| MISSION_DESCRIPTION |
Mission Overview
================
The Hayabusa spacecraft was successfully launched atop a Japanese M-V
launch vehicle on May 9, 2003. The mission plan was to have the
spacecraft briefly alight upon the surface of near-Earth asteroid 25143
Itokawa, fire pellets into the surface, collect the surface material
ejecta and bring these surface samples back to Earth for intensive study.
Japan's Institute of Space and Astronautical Science (ISAS) and NASA
agreed to cooperate on the Hayabusa (aka MUSES-C) mission. Before
launch, the mission name was MUSES-C, which stood for Mu Space
Engineering Spacecraft, a space engineering spacecraft launched by a Mu
rocket developed by ISAS, with C referring to it being the third in the
series. Just after launch, the mission was renamed Hayabusa (Japanese
for falcon).
Science Goals
=============
The overall science goal of the mission is to significantly advance
our understanding of Earth's closest neighbors, the near-Earth asteroids.
Some of these objects continue to pass closer to the Earth than the moon
itself. They represent the left over building blocks of the inner solar
system formation process some 4.6 billion years ago and if we wish to
understand the chemical mix from which the inner planets, including
Earth, formed then the study of near-Earth asteroids is key. Most
objects in the inner portion of the asteroid belt have similar spectral
characteristics. These asteroids, including Itokawa, are so-called
S-type objects that are rich in the minerals olivine and pyroxene. By
carrying out a detailed elemental composition of the surface samples,
scientists will thereafter know the likely composition of existing, and
newly discovered, S-type asteroids. Asteroid compositions run the gamut
from carbon-rich fragile structures, to fractured silicate rock and
slabs of solid iron. These objects will need to be studied to determine
which among them are the most accessible to spacecraft and which are the
richest in mineral wealth. Another reason for investigating near-Earth
asteroids is to understand their compositions and structures to
successfully deflect an object that is found on an Earth threatening
trajectory.
Technology Goals
================
Technology tests: Although the science return to date from the Hayabusa
mission is rich, the mission's main goals are not scientific but rather
the testing of four new technologies including 1.) a demonstration of
the four ion engines in interplanetary space for up to 18,000 hours
2.) use of the on board camera systems to autonomously guide the
spacecraft during the asteroid rendezvous 3.) a demonstration of a
sample collection device for retrieval of surface materials
4.) a demonstration of the sample capsule's ability to carry out an
Earth atmosphere entry direct from an interplanetary trajectory.
Although there are four ion engines onboard the Hayabusa spacecraft,
up to three of them operate simultaneously. The fourth is a backup
engine. These ion engines operate when xenon fuel is first ionized via
a microwave device. The resulting xenon positive ions are then
accelerated across a charged high voltage grid (providing the thrust)
and finally a stream of electrons is used to neutralize the accelerated
xenon ions. Even when all three ion engines are operating full bore,
they are only capable of accelerating the spacecraft to a very modest
12 meters per second per day. The force they generate is 20,000 times
less than a traditional spacecraft thruster that burns chemical fuel
(e.g., hydrazine). However, while chemical thrusters operate for only
a few seconds, these ion engines thrust continuously over many months
and by so doing, they are capable of pushing the spacecraft to its
September 2005 rendezvous with Itokawa.
This is the first flight of a spacecraft with these advanced ion
engines, the first attempt at a touch and go, autonomous landing on an
asteroid's surface, and the first attempt of an asteroid surface sample
return to Earth.
Reaction Wheel Failure
======================
To maintain spacecraft attitude, the Hayabusa spacecraft was equipped
with three momentum wheels mounted in three orthogonal directions and
hydrazine attitude control thrusters on the corners of the spacecraft.
In late July 2005, one of the reaction wheels failed and a second wheel
failed in early October 2005. That left only the z-axis reaction wheel
operational for the remainder of the mission. The spacecraft made an
unplanned surface landing November 20 and a planned touchdown 5 days
later. Just after lifting off from the surface the second time, the
hydrazine attitude fuel was exhausted as it leaked into space causing a
spin up of the spacecraft. Radio contact with the spacecraft was lost
on December 8, 2005 and a signal restored on January 23, 2006. With
communications re-established, the cold xenon gas jets from the canted
neutralizers were used to restore attitude control by firing the
neutralizer gas at specific times during the spacecraft spin cycle. The
high data rate was restored on February 25, 2006. After the April 25,
2006 departure from Itokawa, the Hayabusa spacecraft maintained attitude
control via a careful balancing of the effects from the single
operational momentum wheel, vectoring of the ion engines and the
radiation pressure acting upon the solar panels. [KUNINAKAETAL2007]
Instruments
===========
Using three of the four ion engines at a time, Hayabusa flew past the
Earth on May 19, 2004 to boost its velocity. The spacecraft then caught
up to the target asteroid in September 2005, a potato shaped near-Earth
object named 25143 Itokawa, after the Japanese rocket pioneer, Hideo
Itokawa (1912 - 1999). During the three month operations period
(September - November), the Hayabusa science instruments were designed
to undertake an intensive study of the asteroid's surface. These
instruments are the science camera (AMICA); the surface hopper (MINERVA);
the near infrared and x-ray spectrometers (NIRS, XRS); the Lidar
altimeter (LIDAR); and the sample collection and return systems.
AMICA: The Asteroid Multiband Imaging Camera was used to map the
entire portion of the asteroid's surface that is observable in sunlight.
The asteroid's size, shape, volume, and rotation characteristics were
determined and a (negative) search was carried out for any neighboring
satellites or dust rings that may have been closely orbiting Itokawa.
Making observations with a set of colored filters (see Table 1),
AMICA looked for slight differences in color over the asteroid's surface
- color differences that might indicate changes in mineralogical
composition. The AMICA images will also be used to determine the optical
properties of the surface materials at image resolutions well below one
meter, provide constraints upon the surface particle sizes, and reveal
the history of impacts from other asteroids or comets. Results from the
AMICA instrument are reported in [SAITOETAL2006].
Table 1: AMICA filter bandpasses:
filter: central wavelength (nm): FWHM (nm):
ul 381 45
b 429 108
v 553 72
w 700 70
x 861 81
p 960 75
zs 1008 66
WIDE 650 300
MINERVA: Japanese engineers developed a surface hopper that could take
close up images and thermal measurements of the asteroid's surface
during, and in between, 10-meter hops about the surface. About the size
of a small can, the MINERVA hopper had six sun sensors (photodiodes) and
an electric turntable that was designed to first orient the tiny
spacecraft toward the sun thus allowing its solar panels to power it up.
Once oriented properly, the thermal sensors were designed to determine
Itokawa's surface temperature and then a rotating torque wheel would have
spun within MINERVA causing the outside of the tiny spacecraft to counter
rotate, dig into the surface and hop about 10 meters. Once a hop was
complete, additional surface temperature measurements would have been
made and two of the three onboard cameras would have taken very
high-resolution surface images in stereo. The third camera, with a
longer focal length than the other two, was designed to image the
asteroid's surface while MINERVA was above the surface during mid-hop.
Provided the Hayabusa spacecraft was within 20 kilometers, MINERVA's
images and temperature data could have been radioed to the Hayabusa
spacecraft and then relayed back to Earth. It was designed to last
three asteroid days or 36 hours. MINERVA's final weight was 591 g and
its diameter and height were 12 and 10 cm respectively. Its three
cameras (320 x 240 px) had adjustable shutter speeds. The data rate was
9.6 but due to the spacecraft's slight velocity away from the asteroid,
MINERVA entered into a solar orbit rather than descending to the
asteroid's surface. No asteroid data were received from this instrument.
A description of the MINERVA lander is reported in [YOSHIMITSUETAL1999].
NIRS and X-Ray Spectrometers: The on board, near infrared spectrometer
examined the asteroid's spectral features in the near infrared region
of the spectrum. Whereas the near-infrared spectrometer relied upon
meteorite analogs to identify the surface minerals of Itokawa, the x-ray
spectrometer measured the elemental composition of these minerals
directly. Solar x-rays excite the individual elements of the asteroid's
surface minerals and the resulting x-ray spectral features were
identified and measured by the on board x-ray spectrometer. Some of the
expected elements include iron, silicon, manganese, calcium, aluminum and
sodium. By noting the relative abundances of these elements in the
asteroid's surface minerals and comparing these abundances to those
measured in various types of meteorites on Earth, a link can be forged
between the composition of this type of rocky asteroid and the meteorites
on Earth that likely represent the collision fragments of such asteroids.
Thereafter, the composition can be inferred for newly discovered
asteroids that are spectrally similar to the large group of S-type
asteroids like Itokawa. Results from the NIRS and X-Ray Spectrometer
instruments are reported in [ABEETAL2006], [OKADAETAL2006].
LIDAR: The LIDAR instrument measures the round-trip time of flight of
infrared laser pulses transmitted from the Hayabusa spacecraft to the
surface of Itokawa. The instrument operates in a single autonomous mode,
in which it produces ranging measurements. Surface topography estimates
can be derived from these data, given appropriate corrections for the
position and attitude of the spacecraft. The principal components of
LIDAR are a diode-pumped, Nd:YAG laser transmitter that emits 1.064
micrometer wavelength laser pulses, a 0.126 m diameter telescope, a
silicon avalanche photodiode detector, and a time interval unit with 14
nsec resolution. During the long Home Position phase (~7km from Itokawa)
of the misson, LIDAR provides measurements of the topography of Itokawa
within approximately 12x4.9 m footprints. Results from the LIDAR
instrument are reported in [MUKAIETAL2007].
Sample Collection and Return to Earth: The definitive work on this
asteroid's composition will be done in Earth-based laboratories when the
Hayabusa spacecraft returns its precious samples in June 2010. After
several weeks during which an initial mapping and reconnaissance phase
is undertaken, the Hayabusa spacecraft was designed to descend to the
surface of the asteroid, fire a 5 gram pellet of Tantalum into the
asteroid's surface and immediately collect and store the resulting
ejecta. Tantalum, a rare non-corrosive metal, is used because it is
very resistance to change and any tantalum found in the collected sample
will be easily identified. This sampling maneuver can be done up to
three times. Because the light travel time between the asteroid and
Earth was about 18 minutes at the time of the sampling, the spacecraft
must act without human intervention. As described below, there was no
evidence that these pellets were successfully fired but the spacecraft
did land upon the asteroid's surface so that some surface material may
have been disturbed to an extent that allowed some of it to enter the
sample collection chamber. The landing attempts are outlined in
[YANOETAL2006].
On April 25, 2007, the Hayabusa spacecraft departed from the asteroid
and in June of 2010, the spacecraft will approach Earth and eject the
small (40 centimeters diameter) aluminum sample return capsule. The
sample container will enter the Earth's atmosphere at about 12 kilometers
per second, use ablative shielding to withstand the intense heat
generated by atmospheric friction, and eventually parachute down to the
ground near Woomera Australia. Eager scientists will then collect the
capsule and take it back to Japan so the asteroid surface samples can be
carefully removed and distributed to the scientific community for study.
These sample studies will be carried out using a variety of composition
measuring devices in Earth based laboratories - devices that are not
limited to the modest mass, volume, power, and data rates that can be
accommodated by the Hayabusa spacecraft. Furthermore, as more advanced
future instrumentation is developed and new hypotheses arise, archived
samples from the asteroid will be available for new measurements.
The instruments, with acronym and Principal Investigator (PI) or Team
Leader (TL), are summarized below:
Instrument Acronym PI/TL
--------------------------------- ------- ------------
Asteroid Multiband Imaging Camera AMICA Tsuko Nakamura, Jun Saito
Near Infrared Spectrometer NIRS Masanao Abe
LIDAR LIDAR Tadashi Mukai
X-Ray Spectrometer XRS Manabu Kato
MINERVA MINERVA Sho Sasaki
Target Asteroid
===============
Asteroid 25143 Itokawa: The orbit of the Hayabusa target body, 25143
Itokawa, has a low inclination with respect to the Earth's orbital plane
(1.7 deg.) so it is one of the more accessible asteroids for a
spacecraft rendezvous. Fortunately, this asteroid made a close Earth
approach to within six million kilometers in late March 2001 and an even
closer Earth approach to within 2 million kilometers in late June 2004.
Optical, infrared, and radar observations were undertaken in 2001 and
2004. The ground-based radar observations indicated that the object has
a potato shape of approximate dimensions 548 x 312 x 276 meters
[OSTROETAL2004] while ground-based optical and infrared data suggest
that Itokawa is an S-type asteroid with a composition analogous to
either an LL ordinary chondrite, or a primitive achondrite meteorite
[BINZELETAL2001], [SEKIGUICHIETAL2001], [ABELLETAL2007]. In either case
the asteroid appeared to be largely a silicate rock with a relatively
low abundance of iron. Detailed spectral observations obtained by the
Hayabusa spacecraft were not able to definitively rule out either
compositional interpretation [ABEETAL2006]. The spacecraft imaging
confirmed the general dimensions of the asteroid. Tables 2 and 3
provide the orbital and physical characteristics for near-Earth asteroid
25143 Itokawa as reported in [FUJIWARAETAL2006], [DEMURAETAL2006].
Table 2. Physical Characteristics of Target Body, 25143 Itokawa from
spacecraft measurements.
Magnitude (Abs.) 19.1
Spectral Type S
Albedo 0.3
Size (km) 550 x 298 x 244 meters (bounding box)
Rotation Period 12.1 hrs
Temp. at Subsolar Point 217-445 K
Table 3. Orbital Elements
Semi-Major Axis (AU) 1.324
Eccentricity 0.280
Inclination (deg) 1.72
Perihelion (AU) 0.95
Aphelion (AU) 1.62
Orbital Period (years) 1.52
References
==========
Abe, M., T. Mukai, N. Hirata, O.S. Barnouin-Jha, A.F. Cheng, and 11
others, Near-infrared spectral results of asteroid Itokawa from the
Hayabusa spacecraft, Science 312, 1334-1338, 2006.
Binzel, R.P., A.S. Rivkin, S.J. Bus, J.M. Sunshine, T.H. Burbine,
MUSES-C target asteroid (25143) 1998 SF36: A reddened ordinary chondrite,
Meteoritics and Planetary Science 36, , p.1167-1172, 2001.
Demura, H., S. Kobayashi, E. Nemoto, N. Matsumoto, M. Furuya, and 15
others, Pole and global shape of 25143 Itokawa, Science 312, 1347-1349,
2006.
Fujiwara, A., J. Kawaguchi, D.K. Yeomans, M. Abe, T. Mukai, and 17
others, The rubble-pile asteroid Itokawa as observed by Hayabusa,
Science 312, 1330-1334, 2006.
Kuninaka, Hitoshi, K. Nishiyama, Y. Shimizu, T. Yamada, H. Koizumi.
Re-ignition of Microwave Discharge Ion Engines on Hayabusa for Homeward
Journey. The 30th International Electric Propulsion Conference,
Florence, Italy, Sept. 17-20, 2007.
Mukai, T., S. Abe, N. Hirata, R. Nakamura, O.S. Barnouin-Jha, and
11 others, An overview of the LIDAR observations of asteroid 25143
Itokawa. Advances in Space Research 40, 187-192, 2007.
Okada, T., K. Shirai, Y. Yamamoto, T. Arai, K. Ogawa, and 2 others,
X-ray fluorescence spectrometry of asteroid Itokawa by Hayabusa. Science
312, 1338-1341, 2006.
Ostro, S.J., L.A.M. Benner, M.C. Nolan, C. Magri, J.D. Giorgini, and 11
others, Radar observations of asteroid 25143 Itokawa (1998 SF36),
Meteoritics and Planetary Science 39, 407-424, 2004.
Saito, J., H. Miyamoto, R. Nakamura, M. Ishiguro, T. Michikami, and 29
others, Detailed images of asteroid 25143 Itokawa from Hayabusa, Science
312, pp. 1341-1344, 2006.
Sekiguichi, T., M. Sterzik, N. Ageorges, and O. Hainaut (2001). IAU
Circular 7598, dated 2001 March 10.
Yano, H., T. Kubota, M. Miyamoto, T. Okada, D. Scheeres, and 15 others,
Touchdown of the Hayabusa spacecraft at the Muses Sea on Hayabusa,
Science 312, 1350-1353, 2006.
Yoshimitsu, T., T. Kubota, I. Nakatani, T. Adachi, H. Saito, Hopping
Rover ``MINERVA'' for Asteroid Exploration, ESA SP-440, 83-88, 1999.
Mission Phases
==============
LAUNCH
------
Mission Phase Start Time : 2003-05-09
Mission Phase Stop Time : 2003-05-09
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Launch 2003-05-09 at 13 hrs, 29 min. JST, M-V
launch vehicle, Kagoshima
Japan
CRUISE TO ASTEROID
------------------
Mission Phase Start Time : 2003-05-10
Mission Phase Stop Time : 2005-09-11
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Solar flare 2003-11 Solar panel efficiency
degraded
TCM-1 2004-04-20 14 cm/s, chemical thrust
Trim maneuver 3 2004-05-12 Trim maneuvers 0-2 were
canceled
Earth flyby 2004-05-19 06:21:40 UTC, Altitude above
Earth's surface = 3725 km
Reaction wheel failure 2005-07-31 Y-axis wheel ceases to
operate
SPACECRAFT AT GATE POSITION
---------------------------
Mission Phase Start Time : 2005-09-12
Mission Phase Stop Time : 2005-09-29
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Itokawa arrival 2005-09-12 Spacecraft 20 km from
asteroid. Approach speed =
0.2 mm/s
SPACECRAFT NEAR HOME POSITION
-----------------------------
Mission Phase Start Time : 2005-09-30
Mission Phase Stop Time : 2005-12-07
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Descent to Home position 2005-09-30 6.8 km from surface of
asteroid
Reaction wheel failure 2005-10-02 23:08 UTC, X-axis wheel
ceases to operate
1st descent rehearsal 2005-11-04 Asteroid center-of-mass
determined
Navigation & Guidance 2005-11-09 Navigation and guidance
practice 1st target
marker released (to
space)
MINERVA released 2005-11-12 Released into solar orbit
Sampling attempt 2005-11-19 1st (unsuccessful) sampling
attempt LRF detects
surface feature and
attempts emergency abort.
However, S/C attitude
outside permitted range
to tolerate departure
acceleration - autonomous
decision to continue
descent but S/C never
entered TD mode because
Fan Bean Sensor detected
obstacle and disabled
triggering - no pellets
fired into surface. Only
Doppler data available.
Unknown to ground
controllers, S/C bounces
once and sits on surface
for ~30 min. before
emergency abort command
received from ground.
2nd sampling attempt 2005-11-25 Fan Beam Sensor disengaged
and no target marker
released. Lateral S/C
motion control turned off
- only vertical
autonomous control used.
Conflicts in operations
script may not have
allowed pellet firings.
Shooting command given
but ignition switch in
safe mode. Fuel leak
triggered s/c safe mode
with many difficulties in
recovering.
SPACECRAFT RECOVERY OPERATIONS
------------------------------
Mission Phase Start Time : 2005-12-08
Mission Phase Stop Time : 2007-04-24
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Radio contact lost 2005-12-08 Radio contact lost possibly
due to sudden leak of
attitude gas causing s/c
to spin.
Spacecraft in safe mode 2005-12-09
Beacon signal received 2006-01-23
Spacecraft responds 2006-01-26 Spacecraft anomaly functions
begin responding
Low bit rate com. 2006-02-25 8 bps data rate established
2006-03-04 32 bps data rate established
Chemical fuel expended,
batteries severely
degraded
2006-03-16 256 bps data rate established
Spacecraft stabilized 2006-05-08 Spacecraft stabilized and
pointing properly
CRUISE BACK TO EARTH
--------------------
Mission Phase Start Time : 2007-04-25
Mission Phase Stop Time : 2010-06-12
-------------------------- ---------- ----------------------------
Event Date Description
-------------------------- ---------- ----------------------------
Spacecraft departs 2007-04-25 Ion engines started;
spacecraft begins return
to Earth.
SAMPLE CAPSULE AND HAYABUSA S/C ENTER EARTH'S ATMOSPHERE
--------------------------------------------------------
Mission Phase Start Time : 2010-06-13
Mission Phase Stop Time : 2010-06-13
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