[39] The manned circumlunar vehicle is an important developmental step toward the goal of establishing a manned scientific outpost on the moon. Man's role on the moon or in space can be fulfilled only if he can achieve the means of controlling his environment and this includes the command and control of the flight of his spacecraft. The next two guidelines, figure 1, concern this aspect of the program: (a) Onboard command of the mission and (b) Communications and tracking necessary to support this concept of manned operations in space.

The first guideline states that primary command of the mission should be onboard. The vehicle should be designed solely for manned operations with no systems requirements for carrying out unmanned qualification missions. A primary objective of the circumlunar program is the development of operational techniques for manned vehicles. This development has its beginning in the Mercury program. It will be expanded in the orbital phase of the circumlunar program, and by the conclusion of the circumlunar program, the full scope of manned space operations will have been explored except for lunar landings and takeoffs.

The payload cost of supporting a man in space is very large in comparison with unmanned space operations. There is also a great cost in system complexity for providing the mission abort capability necessary for manned space flight. Therefore, when manned space flight is the basis for design, the maximum advantage must be taken of the command decision and operational capabilities of the crewman. It is impractical to provide a completely automatic mission operated by ground command. Furthermore, it is our opinion that by concentrating on the manned operational concept we can achieve an earlier and greater probability for success toward the ultimate goal of accomplishing reliable flights to and from the surface of the moon.

It should be emphasized at this point that the manned operational concept does not imply that all operations are manually performed. There is a definite requirement for such automated functions as attitude control and abort sensing to obtain high accuracy, short response time, and pilot relief. The correct implication of manned operations is that the crew is given the command control of the vehicle and its systems by [40] judiciously assigning tasks to the crew, by cross training the crew in the various tasks, and by providing means for checking and correcting systems performance.

Figure 2 indicates the system responsibilities of the crew. The primary task is to make command decisions and monitor systems performance. In particular, this includes supervision of navigation and control. The secondary task is to maintain systems performance by accomplishing necessary maintenance and repair or by engaging the appropriate backup systems. The emergency task is to take over by manual modes certain critical functions. At this time, these functions cannot be described in detail. A study is required to determine the extent of the capabilities of the crew to perform these tasks and to specify what is reasonable to expect for routine, urgent, and extreme emergency conditions of operation.

The flight hardware should be designed not only for intrinsic reliability, but also, when practical, it should be designed to incorporate special features for operational reliability such as replacement modules for easy maintenance, self checking, and manual correction modes. Some of the hardware requirements for onboard command are shown in figure 3. This does not represent a configuration for any particular mode of control, but rather a grouping of subsystems showing their relationship to one another. The primary inputs to the crew are from the display console and from the ground complex. Not shown are the pilot inputs to the subsystems. It is anticipated that he will have inputs to every subsystem. A brief description of the subsystems and some of the problems they suggest will be given in the following sections.

Inertial Systems. Applications of gyros and accelerometers supply short term integration for position and velocity determination and short term attitude reference. Both stabilized and body fixed applications may be employed in the best configuration for overall operational reliability. Inertial platforms will be employed for monitoring insertion guidance, abort command, and for abort reentry navigation. The exact role of the inertial platforms in midcourse and normal reentry navigation will be determined by careful study of trade offs between system accuracy, power requirements, weight, and techniques for correcting and updating the system by intermediate reference. Body fixed systems may be attractive for backup modes.

Celestial Optical. These systems include telescopes, star trackers, horizon scanners, and optical ranging devices. They supply inertial attitude and position reference, and local reference information in the vicinity of earth and moon. Optical devices may operate in a variety of modes and careful study will reveal the extent to which they may be [41] employed to obtain maximum operational reliability for manned space flight to the moon.

Onboard Computer. The computer represents a capability to perform a number of digital calculations, some of them special purpose and some general purpose. The entire concept of onboard control depends upon the development of versatile, reliable, long lived computers. The computer must handle all the navigation computations whether insertion, midcourse, reentry, abort, or orbital operations around the moon. Midcourse and reentry guidance concepts must be evolved which will simplify the computer requirements and which will allow relatively simple schemes using redundant hardware for obtaining the capability of checking and correcting system performance.

Onboard Display. The display provides all the system performance indices and mission status parameters necessary for the pilot to carry out his assigned role. It is integrally related to the computer and inertial systems. Display requirements for reentry control have received quite a lot of attention in the study phases of the Dyna Soar program. These must be continued for the circumlunar vehicle with added emphasis on the aspect of control of reentries from aborted missions. Display requirements for insertion guidance monitoring have received less attention, and the other phases of the mission are as yet unexplored from the standpoint of developing displays which will put the pilot squarely in the middle of the onboard systems with means for making real inputs for achieving operational reliability.

Attitude Control. Attitude control employs aerodynamic surfaces, reaction Jets, reaction wheels, etc., for control and utilizes the inertial and celestial optical systems for reference. The accuracy of the reference systems is determined by the navigation requirements which may or may not be reflected as attitude control requirements. Vehicle orientation for midcourse corrective impulse is not expected to require precise control. Other requirements for attitude control are for antenna look angles, solar orientation' control during thrust application for abort and lunar retrograde and escape, rapid reorientation for some abort cases, and control during reentry. Reentry control and low altitude abort control must stress reliable stability augmentation modes.

A multimode system will be necessary to satisfy all the requirements. Aerodynamic control is attractive for the low altitude abort and the atmospheric reentry. Combinations of Jets and wheels will likely provide the long term stabilization requirements. Techniques for obtaining reliable long period limit cycles will be very important for economical use of fuel. Jet propellant performance characteristics must be compatible with operational and system requirements. Either high thrust Jets or gimballed engines will be required for control during [42] the high thrust application required for aborts or lunar retrograde. Careful attention to the propulsion system design can simplify the attitude control requirements.

Propulsion. The propulsion systems provide the small corrective impulse for midcourse guidance and the large impulse for emergency abort, lunar retrograde and escape, and retrograde for reentry control from high altitude aborts. The system should be designed for maximum reliability and flexibility, and for minimum demand on attitude control due to thrust misalinement.

Communications and Tracking. Tracking data provide position and velocity data for the pilot or, if necessary, it can be read directly into the computer. This brings us to the next guideline.

Communications and ground tracking should be provided throughout the lunar mission except when the vehicle is blanketed by the moon. Communications and tracking are important to keep the ground crew informed of the status of the mission and to obtain and relay navigation data to the vehicle. Naturally, for the lunar mission it will be desirable to maintain continuous contact for as long as possible. The orbital mission, however, will be similar to the Mercury program except for the altitude and length of time in orbit. At present, it seems unlikely that the cost in the number of ground stations required to maintain continuous tracking during earth orbits can be Justified. Contact once each orbit appears to be a reasonable and adequate requirement.

Figure 4 describes the operational requirements for communications and tracking for the lunar and orbital missions. The methods employed for transmitting messages should provide the greatest practical coverage for both the lunar and orbital missions. Voice contact once per orbit is considered sufficient for orbital missions; however, other means, such as CW transmission should be provided for essentially continuous contact. For the lunar mission, telemetry will be required only for backup data. The crew will be capable of relaying periodic status reports on men, systems, and vehicle; therefore, the strongest requirement for telemetry will be for providing data in case of disaster. Telemetry for the orbital mission may be as complete as necessary to satisfy the requirements for the development program. Television for the lunar mission may be desirable and practical in the time period involved. There is no apparent requirement for television for the orbital mission. A mission and operations analysis should be made to determine the number and types of communications systems and their duty cycles which will be required for efficient and reliable communications.

Ground tracking will provide trajectory data continuously for the [43] lunar mission to the extent possible and once per orbit for the orbital mission. These data in the form of position and velocity fixes will be relayed to the vehicle for midcourse and orbital navigation. Ground tracking in some form may appear in the guidance loop for approach and reentry control.

Figure 5 illustrates the requirements for ground tracking. It must be emphasized that this is purely speculative. There are shown at least two different systems. One system provides tracking data during the atmospheric reentry phase and terminal point control; the other system has the greater range required for midcourse tracking. The Mercury range may offer the best means of satisfying the close in requirement. A study should be made to determine whether the Mercury range can be modified and relocated to meet the lunar operational requirements taking into account the reentry control capability of the vehicle and the ability to control the time of approach to the corridor.

The midcourse tracking requirement may be satisfied by the presently planned deep space net with facilities at Goldstone, and in Australia and Africa. This system should be studied for applicability to the circumlunar mission taking into account tracking accuracy and requirements for data processing. Radio interferometer systems should also be studied. Finally, it will be important to investigate existing or proposed facilities to insure that the frequencies for all systems can be made compatible in order that a single beacon may be used for midcourse and reentry tracking.

The last figure, figure 6, summarizes the problem areas which have been mentioned in connection with this guideline:

(a) Determine the detailed requirements for communications systems with particular attention to range, power, and duty cycle.

(b) Study the tracking requirements for reentry control and determine the applicability of the Mercury range.

(c) Study the requirements for midcourse tracking and determine the applicability of the deep space net.

(d) Determine the feasibility of providing compatible frequencies for midcourse and reentry beacon requirements.

PRIMARY: COMMAND DECISION, MONITORING, NAVIGATION, AND CONTROL

SECONDARY: SYSTEM REPAIR AND MAINTENANCE

EMERGENCY: MANUAL MODES

 

 

---

 

[45] Figure 3. HARDWARE REQUIREMENTS FOR ONBOARD CONTROL.

(a) NUMBER AND TYPES OF COMMUNICATIONS SYSTEMS (RANGE, POWER, DUTY CYCLE)

(b) TRACKING REQUIREMENTS FOR REENTRY CONTROL (MODIFY AND RELOCATE MERCURY TYPE FACILITIES)

(c) TRACKING REQUIREMENTS FOR MIDCOURSE CONTROL (DEEP SPACE NET, RADIO INTERFEROMETER-ACCURACY, DATA PROCESSING)

(d) COMPATIBLE FREQUENCIES FOR REENTRY AND MIDCOURSE SYSTEMS.

 

---