Andrew Yee
November 3rd 05, 09:13 PM
Public Affairs Department
Japan Aerospace Exploration Agency (JAXA)
Marunouchi Kitaguchi Building,
1-6-5, Marunouchi, Chiyoda-ku, Tokyo 100-8260
Japan
TEL: +81-3-6266-6400
2005/11/2
Hayabusa's Scientific and Engineering Achievements during Proximity
Operations around Itokawa
Hayabusa arrived at its exploration target, near-Earth asteroid Itokawa,
on September 12th of this year after having been propelled there via ion
engines and an Earth swing-by. Since then, it has successfully performed
orbital maneuvers, precisely keeping its position relative to Itokawa. The
Hayabusa project team has made many discoveries while carrying out their
ambitious scientific observations of Itokawa. This release summarizes and
reports the major scientific and engineering achievements in advance of
Hayabusa's unprecedented and historic descent to the surface of Itokawa
for sample collection middle to later this month.
Hayabusa is a technology demonstration spacecraft focusing on key
technologies that are required for future large-scale sample and return
missions, yet is also making new scientific observations and discoveries.
The technology demonstration component of the mission consists of five
goals: ion engine propulsion in interplanetary cruise, ion engine
propulsion in combination with an Earth gravity assist, autonomous
guidance and navigation using optical measurements, collection of surface
samples in an ultra-low gravity environment and the direct recovery of
these samples on the ground after its return from interplanetary flight.
To date the Hayabusa project has accomplished these demonstrations up
through the third goal. Specifically, at the time of arrival at Itokawa,
Hayabusa had driven its proprietary new ion engines for 26,000 hours,
including their operation during an Earth flyby. It has also perfectly
completed a period of hybrid optical navigation (Fig. 1) followed by
precise guidance and navigation of the spacecraft during its station
keeping period around Itokawa. (Fig. 2) These engineering achievements are
the primary mission of Hayabusa and their successful completion is a great
achievement.
The deep-space exploration technologies that the world's space agencies
are pursuing consist of three major elements: high efficiency electric
propulsion for cruise, rendezvous with target destinations and round-trip
flights back to the Earth. As of this time Hayabusa has accomplished the
first and second of these elements, leading the way for the space
exploration agencies of the world. Furthermore, robotic sample collection
and return from an extraterrestrial object has not been executed before,
and is not currently planned, except for Hayabusa, which will attempt to
gather a bulk sample from Itokawa. Hayabusa's success clearly shows that
Japan's deep space exploration technology has reached the level of the
world's most developed space agencies, and that Japan is now in a
leadership position in some select engineering fields. Thus Hayabusa opens
a new era in solar system exploration.
For the scientific aspects of the mission, Hayabusa carries four
instruments that have performed successful observations to date: AMICA, a
visible imager with multi-band filters has exposed 1,500 images amounting
to almost 1 GB of data, NIRS, a near infrared spectrometer has taken
75,000 measurements distributed globally over the body, LIDAR, a laser
altimeter has accumulated 1.4 million measurements globally, and XRS, a
X-ray spectrometer has received and integrated its signal for 700 hours.
In addition to these, spacecraft tracking data has been used to measure
properties of the asteroid as well. These unprecedented scientific
measurements are briefly described and reported in what follows.
(A) Morphological and geological discoveries about Itokawa: The a priori
theoretical assumption that small near-Earth asteroids should have
geologically homogeneous features was completely overturned by the
observation of a wide variety of surface features and types at Itokawa.
The surface is covered with huge boulders and, for the first time, naked
surfaces not covered with regolith have been exposed (Fig. 3, 4, 5, 6, 7).
Previously visited asteroids were covered with thick regolith, thus
Itokawa's surface is like nothing that has seen before, which is quite
fortunate for the Hayabusa mission. The opportunity to observe the true
asteroid surface, which is usually concealed from view, advances our
understanding of spectroscopic observations of asteroids taken from Earth,
and allows us to expand our knowledge of near-Earth asteroids.
(B) Taking advantage of the observations made with the onboard
instruments, sufficiently detailed information about the sampling sites
has been obtained, and the relation between the potential samples and the
spectroscopic data has been correctly correlated. As a technology
demonstration mission, Hayabusa has already finished the preliminary steps
towards the primary sample and return goal (Fig. 8). These samples will
provide important scientific clues concerning the puzzlingly inconsistent
correlations between S-type asteroids and ordinary chondrites, and lead to
an improved understanding of the space weathering effect, which may
clarify our understanding of the early solar system and Earth.
(C) Combinations of the Itokawa images along with spacecraft navigation
information has enabled shape and gravity models to be numerically
defined. The science team has started to study and identify the special
mechanisms that can move boulders and regolith in the ultra-low gravity
environment associated with small objects (Fig. 9). The gravity and slope
information and estimates of the density of boulders and regolith
distribution on the surface, combined with comparisons with meteorites,
will advance our interpretation and understanding of asteroid planetology.
(D) Using the laser altimeter and optical navigation camera, along with
range and range-rate measurements from ground-tracking stations, have led
to a successful mass and density estimate for Itokawa. The density has
been estimated to be 2.3 +/-0.3 gram/cc, which is a little lower than that
measured for rocks on the ground or for other S-type asteroids measured to
date. This may indicate that there is substantial porosity for this body,
and forces conventional views of these small objects to be changed
drastically. When the samples are successfully returned and recovered, the
actual porosity will be clarified and our knowledge of how the Earth
relates to meteorites will be greatly improved.
The exploration of small solar system bodies contributes to an improved
understanding of the Earth itself, as well as to a more comprehensive
interpretation of the constituents and potential resources that these
celestial objects contain. The scientific discoveries reported here will
redefine scientific notions and views of asteroids from the pre-Hayabusa
era, and are a remarkable accomplishment that Japan has contributed to
planetary exploration.
In view of the scientific results described above, JAXA has determined the
landing/sampling sites candidates and the descent target point for
rehearsal, along with their planned dates and times.
The landing/sampling sites must be free of obstacles and smooth enough to
ensure safety, a top priority, while at the same time the surface
inclination and the ground station coverage for Hayabusa must be taken
into account. Taking these issues into consideration, the candidate sites
and schedule were determined (Fig. 10).
The first site candidate is the regolith expanse in the middle of Itokawa,
known as the MUSES-SEA area (Fig. 11), and the second candidate site is
the Woomera desert (Fig. 12) at the tip end of Itokawa, where the terrain
is broad and flat. The rehearsal target is the area located close to the
spin axis, a little east of the first site. The date and time of the
planned events (Japan Standard Time [= UTC + 9 hrs.) are listed below:
1. Rehearsal Descent November 4th, 14 o'clock,
2. 1st Touch-down November 12th, 15 o'clock,
3. 2nd Touch-down November 25th, 15 o'clock.
The purpose of the rehearsal descent is, first of all, to make sure that
the proximity laser range finder works as intended, as its function has
not been calibrated during cruise. The second purpose is to confirm
whether the target marker image can be extracted against the asteroid
surface, using onboard image processing that illuminates it using flash
lamps onboard the spacecraft. The third purpose is to deploy and place the
hopping robot MINERVA on the asteroid surface. Deploying MINERVA conflicts
with the touch-down sequence, so it will be separated in advance of the
sampling runs. The touch down sequence is briefly described in Fig. 13.
In conjunction with this very big challenge, JAXA is also starting a
nation-wide campaign called 'You Name the Landing Site'. The names
assigned to the sites may not be officially registered by the
International Astronomy Union (IAU) as the sites are very small. However,
JAXA, as a finder, declares that the sites will be given those selected
names. The application page is at
https://ssl.tksc.jaxa.jp/hayabusa/
and will be open until 17:00 on November 30th. The application form there
is available from early November. The actual naming will occur after the
completion of the Hayabusa proximity observation period, in early
December.
* Note: The data, including images, in this release are not calibrated and
are not suitable for scientific investigations unless JAXA and the joint
Science Team of Hayabusa validates them. Whenever the images are used the
citation should read 'ISAS/JAXA'.
[NOTE: Images supporting this release are available at
http://www.isas.ac.jp/e/snews/2005/1102.shtml ]
Japan Aerospace Exploration Agency (JAXA)
Marunouchi Kitaguchi Building,
1-6-5, Marunouchi, Chiyoda-ku, Tokyo 100-8260
Japan
TEL: +81-3-6266-6400
2005/11/2
Hayabusa's Scientific and Engineering Achievements during Proximity
Operations around Itokawa
Hayabusa arrived at its exploration target, near-Earth asteroid Itokawa,
on September 12th of this year after having been propelled there via ion
engines and an Earth swing-by. Since then, it has successfully performed
orbital maneuvers, precisely keeping its position relative to Itokawa. The
Hayabusa project team has made many discoveries while carrying out their
ambitious scientific observations of Itokawa. This release summarizes and
reports the major scientific and engineering achievements in advance of
Hayabusa's unprecedented and historic descent to the surface of Itokawa
for sample collection middle to later this month.
Hayabusa is a technology demonstration spacecraft focusing on key
technologies that are required for future large-scale sample and return
missions, yet is also making new scientific observations and discoveries.
The technology demonstration component of the mission consists of five
goals: ion engine propulsion in interplanetary cruise, ion engine
propulsion in combination with an Earth gravity assist, autonomous
guidance and navigation using optical measurements, collection of surface
samples in an ultra-low gravity environment and the direct recovery of
these samples on the ground after its return from interplanetary flight.
To date the Hayabusa project has accomplished these demonstrations up
through the third goal. Specifically, at the time of arrival at Itokawa,
Hayabusa had driven its proprietary new ion engines for 26,000 hours,
including their operation during an Earth flyby. It has also perfectly
completed a period of hybrid optical navigation (Fig. 1) followed by
precise guidance and navigation of the spacecraft during its station
keeping period around Itokawa. (Fig. 2) These engineering achievements are
the primary mission of Hayabusa and their successful completion is a great
achievement.
The deep-space exploration technologies that the world's space agencies
are pursuing consist of three major elements: high efficiency electric
propulsion for cruise, rendezvous with target destinations and round-trip
flights back to the Earth. As of this time Hayabusa has accomplished the
first and second of these elements, leading the way for the space
exploration agencies of the world. Furthermore, robotic sample collection
and return from an extraterrestrial object has not been executed before,
and is not currently planned, except for Hayabusa, which will attempt to
gather a bulk sample from Itokawa. Hayabusa's success clearly shows that
Japan's deep space exploration technology has reached the level of the
world's most developed space agencies, and that Japan is now in a
leadership position in some select engineering fields. Thus Hayabusa opens
a new era in solar system exploration.
For the scientific aspects of the mission, Hayabusa carries four
instruments that have performed successful observations to date: AMICA, a
visible imager with multi-band filters has exposed 1,500 images amounting
to almost 1 GB of data, NIRS, a near infrared spectrometer has taken
75,000 measurements distributed globally over the body, LIDAR, a laser
altimeter has accumulated 1.4 million measurements globally, and XRS, a
X-ray spectrometer has received and integrated its signal for 700 hours.
In addition to these, spacecraft tracking data has been used to measure
properties of the asteroid as well. These unprecedented scientific
measurements are briefly described and reported in what follows.
(A) Morphological and geological discoveries about Itokawa: The a priori
theoretical assumption that small near-Earth asteroids should have
geologically homogeneous features was completely overturned by the
observation of a wide variety of surface features and types at Itokawa.
The surface is covered with huge boulders and, for the first time, naked
surfaces not covered with regolith have been exposed (Fig. 3, 4, 5, 6, 7).
Previously visited asteroids were covered with thick regolith, thus
Itokawa's surface is like nothing that has seen before, which is quite
fortunate for the Hayabusa mission. The opportunity to observe the true
asteroid surface, which is usually concealed from view, advances our
understanding of spectroscopic observations of asteroids taken from Earth,
and allows us to expand our knowledge of near-Earth asteroids.
(B) Taking advantage of the observations made with the onboard
instruments, sufficiently detailed information about the sampling sites
has been obtained, and the relation between the potential samples and the
spectroscopic data has been correctly correlated. As a technology
demonstration mission, Hayabusa has already finished the preliminary steps
towards the primary sample and return goal (Fig. 8). These samples will
provide important scientific clues concerning the puzzlingly inconsistent
correlations between S-type asteroids and ordinary chondrites, and lead to
an improved understanding of the space weathering effect, which may
clarify our understanding of the early solar system and Earth.
(C) Combinations of the Itokawa images along with spacecraft navigation
information has enabled shape and gravity models to be numerically
defined. The science team has started to study and identify the special
mechanisms that can move boulders and regolith in the ultra-low gravity
environment associated with small objects (Fig. 9). The gravity and slope
information and estimates of the density of boulders and regolith
distribution on the surface, combined with comparisons with meteorites,
will advance our interpretation and understanding of asteroid planetology.
(D) Using the laser altimeter and optical navigation camera, along with
range and range-rate measurements from ground-tracking stations, have led
to a successful mass and density estimate for Itokawa. The density has
been estimated to be 2.3 +/-0.3 gram/cc, which is a little lower than that
measured for rocks on the ground or for other S-type asteroids measured to
date. This may indicate that there is substantial porosity for this body,
and forces conventional views of these small objects to be changed
drastically. When the samples are successfully returned and recovered, the
actual porosity will be clarified and our knowledge of how the Earth
relates to meteorites will be greatly improved.
The exploration of small solar system bodies contributes to an improved
understanding of the Earth itself, as well as to a more comprehensive
interpretation of the constituents and potential resources that these
celestial objects contain. The scientific discoveries reported here will
redefine scientific notions and views of asteroids from the pre-Hayabusa
era, and are a remarkable accomplishment that Japan has contributed to
planetary exploration.
In view of the scientific results described above, JAXA has determined the
landing/sampling sites candidates and the descent target point for
rehearsal, along with their planned dates and times.
The landing/sampling sites must be free of obstacles and smooth enough to
ensure safety, a top priority, while at the same time the surface
inclination and the ground station coverage for Hayabusa must be taken
into account. Taking these issues into consideration, the candidate sites
and schedule were determined (Fig. 10).
The first site candidate is the regolith expanse in the middle of Itokawa,
known as the MUSES-SEA area (Fig. 11), and the second candidate site is
the Woomera desert (Fig. 12) at the tip end of Itokawa, where the terrain
is broad and flat. The rehearsal target is the area located close to the
spin axis, a little east of the first site. The date and time of the
planned events (Japan Standard Time [= UTC + 9 hrs.) are listed below:
1. Rehearsal Descent November 4th, 14 o'clock,
2. 1st Touch-down November 12th, 15 o'clock,
3. 2nd Touch-down November 25th, 15 o'clock.
The purpose of the rehearsal descent is, first of all, to make sure that
the proximity laser range finder works as intended, as its function has
not been calibrated during cruise. The second purpose is to confirm
whether the target marker image can be extracted against the asteroid
surface, using onboard image processing that illuminates it using flash
lamps onboard the spacecraft. The third purpose is to deploy and place the
hopping robot MINERVA on the asteroid surface. Deploying MINERVA conflicts
with the touch-down sequence, so it will be separated in advance of the
sampling runs. The touch down sequence is briefly described in Fig. 13.
In conjunction with this very big challenge, JAXA is also starting a
nation-wide campaign called 'You Name the Landing Site'. The names
assigned to the sites may not be officially registered by the
International Astronomy Union (IAU) as the sites are very small. However,
JAXA, as a finder, declares that the sites will be given those selected
names. The application page is at
https://ssl.tksc.jaxa.jp/hayabusa/
and will be open until 17:00 on November 30th. The application form there
is available from early November. The actual naming will occur after the
completion of the Hayabusa proximity observation period, in early
December.
* Note: The data, including images, in this release are not calibrated and
are not suitable for scientific investigations unless JAXA and the joint
Science Team of Hayabusa validates them. Whenever the images are used the
citation should read 'ISAS/JAXA'.
[NOTE: Images supporting this release are available at
http://www.isas.ac.jp/e/snews/2005/1102.shtml ]