Thruster trouble for Hayabusa
Posted by Emily Lakdawalla
29-11-2005 8:59 CST
Hayabusa has been riding an incredible wave of luck lately, resulting in the dramatic success of the sample grab last week. But it looks as though Hayabusa's luck may be running out. The spacecraft is currently in safe mode under spin stabilization, and JAXA controllers are having trouble regaining control. This information is from a press conference that was held today, as reported in the weblog of Shin-Ya Matsuura and translated by visitor "nao". Here are the high points (follow the link for much more detail):
- Hayabusa has two redundant thruster systems, "A" and "B."
- Following the touchdown on November 26, at 9 a.m. JST (00:00 Nov 26 UTC), Hayabusa ascended under thruster system B. At that time, a leak occurred in system B.
- To cope with the leak, the valves in both A and B systems were closed, and Hayabusa was commanded to enter safe mode.
- In safe mode, Hayabusa cannot maintain 3-axis stabilization; it goes into spin stabilization. Under spin stabilization, it is not possible to use the spacecraft's directional high-gain antenna for communications. Even the medium-gain antenna is difficult to use, as the 18-degree cone of its reach spins in and out of contact with Earth.
- On the 26th and 27th, they tried to recover from safe mode by command from NASA's DSN and later Usuda. The recovery involved attempting to return to 3-axis stabilization using thruster system A (the one without the leak). However, the system A thrusters failed to generate enough force, so they failed to regain 3-axis control.
- The exact problem with system A remains "a mystery." Jun'ichiro Kawaguchi reported that there was still enough fuel, and that the fuel system is under the proper pressure. There are apparently anomalous temperatures in part of the fuel system. Kawaguchi speculated that some possible explanations could include an obstruction in the valve, or that a pipe may be frozen. However, he was also searching for theories that could explain the problems that simultaneously cropped up in systems A and B.
- An attempt to contact Hayabusa on November 28 failed.
- After 10:00 am JST on November 29, a communication session was successful, but control has still not been re-established. Kawaguchi said it may take some time to recover.
- They are up against a deadline of "early December" at which they must attempt to leave Itokawa and return to Earth. But in order to do that, they must have the spacecraft under control. So Kawaguchi was focused on recovery first, saying (again, as reported by Matsuura and translated by neo): "Without attitude control, the jet direction of the ion engines cannot be determined and it cannot enter the return phase. If the vehicle cannot leave Itokawa in early December, we have to consider alternative ways. Although there are several alternatives, we can tell nothing without understanding the current condition."
Recovery of Hayabusa will depend upon help from NASA's Deep Space Network, and Kawaguchi was talking about needing help from the biggest of NASA's dishes, the 70-meter stations. These are generally used for communications with the terribly distant Voyagers and for the massive amounts of data coming in from Cassini. I know that Cassini planners do develop contingencies for how to deal with lost communications sessions, planning backup sessions so that they still have a chance to transmit critical data from Saturn if they lose one of their DSN times. Still, Hayabusa could play a little havoc with Cassini over the next couple of weeks.
I also found this one other question-and-answer from the press conference to be notable:
[reporter] Jiji Tsushin: Did you get congratulations for success in landing from NASA?
Kawaguchi: We get many from all of the world. But we are now confused about what to answer under such situation.
They have had so much success under such difficult conditions with this mission. It would be tragic if they couldn't bring Hayabusa home -- tragic for the mission, but more than that, tragic because the loss of Hayabusa would mean that JAXA would get tremendous amounts of press about failure despite their many achievements with this mission. I am hoping fervently for Hayabusa's recovery and safe return!
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