Comunicato ufficiale JAXA per Hayabusa rediviva

Public Affairs Department
Japan Aerospace Exploration Agency (JAXA)
Marunouchi Kitaguchi Building
1-6-5, Marunouchi, Chiyoda-ku, Tokyo 100-8260

March 7, 2006

Current Status of Hayabusa Spacecraft – Communication and Operation

Last November, Hayabusa suffered from a serious fuel leak immediately
following its successful second touching down to the surface of
Itokawa, a near Earth asteroid. Since the chemical engines were not
available, the strong attitude disturbance occurred on December 8th
caused the communication lost since then. According to the analysis,
the chance of having the spacecraft communication resumed was found 60
to 70 percent high during a year ahead, while the spacecraft is
captured well within the ground station’s antenna beam width. JAXA
decided to take an alternative flight plan that makes Hayabusa return
in June of 2010, three years behind the nominal schedule, assuming the
spacecraft starts driving its ion engines from early 2007. In this
context, the Hayabusa project team had started the rescue operation
from the middle of December, 2005. (JAXA Press Release on December
14th, 2005)

Resumption History

On January 23rd of 2006, the beacon, un-modulated radio signal was
received during while the piecewise ‘uplink sweep’ plus ‘commands
transmission’ operation. The spin axis attitude shifted almost 90
degrees and the spacecraft was found with its high gain antenna axis
offset about 70 degrees from the Earth direction, when discovered. In
addition, the spacecraft spin rate was direct and about 1 degree per
second on December 8th. However, when the signal was recaptured, the
spin got retrograde at the speed of about 7 degrees per second.
The communication, especially uplink commanding, first did not go
through easily. But from January 26th, the autonomy function aboard
Hayabusa started responding to the inquiries from the ground, and the
spacecraft status had been revealed one by one till early February.
The information obtained indicated the Hayabusa spacecraft power was
completely lost once, after the spacecraft lost its attitude, and
short circuitry phenomena are observed for the Li-ion battery cells
aboard. This means the battery may not be used any more. While the
chemical fuel was lost last December, this time the oxidizer seemed
lost completely, as the instrumentation reads zero pressure. The Xenon
gas amount aboard remains unchanged.

There was anticipated another attitude disturbance, which may make the
communication lost again. And on February 6th, the Hayabusa project
team decided to start performing the Rhumb-Line attitude control using
Xe gas available aboard. A new software was uploaded on the day. The
control was successfully done and the spin axis has shifted about 2
degrees per day toward the Sun direction that is almost similar to the
Earth direction. (Fig. 1) On March 4th, the antenna between the Sun
direction and the Hayabusa’s antenna axis was reduced down to 14
degrees and the maneuver was successful. (Fig. 2, Fig. 3, Fig. 4)
The communication gradually has been improved and the telemetry data
were received via Low Gain Antenna on February 25th with the speed of
8 bps. And on March 1st, a radio range measurement was correctly
obtained. On March 4th, the telemetry data were received with 32 bps
via Medium Gain Antenna (MGA)-A.

Based on those range data obtained along with the Doppler measurement,
the orbit was determined / estimated successfully after three months
hiatus. Hayabusa currently is at 13,000 km leading the Itokawa toward
its revolution direction from it. And Hayabusa flies about 3 meters
per second with respect to the Itokawa. Hayabusa is at 190 million
kilometers from the Sun, and is at 330 million kilometers from the
Earth. (Fig. 5, Fig. 6)

Flight Plan for the Hayabusa and Chance of Earth Return

There is still some possibility that substantial amount of fuel and
oxidizer are left leaked out on the spacecraft. And a special Baking
operation is inevitable to exclude any gas potential by raising the
spacecraft temperature higher via the heaters aboard, after the
completion of the orbit determination as well as the emergency
operation software installation uploaded. The Baking operation,
however, may cause another fuel gas eruption risk that may easily
tumble the spacecraft again, and the operation needs to be done very
carefully. It may take a few months. A similar Baking operation will
be performed next for the sample recovery capsule, and the capsule rid
will be closed with the sample collection catcher pushed into it.
During the cruise back to the Earth, the ion engines will be operated
and the temperature goes higher. In order that any gas should be baked
out at any operation environment during the cruise, a further Baking
operation will follow with the appropriate number of ion engines
turned on. At highest, three ion engines will be driven at the same
time. This operation takes several months. The cruise with the ion
engines on starts early 2007, so that the spacecraft should go back to
the Earth in June of 2010.

The Xenon gas remained aboard is estimated about 42 to 44 kg. As long
as no further gas eruption occurs, the existing gas amount suffices
the cruise flight ahead to the Earth. Note still ion engines, star
tracker, attitude control computer and so on all have not gone through
the functional verification after this gas eruption accident, while
those must have been exposed to extreme low temperature between
December and January.

Public Release on the Resumption

While the radio communication resumed in January, the spacecraft
status was under a very serious/fragile/subtle condition with no
information that accounts the public for the status. The spacecraft
has been exposed to the sudden gas eruption risk so far. At the end
of February toward early March, the status was obtained and the
information was gathered a lot these days. And today, the public
release was issued with not only the attitude but the orbit
information as well.

For those who have anticipated so far, understanding the spacecraft
status would be appreciated and the project team would like to
apologize for little public information provided.

Diagrams are available at

Fig. 1 Attitude Reorientation
Fig. 2 Precise Attitude Determined with Sun Sensor
Fig. 3 Attitude Control History
Fig. 4 Attitude Direction in which no communication on Jan. 20th but
identified on Jan. 23rd.
Red circle shows the spin direction area estimated for Jan.
23rd acquisition.
Fig. 5 Trajectory in Inertial Frame
Fig. 6 Trajectory in Sun-Earth Line Fixed Frame