ASNARO (Advanced Satellite with New system ARchitecture for Observation)

ASNARO is a Japanese optical high-resolution Earth imaging mission under development by the NEC Corporation and USEF (Institute for Unmanned Space Experiment Free Flyer). The project is funded by NEDO (New Energy and Industrial Technology Development Organization), a Department of METI (Ministry of Economy, Trade and Industry) of the Government of Japan.

The ASNARO project was initiated by USEF in 2008. The overall objective is to develop a next-generation high-performance minisatellite bus system based on open architecture techniques and manufacturing methodologies to drastically reduce the cost and the development period with adoption of up-to-date electronics technologies. The observation requirements call for the provision of high-resolution imagery \[Pan of < 0.5 m, and MS of 2 m GSD (Ground Sample Distance) on a swath of 10 km\]. This implies also the development of a high-performance imager and to demonstrate new technologies in space. ^{1) 2) 3) 4) 5)}

Figure 1: On-orbit illustration of the ASNARO spacecraft (image credit: NEC)

Spacecraft:

The new NEC standard minisatellite bus system under development, the result of a joint study by JAXA/ISAS and NEC, is highly adaptive for various missions. As the payload interfaces are standardized - including mechanical, thermal, electrical and RF interfaces - the bus system can be applied not only for optical observation mission but also for other payloads like the SAR, hyperspectral, and infrared instrument applications.

Figure 2: Illustration of the standard bus portion of the spacecraft (image credit: USEF, NEC)

The minisatellite bus system is comprised of subsystems which can be arranged in building-block style with the SpaceWire network, using high-performance COTS components and improved verification test methods. The SpaceWire bus standard forms the on-board network to link all subsystems.

The ASNARO bus system is comprised of the following subsystems: TTC (Telemetry Tracking and Command), EPS (Electrical Power Subsystem), TCS (Thermal Control Subsystem), SMS (Satellite Management Subsystem), and the AOCS (Attitude and Orbit Control Subsystem).

The network consists of main computers (Network masters), routers and units with SpaceWire interface (target). The standard bus system has two CPUs for the DHS (Data Handling Subsystem) and the AOCS subsystem. Each subsystem’s target units are connected with each CPU (referred to as SpaceCube2 in Figure 3) through the SpaceWire router.

The AOCS includes an RCS (Reaction Control Subsystem). The spacecraft is very agile providing a body-pointing event monitoring capability of ±45º in any direction from nadir. The precise and swift control for the Earth observation maneuvers are performed by RWA (Reaction Wheel Assembly), IRU (Inertial Reference Unit), STT (Star Trackers), GPSR (GPS Receiver) and the control S/W in AOCS.

Figure 3: Block diagram of the ASNARO spacecraft (image credit: NEC, USEF)

Table 1: Overview of spacecraft parameters

Figure 4: Alternate view of the deployed ASNARO spacecraft (image credit: NEC)

Launch: A launch of the ASNARO spacecraft is planned for 2011.

Orbit: Sun-synchronous orbit, nominal altitude = 504 km, inclination = 97.4º, LTDN (Local Time on Descending Node) = 11:00 hours.

Sensor complement: (OPS)

OPS (Optical Sensor):

OPS is a compact pushbroom instrument developed by NEC and NTSpace (NEC Toshiba Space Systems Ltd.). The design introduces the following technologies: ⁶⁾

• Optics subsystem: Use of a TMA (Three Mirror Anastigmat) telescope

• The primary mirror is made of NTSIC (New Technology Silicon Carbide). SiC is considered the most suitable material of spaceborne telescope mirrors, because of high stiffness, low thermal expansion, high thermal conductivity, low density and excellent environmental stability. Newly developed high-strength reaction-sintered SiC, which has two to three times higher strength than a conventional sintered SiC, is one of the most promising candidates in applications such as lightweight substrates of optical mirrors, due to being fully dense and having small sintering shrinkage (±1 %), and low sintering temperature. ⁷⁾

Figure 5: Illustration of the NTSIC primary mirror substrate (image credit: NEC, USEF)

Table 2: OPS performance requirements

In Feb. 2009, the Goodrich Corporation (Charlotte, N. C., USA) was awarded a contract to provide optical subassemblies for the new OPS telescope.

Figure 6: Schematic view of the OPS pushbroom instrument (image credit: NEC, USEF)

Observation modes:

The spacecraft AOCS provides the following observation modes:

1) Snap shot mode: In this mode it is possible to acquire the nominal 10 km x 10 km area’s image. At the moment of imaging, the satellite body is controlled to be fixed to inertial space.

2) Wide view mode: This mode is being used to provide wide area images along with a few sets of neighboring snap shot images.

3) 3D mode: This mode is used to acquire the stereo imagery of the target area. In this mode, the observations are performed from two different orbital positions to obtain 3-dimensional information of the target area.

4) Strip map mode: In this mode, it is possible to acquire zonal imagery - a continuous image with a maximum length of 850 km and a width of 10 km.

Figure 7: Schematic view of the various observation modes (image credit: NEC, USEF)

Figure 8: Summary of the innovation of the spacecraft development architecture (image credit: USEF, NEC)

The establishment of the “bus standards” to innovate the spacecraft development architecture is expected to reduce the hurdle heights for a small business enterprise to enter the “space market” to induce the competition, and reduce the cost and development time of future spacecraft, and finally excite whole space industries (Ref. 5).

2) Koichi Ijichi, Shoichiro Mihara, Masatsigu Akiyama, Keita Miyazaki, Toshiaki Ogawa, Yoshito Narimatsu, Osumu Itoh, “Introduction and the Outline of the ASNARO Project (Advanced Satellite with New system ARchitecture for Observation),” paper: 2009-t-04, Proceedings of the 27th ISTS (International Symposium on Space Technology and Science) , Tsukuba, Japan, July 5-12, 2009 URL: http://www.senkyo.co.jp/ists2009/papers/html/pdf/2009-t-04.pdf

3) Kenichi Saito, Toshiaki Ogawa, Keita Miyazaki, Masatsugu .Akiyama, Osamu Ito, “System outline of the Advanced Satellite with New system ARchitecture for Observation (ASNARO,” Proceedings of the 27th ISTS (International Symposium on Space Technology and Science) , Tsukuba, Japan, July 5-12, 2009, paper: 2009-n-05, URL: http://www.senkyo.co.jp/ists2009/papers/html/pdf/2009-n-05.pdf

4) Paul Kallender-Umezu, “Japan Moving Ahead with Smaller Earth Imaging Satellites,” Space News, Aug. 10, 2009, p.12, URL: http://www.spacenews.com/resource-center/sn_pdfs/SPN_20090810_Aug_2009.pdf

5) Koichi Ijichi, Shoichiro Mihara, Keita Miyazaki, Masatsigu Akiyama, Toshiaki Ogawa, Osumu Ito, “Project Outline of the Advanced Satellite with New System Architecture for Observation (ASNARO),” Proceedings of the 60th IAC (International Astronautical Congress), Daejeon, Korea, Oct. 12-16, 2009, IAC-09.B4.7.6

6) Shouji Morioka, Seiji Kanda, Hiroshi Irikado, Katsuhiko Tsuno, Kazuhiko Oono, Tamio Nakashima, Takashi Sakashita, Yoshito Narimatsu, Toshiaki Ogawa, Shoichiro Mihara, Osamu Itoh, ”Development of A High-resolution Optical Imager for Small Satellite”, 27th International Symposium on Space Technology and Science, Tsukuba, Japan, July 5-12, 2009, paper: 2009-n-06, URL: http://www.senkyo.co.jp/ists2009/papers/html/pdf/2009-n-06.pdf

7) K. Tsuno, H. Irikado, K. Ono, “NTSIC: progress in recent two years,” SPIE Optics and Photonics Conference, San Diego, CA, USA, Aug. 26-27, 2007, SPIE Vol. 6666