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Automated payload requirements for space shuttle
Acta Astronautica.
Vol. 1, pp. 1301-1314. Pergamon Press 1974. Printed in the U.S.A.
Automated payload requirements for space shuttle PHILIP
E. C U L B E R T S O N
AND T H O M A S
HAGLER
N.A.S.A., Washington, D.C. 20546, U.S.A. (Received 4 March 1974)
Abstract--The accommodation requirements for a representative spectrum of automated spacecraft are analyzed and compared to the services provided by the Space Shuttle and Space Tug. The purpose and engineering characteristics of a number of possible items of general purpose Shuttle-payload interface equipment are discussed. The benefits provided to automated payloads by the Space Transportation System are summarized. 1. Introduction THE PLANNED availability of the reusable Space Shuttle near the end of this decade opens a new era in launch, servicing, and retrieval of automated payloads. Effective utilization of this new capability, however, depends not only on the basic Shuttle capabilities but on the d e v e l o p m e n t of interface equipment and p r o c e d u r e s b e t w e e n the payloads and the Shuttle which contribute to low cost operations, simplify payload integration, and hold Shuttle turn-around time to a minimum. This p a p e r will s u m m a r i z e a n u m b e r of contracted and in-house N A S A studies which h a v e begun to define the a c c o m m o d a t i o n requirements for a representative s p e c t r u m of possible future a u t o m a t e d payloads. These studies h a v e further a t t e m p t e d to define in a preliminary manner, a family of interface equipment which will m a t e a large n u m b e r of these potential payloads to the Shuttle.
2. The Space Transportation System The Space Transportation S y s t e m actually consists of two vehicles, the Space Shuttle and the Space Tug. The Space Shuttle is an a p p r o v e d and ongoing program. The characteristics of the Shuttle which are of particular interest for support of a u t o m a t e d payloads are shown in Fig. 1. The second vehicle in the Space Transportation System, the Space Tug, is currently under study. The purpose of the Space Tug is to provide the propulsion to transport payloads f r o m the Shuttle orbit to another orbit or trajectory which cannot be achieved b y the Shuttle directly. Figure 2 illustrates the characteristics of one of the reusable Space Tug concepts under investigation.
3. Representative automated payload characteristics Figure 3 illustrates the classes of a u t o m a t e d payloads which the Space Transportation S y s t e m m a y be required to support. A large space telescope 1301
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P, E. CULBERTSON and T. HAGLER
Fig. t. SpaceShuttlecharacteristics.
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Fig. 2. ReusableSpaceTug concept. illustrates the class of large observatory type satellites. These satellites, generally located in low Earth orbit, are large in size, I0 to 15 thousand kilograms, and require a wide range of services from the Space Transportation System. During the launch phase the large observatories require an environment with controlled temperature and a high degree of cleanliness or order to protect optical surfaces.
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Fig. 3. Representativeautomatedpayloads. After reaching orbit the observatory may require assembly, checkout, and calibration in addition to deployment. While the observatory is operating in orbit periodic visits from the Shuttle are required for servicing and retrieval of data. Finally at the end of the useful life of the satellite or in case of malfunction, on-orbit repair or retrieval for ground refurbishment may be required. The Mariner Jupiter-Saturn Flyby is characteristic of the Planetary class of automated spacecraft. These spacecraft require the utilization of both the Shuttle and Tug to achieve the desired planetary trajectory. During the initial ascent to orbit the planetary spacecraft require status monitoring and data relay through the Shuttle communications system. In addition, a number of the planetary spacecraft are powered by radioisotope electrical power systems which require special cooling during the launch phase. After achieving an initial orbit the Space Tug-Planetary Spacecraft combination may require a navigation update from the Space Shuttle prior to deployment. An Earth Observations Satellite is characteristic of the class of low Earth orbit satellites which observe Earth characteristics and phenomena. These satellites require many of the same services required by the observatory class of satellites. In addition, the Earth observation satellites may require periodic change of sensors as seasons or resource objectives change. Although normally in low Earth orbit the Earth observations satellites frequently require high inclination orbits including polar and sun synchronous. A Synchronous Meteorological Satellite is characteristic of the class of satellites which observe a particular area of the Earth for purposes of communications, meteorology, or traffic management. This class of satellites generally requires the same services as planetary spacecraft. Both the Shuttle and Tug are required to place the satellite in its operational orbit. The geostationary satellites lead all other classes of satellites in routine space activities and commercial
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applications. These activities result in special requirements for accurate positioning of the satellite, prompt repair or replacement of malfunctioning or inoperative satellites, and low cost launch operations.
4. Payload operations The Space Transportation System will provide the capability for a wide range of payload operations for automated payloads. These operations generally fall in three classes. First there are the operations of launch and positioning of payloads for which the Space Transportation System replaces the conventional expendable launch vehicle systems. Second there are the operations which are currently accomplished by expendable launch vehicle-payload combinations but which will be provided more effectively and at much less expense by the Space Transportation System. Examples of this class of payload operations are acoustic, thermal, and contamination protection of the payload during launch; status monitoring and transmission of payload data; and provision of electrical power to the payload. The third class of payload operations are those unique operations which have not been possible with conventional expendable launch vehicle systems. These operations include man supported orbital readiness testing; on-orbit servicing, maintenance, and repair of payloads; Tug-payload navigation update: refurbishment of payloads in orbit: and retrieval of payloads for ground repair or modernization. A. Orbit readiness test
As illustrated in Fig. 4 the Space Shuttle provides a capability for a direct man supported orbital readiness test of automated spacecraft systems after the spacecraft has passed through the launch environment. Although the scope and
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Fig. 4. Orbit readiness test.
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Automated payload requirements for space shuttle
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magnitude of orbit readiness testing will vary from satellite to satellite, the testing will be a coordinated operation between the on-board payload specialist and the ground station which will have responsibility for monitoring and control of the satellite after release from the Shuttle. The payload specialist, in addition to conducting or participating in the orbit readiness test, provides a capability for visual observation of the deployment of solar panels, antenna, and other spacecraft appendages. In certain cases, in order to deploy spacecraft antenna and solar panels, and to exercise the attitude control system, it may be desirable to separate the spacecraft from the Shuttle and fly the Shuttle in an escort mode while the orbit readiness test is being conducted. For those spacecraft which are delivered to a geosynchronous or other high energy orbit by the Space Tug, testing prior to separation from the Shuttle will generally be limited to status and safety monitoring and visual inspection. After delivery of the spacecraft to the required orbit the Space Tug will fly escort with the spacecraft and assist in the orbit readiness test as required.
B. On-orbit servicing One of the most important characteristics of the Space Transportation System is the capability to carry out on-orbit servicing, repair and maintenance of automated spacecraft. In order to make maximum use of this very important capability, automated spacecraft themselves must evolve into new design concepts which facilitate on-orbit operations. Figure 5 illustrates a study concept of a redesigned Earth Observatory Spacecraft in which subsystems are packaged in standard modular form. The subsystem modules are plug-in units easily handled in orbit by man or mechanical manipulator. Figure 6 illustrates one concept for servicing or repair of the standard Earth Observatory Satellite. The replacement modules are brought to orbit in a special rack installed in the Orbiter cargo bay. After docking with the spacecraft a
17 3
SPACECRAFT SUBSYSTEM MODULES A-I ATTITOOE~ MOOULENO,i A-2 SANOVHFBANDC E ~ A T I O N MOOEL A-3 BATTERYMOOULENO. t A.4 SOLARPOW~ NO.1 A-$ POWERCONTROLMODULE A-6 ATTFTUOECONTROLMODULENO. 2
Fig. 5. Standard earth observatory spacecraft.
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Fig. 6. On-orbit servicing of the S/EOS.
crewman from the Shuttle conducts the required module replacement. For this operation the crewman wears an extravehicular spacesuit and is aided by the Shuttle manipulator arm. A Study effort is also underway to determine the effectiveness of carrying out the module replacement by operation of the manipulators from the manipulator station in the crew cabin. This servicing mode would not require any extravehicular activity.
C. Tug-payload navigation update The Shuttle guidance, navigation, and control system provides inertial navigation updated by RF navigation aids and during rendezvous by an alternate optical tracker. An inertial measurement unit provides the navigation reference with star sensors for autonomous alignment and state vector update. The Orbiter will provide through a standard interface to the payload the Orbiter state vector and attitude, Greenwich mean time, and mission elapsed time.
D. Refurbishment of payloads in orbit The Space Shuttle provides a capability to carry out major overhaul or refurbishment of a satellite in orbit. Figure 7 illustrates an observatory class satellite, the large space telescope, attached to the Shuttle for major overhaul or refurbishment. The elements of the large space telescope include the optical telescope assembly, a scientific instrument package, and a subsystem support module which provides a pressurized environment for man to work in a shirt sleeve environment. A pressurized module such as the space lab might be used for storage of components and for an operating base for work on the large space telescope.
E. Payload retrieval The Space Transportation System provides a capability to retrieve and return to Earth an automated satellite which requires repair or modernization. Figure 8
Automated payload requirements for space shuttle
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Fig. 7. Refurbishment of large space telescope.
Fig. 8. Earth observation satellite (retrieval). illustrates the retrieval of an Earth Observation Satellite by using the Shuttle manipulators to capture and place the satellite in the Shuttle cargo bay. Although the primary mode of retrieval is based on a capability to stabilize the satellite to be recovered, studies have been conducted which investigated the feasibility of retrieval of non-cooperative or tumbling spacecraft.
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5. Shuttle baseline payload accommodations In the definition of the various characteristics and components of the Space Shuttle which provide accommodations and services to payloads two important criteria have been observed. The first of these criteria recognizes that the Shuttle will provide transportation and support services to a very large and diverse group of payloads and consequently baseline accommodations are tailored to meet the synthesized needs of a large group of payloads. The other criterion which is of critical importance if the Shuttle is to achieve low operating costs by minimum turn-around time between missions is that changes to the Shuttle subsystems or to any of its permanently installed equipment must be held to an absolute minimum between missions. The application of these two criteria to Shuttle definition has resulted in a set of general purpose payload accommodations for the Space Shuttle. These accommodations will in turn be augmented for each mission by ancillary equipment which will provide any required custom tailoring for the specific payload but will preserve the standard interface to the Shuttle systems. The following paragraphs describe representative Shuttle baseline payload accommodations.
A. Payload bay The payload bay has a clear volume 4.6 meters in diameter by 18.3 meters long. This volume is the maximum allowable payload dynamic envelope. Clearance between the payload envelope and the Orbiter structure is provided by the Orbiter to assure that Orbiter deflection will not create deployment interference between the Orbiter and the payload. B. Payload structural attachments Payload structural accommodations provide attachment points along the length of the payload bay. This design provides flexibility for accommodating a wide spectrum of payloads. Ancillary equipment, including adapters, cradles and pallets will also be used to facilitate mounting of specific payloads. C. Payload deployment and retrieval mechanism The deployment and retrieval of payloads is accomplished by using the general purpose remote manipulator system (RMS) illustrated in Fig. 9. One manipulator arm is provided by the Shuttle and may be mounted either on the left or right side of the cargo bay. If a particular payload requires the use of two manipulator arms, the second manipulator arm is installed as ancillary payload support equipment. The manipulator arm is mounted approximately 2.5 meters from the forward bulkhead of the cargo bay and has a maximum reach from that point of 14.8 meters. Payloads which require more precise alignment with the Orbiter or more rigid connection to the Orbiter for servicing or repair will be accommodated with ancillary equipment. D. Service panels Ground services required by the payload after installation in the orbiter such as electrical power, fluids and gases, filling, venting, draining, etc., will be
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Kgtlm W011glN Fig. 9. Payload deployment and retrieval mechanism.
provided through service panels located on the side of the Orbiter. Distribution of these services to payloads installed in the Orbiter will be provided by ancillary equipment. For propulsive payloads using LH2 and LO2 propellants the Orbiter has a fill, drain, and vent system to aid mission preparation. Propulsive payloads that utilize storable propellants are loaded prior to installation in the cargo bay. Provisions for ground support coolant flow to the payload, while the payload is installed in the payload bay prior to launch, will be available. Standardized payload utility services from the Orbiter systems are provided at the payload bay hatch and on the forward bulkhead of the payload bay. The interfaces provided at the hatch include redundant caution and warning, data, power, communication, and fluid interface connectors. Interface connectors on the forward bulkhead are located below the hatch in the unpressurized area of the payload bay for attachment of umbilicals. Remotely operated mechanisms will facilitate disconnection or reconnection of umbilicals during the mission if required.
6. Ancillary equipment The purpose of ancillary equipment is to allow each automated payload to be individually fitted to the Shuttle while at the same time maintaining a standard Shuttle interface which is not required to change from mission to mission. A second major purpose of ancillary equipment is to allow for mating and calibration of this equipment with a particular payload at a location apart from Shuttle ground operations and on a non-interference basis with Shuttle refurbishment and check out. A particularly key concept in the use of ancillary equipment for Shuttle-
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Payload operations is that while one end of the ancillary equipment may be modified to accommodate a particular payload, the end which connects to the Shuttle systems remains simple, standard, and easily connected. Some of the representative functions that ancillary equipment will serve are listed below and illustrated in Fig. 10. 1. Structural connection between the Shuttle provided mounting points and the payload. This function is served by a general purpose pallet or cradle which attaches to the shuttle mounting points and provides mounting support to any size or shape payloads. 2. Distribution lines for fluids, data, and electrical power from the Shuttle bay wall and bulkhead connectors to the payload. This distribution system may require special fittings at the connection to the payload and installation of a pump in the fluid loop between the Shuttle heat exchanger and the payload. 3. Special installation for very large payloads such as the Space Tug. The Tug tilt table not only provides a structural connection between the Tug and the Shuttle but also provides a means of erecting the Tug from the cargo bay for deployment or retrieval. 4. Local or complete protection (Shroud) for thermal or contamination sensitive elements of a particular payload, e.g., a telescope. Studies have indicated that localized protection of critical components may eliminate the requirement for total shrouding for most payloads. 5. Disconnect and reconnect of fluid, power, and data transmission lines during Tug and payload deployment or retrieval. 6. Monitoring control, and data management of payloads at all times while these payloads are installed in the Shuttle. This function is provided by the payload specialist console.
Fig. 10. General purpose mission equipment.
Automated payload requirements for space shuttle
131 !
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Fig. 11. Payload accommodation--Pallet concept.
Additional detail concerning these examples of representative interface equipment is provided in the following paragraphs. Figure I I illustrates a general purpose pallet which will accommodate all classes of satellites which do not require a propulsive stage (Tug) except for the large observatories. The pallet is attached to the standard shuttle mounting points by 4 mounting lugs. The payload in turn is attached to the payload support platform at the appropriate payload support points. The tilt table (Trunnion) provides a docking connection to each payload and allows the payload to be rotated to the upright position for convenience in deployment, retrieval, or maintenance. The lattice structure along the sides of the pallet provides a convenient location for the installation of special subsystems which may be required to support a particular payload and for mounting the fluid, power, and data umbilicals which supply ground or Shuttle services to the payload. Figure 12 illustrates ancillary equipment for the installation of the Space Tug in the Shuttle. The semimonocoque conical aluminum structure transmits the load from the Tug and payload to the Shuttle while the Shuttle is in the vertical position. The tilt table also provides a capability to erect the Tug and payload in the Shuttle to facilitate either deployment or retrieval of the Tug and payload. Finally the tilt table provides structural mounting for purge gas helium spheres and for the umbilicals which transmit fluids, power and data between the Shuttle cabin and the Tug. One concept of the payload specialist station console and its division into basic and special purpose units is illustrated in Fig. 13. The basic unit contains equipment of common usage among a majority of payloads. The special purpose console, as shown, would house payload unique equipment. The payload unique console would be basically an adjustable rack structure for supporting payload supplied modules.
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Fig. 12. Space Tug installation in the Shuttle.
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The basic console, illustrated b y Fig. 14 contains a caution and warning annunciator display with limit controls located behind a spring-loaded panel which is accessible f r o m the front. T w o cathode ray tubes (CRT) are provided with standard adjustments, plus m o d e and watt controls for overlay of alpha-numerical data on video presentations. The intercom panel and m a j o r discrete control panels are below the C R T assemblies. The control panel also contains the displays for
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Fig. 14. PSS basic console.
Greenwich mean time and mission elapsed time. The shelf contains the keyboard assembly, video and digital tape recorder, and camera controls. The space below the shelf is filled by the two recorders and a power supply. A central patch and connector panel for interfacing the console with Shuttle services and payload bay cabling is located on the side of the payload specialist station basic console. Figure 15 illustrates a payload unique rack which is provided to accommodate special payload requirements which are not generally applicable to a broad spectrum of automated payloads. Figure 15, for example, demonstrates the use of a special panel for monitoring and control of the thermal coolant loop which has
Fig. 15. PSS-paytoad dedicated equipment rack.
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P.E. CULBERTSON and T. HAGLER
been installed between the Shuttle heat exchanger and the payload internal cooling system for a planetary payload which includes a radioisotope power system. The payload unique rack is somewhat smaller than the basic console due to the limited number of payload-unique items which have been found to be required. It is expected that for some flights the payload unique rack may not be required. However, the concept of basic or payload-peculiar equipment and the two rack design concept incorporating provisions for interconnecting the payload unique console to Orbiter services as needed provide a flexible means of satisfying growth requirements. The consoles will reduce the problems of integrating Orbiter and payload software and of facility timesharing, and will contribute to rapid turnaround by allowing console reconfiguration independent of Shuttle ground operations.
7. The benefits of the Space Transportation System for automated payloads Study effort to date has concluded that the Space Transportation System provides a number of significant benefits to automated payloads which cannot be provided by expendable systems. Certain of the benefits are enumerated in the paragraphs below. For all payloads except those very small scientific payloads which can be launched by a Scout class launch vehicle the Shuttle-Tug is a minimum cost launch system. The Shuttle and Tug through repetitive operation will achieve a level of reliability for placing payloads in orbit which cannot be duplicated by expendable systems. The capability of the Space Transportation System to repair early spacecraft anomalies on-orbit or to retrieve the spacecraft for ground repair promises savings in cost and time for automated spacecraft operations. The capability for on-orbit servicing of payloads provides the opportunity to retrieve high quality data, e.g., photographic data and data or samples from other sensors which are incompatible with remote transmission techniques. Refurbishment or major overhaul of an automated satellite offers the potential for extending the useful life of research and development systems by changing the mission equipment. In like manner the useful lifetime of operational systems can be extended by the replacement of obsolete or worn out subsystems. 8. Summary The future availability of the reusable Space Shuttle and associated space systems opens new horizons for an international space program. Low space system operating costs, and innovative and unique space program accomplishments will now be within the realm of both possibility and probability in future space programs focused on the beneficial uses of space. The concept of ancillary equipment which allows the Shuttle to be a standard vehicle with minimum turn-around time and low operating costs and at the same time provides to the payloads the differing installation needs, varying services, and off-line calibration and checkout, is considered an important element of the total Space Transportation System.
Vol. 1, pp. 1301-1314. Pergamon Press 1974. Printed in the U.S.A.
Automated payload requirements for space shuttle PHILIP
E. C U L B E R T S O N
AND T H O M A S
HAGLER
N.A.S.A., Washington, D.C. 20546, U.S.A. (Received 4 March 1974)
Abstract--The accommodation requirements for a representative spectrum of automated spacecraft are analyzed and compared to the services provided by the Space Shuttle and Space Tug. The purpose and engineering characteristics of a number of possible items of general purpose Shuttle-payload interface equipment are discussed. The benefits provided to automated payloads by the Space Transportation System are summarized. 1. Introduction THE PLANNED availability of the reusable Space Shuttle near the end of this decade opens a new era in launch, servicing, and retrieval of automated payloads. Effective utilization of this new capability, however, depends not only on the basic Shuttle capabilities but on the d e v e l o p m e n t of interface equipment and p r o c e d u r e s b e t w e e n the payloads and the Shuttle which contribute to low cost operations, simplify payload integration, and hold Shuttle turn-around time to a minimum. This p a p e r will s u m m a r i z e a n u m b e r of contracted and in-house N A S A studies which h a v e begun to define the a c c o m m o d a t i o n requirements for a representative s p e c t r u m of possible future a u t o m a t e d payloads. These studies h a v e further a t t e m p t e d to define in a preliminary manner, a family of interface equipment which will m a t e a large n u m b e r of these potential payloads to the Shuttle.
2. The Space Transportation System The Space Transportation S y s t e m actually consists of two vehicles, the Space Shuttle and the Space Tug. The Space Shuttle is an a p p r o v e d and ongoing program. The characteristics of the Shuttle which are of particular interest for support of a u t o m a t e d payloads are shown in Fig. 1. The second vehicle in the Space Transportation System, the Space Tug, is currently under study. The purpose of the Space Tug is to provide the propulsion to transport payloads f r o m the Shuttle orbit to another orbit or trajectory which cannot be achieved b y the Shuttle directly. Figure 2 illustrates the characteristics of one of the reusable Space Tug concepts under investigation.
3. Representative automated payload characteristics Figure 3 illustrates the classes of a u t o m a t e d payloads which the Space Transportation S y s t e m m a y be required to support. A large space telescope 1301
1302
P, E. CULBERTSON and T. HAGLER
Fig. t. SpaceShuttlecharacteristics.
CMP/~'qWSllCS: * 01~:
10.7M L ~
BY 4.6 M
,, PAYLON)TO~
. PAYm~ m mV~L m
OiIT: 1600 Ki
m
~
~
:
tom)
Fig. 2. ReusableSpaceTug concept. illustrates the class of large observatory type satellites. These satellites, generally located in low Earth orbit, are large in size, I0 to 15 thousand kilograms, and require a wide range of services from the Space Transportation System. During the launch phase the large observatories require an environment with controlled temperature and a high degree of cleanliness or order to protect optical surfaces.
Automatedpayloadrequirementsfor space shuttle
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Fig. 3. Representativeautomatedpayloads. After reaching orbit the observatory may require assembly, checkout, and calibration in addition to deployment. While the observatory is operating in orbit periodic visits from the Shuttle are required for servicing and retrieval of data. Finally at the end of the useful life of the satellite or in case of malfunction, on-orbit repair or retrieval for ground refurbishment may be required. The Mariner Jupiter-Saturn Flyby is characteristic of the Planetary class of automated spacecraft. These spacecraft require the utilization of both the Shuttle and Tug to achieve the desired planetary trajectory. During the initial ascent to orbit the planetary spacecraft require status monitoring and data relay through the Shuttle communications system. In addition, a number of the planetary spacecraft are powered by radioisotope electrical power systems which require special cooling during the launch phase. After achieving an initial orbit the Space Tug-Planetary Spacecraft combination may require a navigation update from the Space Shuttle prior to deployment. An Earth Observations Satellite is characteristic of the class of low Earth orbit satellites which observe Earth characteristics and phenomena. These satellites require many of the same services required by the observatory class of satellites. In addition, the Earth observation satellites may require periodic change of sensors as seasons or resource objectives change. Although normally in low Earth orbit the Earth observations satellites frequently require high inclination orbits including polar and sun synchronous. A Synchronous Meteorological Satellite is characteristic of the class of satellites which observe a particular area of the Earth for purposes of communications, meteorology, or traffic management. This class of satellites generally requires the same services as planetary spacecraft. Both the Shuttle and Tug are required to place the satellite in its operational orbit. The geostationary satellites lead all other classes of satellites in routine space activities and commercial
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applications. These activities result in special requirements for accurate positioning of the satellite, prompt repair or replacement of malfunctioning or inoperative satellites, and low cost launch operations.
4. Payload operations The Space Transportation System will provide the capability for a wide range of payload operations for automated payloads. These operations generally fall in three classes. First there are the operations of launch and positioning of payloads for which the Space Transportation System replaces the conventional expendable launch vehicle systems. Second there are the operations which are currently accomplished by expendable launch vehicle-payload combinations but which will be provided more effectively and at much less expense by the Space Transportation System. Examples of this class of payload operations are acoustic, thermal, and contamination protection of the payload during launch; status monitoring and transmission of payload data; and provision of electrical power to the payload. The third class of payload operations are those unique operations which have not been possible with conventional expendable launch vehicle systems. These operations include man supported orbital readiness testing; on-orbit servicing, maintenance, and repair of payloads; Tug-payload navigation update: refurbishment of payloads in orbit: and retrieval of payloads for ground repair or modernization. A. Orbit readiness test
As illustrated in Fig. 4 the Space Shuttle provides a capability for a direct man supported orbital readiness test of automated spacecraft systems after the spacecraft has passed through the launch environment. Although the scope and
CHECKOUANO T ~ VISUAL STATUS
,-"¢'~, ......¢-~L,,
j . ~ t e,
~.....
"~~:",--.
..... "%"~.~
"~ _.-P.JMAR,
j>'-,.. ~
Fig. 4. Orbit readiness test.
CHECKOUT
Automated payload requirements for space shuttle
1305
magnitude of orbit readiness testing will vary from satellite to satellite, the testing will be a coordinated operation between the on-board payload specialist and the ground station which will have responsibility for monitoring and control of the satellite after release from the Shuttle. The payload specialist, in addition to conducting or participating in the orbit readiness test, provides a capability for visual observation of the deployment of solar panels, antenna, and other spacecraft appendages. In certain cases, in order to deploy spacecraft antenna and solar panels, and to exercise the attitude control system, it may be desirable to separate the spacecraft from the Shuttle and fly the Shuttle in an escort mode while the orbit readiness test is being conducted. For those spacecraft which are delivered to a geosynchronous or other high energy orbit by the Space Tug, testing prior to separation from the Shuttle will generally be limited to status and safety monitoring and visual inspection. After delivery of the spacecraft to the required orbit the Space Tug will fly escort with the spacecraft and assist in the orbit readiness test as required.
B. On-orbit servicing One of the most important characteristics of the Space Transportation System is the capability to carry out on-orbit servicing, repair and maintenance of automated spacecraft. In order to make maximum use of this very important capability, automated spacecraft themselves must evolve into new design concepts which facilitate on-orbit operations. Figure 5 illustrates a study concept of a redesigned Earth Observatory Spacecraft in which subsystems are packaged in standard modular form. The subsystem modules are plug-in units easily handled in orbit by man or mechanical manipulator. Figure 6 illustrates one concept for servicing or repair of the standard Earth Observatory Satellite. The replacement modules are brought to orbit in a special rack installed in the Orbiter cargo bay. After docking with the spacecraft a
17 3
SPACECRAFT SUBSYSTEM MODULES A-I ATTITOOE~ MOOULENO,i A-2 SANOVHFBANDC E ~ A T I O N MOOEL A-3 BATTERYMOOULENO. t A.4 SOLARPOW~ NO.1 A-$ POWERCONTROLMODULE A-6 ATTFTUOECONTROLMODULENO. 2
Fig. 5. Standard earth observatory spacecraft.
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Fig. 6. On-orbit servicing of the S/EOS.
crewman from the Shuttle conducts the required module replacement. For this operation the crewman wears an extravehicular spacesuit and is aided by the Shuttle manipulator arm. A Study effort is also underway to determine the effectiveness of carrying out the module replacement by operation of the manipulators from the manipulator station in the crew cabin. This servicing mode would not require any extravehicular activity.
C. Tug-payload navigation update The Shuttle guidance, navigation, and control system provides inertial navigation updated by RF navigation aids and during rendezvous by an alternate optical tracker. An inertial measurement unit provides the navigation reference with star sensors for autonomous alignment and state vector update. The Orbiter will provide through a standard interface to the payload the Orbiter state vector and attitude, Greenwich mean time, and mission elapsed time.
D. Refurbishment of payloads in orbit The Space Shuttle provides a capability to carry out major overhaul or refurbishment of a satellite in orbit. Figure 7 illustrates an observatory class satellite, the large space telescope, attached to the Shuttle for major overhaul or refurbishment. The elements of the large space telescope include the optical telescope assembly, a scientific instrument package, and a subsystem support module which provides a pressurized environment for man to work in a shirt sleeve environment. A pressurized module such as the space lab might be used for storage of components and for an operating base for work on the large space telescope.
E. Payload retrieval The Space Transportation System provides a capability to retrieve and return to Earth an automated satellite which requires repair or modernization. Figure 8
Automated payload requirements for space shuttle
~am~t
U
~
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lm~ m
Y
Fig. 7. Refurbishment of large space telescope.
Fig. 8. Earth observation satellite (retrieval). illustrates the retrieval of an Earth Observation Satellite by using the Shuttle manipulators to capture and place the satellite in the Shuttle cargo bay. Although the primary mode of retrieval is based on a capability to stabilize the satellite to be recovered, studies have been conducted which investigated the feasibility of retrieval of non-cooperative or tumbling spacecraft.
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5. Shuttle baseline payload accommodations In the definition of the various characteristics and components of the Space Shuttle which provide accommodations and services to payloads two important criteria have been observed. The first of these criteria recognizes that the Shuttle will provide transportation and support services to a very large and diverse group of payloads and consequently baseline accommodations are tailored to meet the synthesized needs of a large group of payloads. The other criterion which is of critical importance if the Shuttle is to achieve low operating costs by minimum turn-around time between missions is that changes to the Shuttle subsystems or to any of its permanently installed equipment must be held to an absolute minimum between missions. The application of these two criteria to Shuttle definition has resulted in a set of general purpose payload accommodations for the Space Shuttle. These accommodations will in turn be augmented for each mission by ancillary equipment which will provide any required custom tailoring for the specific payload but will preserve the standard interface to the Shuttle systems. The following paragraphs describe representative Shuttle baseline payload accommodations.
A. Payload bay The payload bay has a clear volume 4.6 meters in diameter by 18.3 meters long. This volume is the maximum allowable payload dynamic envelope. Clearance between the payload envelope and the Orbiter structure is provided by the Orbiter to assure that Orbiter deflection will not create deployment interference between the Orbiter and the payload. B. Payload structural attachments Payload structural accommodations provide attachment points along the length of the payload bay. This design provides flexibility for accommodating a wide spectrum of payloads. Ancillary equipment, including adapters, cradles and pallets will also be used to facilitate mounting of specific payloads. C. Payload deployment and retrieval mechanism The deployment and retrieval of payloads is accomplished by using the general purpose remote manipulator system (RMS) illustrated in Fig. 9. One manipulator arm is provided by the Shuttle and may be mounted either on the left or right side of the cargo bay. If a particular payload requires the use of two manipulator arms, the second manipulator arm is installed as ancillary payload support equipment. The manipulator arm is mounted approximately 2.5 meters from the forward bulkhead of the cargo bay and has a maximum reach from that point of 14.8 meters. Payloads which require more precise alignment with the Orbiter or more rigid connection to the Orbiter for servicing or repair will be accommodated with ancillary equipment. D. Service panels Ground services required by the payload after installation in the orbiter such as electrical power, fluids and gases, filling, venting, draining, etc., will be
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Kgtlm W011glN Fig. 9. Payload deployment and retrieval mechanism.
provided through service panels located on the side of the Orbiter. Distribution of these services to payloads installed in the Orbiter will be provided by ancillary equipment. For propulsive payloads using LH2 and LO2 propellants the Orbiter has a fill, drain, and vent system to aid mission preparation. Propulsive payloads that utilize storable propellants are loaded prior to installation in the cargo bay. Provisions for ground support coolant flow to the payload, while the payload is installed in the payload bay prior to launch, will be available. Standardized payload utility services from the Orbiter systems are provided at the payload bay hatch and on the forward bulkhead of the payload bay. The interfaces provided at the hatch include redundant caution and warning, data, power, communication, and fluid interface connectors. Interface connectors on the forward bulkhead are located below the hatch in the unpressurized area of the payload bay for attachment of umbilicals. Remotely operated mechanisms will facilitate disconnection or reconnection of umbilicals during the mission if required.
6. Ancillary equipment The purpose of ancillary equipment is to allow each automated payload to be individually fitted to the Shuttle while at the same time maintaining a standard Shuttle interface which is not required to change from mission to mission. A second major purpose of ancillary equipment is to allow for mating and calibration of this equipment with a particular payload at a location apart from Shuttle ground operations and on a non-interference basis with Shuttle refurbishment and check out. A particularly key concept in the use of ancillary equipment for Shuttle-
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Payload operations is that while one end of the ancillary equipment may be modified to accommodate a particular payload, the end which connects to the Shuttle systems remains simple, standard, and easily connected. Some of the representative functions that ancillary equipment will serve are listed below and illustrated in Fig. 10. 1. Structural connection between the Shuttle provided mounting points and the payload. This function is served by a general purpose pallet or cradle which attaches to the shuttle mounting points and provides mounting support to any size or shape payloads. 2. Distribution lines for fluids, data, and electrical power from the Shuttle bay wall and bulkhead connectors to the payload. This distribution system may require special fittings at the connection to the payload and installation of a pump in the fluid loop between the Shuttle heat exchanger and the payload. 3. Special installation for very large payloads such as the Space Tug. The Tug tilt table not only provides a structural connection between the Tug and the Shuttle but also provides a means of erecting the Tug from the cargo bay for deployment or retrieval. 4. Local or complete protection (Shroud) for thermal or contamination sensitive elements of a particular payload, e.g., a telescope. Studies have indicated that localized protection of critical components may eliminate the requirement for total shrouding for most payloads. 5. Disconnect and reconnect of fluid, power, and data transmission lines during Tug and payload deployment or retrieval. 6. Monitoring control, and data management of payloads at all times while these payloads are installed in the Shuttle. This function is provided by the payload specialist console.
Fig. 10. General purpose mission equipment.
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Fig. 11. Payload accommodation--Pallet concept.
Additional detail concerning these examples of representative interface equipment is provided in the following paragraphs. Figure I I illustrates a general purpose pallet which will accommodate all classes of satellites which do not require a propulsive stage (Tug) except for the large observatories. The pallet is attached to the standard shuttle mounting points by 4 mounting lugs. The payload in turn is attached to the payload support platform at the appropriate payload support points. The tilt table (Trunnion) provides a docking connection to each payload and allows the payload to be rotated to the upright position for convenience in deployment, retrieval, or maintenance. The lattice structure along the sides of the pallet provides a convenient location for the installation of special subsystems which may be required to support a particular payload and for mounting the fluid, power, and data umbilicals which supply ground or Shuttle services to the payload. Figure 12 illustrates ancillary equipment for the installation of the Space Tug in the Shuttle. The semimonocoque conical aluminum structure transmits the load from the Tug and payload to the Shuttle while the Shuttle is in the vertical position. The tilt table also provides a capability to erect the Tug and payload in the Shuttle to facilitate either deployment or retrieval of the Tug and payload. Finally the tilt table provides structural mounting for purge gas helium spheres and for the umbilicals which transmit fluids, power and data between the Shuttle cabin and the Tug. One concept of the payload specialist station console and its division into basic and special purpose units is illustrated in Fig. 13. The basic unit contains equipment of common usage among a majority of payloads. The special purpose console, as shown, would house payload unique equipment. The payload unique console would be basically an adjustable rack structure for supporting payload supplied modules.
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Fig. 12. Space Tug installation in the Shuttle.
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The basic console, illustrated b y Fig. 14 contains a caution and warning annunciator display with limit controls located behind a spring-loaded panel which is accessible f r o m the front. T w o cathode ray tubes (CRT) are provided with standard adjustments, plus m o d e and watt controls for overlay of alpha-numerical data on video presentations. The intercom panel and m a j o r discrete control panels are below the C R T assemblies. The control panel also contains the displays for
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Fig. 14. PSS basic console.
Greenwich mean time and mission elapsed time. The shelf contains the keyboard assembly, video and digital tape recorder, and camera controls. The space below the shelf is filled by the two recorders and a power supply. A central patch and connector panel for interfacing the console with Shuttle services and payload bay cabling is located on the side of the payload specialist station basic console. Figure 15 illustrates a payload unique rack which is provided to accommodate special payload requirements which are not generally applicable to a broad spectrum of automated payloads. Figure 15, for example, demonstrates the use of a special panel for monitoring and control of the thermal coolant loop which has
Fig. 15. PSS-paytoad dedicated equipment rack.
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been installed between the Shuttle heat exchanger and the payload internal cooling system for a planetary payload which includes a radioisotope power system. The payload unique rack is somewhat smaller than the basic console due to the limited number of payload-unique items which have been found to be required. It is expected that for some flights the payload unique rack may not be required. However, the concept of basic or payload-peculiar equipment and the two rack design concept incorporating provisions for interconnecting the payload unique console to Orbiter services as needed provide a flexible means of satisfying growth requirements. The consoles will reduce the problems of integrating Orbiter and payload software and of facility timesharing, and will contribute to rapid turnaround by allowing console reconfiguration independent of Shuttle ground operations.
7. The benefits of the Space Transportation System for automated payloads Study effort to date has concluded that the Space Transportation System provides a number of significant benefits to automated payloads which cannot be provided by expendable systems. Certain of the benefits are enumerated in the paragraphs below. For all payloads except those very small scientific payloads which can be launched by a Scout class launch vehicle the Shuttle-Tug is a minimum cost launch system. The Shuttle and Tug through repetitive operation will achieve a level of reliability for placing payloads in orbit which cannot be duplicated by expendable systems. The capability of the Space Transportation System to repair early spacecraft anomalies on-orbit or to retrieve the spacecraft for ground repair promises savings in cost and time for automated spacecraft operations. The capability for on-orbit servicing of payloads provides the opportunity to retrieve high quality data, e.g., photographic data and data or samples from other sensors which are incompatible with remote transmission techniques. Refurbishment or major overhaul of an automated satellite offers the potential for extending the useful life of research and development systems by changing the mission equipment. In like manner the useful lifetime of operational systems can be extended by the replacement of obsolete or worn out subsystems. 8. Summary The future availability of the reusable Space Shuttle and associated space systems opens new horizons for an international space program. Low space system operating costs, and innovative and unique space program accomplishments will now be within the realm of both possibility and probability in future space programs focused on the beneficial uses of space. The concept of ancillary equipment which allows the Shuttle to be a standard vehicle with minimum turn-around time and low operating costs and at the same time provides to the payloads the differing installation needs, varying services, and off-line calibration and checkout, is considered an important element of the total Space Transportation System.