Hayabusa's Scientific and Engineering Achievements during ProximityOperations around Asteroid Itokawa (Forwarded)

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 ]