In October 2000, The Boeing Company acquired three units within Hughes Electronics Corporation: Hughes Space and Communications Company, Hughes Electron Dynamics, and Spectrolab, Inc., in addition to Hughes Electronics' interest in HRL, the company's primary research laboratory. The four are now part of Boeing's newest subsidiary, Boeing Satellite Development Center.
Boeing 601HP Thruster:
- 13 centimeters in diameter
- 2568 seconds ISP
- 18 mN of thrust
Boeing 702 Thruster:
- 25 centimeters in diameter
- 3800 seconds ISP
- 165 mN of thrust
With the delivery of the PAS-5 satellite to PanAmSat Corporation in 1997, Hughes Space and Communications Company launched a new era in satellite propulsion technology.
PAS-5 is the world's first commercial satellite to carry a revolutionary propulsion system which is 10 times more efficient than the systems currently in use: xenon ion propulsion. By the third quarter of 2000, 11 on-orbit satellites were using XIPS.
The xenon ion propulsion system, or XIPS (pronounced "zips"), is the culmination of nearly four decades of research into the use of electric propulsion as an alternative to conventional chemical propulsion. Available on the Boeing 601HP, or high power, and Boeing 702 satellite models, the increased efficiency possible with XIPS allows for a reduction in propellant mass of up to 90% for a satellite designed for 12 to 15 years operation. Less propellant results in reduced cost for launch, an increase in payload, or an increase in satellite lifetime, or any combination of the above.
Whatever the choice, the results are a sizable competitive margin.
The on-board XIPS system is used primarily for spacecraft stationkeeping. Small thrusts are required to correct for the tug of solar or lunar gravity and to reposition the satellite in its proper orbit and altitude. A satellite's lifetime as well as its launch weight is thus determined by the amount of fuel aboard for its thruster system.
While most current satellites use a chemical bipropellant propulsion system, a XIPS-equipped satellite instead uses the impulse generated by a thruster ejecting electrically charged particles at high velocities. XIPS requires only one propellant, xenon, and does its stationkeeping job using a fraction of that required by a chemical propellant system.
The heart of the XIPS is the ion thruster, measuring less than 10 inches across. Two other key units include a tank containing xenon gas and a power processor.
Thrust is created by accelerating the positive ions through a series of gridded electrodes at one end of the thrust chamber. The electrodes, known as an ion extraction assembly, create more than 3,000 tiny beams of thrust. The beams are prevented from being electrically attracted back to the thruster by an external electron-emitting device called a neutralizer.
Ions ejected by the Hughes-designed XIPS travel in an invisible stream at a speed of 30 kilometers per second (62,900 miles per hour), nearly 10 times that of its chemical counterpart. And, because ion thrusters operate at lower force levels, attitude disturbances during thruster operation are reduced, further simplifying the stationkeeping task.
Chemical thrusters in use today are limited by how much energy is released during the combustion process. Ion thrusters are dependent on the amount of electrical power available. More power means faster-moving ions and higher thrust. The Boeing 601HP XIPS uses 500 watts from the satellite's 8-kilowatt solar array. For the Boeing 702 model, XIPS uses 4,500 watts from the 10- to 15-kilowatt solar array. XIPS operations have no effect on broadcasting and telemetry operations.
A typical satellite will use up to four XIPS thrusters (two primary, two redundant) for stationkeeping, all connected to the same xenon supply. Each primary device will be switched on and off by a smart power unit that monitors and diagnoses operations automatically. In normal operation, each Boeing 601HP ion thruster will operate for approximately 5 hours per day. Each Boeing 702 ion thruster will operate for approximately 30 minutes per day.
The Boeing 601HP satellite uses the 13-centimeter XIPS to perform all north-south stationkeeping and spacecraft momentum control in two axes. The 13-centimeter thruster operates at a specific impulse rate (ISP) of 2568 seconds with 18 millinewtons (mN) of thrust. The satellite flies four 13-centimeter xenon thrusters and two power processor units. Orbit and momentum control are accomplished through a series of two burns on each day of the stationkeeping cycle. Only two of the four thrusters are required to perform a complete mission of on-orbit maneuvers.
The Boeing 702 uses its high-power capacity to take full advantage of XIPS technology with the previously developed higher-power 25-centimeter thrusters. The 25-centimeter thruster operates at an ISP of 3800 seconds with 165 mN of thrust. The satellite flies four 25-centimeter thrusters and two XIPS power processors. The HS 702 uses the XIPS to perform all stationkeeping and spacecraft momentum control. Like the HS 601HP, only two of the four thrusters are required to perform the entire on-orbit mission maneuvers. These functions are accomplished autonomously with a series of four daily burns providing precise orbit control. This strategy maintains a �0.005 degree stationkeeping box, allowing for collocation of many satellites in a single orbital slot.
The Boeing 702 offers the additional option of XIPS orbit raising. Using XIPS to augment transfer orbit further reduces the amount of chemical propellant loaded. Larger payloads can thus be accommodated, with greater flexibility in the choice and use of a launch vehicle. Chemical propellant is used to place the satellite into a supersynchronous elliptical transfer orbit, and pre-programmed XIPS maneuvers are used to circularize the orbit and position the satellite in its final orbit.
Hughes has been investigating the use of ion propulsion since the early 1960s. Early research focused on the gas cesium, which was later discarded due to its corrosive nature. Mercury was then used, but was later rejected because of its environmental impacts.
In 1984, Hughes Research Laboratories, a unit of Hughes Electronics Corporation, began investigating the use of xenon and found that it offered the highest thrust of all the inert, non-reactive gases. And, because it is an inert gas, it is neither corrosive nor explosive, and therefore does not pose a risk to the life of the satellite or a safety hazard to personnel loading the xenon propellant tanks. Development units were constructed and evaluated at that time by Hughes Electron Dynamics Division, now Boeing Electron Dynamic Devices, Inc.
In 1992, Hughes Space and Communications Company committed to the XIPS technology, identifying it as the basis for next-generation satellites. The highly focused beam inherent in the system provides higher thrust efficiency and reduces the potential of spacecraft contamination from the beam.
The initial design work was done by Hughes Research Laboratories, and XIPS production is now performed at Boeing Electron Dynamic Devices, where competencies and facilities already exist due to the company's expertise in traveling wave tube design and construction techniques.
The first shipment of XIPS thrusters was the culmination of an extensive program of testing, performance documentation, and measurement. Hundreds of hours of burn-in testing were performed to assure that there would be no early wear-out problems. Vibration testing simulating the launch environment was conducted, followed by post-vibration testing and extensive thermal-vacuum testing, where the thruster was cycled many times from a very cold to an extremely hot temperature, simulating what will be encountered in space.
Five massive vacuum chambers, measuring 9 feet in diameter, are used to test XIPS thrusters. Three chambers are used for flight unit acceptance testing, and two chambers are committed to the on-going life testing of two 13 centimeter qualification units. In addition, Boeing Electron Dynamic Devices is currently building another vacuum chamber dedicated to qualification and lifetime testing of the Boeing 702 thruster. The new chamber weighs in at 180,000 pounds and measures 20 feet in diameter by 40 feet in length.
Two qualification thrusters are currently in life test, with the initial thruster qualification unit, which was built in 1995, having demonstrated more than 8,000 hours of lifetime testing. The second qualification unit, built in 1996, has demonstrated more than 4,000 hours of lifetime testing.
In addition to the XIPS thrusters being built for Boeing Satellite Development Center, Boeing Electron Dynamic Devices also has an $8.1 million contract from NASA to produce a 30-centimeter xenon ion engine for use on the New Millennium program's Deep Space 1 spacecraft. The initial contract, awarded in 1995, calls for delivery of one Pathfinder thruster, two flight thrusters, and associated power processor and digital control and interface units to NASA by the end of 1997. Deep Space 1 was launched on Oct. 24, 1998.
From the 1963 launch of Syncom, the world's first communications satellite, to the introduction of the 702 spacecraft model 32 years later, Hughes Space and Communications Company, now Boeing Satellite Development Center, has maintained its leadership position in satellite systems design and manufacturing. XIPS is likely to be the single most important technological contribution to customer value and success over the next decade of satellite communications.
Boeing Satellite Development Center is the world's leading manufacturer of commercial communications satellites, and is also a major supplier of spacecraft and equipment to the U.S. government, and builder of weather satellites for the United States and Japan.