Hayabusa Landed on and Took Off from Itokawa successfully (Forwarded)

Institute of Space and Astronautical Science
Japan Aerospace Exploration Agency
Sagamihara City, Japan

2005/11/24

Hayabusa Landed on and Took Off from Itokawa successfully: Detailed
Analysis Revealed

Hayabusa attempted its first soft-landing on Itokawa for the purpose of
touch down and sample collection on November 20-21, 2005. Below is the
data information with the related advance report on its status.

Hayabusa started descending at 9:00pm on Nov. 19th, 2005 (JST [1200
UTC]) from 1km in altitude. The guidance and navigation during the
process of approach was operated normally, and at 4:33am on Nov. 20th
[1933 UTC Nov. 19], the last approach of vertical descent was commanded
from ground, of which soft-landing was successfully achieved almost on
the designated landing site of the surface. Deviation from the target
point is now under investigation but presumed within a margin of 30cm.
The approaching trajectories in the quasi-inertial coordinate system and
Itokawa-fixed coordinate system are shown in Data-1. Information on the
altitude and its rate during the descent as measured by Doppler data is
shown in Data-2.

The velocity at the time of starting descent was 12cm/sec. At the
altitude 54m at 5:28am [2028 UTC Nov. 19], wire-cutting of target marker
was commanded, after which, at 5:30am [2030 UTC Nov. 19] at altitude
40m, the spacecraft autonomously reduced its own speed by 9cm/sec to
have substantially separated the target marker. It means that Hayabusa's
speed became 3 cm/sec. Separation and freefall of the marker was
confirmed from the image (Data-3) as well as from descending velocity of
the spacecraft at the time of reducing the speed. The marker is presumed
to have landed on southwest (upper right on the image) of MUSES Sea.

Hayabusa then switched its range measurement from Laser Altimeter
(LIDAR) to Laser Range Finder (LRF) at the altitude 35m and moved to
hovering by reducing descending speed to zero at 25m above the surface,
below where Hayabusa, at 5:40am [2040 UTC Nov. 19] at altitude 17m, let
itself to freefall, functioning itself to the attitude control mode
adjustable to the shapes of the asteroid surface. At this point, the
spacecraft autonomously stopped telemetry transmission to the Earth (as
scheduled) to have changed to transmission with beacon mode more
efficient for Doppler measurement by switching to low gain antenna (LGA)
coverable larger area.

Since then, checking of the onboard instruments was not possible on a
real time basis (as scheduled), but as a result of analyzing the data
recorded onboard and sent back to the Earth in the past two days,
Hayabusa seemed to have autonomously judged to abort descending and
attempted emergency ascent because its Fan Beam sensors for obstacle
checking detected some kind of catch-light. Allowable margin is set for
Hayabusa for its attitude control, in the case the spacecraft takes off
the ground by accelerating the velocity on its own. Under such
circumstances, the then spacecraft's attitude was out of the margin,
because of which continuing of safe descent was consequently chosen. As
a result, Hayabusa did not activate its Touch Down Sensor function.

At the timepoint of Nov. 21, Hayabusa was judged not to have landed on
the surface. According to the replayed data, however, it was confirmed
that Hayabusa stayed on Itokawa by keeping contact with the surface for
about 30 minutes after having softly bounced twice before settling. This
can be verified by the data history of LRF and also by attitude control
record (Data-4).

This phenomenon took place during switching interval from Deep Space
Network (DSN) of NASA to Usuda Deep Space Center, because of which the
incident was not detected by ground Doppler measurement. The descending
speed at the time of bouncing twice was 10cm/sec. respectively. Serious
damage to the spacecraft has not been found yet except heating sensor
that may need checking in some part of its instrument.

Hayabusa kept steady contacting with the surface until signaled from
ground to make emergency takeoff at 6:58am (JST [2158 UTC Nov. 19]). The
Touch Down Sensor supposed to function for sampling did not work because
of the reason above stated, for which reason firing of projector was not
implemented in spite of the fact that the spacecraft actually made
landing. The attitude at landing is so presumed that the both bottom
ends of +X axis of sampler horn and either the spacecraft or tip end of
the solar panels was in contact with the surface. Hayabusa became the
world-first spacecraft that took off from the asteroid. Really speaking,
it is the world-first departure from an celestial body except the moon.

After departure from the asteroid by ground command, Hayabusa moved into
safe mode due to the unsteady communication line and the conflict with
onboard controlling and computing priority. The comeback from safety
mode to normal 3-axis control mode needed full two days of Nov. 21 and
22. Owing to this reason, replaying of the data recorded on 20th is
still midway, which means the possibility to reveal much more new
information through further analysis of the data. As of now, the
detailed image of the landing site to know its exact location has not
been processed yet. Hayabusa is now on the way to fly over to the
position to enable landing and sampling sequence again. It's not certain
yet if or not descent operation will be able to carry out from the night
of Nov. 25 (JST). We will announce our schedule in the evening of Nov. 24.

Descending and landing operation will all depend upon availability of
DSN of NASA. We would like to express our sincere gratitude for
cooperation of NASA for tracking networks including backup stations.

[NOTE: Images supporting this release are available at
http://www.isas.jaxa.jp/e/snews/2005...hayabusa.shtml ]