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j.81 NATIONAL RECONNAISSANCE OFFICE 

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WASHINGTON, D.C. 

THE NRO STAFF 

9 January 1970 

MEMORANDUM FOR THE DIRECTOR, NATIONAL RECONNAISSANCE OFFICE 

SUBJECT: TAGBOARD 

HANDLE VIA 

Attached is the memorandum you requested for Mr. 

Packard summarizing the TAGBOARD flight on 10 November 

1969. 

1 Attachment 

All copies of this paper retrieved and destroyed per 

General Allen. 

mjn/Feb 2 

BYEMAN 

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j..S1 NATIONAL RECONNAISSANCE OFFICE 

WASHINGTON, D.C. 

OFFICE OF THE DIRECTOR 

HANDLE VIA 

BYEMAN 

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MEMORANDUM FOR THE DEPUTY SECRETARY OF DEFENSE 

SUBJECT: TAGBOARD Flight - Nov 10, 1969 

The technical investigation and analysis of the unsuccessful TAGBOARD mission over South China on Nov 10, 

1969 has been completed. A brief summary of the flight 

and the technical analysis is presented below. 

The B-52 carry out phase, drone launch and initial 

cruise were all successful. The drone obtained both the 

programmed altitude of 84,000 feet and a mach hold of 3.27. 

Telemetry received showed the drone was performing normally 

at 350 miles, 12 minutes, from the launch point. At 12 

minutes and 14 seconds after launch time the telemetry was 

turned off to preclude signals from being transmitted over 

denied territory. During the terminal phase of the flight, 

the drone was not acquired visually or electronically and 

the hatch (payload) was not recovered. There was no reported SIGINT that could be correlated with any portion 

of the mission. 

Earlier it was reported that preliminary analysis 

indicated TAGBOARD flew the programmed flight path, but a 

probable beacon failure as it approached the recovery area 

precluded recovery. As a result of a comprehensive investigation and analysis, it now appears that approximations in 

the drone's inertial navigation system (INS) computer program 

caused the drone to not fly the programmed route and, therefore, 

not complete the mission. 

For the drone to successfully fly the prescribed route, 

the INS is programmed "to satisfy" a series of destination 

points. "To satisfy" means that the drone has reached a point 

along the route where a function such as change in heading, . 

beacons on, etc. is programmed to be performed. These destination points must be satisfied in order, and if one point is 

not satisfied, the INS will not satisfy the following destination points. 

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The various destination points are satisfied based 

on the computation of the drone's "Distance to Go" (DTG). 

DTG is computed as the angle between the drone's present 

position and the next destination point in the route. A 

destination is satisfied either when the DTG is equal to 

or less than the look ahead angle (the satisfy criterion 

for programmed turns greater than 14 degrees), or when the 

DTG is less than 10 miles from the destination point (the 

satisfy criterion for programmed turns of 14 degrees or 

less). This second criterion, the ten mile distance value, 

is critical to the analysis of the TAGBOARD flight because 

at destination point 3 (363 miles from the launch pOint), 

the actual functions to be performed were for the drone's 

Command Receiver and Telemetry to be turned off - no turn 

was scheduled. 

CO~TROl SYSTEM 

The drone's INS computer uses sines and cosines to 

solve the "destination satisfy" equations. Errors in the 

computed sines and cosines are introduced as a function of 

latitude and longitude. In the specific case of the November 10 TAGBOARD mission route, the post flight analysis 

gives an actual computed error at destination point 3 of 

11.6 miles, which means it is possible that the drone's 

computed DTG value never reached the 10 mile satisfy criterion. This is supported by the fact that telemetry placed 

the actual position of the drone 9 miles past destination 

point 3 with no print-out verification that the destination 

had been satisfied. The Command Receiver and telemetry 

were therefore turned off by the back-up command sent from 

the B-52 rather than by the INS program. By not satisfying 

destination point 3, the drone should have continued on 

basically a straight course until fuel exhaustion. Self 

destruct would have occurred upon descent at the pre-set 

altitude of 52,500 feet (debris impacting in an isolated 

region approximately 75 miles East of the Aral Sea in the 

Soviet Union). It is also possible that the drone could 

have experienced structural or mechanical failure at any 

position along the straight line course after destination 

point 3 with resultant self destruction when the drone 

descended to 52,500 feet. 

Extensive flight data analysis, tests and simulations 

have been conducted by both Lockheed, the prime contractor 

and Minneapolis-Honeywell, the sub-contractor who builds 

the INS and writes the software program. The 10 mile 

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destination satisfy limit had been adequate in all previous 

test flights to overcome computational errors and allow 

"destination satisfy." However, the recent tests and analysis 

have proven that the 10 mile limit is marginal for certain 

latitudes and longitudes, including destination point 3 

in the actual flight path. The worst case possible computed error (latitude, longitude position) in the Northern 

Hemisphere is 13.3 miles. It is important to note that the 

small computer in the drone's INS is limited in its memory 

available and in the accuracy of its sine and cosine computations. The larger SAC computer, which cut the mission 

tape, has greater memory available and is more accurate 

in the sine and cosine computations. Therefore, pre-mission 

analysis of the tape did not exhibit errors of sufficient 

magnitude to identify the destination satisfy problem. 

Fortunately the fix for the computer program to assure 

destinations are satisfied is relatively simple and has 

been accomplished. Essentially the fix is a software change 

that increases the distance satisfy criterion from 10 to 

17 miles. This 17 miles compensates for sine/cosine computation errors. It does not mean that the drone has an 

actual position error of 17 miles. Numerous laboratory 

simulations (worst case latitudes and longitudes) have 

been run with the new 17 mile limit set in the computer 

program, and in all cases the destinations have been satisfied. The destination satisfy capability of all future 

flights will be verified by a pre-mission run of SAC's tape 

through the actual airborne computer. 

The TAGBOARD Program Director has briefed 

details of the flight and on the comprehensive 

vestigation and analysis accomplished. He has 

his confidence and the contractor~1 confidence 

definition of the problem and in the fix. 

me on the 

flight inexpressed 

in both the 

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