The design and the prototype for the expert system for the Hubble Space Telescope's electrical power system are discussed. This prototype demonstrated the capability to use real time data from a 32k telemetry stream and to perform operational health and safety status monitoring, detect trends such as battery degradation, and detect anomalies such as solar array failures. This prototype, along with the pointing control system and data management system expert systems, forms the initial Telemetry Analysis for Lockheed Operated Spacecraft (TALOS) capability

Eddy, Pat

English

NASA Technical Reports Server

N88-16380
A KNOWLEDGE-BASED SYSTEM FOR MONITORING
THE ELECTRICAL POWER SYSTEM
OF THE
HUBBLE SPACE TELESCOPE
BY
PAT EDDY
LOCKHEED ARTIFICIAL INTELLIGENCE CENTER
2710 SAND HILL ROAD, MENLO PARK, CA. 94025
ABSTRACT
Lockheed is currently in the process of developing expert
systems that perform on-line monitoring, statusing and trend
analysis of ma3or Hubble Space Telescope (HST) systems. The
three major systems under development are the Pointing Control
System (PCS) [KLSRD87], the Data Management System (DMS) and
the Electrical Power System (EPS). These expert systems are
part of the TALOS [CW87] system for assisting in HST ground
operations which is being developed at Goddard Space Flight
Center. This paper will treat the EPS expert system (a part
of the TALOS distributed architecture).
This paper will describe the design and the prototype for
this system as demonstrated on 9/23/87 at the LMSC Artificial
Intelligence Center, Menlo Park, California. This prototype
demonstrated the capability to use real time data from a 32k
telemetry stream and perform operational health and safety
status monitoring, detect trends such as battery degradation
and detect anomalies such as solar array failures. This
prototype along with the PCS and DMS prototype expert systems
form the initial TALOS capability.
INTRODUCTION
Lockheed Missiles and Space Company (LMSC) is the prime
contractor for the Support Systems Module (SSM) and Integration
Systems Engineer for the Edwin P Hubble Space Telescope (HST).
Additionally, LMSC is the HST Mission Operations Contractor,
responsible for the ground operations that ensure the health
and safety of the HST.
The HST is a complex, state-of-the-art satellite with
unique ground operations requirements. Accordingly the ability
to reliably monitor telemetry in real-time is highly
desirable. To this end the Telemetry Analysis Logic for
Operating Spacecraft (TALOS) system is being developed.
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The Talos system consists of real-time and off-line deep
analysis knowledge-based modules. This paper will concentrate
on the real-time monitoring and analysis EPS monitoring
system. The basis for this system is L'STAR, a Lockheed
proprietary tool. This shell [SRLK87] consists of a
multiprocessing architecture for performing real-time
monitoring and analysis using knowledge-based problem solving
techniques.
In order to handle asynchronous inputs and perform in
real-time, the system consists of three separate processes
which run concurrently and communicate via a message passing
scheme. The Data Management Process gathers, compresses, and
scales the incoming telemetry data before sending it to the
other tasks. The Inferencing Process consists of a proprietary
high performance inference engine, written in the C programming
language, which can run at a rate of close to i000 rules per
second. It uses compressed telemetry data to perform a
real-time analysis on the state and health of the Space
Telescope. The I/O Process receives telemetry monitors from
the Data Management Process and status/health messages from the
Inference Process, updates its graphical displays in real-time,
and acts as the interface to the console operator. The I/O
Process resides on DEC VAXStation II/GPX high resolution color
graphics workstation. It consists of a hierarchy of displays
which the user may traverse using a mouse. The three tasks run
concurrently and may reside on the same or different
processors. Furthermore, the multitasking architecture has
been designed in such a way that multiple inference processes,
multiple data management processes, and multiple I/O processes
can run concurrently and communicate with each other. It
processes several hundred telemetry monitors per second.
The population of L'STAR with HST EPS knowledge has
produced a very fast and reliable operator assistant to be
described in this paper.
EPS REAL-TIME TELEMETRY MONITOR
The TALOS EPS real-time telemetry monitor will provide
operators with the following real-time telemetry capability:
o
o
o
o
o
o
o
o
o
o
HST Mode/Configuration Monitoring.
Real-time EPS Statusing.
Command Verification.
Multi Orbit Health History Tracking.
Ability to Handle Unexpected Telemetry Loss.
Correlation of Temperature, Power Error Histories.
Real-time warning of approaching intelligent
thresholds.
Real-time comparison of an EPS model generated power
profile with telemetry based EPS status.
Projection of telemetry based EPS status in accordance
with load and time parameters defined by a model
generated power profile.
Suggested load changes to prevent exceeding limits.
104
One of the key elements required for this system to be able
to reason about the health and safety of the HST is knowledge
about the present and projected future operational mode of the
HST. Accordingly, this system establishes the following
contexts for the reasoning process:
o
o
o
o
o
o
o
o
o
o
Battery Reconditioning
Off Normal Roll
Stationary HST
Maneuvering HST
Orbit Day
Eclipse
Hardware/Software Sunpoint
Solar Array Repositioning
Seasons Of The Year
Orbital Decay
This system provides the operator with a top level
functional diagram of the end to end power flow of the EPS
starting with the Solar Arrays and ending with the Power
Distribution Units. Lower level displays show more detailed
diagrams of EPS components until all telemetry values are
accounted for. The EPS statusing capability consists of the
following:
o
o
o
o
o
o
o
o
o
o
o
o
o
o
EPS Configuration
SA power output
Status of K relays
Structure Current
Battery voltage/temperature
Battery Recharge Ratio
Diode Bus Current/Voltage
Sun to Orbit Ratio
Power Distribution Unit Current
Battery Shunt CKT Status
Solar Panel Assembly Connect/Disconnect
Distribution Bus On/Off
Heater Status
Voltage VS Temperature Change Current Controller
Activation Curves
The following capabilities will provide an EPS real-time
telemetry monitoring assistant that uses temporal reasoning and
communicates with other expert systems:
o Command verification will allow the automatic
indication of command group execution on a display of the
mission timeline. In addition, the EPS expert system will
receive indication of a command reject from the DMS real-time
monitor and such information as maneuver status from the PCS
monitor.
o Multi-orbit health, history tracking will display and
compare a 15 orbit history set of events such as the following:
Trickle Charge Time
Maximum battery Voltage at Eclipse
Minimum Battery Voltage at Eclipse
105
o Management of unexpected telemetry loss is necessary
to support multi-orbit event tracking above. It will be
accomplished by designating a beginning/end of orbit event that
occurs at a predictable time such as K-relay closure. If the
required data has not been collected by the end of orbit then
that orbit will be shown as missing data and the data
collection process will be reinitialized for the beginning of
the next orbit.
o Correlation of temperature, power and error histories
will allow the operator to compare any multi-orbit health
histories for the purpose of identifying failure trends.
o Intelligent threshold warnings consits of monitoring
real-time EPS telemetry to provide operator warnings of
approaching anomalies as a result of reasoning about the
current operational mode on future loads.
o EPS status and power profile comparison compare an EPS
model generated power profile with the actual EPS to show a
projected status based on the load as defined by the EPS
model. The operator may project the power status to a number
of orbits or hours in the future.
o Projection of load and time changes will allow the
system to obtain the results of proposed load and time changes
by extrapolating the telemetry based EPS status into the
future. In addition, the expert system will have access to the
projected electrical activity as defined by the power profile
and will be able to warn the operator of HST components or
science instruments that are scheduled to come on and approach
load limits.
o Suggested load changes will give the operator access
to the projected loads created by HST components in their
operational configurations. When the power profile deviates
from the current EPS status the system will be able to access a
load shedding component list and make recommendations to the
operator.
ACKNOWLEDGEMENT
This work was done under the sponsorship of Tom Laffey of the
Lockheed Artificial Intelligence Center.
106
CONCLUSIONS
The work accomplished to date provides the operator with an
intelligent assistant that reasons about current system status
such as the following:
o
o
o
o
o
Battery Voltage
Charge Current
Bus Voltages and Current
Component Temperatures
Solar Array Output
It then advises the operator whether the above parameters
are normal in accordance within the following contexts:
o
o
o
o
o
HST maneuvering
HST Stationary
Solar Arrays repositioning
Orbit Day
Eclipse
Thus, this system advises the operator that a given current
is normal, not just within limits, while taking into account
maneuvering status and time of day. Future work will add
safemode, seasons, and orbital decay to this reasoning process.
The above information is presented in meaningfull displays
showing the end to end energy production and usage along with
lower level detailed displays. Warnings and adviseries are
provided. This work is on-going and future work includes
completing the requirements listed in this paper.
REFERENCES
[CW87]
[KLSRD87)
[SRLK87)
B. Cruse and E. Wende. Expert system support for
HST operations. In Proceedings of the 1987 Goddard
Conference on Space Applications of Artificial
Intelligence and Robotics, NASA Goddard Space
Flight Center, May 1987.
S. Kao, T. Laffey, J. Schmidt, J. Read, L. Dunham.
Monitoring the PCS of the Hubble Space Telescope.
Third Conference On Artificial Intelligence for
Space Applications, George C. Marshall Space Flight
Center, November 1987.
J. Schmidt, J. Read, T. Laffey, S. Kao. A
Multiprocessing architecture for real-time
monitoring. Third Conference On Artificial
Intelligence for Space Applications, George C.
Marshall Space Flight Center, November 1987.
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A knowledge-based system for monitoring the electrical power system of the Hubble Space Telescope

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