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EFFECTS OF POINTING AND TARGET TRACKING 

ON DORIAN PHOTOGRAPHY 

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If the smear free, or static, resolution of a system is 

better than the design goal, smear can be tolerated up to 

the point that the dynamic (with smear) resolution equals the 

design goal. For the Dorian System the on-axis tolerance in 

terms of angular rate is radians/second (2 sigma). 

Although many factors are involved, the key item in achieving 

this specification is the reduction of the residual smear 

attributable to tracking errors to about ■radians/ 

second (2 sigma). 

While this tracking error and the associated noise are 

the main contributors to smear, pointing accuracy is also a 

major concern, since any deviation of the target from the 

center of format produces smear which degrades the photography. 

Pointing errors of more than of arc will exclude 

a target entirely from the 9000' diameter field of view. It 

is evident then that accurate pointing is critical to both 

acquisition and reduced smear. 

There is high confidence that man can point the system 

well within the specified limits, since by use of the acquisition and tracking scope he can compensate for ephemeris and 

target location errors. To achieve this same goal automatically with an Image Velocity Sensor will take a great deal 

of effort and success depends on several current and proposed 

projects to be successfully completed and demonstrated in the 

next 2-3 years. 

The Smear Budget 

The first step in establishing the smear budget is to 

identify the direct causes of smear and apportion the total 

smear tolerance among the direct causes on the basis of their 

2-sigma variabilities. On-axis smear is caused by steadystate angular velocity errors in tracking the central point of 

the target (tracking rate error), random perturbations about 

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the steady-state tracking rates (tracking jitter), and 

vibrations of the camera platen and the optical elements. 

The current smear rate tolerances allocated to tracking-rate 

error and vibration and jitter in microradians/second (2 sigma) 

are: 

Manned/ 

Automatic Automatic 

Navig/Control 

Vibration 

Image Motion 

Pointing and Tracking are associated directly with 

Navigation/Control and Image Motion and are the subject of 

the succeeding paragraphs. While Vehicle Vibration is also 

very important it will not be considered here. 

Pointing 

The Dorian System will achieve its goal of collecting 

Illresolution photography only under specified conditions. 

One of the prerequisites is that the selected target be 

acquired in the center of the photographic format. Any 

deviation from this degrades the resolution The 

problem of where the selected targets will be in the format 

(9000' diameter at nadir on the earth from 80N.M.) and therefore what resolutions will be achieved will be in part 

determined by how well the MOL system is able to point at the 

target. Pointing accuracy is a function of target position 

accuracy, orbiting vehicle position accuracy and the MOL 

system electro-mechanical pointing accuracy. 

Each of the three prime contributors to the pointing 

problem (geodetics, ephemeris, AVE) will be discussed 

individually, then in a systems context. Results from the 

latest (1 April '68) Mission Payload System Segment Performance 

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Analysis Progress Report (CDRL-100) will be used in assessing 

the total system pointing capability. 

Target location (geodetics). The main optical system 

has a half angle field of view of approximately 0.54° (4500' 

at nadir from 80NM) which establishes the upper bound for 

allowable target position error for the automatic MOL system. 

Although acquisition is the first and paramount requirement, 

accuracy of positioning the target within the field of view 

has an important impact on resolution. This is true primarily 

because all rate nulling systems assume that the target is in 

the center of the format. 

Figure la shows the smear that results from target 

position errors. Noting that the root sum square error 

budget for the Navigation and Control System is radian/ 

second and assuming that the allocation to target error would 

be comparable, it follows that the target location should be 

within if this error source is not to 

produce excessive smear. 

Extensive effort has been devoted to establishing 

accurate geodetic positions for missile targets. SAC has 

identified 2077 targets and has designated 1406 as "Hard" 

sites and 671 as "Soft" sites. Hard sites require horizontal 

position accuracies of 450 ft (90% CE), while soft sites have 

a requirement for 1000 ft (90% CE). As of 29 Dec '67,' ACIC 

reported the following status on these targets: 

Horizontal Uncertainty Nr. of Targets 

(90% CE) 

0-450' 732 

451' - 750' 792 

751' - 1000' 498 

1000' 55 

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Residu

al Velocity -12 RAD/

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TARGET LOCATION ERROR —100 FT 

Figure la Residual Image Motion After IMC (2 a) 

Residu

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EC 

Figure lb IN-TRACK POSITION ERROR -✓1000 FT Handle via BMAN 

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The positioning accuracies discussed above pertain to 

only the SAC missile targets which have the highest priority. 

Intelligence targets for satellite photography are located 

by many agencies, using various methods, and in most instances 

much less accurately than these missile targets. The large 

fields-of-view of current photographic satellite systems do 

not require very accurate target locations to insure that the 

target is within the frame. Most important to MOL, however, 

is that even among the highest priority targets there are a 

large number whose locations are not known within the 

limit necessary to achieve the MOL photographic design goals. 

In most of the Eastern Eurasian land mass, target location 

accuracies even approaching those in the SAC missile target 

deck are not available. ACIC indicates that using DAFF 

(KH-5) photography accuracies from 1000 to 2000 ft in these 

areas are achievable but not necessarily programmed. 

Investigations to date indicate the following in regard 

to target positions: 

1. There is no standard method of defining a 

reference point for the center of a collection requirement 

target. 

2. Target coordinates are not referenced to the 

same datum. 

3. The accuracy of the target coordinates 

presently used by Imagery Collection Requirements Sub-Panel 

(ICRS) is not known. 

4. The accuracy of target location varies with 

geographic location. ACIC estimates that by 1970 most 

targets of interest will be in areas where source material 

will give them the capability to provide locations within 

about 750 ft. to 1000 ft. 

The seriousness of this problem to the automatic unmanned 

MOL becomes evident when it is realized that all necessary 

improvements to the geodetic situation must occur in the 

next 2 to 3 years. No large scale effort to dramatically 

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improve in this time frame is currently evident, although 

the capability to do so is said to exist. 

Ephemeris Prediction 

The solution to this problem is primarily the responsibility of the Satellite Control Facility which will provide 

the ephemeris to the MOL. The MOL Computer will interpolate 

the ephemeris table provided and with the aid of inputs 

from the low G accelerometer will refine its predicted 

positions against time. 

The MOL specification to meet precision acquisition and 

smear requirements rpanirps the navivational oanability of 

the system to be 

(For the effects of in-track error on 

smear see Figure lb.) The numbers quoted are two sigma, and 

assume error propagation of 2.5 orbit revolutions. These 

requirements imply something substantially beyond the capabilities of current ground tracking and orbit prediction. 

These accuracies require such things as employment of a low G 

accelerometer (LGA), a much improved atmospheric model, 

improved tracking capabilities and advanced orbital prediction 

techniques. 

Current estimates of navigation prediction accuracy 

after 21/2 orbits, based on ground tracking and computation alone 

are given below: 

IN-TRACK ERROR (TWO SIGMA, FT) 

(No LGA, Radar Data Only) 

Internal To 

Data Fit 2.5 Revs 

(No Predict) Predict 

Current 

No Drag 1600 2000 

Low Activity 1800 3200 

High Activity 3600 8800 

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It should be noted that the current capability is only 

marginally adequate to acquire the targets in the 4500 foot 

radius allocation and that during periods of high solar 

activity that the targets would not be acquired at all. 

The estimated prediction capability for the 1970 - 72 

time period not using the low G accelerometer is shown in 

Figure 2. This estimate is based on the Space Ground Link 

System (SGLS) and the Advanced Orbit Ephemeris System (AOES) 

reducing the current conservative in-track prediction 

estimate of about 8800 ft. to about 6000 ft. The improved 

atmospheric modeling based on LOGAX data to further reduce 

the error to 3000 ft. and the combination of these in conjunction with the low G accelerometer to ultimately equal or ' 

better the specified 1800 ft. is shown in Figure 3. Figure 4 

is an error budget table for 1970 - 72 based on all the 

above improvements contributing properly and utilizing the 

low G accelerometer. 

While these accuracies may be achieved there is great 

dependence on several large improvements occurring in series. 

In any case the feasibility and practical demonstration of 

these combined innovations will not occur until 1970 at the 

earliest. 

AVE 

The mechanical pointing or AVE pointing requirement of 

appears to be reasonably achievable based 

on analytical and test data to date. The task is demanding 

but considered well within the state of art. 

System Pointing 

An analytical estimate of pointing accuracies achievable 

in the 1970 - 1972 time period is provided as Figures 5 and 

6. These estimates are based on the following assumptions: 

a. Target location accuracies less than 

b. All improvements to the ephemeris prediction 

system operating properly (AOES, ADS, SGLS, Improved 

Atmospheric Model). 
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Estimated Vehicle Position Errors, No LGA, 2 a 

Propagation "'Revs 1.25 2. 5 3.5 

I-r-track Error — Ft 

1. Drag + Geopotential 

2. Ephemeris Interpolation 

3. Attitude (1%)* 

Altitude 

1. Drag + Geopotential 

2. Ephemeris Interpolation 

3. Attitude (1%)* 

Cross-Track 

1. Atmospheric Rotation + Geopotential 

2. Ephemeris Interpolation 

RSS 

RSS 

RSS 

*Allocations 

Figure 2 

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MINIMIZATION OF EPHEMERIS UNCERTAINTY 

2-SIGMA IN-TRACK FOR 2.5 REV PREDICT SPAN 

(1000 ft) 

CURRENT 

SGLS AOES 

SGLS AOES 

LOGAX 

SPEC 

SGLS AOES 

LOGAX LGA 

Figure 3 

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Estimated Vehicle. Position Errors with LGA, 2 0' 

Propagation — ;1,7s 1. 25 

In-Track Error - Ft 

1. Geopotential 

2. Position Estimation Procedure (1%* 

3. Ephemeris Interpolation 

4. Attitude Control Rotations 

5. LGA Systematic Errors (1%)* 

6. LGA Random Errors (0.1%)* 

2. 5 3.5 

Altitude 

1. Geopotential 

2. Ephemeris Interpolation 

• .3. Position Estimation Procedure (1%)* 

4. LGA Systematic Errors (1%) 

RSS 

Cross-Track(Same as Figure 2) 

*Allocations 

Figure 4 

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REVS 

0 AUTOMATIC MODE - INCLUDES EPHEMERIS AND TARGET LOCATION 

ERRORS WITH NO LEARNING EXCEPT LOW G ACCELEROMETER 

0 SPEC REQUIREMENT - EXCLUDES EPHEMERIS AND TARGET 

LOCATION ERRORS 

03 POINTING ANGLES DERIVED FROM ATS 

SAME AS 1 BUT EXCLUDES LOW G ACCELEROMETER 

Figure 5 

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TWO SIGMA POINTI

NG ERROR (ARCYIN) 
Pointing Error* 

(2 Sigma) 

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Line-of-Sight Pointing Error 

Automatic Mode (A Mode) 

Including all errors without LGA 

Including all errors with LGA 

Neglecting vehicle ephemeris and 

target positions error 

Pointing Angles Derived from ATS 

With ATS boresighting on two targets 

With ATS boresighting on three targets 

ATS Pointing Error (Automatic Mode, 

after boresighting) 

Including all errors without LGA 

Including all errors with LGA 

Neglecting vehicle eph emeris and 

target positions errors 

(2 Target Boresighting) 

(3 Target Boresighting) 

* Assumes uniform target density on the ground 

Primary optics scan field 

2 fr_ 40° 

-30 < 1 < 200 

ATS scan field 

"DI< 450 

< Z < 700 

Figure 6 

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c. AVE pointing error of no more than 

of arc. 

It is important to emphasize that large improvements in 

target location and emphemeris prediction are mandatory for 

the unmanned system but are only desirable for the manned 

system. This is true since man, using the acquisition and 

tracking scopes to point and track targets, effectively 

eliminates the navigation and geodetic errors. 

Image Motion Compensation 

Smear due to image motion which would result in photographic degradation comes from two sources: 

1. Changing relationships between the orbiting 

vehicle and the ground target and 

2. Tracking rate errors. 

In the first case the scene appears to expand and turn 

about the nulled axis (the tracked point) as the target is 

approached and the reverse action takes place as the target 

is passed. 

At extreme look-angles, geometric image motion near the 

periphery of the format can be as much as 7.5 times the 

budgeted on-axis smear rate of radian/sec (2-sigma). 

The effect of this off-axis smear at the edge of the format 

is to degrade the ground resolution to a value three times 

the on-axis ground resolution (for the nominal exposure time). 

With a focal plane shutter, only a narrow strip of the 

format is exposed at a given instant. If the image motion 

within this strip can be matched by moving the film, the 

smear occurring in the area of the slit can be eliminated 

without effecting smear of points beyond the slit. This 

technique is called across-the-format IMC (X-format IMC). The 

nulling of this motion is to be achieved by manipulating the 

platen and the solution seems quite feasible at this time. 

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The more serious and currently assessed as more 

difficult motion compensation is that of nulling in-track 

rates. 

Reduction of the tracking-rate error is accomplished in 

two control steps: preprogrammed computer control followed 

by fine control by either a crewman or an Image Velocity 

Sensor (IVS). The tracking-rare error Allowed by specification 

in programmed rate control is radians/second, 

2 sigma. The crewman or IVS is required to reduce the trackingrate error from this level to about radians/second 

or less. radians/second smear would yield photography on the order of assuming a set of conditions 

which would yield photography with a residual tracking rate 

error of radians/second. 

It is therefore evident that without man or the IVS the 

very high resolution goals for MOL cannot be achieved. 

Extensive simulation test runs by the crewmembers 

provide a high degree of confidence that the specified levels 

of residual smear can be easily achieved. The same confidence 

for the IVS accomplishing this job is not enjoyed at this time. 

It is too early in the IVS testing program to state that 

the specified rate nulling job cannot be accomplished 

automatically in the necessary time frame. It is, however, 

safe to say that much redesigning, testing, and perhaps 

re-inventing must be done before a confidence factor approaching 

the current confidence in man's ability is achieved. 

Recent evaluations of the contenders for the IVS 

production contract were given the following general evaluation 

by General Electric (direct quotes): 

a. All sensors correctly sense input velocities 

for some scene conditions. 

b. All sensors have center of power tracking 

characteristics. 

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c. All sensors sensitive to scene detail. 

d. All sensors have light level problem. 

e. All sensors have "cloud" problem. 

On the basis of this test program which was quite comprehensive one vendor was recommended for elimination and the 

other two were "sent back to the drawing board" to try to 

eliminate the deficiencies noted in their hardware. 

There were two basic deficiencies evident in all 

contenders. One was that they focused on what G.E. terms 

"Center of Power" (the area in the format providing the most 

stimulus to the sensor). This means that the velocity of the 

"Center of Power" rather than the desired center of format 

will be measured and compensated for. The other and more 

serious problem comes from the fact that all sensors centered 

on clouds when they were present. This characteristic 

introduces significant errors the magnitude of which depends 

on the altitude and velocity of the cloud deck and the percent 

of cloud cover. It is estimated that if the sensor measures 

on a cloud rather than tte target desired that an induced 

error of about 100 X 10 radians/sec for each 1000' of cloud 

altitude above the target, would result. 

Careful study of the General Electric Company's IVS 

Vendor evaluation report (DIN 50366-38-1, 240 Pages) leaves 

little doubt that the IVS is a high risk item in terms of the 

MOL goal of achieving very high resolution photography in an 

automatic mode. 

Summary 

The ability of the MOL system to provide 

resolution of specified targets depends not only on the AVE 

under development but also on the accomplishments of other 

agencies such as ACIC and the AFSCF. Without considerable 

improvement in geodetic and ephemeris prediction accuracy in 

the next 2-3 years, the photographic resolution desired, and 

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even automatic target acquisition in many cases is in 

doubt. This fact coupled with the development and testing 

difficulties and uncertainties associated with the IVS makes 

the unmanned version of MOL appear as a rather high risk 

development at this time. There is consolation however in 

the fact that man can essentially eliminate most of the 

difficulties associated with tracking and pointing. This 

fact provides confidence in the manned version as an 

operational reconnaissance system as well as a test bed 

available for developing more sophisticated automatic systems. 

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