Status of the Hayabusa
December 7, 2005
Japan Aerospace Exploration Agency
As has been reported, it is estimated that part of a series of
attitude and orbit control commands to restore the Hayabusa from its
safe-hold mode have not gone well, and the functions of its major
systems, including its attitude and communication network, have
significantly deteriorated. However, on Nov. 29, a beacon line through
a low gain antenna was restored.
On Nov. 30, we started a restoration operation by turning on and off
the radio frequency modulation through the autonomous diagnostic
function. Subsequently, on Dec. 1, telemetry data were acquired at 8
bits per second through the low gain antenna, although the line was
weak and often disconnected. According to the data transmitted so far,
the attitude and orbit control commands sent on Nov. 27 did not work
well due to an unknown reason, and either major attitude control
trouble or a large electric power loss seems to have occurred. It is
estimated that the overall power switching systems for many pieces of
onboard equipment were reset as their temperature dropped
substantially due to the evaporation of leaked propellant, and also
because of a serious discharge of electricity from the batteries of
many sets of onboard equipment and systems due to declining power
generation. Details are still under analysis.
On Dec. 2, we tried to restart the chemical engine, but, even though
a small thrust was confirmed, we were not able to restore full-scale
operations. Consequently, the cause of the anomaly on Nov 27 is still
under investigation, and we suspect that one of the causes could be
the malfunction of the chemical engine.
On Dec. 3, we found that the angles between the axis of the onboard
high gain antenna (+Z angle) and the Sun, and also that with the earth,
had increased to 20 to 30 degrees. As an emergency attitude control
method, we decided to adopt a method of jetting out xenon for the ion
engine operation. Accordingly, we immediately started to create the
necessary operation software. As we completed the software on Dec. 4,
we changed the spin speed by xenon jet, and its function was confirmed.
Without delay, we sent an attitude change command through this
As a result, on Dec. 5, the angle between the +Z axis and the sun, and
the earth, recovered to 10 to 20 degrees, and the telemetry data
reception and acquisition speed was restored to the maximum 256 bits
per second through the mid gain antenna.
After that, we found that there was a high possibility that the
projectile (bullet) for sampling had not been discharged on Nov. 26,
as we finally acquired a record of the pyrotechnics control device
for projectile discharging from which we were not able to confirm
data showing a successful discharge. However, it may be because of the
impact of the system power reset; therefore, we are now analyzing the
details including the confirmation of the sequence before and after
the landing on Nov. 26.
As of Dec. 6, the distance between the Hayabusa and the Itokawa is
about 550 kilometers, and that from the earth is about 290 million
kilometers. The explorer is relatively moving from the Itokawa toward
the earth at about 5 kilometers per hour.
We are now engaging in turning on, testing, and verifying onboard
equipment of the Hayabusa one by one to start the ion engine. We
currently plan to shift the attitude control to one using the Z-axis
reaction wheel, and restart the ion engine. The restart is expected to
happen no earlier than the 14th. We are currently rescheduling the
plan for the return trip to earth. We need to study how to relax the
engine operation efficiency. We will do our utmost to solve the
problem with the attitude control (such as the restoration of the
chemical engine), then find a solution for the return trip.
Since Nov. 29, our reports have been limited due to difficulties in
confirming telemetry data. We apologize for any inconvenience.
We will inform you as soon as the ion engine is restarted.
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Japan Aerospace Exploration Agency (JAXA)
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