THE SIGNIFICANCE Cr TEE DISCOVERER PROORAM

The DISCOVERER program is providing vital technical and scientific

advances to the whole of aerospaoe technology. While many of the reedits

of the DISGMANUMtprogram are directed primarily toward applications in

the SANDS and N1DASprograns the long term benefits of DISCOVERER are

serving to increase significantly man's knoWledge of the spatial environment,

to enhance his skills and techniques in space operations, and to provide

experience Sala* development and operation of a reliable space vehicle.

Many difficulties, same self-impond dub to the nature of the experiment,

have been met and solved in the mamma program. In general, most of

these problems are common to.both SAMOS and MIDAS' Problems have been found

and solved in a relatively inexpensive eystem prior to their °contemn in

the latter vastly more complex and expensive programs. From this viewpoint

DISCOVERER is a nest bed" for space programs.

From inception to the present, the DISCOVERER program has demonstrated

constant technical growth in improvedhardware methods, reliability,

techniques, and new discoveries. The significant features of the program

to date can be summarised as follows: (a) development of a reliable workable

and veriatile satellite airframe - ANNA, (b) adoption, modification and

improvement of an existing rocket engine for reliable spaoe vehicle application, (c) demonstration of the ability to achieve repeatedly a predetermined orbit with good precisions (d) demonstration of on-orbit stabilisation of a satellite vehicle in such &manner that its orientation relative

to the earth's local vertical remains constant, (e) development of a complex

ground environment permitting high precision in vehicle position determination and forecasting in orbit, (f) command and monitoring of functions within

the orbiting vehicle, either by pre-programming or by instructions from the

ground, (g) colleotion . of new and significant information on the spatial

environment,. (R) determination of the environment within the vehicle, particularly local temperatures and pressures, and the development of techniques

for the prediction of the environment with alternative equipments and alternative types of orbits, (i) development of recovery tehhniques.

3. ►stem Considerationa:- In the remarks to follow, aajor emphanis has been

placed on those aspects of DISCOVERER which are most pertinent to SANDS end

MIDAS and those which have overall scientific importance.

A. Loan& to Orbit Iniection- The AGENA vehicle has been designed for use

with both the THOR and ATLAS boosters. In either combination the ascent

technique used by the MENA vehicle is substantially the same* however, there

are significant differences in the method of utilising the boOster. In the

DISCOVERER program, in order to conserve Wight, the THOR booster follows a

pretprogrammed trajectory using only its autopilot. Further, the TEDR thrust

is not out off by command at a pre-determined velocity, but its fuel burns

to near exhaustion. This relatively inaccurate booster per/breezes compared

with the ATLAS boosted AMA, and coupled with lower altitude of DISCOVERER

orbits, imposes severe orbital injection requirements. SpeoificaLly these

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requirements are such that at an injection altitude of 120 statute miles

(typical) as angular error of plus or minus 1.1 degrees or a velocity deficit

of only...100 feet per second below the value for a circular orbit will result

in a failure to complete the first orbit. To insure an optimum. payload

weight in relation to high probability of achieving orbital injection, the

DISCOVERER program successfully undertook are-exploration of the problem

of roOket engine performance prediction for the AMEBA engine.' This Study

led to new theories and the improvement of existing ones to assist in the

determination ofs (1) sea level engine performance, (2) methods of extrapolation to vecnum performance, (3) degree of anticipated performance deviation in flight, (4) vehicle propellant loading and weighing techniques, and

(5) determination of the proper level of conservatism in flight performanoe

prediction. The outgrowth of this effort was improved performance prediction

and, based on numerous simulated altitude firings at 13811 and AMC, a revision in the mdhod of estimating vacuum/ engine performance from ground tests.

This effort, then, is responsible for resolution of a problem area that could

have plagued both the SAND$ and MIDAS program with failures to orbit. Numerous advances and redesigns of the hyriad valves and regulation of the system

have also been and will continue to be made as imprOvements to the

system because of DISCOVERER sponsored ground and flight tests. As a result

of DISCOVERER developments, it has been possible to repeatedly inject DISCOVERER vehicles into orbit with an injection angle error not exceeding

0.4 degrees. The precision components and techniques developed in this aspect

of DISCOVERER are directly applicable to MINDS, MIDAS, and programs with a.

man-in-apace application.-

Orbttal Operations - Precise Position Determination and Forecasting In.

- • DISCOVERER tracking and orbital computation tetniques have been

developed to a high order of precision. Data from each orbitalpeas are Used

to refine the vehicle ephemeris so that the'exact location of the. vehicle .

is known at all times. This ptecision has become routine. The orbital

parameters of DISCOVERER II were known after the first pass with sufficient

accuracy to predict the time of arrival at subsequent tracking points with

an accuracy of the order Of a second. On same flight, the final signal

initiating the recovery sequence on the seventeenth pass was given within

five seconds of its planned time, artist a total orbiting time of approximately 100000 seconds - 1 part in 20000. The procedures, equipments, and

techniques responsible for such results are applicable to all apace operations.

Qn-Orbit Stabilisation - The DISCOVERER on-orbit stabilisation system,

as the point of departure for similar SANDS and MIDAS systeis, demonstrated

the first earth-center stabilised vehicle. This system has been perfected

to the point that the Draymnaumt vehicle attitude errors are of the order of

10 in pitch, 0.5 degrees in roll, and 1.5 degrees in yaw.

7. Atmospheric Density - New and scientifically important information on the

density in the upper atmosphere has resulted from the DISCOVERER program.

Atmospheric density data derived from the orbital decay of mom= vehicles

end other satellites have invalidated the altitude density curve recommended by

the ARM model atmosphere panel in 1959. Also, much new evidence on atomspheric density changes frith diurnal, seasonal, and ennuis variations has been

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accumulated. These data are being furnished to the scientific comeunity.

Vehicle Internal Pressures - The DISCOVERER program has produced new data

relating to satellite internal pressure conditions which have had a significant effect on environmental testing concepts and added new knowledge on the

spatial swim/•ent. The ambient pressure of the typical DISCOVERER orbit

at the overate height of 200 miles is 10-1 ma of mercury. It vas determined

from DISCOVERER data that at the end of the first orbit, internal vehicle

pressures were usually about lir' me,_ and after 25 orbits (38 hours) the

pressure had not fallen below about 10 r2 mm of mercury. This effect has =

been determined to be the result of outgassing from surfaces exposed to a

vacuum. The above condition is of aignificanoe when related to our ability

to simulate orbital conditions in environmental teat chambers for relatively

short term orbital operations.

Vehicle Temperature' - The DISCOVERER program has brought to light new

informatiOn, revising previous thedries and experimental procedures, on.

the maintenance of the desired thermal balance within near-earth orbiting

satellites.- Using accepted practices for the maintenance of the required

internal satellite temperatures on the early nasoovsam satellites, it

was soon learned that these methods were inadequate and erroneous. Modification of previously accepted techniques and the installation of heating

devices raised the observed low internal satellite temperatures to a proper

temperature. These dater* of particular significance to man-in-apace,

SAMS, and MIDAS programs.

ANNE= - The problem of recovering a DISCOVERER capsule from orbit

is extremely complicated because in addition to the relatively straightforwardprocess of putting the satellite on orbit, the following' four

processes meet be completed sucoessfullys (1) a recovery teem must be

located so that one of the satellite orbits passes over it, (2) the recovery

capsule east be related from the parent satellite at the correct time within

quite narrow limits. Each second of timing error represents five miles

displacement of the recovery point, (3) the capsule retro-velocity vector

must be within 10 degrees of the desired direction in order that the capsule

will re-enter within the recovery area (4) following the deceleration and

heating phase, the capsule must be furthe r slowed by a parachute, (5) in

the final phase, the capsule must be recovered from the air or from the sea.

The first two of these processes have been satisfactorily accomplished on

several flights. The last two processes, Parachute deceleration and pick-up,

have been also satisfactorily demonstrated in tests on many occasions, using

capsules dropped from high-altitude telloons. The third item, the proVision

of the correct retro-velocity lathe desired direction has been a major

problem. It is the Purpose of the presently proposed diagnostic flight to

solve this problem.

atgzdemg- Air Frame - Weight is a major consideration in satellite

design. The objective is to provide maximum strength with sdxdmum weight.

This result was achieved in the AGENA by the use of the new material magthorium which possessed the qualities of light weight, strength, and favorable
high temperature characteristics. Methods of fabricating Nis new material

were developed and subsequent flight resultsbave verified the structural

integrity of the resulting air frame. In like manner, novel techniques

were employed lathe fabrication of the propellant tanks. A scheme 1,83

devised wherein spun anima was turned and tapered to provide tankage of

minimum weight with the required structural integrity. The MIDAS and SAMOS

satellites are the identical basic air frame and tank configuration developed in DISCOVERER with those necessary provisions to carry the appropriate

poyloads.

AGM Engine Develonment, (a) Model - 804S - This EngineOchich is a

significant improvement over the basic 8001 Mistier, was flown sucoessfully

in seven DISCOVERERS before its first use in MIDAS. Its reliability performance characteristics and capabilities were well established facts which

permitted MIDAS to launch with a high degree of confidence that the expensive and complex payload equipment would indeed go into orbit with a high

probability of performance. Before the first SANDS launch, using this same

engine, at least three additioni. DISCOVERER-launches will have taken place.

Auxillrarr Power - Power system components for use generally in satellite

systems, and specfically in SANDS and MIDAS, have been designed, developed,

and tested in the DISCOVERER program. Chief among such components are static

electronic inverters to covert battery energy into the various A/C voltages

required by the other subsystems. The first static inverters ever flown

were aboard DISCOVERER vehicles. They are considered essential system elements since they halve the weight and double the efficiency of their rotary

counterparts, and it is not likely that the long lifetimes required in other

programs can be achieved with rotary units. The DISCOVERER power system incorporates a silver-perioxide-sins primary battery as a prime energy

source. This batterybas been developed specifioally for satellite operations

and incorporates refinements for high:efficiency and performance in sero

gravity environmental conditions. An advance in silver-percocide-sinc battery design was necessary in this development to increase the energy-to-weight

efficiency. Much has been learned in the DISCOVERER program regarding internal

and external circuit design to enhance inverter performance and reliability,

and to wet survival of inverters under a wide variety ofselfunctions or

overloads. Design features have been evolved to minimise standby power losses

so that efficiengy can be maintained at a high level even under fluctuating

loads. Inverter development history has been, and continues to be, marked

by high enure rates in system checkouts on the ground; many failure causes

involving procedures design, and quality control, have been isolated and

corrected in the DISCOVERER program.

14.- guidance and Ontrol - Major elements of the AMA guidance and control

system which are cowman to SAMOS, MIDAS, and NASA programa have been tested

during DISCOVERER operations. Some of these guidance elements are: The

H/PD" timer and the Minneapolis Honeywell inertial reference package, which

will be used on all SAMOS and MIDAS flights; the DISCOVERER gas control system,

which is providing the basic experience leading to *proved SANDS and MIDAS

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-CREDENTIAL

systems; and the DISCOVERER horizon Scanner, which will be on the early

SANDS and MIDAS : flights. In addition, DISCOVERERAIlltest the new engine fuel

driven hydraulic pump which will be used on all SANDS and MIDAS flights. It

is anticipated that the NASA AGENA guidance and control system will also

lean heavily on DISCOVERER.experience. Within the DISCOVERER progress itself

the techniques of earth centered stabilisation and • gpro compass satellite •

yaw control were accomplished for the first time.

Decoverr Technicues - Solving the recovery problem is important to the

DISCOVERER grogram and science in general because many biomedical experiments

and scientific measurements depend on recovery; however, in addition to the

man-in-space and scientific aspects and DISCOVERER recovery effort has many

direct applications to the SANDS recovery program. The SANS recovery

program will use the DISCOVERER experience in the .following areas: (1)

Ablation phenomena. (2) Recovery capsule detection. (3) Recovery force

deployment and operations. (4) Aerial pick-up tethnique. The aerial pickup techniques will be identical except that a larger winch will be used for

the SANDS recoveries. These techniques have been continuously improved

under the DISCOVERER program. The SAWS recovery force may be depleyed

over land but it is expected that the procedures will be outgrowths of the

DISCOVERER operation. The DISCOVERER experience was largely responsible

for the selection of a crystal controlled recovery beacon for SANDS, dye

marker and flashing light detection aids will be the same. The ablation

phenomena studies, which will be accomplished on the next DISCOVERER flight

will be of general interest but are particularly pertinent to SANDS and MERCURY

which have the shallow angle, long heat pulse, re-entry trajector.

Future goals - The basic AGENA vehicle and the =NAB follow-on

version are develppment and testing products of the DISCOVERER program. These

products are major advances in all fields of space technology 'hi& have been

achieved in a mirdmum time at a relatively low coat. The DISCOVERER program

is providing, on a broad front, tested hardware for the R and D versions

of SANDS and MIDAS. Also, because of the experience and success achieved

in theDISCOVERER the NASA cancelled the VEGA program in favor of the AGENA-B

vehicle. This action was taken because it was apparent to NASA management that a reliable relatively inexpensive vehicle was available from

DISCOVERER. The development of the dual-burn AGENA-B vehicle in DISCOVERER

has drastically cut the development time required to deliver a tested

satellite vehicle for subsequent SANDS and MIDAS operatioral programs.

17. The immediate future goals for DISCOVERER include the following:

(1) Achieve successful orbital recovery. (2) Successfully recover biomedical specimens from orbit. (3) Demonstrate the design integrity and

operation of the AGENA-B version. (4) continue component development

leading to overall improved reliability, (5) Conduct geophysical and astrophysical experiments in order to gain new knowledge of the earth and the

near spatial environment. Examples of specific future goals within

selected subsystems include: (a) Propulsion - Model 8096 - This model will

provide an improved injector, an uncooled nossle extension to the 45:1 area

__ratio, and pumo inducers and a restart capability. This development adds

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