[meteorite-list] Hayabusa Update - December 14, 2005

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Dec 14 12:09:47 2005
Message-ID: <200512141708.jBEH8CC01963_at_zagami.jpl.nasa.gov>

http://www.isas.jaxa.jp/e/snews/2005/1214.shtml

Status of the Hayabusa
Japan Aerospace Exploration Agency
December 14, 2005

Hayabusa spacecraft currently undergoes the recovery operation to resume
the communication with the ground stations. It was hit by an abrupt
disturbing torque owing to the fuel leak that occurred before, and has
been out of the ground contact since December 9th. The project team has
a good expect to have the spacecraft resume the communication soon.
However, the project is now not so sure to make the spacecraft return to
earth in June of 2007 and has decided to lengthen the flight period for
three years more to have it return to the Earth in June of 2010.

On December 8th, Usuda station observed the sudden shifts of the
range-rate measurements at 4:13 UTC with the corresponding gradual
decrease of signal intensity AGC (Automated Gain Controller) read. The
measurement and the intensity change slowly and are currently estimated
due to the out-gassing effect that derived from the fuel leak-out at the
end of last month. The leak occurred on November 26th and 27th. Since
the beacon signal communication resumed on 29th, the project has made an
effort to exclude the vapor gas of the fuel from the spacecraft. The
project has by now identified the out-gassing has successfully been
performed, as its exponential acceleration decay has shown so far.

On December 8th, the spacecraft was under the resume operation phase for
the chemical propulsion, and was given a slow spin whose period is about
six minutes. From the beginning of December, the project has introduced
the Xenon gas thruster control strategy for emergency, replacing the
chemical propulsion system. But the control capability of it was not
enough strong for the spacecraft to withstand the disturbance on
December 8th. Current estimation says the spacecraft may be in a large
coning motion and that is why the spacecraft has not responded to the
commands sent from the ground station.

The spacecraft has been out of communication since December 9th.
Analysis predicting the attitude property relating to both the Sun and
Earth shows that there will be high possibility counted on for the
resumption of the communication from the ground for several months or
more ahead. However, the spacecraft may have to undergo another long
term baking cycle before it starts the return cruise operation using ion
engines aboard. And it is concluded that the commencement of the return
cruise during December is found difficult. The project has determined
that the return cruise should start from 2007 so that the spacecraft can
return to the Earth in June of 2010, three years later than the original
plan, as long as no immediate resumption tales place very soon.

The spacecraft operation will shift from the normal mode to the rescue
mode for several months to one year long. Long term predict indicates
high probability of having the spacecraft communicated with the ground
station again, with the spacecraft captured well in the beam width of
the Usuda deep space antenna.(See Reference-3)

The spacecraft will take the advantage of Xenon gas attitude control
again after enough length of baking operation. The Xenon gas that
remains is adequate for the return cruise devised by the ion engines
carried by Hayabusa.

The Hayabusa web page will report anything updated, as soon as it
becomes available.


(Supplement) Hayabusa Rescue Operation

Hayabusa spacecraft is designed to allow the spin-stabilization and the
attitude will converge to a certain pure spin around its high gain
antenna axis ultimately. About the current state affected by the
disturbance on December 8th, the attitude is conceived not to meet
either of the Sun and Earth geometry requirement in terms of power and
communication.

Once the coning motion damps, there will be some high probability that
the spacecraft spin attitude satisfies both the power and communication
conditions in several months. A long term predict is given in
Reference-1, which infers the probability is well assured for the
resumption.

There will be little possibility that the spacecraft position is out of
the deep space antenna beam width for at least several months.

The Hayabusa system is designed to be initialized even once the whole
power is down. Actually, on November 29th, the Hayabusa system restarted
as these procedures functioned as prescribed.

There has been come up with a new trajectory synthesis that makes the
spacecraft return to the earth in June of 2010. (Reference-2)
Without immediate communication resumption, the project thinks it should
take this new schedule soon.


(Reference-1)
The figure below shows the attitude area that meet both power and
communication conditions until March of 2007, when the spacecraft is
supposed to restart its return cruise. The chance of acquiring the
spacecraft signal is not low but around 60 to 70 %.

[Image]

Attitude range that meets both power and communication requirements
between December of 2005 and March of 2007


(Reference-2)
An Orbit Synthesis Example for Hayabusa Return starting in 2007

New trajectory (red line) leaving Itokawa vicinity in spring of 2007,
returning to Earth in June of 2010 is shown here. The Xenon gas
consumption meets the current amount that remains. There will be some
strategy needed and left for the operational discussion on how the
attitude is protected against unexpected disturbance.

(Reference-3)
Chance of Communication Resumption

Provided the attitude changed randomly affected by the disturbance
torque, here is shown the chance of having the communication resumed
based on the power availability and communication conditions.
Cumulative probability column P0 shows the chance becomes higher than
60% by the end of 2006. And as P3 shows, the resumption will take place
most probably up to April of 2006 and next from December of 2006.
Received on Wed 14 Dec 2005 12:08:12 PM PST