Computer System Specification Sheet

Kenneth M Rock
August 1995

The computer system responsibilities are threefold. Primarily, it will control the spacecraft motion through the transit from earth orbit to landing on the lunar surface. The secondary responsibility of the computer system is to control spacecraft operations and experiments on the lunar surface. The final responsibility is to monitor system integrity throughout the mission.


The computer system group will select the primary and backup computer systems and write a system theory of operation. The computational requirements of this mission are small compared to past imaging missions (see Table 1.0 and 2.0), therefore, the computer system design could use existing off the shelf, space-qualified computers. These computers, however, have become relics in an age of rapidly advancing computer technology. Thus, we should consider using a newer, compact, lightweight, and high performance microcomputer. A backup computer system, which can take on all computing requirements in the event of main computer failure, must be planned.

Data Storage

The computer group will determine overall data storage requirements and select a data storage system(s) for the spacecraft. In an effort to conserve power, the computer system may need to be shut down during the lunar night. The system will need to use random access data retrieval (e.g. a hard drive, disk drive or optical disk drive). The data storage device(s) will record transmissions to the DSN and be capable of playback in case of signal receiving errors. A direct communication link will be used as the backup plan for data storage.


The computer group is responsible for incorporating all spacecraft component needs into the system. This responsibility extends to designing computer interfaces, such as wiring, filters and converters.

System Code (kwords) Data (kwords) Throughput (KIPS)
Lander NGC

Rate Gyros 0.80 0.50 4.50
Kinematic Integration * 2.00/2.00 0.20/0.20 7.50/7.50
Error Determination * 1.00/1.00 0.10/0.10 6.00/6.00
Thruster Control * 0.60/0.60 0.40/0.40 1.20/1.20
Momentum Wheel Control 1.00 0.30 5.00
Ephemeris Propagation 2.00 0.30 2.00
Complex Ephemeris 3.50 2.50 4.00
Orbit Propagation 13.0 4.00 20.0
Altimeter 0.00 0.00 2.0
System Health Monitoring * 33.0/18.0 30.5/21.5 124.5/114.0
Operating System 19.4 8.6 100.5
Lander Experiments

Command Processing 1.00 4.00 3.50
Monitors 4.00 1.00 15.0
Fault Correction 2.00 10.0 5.0
High Resolution UV/VI's Camera 0.00 0.00 1728.0
Rover Relay ??? ??? ???
Coring Devices ??? ??? ???
Mass spectrometer (O2 Plant) 0.00 0.00 14.6
Operating System 19.4 8.6 27.0
Totals 123.3 93.2 2179.0
* denotes previously separate calculations for orbiter/Lander, where complete code/data/throughput were added due to possible dissimilarity between fundamental routines

Table 1.0: Computer Sizing

Lines of code27,000-31,000
ROM1.973-2.677 Mbits
RAM0.871 Mbits

Table 2.0: Memory Requirements

Computer System Interface Sheet

Input Group Interface/Information Output Group
NGCTrajectory Control ProcessingNGC
NGCAttitude Control ProcessingNGC
NGCNGC Systems Control Management
SensorsSensing Devices Data Management
ChemicalOxygen Plant Control & Data Management
PropulsionPropulsion Systems Control Management
CommunicationsCommunications Data Management
PowerPower Systems Load Management
ThermalThermal Systems Control

Structural Design RequirementsStructures

Computer System Power RequirementsPower

Computer System Thermal RequirementsThermal

Computer System References Sheet

Carrico, J., Carrington, D., Hametz, M., Jordon, P., Peters, D., Schiff, C., and Richon, K., Newman, L. "Maneuver Planning and Results for Clemintine", AAS/AIAA Spaceflight Mechanics Meeting AAS-95-129, AAS Publications office, San Diego, CA, 1995

Griffin, M. D., French, J. R. "Space Vehicle Design", AIAA Pub., Washington DC, 1991.

McDonnell Douglas Commercial Delta, Inc., "Commercial Delta II Payload Planners Guide". December 1989.

Middour, J., Hope, A., Dasenbrock, R., Bakeris ,D., "Trajectory and Maneuver Planning Products and Procedures for Clemintine Operations", AAS/AIAA Spaceflight Mechanics Meeting 95-125, AAS Publications Office, San Diego, CA, 1995

Pisacane, V. L., Moore, R. C. "Fundamentals of Space Systems", Oxford University Press, New York, 1994.

Regeon, P., Chapman, R. J., "Clemintine Orbiter Spacecraft System Design", AAS/AIAA Spaceflight Mechanics Meeting 95-130, AAS Publications Office, San Diego, CA, 1995.

Soyka, M. T.,"Sensor Description for the Clemintine/DSPSE Mission", ASE 389P-Remote Sensing Paper, University of Texas at Austin, Feb 1993.

Wertz, J. R. "Spacecraft Mission Analysis and Design", 2nd ed., Kluwer Academic Publishers, Boston, 1993.

Helpful Contacts

Southwest Research Institute
Instrumentation and Space Research Division
P.O. Drawer 28510
San Antonio, Texas 78228-0510
(210) 522-2748

Loral Federal Systems-Manassas
Space and Technology Business Development
9500 Godwin Drive
Manassas, Virginia 22110
(703) 367-5045


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