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ASNARO-2 (Advanced Satellite with New system ARchitecture for Observation-2)

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ASNARO-2 is a Japanese SAR (Synthetic Aperture Radar) Earth imaging mission under development by the NEC Corporation and USEF (Institute for Unmanned Space Experiment Free Flyer). ASNARO-2 is a follow-up minisatellite mission of ASNARO. Like its predecessor, 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. 1)

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Figure 1: Illustration of the ASNARO-2 spacecraft (image credit: NEC)


Spacecraft:

ASNARO-2 is a minisatellite which features NEXTAR (Next Generation Star) bus. NEC's small standard satellite bus module NEXTAR is based on NEC's long term experience in space division and is highly adaptive for various missions: remote sensing by optical or SAR (Synthetic Aperture Radar) sensor, ETS (Engineering Test & evaluation in Space) and scientific missions. The characteristics of small satellites are lighter, more affordable and have shorter delivery times. The NEXTAR program exhibits these characteristics. In addition, NEXTAR realizes high performance. 2) 3) 4)

Figure 2 is the block diagram of ASNARO-2. The block diagram is almost identical to that of the ASNARO mission except for the mission control subsystem (purple box in Figure 2 on the upper right).

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Figure 2: Block diagram of the ASNARO-2 bus (image credit: NEC)

 

Spacecraft mass

Bus: 305 kg (dry)
Payload: 220 kg
Propellant: 45 kg
Total mass: 570 kg

Design life

5 years

Electrical power

SAP Power: 1300 W (EOL)
For observation: 1200W

RF communications of payload data

X-band downlink, 16QAM(Quadrature Amplitude Modulation) scheme, data rate ~800 Mbit/s

Table 1: Some performance parameters of ASNARO-2

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Figure 3: Alternate view of the deployed ASNARO-2 minisatellite (image credit: NEC)

 

Launch: The ASNARO-2 minisatellite was launched on 17 January 2018 (21:06:11 UTC, or 06:06:11 JST on 18.01.2018) on the Epsilon-3 vehicle from the JAXA Uchinoura Space Center, Japan. After 52 minutes and 35 seconds into the flight, the separation of ASNARO-2 was confirmed. 5) 6)

The Epsilon launcher is a three-staged solid propellant launch vehicle + compact liquid propulsion system.

Orbit: Sun-synchronous (dawn-dusk) near-circular orbit, altitude = 504 km, inclination = 97.4º. The same altitude as ASNARO-1 was selected to construct a constellation with ASNARO. The LTDN (Local Time of Descending Node) is 6:00 hours for securing sufficient battery charging time. The different local time from ASNARO makes it possible for multi-time observation by the constellation with ASNARO.

 


 

Sensor complement: XSAR

XSAR (X-band Synthetic Aperture Radar):

The XSAR instrument is designed and developed by the Mitsubishi Electric Corporation. The objective is to provide high-resolution imagery (< 1 m).

Parameter

Spotlight mode

Stripmap mode

ScanSAR mode

Frequency

X-band

Resolution

< 1 m

< 2 m

< 16 m

Swath

> 10 km

> 12 km

> 50 km

Off-nadir angle

15-45º

Polarization

HH / VV (selectable)

Data Compression

1/2, 1/4, Non

Data quantization

8 bit

Table 2: Specification of the XSAR instrument

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Figure 4: Illustration of the various observation modes (image credit: NEC)

Introduction of TWTA (Traveling Wave Tube Amplifier) technology:

Use of a MPA (Multi Port Amplifier), composed of TWTAs. This concept is adopted for the HPA (High Power Amplifier) of the small SAR instrument. At X-band, TWTA is suitable to the concentrated HPA. This is because the SSPA (Solid State Power Amplifier) implementation is not enough for this high power and high efficiency at X-band. For ASNARO-2, the gridded pulse TWTA is needed due to the lower power consumption. NEC has experience and heritage devices of CW (Continuous Waveform) TWTA for satellites and gridded pulse TWTA for aviation/ground implementations. The TWTA for ASNARO-2 was developed based on these heritages.

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Figure 5: Photos of CW TWTAs for satellites developed by NEC (image credit: NEC)

 


1) "Advanced Small Radar Satellite Called "ASNARO-2" to be Launched by the Third Epsilon Launch Vehicle," METI, 12 Sept. 2017, URL: http://www.meti.go.jp/english/press/2017/0912_001.html

2) Azusa Muta, Toshiaki Ogawa, Tatsuji Moriguchi, Akihiro Matsushita, Shoichiro Mihara, "Outline and Program status of ASNARO-2 (Advanced Satellite with New System Architecture for Observation) Satellite System," Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013,

3) Yusuke Kobayashi, Toshiaki Ogawa, "Multiple Applications of NEXTAR Platform to Earth Observation Represented by ASNARO Satellite Series," Proceedings of the 4S (Small Satellites Systems and Services) Symposium, Port Petro, Majorca Island, Spain, May 26-30, 2014

4) Y. Yokota, Y. Okada, K. Iribe, M. Tsuji, A, Ando, Y. Kunii, "Newly developed X-band SAR system onboard Japanese small satellite "ASNARO-2"," Published in: Synthetic Aperture Radar (APSAR), 2013 Asia-Pacific Conference, 23-27 Sept. 2013, Tsukuba, Japan, IEEE Xplore: 09 January 2014

5) "Launch Result, Epsilon-3 with ASNARO-2 aboard," JAXA Press Release, 18 January 2018, URL: http://global.jaxa.jp/press/2018/01/20180118_epsilon3.html

6) "Launch Date of Epsilon-3 Encapsulating ASNARO-2," JAXA Press Release, 8 Dec. 2017, URL: http://global.jaxa.jp/press/2017/12/20171208_epsilon3.html
 


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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