I US005716029A United States Patent (19) 11 Patent Number: 5,716,029 Spitzer et al. 45 Date of Patent: Feb. 10, 1998 54 CONSTANTSUN ANGLE TRANSFER ORBIT Meserole, J., "Launch Costs to GEO Using Solar Powered SEQUENCE AND METHOD USING Orbit Transfer Vehicles". American Institute of Aeronautics ELECTRIC PROPULSION and Astronautic (AIAA) Paper 93-2219. AIAAJSAE (75) Inventors: Arnon Spitzer, Los Angeles, Calif.; ASME/ASEE 29th Joint Propulsion Conference and Solomon A. De Picciotto, Aurora, Colo. Exhibit. Jun. 28-30, 1993. 73 Assignee: Hughes Electronics, Los Angeles, Free, B. "High Altitude Orbit Raising With On-Board Calif. Electric Power", International Electric Propulsion Confer ence Paper 93-205, American Institute Of Aeronautics and (21) Appl. No.: 558,572 Astronautics AIAA/AIDAVDGLA/JSASS 23rd International 22 Filed: Oct. 31, 1995 Electric Propulsion Conference. Sep. 13–16, 1993. Related U.S. Application Data Primary Examiner-Galen L. Barefoot 63 Continuation-in-part of Ser. No. 217,791, Mar. 25, 1994, Attorney, Agent, or Firm-Elizabeth E. Leitereg; Terje Pat No. 5,595,360. Gudmestad; Wanda K. Denson-Low (51) Int. Cl. ... ... B64G 1/10 52 U.S.C. ................................................... 244/158 R 57 ABSTRACT 58) Field of Search ................................ 244/158 R, 164, 244/168, 169, 172 An apparatus and method for translating a spacecraft (102. 108) from an injection orbit (114) about a central body (100) 56) References Cited to synchronous orbit (122) in a time efficient manner. The U.S. PATENT DOCUMENTS spacecraft (102, 108) includes propulsion thrusters (50) 4,943,014 7/1990 Harwood et al. ....................... 244/169 which are fired in predetermined timing sequences con trolled by a controller (64) in relation to the apogee (118) FOREIGN PATENT DOCUMENTS and perigee (120) of the injection orbit (114) and successive 0 047 211 3/1982 European Pat. Off.. transfer orbits (114), During transfer orbit, the spacecraft's WO 88/02332 4/1988 European Pat. Off. inertial attitude is adjusted to track sun movement. The OTHER PUBLICATIONS spacecraft is injected into a particular injection orbit that offsets moments created by tracking sun movement to Porte et al. "Benefits of Electric Propulsion For Orbit Injection of Communication Spacecraft", 14th AIAA Inter maintain stable transfer orbits. national Communication Satellite Systems Conference and Exhibit, 26 Mar. 1992, pp. 1-9. 16 Claims, 8 Drawing Sheets U.S. Patent Feb. 10, 1998 Sheet 1 of 8 F.G. 1. U.S. Patent Feb. 10, 1998 Sheet 2 of 8 5,716,029 U.S. Patent Feb. 10, 1998 Sheet 3 of 8 5,716,029 66 FIG.5. R 6 FIG.6 U.S. Patent Feb. 10, 1998 Sheet 4 of 8 5,716,029 FIG.108 SUPERSYNCHRONOUS ORBIT 82 REORIENT SPACECRAFT TO THE 8O 84 FIRE ELECTRC THRUSTERS CONSECUTIVELY AROUND APOGEE 86 REORIENT SPACECRAFT TO AN IN PLANEATTITUDE 88 FIRE ELECTRIC THRUSTERS CONTINUOSLY AROUND ORBIT 90 NO GEOSYNCRONOUS ORBIT 2 YES 92 DISCONTINUE CONTINUOUS FRING. FIRE ELECTRIC THRUSTERS FOR STATIONKEEPNG 94 FIG. 11. 17OO 16OO 1500 1400 : 1300 12OO (chemical +Xips) 1100 OOO 20 40 60 80 1 OO 120 TOD (DAYS) U.S. Patent Feb. 10, 1998 Sheet 5 of 8 5,716,029 U.S. Patent Feb. 10, 1998 Sheet 6 of 8 5,716,029 104 U.S. Patent Feb. 10, 1998 Sheet 7 of 8 5,716,029 F.G. 16a 1 OO TIME U.S. Patent Feb. 10, 1998 Sheet 8 of 8 5,716,029 5,716,029 1 2 remain aligned with the velocity vector in order to provide CONSTANTSUN ANGLE TRANSFER ORBIT maximum thrust. Because the launch vehicle injects the SEQUENCE AND METHOD USING spacecraft into either a subsynchronous or supersynchro ELECTRIC PROPULSON nous orbit, the spacecraft must include its own propulsion system to effect a translation from injection to geosynchro RELATED APPLICATION nous orbit and to perform orientation and other stationkeep This Application is a continuation-in-part of application ing maneuvers. This raises several considerations for select Ser. No. 08/217,791 filed Mar. 25, 1994, now U.S. Pat. No. ing a particular injection orbit translation strategy. Ideally, 5,595,360. an injection orbit is selected so that the weight of the O spacecraft without fuel, the dry weight, is maximized. The BACKGROUND OF THE INVENTION dry weight generally includes the weight of the instrumen tation and the underlying spacecraft structure for the instru 1. Field of the Invention mentation. Optimizing dry weight requires a trade-off This invention relates to an apparatus and method of between the capability of the launch vehicle, how high translating a spacecraft from a particular injection orbit to a above the earth the spacecraft can be launched, and the synchronous orbit in a time efficient manner while main 15 propulsion system of the spacecraft, the on-board thrusters taining a constant Sun angle to improve power efficiency and and fuel carried by the spacecraft to translate from injection allow spin stabilization control. orbit to geosynchronous orbit and perform stationkeeping 2. Description of the Related Art maneuvers. Greater injection orbits, i.e. higher apogees, In order to place a spacecraft into a final orbit, such as a 20 reduce the amount of propellant expended by the spacecraft geosynchronous orbit, about a central body, such as the propulsion system to achieve geosynchronous orbit. On the earth, the spacecraft is first launched into an injection orbit other hand, the capability or payload capacity of the launch by the spacecraft launch vehicle. From this injection orbit, vehicle decreases with an increase in the targeted apogee the spacecraft is translated through a series of orbits to the altitude, so that a more powerful launch vehicle is required geosynchronous orbit. In order for the spacecraft to translate 25 to inject a spacecraft having the same mass to an injection from its injection orbit to the geosynchronous orbit, propul orbit having a higher apogee. Thus, in order to optimize the sion thrusters fire to exert a force on the spacecraft and move weight of the spacecraft at arrival in geosynchronous orbit, it through the transfer orbit. defined as the beginning of life weight (BOL), there is a There are a number of strategies for translating a space trade-off between the capability of the launch vehicle and the craft from its injection orbit to geosynchronous orbit. In a amount that the propulsion thrusters need to be fired. Of first strategy, a launch vehicle injects the spacecraft to an course, the more that the propulsion thrusters are fired, more elliptical orbit having an apogee greater than the geosyn propellant mass is required, leaving less mass allocated to chronous orbit, defined as a supersynchronous orbit. Once useful instrumentation. the spacecraft has reached supersynchronous orbit, propul Further adding to the above considerations is that there sion thrusters are fired when the spacecraft is in a predeter 35 are two types of spacecraft propulsion thrusters, electric and mined orientation and in proximity to apogee or perigee. chemical. Chemical propulsion thrusters provide the Firing the propulsion thrusters at apogee to create thrust in required thrust for translating the spacecraft from injection the direction of orbital velocity raises perigee, and firing the orbit to geosynchronous orbit and are capable of exerting a propulsion thrusters at perigee to create thrust in a direction substantial force on the spacecraft. However, chemical pro opposite the orbital velocity lowers apogee. These apogee pulsion thrusters expend a great deal of mass (propellant) in and perigee firings or bums translate the spacecraft from achieving a predetermined orbitorientation. Electric propul supersynchronous orbit to geosynchronous orbit. In a second sion thrusters, on the other hand, create significantly less strategy, the spacecraft is injected into an elliptical orbit thrust than the-chemical propulsion thrusters, but they having an apogee less than the geosynchronous, defined as expend much less mass (propellant) in doing so. That is, a subsynchronous orbit. Once the spacecraft is in subsyn 45 electric propulsion thrusters use propellant (mass) much chronous orbit, the propulsion thrusters are once again fired more efficiently than chemical propulsion thrusters. Using when the spacecraft in proximity to apogee and perigee and electric and chemical propulsion thrusters to effect transla in a predetermined orientation. Firing at apogee to create tion from injection orbit to geosynchronous orbit is thrust in the direction of orbital velocity raises perigee, and described in Forte, P. "Benefits of Electric Propulsion for firing at perigee to create thrust in the direction of orbital 50 Orbit Injection of Communication Spacecraft." American velocity raises apogee. The apogee and perigee bums cause Institute of Aeronautics and Astronautics (AIAA) Paper the spacecraft orbit to spiral out to the geosynchronous orbit. 92-1955, 14th AIAA International Communication Satellite Such a spiraling-out mission using a specific type of thruster Systems Conference & Exhibit (Mar. 22-26, 1992). A com is described in Meserole, J. "Launch Costs to GEO Using bined electric and chemical propulsion system is also Solar Powered Orbit Transfer Vehicles.' Anerican institute 55 described in Free, B. "High Altitude Orbit Raising with of Aeronautics and Astronautics (AIAA) Paper 93-2219, On-Board Electric Power." International Electric Propul AIAAVSAE/ASME/ASEE29th Joint Propulsion Conference sion Conference Paper 93-205, American Institute of Aero and Exhibit (Jun. 28-30, 1993). nautics and Astronautics (AIAA)/AIDA/DGL A/JSASS European Publication No. 0 047 211 to Mortelette 23rd International Electric Propulsion Conference (Sept. describes a transfer orbit strategy in which the spacecraft is 13-16, 1993). injected in a natural orbit where the apogee equals the Because chemical propulsion thrusters exert a much semi-major axis of the desired geosynchronous orbit and the higher force than electric propulsion thrusters, they enable perigee is much smaller than the semi-major axis.