The Space Congress® Proceedings 1983 (20th) Space: The Next Twenty Years Apr 1st, 8:00 AM Future Requirements and Applications for Orbital Transfer Vehicles D. E. Charhut General Dynamics Convair Division, San Diego, California W. J. Ketchum General Dynamics Convair Division, San Diego, California Follow this and additional works at: https://commons.erau.edu/space-congress-proceedings Scholarly Commons Citation Charhut, D. E. and Ketchum, W. J., "Future Requirements and Applications for Orbital Transfer Vehicles" (1983). The Space Congress® Proceedings. 1. https://commons.erau.edu/space-congress-proceedings/proceedings-1983-20th/session-iic/1 This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. FUTURE REQUIREMENTS AND APPLICATIONS FOR ORBITAL TRANSFER VEHICLES By: D.E. Charhut* W.J. Ketchum** General Dynamics Convair Division San Diego, California ABSTRACT — Storage/reconstitution — Threat avoidance/defense The capability of the Space Shuttle will be enhanced by use of the high-energy Centaur to provide payload High OTV performance (through high I Sp and low transfer to higher orbits (geosynchronous, etc.) and vehicle weight) minimizes propellants and maximizes for planetary escape missions. Future orbital transfer payload. Hydrogen-oxygen is currently the highest vehicles (OTV) requirements for NASA, military, and performing chemical combustion rocket propulsion commercial exploitation of space will require system (50% higher ISp than solids or storables). Cen­ taur (Figure 1) is being incorporated improvements and technological developments into the Space such Transportation System (STS) to take advantage of as increased performance, increased reliability, and this in the near future at affordable cost, and methods increased mission versatility. Eventual OTV space to further improve performance and versatility are basing should offer further cost reductions through being considered. As part of the STS, Centaur mis­ vehicle reuse, freedom from Shuttle constraints, and sion assignments include Galileo, ISPM, and two for possible STS propellant recovery. DoD (Figure 2). Under a joint NASA/Air Force pro­ gram, NASA and the Air Force are sharing develop­ This paper summarizes Centaur characteristics, per­ ment costs of the Centaur G (short version). NASA is formance, and program status and presents future funding Centaur G ' (long version). considerations for orbital transfer vehicles into the Space Station era, including their capabilities, opera­ Hydrogen-oxygen OTV are expected to improve and tional requirements, and the technology develop­ endure for many years until noncombustion propul­ ments required to make them a reality. sion (chemical-electric) becomes available to effec­ tively remove Isp limits. INTRODUCTION CENTAUR The goal of space transportation is to provide in­ Centaur is the world's first liquid-hydrogen-powered creased launch opportunity at lower cost. This paper space vehicle. Today, it is the United States' premier addresses orbital transfer vehicles (from low earth upper stage for launching large geosynchronous com­ orbit to higher orbits) and how improvements to this munications satellites, solar exploration spacecraft, segment of the space transportation system can and observatories to study the farthest reaches of contribute to this goal for a number of applications: space. • Commercial programs — Satellite placement The flight-proven Centaur system has been launched — Satellite servicing 67 times on Atlas and Titan boosters. It has per­ • NASA programs formed flawlessly during the last decade of operation, — Planetary missions due in part to the improved guidance, navigation, and — Satellite placement electronics systems incorporated in the early 1970s. It —- Manned orbital operations is currently undergoing performance improvements • DoD programs for INTELSAT that will enhance its capabilities for the — Satellite placement 1980s. • Director, Advanced Space Programs Integrating a modified Centaur high-energy stage •* Project Manager, Orbital Transfer Vehicles with the Space Shuttle offers a significant increase in IIC-26 the high earth orbit and earth-escape performance craft. With on-orbit rendezvous and assembly of the capabilities of the STS. Centaur is the only affordable Centaur and spacecraft payload weights of more than near-term solution for attaining this capability. 20,000 pounds can be placed in geosynchronous Figure 3 shows Centaur performance for planetary equatorial orbit. and geosynchronous earth orbit missions, indicating its capability to perform the Galileo "direct" mission This approach allows the spacecraft to use the full as well as placement of heavy payloads at GEO for 60-foot length of the cargo bay; however, it uses only DoD and other users. about one-third of the lift capability of the Orbiter carrying the spacecraft. Adding a propulsion stage to Studies were begun in 1979 to integrate Centaur into the spacecraft would use some of this excess capabil­ the Space Shuttle using the current D-l configuration ity, and Centaur could thus place even greater with 30,000 pounds of propellant and cylindrical 10- spacecraft weights into geosynchronous orbit. foot-diameter tanks. Delay of the Galileo mission, however, increased energy requirements to the extent FUTURE REQUIREMENTS that additional propellant is required to perform the mission. A decision was made to increase the LH2 The basic drivers for increased capability tank diameter to the maximum orbit allowed within the transfer vehicles (OTV) include cargo bay (14.2 feet), and to lengthen the existing performance, opera­ LO2 tank by 2.5 feet (Figure 4). These modifications tions, and cost-effectiveness. Spacecraft growth from increase the usable propellant weight to 45,000 the current 5,000-pound range to 10,000 pounds and pounds and use the Shuttle cargo bay more efficient­ more is already beginning to happen. High velocities ly. The resulting configuration — Centaur G' — has are needed for planetary and maneuvering spacecraft. a vehicle length of 29.1 feet, with 30 feet of the Orbi- In the 1990s, missions are contemplated with round- ter cargo bay available to the spacecraft. trip capability to service satellites at GEO and others for manned sortie. For this, OTV must fulfill the By maintaining the Centaur D-l LO2 tank diameter, following requirements: the basic vehicle proplusion system remains un­ • Very high performance: 15,000 to 30,000-pound changed, although the larger LH2 tank does require payloads, servicing and round trip. an increased-diameter forward stub adapter and equipment module. • Low acceleration: maximize size of large space structures. For longer spacecraft, a shorter Centaur version uses • Reusability: reduce operating costs and return only 29,500 pounds of propellant at a slightly higher payloads. engine mixture ratio of 6:1 (the standard ratio is 5:1). • Aerobraking: double round-trip payload (versus This configuration, called Centaur G, is only 19.5 feet all propulsive). long and allows spacecraft up to 40 feet long in the • Manrating: Orbit transfer and sortie for crew Orbiter. modules. • Spacebasing: free from Shuttle constraints. Shuttle/Centaur G will have the geosynchronous capability to deliver large communications satellites Operations in space require quick reaction, restart for weighing 10,600 pounds with lengths up to 40 feet. orbit relocation, or low acceleration to transfer very This is more than double the IUS capability, with large, delicate spacecraft. Future space only five percent less spacecraft transportation length. For heavier systems (Figure 5), including spacecraft, Centaur J, with propellant tanks resized growth versions of ex­ to hold 35,000 pounds, will be capable of launching a isting or new vehicles, should be more cost effective. 14,000-pound spacecraft up to 37.6 feet long into Increased capability tends to lower the cost per pound geostationary orbits. of payload delivered to high orbit. These capabilities will dramatically enhance the ENGINES United States' ability to launch large communication satellites. Without Shuttle/Centaur, the size of com­ Design studies and tests by the major engine contrac­ munication spacecraft would be limited until further tors indicated the feasibility of increasing hydrogen- performance improvements can be realized with oxygen Isp to 480 seconds (compared with 450 Ariane or the IUS, or until the United States can seconds currently). Figure 6 indicates several can­ afford to develop a new cryogenic OTV. didate engines. The limiting factor for Shuttle/Centaur geosyn­ Relatively small increases are not without great conse­ chronous payload capability is the maximum lift quence for such future missions as GEO round trips. capability of the Orbiter: 65,000 pounds. One way to For example, a 20-second Isp increase could double increase this capability is to use one Orbiter to launch the round trip payload of a shuttle-launched, all- Centaur and a second Orbiter to launch the space­ propulsive, reusable (ground-based) OTV. IIC-27 LOW THRUST Studies performed for the Air Force and NASA have concluded that the use of a toroidal liquid oxygen Spacecraft that are much larger and more complex tank with the main propulsion engine mounted in the are being proposed (large geostationary communica­ central void space provides the minimum