ISACS-DOC: AUTOMATIC MONITORING AND DIAGNOSTIC SYSTEM FOR SPACECRAFT

Ryoji Takaki1 , Masashi Hashimoto1 , Hideyuki Honda1 , Akinari Choki1 , Mitsue Mizutani2 , Kazuya Nomura3 , andTakayuki Kosaka3
1Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Center for Planning andInformation Systems, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 229-8510 JAPAN,{ryo,masashi,honda,akinari}@isas.jaxa.jp
2Fujitsu Advanced Solutions limited, 1-2-4 Shinkoyasu, Kanagawa-ku, Yokohama, Kanagawa, 221-0013 JAPAN,
mitsue@fasol.fujitsu.com3Fujitsu limited, 1-9-3 Nakase, Mihama, Chiba, Chiba 261-8588 JAPAN, nomura.kazuya@jp.fujitsu.com,
kosaka@ssd.ssg.fujitsu.com

ABSTRACTISACS-DOC (Intelligent SAtellite Control SoftwareDOCtor), which is automatic monitoring and diagnostic
system for spacecraft, has been developed and operated
at ISAS/JAXA ( Institute of Space and Astronautical Science of Japan Aerospace Exploration Agency). It aims
to rapidly and accurately capture important changes andsignals of anomaly during routine operations without thecontinuous presence of specialists. Three ISACS-DOCshave been so far constructed for the features of deep orsemi-deep space missions. Development of a next generation ISACS-DOC has just started for low earth orbit
satellite. This paper presents overview of the next generation system as well as what we learned through the development and operations of the three previous systems.
Key words: monitoring and diagnostic system; spacecraft; anomaly.

1. INTRODUCTION
To satisfy the high-grade observation requirements of ascientific satellite, the number of devices per satellite isincreasing, software functions are becoming complicatedand enhanced, and the number of operating stations is
also increasing with the enrichment of satellite operating
facilities. To realize accurate and safe satellite operations,the following issues should be resolved• Each component has a function to detect and reportan abnormality. Because of various abnormality reports, however, visual checks are substantially impossible.

• It is impossible to identify a true abnormality frommultiple reports and determine an appropriate action
in a limited time.
• It is not difficult to detect an abnormality in eachcomponent, but it is difficult to find the phenomenonof influence between components.
• An apparently true abnormality can be detected bya device but a general judgment must be made not
only from abnormality information but also frommultiple trend information. However, when there isa great volume of information, it is difficult to findand detect abnormal symptoms by human intuition.
• A trained expert may be able to find the signs offault by experience and intuition, but an operator for
regular operations cannot be expected to find suchsigns.
Under these circumstances, a monitoring and diagnostic system for satellite operations is needed for flexible operations linking satellite operation planning, tracking control, and data processing. Since 1992, therefore, the Institute of Space and Astronautical Science of
the Japan Aerospace Exploration Agency (ISAS/JAXA)
has been conducting research and development on aground system for monitoring and diagnosing the statusof satellites using AI techniques. This system is calledIntelligent Satellite Control Software-DOCtor (ISACSDOC) (Hashimoto et al. 1997; Hashimoto et al. 2001;
Hashimoto et al. 2003).
So far, this system has
been applied to the Geomagnetic Observation Satellite GEOTAIL (launched in 1992), Mars Explorer NOZOMI (launched in 1998), and sample-return probe
HAYABUSA (launched in 2003). Fig. 1 shows theISACS-DOC system configuration for NOZOMI. With
three computers, this system realizes the following two
key functions:1. Data collection function: Data necessary for monitoring and diagnosis is automatically collected fromvarious data distribution devices of the ISAS/JAXA
ground control system in real time through a network. From this data, the diagnostic files necessaryfor diagnosis are created. The data varies widelyfrom orbit data, latest real-time telemetry data, andattitude data to ground station status data. In Fig. 1,
the computer called WS is in charge of this function.
2. Monitoring and diagnostic function: For actual diagnostic work in another computer (PC-1 in Fig. 1),
diagnostic information files created in function 1 areautomatically transferred to this computer. With asatellite-related knowledge database necessary for
diagnosis, this computer diagnoses transferred diagnostic information files and displays various information.
Another personal computer (PC-2 in Fig. 1) copies all thedata from PC-1. PC-2 can be operated anytime to see theresults of monitoring and diagnosis on any past data.
Fig. 2 is an example of abnormalities diagnosed byISACS-DOC for HAYABUSA. The pressure of a hydrazine tank was lower than the expected value and leakage of He gas was suspected in this case.
For GEOTAIL, the first ISACS-DOC system was constructed by using a diagnostic expert system construction
tool (packaged software MANADESHIKUN). To date,ISACS-DOC systems for NOZOMI and HAYABUSA
have also been developed and put into service. This papersummarizes the operational knowledge about the monitoring and diagnostic system ISACS-DOC that has been
researched and developed and applied to actual scientificsatellite operations. The issues and overview of the nextgeneration system are also described.

2. KNOWLEDGE ACQUIRED SO FAR

cause of an abnormality with high accuracy is also effective for executing a diagnosis and presenting its results.
Since the character of the system has changed from diagnosis to monitoring the following modifications weremade. First, the knowledge structure was changed fromFault Tree Analysis (FTA), which is popular for diagnosis
and has a deep hierarchical structure , to the flat Decision
Tree, which is suitable for monitoring. The new structure was found to be effective. In addition, the diagnosticsystem was changed from manual data input using an interactive system suitable for diagnosis to automatic datainput. ISACS-DOC was also modified to automaticallyprocess all data and present an abnormality report to theoperator as early as possible.

2.2.

Diagnostic Data

Data for diagnosis is now acquired and stored uniquely byISACS-DOC. At the beginning of development, ISACSDOC needed to acquire, convert, and store data uniquely
because such foundations as EDISON (an engineering
database)(Honda et al. 2003), were not established. Now
that such foundations are established, linkage with themis necessary. Since diagnostic data itself requires groundstation data as well as satellite telemetry data, the total
handling of information from satellite to ground will effectively realize more accurate monitoring.

2.3.

Linkage with Simulator

The abnormality detection technique proved to be very
effective not only by the mere limit check of status information and measured values but also by comparison
with simulation data. Since there are a lot of difficulties
in simulator development, however, it is risky to totally
rely on the simulator. Therefore, we think that ISACSDOC should not have a simulator but an interface for asimulator and other external modules for switching to an
external module as required.

This section gives the operational knowledge acquired
from the three ISACS-DOC systems developed so far anddescribes necessary future improvements.

2.4.

2.1. From Fault Diagnosis to Monitoring

The monitoring and diagnostic system now has a functionof immediate notification to the operator by an alarm display on the monitor screen with an alarm tone. The alarm
notification function by e-mail, which is now in test service, requires further study on the result display method
and the alarm clearance timing.

ISACS-DOC was first developed as a fault diagnosis system using an expert system that could indicate several
causes of fault with their possibilities. When ISACSDOC was actually used, however, the presentation of several causes of fault confused the operators and prevented
early solutions. Therefore, instead of diagnosis, reliable
detection and the presentation of related information andactions were found to be effective. During operation,
it is important to present accurate information, such as
what is abnormal and what can be done. Identifying the2.5.

Notification to the Operator

Knowledge Production Techniques

Now, various knowledge production techniques havebeen proposed and are in use. The main techniques aredata mining, automatic learning, semiautomatic learning,and model-with-meaning diagnosis, as well as a rule base

Figure 1. ISACS-DOC system configuration for HAYABUSA

Figure 2. A diagnosed result of RCS abnormality

using the diagnostic tree. As the result of surveying thesetechniques, we think the currently adopted rule base is
the most effective under the special situations of satellite
monitoring and diagnosis (the greatest feature is the verysmall number of samples).

operation technology through their incorporation into thenext satellite control systems.

3.

ISSUES OF THE NEXT-GENERATION SYSTEM

2.6. System development
Now, a total of two ISACS-DOC systems are in service.
The oldest system for GEOTAIL has been in service formore than 10 years. The system is expected to work for
GEOTAIL for another decade, until the satellite is put outof operation. In the worst case, not the satellite itself but
the life of the ground facilities may be significant. Atsystem development, due care should be taken in the selection of the hardware, OS, and development language.
It is important to develop a system that allows stable operation and maintenance in a comparatively long span of
about 10 or 20 years.
This system is aimed at the actual application to a satellite. A system difficult for an operator to use is put outof service in the end. The operators’ opinions are veryimportant. Therefore, the conventional policy of spiraldevelopment that improves a system by repetitive design,manufacture, and verification will remain necessary also
in the future.

2.7. Significance of This System
Based on the experiences so far, the purpose and significance of the system are reviewed. First of all, the purposeof ISACS-DOC is to accurately grasp serious changes
and abnormality signs during regular operation without
experts in the satellite control room to enhance the safetyof satellite operations. If the cause of an abnormality cannot be identified from detected signs, it is preferable toconsult an expert by presenting the related informationand contact address. If the cause can be identified withhigh reliability, it is preferable to present diagnostic results and solutions. To do so, information from the satellite to the ground facilities needs to be integrated and visualized. Therefore, ISACS-DOC can be positioned asa system to support monitoring by an operator in regular
operation and to support diagnosis by an expert in abnormal operation.
From the general viewpoint of satellite control systems,
ISACS-DOC is considered to implement ordinary satellite control systems. The main purpose of this system
is to improve the probability of abnormality recognition.
To achieve this purpose, the system should be independent of existing satellite control systems and should notaffect their operations. Independence of existing facilities makes post-launch tuning and trial monitoring anddiagnosis easy and more accurate. Especially, the monitoring and diagnostic techniques verified by this system
will contribute to the continuous improvement of satellite

The next-generation ISACS-DOC is being developed forASTRO-F, which is to be launched in 2005. ASTRO-F isthe second space mission for infrared astronomy in Japanand it has a 67cm telescope cooled down to 6K, and willobserve in the wavelength range from 1.8 (near-infrared)
to 200 (far-infrared) micron. ASTRO-F will be launched
into space by a M-V rocket. ASTRO-F is a low-altitude
earth orbiter different in various aspects from the deep
space spacecraft targeted by the past ISACS-DOC systems. There are certainly many items to discuss about themonitoring and diagnostic system. Improvement items
based on past experiences can also be considered as issues of the next-generation system.

3.1.

Support of the Earth Orbiter

The greatest difference in terms of ISACS-DOC is therequirement for high-speed data processing. This isbecause of the short visible time (deep space spacecraft HAYABUSA: 8 hours, ASTRO-F: 10 min/pass and4 passes/day) and high transfer rate (HAYABUSA: 16Kbps, ASTRO-F: 4 Mbps). In other words, a large volume of data needs to be processed in a short time. Forhigh-speed data processing, it may be necessary to enhance the system processing performance, to set monitor items strictly, and to set priorities. To enhance thesystem processing performance, parallel processing will
be implemented. Regarding the priority setting, the toppriority item will be processed by real time and dealt withon the same pass if possible. Items of other priorities may
be processed offline and dealt with on the next pass. Processing a large volume of data in a short time will demandhigh-speed processing by the system and have a great impact on operation. This is because the operator does nothave enough time to judge an abnormality and take action, even when the system notifies the operator of theabnormality by a warning. Therefore, the system mayneed not only to give a mere warning but also to havestrong linkage with the satellite control system, such as
the automatic preparation of an emergency action command.

3.2.

System Arrangement

For next-generation system development, we are planning hierarchical data processing and module configuration. Hierarchical levels are prepared for various conversions from telemetry data and data processing, and thedata is defined on each hierarchical level to clarify therole assignments of modules in the system and strengthenthe linkage with other systems by using modules of thecommon infrastructure.

3.3. Knowledge Production Techniques
Knowledge collection and production vital to this system are expected to be more efficient. Therefore, weare considering the preparation of knowledge templates
about scientific satellites by utilizing the experiences sofar. Many knowledge bases were previously collected almost manually by experts and those with experience, andthen incorporated into systems. This is expected to beautomated to some extent. Therefore, we are thinking ofarranging the knowledge already collected and summarizing common knowledge into templates to have many
diagnostic rules incorporated into systems automatically.

4. CONCLUSION
Regarding the satellite monitoring and diagnostic system
ISACS-DOC that has been developed and operated by
ISAS/JAXA so far, this paper introduced knowledge acquired especially during development and operation. The
conception of the next-generation system based on thesewas also introduced. This is our first attempt to support
an low earth orbiter with ISACS-DOC, and various issues
are anticipated to occur. However, we will continue theresearch and development for a better system.

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[Hashimoto et al. 2003] Hashimoto M., Honda H.,
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Spacecraft Operation Needs (EDISON), Proceeding ofthe 24th International Symposium on Space Technology and Science, 2003