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Sheets 

4 December 1967 

Subject: Auxiliary Memory Unit, (AMU) Profile 

INTRODUCTION 

A study has been made into the use of the AMU during orbital operations. 

The purpose of this study was to: 1) Determine the different kinds of 

information that may be stored in the AMU; 2) Estimate the number 

of times information might be extracted from the AMU during a 30-day 

flight; 3) Predict (from item 2) if the AMU's specified access 

limitations will be exceeded for a 30-day flight; and 4) Determine the 

need for an optimum loading of the AMU to reduce the accessing problem. 

PROPOSED AMU STORED INFORMATION 

AND NUMBER OF ACCESSES 

It has been suggested that the following information would be stored and 

be accessed from the AMU. As noted below, most information must be 

accessed once for each photographic rev (anticipated to be from 10 to 

13 times per day) while some others must also be accessed to support 

R&D events (anticipated to be from 0 to 3 times per day). The number 

of accesses for the other information is still under investigation. 

Therefore, the number of accesses listed for each item below is only 

a best estimate, but still provides useful information. 

I. Target List 

This data identifies, through a code number, latitude, longitude, 

altitude and other information for each target to be observed. It is 

anticipated that the information will be accessed once per payload rev, 

or ten (10) to thirteen (13) times per day. 

2. Propellant Gauging Program 

This program allows for the determination of the amount of gas 

propellant remaining in the propellant tanks used for attitude control. 

Depending upon the activity of the OV and the required monitoring, it is 

anticipated that access of the gauging information will be required from 

three (3) to five (5) times per day. 

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3. TLM Access Programming 

This program allows the flight crew to use the LM keyboard to 

access any TLM point (except Gemini B) being sent to the ground. The 

resulting information is in percentage of full scale and not converted to 

engineering units. It is suggested that access to this program will be 

from thirteen (13) to sixteen (16) times per day. (Any OV contingency 

will greatly increase the number of accesses of the AMU for the TLM 

Access Program.) 

4. Cue Present Program 

This program is used to access the cues which identify/locate 

the targets and is accessed during target prepass activities. It is anticipated that such information will be required once per payload rev or 

from ten (10) to thirteen (13) times per day. 

5. Payload Prepass Set-up Program 

This program is used to access the targets from the AMU. 

This information will be required from ten (10) to thirteen (13) times 

per day. 

6. Bore sight Alignment Programs 

This program is expected to be used once per day to align the 

tracking mirrors with the acquisition scope. 

7. Servo Bias Determination Program 

This program is used to determine the servo rate loop bias so 

that the main optics will be properly slaved to the acquisition scope. 

Access will be once per day. 

8. DCSG Self-Test Program 

This program is used to run operational checks on the DCSG 

components. Presently DAC and GE differ in their opinions on the 

importance and the frequency of performing these tests. GE feels 

that such programs are not critical to the successful completion of 

the mission requirements. Therefore, they recommend that such 

programs be located in the AMU and accessed approximately once per 

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orbit. DAC believes that the self-test programs should be run 

whenever the computer has time during its on-time. Therefore, they 

recommend that these programs be located in the computer core. 

The content, the purpose, the duty cycle and, therefore, the 

location (computer core or AMU) of these programs are now being 

studied. Should these programs be located in the AMU, it is anticipated 

that they would be accessed from thirteen (13) to sixteen (16) times per 

day. 

9. System Readiness Check Programs 

These programs are used to run operational checks on the whole 

OV system to determine its readiness to perform mission operations. 

Presently DAC and GE also differ on the frequency and use of these 

programs. DAC feels that these programs will be frequently used and 

therefore should be located in the computer core. GE feels that these 

programs will be used only as necessary and therefore should not be 

located in the computer core. 

The content, the purpose, the duty cycle and, therefore, the 

location (computer core or AMU) of these programs are now being studied. 

Should these programs be located in the AMU, it is anticipated that they 

would be accessed from thirteen (13) to sixteen (16) times per day. 

10. Diagnostic Programs 

These programs are used for limited isolation of malfunctions 

during contingencies. Nominally, it is anticipated that these programs 

will not be accessed. However, for planning purposes, it is anticipated 

that these programs might be accessed ten (10) times during a 30-day 

mission. 

11. OV Sequence Programs 

These programs are used in lieu of using numerous commands for 

the turn-on of certain subsystems that require a fixed sequence of steps. 

No firm need and recommendation has been expressed for the use of 

such programs and for their storage on the AMU. However, for planning 

purposes, it is anticipated that these programs might be accessed from 

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the AMU some twenty (20) times during a 30-day flight. 

12. Remaining Programs 

Executive control programs and mission critical application 

programs will also reside in the AMU. Nominally, these programs will 

not be accessed except when the content of the computer's fixed core is 

uncertain such as after a power interrupt. However, for planning purposes, 

it is anticipated that these programs might be accessed from the AMU 

some ten (10) times during a 30-day flight. 

PREDICTED AMY ACCESSES 

Table I sums up the number of accesses required of the AMU during a 

30-day mission. Plans now call for the AMU accessed information of 

Item 1 through 13 to be put into what is called a dynamic core section 

of the computer(s) whereas all other information will reside in the fixed 

core section. The information in the dynamic core will remain there 

until replaced. This will preclude the bumping of fixed core programs 

which would have to be re-entered after the AMU programs and would 

require a total of two accesses to the AMU. 

PREDICTED AMU ACCESS VS SPECIFICATION LIMITATIONS 

The IBM AMU Procurement Specification states that, "The design of 

the AMU shall be such as to preserve or maintain magnetic tape life and 

its ability to meet the specified performance for a minimum of 1,000 

full-length passes across the magnetic tape heads without tape replacement. " The AMU contractor has further clarified this requirement by 

stating that the number of accesses of any one spot on the AMU tape is 

limited to 1,000. The predicted number of accesses listed in Table I 

assume that the information is located on the AMU tape in a. random 

manner and allowing a 10% increase for accessing such things as 

executive programs. Locating the desired information would require 

a search of the whole AMU tape with the possibility of accessing all 

AMU data each time. Using this assumption, the orbital operations 

alone, without adding the accesses required for prelaunch and countdown 

checkout, exceed the requirements of the procurement specifications. 

However, optimum loading and spacing of the AMU information can 

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reduce the number of total accesses. 

OPTIMUM LOADING OF AMU 

The performance of photographic and R&D missions will be accomplished 

by completing a sequence of ordered events. While it is still being 

studied, it is anticipated that the first nine (9) items of Table I could be 

accessed in the order listed. Therefore, if these items are recorded 

on the AMU in the order listed in Table I and allowed enough space on the 

tape between each item for the tape to stop'start between readings, then 

each piece of information would be accessed only once for each photographic and/or R&D mission, plus a second time when the tape returns 

to the beginning of the sequence. Because the schedule of the accessing 

to the diagnostic programs, OV sequence programs and executive programs 

is random, it is assumed for the worse case that all items of information 

would have to be accessed in retrieving the diagnostic programs. So each 

of the first ten (10) items would be accessed each time the diagnostic 

program is retrieved or first nine (9) items for access to the OV sequence 

programs. This adds ten (10) accesses (plus ten more for return) plus 

nine (9) accesses (plus nine more for return) per flight to the number of 

accesses called for the first nine (9) items. 

It is also assumed that there will be periods when additional accesses 

to the AMU will be required, such as reloading the fixed core during/ 

following the periods of contingencies and to repeat a computer load 

from the AMU to increase confidence. Therefore, 10% additional accesses 

are added as a safety factor. It is planned that it will not be required to 

access the AMU to set up or perform an RTS pass. This control will 

be in the fixed core of the computer. Table II then sums up the number 

of anticipated accesses during a 30-day flight utilizing optimum AMU 

loading. Figure I shows a recommended optimum loading order for 

the AMU tape. 

CONCLUSION 

As the previous discussion indicated, required flight operational access 

to the AMU tape can readily exceed access limits of the procurement 

specification if the loading of the AMU is not considered. By optimizing 

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the AMU load, the required number of accesses can be reduced. Using 

the interpretation of the procurement specification stated earlier, 

optimization of the AMU load still does not reduce the access below the 

specification's 1, 000. Therefore, a study is necessary to determine if 

a means can be found to increase the number of AMU accesses. If no 

means can be found for increasing the number of accesses, then it is 

suggested that flight operations be reviewed with the intention of reducing 

the number of times the AMU must be accessed for mission passes. 

In addition, while not discussed in this report, test planning must limit 

the AMU accessing during in-house acceptance testing and pad checkout. 

It is anticipated that the AMU will be replaced during pre -launch checkout 

at VAFB because some 1,000 hours of testing are planned for at Huntington 

Beach and on the pad. However, control of the AMU accesses will still 

remain uncertain and this must be considered by those writing DCSG 

software and checkout procedures. A study is now underway to better 

define the anticipated AMU accesses required during acceptance and 

prelaunch checkout and a recommendation as to how and when the AMU 

will be changed.