Spacecraft computer program status

FM/Deputy Chief, Mission Planning and Analysis DivisionAUG 22 1967EG23-145-67-739EG/Chief, Guidance and Control DivisionSpacecraft computer program status

Reference is made to MSC memorandum 67-FM-T-52, “Spacecraft computer program status – particularly Sundisk,” dated August 1, 1967.

The referenced memorandum reviews the status of the Sundisk computer program, and includes comments that could be misleading to those addressees who do not have the developmental background of the digi- tal autopilot (DAP).

This memorandum is written to review the present responsibility for DAP designs, and to present appropriate comments on present DAP status.

It is the understanding of the Guidance and Control Division that the management responsibilities for the DAP development, programming, veri- fication, and spacecraft integration are as follows:

a. Development (including requirements definition and design verification) – Systems Analysis Branch (GCD)

b. Software programming (including documentation) – Flight Software Branch (FSD)

c. Software verification (including documentation) – Flight Software Branch (FSD)

d. Spacecraft integration – GCD Project Offices

In addition, the Systems Analysis Branch has the responsibility to provide technical support to FSD for items (b) and (c). Examples are (1) review and initiation of DAP test plans, (2) analysis of DAP test results, and (3) initiation of independent DAP verification (design and software) by other support contractors.

If, as possibly indicated in the reference, this division of responsi- bility is not presently in effect, there is a misunderstanding, and MPAD, FSD, and GCD must initiate action to clarify the responsibilities in the DAP area.

Specifically, with regard to the present status of DAP programs, as mentioned in the reference, several comments are appropriate.

a. “Workable” DAP's for both CSM TVC and LM have been available approximately one year ago, and are documented in the 207/208 GSOP.

b. Following the flight schedule reshuffle, the decision was made to modify the LM DAP to reduce (1) computer memory requirements, (2) computer execution time (particularly in powered descent), and (3) control system sensitivity to knowledge of environmental conditions. It should be noted that a significant number of potential design defi- ciencies have been established by the detailed LM-1 verification studies, and appropriate modifications have been included into the simplified LM DAP.

c. TVC DAP performance has been sacrificed to accept a first structural bending mode frequency of 0.8 cps. This was considered a compromise in order to accommodate the significant uncertainties in the modal data. However, with the present low performance control gains, the CSM docked configuration is considered unacceptable from a crew display and monitoring viewpoint. MIT has been directed to investi- gate alternatives to correct this established design deficiency, and is actively pursuing this objective at this time.

d. Dr. Kenneth Cox attended the July 19, 1967, Software Development meeting at Cambridge, and stimulated a detailed discussion on general DAP development status. As a result, the management of MIT agreed to review the manpower requirements in the area of DAP develop- ment, and to initiate action to remedy the recognized DAP documenta- tion deficiencies.

Since the management of the flight software programming task (which is a major portion of the present MIT contract) has been delegated to FOD, this responsibility should include the total product. It is our understanding that this applies to the DAP's as well as all other soft- ware programs. Configuration control of the DAP programs should be exercised in the same manner as in the case for other spacecraft com- puter programs. A single point management contact (Howard W. Tindall, Jr.) presently exists, and successful completion of the total DAP designs is dependent upon close coordination between responsible ele- ments of MPAD, FSD, and GCD.