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.
Syncom
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.
Focusing
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
HS-601/702
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.
Notes
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.
References
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
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