Industry's practice of testing space qualified hardware is examined. An overview of the Global Positioning System (GPS) Test Program is discussed from the component level to the sub-system compatibility tests with the space vehicle and finally to the launch site tests, all related to the Rubidium clock

Earl, C. E.

Koide, F. K.

Ringer, D. E.

English

NASA Technical Reports Server

CONTRACTOR POINT OF VIEW
FOR
SYSTEM DEVELOPMENT & TEST PROGRAM
F. K. Koide
Defense Electronics Operations
Rockwell International
Anaheim, California
D. E. Ringer C. E. Earl
North American Space Operations Defense Electronics Operations
Rockwell International Rockwell International
Seal Beach, California Anaheim, California
ABSTRACT
This paper will present industry's practice
of testing space qualified hardware. An over-
view of the GPS Test Program will be discussed
from the component level to the sub-system
compatibility tests with the space vehicle
and finally to the launch site tests at Van-
denberg AFB, California, all related to the
Rubidium clock.
INTRODUCTION
Rockwell International has been involved in the development and pro-
duction of space qualified Rubidium Frequency Standards for the GPS
Program since the initial inception of the program in 1974. To date,
we have produced a total of 29 Rubidium clocks consisting or proto-
types, engineering models, and production units.
The first series of six satellites are in orbit and have been declared
operational, with each carrying three redundant Rubidium clocks.
Initial test results demonstrated navigation accuracies of a few
meters in three dimensions. Rockwell is currently in the process of
developing Rubidium clocks on the Phase II/III Program for the GPS
Satellites 9 through 12.
The Rubidium clock test cycle covers two major phases, the pre-pro-
duction and the acceptance level testing. The pre-production covers
the board, system assembly, and assembly tests. The acceptance level
testing includes the environmental and certification tests. All
Rubidium clock tests are performed in different test facilities of
Rockwell's Defense Electronics Operations in Anaheim, California.
291
https://ntrs.nasa.gov/search.jsp?R=19810018943 2020-03-21T13:00:43+00:00Z
The space vehicle undergoes integrated acceptance testing through test
conditions simulating and exceeding the environments which it will en-
counter from launch through on-orbit operation. The acceptance test
of the space vehicle is performed at Rockwell's Space Operations and
Satellite Systems Division at Seal Beach/Downey, California, and the
North American Aircraft Division located in Los Angeles, California.
SPACE QUALIFIED TEST PROGRAM
Rubidium Clock Automated Test Station
Rockwell's Rubidium clock has been developed from a commercial
Efratom Rubidium Frequency Standard. Extensive modification and
repackaging have been performed to meet spacecraft requirements
and to improve reliability and stability. Acceptance testing of
production clocks are required to assure compliance with the
design goals and conformity to the procurement specification.
Computer automation of the Rubidium clock testing is utilized
because of the large amount of data to be gathered over an
extended time period and the need to extensively process this
data.
A central or a time share computer concept was selected to
allow for greater versatility of utilization and to allow im-
plementation of additional test stations. The computer system
utilizes a sophisticated version of BASIC as the programming
language available to users and can be extended to service up
to 16 terminals. The time share computer is a pdp-11/35 micro-
computer which includes 256K, 16 bit word fixed head disc, 1.2
mega bit word movable head disc, dual dectape storage and 28K
words of core memory. It is essentially a minimum system re-
quirement to support the data storage and processing require-
ments .
In the existing configuration, four terminals or test stations
are supported by the pdp-11/35 minicomputer. Three of the four
test stations are equipped with micro-computer systems that
provide redundant data collection and storage capabilities if
the time shared computer should fail. At the end of the test,
these data would then be transferred to the pdp-11/35 for
analysis. System redundance prevents the loss of test time
without interruption. A functional block diagram of the
Rubidium clock test station and a photo of three of the four
test stations are shown in Figures 1 and 2 respectively.
A valuable feature of the RSTS time share concept utilized is
the ability to access data being stored on disc from one program
using one I/O port by executing an independent program from a
292
second port. This feature allows data analysis without interrup-
ting data collection program while using a number of different
programs.
Failsafe features are incorporated into all test stations to
protect against loss of data in the micro-computer due to trans-
ient in the power line voltage, clock supply over-voltage and
current, over and under base-plate temperatures, and water flow
rate restriction in the vacuum pumps.
Rubidium Clock Test i
The testing of Rockwell's Rubidium clock is controlled by two
specifications, one an assembly and alignment procedure and the
second an Acceptance Test Procedure (ATP). These test procedures
have been witnessed and certified by Quality Engineering. There
are approximately 76 inspection points where a Quality Assurance
Inspector must approve and stamp off the work before additional
testing can proceed. All these steps are planned and recorded
in a FAIR book system. FAIR is an acronym for Fabrication-
Assembly- Inspection-Record.
This system also keeps track of all parts installed into the
Rubidium clock. If a failure occurs during assembly, the retest
must start over per the retest matrix listed in the assembly
procedure. If a failure occurs during the ATP, the failure
must be documented by Reliability Engineering, who also notifies
the prime contractor, and generates a failure analysis report.
At the completion of a successful ATP the test data is assembled
into a data package by Quality Engineering and a formal data
review is conducted with the prime contractor, Air Force (SAMSO)
and the technical consultants for the Air Force.
After the data review, the Rubidium clock is packaged and shipped
to the prime contractor. The data is impounded in the Data
Submittal department where it is available for review at a later
date. This data includes all acceptance test record cards,
"FAIR" books, computer printouts and strip charts.
Figure 3 shows the Product Acceptance test flow for the Rubidium
clock from the Module Assembly level to the point of shipment,
the space vehicle factory test. A typical calendar time for
product acceptance test is approximately three months.
Space Vehicle Factory and Launch Site Tests '
As prime contractor for the GPS Space Vehicle, installation of
sub-systems and integration tests are initiated at Rockwell's
293
Seal Beach Operation Factory Test Clean Room Facility. Figure 4
shows the test flow and the type of tests performed at these
levels on the space vehicle. The Rubidium clock is primarily
tested for interface compatibility with the different sub-systems.
The performance of the individual sub-system is tested at each
phase of buildup to assure reliable operation during the five year
mission life. The test criteria are structured to verify that
each sub-system performance is within specified limits, and the
performance is monitored for stability and continuity from test
phase-to-test phase. Departures from expected performance, even
well within specification limits, are evaluated in detail and
corrective actions are implemented.
Two mobile vans equipped with test systems to perform factory
tests follows the space vehicle to Rockwell's acoustics and
thermal vacuum chamber environmental test facilities located
in the Los Angeles area.
At Rockwell's Los Angeles Operation Acoustic Chamber, the space
vehicle is subjected to a broad spectrum of acoustic frequencies
to simulate the lift-off, boost, and separation environment.
The thermal vacuum chamber at Rockwell's Downey, California,
operation siumlates the heat, cold, and vacuum of space to
verify assembly, workmanship of space vehicle components.
Figure 5 shows the qualification space vehicle in a thermal
vacuum chamber. Each individual sub-system component is mounted
on the Space Vehicle thermal control plates and driven to tem-
peratures exceeding on-orbit temperatures by 21°C for qualifica-
tion testing and 11°C for acceptance testing. The thermal design
of the entire spacecraft is thus validated by thermal-vacuum
testing in a large vacuum chamber with a typical test time of
about 3 months. Each Rubidium clock is turned on in a programmed
sequence to test stability at the temperature extremes with the
four different sub-systems during the thermal vacuum tests.
These four sub-systems include navigation; electrical power
(Ni-Cd batteries); attitude and velocity control; and the
telemetry, tracking, and command (Figure 6).
After the completion of the Thermal Vacuum Test, the space
vehicle is shipped to Rockwell's Seal Beach Clean Room Facility
for a series of final tests. These tests include the mission
profile, space vehicle's static and dynamic balance and func-
tional tests. One of the key tests is the spin balance which
is designed to make precision determinations of the Space Vehicle
Mass Properties.
At Vandenberg AFB, the space vehicle is prepared for launch by
performing satellite and master control L&S band RF link com-
294
atibility tests and a simulated flight and mission dress re-
hearsal (Figure 7). Normally, one of three redundant Rubidium
clocks is turned-on as a master clock for the L-Band RF link
compatibility tests. The S-Band links with the Satellite Control
Facility located in Sunnyvale, California, and is used as a down-
link to receive the telemetry and other information from the
satellite.
SUMMARY
It has been shown that the role of automation is essential in the
development of a Space Qualified Test Program. Use of automation has
been a key factor in the success of the test program to date. Because
of the accelerated schedules and heavy demand on test systems, it is
highly unlikely that the present state of development could have been
achieved without automation techniques. Expertise in the field of
precision frequency and time measurements as well as the capability
to interface special test equipment with computer technology are
essential in meeting test requirements for the space-qualified clocks.
Automatic test systems have essentially provided unattended operation
24 hours a day, thus reducing cost and increasing productivity.
The test program plays a major role in producing Rockwell International
products for Government contracts. By employing a regimented type
test program, it has been shown that tests uncover latent faults
which otherwise may have gone undetected. The program has also
demonstrated interface compatibility among sub-systems. The use of
well documented test procedures has provided uniform testing from
location-to-location; test personnel-to-test personnel; and inspector-
to-inspector.
In conclusion, when involved in a major program such as GPS, a con-
siderable amount of effort is expended in tests and as such is
a key element in the success of the program.
295
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QUESTIONS AND ANSWERS
DR. VESSOT:
If you could explain a little more about what I consider to be the
most important test -- and that is the on-going operation of the
clock and the monitoring of its operation for very, very long
periods of time. Even though these are extreme stages of testing,
in my opinion, you do not observe the clock operating for as long
as you possibly can while it is in your possession before it goes
into space.
A lot of those long-term tests I feel are very minor.
MR. KOIDE:
The long-term tests uses trade-off schedules -- production schedule
trade-offs. So, we felt that the long-term type testing will be
the Allan variance test which will get out to 100,000 seconds. We
get our data points up to about seven data points to give us some
assurance of confidence that it has maintained this particular
level of task.
DR. VESSOT:
This is not the kind of test I had in mind — which is the test
wherein you prove that this device is going to work for a period
of several months while you still have it on the ground. At no
time while it is in your possession, I feel, should you fail to
take data from the clock in the operating condition.
This is the clean shake, shock, vibration, thermal vac, and
all the rest of it -- keep it running and monitor it.
MR. KOIDE:
Yes, we do have the acceptance level testing for the rubidium fre-
quency standard. Once the rubidium frequency standard gets over
to the factory test level and integrated into the space vehicle,
you are primarily concerned with the interface compatibility be-
tween systems.
So, you do monitor all the time — you do the test while you
are testing or monitoring the telemetry lines. You do a lot of
other types of tests, but is mainly for the interface compatibility
of other systems.
303
DR. VESSOT:
But does that interfere with the frequency or the stability testing?
MR. KOIDE:
No, that is not the prime function when we get into the vehicle
testing.
DR. VESSOT:.
I suggest that is a mistake; that you can't avoid that issue of
keeping an eye on the piece while you still have it as long as you
possibly can.
MR. KOIDE:
Well, we try to do that. We are trying to set up a long-term test,
a life test for the RFS and that is another issue.
304


Contractor point of view for system development and test program

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