geosynchronous satellite communications through the application of the then current technology and employing the rocket launchers available at the time. Harold Rosen and his colleagues, Don Williams and Tom Hudspeth conceived, promoted and ultimately lead the full scale development of this major innovation in global communications.

The spin-stabilized Syncom design incorporated major advantages not realized in competing geosynchronous spacecraft concepts. Its large, spinning angular momentum facilitated the attitude stabilization of an integral solid rocket “stage” permitting the attainment of a 24 hour orbit consistent with the relatively limited performance capability of the then available launch vehicles.

On-orbit spin axis attitude control and latitude/longitude station-keeping required only two small thrusters.2 The “management” of onboard spacecraft propellant was implemented by the outboard placement of the propellant tanks in Syncom’s spinning, gravity-like centripetal field. The spacecraft’s thermal environment was benign and near room temperature due to spin “toasting” in the sun’s rays. Finally, the Syncom spacecraft provided a “built-in” spin-scan for body mounted sun, and later earth, sensors with no moving parts.

This all-spinning spacecraft design does, however, incorporate three significant performance limitations. The design’s cylindrical solar panel results in a factor of 1/π (3.14) or 31.8% geometric illumination efficiency (with respect to 100% for a flat, sun oriented solar panel). The incorporation of high gain, earth-oriented “pencil” beam antennas necessary for optimum communication performance (and small, inexpensive ground terminals) requires the electrical or mechanical de-spinning of directional, earth oriented communication antennas. Finally, the dynamic spin stability of this all spinning configuration requires the spacecraft to be “disk” shaped (with respect to mass properties) limiting the length of the overall configuration. Over the long history of Hughes’ spin-stabilized spacecraft, most of these performance limitations were largely mitigated by further spacecraft design initiatives as well as through the increase in satellite accommodation due to the ever-growing launcher rocket size and performance.


Syncom, as well as the Syncom “clone”, Early Bird (the first geosynchronous, commercial communication satellite), and Intelsat II, a larger version of Syncom/Early Bird produced by Hughes for Comsat and Intelsat respectively, incorporated a linear slotted array transmit/receive antenna mounted on and collinear with the spacecraft’s spin axis. This antenna array produced a toroidal or “pancake” antenna beam, symmetrical about Syncom’s spin axis. This antenna pattern resulted in a “squinting” or “focusing” of the spacecraft’s transmitted radiated power directed normal to the spacecraft’s spin axis (as well as that small fraction of the beam – about 5% – covering the earth) to be augmented by a factor of four (or 6 dB). This toroidal antenna beam, however, resulted in roughly 95% of Syncom’s precious transmitted power escaping, radiated uselessly into space. This modest antenna focusing (or gain) combined with a 2 watt traveling wave tube amplifier (TWTA) permitted the relay of one television channel employing the very large (85 foot dish antenna) and very sensitive (cryogenically cooled receiver) government receiving ground terminal located at Point Mugu, CA.

Clearly, the improvement in communication performance available through focusing the downlink transmitted power or “Effective Isotropic Radiated Power” (EIRP) via an earth coverage (17.4 degree diameter conical) beam offered a tremendous communications performance enhancement (about a factor of 20) permitting networks to be implemented using much smaller, cheaper and more practical fixed antenna ground receiving terminals. An additional factor of 50 or so could be achieved through the use of even smaller earth-oriented beams covering limited geographical areas (i.e. single countries).

The initial step toward substantially higher gain, earth oriented antenna beams was implemented via NASA’s Advanced Technology Satellite (ATS) program which was awarded to Hughes in 1962. The first spacecraft in this series (ATS I), launched in late 1966 incorporated an electronically despun earth-coverage antenna beam. A mechanically despun earth coverage antenna, (coupled to the spinning transmitters via an RF rotary joint) was demonstrated on ATS III, launched in November 1967, providing an important despun antenna design demonstration which supported a long, evolving line of future Hughes commercial and government communication satellites.

In the mid 1960’s Hughes recognized, and subsequently developed, the market for national communication satellite systems. The first sale was to Telesat of Canada, an entity created by the Canadian Parliament to establish and operate a national communication satellite (Anik) network. In support of this new marketplace, Hughes designed the HS 333 spacecraft series. The steadily improving performance of the Delta launch vehicle permitted an HS 333 spacecraft mass of 650 pounds, a solar panel generating about 300 watts of electrical power and twelve 6 watt TWTA transmitters (Vs. Syncom’s 80 pounds, 28 watts and single 2 watt TWTA).

The major improvement in transmit performance was, however, the 333’s antenna design which incorporated a mechanically despun, five foot diameter, “offset fed” antenna reflector whose beam was shaped and significantly narrowed (with respect to an earth coverage beam) to cover only the Canadian customer’s specified geographical area. In the case of Anik, this antenna beam narrowing provided an antenna gain performance increase of about a factor of 50 with respect to an earth coverage antenna beam or a factor of 1,000 over Syncom’s toroidal antenna pattern. This narrow beam, high antenna gain was also facilitated by the use of the, 4 GHz, C-Band downlink radio frequency (RF) with respect to Syncom’s 1.8 GHz, L-Band downlink frequency (the antenna diameter for a given, fixed beam width being inversely proportional to its operating frequency). The increased number of simultaneous transmitters and their increased power (12 six watt transmitters Vs. Syncom’s single two watt TWTA) provided another factor of 36 for an overall transmit EIRP performance improvement over Syncom and Early Bird of about a factor of 36,000! Anik’s 12 six watt TWTAs implemented up to 7,000 telephone circuits or 12 simultaneous color TV channels. The Anik ground receiving terminals incorporated fixed (~10 foot diameter) parabolic antennas and receivers operating at ambient temperature, a practical and much more modest receiving terminal performance requirement than for any previous satellite communication network.  Subsequent HS-333 systems were produced for Indonesia and the Western Union Corporation bringing the total sales of this very innovative and successful design to eight spacecraft.

The Disk and the Pencil

Classical mechanics demonstrates that a spinning rigid body is stable spinning about either its maximum (i.e. a flattened disk) or minimum (i.e. a rod or pencil) axis of inertia. As a practical matter, there is no such thing as a perfectly rigid body, certainly not a spacecraft3 containing liquid fuel and other flexible components. In the presence of these non-rigid spacecraft elements, an all-spun configuration is stable only when spinning about its axis of maximum inertia.

However, if a portion of the spinning configuration is despun, a simple design measure to overcome the constraint of spinning only about the spacecraft’s axis of maximum inertia is available. By incorporating a passive, mechanical damper on the configuration’s despun element tuned to the spacecraft’s “nutation”4 frequency it is practical to spin-stabilize a spacecraft about its spinning axis of minimum inertia.

Tony Iorillo, a young Hughes engineer, had this insight in the mid 1960’s and demonstrated its validity both analytically and experimentally over the course of a few months. This innovative technique for the stabilization of a spinning spacecraft was dubbed “Gyrostat” stabilization. The first flight demonstration of Gyrostat stabilization came with the launch of the Hughes/Air Force TACSAT I on February 9, 1969. The TACSAT configuration’s despun “platform” incorporated its communication antennas as well as the entire suite of communications electronics. The freedom to lengthen TACSAT’s cylindrical solar array resulted in a prime power of one kilowatt, at the time, the most powerful spacecraft ever launched.

The impact of Tony’s insight on the Hughes’ family of spin stabilized spacecraft can hardly be overstated. The ability to lengthen the spinning solar panel largely satisfied the near term pressure for significantly increased spacecraft prime power. Additionally, the despun location of the entire communication “payload” permitted direct connection of the communications electronics to earth-oriented antennas enabling lower RF losses and relieving the communication frequency plan constraints with respect to a single RF rotary joint. This design break-through extended the life of Hughes’ spin-stabilized spacecraft product line into the early 21st century and enabled future contracts for upwards of 100 spacecraft valued well in excess of $5 B!

The Space Shuttle and “Slicing the Bologna”

 A key element of NASA’s vision for the Space Transportation System (STS or the Space Shuttle) was that the Shuttle would supplant the government’s family of expendable launchers (Delta, Atlas, Titan, etc.),  and become America’s exclusive system for access to space. NASA’s case for the Shuttle projected a dramatic step increase in launcher cost-effectiveness through the recovery and reuse of most of this manned launcher system’s components combined with tens of launches per year. The STS Program was approved by Congress and development was initiated in 1972.

To attract spacecraft customers to come on board, in the mid 1970’s NASA promulgated a pricing formula for the trip to low earth orbit (LEO). This formula was based on the spacecraft customer’s utilization of the Shuttles 60 foot long (by 15 foot diameter) payload bay length or the fraction of the available Shuttle, payload mass capability, about 55,000 pounds whichever was the greater. (Some wag likened this pricing formula to “Slicing a 15’ X 60’ Chub of Bologna” and the characterization stuck.) Based on NASA’s total price for a Shuttle launch, adjusted by their pricing formula, projected launch costs for a typical mid-70’s Hughes spacecraft was a small fraction of that charged for an expendable launch vehicle.

Following this realization, Hughes’ reaction was almost immediate. Harold Rosen’s initial concept for a Shuttle optimized spacecraft was a “wide-body” spin- stabilized spacecraft occupying the full Shuttle payload bay diameter, approximately ¼ of the payload bay length and consuming about 30% of its payload mass capacity. This new spacecraft design, dubbed “Syncom IV”, incorporated the integral propulsion necessary to transfer the spacecraft from LEO to geosynchronous orbit. In addition to a large, solid-propellant perigee kick motor (PKM), a new, high performance bi-propellant propulsion system was incorporated to augment orbit injection, for attitude control and for orbital station-keeping.  Syncom IV was secured to the Shuttle’s payload bay using a “cradle” adapter encircling the lower half of the spacecraft’s cylindrical drum. Deployment in orbit was implemented through a “Frisbee” ejection, clearing the payload bay with a small residual separation velocity and slow spacecraft spin.

Hughes conducted a vigorous marketing campaign to demonstrate to potential Syncom IV customers the unmatched cost-effectiveness of the available communication capabilities that could be delivered on orbit at a bargain basement price. One of Hughes’ potential Syncom IV customers was Satellite Business Systems (SBS – a joint venture of IBM, Aetna and Comsat). During a marketing visit in 1977, Harold Rosen was briefing the Syncom IV design to SBS when their CEO interrupted to express great reluctance to enter into Syncom IV procurement as the Shuttle had not yet flown and expressed his concern that it would, perhaps, never fly! In that case, what would SBS do with an expensive satellite that could not be launched?

Prompted by SBS’s (and other customers’) skepticism of the Shuttle program’s integrity and schedule, within a few weeks Dr. Rosen configured a new spacecraft design which was compatible with launch on either the shuttle or the Delta, expendable launcher. This dual launch design was originally only intended to provide a backup capability in the absence of Shuttle launch availability. However, this new spacecraft design became the HS 376/393/Intelsat product line which comprised about 80 spacecraft (many of which were launched on the Shuttle) and carried the HSCC’s family of spin stabilized spacecraft into the early 21st century.

The Shuttle finally became operational in mid-1981 and the wide-body Syncom IV design became basis for the five spacecraft Leasat series for the US Navy. A few additional wide body STS launched spacecraft were also purchased by the U.S. Government in support of classified missions. (These classified versions of Syncom IV adopted a new, high capacity, weight efficient nickel-hydrogen battery design.)

Hughes was at least two years ahead of their competitors in recognizing the outstanding competitive opportunity offered by NASA’s STS launch pricing policy.

These Hughes’ STS compatible spacecraft designs, incorporating spin-stabilized integral propulsion for transfer to geosynchronous orbit, implemented a near perfect match to NASA’s Shuttle payload capabilities and pricing formula. During the mid 1980’s, life for Hughes in the Comsat marketplace was very good indeed!

“The jig’s up!”

This major marketplace advantage was ended abruptly in January of 1986 by the catastrophic Shuttle Challenger explosion shortly after its lift-off from Cape Canaveral. Within months of the loss of Challenger and her crew5, the government suspended STS launches of unmanned payloads. Continuing this Shuttle launch service was judged to be no longer acceptable due to the additional Shuttle launches required and the added risk to the Shuttle and her crews. Hughes, in a single stroke, lost the large pricing and capacious Shuttle payload bay advantage that had provided a significant marketplace edge for their spin stabilized family of spacecraft. With NASA’s decision to suspend STS launches of unmanned spacecraft, S&CG’s management realized that “The jig’s up!” and Hughes would need to initiate a body stabilized spacecraft design to remain competitive utilizing the available, and much more expensive, family of expendable launch vehicles. After many years of external and internal pronouncements that the era of spin-stabilized ComSats was finished due to the greater power efficiency offered by flat, sun-oriented solar array panels and a somewhat more compact, weight-efficient body stabilized configuration, Hughes concluded that the time had come to incorporate a body stabilized design into their Comsat portfolio.6


In 1986, Based on Hughes’ persuasive business case, their new owner, General Motors, endorsed a substantial investment of Hughes’ internal funds to develop a new, state-of-the-art, body stabilized Comsat design aimed at “leap-frogging” their competition by incorporating the very latest, proven, high performance space technology. This new spacecraft design was designated the Hughes Satellite 601 (HS-601). With eventual sales exceeding 90 units, the HS-601 Comsat design (followed by the late 90’s body stabilized HS-702 upgrade) continued Hughes’ position as the world’s leading supplier of communication satellites well into the 21st century.

The 601 design incorporates an internal high-speed momentum wheel gimbaled about two axes to control/stabilize spacecraft attitude. Attitude sensing is via earth and sun sensors augmented by precision inertial gyroscopes. The buildup in the small angular momentum (spin axis) errors due to external disturbances (primarily solar pressure imbalance) is cancelled through the use of magnetic torque rods, which conserves spacecraft propellant. The design provides the integral propulsion necessary to inject the spacecraft into geosynchronous orbit from either a low earth circular orbit (through the incorporation of a spin stabilized, solid propellant “perigee kick motor”) or from a highly elliptical geosynchronous transfer orbit utilizing a 100 pound liquid-propellant thruster. This high performance bi-propellant system, first implemented on Syncom IV, provides orbit injection augmentation as well as on-orbit latitude station-keeping. Later versions of the 601 configuration (601-HP) incorporate Xenon ion propulsion for on-orbit latitude station-keeping saving a substantial mass of liquid propellant. Prime spacecraft power is implemented using dual 3 or 4 section, deployable, sun oriented solar panels initially populated with silicon solar cells. Using advanced gallium arsenide (GaAs) solar cells, this design’s maximum prime power generation capability is approximately 10 KW. (This large prime power availability enables the economic transmission of colored television directly to individual homes utilizing fixed, ~1 meter diameter receiving antennas.) An advanced, highly efficient Nickel-Hydrogen (NiH) battery, proven on previous government programs, provides power during on-orbit earth eclipses.  The heat generated by internal electronics is conducted via heat pipes to thermal radiating mirrors located on the north and south faces of the cubic 601 spacecraft.

This new spacecraft represented a major design departure from the previous Hughes, space proven spinning spacecraft “bus” technology. Everyone knew that Hughes had their reputation and a great deal of their customers’ confidence riding on demonstrating the efficacy of this new 601 spacecraft configuration.

Following the HS-601 design/development program and Hughes’ vigorous marketing campaigns in 1987/1988, the first 601 contract was awarded for two HS-601 Comsats by AUSSAT Pty Inc. in July of 1988.7 In the same month Hughes was awarded the US Navy contract for their UHF Follow-On program. This Navy Comsat was also a 601 design and was for the development, manufacture and launch of the first spacecraft with options for 9 additional units over a total period of about ten years. Both the AUSSAT and UHF Follow-On fixed-price contracts incorporated major financial penalties8 for any spacecraft failures and/or performance shortfalls. Both also called for the spacecraft to be delivered on-orbit which made Hughes responsible for the procurement of the launch vehicles and launch services.

Contracting for on-orbit Comsat delivery was not new for Hughes. However, the very first HS-601 launch (scheduled for April of 1992) was from Xichang, China aboard a new Chinese launch vehicle design, the Long March 2E rocket, lifting off from a recently constructed launch pad complex and was contracted with a newly minted Chinese commercial launch supplier (The China Great Wall Industries Corporation). So, with an unproven spacecraft, an unproven launcher, a new launch facility, and a novice commercial launch supplier, Hughes faced several additional and risky unknowns!  Moreover, prior to the first HS-601 launch, Hughes had entered into fixed-price contracts for 24 additional HS-601 spacecraft. The risks and stakes with respect to this first spacecraft launch were probably as high as the Hughes’ space enterprise had ever taken on!

The first HS-601 launch (Australia’s Optus IB) was scheduled for April, 1992 from the Xichang launch complex. The Long March 2E rocket ignited on schedule but then, automatically shut down due to the failure of one of the Long March’s four “strap-on” booster assist rockets to ignite. After the identification and correction of this ignition fault, the Optus IB second launch attempt occurred on August 14, 1992. This time the Long March rocket performed flawlessly separating the spacecraft in low earth orbit. Following the firing of the spacecraft’s solid perigee kick motor and several burns of the liquid, 100 pound thruster, the spacecraft was placed into geosynchronous orbit. Subsequent deployments of Optus IB’s’ solar panels and communication antenna reflectors were executed without incident. Hughes’ initial HS-601 mission was, to everyone’s gratification and great relief, an unqualified success! It would be followed by more than ninety additional 601 flights before the product line was gradually supplanted by the upgraded HS-702 series introduced in the late 1990’s.

In response to the quest for even greater spacecraft power and performance the HS-702 body stabilized spacecraft incorporated prime power capability in excess of 16 KW through increasing the maximum number of deployable solar panels from four to six. Larger Xenon ion thrusters capable of augmenting liquid propulsion orbit insertion and for longitude on-orbit station-keeping were incorporated to reduce launcher costs and/or to convert the saved weight of the reduced liquid propellant load into additional communication payload capability. The 702 control system design is a “zero momentum” configuration incorporating multiple reaction wheels for increased attitude control flexibility. A series of “Geo-Mobile” (GEM) Comsats which featured multiple (~200) rapidly switchable spot beams controlled by an advanced on-board digital signal processor (DSP) and interconnecting small mobile or fixed ground terminals was added to the 702 inventory in the early 2000’s. (Six of these GEM Comsats are in operation for HSCC’s Thuraya and Direct TV customers.) The Boeing 7029 spacecraft design is currently in production for multiple commercial and government customers.

Four Decades of Innovation and Excellence

Hughes became the pioneer of geosynchronous satellite communications with the 1963 launch of Syncom. Hughes also became the world’s leading producer of communication satellites during the last four decades of the 20th century. Of the communication satellites launched during this period, 165 were Hughes’ products, more than all the other suppliers combined. At the end of the 20th century upwards of 200 active communication satellites occupied the geosynchronous orbit belt. Geosynchronous communication satellites now implement global and regional communication networks which enable the transmission of television, data, messaging and telephony on a scale and at a modest cost nearly unimaginable in the early 1960’s.  Hughes’ communication satellite innovations have spawned a multi-billion dollar space industry which has truly changed the world.


1) The Hughes’ space enterprise was initiated as the “Space Division” of the Hughes Aircraft Company’s Aerospace Group in 1961. In 1970 Hughes’ space activities were consolidated in the “Space and Communications Group” (S&CG) under the leadership of Albert D. (Bud) Wheelon. In 1992, following the Hughes re-organization under their new CEO, Mike Armstrong, it was re-named the “Hughes Space and Communication Company” (HSCC).  This history refers to the space component of the Hughes enterprise as simply “Hughes”.

2) This simple spacecraft thruster control system was patented by Don Williams and    Hughes. The famous “Williams’’ Patent”, in effect, denied Hughes’ growing competition the use of spin stabilization in their spacecraft designs without the risk of legal sanctions. TRW’s Intelsat III and DSCS designs (as well as several others) did, in fact, infringe on the Williams patent and were the subject of protracted legal actions culminating in penalties of $114 M awarded to Hughes in 1994.

3) The first successful U.S. satellite, Explorer, launched in 1958 and designed to be spun   about its minimum inertia axis, clearly showed that a non-ridged spacecraft was indeed unstable spinning about its minimum inertia “pencil” axis. Within a few hours, Explorer’s initial spin axis diverged to transfer its entire spin angular momentum about its axis of maximum inertia which was perpendicular to its “pencil” axis.

4) When disturbed (firing of a thruster, etc.), a spinning body’s axis of spin cones about its undisturbed position (its angular momentum vector). This coning motion is termed “nutation”. The frequency (number of rotations per second) of this coning motion is determined by the spacecraft’s inertial properties. (the ratio of maximum to minimum inertia axes)

5) The Challenger disaster was also a very personal tragedy for the Hughes family. One of the ill-fated Challenger crew members was Greg Jarvis a seasoned, a well-liked, respected and talented Hughes engineer.

6) Their existing contracts plus a few follow-on contracts for the Hughes Gyrostat configuration maintained this, now declining, spin stabilized product line through launches extending into the early 21st century.

7) AUSSAT (an Australian government entity) transferred responsibility for their satellite communications programs to Optus, a newly established, private Australian company, in late 1991.

8) The Optus IB contract called for Hughes to replace any failed spacecraft at no cost to their customer. The UHF Follow-On contract incorporated orbital incentives requiring Hughes to repay 50% of the contracts’ basic and/or option prices (declining to zero over the spacecraft’s 10-year contractual orbital lifetime) for failure of any spacecraft to satisfy on-orbit performance requirements.

9) Following the acquisition of the Hughes’ space business by the Boeing Company in 2000, the Hughes’ spacecraft product line nomenclature (HS-XXX) was revised to Boeing XXX.


1)    Boeing Satellite Development Center Web Site

2)    “The SYNCOM Story” – Harold Rosen

3)    “A (Very) Short History of the Space and Communications Activities of Hughes Aircraft       Company” – Steve Dorfman