Lunar and Planetary Science XXXV (2004)

1724.pdf

CHARACTERISTICS AND CURRENT STATUS OF NEAR INFRARED SPECTROMETER FOR
HAYABUSA MISSION. M. Abe1 , Y. Takagi2, S. Abe3, K. Kitazato1,4, T. Hiroi5, Y. Ueda4, F. Vilas6, B. E. Clark7,and A. Fujiwara1, 1Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(3-1-1 Yoshinodai, Sagamihara-shi, Kanagawa-ken 229-8510, Japan; abe@planeta.sci.isas.ac.jp, Kitazato@planeta.sci.isas.ac.jp,
fujiwara@planeta.sci.isas.ac.jp), 2Toho Gakuen University(3-11 Heiwagaoka, Meito-ku, Nagoya 465-8515, Japan;
takagi@toho-jc.ac.jp), 3Astronomical Institute Academy of Sciences Czech Republic(251 65 Ondrejov, Czech Republic, Europe; avell@asu.cas.cz), 4University of Tokyo(7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;
yueda@space.eps.s.u-tokyo.ac.jp), 5Brown University(Providence, RI 02912, USA; takahiro_hiroi@brown.edu),
6
National Aeronautics and Space Administration(Lyndon B. Johnson Space Center, Houston, TX 77058, USA;
Faith.Vilas1@jsc.nasa.gov), 7Ithaca College(267 Center for Natural Sciences Ithaca, NY 14850-7288 USA;bclark@ithaca.edu).
Introduction: NIRS is a near infrared spectrometer on-boarded the spacecraft HAYABUSA (MUSESC), which aims to return samples from a near-earth
asteroid, (25143) Itokawa (1998 SF36). HAYABUSA
was successfully launched by Japanese M-V-5 rocket
on May 19, 2003. After the earth swing-by in Jun 2004,
the spacecraft will arrive at the asteroid in summer
2005. During the rendezvous phase with the asteroid,
we will observe the asteroid surface using NIRS andobtain reflectance spectra of the surface materials
across the wavelength range of 850nm to 2100nm.
Based on ground-based observations [1],[2],[3],(25143) Itokawa appears to be an S(IV) type asteroid.
NIRS can detect absorption bands due to olivine andpyroxene and investigate the mineralogical composition of the surface materials. Combining with the datafrom asteroid multiband imaging camera (AMICA)
and X-ray spectrometer (XRS), we can reveal a relationship between asteroids and meteorites.
NIRS’s characteristics: NIRS is divided into twocomponents. One is a data processing unit and other isa sensor unit. The former is named as NIRS-E, thelatter is named as NIRS-S (cf. Figure 1). NIRS-E ispackaged in the NIX-E, which is a common sharedpackage with XRS that consists of an onboard computer and a power supply unit. NIRS-S is attachedinside the –Y-panel (one of the side panels of thespacecraft), and the line of sight is approximately
turned in the direction of –Z-axis through the hole on
the –Z-panel (bottom panel). The weight of NIRS-E is0.271kg and NIRS-S is 1.534kg. NIRS-S has a lengthof 336 mm, a width of 165 mm, and a height of 100mm. The power dissipation of NIRS is 2.45W during
the stand-by condition. Maximum power dissipation is9.5W at maximum drive of the electric cooler. NIRS-S
has a 64-channel InGaAs photodiode array as a detector and a grism (grating – prism) system. Spectral resolution is 23.6nm/channel. The second order light isseparated from the first order image by a cross disperser attached to the grism. The filed of view is 0.1 x
0.1 degrees. Aperture size of collecting area affectedby front hood is 27.2mm of the diameter. NIRS-S hasa shutter on the slit between two off-axis parabolic
mirrors. The shutter can open and close the slit at afrequency of 7.63Hz. Integration time can be selectedfrom 0.256 msec to 57.344 msec by every 0.256msec.
Total F-number of this sensor is 1.0. The operated
temperature of the detector sets normally at -15 °C.
This temperature is controlled by system heater of theoptical bench and electric cooler in the detector. NIRSS has calibration lamp and LED in order to monitor thevariation of the responsivity and relationship between
the channel and observed wavelength. We summarize
the NIRS’s characteristics in Table 1.
NIRS’s prelaunch calibration: We measured initial property of NIRS before launch. The relationshipbetween the channel number and wavelength of calibration light was expressed as,
L = -23.56 n +2271.4,
where L is the wavelength in nanometer, n is the channel number counted from 1 to 64. As shown in Figure
2, responsivity at -15 °C is larger than 100
V/(W/m2/sr/nm)/s between 810 nm and 2130nm
wavelength (200 at 850nm, 2150 at 1550nm, 1200 at
2050nm, and 600 at 2100 nm). Noise level is about
1mV and gain of the output is 1769DN/V. Dynamic
range of the output is 14bit (16383DN). Saturationlevel of the data is about 1.6V at -10 °C. Dark currentof the detector is 17pA that is 3.3V/s as the output
voltage at -4 °C. The dark current becomes half value
as the detector temperature decreases about 8 °C. Assuming Itokawa’s bidirectional reflectance is 0.07,
output voltage at observing the asteroid is about 1V at
1500nm for 25.6msec which is a nominal integration
time, and we can detect the flux from Itokawa morethan 100 of signal to noise ratio for all of observing
wavelength range without saturation.
Current status of the cruising phase: After the
successfully launch, initial operation of NIRS had been
held at May 12 and 16. During initial operation we
have checked and confirmed NIRS’s function andproperty. Obtained on-board lamp and LED data

Lunar and Planetary Science XXXV (2004)

References: [1] Abe M. et al. (2002) LPS XXXIII,
Abstract #1666. [2]Binzel R. P. et al. (2001) MAPS, 36,1167-1172. [3] Kelley M. S. et al. (2001) MAPS, 36,suppl., A95. [4] Ishiguro M. et al. (2003) PASJ, 55,691-699. [5] Ostro S. J. et al. (2001) BAAS, 33, 1117.
[6] Sekiguchi T. (2003) A&A, 397, 325-328.
[7] Dermawan B. et al. (2002) PASJ, 54, 635-640.
[8] Kaasalainen M. et al. (2003) A&A, 405, L29-L32.
Table 1. Characteristics of NIRS-S-----------------------------------------------------------------Spectral range
850-2100nmSpectral resolution
26nm
Field of view
0.1deg x 0.1deg
Collecting area
560mm2Detector array
InGaAsNumber of channel
64
Size of detector element 50um (W) x 100um (H)Mass
1.534kg------------------------------------------------------------------

Figure 1. Photograph of NIRS-S
2500

Responsivity [(V/s)/(W/m2/nm)]

agreed with that obtained before the launch. Responsivity and relationship between the channel and observed wavelength had not changed before/after thelaunch. At May 23 and June 5, we checked and measured co-alignment between the line of sight of NIRS
and –Z axis of spacecraft coordination by observing
alpha Scorpius. We confirmed that the co-alignment
has not changed before/after the launch. From June toDecember, the spacecraft used ion thruster engines foralmost time to put the spacecraft into the earth swingby orbit. During this period we only obtained lamp andLED data for about once per month to monitor thevariation of the responsivity and relationship of thechannel and wavelength, except for the chance to observe Mars on November 11 and 18. In this observation, we succeeded at obtaining the reflectance spectrum of the surface material of Mars and detecting theatmospheric CO2 absorption band. On January 6, 2004,
we performed simultaneous observations with NIRSand AMICA, and checked and measured co-alignment
between the line of sights of NIRS and AMICA. We
are planning to observe the Moon and the Earth at theearth swing-by in June of this year. This is only achance of the area source observation. Until the arrivalat the asteroid, we will perform point source (brightstar and planet) observations several times, and monitor the lamp and LED data about once per month.
Observing plan during rendezvous phase: Asteroid (25143) Itokawa is about a 300-m sized body[4],[5],[6]. After arriving at Itokawa, the spacecraft
will stay around the home position (HP), which isabout 6 km in altitude above the asteroid surface. Atthe HP, apparent diameter of the asteroid is about 3
degrees, and spatial resolution of NIRS is about 10 m
at the asteroid surface. During the HP keeping phase,
we will perform global mapping by slewing the spacecraft attitude along the meridian iteratively. Because ithas been known that the spin rotation period of Itokawa is about 12 hours[7],[8], if we set 0.025deg/secof the slewing rate, 4 degrees of the slewing amplitude
and 6 minutes of the slewing period, we can make thefootprint cover all of the surface. Solar phase angle atthe HP is less than 30 degrees all of the time. We will
also obtain the reflectance spectrum for high solar
phase angle apart from the HP. Combining the resultof AMICA and XRS observation we estimate the distribution of the surface material and the physical condition, and then select the sampling point. Before thesampling of the surface material, the spacecraft descends from the HP to the surface. During descending
phase, NIRS will also observe the surface include thesampling point more high spatial resolution than thatobtained form the HP.

1724.pdf

2000
1500
1000
500
0700

900

1100

1300

1500

1700

Wavelength [nm]1900

Figure 2. Responsivity of NIRS

21002300