Andrew Yee
November 25th 05, 01:03 AM
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/2005/1124_hayabusa.shtml ]
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/2005/1124_hayabusa.shtml ]