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Original †Original text - http://smatsu.air-nifty.com/lbyd/2007/04/post_ce17.html "The situation is getting even more harder." - JAXA announces Hayabusa's return voyage to Earth. †A press conference about Hayabusa's return mission was held at JAXA Tokyo office on 4:30pm, April 24, 2007 (JST) Attendants: Professor Jun'ichiro Kawaguchi (Project Manager), Prof. Hitoshi Kuninaka (Ion Engine Manager), Associate Professor Makoto Yoshikawa (Project Scientist) Explanation of the state by Project Manager Kawaguchi †We declare the start of Hayabusa's return-to-the-Earth misson on 5:00pm, April 25, 2007 (JST). In addition, we open an archive of Hayabusa's yielded data to the public at 4:30pm today. The situation is getting even more harder. Finally, only one ion engine can be operated at a time. Explanation of the state of ion engines by Professor Kuninaka †
The state of thruster operation Total operation time of the B thruster has reached 9600 hours, and partial decline of performance has been observed. Furthermore, we have observed unstable maneuvers of Hayabusa, due to temperature rise on passing the closest point to the Sun. Drive performances of A and C thrusters are not stable. So far, only the D thruster will be used for acceleration to return. Operation history of each ion thrusters
Designed life of each thrusters is 14000 hours. Explanation using graphs on press release The intended plan was to operate two ion thrusters and a wheel when near to the Sun, and operate one ion engine without using a wheel far from the Sun. However, due to unstable performance of the B thruster, we decided to achieve the return mission by using one engine and a wheel continuously. Explanation of public release of yielded data by Associate Professor Yoshikawa †We publicly release all data yielded from Hayabusa's four sensors. Data are freely accessible. No registration or password required. Please note that every documents are written in English (not in Japanese), as we expect these to be viewed by researchers all over the world. This time we release level 1 data, which are closest to raw data. We will release some calibrated (level 2) data as well, followed by updates in the future. Although Itokawa's shape model consists of highly processed data, we have released the data in response to the numerous requests. The data archive still lacks sufficient documentations (ex. time and condition of yielding), although we regard them mandatory. The released images include every failure-exposures as well. Supplement from Professor Kawaguchi †Precisely speaking, the status is "not impossible to return". The ion engine that can be operated normally is only the D engine. The engine must be operated for several thousand additional hours. The operation time will certainly exceed its designed life. Additionally, data including the image with a target marker is not included in this release. The image is included in the probe operation data, which are not included in the release this time. In the future, we plan to reorganize and release these data for scientific analysis, but currently we don't have enough time. Session for questions and answers †Jiji Press: Does the combination of the wheel and a specific engine have its own advantage? Kuninaka: A combination of the D engine and the wheel is not too bad. The combination hardly make torque around the roll axis. Kyodo Press: What does the voltage of the neutralizer mean? Kuninaka: Neutralizer emits electrons that compensates the electric current from the ion stream. Increased voltage of the neutralizer means increased difficulty to emit electrons. The neutralizers are designed to apply voltages up to 100V. However, higher voltages shorten their life. Designed voltage is 50V. We halted the (B) engine because the voltage will shorten its life. Operating two engines simultaneously increase the temperature and affect the lifetime. Moreover, Hayabusa is not designed to throttling two engines independently. Thus, it is impossible to operate engine B and D simultaneously in optimal throttling for each engines. By operating engines one by one, It is possible to apply optimal conditions for each engines. Asahi Shimbun: Is it possible to return using only the D thruster? And are there possibilities to operate thruster A and C? Kuninaka: There is an orbit to return with only one engine. In ground tests, we performed a operation test up to 20,000 hours. It is difficult to design a return orbit with only engine D operating less than 20,000 hours. However, it is possible to survive more than 20,000 hours because we have not tested more than 20,000 hours on the ground. Kawaguchi: As a project manager, I should say moderately. Talking about the thrusters, though they were designed with 14,000hours lifetime, some are showing lower performances than expected before 10,000hours of operation. So, I think the operation over 14,000 to 20,000 hours are extra. And the wheel may also break down. In fact, two out of three wheels have been broken. A reporter: Will the date to return can be changed? And I heard that the rotation speed of the wheel will be decreased. Is it possible to return without using the Z-axis wheel? Kuninaka: Now we operate the wheel in 3,500rpm. Nominal speed is around 4,000rpm. We will slow the speed until about 1,800rpm gradually, because only one ion engine is operated and it makes smaller disturbance. Kawaguchi: Today's conference is to report how much trouble we
have. It is my point. Not to report a new start on the voyage.
Asahi Simbun: Which does the situation seem like "red-" or "yellow-signal"? Kawaguchi: It is hard to say quantitatively. If either the ion engine or the wheel breaks down, then it is hard to return. On early April, the trouble was only about the wheels. So, now we have increased amount of worries. I can say just "it is not definitely impossible to return". Jiji Press: How fine images have you yielded during the touch down? Yoshikawa: So far, distance information is not added to public data. Images during touch-down were taken from approximately 60m high. Now we are working to add supplemental information into headers of photo images. Kita (free-lance): If you compare the situation to a game to pile up and pull out blocks, how many blocks can you pull out? Kuninaka: It's a difficult question. If we miss a chance to return in 2010, next chance to return will be in 2013 at the earliest. Additional extension of the flight is quite tough for the mechanism. We have just few blocks remaining. Originally, we design probes not to pull out any blocks. But the reality is like this. Anyway, we still hang in there, and we will. Aoki (free-lance): The public release contains characteristic images that is distinct from the past. Could you explain them? (See the media release) Yoshikawa: Picture #5 is a part of Komaba Crater with rough surface near from Muses Sea. #6 is a magnification of #5 and related to a recent paper by Dr. Miyamoto at the University of Tokyo. #7 is a map of Pencil Holder with rugged surface. Matsuura: How long do the ion engines have to be operated to return in 2010? Kawaguchi: One third of the last three years, that is, 8,000 to 10,000 hours operation of ion engines is necessary. This is the case of one engine operation. It is possible to operate engines in worse condition to save total operation time. Kuninaka: Engines in worse condition can be used up to approximately 1,000 hours. In other words, there is possibility to save 1,000 hours total operation time. Including that, we considering several options. On conversation after the conference †Kawaguchi: This annoucement of the return trip does not mean any drastic changes from tomorrow. It is like a ship crossing the equator. In fact, Hayabusa have been already accelerating. This milestone event was held in response to the requests from the media people. Kawaguchi: I think we cannot be optimistic. I just can say "It is not impossible to return". (Glancing Dr. Kuninaka) However, he doesn't seem to think so. Kuninaka: Dr. Kawaguchi says so, but I think we still have some options in our hand.
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