Top| Outline | Mission | Topics | Archives @@Japanese

Hayabusa on November 20th made a first attempt to touch down slowly to the surface
for collecting surface samples. What follows quickly summarizes the results.

Hayabusa started descent at the distance of about 1 kilometer from Itokawa, at 21:00
JST (12:00 UTC) on November 19th. Approaching, descending and the guidance and
navigation were all performed in order as planned. And having been directed from the
ground at 04:33 JST on November 20th (19:33 UTC on November 19th) for the final
vertical descent, Hayabusa succeeded in making it descend close to the intended area.
Current analysis concluded the guidance accuracy was within 30 meters in terms of the
hovering point. Reference-1 attached shows the trajectory in both semi-inertial and
Itokawa-fixed coordinates. And the altitude and descent rate information are drawn in

When the final vertical descent commenced, the speed was about 12 cm/second.
Hayabusa flight computer commanded the target marker to be released at the altitude
of 54 meters at 05:28 JST (20:28 UTC), followed by the spacecraft deceleration of 9
cm/second at 40m at 0530 JST (20:30 UTC) forcing the marker depart from the
spacecraft. It was confirmed that the marker was actually positioned and placed properly
through both the camera images and the telemetry information, which indicate the
descent speed of the spacecraft. (See Reference-3)Latest estimation says the marker
landed in South-West (Upper-Right in the image) area of the MUSES-Sea. Hayabusa then
switched the Laser altimeter to Laser Range Finder (LRF) at the altitude of about 35
meters and started hovering at the altitude of about 25 meters by canceling the residual
descent velocity. And as scheduled, the spacecraft made a free fall until it reached the
17 meters altitude at 05:40 JST (20:40 UTC), and the Terrain Alignment Control mode
commenced, when the telemetry transmission was terminated and it was taken over by
the beacon-only radio configuration via a wide angle Low Gain Antenna. Since then,
neither instruments information nor house keeping information were obtained in real time
on the ground. However, according to the data reproduced so far, Hayabusa-carried Fan
Beam Sensor (FBS), an obstacle detector, seemed to have received the laser reflection
signal from something around and an emergency ascent command was requested issued
from the Data handling Unit (DHU), the primary flight computer aboard. But at that instance,
the attitude deviation was large and did not meet the emergency ascent burn requirement
and the ascent was cancelled. As a result, the spacecraft decided to continue the
descent as long as no interruption was directed and nothing was commanded from the
ground, while the touching-down trigger including take-off sequence was cancelled at the
same time.

A quick look data after the transition to terrain alignment mode on November 20th did not
conclude any definite evidence of touching-down or landing, since no telemetry data were
available in real time. The data reproduced said that Hayabusa made slow speed bouncing
(touching-downs) twice, followed by the complete landing & staying still for 30 minutes long.
This was confirmed by the LRF read-out and attitude history. (Reference-4) The ground
monitoring on the day could not identify this fact as the operation was switched from DSN
Goldstone station to the JAXA Usuda antenna (UDSC) and no direct real-time telemetry
was available. The touching-down speed at both bouncing, was about 10 cm/second. As of
today, no serious damage was found and reported as for the instruments. However, there
are found some anomalous measurement at a few instruments such as the heater
electronics. They are not serious. Hayabusa continued this landing status stably before the
emergency take-off was directed from the ground at 06:58 JST (21:58 UTC). No projectile
was shot, since the FBS detection disabled the triggering sequence as stated above. Landing
attitude seems that sitting on the sampler horn sustained by two corners of the spacecraft
bottom plate or by the tip-ends of the solar array panels. Hayabusa now became the first
spacecraft that has taken off from the extra-terrestrial bodyfs surface.

Hayabusa, unfortunately, fell into a Safe Mode owing to both the control authority fighting and
the radio communication conjunction that happened to take place at that period. It took
whole two Usuda passes to recover it and there are still some data left not reproduced, which
may tell more about the story on November 20th. As of today, actually detailed images and
some other information helping the exact touching-down site identified have not been
reproduced by now. Hayabusa is now en route back for the starting point from which the next
attempt can commence on 25th night (JST). Whether the next trial is will be clarified on 24th
night (JST).

The activity performed was under the collaborative works stipulated in the MOU between the
United States and Japan. This first touching-down and landing relied primarily on the use of
Deep Space Network (DSN) stations of NASA. JAXA herewith expresses its appreciation to
the support provided by NASA.



(Reference-1) Approach and Descent Trajectory to Itokawa

The trajectory taken for the approach and landing on November 20th is depicted below.
Fig. 1a draws it in semi-inertial coordinate in which the Earth direction is downward.
Fig. 1b draws it in the Itokawa-fixed coordinate. Note the trajectory had been synthesized
and updated gradually. However, the actual flight path was quite similar to the original plan.


Fig. 1aPlanned and Actual Descent Path (Semi-Inertial Coordinate)

Fig. 1bPlanned and Actual Descent Path (Itokawa-fixed Coordinate)


Fig. 1c corresponding to Fig. 1a shows the spacecraft position estimated based on the
terrain landmarks along with the trajectory synthesized adaptively. This proves the
guidance and navigation were correctly and accurately conducted.


Fig. 1c An Outline of Guidance and Navigation (Semi-Inertial Coordinate)


This landmark tracking/position estimation technique performed and supporting on the
ground has less accuracy while Hayabusa is in a distance. However, as this plot shows,
the accuracy is well assured when the distance becomes close within 1 kilometer.
What this plot shows is how precisely the approaching guidance & navigation was
accomplished in the approach phase.



(Reference-2) Altitude and Descent Rate History

Fig. 2a shows the Doppler velocity history received at the Usuda station, which
approximately indicates the descent velocity to the surface. The initial descent speed
was found about 12 cm/second and it was decelerated gradually during the vertical
descent for about an hour. Note the gravity acceleration was compensated for during it.

Fig. 2b presents the altitude (precisely speaking, it is the distance from the center of
mass of Itokawa) information integrating the Doppler velocity, also it was updated from
time to time based on the terrain landmarks tracking. Green spots represent the Laser
Altimeter read indicating the height to the surface. Combining these two figures gives an
outline of the events.

Spacecraft Time on November 19th
Fig. 2a Doppler Velocity History : Descent Velocity

Spacecraft Time on November 19th
Fig. 2b Altitude History : Distance to the Center of Mass of Itokawa


When the target marker was released, the altitude was about 40m with the descent
velocity of about 9cm/second. And the Hayabusa started hovering by canceling the
descent velocity at the altitude of 20m. This was followed by the terrain alignment
maneuver at 17m altitude. The descent velocity after that gradually gained and had
increased. This was due to the Itokawa gravity, whose component to the Earth direction
contributed to this increase. The integrated Doppler infers the distance traveled to the
anti-Earth direction and it said the spacecraft drifted and reached several tens meters.
This is interpreted by the drift motion along the MUSES-Sea toward South (upward in
the image). Note the surface line drawn in Fig. 2b is inaccurate with some offset.

The Doppler velocity rise at 06:10 JST (21:10 UTC) was due to the touching-down to the
surface, which is described later. Unfortunately, no subsequent Doppler info was available
on the ground but the LRF data recorded aboard tells the touching-down and the
further motion.



(Reference-3) Target Marker separated and its Tracking aboard

The target marker separated this time carried the names of 880,000 people who
participated in the campaign from the world. It was placed in the south-west (See Fig. 3a)
area of the MUSES-Sea. When it hit to the surface, the descent speed was about 9 cm/

The target marker was specifically designed and fabricated made of aluminum shell filled
with polyimide balls to absorb kinetic energy through multi-collisions. It dramatically
suppresses the bouncing and the function had been tested and verified via drop tower
tests with vacuum chamber on the ground.

The target marker was illuminated by the flash lamps aboard every two seconds and
subtracting the images with the lamp on and with the lamp off gave where the target
marker was. This task was performed onboard by itself.


Fig. 3a The Target Marker separated from Hayabusa
(taken at 05:33 JST at the altitude of 32m)

Fig. 3b Target Marker Tracking Behavior aboard


The target marker after the separation started tracked by the Hayabusa-carried onboard
image processor and the guidance computer at 0533 JST, and had been kept tracked
through the transition to hovering mode at 05:39 JST (20:39 UTC). (RES_X and RES_Y
show the residual tracking errors)

Hayabusa then moved to the next control mode of guiding itself to be aloft right above the
marker and the control was successfully done and confirmed on the ground as well.

At 05:41 JST, Hayabusa detected some laser light reflection at the obstacle detector FBS,
and interrupted this target marker tracking at the instance. As the figure above shows,
the autonomous identification to localize the marker continued functioned even after that.

Through these events, the autonomy functions of both the etarget marker extraction
processingf and the eautonomous guidance to the markerf were verified satisfactorily.



(Reference-4)ProximityLaserRange Finder (LRF) Measurements

Fig. 4a shows the LRF data history showing the landing motion after the terrain alignment.


Fig. 4aLRF data during Touching-Downs and Landing (D-beam only, m)

Fig. 4bAttitude Error Angle History (around Y-axis, degree)

      The LRF data indicate that Hayabusa first a little raised its altitude when the terrain
alignment control was initiated, and a free fall motion followed in accordance with the
scenario as planned. The height became almost zero at 06:10 JST (21:10 UTC). And
then another bouncing was observed later at 06:30 JST (21:30 UTC). This resulted in
very soft landing on the surface and the spacecraft continued to sit on the surface
for half an hour, before the emergency take-off command was sent at 07:14 JST
(22:14 UTC).


Fig. 4c presents the cumulative firing time for one chemical engine during the period


This shows there are three instances when the RCS (Reaction Control System jet)
firings are concentrated. The first one is at 05:40 JST (20:40 UTC), and the second one is
at 06:10 JST (21:10 UTC), and the third one is at 06:30 JST (21:30 UTC) when some
external torque may have been applied to the spacecraft. The first instance corresponds to
the start of the terrain alignment control, while the latter two were due to the landing motion.

During the period from 06:40 JST (21:40 UTC) to 07:10 JST (22:10), the same engines had
been used at almost 100% duty, with the LRF read-out of almost zero. The attitude changed
slowly in accordance with the Itokawa rotation speed. The chemical engines were
programmed to be driven 15 milliseconds per one second and some thruster may have been
driven two times of the duty ratio, in case the thruster is used for two axes control.
The cumulative firing time shown here represents the external torque whose magnitude
exceeded that of the thruster permanently. These histories together with Fig. 2a and 2b in
fer Hayabusa kept sitting on the surface. The landing attitude was that with its ion engines
panel (+X panel) toward the east.
yNoticezWeb Data Citation Policy | E-mail