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MOL DORIAN 

IMAGE VELOCITY SENSOR SUB-SYSTEM 

AD/HOC REVIEW GROUP 

FINAL REPORT 

SEPT. 19, '68 

BRIAN O'BRIEN, CHAIRMAN 

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I. INTRODUCTION 

The Image Velocity Sensor problem has been a critical item since 

the beginning of the MOL Program because it is essential to the performance 

of the unmanned system and highly desirable for the manned version of 

MOL. At the time MOL was originally conceived, the image tracking 

function was to be a manual task and the automatic tracking, by means of 

a closed loop device such as an Image Velocity Sensor, was not yet 

considered technically practical. In the early phase of the MOL Program 

several schemes were proposed and eventually, because of the criticality 

of this problem, three approaches, presented by Itek, Goodyear, and Hycon 

were started. 

In the spring of 1968 significant problems were uncovered when 

General Electric conducted some of the early simulations and tests on the 

breadboard models supplied by each of the three subcontractors. The 

problem of whether appropriate closed loop image tracking techniques 

could be perfected in time for the required integration into the system 

became a critical program concern. The program development schedule called 

for elimination of one of the three competing contractors and General 

Electric recommended the termination of the Itek contract. MOL program 

management, however, elected to continue with the three because the 

other subcontractors were also having difficulties and there were some 

questions concerning General Electric's test and evaluation techniques. 

In view of the foregoing, it was decided to convene an IVS Ad Hoc 

Committee to review the MOL image tracking problem, to compare the 

proposed approaches, and, if appropriate, to recommend alternate methods 

for accomplishing the image tracking task. Ideas such as laser ranging 

and open loop operations with the aid of precise celestial target 

referencing were proposed as alternate schemes. 

While the Committee was being formed, General Electric and the subcontractors continued with their work and made significant progress 

toward eliminating some of the deficiencies discovered in earlier tests. 

The Committee convened on 20 September and after a thorough review of 

the subcontractors' work and the General Electric evaluation process, 

it was the concensus of the Committee that the MOL Program can proceed 

with the selection of one of the proposed schemes and that it is probable 

that target tracking will be adequate to meet system requirements, and 

the introduction of alternative schemes would serve no useful purpose. 

Some questions remain on the validity of the specifications, the 

fundamental understanding of the various schemes, the ultimate choice 

of subcontractor, the validity of the simulation, and the operation of 

the system in the presence of clouds. These subjects and the Committee's 

recommendations are discussed below. 

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II. SPECIFICATIONS 

1. Status 

a. General 

The critical performance requirements which are being 

applied to the IVS vendors by GE are, in some cases, more severe than 

is required by the DORIAN system. In some cases, the performance 

requirements, as established by the Air Force, are well understood. 

In other cases, the specification is a considered choice based on a 

desirable characteristic which appears obtainable at little penalty. 

It is recognized that these matters deserve continued intensive.attention, 

but there appears to be no instance where a significant problem is being 

created. Detailed discussions with Aerospace personnel involved in 

formulating the specifications indicated that each issue of concern 

to the Committee was recognized by Aerospace and was under consideration. 

b. Light Level Performance 

No formal specification has yet been made. The revised 

Wiener spectrum indicated as forming the current requirement was a 

matter of disagreement between Aerospace and GE. It appears that, 

assuming the more favorable IVS illumination as a result of using all 

the diverted light below 150 sun angle, the anticipated specification 

is reasonable with a questionable area remaining in the region of high 

illumination and low modulation. There is a question about the 

specification of Wiener spectrum at 100 feet per cycle. For purposes 

of vendor selection and proof of feasibility of devices it appears desirable to agree to a Wiener spectrum box outlin quickly and refine it as 

necessary later. 

c. Dynamic range 

The IVS is required by GE to operate over 0-600 rad/sec. 

The 600 rad/sec is considered by GE to represent both open loop performance 

and residual rate at end of slew plus 3 seconds. It appears that in 

either case the number could be lower but the large capture rate requirement is stated to be achievable by all vendors. The Air Force, however, 

should consider carefully the specification of open loop performance with 

the goal of best optical performance without IVS lock-on. 

d. Linearity 

The null region requirement of + 10% monotonic appears 

reasonable. The large signal region requirement of + 25% monotonic with 

no saturation until 1000 rad/sec is overly severe but does not seem to 

limit the IVS vendors. 

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é. Accuracy 

20 rad/sec. This value seems achievable and reasonable 

although a slightly larger value could be accepted in view of the remainder 

of the budget contributions to the overall specification of 42 rad/sec. 

2. Recommendations 

a. Determine the Wiener spectrum illumination region to be 

specified as soon as possible but continue to study the implications 

of the specification intensively. 

b. Obtain a tightened specification for open loop performance 

based on acceptable optical performance without IVS lock-on. 

c. Monitor the IVS specifications levied by GE and insure that 

the performance of the IVS under conditions of good DORIAN performance 

is not jeopardized by attempting to meet the extremes of 

the specification and, similarly, to insure that unessential complication 

of the IVS is not introduced. 

III. IVS SELECTION 

1. General Observations 

In the Committee's judgment, none of the contractors exhibited 

a complete understanding of the possible behavior of his own system. 

This may be an unfair judgment. The Committee believes, however, that 

in the best interests of the MOL program, a basic understanding of the 

Goodyear and Hycon systems should be developed before a final selection 

between them is made. Considering not only the immediate problem of the 

current MOL program, but also the future, e.g., the search for higher 

resolution, one should also include the Itek system in this analysis. 

Since, the three systems operated on different principles, the Air Force 

should thoroughly understand these differences and examine the 

limitations of each in environments other than those now specified for 

MOL. It is likely that each scheme will have special advantages in 

particular environments. It may also result that even in the specified 

MOL environment of rates, contrasts, light levels, etc., peculiar 

advantages or difficulties will be found. 

A basic understanding of the several systems would permit an 

analysis which could answer, for example, such questions as: 

As presently mechanized, the Itek system works on information 

in the high frequency part of the Wiener spectrum of the scene. Goodyear 

and Hycon work on much lower spatial frequencies. What are the limitations, 

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or possiblities, in applying the Itek principle to other parts of the 

spectrum? 'What part of the spectrum should be used by the sensors?• 

For example, is there a band of spatial frequencies over which all 

scenes have similar Wiener spectral intensities? If so, which of the 

three systems can best be optimized to work in this band, and what 

advantages, other than scene-insensitivity, are gained? Goodyear works 

with quantities which are quadratic in illumination level, while Itek 

and Hycon are intrinsically linear in illumination level. Hence one 

would expect the Itek and Hycon principles to degrade more gracefully 

as one designs for lower and lower light levels. Are there interesting• 

light levels at which this phenomenon has a useful effect? 

The Committee would feel more confident in a final selection 

if there was available an evaluation of all of the systems within a framework as basic as that suggested by the preceding questions. 

4, 

2. Subcontractor System Evaluation 

a. Itek 

The Itek system works by integrating the effect of image 

smear over a period of about 44 ms. The resulting smoothing effect 

reduces the high frequency content of the Wiener spectrum of the image, 

and the servo generates a compensating motion which maximizes that 

spectral content of the image. The spectral band in question, said to 

be around fifteen feet per cycle, is such that the Itek system will be 

inherently more sensitive to image focus than the others. 

Since the Itek device works on scene content in the region 

of fifteen feet per cycle, the present specification, which is keyed to 

wave lengths of 100 feet per cycle, is not directly applicable to its 

design considerations. 

The contractor has chosen to work with a standard vidicon 

and standard TV scan rates. This gives him a sampling system with a 

particular fixed upper limit on its bandwidth,.and fixed his integration 

time in a not very controllable way. It is likely that an optimum 

system using his principles would require both an integration time 

different from his present 44 ms, and an internal sampling rate difference 

from 30 scans per second. The TV method can be made to work but the 

approach has not progressed far enough to be considered a candidate 

for Dorian. 

On an engineering basis the TV method requires handling 

high voltages in the image intensifier which are undesirable if other 

means are available. The TV method is mechanically passive. 

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b. Goodyear 

The correlation device is in an advanced stage of development and probably will be suitable for the DORIAN system. It operates 

on quantities which are quadratic in both illumination and modulation 

(unless slicing takes place). The full implications of these facts are 

not understood by the Committee. However, such a system is normally 

plagued by the basic limitation of correlation techniques when used for 

servo purposes. If the true correlation of the compared scenes is low, 

the uncertainty of the calculated or derived correlation is very large. 

This results in noisy or spurious signals and attendant servo stability 

troubles. While the method of using and inserting the IVS signals into 

the scan mirror servo may protect it from spurious commands, this 

limits the usefulness of the correlation method. Roughly the true 

correlation of the compared scenes must be high (above 70%) to have a 

certainty of the derived correlation value better than 50%, which 

probably means the correlation device will require frequent recycling 

under actual scene conditions. However, the long focal length and 

consequent narrow acquisition angles of the DORIAN system seems to 

promise sufficiently high actual correlation between the stored and 

compared scenes that the method is expected to work. The practical 

response rate when recycle time is considered may be somewhat: slower than 

described. This correlation device is also passive in a mechanical 

vibration producing sense. 

The Goodyear device works on what could be called a "matched 

filter" technique. Considerable analysis is available on this technique, 

most of which would have to be modified somewhat to include the effects 

of the large and variable "dc" component of the optical signals. It is 

not yet fully clear what spatial frequencies in the scene are important 

to the operation of the present Goodyear device, although it is probably 

the lower frequencies. (This is evidenced by the fact that the system 

is insensitive to defocus.) An analysis in terms of matched filters 

might suggest ways of optimizing this frequency selection against focus. 

changes and cahnges in scene. 

The contractor's belief that his "dynamic null",problem 

is an artifact of the simulator seems to the Committee to be correct. 

The question should be examined with greater analytical power than the 

Committee has seen applied to it. The Committee has already suggested 

certain additional tests and a good analysis may suggest more definitive 

ones, or even show that present data are already adequate. 

The sub-contractor showed that his correlation can be used 

for contrast enhancement, but his discussion was inadequate to 

demonstrate exactly how this capability could be effectively exploited. 

Neither did he show whether, were it exploited, it would lead to useful 

advantages in performance. The Committee believes that more understanding 

is required before the usefulness of this future can be evaluated. 

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The sub-contractor mentioned several modifications to his 

system which would add new features not covered by the present MOL requirement or specifications. The Committee suggests that the Air Force may 

be interested in having these matters explored further. However, the. 

Committee does not believe that they are relevant to the choice that 

must soon be made. 

c. Hycon 

The Hycon system makes a comparatively direct masurement 

of velocity. Its operation can be, if the designer chooses, linear in 

applied illumination and contrast. Its operation depends for the most 

part upon principles well known and understood in electrical engineering. 

The vendor has ready control over the spatial frequencies to which his 

system is sensitive, and has exercised this control for optimization. 

Even within the framework of his present mechanization, 

he has a wide latitude of design choice in selecting the important parameter 

of operation. The principles he exploits can be adapted to designs for 

an even wider range of operating conditions. 

It appears to the Committee that Hycon's remaining problem, 

in the present instance, "Scalloping", can be solved adequately by 

shaping the illumination across the field, Analytically, the problemis like that of illuminating an antenna for minimum side lobes or 

designing a filter for minimum echoes. Analysis provides both a solution 

and an estimate of its limitations. 

Hycon asserts that the weight and bulk of their system 

can be reduced. This appears likely. The signal drop out problem 

experienced in test appears adequately handled by the feedback memory 

technique. This device has a mechanically active element; namely, the 

rotary chopper disc which rotates at 30 Hz. With careful attention to 

bearings and balance, the residual vibratory disturbance should not 

cause difficulty. This device appears to be the most applicable to the 

DORIAN system IVB requirement. 

IV. CONCLUSIONS 

1. With respect to the selection of a contractor and system for 

the MOL mission, the Committee agreed that: 

a. On the basis of information now available, either Goodyear 

or Hycon could be selected with high confidence of success; 

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b. There is no possibility that, by the time a decision must 

be made the level of confidence in Itek will be comparable to that in 

either of the others. 

c. A selection between Goodyear and Hycon will depend upon 

engineering, and possible programmatic, factors on which the Committee 

is not prepared to judge in this report. 

2. With respect to a consideration of whether to terminate one or 

more contractors now, or when to terminate all but one, the Committee 

observes: 

a. There seems to be no immediate benefit to the MOL program 

in continuing Itek, 

b. The advantage in continuing both of the other contracts for 

the present are, first, the value of competitive pressure, and second, 

the possibility that further exploration of some of the engineering 

factors (e.g. weight, power, vibration, reliability) will show a clear 

advantage to the MOL program in one of the approaches. 

c. The principal disadvantages to continuing more than one 

contractor probably lie in the costs of testing and in the demands on 

G.E. and Aerospace talents. 

V. RECOMMENDATIONS 

a. It is recommended that the present phases be completed on all 

devices except that further tests be conducted by General Electric only 

on the Goodyear and Hycon devices, and that the Itek device be sent to 

the Avionics Laboratory for further study. It is recommended that the 

Goodyear device be carefully reviewed for possible correlation with real 

scenes that may limit its effective response. 

b. It is recommended that the Hycon device be reviewed for correction 

of the signal drop out that may be experienced under real scene conditions. 

Attention should be given to bearing noise vs. life in the Hycon device 

rotor to insure that the residual 30 Hz. mechanical disturbance does not 

cause any difficulty in the adjacent optical or camera units. 

c. It is recommended that both the Goodyear and the Hycon devices 

be continued even though they both probably will not meet the low modulationhigh illuminance corner of the present tentative specification. 

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d. It is recommended that an early final choice be made 

between the Goodyear and the Hycon devices as soon as significant 

progress has been made at the end of the test program on the latest 

versions of these devices. 

VI. SUPPLEMENTARY SUBJECTS 

1. Simulator 

The IVS Simulator appears to be a good design, but there are 

certain defects which seem to penalize the Goodyear more.. than the Hycon 

device. The first, which is fundamental, is that reasonable space 

limitations require short working distances from device to target platen, 

so that the field angles are much higher than those to be encountered 

in MOL. It is recommended that General Electric and Goodyear explore 

this to their mutual satisfaction so that allowance can be made in the 

interpretation of test results. 

A second defect is the specular reflection from the semi gloss 

photographic paper used in the target. It should be possible to reduce 

this either by good matte paper or by combining high gloss (orferrotyped) 

paper with properly placed flood lights. It is recommended that this 

be done. 

There are uncertainties about the behavior of IVS on three 

dimensional targets with shadows. Since a model is already completed 

it is recommended that the engineering models of Goodyear and Hycon be 

tested on the simulator using this model as well as the flat print for 

target: The high gloss paints on this model may have to be dulled. 

More important, it should be recognized that even with a model in correct 

scale the perspective will be distorted by the short working distance 

which may complicate IVS performance, so that test results should-be 

interpreted with caution. 

2. Clouds 

At the request of the Air Force, all contractors spoke to the 

question of IVS operation in the presence of clouds. Ingenious ideas 

came forth, but all discussion was speculative. 

The Committee believes that the Air Force must clarify its own 

understanding of the requirement to operate in the presence of clouds, 

before this issue can be used as a criterion for choice between IVS 

systems. Indeed, the Committee believes that this clarification should 

take place before money is spent with contractors in attempting to meet 

a cloud requirement. 

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The basic question is: how important is it for the system to 

operate in the presence of clouds? In the MOL environment, this spawns 

more complicated questions: 

How often; when the primary target is obscured, can one 

successfully photograph an alternate? How good is the resulting photograph, 

and how much does this quality improve with good IVS sensing? What 

then are the requirements to be met by a useful IVS? 

The Committee saw no evidence that the Air Force had addressed 

these questions, and recommends that none of the contractors be 

required to demonstrate their device's capability in the presence of 

clouds until it is better understood by the Air Force. 

It is suggested that the open loop tracking capability to permit 

good photography if the IVS loses track in the presence of clouds be • 

improved as much as reasonably possible. 

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