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2005.12.08

Bullets were not engaged?

JAXA/ISAS held a press briefing on the 7th on the status of Hayabusa. A space journalist Shin-ya Matsuura's blog records the statements by JAXA, followed by the Q&A session. English translation is available on his blog.

Current situation is very complex and confusing.

Remember that Hayabusa's high gain antenna is fixed at the top of the spacecraft. It needs to be in the 3-axis attitude control with a reaction wheel and thrusters to be in contact with the Earth. Currently JAXA is trying to understand the status of the thruster systems, so they cannot download the entire data to analyze what happened on the 25th, the second touch down attempt to Itokawa. Communication with the medium gain antenna is intermittent due to inappropriate orientation of the spin. The low gain antenna is the only reliable channel until it regains the attitude control, but it carries only 8 bps of data rates. The angle of the spin axis is slowly approaching to nominal and they get 256 bps every minute in 6 minutes with the medium gain antenna.

On the 27th JAXA noticed low thrust, the spacecraft was coming back to Itokawa. So they issued a series of commands to resume the spin-oriented control and to move away from the asteroid. They are now speculating that the spacecraft lost its orientation for some reason, possibly due to one thruster of the pair not working because of the frozen propellant pipe. By analyzing the telemetry obtained today (7th), solar panel lost its power and it caused the battery to become empty.

They also speculates they lost the propellant by about a few kilogram into the interior of the spacecraft. The temperature went down due to the possible vaporization. The leak had been confirmed in the operation on the 26th, to the upper side of the spacecraft. On the 30th they confirmed the downward thrust and the spin velocity was also reduced. They theorize the vaporization of the propellant inside the spacecraft caused these effects.

The power loss on the 27th caused a major confusion. The absolute time data in the data handling unit (DHU) and the partition information of the data recorder (DRAM) are all gone. The downloaded data for the activation of pyrotechnic indicates the projectile for the sampling was not engaged on the 25th. On the other hand they successfully replayed the commands sent from the Earth during the descent to the asteroid. They found a command to disable the system of the projectile engagement was among them. The reason is now being analyzed but they are now 80% confident that the bullets were NOT fired during the touch down maneuver.

The data is difficult to understand. On the 20th, their first attempt of touch down, the spacecraft stayed on the surface of Itokawa for about an hour. However the temperature of the projectile engagement system is higher on the second attempt than the first. This suggests the projectile may have been engaged. It's not consistent. They need imagery data to understand more detail. The partition table was lost, so they are not certain what kind of data they are now looking at. They will try to download all the scientific data before Hayabusa begins its return leg.

On the 2nd of December they tried to restart the chemical thruster system. A small thrust was generated but the full thrust was not achieved. On the 3rd, the angle of the high gain antenna, Sun and Earth became larger, to 30 deg. They started a new software to control the attitude by using Xenon gas of the ion engine. On the 4th they started the new attitude control with Xenon and on the 5th the angle was reduced to 10 to 20 degrees. On the 6th Hayabusa is away from Itokawa by 550 km, and they restarted the only remaining reaction wheel at 1,000 rpm.

They are now planning the return leg of the spacecraft. The journey will start not before the 14th of December. Starting on the 14th or 15th will bring the spacecraft back to Earth in June 2007. A new attitude control scheme with Xeon gas of the ion engine gives some hope on the successful return. However this option requires the operation of the ion engine to take longer. Alternative schedules are to stay in the current orbit for another three or three and a half years. They are trying their best for the return in June 2007, by recovering the thruster system by 14th or 15th.

The trouble of the chemical thruster was narrowed down to malfunctioning latching valves. Hydrazine was leaking. On the 2nd they sent commands to open the latching valves in the systems A and B but they did not function. Either the power system of the valves or electrical circuits are in question.

By courtesy of NASA, they are using 70m DSN for two hours each day until tomorrow (8th). They will ask for 34m parabola for another week.

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