Click for next page ( 6


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 5
2 Modes of Shuttle Use I. ASSUMPTIONS AND OBJECTIVES An interdisciplinary group was convened to identify major demands placed on the Shuttle, particularly by the sortie mode. The group considered experiments carried to near-earth orbit by Shuttle, either (1) in pressurized modules; (2) on unpressurized 3-m pallet elements; or (3) on free-flying spacecraft, initially mounted to, but eventually ejected from, 3-m pallet elements. Deep-space planetary missions were excluded from these considerations, as was the Large Space Telescope. The group identified ten different modes under which a potential experiment could be performed. These modes are summarized in Table 1. The discipline groups were invited to propose representative experiments, using a simple proposal form, a copy of which is shown in Figure 1. Some 70 experiments were proposed and were used by the group to identify major demands on the sortie mode. The general conclusions summarized in Section II were based on these experi- ment proposals. No attempt was made to identify priorities. Considerations that led to specific choices of experiment mode were not explored in any depth; it was assumed that the choices were made after proper consideration of alternatives within the various discipline groups. The critical elements in these deliberations were instrument weight and the role of man; fiscal considerations appear to have entered only peripherally. In a comprehensive analysis, the requirements for a human operator should be evaluated against the availability of Shuttle-furnished communication facilities and communication satel- lites; possible simplifications in experimental design as a result of manned operation should be judged against the weight penalties of necessary human-support systems. Due to limitations in time, these

OCR for page 5
MODES OF SHUTTLE USE TABLE 1 Possible Experiment Modes A. A payload that remains on the pallet throughout a flight, using orbiter communications B. A payload that remains on the pallet throughout a flight, using its own communications direct to earth C. A payload that remains in the pressurized Spacelab throughout a flight D. A payload taken to orbit, ejected from the orbiter, used as an automated free-flyer and never visited nor recovered E. As D, but visited and not recovered F. As D, but visited and recovered G. As D, but recovered with the same Shuttle flight that ejected the payload H. A payload taken to orbit to replace an essentially identical spacecraft already in orbit I. Instrumentation deployed from orbiter on booms or similar devices, outside payload bay J. Instrumentation requiring orbital assembly, e.g., a very large telescope tradeoffs were addressed only tangentially in many cases. A more definitive study would require assigning priorities to the various experiments and a more careful fiscal analysis of available experi- ment options. Detailed requirements for specific experiments were identified using an interrogation form, shown in Table 2. This information was made available to NASA and ESRO personnel and is expected to aid in future design of the sortie mode. It should be possible with these data to identify generally useful support systems that could be Title of Experiment: Brief Statement of Objectives: 1 £ n i III Si-S S 1 s 1 § 1 c , * < . O Q IU IL a X - -. * CM flO V | 5 & V Q, S •8 1 1 Applicable exp. modes Inapplicable exp. modes Preferred exp. mode Weight classification Energy requirement Size classification Look direction Orbit requirement Frequency of flights FIGURE 1 Experiment proposal form.

OCR for page 5
Scientific Uses of the Space Shuttle TABLE 2 Sortie Mode Requirements EXPERIMENT TITLE 1. Role and No. of Men a. % Time Demand on Shuttle Payload Support Crew b. Extra Specialists in Orbiter Cabin c. Extra Specialists in Lab Module d. Other 2. Shuttle Flights and Requirements a. Inclination b. Attitudes on Orbit c. Altitudes d. Number of Total Flights e. Rate of Flight f. Duration in Orbit g. Other 3. Volume and Weight of Instrumentation a. In Lab Module b. In Pallet Area c. In Orbiter Cabin d. For Deployment on Booms Outside Payload Bay e. Free-Flyer(s) f. Other 4. Support Requirements a. Power Level and Total Energy b. Pointing (1) General Direction (2) Stabilization Limits c. Data: Storage d. Communications (1) To Earth (2) To Shuttle e. Thermal Control f. Booms, Special Tools, Airlocks, and Windows g. Visual or Access to Payload h. Other 5. Special Considerations a. Contamination b. Noise and Vibration c. Hazardous Materials or Procedures d. Cryogenics e. Radiation Belt Concerns f. Other 6. Schedule Considerations a. For a Given Flight (Date Windows) b. Minimum Lead for Specific Flight c. Other

OCR for page 5
8 MODES OF SHUTTLE USE incorporated into the pressurized module and basic pallet elements. Use of standard power, energy, pointing, and communications equipment could lead to major cost economies and conveniences for potential sortie mode experimenters. II. GENERAL CONCLUSIONS Study of the various experiment proposals led us to some general conclusions: 1. There is a general desire for manned interaction in real time with experiments. The demands are most strongly stated by life scientists, space physicists, and solar astronomers. The manned interaction can occur in several ways: either with man in the Shuttle cabin, in the pressurized module, or on the ground. The merits of these various possibilities are discussed below. Pressurized modules are essential for some experiments in the life-science area. 2. A major fraction of all experiments proposed can be imple- mented using unpressurized 3-m pallets. 3. A significant number of experiments, especially in the area of high-energy astronomy, require extensive observing time and are best implemented using free-flying spacecraft. 4. There is a clear need for a design and management philosophy that will allow for maximum flexibility and that will minimize difficulties and costs associated with spaceflights. 5. Certain natural events of great scientific interest are infrequent and short-lived. Typical examples are outbursts of supernovae, novae, flare stars, solar flares, and geomagnetic storms. Dedicated instru- ments, perhaps with dedicated pallets, should be held in standby status for such opportunities. The logistics of Shuttle operations should permit inclusion of such payloads, preferably in the next scheduled Shuttle launch, even if bumping of another payload is required. Guidance for such emergency programming should come from a rating of scientific priorities. 6. It is extremely important to provide the opportunity to fly small experiments on a cost-effective basis. We believe that this can be accomplished by providing small standardized pallet elements (a pointed element and an unpointed element, each one half standard element in size, for example) on which experiments can be integrated and placed in a standby status until a Shuttle mission able to carry additional weight can be identified. The small elements could then be fitted into Shuttle flights on a space-available basis. If this concept is

OCR for page 5
Scientific Uses of the Space Shuttle 9 to be carried out in a cost-effective way, considerable attention should be paid to the management of this type of opportunity. We believe that the present rocket and balloon programs should serve as models for this mode of operation. Careful consideration should be given to make the standardized pallets as self-sufficient as possible and to make the interface of these pallets with the orbiter or sortie lab as simple as possible, in order to maximize opportunities for flight. 7. There is a general recognition of the potential importance of the mission specialist. The mission specialist should play a role analogous to the mission manager on NASA-Ames airborne science flights, to the Los Alamos physicist working with a team of visiting physicists running on the Meson Facility, or to the science coordinator on board an oceanographic research ship. He should be a facility person familiar with facility requirements but also familiar with the needs and scientific objectives of the user groups. III. PALLET MODE OF OPERATION It is important to distinguish at least two major kinds of pallet operation. The first is a pallet-only mode in which the entire Shuttle payload is an integrated set of pallet sections. The second consists of a given set of experiments contained on a single pallet section. In both of these operations the experiments best suited for flight are those whose objectives can be met in a relatively short time, that is, from a week to several weeks. For a pallet-only mission, the experiment control may be from the orbiter cabin, at the Payload Specialist's station, or directly from the ground through available telemetry links. For essentially continuous control and operation of this kind of payload, it may be necessary to have the use of a data relay satellite. It is expected that the common support equipment needed for these experiments would be provided by the pallet, drawing perhaps on the orbiter facilities as needed. These common facilities include power, up and down telemetry, thermal control, data handling, and such specialized equipment as pointing platforms. In this instance, each separate pallet module would receive these services from a common source, and the entire unit (set of modules) would be integrated prior to delivery for launch. Such a mission could be discipline-dedicated or multidisciplinary in nature. It should be recognized that the integration problem for multidisciplinary mis- sions may be significant.

OCR for page 5
10 MODES OF SHUTTLE USE A single-pallet-element mission could be flown attached and integrated to other pallets or simply added on to a nonpallet mission (i.e., on some Tug or large free-flyer delivery mission). Single elements have the advantage that they may be fully dedicated to a particular investigation and may be more accessible to the experi- menter during experiment installation and checkout. Further, it should be possible to obtain more frequent flight opportunities for individual elements than for a full pallet payload. To meet the desires of the users, this pallet section (or module) should be as autonomous as is practical. That is, it should contain its own power conditioning unit, data-handling system, thermal control, and pointing controls. It may draw upon the Shuttle system for raw power and utilize the Shuttle telemetry system. Where high data rates on a nearly continuous real-time basis are required, a data relay satellite may be required. The present Shuttle design does not include a steerable high-gain antenna that would permit a high-data-rate transmission through the relay satellite. Thus pallets or pallet sections may have to include their own steerable antenna (1-m) to make this possible. IV. SHUTTLE-LAUNCHED FREE-FLYERS Many scientific objectives can be met only by the use of free-flying satellites. These include (a) missions that require observation time substantially longer than the maximum of 30 days provided by the Shuttle itself, (b) missions that have a need for higher altitude orbits than can be obtained from the Shuttle, and (c) missions that include experiments requiring substantially smaller contamination than the Shuttle payload bay can provide. Such free-flyers may well be pallet-sized and could be launched from a pallet in the payload bay. A very significant feature of these is that they may be retrieved by the Shuttle and refurbished for subsequent redeployment, should that prove to be economically and scientifically desirable. It is possible that some kind of standard free-flyer should be designed to reduce costs—particularly for missions that can be performed in a Shuttle-compatible orbit—and to facilitate retrieval and refurbishment of the satellite. An attractive feature of the Shuttle-compatible free-flyer is the possibility of recalibrating instru- ments after they are returned to the ground.

OCR for page 5
Scientific Uses of the Space Shuttle 11 V. ROLE OF MAN A. General-Purpose Payload Specialist Station A standard interface can be established between the specialist station and the payload by using a digital computer-to-computer interface, switches to operate standard relays in the payload, and selsyn-to- selsyn controls for interfaces requiring analogue control. A station with the following capabilities could serve a multitude of experi- mental requirements: 1. Display computer with two-color TV screens (one used for status information, the other for data display). A camera is required for recording selected displays, and pictures should be available immediately. 2. Teletype keyboard for controlling displays and for com- manding the experiment computer. (Tape input would be desirable.) 3. Digital displays of key control parameters (ten might be adequate). 4. A set of switches to operate standard relays in the payload. 5. Analogue controls (probably using selsyns) to operate an equivalent control in the payload. It would be desirable to have a number of simple selsyns (about ten) and two joystick-type controls for two dimensions. 6. TV monitor display. The control console would interface through standard connectors with the control package mounted on the pallet. The control part of this package is the experiment computer that controls most of the functions in the experiments and records the experimental data. This computer is reprogrammable from the ground and from the payload specialist station. It has access to on-board data storage and to the telemetry readout. Substantial on-line memory (> 128 kbits) and mass data storage should be included in the computer's capabilities. As required, this control package would have digital channels for special displays on the console. The package could also contain selsyns that control the experiments directly or control the circuit that generates the driving voltages required by the experiment. Prior to integration into the Shuttle, the performance of the pallet payload would be checked out with a copy of the payload specialist station. The interfaces would be standard and have a margin for

OCR for page 5
12 MODES OF SHUTTLE USE variability between units so that identical performance can be expected after the pallet is mounted on the Shuttle. B. Utilization of the Pressurized Module The pressurized module with its closed and controlled atmosphere is clearly necessary for the primary life-sciences missions, as described in the report of that working group. However, use of a smaller pressurized module can provide very significant benefits for other scientific disciplines as well. In several areas it is vital that real-time control of the experiments be carried out on the basis of real-time evaluation of observations. Some very complex coordinated pallet- mounted instrumentation facilities are under consideration, and in these cases, the general-purpose payload specialist console may not provide an adequately flexible facility for display and control of the large number of unique parameters of importance for the mission. For example, to carry out an experiment that requires deployment of both a boom package and a maneuverable subsatellite in changing sequences of directions, with known and varying sensor orientation, there must be an opportunity for continuous feedback between the output of any of the remote sensors and the control circuits. If the presently planned Tracking and Data Relay Satellite (TDRS) system provides global and continuous coverage for all types of Shuttle missions, including high-inclination ones, and if the necessary extensive real-time ground data reduction and command facilities are provided, it is possible, in principle, to carry out this manned evaluation and control from a sophisticated central ground labora- tory. However, there are certain additional important advantages associated with use of an on-board scientist in a small pressurized module. The on-board scientist with access to the display and command console will be able to respond to unexpected situations by effecting limited repairs, by replacing redundant system elements, and by evaluating the stability of prelaunch calibrations. Moreover, there are potential hazards associated with deployment and recovery or retraction of subsatellites and booms, and it may be decided that on-board control provides greater safety for these operations than does dependence on a remote radio link.

OCR for page 5
Scientific Uses of the Space Shuttle 13 C. Ground Experiment Operation Many sortie experiments can most effectively be operated from a ground terminal. This approach has the potential advantages of allowing the following: 1. Senior investigators and their staffs to conduct their observing programs directly; 2. Use of general-purpose instruments on the Shuttle by a number of different groups of investigators; 3. Application of relatively powerful ground computing and data-handling systems to the implementation of the experiment; 4. Experiment implementation to be conducted from a single location where all orbit, attitude, experiment telemetry data, and preflight calibration and test data reside; 5. All the experiment information to be available to the best trained experts in the case of anomalous experiment behavior; 6. Experiment operation to be conducted relatively indepen- dently of the Shuttle sortie on-board time line; 7. Operation of the sortie experiment in a mode similar to that of the free-flyers with which many investigators are trained. In order to use a substantial class of Shuttle experiments effectively, it is necessary to have real-time data displays available on the ground, for the use of a team of scientists in making decisions on the modification of observing programs. This mode of operation is particularly important for the astronomical disciplines: ultraviolet, optical, and infrared astronomy; solar physics; and high-energy astrophysics. The presently planned data link through the TDRS sys- tem is inadequate in bandwidth, and we recommend that a wide- band link be made a standard capability of the orbiter/sortie lab (pallet and module) configuration from the onset of Shuttle operations. A data rate of 256 kbps continuously would meet most requirements. A few specialized requirements, such as observation of candidate black holes in high-energy astrophysics, require con- siderably higher rates (10 Mbps). These requirements can probably be met by the use of temporary storage on the pallet and subsequent playback through the TDRS system at a lower rate.