Appendix E

Perspectives on Yohkoh



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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT Appendix E Perspectives on Yohkoh

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT This page in the original is blank.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT INTERNATIONAL COOPERATION IN THE YOHKOH PROGRAM T. Kosugi Institute of Space and Astronautical Science 1.0 Introduction The Yohkoh satellite, formerly named Solar-A before launch, is the second X-ray solar-physics satellite of the Institute of Space and Astronautical Science (ISAS), and was launched by an M-3S-II launch vehicle on August 30, 1991. It is fully operational even after 7 years have elapsed and is expected to be so during the coming solar maximum in 2000-2001. The Yohkoh mission aims at unveiling energy-release and particle-acceleration processes in solar flares, as well as at deeply understanding structures and dynamics seen in the solar corona. To achieve these goals, it carries four scientific instruments: (1) a hard X-ray telescope (HXT), (2) a soft X-ray telescope (SXT), (3) a set of wideband spectrometers, and (4) a set of Bragg crystal spectrometers (BCSs). Each of the four instruments has its own advantages over its predecessors, but more important is that these four instruments were so designed as to principally observe a single object, that is, a solar flare. The intention was to obtain a coordinated set of complementary observations taken simultaneously. This goal has been fully achieved, resulting in fruitful scientific return not only in number (467 papers in refereed journals, 597 proceedings papers, 34 Ph.D. theses, and 39 master 's theses as of August 1998) but also in quality. From the beginning, Yohkoh was planned by ISAS as an international collaborative mission with the National Aeronautics and Space Administration (NASA—United States) and Science and Engineering Research Council (SERC; at present the Particle Physics and Astronomy Research Council —United Kingdom) as international partners. Inside Japan, the Yohkoh collaboration includes the National Astronomical Observatory of Japan (NAOJ), major universities, and others. Participating institutions are listed in Table E.1. 2.0 Historical Background Prior to the Yohkoh mission planning, solar physicists in Japan had much experience working with U.S. and U.K. scientists but more on an individual basis than as a result of large-scale organized programs. Many leading Japanese solar physicists had been regular visitors to the United States and had developed collaborative research, frequently exchanging data as well as ideas. The collaboration drastically expanded when ISAS and NASA simultaneously and independently planned the Solar Maximum Mission (SMM) and Hinotori satellites, respectively, for the previous solar maximum around 1980. Although these two missions differed much in size and as a result Hinotori covered a smaller field in science than SMM, the two missions aimed at essentially the same scientific objective: understanding solar flares, with similar instrumentation, that is, hard X-ray imaging based on collimator technique and Bragg crystal spectroscopy. Under such circumstances, a cooperative relationship naturally developed between the two missions, ranging from exchanging observation schedules to exchanging data and participating in joint data analysis projects. Because U.K. scientists participated in the SMM program, Japan-U.K. collaboration also developed during this period. This positive experience led to discussions for a collaboration on a future satellite mission, first among Japanese, U.S., and U.K. scientists in 1982 and 1983, and subsequently among ISAS, NASA, and SERC. The result of these discussions was an informal decision to proceed with a joint mission to be led by ISAS. In 1985 letters were exchanged between ISAS and NASA, in which ISAS offered, and NASA accepted, the opportunity for direct involvement of U.S. scientists in the Solar-A (Yohkoh) mission. It was decided at this stage that the U.S. involvement was to participate in the SXT experiment by providing its hardware; this would complement the HXT experiment built in Japan. Subsequently, SERC offered,

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT TABLE E.1 Institutions Participating in the Yohkoh Program Type of Participation Institution Country On-board Instruments HXT ISAS Japan   University of Tokyo Japan   NAOJ Japan SXT ISAS Japan   NAOJ Japan   University of Tokyo Japan   Lockheed Palo Alto Research Laboratory United States   NASA/MSFC United States WBS ISAS Japan   Rikkyo University Japan   NAOJ Japan BCS ISAS Japan   NAOJ Japan   Mullard Space Science Laboratory United Kingdom   Rutherford Appleton Laboratory United Kingdom   National Institute of Standards and Technology United States   E.O. Hulburt Center for Space Research, Naval Research Laboratory United States Ground-Based Observations, Etc.   NAOJ Japan   Kyoto University Japan   Nagoya University Japan Communications Research Laboratory Japan   Stanford University United States   University of California at Berkeley United States   University of Hawaii United States   Others   and ISAS accepted, U.K. participation in Solar-A (Yohkoh) via the BCS experiment, in collaboration with U.S. groups. While the above discussions were in progress for establishing the international collaboration framework, Japanese scientists worked hard inside and outside ISAS to find a good solution for the conceptual design of a satellite suitable for deploying the two telescopes (HXT and SXT). The biggest challenge was a total revision of the HXT instrument. The initial design, which had been based on a rotating modulation collimator similar to that on board Hinotori, had to be abandoned and a completely novel design of a multielement, Fourier-synthesis telescope adopted instead. This revision made a three-axis stabilized satellite possible, which enabled SXT to operate at full sensitivity and flexibility via long exposure of its charge-integrating CCD sensor. Such efforts for optimizing the instruments, based on a desire to have a set of fully developed, coordinated instruments on board a single satellite, have been and still are indispensable for realizing such a successful mission as Yohkoh.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 3.0 Cooperation The international Solar-A (Yohkoh) team was organized in 1986 just after NASA's announcement of opportunity (AO) process for selecting a U.S. SXT team was completed. It is noteworthy here that NASA's AO clearly stated, in accordance with the agreement with ISAS, that U.S. scientists selected through this AO process would be designated as co-investigators on Yohkoh by ISAS and would join the overall Yohkoh mission science team headed by a Japanese project manager and project scientist and that some of the U.S. scientists would be expected to spend substantial time in Japan to participate in the Yohkoh mission development, science operations, and data analysis activities. Consequently the selected U.S. SXT team included not only instrument builders but also some providing ground-based observations and some mainly interested in observations with the other instruments on board Yohkoh and in theoretical work. The international Yohkoh team was organized on this principle, the essence of which is fully reflected in the basic team organization as shown in Table E.2. The actual cooperation in the subsequent stages has been developed on the basis of this basic principle as discussed in the following sections. TABLE E.2 Yohkoh Team Organization Position Name Affiliationa Project manager Y. Ogawara ISAS Secretaries to manager T. Kosugi University of Tokyo   S. Tsuneta University of Tokyo   T. Watanabe NAOJ Project scientist Y. Uchida University of Tokyo Principal investigators (PIs) HXT K. Kai NAOJ   K. Makishima University of Tokyo SXT T. Hirayama NAOJ   L.W. Acton LPARL; PI to NASA WBS J. Nishimura ISAS BCS E. Hiei NAOJ   J.L. Culhane Mullard Space Science Laboratory, PI to SERC aAffiliations given here are those in the team formation stage in 1988. 3.1 Design, Fabrication, Integration, and Testing In the Yohkoh program, ISAS took the responsibility for the satellite system integration. Under the guidance of the ISAS project manager, each instrument subteam conducted the design, fabrication, integration, and testing for the instrument for which the subteam was responsible. To be noted here is the fact that the instrument building itself was a joint effort among the participating institutions and scientists regardless of whether it was domestic or international. This was especially so in the design phase. For an international instrument, SXT or BCS, a large number of international meetings were held. These meetings not only helped to define clear interfaces between the Japanese and foreign hardware, but also to find the best instrument designs as a whole. In addition there were meetings for defining the on-board central data processor and some other bus module instruments that would have crucial impacts on the mission science.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT Once the decision was made on the design including task sharing, there was a clear division of responsibilities among the participating institutions. For example in the case of SXT, our U.S. partner provided the telescope optics including the CCD camera and its front-end controller, while the Japanese side was responsible for observation control and on-board data processing software for optimizing the data volume within the limited capacity of the on-board data recorder. 3.2 Mission Operations In the sense that Yohkoh is a Sun-pointing satellite and that all the instruments on board cover the full Sun without any satellite attitude maneuvers, the Yohkoh mission operations are simple in comparison with those of other X-ray astronomy satellites of ISAS. However, Yohkoh needs to operate semiautonomously in responding to flare occurrence; flares are predictable neither in time nor location. In addition, once a flare occurs, high-cadence observations with proper exposures are of vital importance to accommodate the highly variable phenomenon. Although Yohkoh was designed in such a way that flare observations can be conducted mostly in an automated way by the on-board central data processor, the parameters of its observing programs must be specified from the ground in advance based on solar activity prediction. The use of ground-based observation networks in collaboration with Yohkoh has been one of the key elements for fully achieving the mission objectives. Mission operations of Yohkoh have been conducted to match these conditions in the framework of the international Yohkoh team. A weekly operation meeting is held at ISAS every Monday to discuss weekly operations planning. Also discussed in this meeting are operation problems, if any, and their troubleshooting, and the latest science topics mainly from the previous week's operations. These meetings are attended by most of the Yohkoh team members who work in and near ISAS, including U.S. and U.K. colleagues either resident or visiting. Collaborative observations with other satellites, such as the Compton Gamma Ray Observatory, Ulysses, the Solar and Heliospheric Observatory (SOHO), and the Transition Region and Coronal Explorer, and ground-based observatories, have been pursued so far as “campaigns observations ” based on the decisions made at the weekly meetings. Daily operations are planned primarily at the Sagamihara Spacecraft Operation Center (SSOC) in ISAS by two duty scientists (SSOC “Tohban ”), assigned on a weekly basis, with the assistance of an SXT chief observer. The operation plan prepared by them is forwarded to the Kagoshima Space Center (KSC) of ISAS, where two duty scientists (KSC “Tohban”) who are assigned on a 2-week basis are responsible for making final checks of the operation plan and conducting real-time operations. The KSC Tohban duties include uploading commands, receiving downlink telemetry, and providing routine monitoring of the satellite housekeeping, as well as the scientific data. When anomalies are found, an immediate notification is sent to SSOC, as well as to other relevant personnel. The KSC Tohban duties include the worldwide circulation, via e-mail, of the current Yohkoh observation status. This facilitates the simultaneous observation of specific active regions on which Yohkoh (usually autonomously) concentrates its observations. These Tohban duties, as a whole, are shared by all participating scientists—irrespective of nationality. Another important aspect of the Yohkoh operations is the participation of NASA's Deep Space Network stations, and the Wallops and Santiago stations, as stored data downlink stations. Because the on-board data recorder becomes full in only 40 minutes at the highest data recording rate, downlinks at these stations are of crucial importance for continuous data coverage. Data downlinked at these stations arrive at ISAS in 1 or a few days via network (NASCOM line). A limited number of Yohkoh SXT full-Sun images are delivered on a daily basis to the U.S. National Oceanic and Atmospheric Administration and other sites for space weather prediction purposes. This distribution is managed in Japan by the Central Communications Laboratory.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 3.3 Data Analysis The downlinked data are reformatted and made accessible online immediately after the original data arrive at ISAS. Exabyte tapes containing reformatted data are distributed to major home institutes of the Yohkoh team with no delay longer than about a month. One year after the data acquisition the same reformatted data are sent to NASA' s Space Science Data Center (NSSDC) for the use of the international science community, outside the Yohkoh team. In addition to NSSDC, the Solar Data Analysis Center at NASA's Goddard Space Flight Center (NASA/GSFC) has played an important role for making the Yohkoh data easily accessible by those who are not familiar with Yohkoh. The full Yohkoh analysis software package is also made available together with its users' guidebook; this software package is now installed in many sites worldwide and has been a model for software developments in subsequent missions. The 1-year period is reserved for Yohkoh team members for their preferential data analysis. Because the Yohkoh operation is based not on a science proposal and refereeing process but on team discussion, no specific observations can be analyzed exclusively by one person. Instead, cooperative data analysis has been encouraged in the Yohkoh team among various groups, say, between different instrument subteams, or between Japanese and U.S./U.K. members. To moderate possible collisions or conflicts in data analysis, the Yohkoh team organized a “Team Bulletin Board” and a system of data use coordinators (DUCs). The former is a World-Wide-Web-based team circular and has been used to distribute individuals' data analysis activities to team members. DUCs are assigned for the individual instruments to monitor data analysis activities, help individual data users who are not familiar with the instruments, and advise individual data users to initiate a joint data analysis program if there are any other analyses in progress on the same or similar topics. Thanks probably to the large amount of newly found topics that Yohkoh has provided almost continuously, no serious collisions or conflicts have been reported. We have heard some arguments against the 1-year data reservation by the Yohkoh team from team outsiders, claiming that the data should be opened without any reservation period. Most of the arguments are based on a misunderstanding of the situation. The Yohkoh operations have been maintained as a result of sacrificing contributions by young scientists, especially graduate students, from universities in Japan. Even senior scientists suffer from a heavy burden of operational duties. In such a circumstance, completely opening newly acquired data to those who do not share operation duties might not be fair. Hence, the Yohkoh team has been flexibly interpreted as including those who contribute to the operations, with “contribute” here interpreted in its widest meaning. Ground-based observers may be treated as team members if they make observations cooperatively with Yohkoh. Furthermore, those conducting even theoretical work together with a Yohkoh team member have been allowed to analyze newly obtained Yohkoh data. Thus, the 1-year reservation rule has been applied as a minimal request from the team to outsiders. With regard to data analysis, two more points are worth mentioning: (1) In 1993 and 1994, a guest investigator program was made available by funding from NASA. To our regret, Japan had no corresponding system to support interested scientists outside the Yohkoh team. It was only a few years ago that the Japanese government started a new program that expanded the number of postdoctoral research fellows. The Yohkoh team has begun to use this new program as a tool for providing opportunities to young scientists to participate in Yohkoh data analysis. (2) Since 1997 a series of small coordinated data analysis workshops (CDAWs), each of which is devoted to a specific data analysis topic, have been held as Yohkoh-SOHO joint meetings twice every year. CDAWs emphasize actual data manipulation, notably the coalignment of images from a wide variety of instruments, and they contribute to developing a cooperative atmosphere not only within the Yohkoh team but also between team members and team outsiders.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 4.0 Lessons Learned When we, Japanese solar physicists, started the Solar-A program more than a decade ago, we did not understand what constitutes international collaboration. Even now we may have learned only a little about it. In spite of this, most of those involved in the Yohkoh program agree that the Japan-U.S.-U.K. collaboration has been fruitful on all sides. First, we are now confident that, even though our systems for performing activities may differ, Japanese, U.S., and U.K. scientists can pursue the same scientific objectives by sharing our duties and responsibilities as equal partners in a unified team. Differences, large and small, have been overcome by mutual understanding. Scientists who share a common exploration of remarkable discoveries can be unified into a team even in competitive circumstances. Second, the Yohkoh experience has taught us that international cooperation provides an excellent opportunity to learn new methods. Each system may have its own unique advantages. Learning from our international partners has proven quite useful, and I hope that they have also learned from us. To be more specific, for example, a mature analysis software methodology that was first developed for SMM observations has been extended and introduced as a standard in the Yohkoh team. This methodology has been contributing in a major way to enhancing our level of activity. Third, a new generation of scientists who are experienced in international cooperation has emerged from the Yohkoh program. I hope that, under the leadership of these young scientists, the next ISAS solar-physics mission, Solar-B, will provide another example of success in the near future. 5.0 Concluding Remarks The Yohkoh program, the first Japanese international satellite program in the field of solar physics, has provided us with many lessons. The program has been a great success, I believe, thanks to great efforts by our colleagues on the team. The Japanese solar physicists have learned from ISAS as well as from our foreign colleagues how to organize an international cooperation in the satellite mission. Especially important was the principle upon which the international Yohkoh team was organized. The essence was given in the agreement between ISAS and NASA, which has been a good guide for making decisions in a cooperative manner. Preparation of the satellite, mission operations, and cooperative data analysis have been conducted on the same principle: a single, unified team working on a task-sharing basis with everyone 's burdens as equal as possible. In the Yohkoh program, team members have equal rights to have access to data taken with any instrument. This has promoted collaborative data analysis between those who have become involved in the team from different starting points. Also the data have been opened to others as far as possible, within the minor constraint of reservation of newly obtained data by the Yohkoh team for 1 year. I believe this open-data policy has been effective in expanding the number of Yohkoh data users beyond the Yohkoh team. This brief paper is not intended to describe fully all aspects of the Yohkoh program. Instead it is almost a private memo on what the author has been involved in as one of the secretaries of the program under the guidance of the project manager, Professor Y. Ogawara. Each topic is touched on briefly, without detailed information on the individuals who have mainly contributed to the program.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT YOHKOH—THE VIEW FROM EUROPE: AN ACCOUNT OF THE COLLABORATIVE PRODUCTION OF THE U.K./U.S./JAPANESE BRAGG CRYSTAL SPECTROMETER J.L. Culhane Mullard Space Science Laboratory 1.0 Historical Background 1.1 Origins and the Nature of Yohkoh and the Bragg Crystal Spectrometer Japan, U.S., and U.K. research groups had flown three high-resolution Bragg Crystal X-ray spectrometers in the early 1980s. The instruments—on the Hinotori (National Astronomical Observatory of Japan (NAOJ) / Institute for Space and Astronautical Science (ISAS), P78-1 (U.S. Naval Research Laboratory (NRL) and Solar Maximum Mission (SMM) / (Lockheed/Mullard Space Science Laboratory (MSSL) / Rutherford Appleton Laboratory (RAL)) spacecraft—obtained several important results on solar flares and active regions. The Bragg crystal spectrometer (BCS) was accepted for flight on Solar-A (Yohkoh) by ISAS in late 1986. The U.K. Science and Engineering Research Council (SERC) support for MSSL and RAL, and U.S. NRL internal funding from its E.O. Hulburt Center for Space Research, were agreed on in January 1987. Instrument heritage was derived from the U.K.-designed curved or bent crystal spectrometer, which was flown on the National Aeronautics and Space Administration (NASA) SMM in February 1980. This configuration was chosen because: The Yohkoh mission plan emphasized solar flare observations with focus on time and spectral but not spatial resolution; Flight heritage existed from the instrument; An instrument with 10 times greater sensitivity than its predecessors could be accommodated on Yohkoh; and A conventional scanning spectrometer would have been massive and complex. 1.2 Attitudes Having pioneered the technique in the 1960s and following SMM, U.K. hardware groups retained substantial interest and expertise in high-resolution solar X-ray spectroscopy. Because Japan's Solar-A looked set to become the world's next major solar physics mission, discussions about U.K. involvement (K. Tanaka/Culhane/Gabriel) began in the early 1980s. The U.K. X-ray astronomy community had already engaged in a highly successful collaboration with ISAS in the Ginga mission. In Japan, although there was interest in X-ray spectroscopy following the success of Hinotori, there was uncertainty about the capability of the curved crystal technique, particularly as to its sensitivity. Given in addition the modest spacecraft resource available on Solar-A, the Japanese community took some time to reach a consensus for acceptance of the BCS.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT In the United States, the NRL and National Institute of Standards and Technology (NIST) groups possessed unrivaled skills and facilities for bending, mounting, and calibrating curved crystals. The NRL group in particular wished to follow up its very successful solar flare work undertaken with P78-1. Although U.K. and U.S. groups were involved at the hardware phase of Yohkoh, the wide availability of the Yohkoh shared software has allowed European groups to participate significantly in the data analysis phase of the mission. Groups from the Czech Republic, France, Germany, Italy, and Russia have been involved in Yohkoh data analysis. Many European groups have used the Yohkoh Data Archive Centre at MSSL. 1.3 Politics The main parties for implementation of the Yohkoh mission were ISAS and NASA. In the United Kingdom the MSSL group, supported by RAL, proposed a bilateral involvement with Japan and secured U.K. funding subject to Japanese acceptance of the BCS for flight on Yohkoh. The hardware groups proposed on behalf of the U.K. solar community, although this was comparatively small at the time. With the limited U.K. resources available and the need to access the world-leading curved crystal skills at NIST, involvement of the United States was important. Flexible and imaginative use of the NASA Explorer budget line had enabled major NASA participation in provision of the soft X-ray telescope (SXT). Given the required level of U.S. funding for SXT, support for other instruments was not possible. With the agreement of the superintendent of the NRL Space Science Division (Herb Gursky), internal funds were used to procure the mounted bent crystals and to fabricate the instrument structure. Following acceptance of the BCS by ISAS, a Japanese principal investigator (Professor E. Hiei) and an instrument scientist (Dr. T. Watanabe) assumed responsibility for the BCS program in Japan. 2.0 Cooperation 2.1 General Implementation Following the ISAS/U.K. collaboration for Ginga, a generic, or umbrella, agreement between SERC (later the Particle Physics and Astronomy Research Council (PPARC)) and the Ministry of Education, Science, Sports, and Culture (Monbusho) was already in place. A specific subagreement between ISAS and MSSL enabled the Yohkoh collaboration for the BCS. A separate agreement between MSSL and NRL enabled the U.S. participation. Features of the collaboration, which were new for U.K. participants, included: The existence of a Solar-A mission science team. Although informal and evolving, U.K. (and U.S.) participants became members and accepted rights, duties, and responsibilities. A language barrier, which made the role of the Japanese instrument scientist mission critical. By comparison with European Space Agency and NASA programs, a degree of flexibility in interface definition, which may have been related to the scale of the Solar-A program. A very different software and mission operations philosophy, with operations conducted by the participating scientists. A consequent Japanese sensitivity to “data rights” issues given that it was unreasonable to expect practicing solar scientists to be disadvantaged by the need to operate the mission.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 2.2 Software and Operations Implementation Prior to the launch of Yohkoh, the approaches to data analysis software differed significantly among Japanese, U.S., and U.K. participants. By virtue of the investment and effort particularly by the Lockheed group, the mission has developed a software structure (SolarSoft) that has been extended to subsequent missions (e.g., Solar and Heliospheric Observatory (SOHO), Transition Region and Coronal Explorer (TRACE)). Software is maintained at sites in the U.S. (Lockheed and NASA's Goddard Space Flight Center) and in the U.K. (MSSL), as well as at ISAS. Expertise in the use of the Yohkoh instruments is also available at these sites. The “mission science” approach to Yohkoh data exploitation has allowed the broadly based development of appropriate analysis software and its resulting wide availability. The Japanese approach to operations, which entails mission science team members sharing operational duties on a rotational basis, was at first unfamiliar to U.K. participants. Although language and cultural differences were initially a problem, these difficulties have been largely overcome with, as in the case of the approaches to software development, a willingness on the part of all participants to take a flexible and responsive approach. The PPARC continues to support mission operations in Japan. It is arguably the case that mission operations, when conducted by dedicated, competent, and committed people, are much less likely to lead to operational errors, or in worst case, loss of mission. Yohkoh experience in this regard compares favorably with that of other missions. 2.3 Rights and Benefits The need for Yohkoh science team members and associates to devote substantial time to operations generates a requirement that these individuals should retain a meaningful opportunity to achieve and to participate in major scientific discoveries. This in turn has led to the reservation of rights to current data for a period of 1 year for the Yohkoh science team members. The smaller size of the U.K. community and the ability to explain the situation to them meant that the data rights issue posed less difficulty than in the United States. The richness of the mission data has meant in practice that few priority disputes have occurred. Instead there have been sufficient outstanding results for all participants to feel amply rewarded. The U.K. community in particular has benefited from: Participation in a world-leading mission whose results have revolutionized solar physics; Recognition of the achievements of U.K. participants, which is leading to significant growth in the strength and size of the U.K. community; Strengthened ties with European solar physics groups through joint analysis of Yohkoh data; Use of the data in space weather and other applied programs; and Exploitation of Yohkoh in the area of public understanding of science, or public outreach. 3.0 Lessons Learned Highly effective collaboration can be achieved among Japanese, U.S., and European scientists in executing major missions in solar physics.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT All participants have learned the virtues (and difficulties) of each other's methods and approaches, in such areas as software methodology, operations, mission optimization, and selection procedures. The benefits of the science team approach, previously applied by U.S. and U.K. groups to a single instrument on SMM, can be achieved for an entire mission. The U.K. solar physics community has learned better to work coherently and has been significantly strengthened as a result. A new software base (SolarSoft) has been developed that is being applied to a growing range of solar physics space missions and ground-based data sets. Different schools of solar physics have been engaged with each other to mutual benefit. 4.0 Issues for the Future Can the Yohkoh hardware, software, and operations methodologies be applied effectively to Solar-B? Can we learn from the TRACE mission experience on operations in Sun-synchronous orbit? Can the science team approach remain effective in the more complex Solar-B mission with its greater diversity of instruments?

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT COMMENTS ON THE SOLAR-A (YOHKOH) MISSION H.S. Hudson University of California, San Diego and Solar Physics Research Corporation 1.0 Introduction / Mission Profile The Solar-A spacecraft, which became Yohkoh upon launch, was the second Sun-observing satellite of the Institute of Space and Astronautical Science (ISAS), following Hinotori (1981). The participants in Solar-A were ISAS and other Japanese institutions under the ISAS lead, plus various U.S. and U.K. institutions under the management of the National Aeronautics and Space Administration (NASA) and Science and Engineering Research Council (later the Particle Physics and Astronomy Research Council, PPARC). The fundamental objective of Solar-A was the study of solar flares at high energies—these were the Hinotori target as well—and the mission continues successfully at present, following an August 1991 launch. The author of these notes acted as a go-between during the original planning of the U.S. participation in Solar-A, aided NASA in the selection of its team, and since launch has acted as the senior resident U.S. representative for mission operations and science. Because the notes below are verbose, the key points are summarized as bullets first: Solar-A was launched 8 years ago, became Yohkoh, and continues to provide widely used data. Current research notes are maintained on a World-Wide Web periodical, found at <www.solar.isas.ac.jp/sxt_co/index.html>. From the U.S. point of view, Yohkoh has been a success, both scientifically and with regard to popular impact. The major shortcoming on the U.S. side was probably the lack of a guest investigator program, from the point of view of both funding and perception. 1.1 Hardware and Software Yohkoh carries four instruments: (1) a hard X-ray telescope (HXT) (an imager based on shadow formation, a development of Minoru Oda 's1 original “modulation collimator”); (2) a grazing-incidence soft X-ray telescope (SXT) in the heritage of many rocket observations and the Skylab Apollo Telescope Mount; (3) a Bragg crystal spectrometer (BCS) for high-resolution soft X-ray emission-line spectroscopy; and (4) an X-ray/gamma-ray counter instrument. All the instruments worked properly (and are still working). The data and an extensive shared software environment are broadly distributed; the software system, with heritage from the Solar Maximum Mission, has further evolved to become SolarSoft, a large IDL-based software environment widely used in other space missions. 1.2 Operations and Science The Yohkoh operations, based at ISAS, involve a multinational team, but with the principal burden falling on the Japanese community of solar scientists. NASA provides extensive downlink telemetry coverage via Wallops and Deep Space Network tracking stations, but uplink is solely through ISAS's Kagoshima Space Center in Kyushu. The Yohkoh data continue to be valuable, in spite of the 1   Oda was one of the pioneers of X-ray astronomy and returned from the Massachusetts Institute of Technology to foster this new branch of astronomy in Japan. He later became a director general of ISAS.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT new missions (Solar and Heliospheric Observatory (SOHO) and Transition Region and Coronal Explorer (TRACE)), because of the complementarity of the data sets. In the tradition that has developed in solar astronomy, the data are widely shared among research workers using these instruments (and ground-based observatories), now aided by an extensive network of Web resources. For those interested, a weekly Web journal written by the SXT2 observers routinely documents the science operations (for example, many of the weekly pages describe aspects of the coronal mass ejection-predicting sigmoid patterns discovered with Yohkoh observations). A chronological list of these pages is available online at <www.solar.isas.ac.jp/sxt_co/index.html>. 2.0 Historical Background 2.1 Planning The initial impetus for Solar-A came from Japan, stimulated by the strength of the X-ray astronomy group at ISAS, as well as the success of Hinotori in 1981. Two communities of solar researchers in Japan wished to continue observations from space, essentially the community derived from the cosmic-ray side and with roots in classical solar astronomy. Much of the heritage of X-ray and gamma-ray astronomy rests on the cosmic-ray community (for example, the founding fathers of X-ray astronomy in the United States, including Minoru Oda and Bruno Rossi, came from schools of cosmic-ray research). In terms of spacecraft design, there was a clear distinction between these two communities. One group preferred the old technology of spin-stabilized spacecraft (all that ISAS had done prior to Yohkoh, including Hinotori), and the other preferred three-axis stabilization to permit long, steady telescope exposures. The astronomers won this debate, and Yohkoh was on its way, but a flare-oriented mission really required a state-of-the-art hard X-ray or gamma-ray imager. This instrument had to overcome the handicap of a nonrotating spacecraft, and a Japanese team led by Keizo Kai (National Astronomical Observatory of Japan (NAOJ)), and including T. Kosugi (NAOJ), K. Makishima (University of Tokyo), and T. Murakami (ISAS) accomplished this difficult task. A similar community existed in the United States, and it is interesting to note that the recent Small Explorer selection of the high-energy solar spectroscopic imager (HESSI) essentially changed to the other branch of flare research following Skylab and subsequent U.S. solar missions, all of which have had three-axis stabilization. HESSI, however, aims at high-resolution hard X-ray and gamma-ray imaging spectroscopy, using an inexpensive spin-stabilized satellite not so different conceptually from Hinotori. The United States was presented with the Japanese decision for a three-axis spacecraft and by an almost effortless consensus decided that an SXT based on grazing-incidence mirror technology and a charge-coupled device (CCD) detector would be an ideal U.S. contribution. The results from Skylab, the Orbiting Solar Observatory series of spacecraft, and many rocket flights strongly pointed in this direction. The U.S. research groups had thus for many years pursued this kind of observation, but with limited technology. On Skylab, for example, film was the image readout device. To do coronal imaging in its natural soft X-ray emission range with a CCD detector had great appeal. A CCD is linear and very sensitive, therefore, a satellite-borne SXT could basically add the time dimension to the two spatial dimensions shown off by the earlier observations. The major Japanese instrument on Yohkoh, therefore, became the hard X-ray imager, which operated without the advantage of spin stabilization. The HXT became successful as the third (following the Solar Maximum Mission and Hinotori) solar hard X-ray imager, greatly extending the energy range and sensitivity of the previous observations. 2   The hardware, camera software, and data analysis software for the soft X-ray telescope were prepared by Lockheed Palo Alto Research Laboratory, with Loren Acton (now at Montana State University) as the principal investigator.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 2.2 Motivation Yohkoh was relatively easy to promote as a cooperative program. The X-ray astronomy group at ISAS, led originally by Minoru Oda and later by Yasuo Tanaka, had achieved independent success with Japanese satellites and instrumentation. However, it was clear that to do the best science required international cooperation. The X-ray astronomy group, the ISAS patron of Yohkoh, therefore, had a strong interest in pursuing U.S. collaborations. From the U.S. point of view (here, C. Pellerin, at NASA headquarters, was a key player), the Japanese once-per-year launch schedule made them excellent partners for small missions of a type that NASA was drifting away from in favor of gigantism (the “Great Observatories ” program was one example). New technology for observations could be developed and both partners could benefit from it, with the advantage of small missions on relatively short and fixed ISAS-type schedules. Furthermore, Yohkoh would be cheap and could be administered under the line-item Explorer program funding. Thus Yohkoh became a favorite at NASA as well as ISAS, and its success led to further successful collaborations on Asuka (Astro-D) and now Astro-E; this series of missions seems to have confirmed the wisdom of the program encouraged by Pellerin and Tanaka. More recent and near-future ISAS astronomy missions, notably Haruka (radio) and Astro-F (infrared), do not have non-Japanese hardware contributions. 2.3 Political Mechanisms The ISAS and NASA administrative systems differ radically in terms of the selection process. NASA required an announcement of opportunity (AO) competition for its contribution to Yohkoh. David Bohlin of NASA HQ developed the AO and oversaw the program development. In the case of Solar-A, the mismatch of national styles was really no problem; a science working group (convened by D. Bohlin and chaired by H. Hudson) discussed the science and rather easily concluded that a grazing-incidence SXT must happen. The AO therefore could more or less focus on this item, the Japanese preference anyway, as endorsed by the U.S. working group, and the AO could have a fairly sharp definition of the scientific investigation. In response to the narrowly defined AO for U.S. participation in Solar-A, there were three proposals; all were good but involved interestingly different technologies. The system had worked admirably! Better yet, the SXT was then built and is still working well. 2.4 The U.K. Involvement At an early stage in the Solar-A concept development, the inclusion of a Bragg crystal X-ray spectrometer looked possible, as long as it was minor from the point of view of spacecraft resources and did not tap NASA funding. This would fill a gap in the observations, because SXT could only coarsely characterize flare plasma conditions via its broadband filters. The inclusion of spectroscopy of X-ray emission lines would then parallel the spectroscopy of gamma-ray emission lines, already on board Solar-A in the form of BGO (bismuth germanate) scintillation counters. A consortium, led by L. Culhane of Mullard Space Science Laboratory (MSSL), that consisted of Naval Research Laboratory and National Institute of Standards and Technology programs in the United States and MSSL and Rutherford Appleton Laboratory in the United Kingdom, could build this experiment at no cost to NASA, so it was included. With this experiment, the Solar-A payload consisted of two spectrometers and two imagers.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT 3.0 Cooperation 3.1 Administration On the U.S. side, Marshall Space Flight Center (MSFC) (John Owens) provided low-key but technically effective management. As a result of this good experience, perhaps in spite of the general NASA desire to focus space science at other centers, MSFC has again been given the lead role for U.S. involvement in Solar-B. The partners in Solar-A brought different team structures to the experiment. For example, the acronym “PI” in ISAS jargon refers to “physical instrument,” that is, the flight hardware, rather than “principal investigator.” In addition, the ISAS “principal investigator” role differs strikingly from the NASA one anyway; each Solar-A instrument had a Japanese principal investigator, but these individuals did not necessarily do detailed scientific or technical work, and the more effective team management was at a lower level of seniority. On the U.S. side, a NASA experiment team has co-investigators with carefully defined rights and responsibilities; at ISAS no such legalistic organization exists, and in fact the entire community has a right to participate because of ISAS's unique status in Japanese space research. 3.2 Communication Problems: Shared Software In the Yohkoh program, as mentioned, a common data environment for all the instruments was agreed on at the outset. For the SXT and BCS3 (with heavy foreign involvement) this worked fine, but for the HXT and wideband spectrometer (WBS)4 it did not work so well. The Japanese groups tended to prefer to work with FORTRAN and mainframe computer implementations and were not able to contribute much directly to what became SolarSoft. For HXT this did not present much of a problem; the data were so interesting and important that foreign users provided the SolarSoft structure for data analysis, by adapting the key Japanese FORTRAN developments. This kind of problem of course is not unique either to Yohkoh or to Japan. SOHO did not initially adopt a shared software environment as a project, and at present—even though SolarSoft is an available standard—data from several of the instruments cannot be handled efficiently except with essentially proprietary software. 3.3 Communication Problems: Data Rights One of the knottiest communication problems had to do with data rights. The Japanese and American positions seemed to differ diametrically, especially at the agency level, and these differences resulted in a long negotiation. In the end, the policy embodied in the U.S. AO required the current year's worth of data to be reserved for Yohkoh team members and their collaborators and, following the 1-year proprietary interval, to be in the public domain. This policy has continued to the present. The free use of images for educational and technical purposes (e.g., forecasting) was discussed and eventually approved. A certain degree of community confusion became a by-product of the protracted (and probably overinterpreted) discussion of data rights. Some U.S. researchers developed the impression that Yohkoh data were to be closely held by the investigators, because of Japanese pressure (“gaiatsu” in reverse?). The lack of a guest investigator program probably exacerbated this feeling. In fact, the broad circulation of data analysis software and the wise decision to archive essentially raw data rather than “data products” 3   The BCS observes selected narrow spectral bands in the regions of strong soft X-ray emission lines of S XV, Ca XIX, Fe XXV, and Fe XXVI. L. Culhane of MSSL is the principal investigator. 4   The WBS is an array of proportional counters and scintillation counters for broadband X-ray and gamma ray spectroscopy. Masato Yoshimori of Rikkyo University is the principal investigator.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT resulted in a rather flexible access to the data. Moreover, the Sun cooperated by producing more than enough remarkable objectives for study, and little hard competition for results developed in practice. 3.4 Resolution of the Data-Rights Issue: Who Got What? Within the 1-year exclusion rule, the Yohkoh data have been broadly distributed from ISAS, from the Solar Data Analysis Center at NASA Goddard Space Flight Center, and from the European center at MSSL (United Kingdom). The Yohkoh database-style raw data accompanied by full analysis software, which embodies the instrument calibrations, has worked well and provides a model for later missions. The software environment became SolarSoft and now also embraces various ground-based data sets. The result has been that Yohkoh data users in relatively obscure locations have been able to make substantial contributions. Between the main partners, Japan and the United States, which side has been obtaining most of the best scientific results? The answer seems to be that both sides are doing Yohkoh science quite well. The felicitous lack of competitive pressure and the friction that might have gone with it may reflect the different styles of the two communities. The major early phenomenological discoveries of Yohkoh —one could list the soft X-ray jets, the hot cusp sources, the nonmagnetostatic nature of active regions, the “loop-top” hard X-ray sources—were mainly announced by the Japanese side. That this transpired may have resulted partly from the 1-year exclusionary rule, but also partly from the fact that the distribution of databases and software tools, and ISAS Internet access, really did take some start-up time to become efficient. The Japanese have also led the way in applying Yohkoh data to the refinement of traditional solar problem areas, such as the magnetohydrodynamic modeling of magnetic reconnection in solar flares. Major non-Japanese science results, on the other hand, may have tended to be in areas not well known in Japan, such as the study of X-ray counterparts of meter-wave coronal phenomena and coronal mass ejections, various nonflare applications of the soft X-ray images, and theoretical interpretation of some of the discoveries. In summary, the Yohkoh experience clearly shows the value of prompt dissemination of data and software, rather than any policy of private access. 3.5 What the United States Did Wrong The extensive successes of the mission might suggest that very little went wrong. However: During the hardware development for SXT there was a definite mismatch between the engineering styles of ISAS and NASA. To me this was most obvious in the area of CCD camera development, the responsibility of the Jet Propulsion Laboratory. There were many agonizing difficulties, with communication problems, schedule and cost impacts, and hard feelings. Although the successful Lockheed proposal for SXT was based on the concept that flightworthy CCDs existed, in fact they did not, and NASA had to pay for a special production run at Texas Instruments (Japan) late in the program. Quite near launch, a NASA administrative blunder almost caused the unspeakable horror of a launch slip. This was the result of an unnecessary “end-to-end” focus test (the Hubble focus problem had just been discovered) within months before launch. The test damaged the flight CCD and a backup had to be substituted at the last minute. An important component of SXT, the aperture entrance filter, ruptured about 14 months into the mission (the exact reason for this event is not currently known). This problem made it impossible to derive adequate coalignment information for SXT images from SXT data. Luckily, sensors on the HXT could be used; these are now decaying but still work almost well enough.

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U.S.-EUROPEAN-JAPANESE WORKSHOP ON SPACE COOPERATION: SUMMARY REPORT There was no independently funded guest investigator program for SXT. As mentioned elsewhere in these notes, this situation not only reduced the data analysis effort directly because of lack of funding, but also probably contributed to the wrong impression regarding data policy. 3.6 How the United States Has Benefited from Yohkoh and How Science Is Benefiting in General It is difficult now to attend a solar session of any major meeting, on any continent, and not see Yohkoh data being used. There are two aspects to this. First, the Yohkoh movie of the soft X-ray corona, some 50 images per day, nicely characterizes the solar origins of space weather. The movie essentially provides maps to the origins of the Geostationary Operational Environmental Satellite (GOES) soft X-ray photometry, provided by the National Oceanic and Atmospheric Administration, long used to characterize the time development of coronal magnetic activity. Second, the movie of routine images itself, but even more so the special data sets covering flares and other activity, form the basis for a great deal of unique Yohkoh research. In the sense that science is fundamentally international and no one nation's property, the solar community worldwide benefits a great deal from the existence of the Yohkoh data. However, national programs exist at least partly because of national interests, so it makes sense to inquire about narrow U.S. benefits. One main measure of the benefit of a “big science” program, of which Yohkoh represents a small example, might be the training of graduate students, especially in terms of their participation in the instrumentation. Because the lead U.S. institutions involved in Yohkoh are large commercial or public laboratories, students were not involved to a great extent in the instrumentation. However the SXT team made a special point to incorporate universities (specifically Stanford, Berkeley, and Hawaii, and now Montana State) directly into the project, so that observational Ph.D. theses based on Yohkoh data or related theory did happen. Probably as many Yohkoh-based Ph.D. theses have been written outside Japan as inside, including several in Europe from groups not connected in any formal way with the instrument groups. A separate plus on the U.S. ledger, of course, has to do with the successful development of high-technology instrumentation mainly from U.S. sources. This contributes to the development of optics, detectors, and software technology, for example. 4.0 What Lessons Were Learned, and How Can We Apply Them? The era of a simple U.S.-Japanese collaboration on a small space mission seems to have ended, because ISAS no longer schedules small missions. This is a flip-flop in comparison with the U.S. programs, which, starting about the time Yohkoh began development, saw a renewal of interest in flexible small flight opportunities. So the cultures of space science in the two countries seem to have traded places to a certain extent. This is also reflected in the speed of development of the programs, with the U.S. space programs now happening on astonishingly short development schedules (e.g., TRIANA, HESSI, or many other Small Explorers (SMEXs) and University Explorers (UNEXs)). For larger missions, such as Solar-B (in phase A following an AO and selection on the U.S. side), the Yohkoh experience may not play much of a role. In comparison the Solar-B payload is extremely complex, and the science that it addresses equally so. How do two quite different science communities plan such a mission together? The basic mechanism regulating the growth of science knowledge, the open literature, moves so ponderously and with such apparent confusion and misunderstanding, that it cannot serve as a good basis for decision making involving a broad community. Thus we have science working groups to define future missions. In the case of Solar-A the next step was pretty clear scientifically; for Solar-B or any other major mission, other forces come into play. Thus the main legacy of Yohkoh may simply be the goodwill of the groups participating in it and the enhanced communications resulting from working within the same program so closely.