Computerized Control: Boon to ARIA
Major General David M. Jones
With electronic computer systems established firmly in practically every human process from manufacturing to medicine, it followed naturally that computer technology would be applied to the complex field of operational control for test instrumentation aircraft. Such an application has become a fact at the Air Force Eastern Test Range near Cape Kennedy, where computer techniques of a wide variety have made possible our great progress in national missile and space programs.
Computerized operational control for Apollo Range Instrumentation Aircraft (ARIA) is in-being at Patrick Air Force Base, Florida, home of the eight-plane fleet of ARIA EC-135Ns and headquarters of the Eastern Test Range. Immediate dividends have thus been realized in better control and utilization of the ARIA fleet, improved support for missile and space missions, and more efficient programming of maintenance and training. The feasibility of applying similar computer techniques in other aircraft operational environments becomes more apparent each day.
The ARIA is a complex aircraft with a complex mission. Its precise and positive positioning and control are essential to the manned space missions of the National Aeronautics and Space Administration (NASA) and to missile programs of the Department of Defense. A smoothly functioning Aircraft Operations Control Center (AOCC) was set up at Patrick at the outset of the ARIA program. Now the computer has been added to provide the Information System that makes up the AOCC/IS.
As aircraft become more complex and versatile to satisfy complicated mission requirements, so has control of such aircraft become more demanding. Effectiveness of control is dependent on the quality of information that flows between the command post and the aircraft crew. Efficiency in the management of air operations requires a constant feedback of information, such as aircraft position, fuel remaining, mechanical status, and preliminary estimates of accomplishments. These data must be updated constantly, as they will have effects on other decisions. This is most important when contingencies occur.
The aircraft controller finds himself looking for solutions to problems that arise when events do not occur as planned. An example is an aircraft having maintenance difficulties before takeoff. One of the questions facing the controller is: What is the latest time that this aircraft can take off and still accomplish the mission as planned? Another: If this mission is not accomplished, how is this going to affect the overall plan? Another: Considering the importance of the mission and aircraft generation time, what other aircraft should be programmed to accomplish this mission?
These and thousands of similar questions are answered each day by aircraft controllers working in both wartime situations and normal peacetime operations. In some instances the possible courses of action may be staggering. The selection depends greatly on the ability, intelligence, and experience of the controller. Here is where a computer that examines all possible solutions and recommends courses of action is welcome.
A computer that examines all possible solutions and eliminates those that do not meet a preset criterion helps the controller make a sounder decision. The real-time computer allows the controller to test his solution by extrapolating ahead and examining what the situation will be one, two, or more hours from the present for a given solution. In this way the controller can validate his decision before it is actually selected-a process that could be difficult and lengthy without the aid of a computer.
ARIA, as part of a worldwide communications network, provides two-way voice relay between the Apollo spacecraft and the Mission Control Center at Houston, Texas. The ARIA fleet is made up of eight modified Boeing C-l35 transports. It supplements instrumented ships and land-based stations in obtaining critical data from spacecraft while in parking orbit, trans lunar injection, and re-entry. Using its 7½-foot steerable antenna, ARIA also receives telemetry signals via VHF and S-band systems. This vital information, containing data ranging from position of switches to heartbeat rates, is recorded and retransmitted to ground stations within VHF and UHF range.
Understanding the complexity of control problems requires a brief examination of the Apollo mission. The position in parking orbit when the SIV-B stage of the Saturn V rocket is ignited to start the trip to the moon is a function of time. The point at which trans-lunar injection (TLI) occurs moves continuously with time within the launch window. TLI should occur in the second revolution if the mission is normal, and in the third revolution as the last opportunity. The net effect of having a large launch window (and consequently variable launch azimuth) and two opportunities for the TLI is that the TLI point may be located somewhere in an area of around 20 million square miles in the Indian and Pacific oceans. As NASA requires telemetry collection and voice relay for certain critical periods prior to and during TLI, it is necessary that ARIA be able to react in real time to provide that support.
A somewhat similar situation occurs during re-entry. Weather, sea conditions, or other factors could cause a change in the recovery area. This was experienced during Apollo 9, when sea conditions made it desirable to move the impact area 400 miles to the south of the original area. During re-entry, ARIA provides voice relay before and after communications blackout. It also uses HF homing to determine spacecraft location and again supply voice relay from the spacecraft to recovery forces. The name of the game is mobility.
The problem of supporting Apollo missions is complicated further by the fact that TLI could occur over a vast ocean area a great distance from any base. Fuel and wind conditions can be vital factors in whether the aircraft can reach test support positions at the proper time and then proceed to a land base.
The AOCC-Information System takes all factors into consideration and computes test support positions, acquisition information, flight plans, and other pertinent data. It also keeps track of each ARIA and the Apollo spacecraft and displays them dynamically on a wall display system.
The operator of the system is the navigation adviser, a member of the controller advisory team. He uses a keyboard to send command messages to the computer. Response to the command message returns to the AOCC and is displayed on a cathode-ray tube in front of the navigation adviser. Such response may be a flight plan, a list of current test support points, a status report, an instrumentation almanac, a list of recovery bases for an ARIA experiencing a malfunction, or simply a message to the operator that there was an error in the input.
The heart of the AOCC/IS is an IBM 360/65 computer located at the Eastern Test Range’s Technical Laboratory and slaved to the AOCC in the nearby ARIA headquarters. Inputs to the computer come from each of the eight ARIA, from the Mission Control Center in Houston, and from the ARIA mission controller in the AOCC at Patrick. Outputs appear on the dynamic display board in the AOCC, on a cathode-ray tube display on the navigation adviser’s console, and on a teletype communications system between the aircraft and the AOCC.
Software for this operation is unique to the ARIA operation and was developed in-house at Air Force Eastern Test Range to support Apollo. The program consists of seven modules, each of which can operate independently as a complete program.
Orbit generator module: This program locates the spacecraft and determines its orbit track in relation to the surface of the earth.
TSP module: The Test Support Position module presents the exact location where the ARIA is expected to be at the proper time to receive and record telemetry information and/ or make voice relay during a critical point of the mission. The TSP is computed when the spacecraft trajectory and mission requirements are figured in with the criteria for the TSP relative to the spacecraft position.
Navigation module: This program computes new flight plans for the ARIA fleet when ever the mission departs from nominal parameters. This includes trajectory change, deviation in Schedule of activities, change in ARIA status, and others.
Instrumentation almanac module: This program determines the “look angles” needed or spacecraft acquisition at the TSP coordinates and other important acquisition data. The large telemetry antenna in the nose of the ARIA has a rather narrow effective reception angle for maximum efficiency and consequently must be pointed precisely to get good results at maximum ranges. The acquisition information or instrumentation almanac is sent to the aircraft by teletype. Each of the ARIA has two teletype machines on board, eliminating the need for extended voice communication between the controller and ARIA.
Re-entry trajectory module: This module determines the trajectory of re-entry. It gives the splash-down point in the same manner that the orbit generator module determines the spacecraft trajectory.
Flight-following module: This program is one of the most valuable to the ARIA controller as it keeps track of each aircraft from prior to takeoff until after the last landing. The program monitors position, fuel remaining, fuel consumption rates, ETA’S at significant points, status with respect to attainability of assigned TSP on time, and feasibility of the ARIA in reaching its assigned recovery base. This is a dynamic program that integrates status reports coming from ARIA in real time with all other updated information in the core.
Data display control module: This program controls a large dynamic wall display at the AOCC. It selects data from storage, modifies it if needed, and forwards it to an interface program which updates the wall display. The display is set against a background map of the area in which action is occurring. The positions of the spacecraft and the ARIA fleet are indicated.
The seven modules are connected so that the output of one module is routed directly to any of the other modules needing the information concerned. This creates a chain reaction which supplies the best available answers to the following typical questions: Where is the spacecraft trajectory? Where are the Test Support Positions? Assuming the eight ARIA are standing by at their assigned deployment base, how are the TSP’S going to be assigned to ARIA? What is the latest take-off time for each ARIA? In case of abort or degradation of one or more ARIA, how will TSP’S be assigned in an optimum manner? In case of nonnominal bum of the booster or any other contingency, how can ARIA provide best support? In case of aircraft emergency, what bases can ARIA reach and with how much fuel remaining over each base?
The real-time capability of the system, combined with the ease of entering command messages through a keyboard in plain language, makes the system attractive to other agencies involved in aircraft control. The system is constantly being improved to make the ARIA operation more efficient and economical and at the same time to support any changes in requirements developed by NASA.
The AOCC/IS is at present a highly sophisticated computer system used almost exclusively in support of the Apollo space missions. In assessing its capabilities, however, one can readily see that the system could be used profitably for many other aircraft control situations. For example, the flight-following module with few modifications would be of great value to air traffic controllers.
By combining the human judgment and experience of seasoned air controllers with the high-speed calculating and large-volume memory capabilities of the computer, Air Force Eastern Test Range has produced an aircraft operations control system that works. The pay-off is in better and more economical employment of time, people, and equipment and in improved service and support for national missile and space programs.
Air Force Eastern Test Range
Major General David M. Jones is Commander, Air Force Eastern Test Range, Cape Kennedy, Florida. He enlisted in the Arizona National Guard, 1932, completed flying training, 1938, and Hew with attack units. During the War he took part in the Doolittle Tokyo raid, and as Commander, 319th Bomb Group, was shot down over Bizerte, December 1942, remaining a prisoner the rest of the war. Postwar assignments included several operational commands, and since 1956 he has been DCS/O, Air Proving Ground Command, Eglin AFB, Florida; Test Director, B-58 Test Force, Carswell AFB, Texas; Deputy Commander/GAM-87 “Skybolt” and Deputy for Systems Management/Vice Commander, Aeronautical Systems Division, Air Force Systems Command, Wright-Patterson AFB, Ohio; DCS/Systems, Hq AFSC; and Deputy Associate Administrator for Manned Space Flight, NASA. General Jones is a graduate of Command and General Staff School, Armed Forces Staff College, and National War College.
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.