An Earth Orbiting Satellite Service and Repair Facility
Unknown, et. all
The Raptor Corporation was formed in September, 1989, to design and develop a commercial facility for the repair and servicing of satellites in geosynchronous Earth orbit. The product of that effort is a conceptual design for the Geosynchronous Satellite Servicing Platform (GSSP). Upon completion in 2010, the GSSP will be capable of telerobotically servicing a wide array of telecommunication satellites.
By the year 2000, telecommunication satellites will generate over $9 billion in revenues for the nations and corporations dependent upon their services. The current average lifespan of a satellite in geosynchronous orbit is 7 years; after 13 years in orbit, the failure rate is 98%. While continuing advances in technology may extend the lifetime of satellites in the future, the cost of constructing, insuring and launching a satellite will remain formidable, if not prohibitive. The GSSP will help lower these costs by extending the useful life of satellites with its servicing capabilities. The Raptor Corporation will also provide a low-cost alternative to companies and countries desiring satellite ownership by selling refurbished satellites at a cost well below that of a new satellite. Through servicing and sales, the GSSP will generate over $750 million annually. Tables 2.2 and 2.3 detail the projected cost, price and revenue structure for the GSSP.
The Task
Servicing of active and inactive satellites will entail component replacement, component repair, component refueling, or any combination thereof. Servicing tasks will be performed telerobotically from either the GSSP operations module or a ground based telerobotic command center. Component replacement comprises the main service task identified by the Raptor Corporation -- 75% of satellite failure is due to component failure. Component replacement also provides another market opportunity; the GSSP can upgrade and enhance satellites as technologies improve.
Component repair will performed when the failed component is readily repairable. If repair cannot be effected robotically, the component will be placed in the operations module airlock, and servicing will be performed by technicians.
Refueling will be performed on-orbit at satellite location by the SRV by modular changeout of satellite fuel cells.
A typical mission scenario is depicted in Figure 1.1. A satellite targeted for service is captured and transferred to the GSSP by a Satellite Retrieval Vehicle (SRV). The SRV is a modified Orbital Maneuvering Vehicle (OMV), which is scheduled to enter service during the initial stages of Space Station operations. After four satellites are berthed at the GSSP by SRVs, two Raptor technicians in a Crew Transfer Capsule (CTC) will travel to the GSSP using a Titan IV launch system. The CTC, an Apollo derived crew capsule, will rendezvous and dock with the GSSP, remaining there throughout the two week mission duration. The technicians will telerobotically repair the satellites, which are transferred in and out of the service bay using the Main Remote Manipulator System (MRMS). If repairs cannot be completed telerobotically, the technicians will repair the component in the operations module. If the component is too large to fit though the airlock between the service bay and the operations module, one of the technicians will enter the service bay, using an EVA suit and repair the satellite. Upon completion of repairs, the SRVs will redeploy the satellites to their original position, and the technicians will return to earth in the CTC.
Designed for a 25 year lifespan, the GSSP will consist of a habitation module, an operations module, a service bay and a truss assembly. Two SRVs will be stationed at the GSSP.
The habitation module is 34 feet long and 14 feet in diameter, with 3,000 cubic feet of living area pressurized to 10.2 psi. The habitation module serves as a safe haven during solar flares. The operations module is based on the Space Station Freedom resource node structure, and measures 17 feet long and 14 feet in diameter. The operations module contains all communication, telerobotic and computational equipment. A two chamber airlock located in the operations module serves for EVA preparation and as access to the service bay.
The service bay is an enclosed octagonal structure with dimensions 30 x 30 x 40 feet and constructed of an aluminum space frame enclosed with monocoque sheets of Kevlar.
The truss assembly is a dual purpose structure providing a construction foundation for the GSSP and acting as a track system for the main remote manipulator system. Additionally, the truss removes solar panels and thermal radiators from the proximity area of the service bay.
Construction of the facility requires four stages to completion, as depicted in Table 7.1, with all work performed in GEO. The first three stages will be performed telerobotically from ground control, and final construction and initial satellite servicing performed telerobotically by technicians at the GSSP.
Subsystems for the GSSP were chosen with both safety and cost effectiveness as prime considerations. With a planned two week, two crew member mission scenario as a baseline, an open looped environmental control and life support system was chosen. Cabin pressure is maintained at 10.2 psi, ensuring safety and eliminating prebreathing when EVA activities are necessary. The actual composition of the cabin atmosphere is shown in Table 9.1 Consumables are resupplied for each mission, and waste material is filtered, stabilized, stored and disposed of. Tables 9.2 and 9.3 list consumables and waste requirements.
A system of photovoltaic solar cells in a planar array will provide the GSSP's power needs. The system generates 35 KW continuous power, is 850 square meters and weighs 2,500 kg. While not the most efficient system, the solar array meets the two main design criterion -- safety and cost effectiveness. Ammonia heat pipe radiators will be used for thermal heat rejection. A decision matrix for power systems can be found in Table 10.2 and thermal system comparisons in Table 11.1
The GSSP will be located in geostationary orbit at 255� East longitude. This position is advantageous because it allows for direct communications to U. S. ground stations, and is located near U. S. satellites, which will be the largest market for GSSP services. The 255� East GEO position is also desired for simplified stationkeeping purposes.
In geosynchronous orbit, the guidance, navigation and control systems are designed primarily for orbit maintenance. An inertial guidance system has been chosen for the GSSP. This system will provide the SRV, which uses a relative navigation scheme, with an inertial frame of reference. The inertial reference point location at the GSSP provides superior SRV navigation during proximity operations. Stationkeeping for the GSSP will be performed by electro-thermal hydrazine thrusters. Catalytic hydrazine thrusters will be used for the attitude control propulsion system. These two systems are advantageous because they require approximately the same supply pressure, so a common propellant feed system can be used.
The GSSP will use a direct communication link with a ground station. The tracking and data relay satellite system will be used to communicate with the Space Station and to track the SRV and the CTC.
The key to both safety and economic design constraints is automation. Telerobotic hardware aboard the GSSP includes a space arm manipulator system, a flight telerobotic servicer and servicing robots for use inside and outside the service bay.
The main remote manipulator system is a 7 DOF robotic arm, operated from the ground station or the GSSP. The MRMS will be used to construct the GSSP and to grapple and maneuver payloads around the GSSP.
The flight telerobotic servicer is an advanced system used to perform high dexterity operations. The FTS employs an advanced vision system for control, and will be mounted on the SRVs and the MRMS. The FTS and MRMS will also be used for GSSP inspection, repair and maintenance.
A set of specialized arms, situated in the service bay, will use changeable end effectors to provide a flexible array of satellite servicing.
CSR/TSGC Team Web