III III || US005595360A United States Patent (19) 11 Patent Number: 5,595,360 Spitzer 45) Date of Patent: Jan. 21, 1997 54) OPTIMAL TRANSFER ORBIT TRAJECTORY Meserole, J., "Launch Costs To GEO Using Solar Powered USENGELECTRIC PROPULSION Orbit Transfer Vehicles', American Institute of Aeronautics and Astronautic (AIAA) Paper 93-2219, AIAA/SAE/ 75) Inventor: Arnon Spitzer, Los Angeles, Calif. ASME/ASEE 29th Joint Propulsion Conference and Exhibit, Jun. 28-30, 1993. (73) Assignee: Hughes Aircraft Company, Los Free, B. "High Altitude Orbit Raising With On-Board Angeles, Calif. Electric Power”, International Electric Propulsion Confer ence Paper 93-205, American Institute Of Aeronautics and (21) Appl. No.: 217,791 Astronautics AIAA/AIDA/DGLA/JSASS 23rd International (22 Filed: Mar 25, 1994 Electric Propulsion Conference, Sep. 13-16, 1993. Parkhash, "Electric Propulsion for Space Missions' Electri (51) int. Cl. ................ B64G 1/10 cal India vol. 19, No. 7, pp. 5-18., Apr. 1979. (52 U.S. C. ........................................................ 244/158 R Davison, "orbit Expansion by Microthrust” Royal Aircraft 58 Field of Search ................................ 244/158 R, 164, Est. Tech Report 67249 Sep. 1967. 244/172, 168, 169 Primary Examiner-Galen L. Barefoot 56 References Cited Attorney, Agent, or Firm-Elizabeth E. Leitereg; Terje Gud U.S. PATENT DOCUMENTS mestad; Wanda K. Denson-Low 4,943,014 7/1990 Harwood et al. ....................... 244/169 57) ABSTRACT FOREIGN PATENT DOCUMENTS An apparatus and method for translating a spacecraft (10) from an injection orbit (16) about a central body (10) to 0047211 3/1982 European Pat. Off. ............... 244/169 geosynchronous orbit (18) in a time efficient manner. The 2850920 6/1979 Germany ........................... 244/158 R spacecraft (10) includes propulsion thrusters (50) which are WO8802332 4/1988 WIPO. fired in predetermined timing sequences controlled by a OTHER PUBLICATIONS controller (64) in relation to the apogee (66) and perigee (72) Porte et al. "Benefits of Electric Propulsion For Orbit of the injection orbit (16) and successive transfer orbits (74, Injection Of Communication Spacecraft", 14th AIAA Inter 76). national Communication Satellite Systems Conference and Exhibit, 26 Mar. 1992, pp. 1-9. 14 Claims, 4 Drawing Sheets U.S. Patent Jan. 21, 1997 Sheet 1 of 4 5,595,360 U.S. Patent Jan. 21, 1997 Sheet 2 of 4 5,595,360 U.S. Patent Jan. 21, 1997 Sheet 3 of 4 5,595,360 U.S. Patent Jan. 21, 1997 Sheet 4 of 4 5,595,360 FIG.O NJECTSPACECRAFT INTO A A SUPERSYNCHRONOUS ORBIT 82 REORIENT SPACECRAFT TO THE DESIRED BURN AT TITUDE 8O 84 N FIRE ELECTRC THRUSTERS CONSECUTIVELY AROUND APOGEE 86 REORIENT SPACECRAFT TO ANN PLANE AT TITUDE 88 FIREELECTRIC THRUSTERS CONTINUOSLY AROUND ORBIT 90 NO GEOSYNCRONOUS ORBIT 2 YES 92 DISCONTIUE CONTINUOS FRING. FIRE ELECTRIC THRUSTERS FOR STATIONKEEPNG 94 : a. 1 Z axip. eahVbrid -117 -sa/ / O 2O 40 60 8O 100 12 O TOD (DAYS) 5,595,360 1. 2 OPTIMAL TRANSFER ORBIT TRAJECTORY perform stationkeeping maneuvers. Greater injection orbits, USINGELECTRIC PROPULSION i.e., higher apogees, reduce the amount of propellant expended by the spacecraft propulsion system to achieve geosynchronous orbit. On the other hand, the capability or BACKGROUND OF THE INVENTION payload capacity of the launch vehicle decreases with an 1. Technical Field increase in the targeted apogee altitude, so that a more powerful launch vehicle is required to inject a spacecraft This invention relates to an apparatus and method of having the same mass to an injection orbit having a higher translating a spacecraft from an injection orbit to a geosyn apogee. Thus, in order to optimize the weight of the space chronous orbit in a time efficient manner while optimizing craft at arrival in geosynchronous orbit, defined as the the energy required for injecting a particular payload. 10 beginning of life weight (BOL), there is a trade-off between 2. Discussion the capability of the launch vehicle and the amount that the In order to place a spacecraft in geosynchronous orbit propulsion thrusters need to be fired. Of course, the more about a central body, such as the earth, the spacecraft is first that the propulsion thrusters are fired, more propellant mass launched into an injection orbit by the spacecraft launch is required, leaving less mass allocated to useful pay load? vehicle. From this injection orbit, the spacecraft is translated 15 Further adding to the above considerations is that there through a series of orbits to the geosynchronous orbit. In are two types of spacecraft propulsion thrusters, electric and order for the spacecraft to translate from its injection orbit to chemical. Chemical propulsion thrusters provide the geosynchronous orbit, propulsion thrusters fire to exert a required thrust for translating the spacecraft from injection force on the spacecraft and move it through the transfer 20 orbit to geosynchronous orbit and are capable of exerting a orbit. substantial force on the spacecraft. However, chemical pro There are a number of strategies for translating a space pulsion thrusters expend a great deal of mass (propellant) in craft from its injection orbit to geosynchronous orbit. In a achieving a predetermined orbitorientation. Electric propul first strategy, a launch vehicle injects the spacecraft to an sion thrusters, on the other hand, create significantly less elliptical orbit having an apogee greater than the geosyn 25 thrust than the chemical propulsion thrusters, but they chronous orbit, defined as a supersynchronous orbit. Once expend much less mass (propellant) in doing so. That is, the spacecraft has reached supersynchronous orbit, propul electric propulsion thrusters use propellant (mass) much sion thrusters are fired when the spacecraft is in a predeter more efficiently than chemical propulsion thrusters. Using mined orientation and in proximity to apogee or perigee. electric and chemical propulsion thrusters to effect transla tion from injection orbit to geosynchronous orbit is Firing the propulsion thrusters at apogee to create thrust in 30 the direction of orbital velocity raises perigee, and firing the described in Forte, P. "Benefits of Electric Propulsion for propulsion thrusters at perigee to create thrust in a direction Orbit Injection of Communication Spacecraft.' American opposite the orbital velocity lowers apogee. These apogee Institute of Aeronautics and Astronautics (AIAA) Paper and perigee firings or burns translate the spacecraft from 92-1955, 14th AIAA International Communication Satellite supersynchronous orbit to geosynchronous orbit. In a second 35 Systems Conference & Exhibit (Mar. 22-26, 1992). A com strategy, the spacecraft is injected into an elliptical orbit bined electric and chemical propulsion system is also having an apogee less than the geosynchronous, defined as described in Free, B. "High Altitude Orbit Raising with a subsynchronous orbit. Once the spacecraft is in subsyn On-Board Electric Power.” International Electric Propul chronous orbit, the propulsion thrusters are once again fired sion Conference Paper 93-205, American Institute of Aero when the spacecraft is in proximity to apogee or perigee and 40 nautics and Astronautics (AIAA)/AIDA/DGLA/JSASS 23rd in a predetermined orientation. Firing at apogee to create International Electric Propulsion Conference (Sept. 13-16, thrust in the direction of orbital velocity raises perigee, and 1993). firing at perigee to create thrust in the direction of orbital Because chemical propulsion thrusters exert a much velocity raises apogee. The apogee and perigee burns cause higher force than electric propulsion thrusters, they enable the spacecraft orbit to spiral out to the geosynchronous orbit. 45 translation from injection orbit to geosynchronous orbit in a Such a spiraling-out mission using a specific type of thruster substantially shorter period of time than electric propulsion is described in Meserole, J. "Launch Costs to GEO Using thrusters. Furthermore, current transfer orbit strategies for Solar Powered Orbit Transfer Vehicles.” American Institute translating a spacecraft from injection orbit to geosynchro of Aeronautics and Astronautics (AIAA) Paper 93-2219, nous orbit fail to describe a viable burn strategy using AIAA/SAE/ASME/ASEE29th Joint Propulsion Conference 50 electric propulsion thrusters exclusively to translate the and Exhibit (Jun. 28-30, 1993). spacecraft to geosynchronous orbit. Moreover, substitution Because the launch vehicle injects the spacecraft into of electric propulsion thrusters in chemical propulsion either a subsynchronous or supersynchronous orbit, the thrusters transfer orbit strategies would require an unaccept spacecraft must include its own propulsion system to effect able transfer orbit duration (TOD). a translation from injection to geosynchronous orbit and to 55 Electric propulsion thrusters also introduce yet another perform orientation and other stationkeeping maneuvers. consideration, that of stationkeeping and maneuvering. This raises several considerations for selecting a particular Because electric propulsion thrusters expend substantially injection orbit translation strategy. Ideally, an injection orbit less propellant for a given thrust than chemical propulsion is selected so that the weight of the spacecraft without fuel, thrusters, and that thrust is relatively low compared to the dry weight, is maximized. The dry weight generally chemical propulsion thrusters, they are more desirable for includes the weight of the instrumentation