Toshinori Kuwahara1)*, Kazuya Yoshida1), Yoshihiro Tomioka1), Kazufumi Fukuda1), Hiroo Kunimori2), Morio Toyoshima2), Tetsuharu Fuse2), Toshihiro Kubooka2)

1) Tohoku University, Japan 2) National Institute of Information and Communication Technology, Japan

August 12, 2013 1 Micro-satellite Development Activity in Japan Micro-satellite missions planned in 2013  H-IIA Piggyback (ALOS-2)  SPROUT: Nihon University  RISING-2: Tohoku University  UNIFORM-1: Wakayama University  SOCRATES: AES Co., Ltd.

 H-IIA Piggyback (GPM)  STARS-II: Kagawa University  TeikyoSat-3: Teikyo University  ShindaiSat: Shinsyu University  KSAT2: Kagoshima University  INVADER: Tama Art University  OPUSAT: Osaka Prefecture University  ITF-1: University of Tsukuba

 Others  Several 50kg-class microsatellites © JAXA

2 SPRITE-SAT (44kg) Micro-satellite Development at SRL

#1：SPRITE-SAT (RISING-1)  Launch: Jan. 2009 (H-IIA)  Demonstration of © JAXA  Image acquisitions by mission camera RISING-2 (42kg)  Coarse attitude control  Deployment of the boom #2：RISING-2  FM ready. Launch in 2013 (H-IIA)  Mission  Multi-spectrum observation with a Liquid Crystal Tunable Filter (650-1000nm) RAIKO (2.6kg)  High resolution stereo images of cumulonimbus  Terrestrial luminous events in upper atmosphere #3：RAIKO  Launch: July 2012 (H-IIB) (Deployment from the ISS: Oct. 2012)  Mission RISESAT (55kg)  Technology demonstrations (Communication URX, S, Ku, Image acquisition, De-orbit) #4：RISESAT  Launch (2013 ~)  Mission  International Scientific Missions  Satellite-to-ground laser communication 3

RAIKO  Deployment: Oct. 4, 2012  Re-entry: Aug. 5, 2013

5 RISESAT Project Background

Hodoyoshi Program (Professor Nakasuka, The University of Tokyo)  Development of five 50kg class micro-satellites  One of the satellites is an international scientific micro-satellite (RISESAT)  RISESAT also has some technology demonstration missions.

RISESAT: Rapid International Scientific Experiment Satellite Mission Objectives  Demonstrate international scientific missions by inviting instruments from abroad  Investigation on advanced bus system technologies for future scientific microsatellites  Development of a reliable, robust and cost effective micro-satellite bus system Expected effects  Realization of mechanism of rapid demonstration of scientific missions in the future  Improvement of microsatellite technologies which enables future challenging scientific missions  Commercial spin-off of providing cost-effective microsatellite bus systems 6

RISESAT System Specifications

Launch configuration

After panel deployment

7 Payload Instruments Camera Instruments Sensor Instruments

High Precision Telescope Meteor counter TriTel – 3D Dosimeter - HPT - DOTCam (Hungary) (Taiwan(NCU)) (Taiwan(NCKU))

TIMEPIX – Particle counter (Czech)

Ocean Observation Camera - OOC (Hokkaido University) Technology Demonstration MEMS Magnetometer (Sweden) Laser Communication Transmitter VSOTA (NICT, Japan)

8 Optical Communication with VSOTA (1)

 Collaborative research between National Institute of Information and Communication Technology (NICT) and Tohoku University  VSOTA: Very Small Optical Transmitter for Component Validation  Objectives:  Satellite-to-Ground Data Downlink demonstration for future realization of G-bit optical data downlink  Future alternative for RF communication on micro-satellite → no frequency allocation problem  Dual-band:  980 nm  1540 nm  Installation: Fixed to sat. body.  Attitude control: Target pointing mode

 Bit rate: 100Kbps～ 9

Optical Communication with VSOTA (2)

SOCRATES (50kg)* RISESAT (60kg) Advanced Engineering Tohoku University - NICT Services Co., Ltd - NICT Laser Terminal VSOTA SOTA 980nm 980nm Downlink 1550nm 1550nm Pilot signal detector none 1060nm Satellite’s Attitude Control Coarse (Mechanical Gimbals) Pointing Mechanism + ! Fine Pointing Mechanism Bit Rate 100Kbps ~ 10Mbps 1Mbps/10Mbps Satellite Attitude Control Better than 0.1 deg unknown Accuracy down to 0.04 deg and more. mass ~1kg ~6kg† *Hideki Takenaka, et al., “Experiment plan for a small optical transponder onboard a 50kg-class small satellite," 2011 International Conference on Space Optical Systems and Applications, Santa Monica, May 11-13, 2011. †Hideki Takenaka, et. Al., “Experiment plan for Space Communications Research Advanced Technology Satellite," IEICE Technical Report, 2011. 10 Laser Transmitter: VSOTA © NICT  VSOTA: Very Small Optical Transmitter for Component Validation  VSOTA-COL: Collimator Assembly  VSOTA-E: Laser diode driver electronics  VSOTA-CNT: Electrical controller of VSOTA-E. Space Plug-&-Play Avionics Compatible VSOTA-COL

SHU

11 Mechanical Configuration

Launcher Interface

Payload Segment

12 System Architecture

Telemetry, Tracking & Command Command & Data Handling Orbit determination New Development

[UHYB] [SCU] Satellite central unit Re-design UHF [DPD] [CPU-N] [CPU-R] antenna Processor unit Processor unit hybrid Data Fine Attitude Control System Decoder (nominal) (redundant) [GPSR] [URX] GPS receiver UHF [TTR] [ACU] receiver Telecommand, [CTR] Attitude Control Command and [STX] telemetry, [MTQ] Unit telemetry router S-band and recovery Magnetic transmitter Torquers (3-axes) [RW] Reaction wheels (4) [DOM] [GAS] De-orbit [PCU] Geomagnetic [STT] Mechanism Power control Sensor Star Trackers (2) unit (3-axes) [SPDM] Solar Coarse [SAS] [FOG] Panel Depl. Mech. Coarse sun Gyroscope (3-axes) [SCP] Attitude sensors [BAT] Solar cells Control Battery unit [SES] System Sun earth sensors (4) Power Supply System Payload

Main Bus Com. Line [XTX] [MMC] [SHU] X-band Coder Micro monitor Science handling unit Scientific Data Line transmitter camera Power Line

High-speed Downlink Other General Lines Laser Link Pay 1 Pay 2 Pay 3 Pay 5 Pay 6 Main computing unit Pay 4 Terminal NCU/FPTI NCKU OOC MTA EK IEAP ASTC 5R1_2012/02/07 VSOTA Antifuse FPGA Attitude Control Error Budget Ground Measurement

GPS signal real-time processing

ACS 14 Coarse Control Fine Control STT (2) Magnetometer (1 x 3 axes)

GPS (1) Magnetic Torquers (3 axes)

FOG (1 x 3 axes) Fine Sun Sensor (4)

Coarse Sun Sensor (8)

RW (4)

SCU ACU Attitude Control Modes

Detumbling Mode ω < 0.5 º/s Spin-stabilization Safe Mode ω ≥ 5 º/s TC TC

ω ≥ 5 º/s Coarse Sun /Contingency Level 2 Pointing Mode Coarse Pointing TC TC Fine Pointing Fine Sun Satellite controls its attitude ω ≥ 5 º/s Pointing Mode to point the (laser) direction /Contingency Level 2 toward an optical ground TC TC station during fly-over

Mission Operation Nadir Pointing Mode

TC TC TC TC

Inertial Pointing Target Pointing

Mode Mode 16 Attitude Control: Target Pointing Mode  Collimators are mechanically fixed ACU(H/W)-in-the-loop (handshake) to satellite structure (bottom)  Satellite controls its attitude to point the laser direction toward an optical ground station during fly- over  Required control accuracy:  0.4 deg (3σ） for 100 Kbps  Simulation results illustrate good feasibility. Ground verification is on- going.

17 On-going Improvement of Attitude Control Accuracy  GPS real-time position estimation  Extended Kalman Filter for real- time/forward position estimation.  Attitude filter EKF  Extended Kalman Filter for sensor fusion between Star Trackers and FOG for real-time/forward attitude estimation.  HPT as guidance sensor  HPT/LCTF is being modified to be used for fine-guidance sensor in closed-loop control. (pilot laser beam from G.S.)  Ground testing  Dynamic closed-loop simulation/evaluation environment.

18 Conclusion and outlook  Micro-satellite RISESAT demonstrates satellite-to-ground dual- band laser communication on micro-satellite. The pointing of laser beams are achieved purely based on satellite attitude control.  RISESAT carries dual-band laser communication transmitter developed by NICT.  RISESAT is capable of target pointing attitude control for optical link between ground stations.  The RISESAT system is now under development. The flight model will be ready by early 2014.

 Combination of RISESAT’s attitude control capability and the fine pointing mechanism in the future will allow “light-weight G-bit optical communication system” for micro and nano-satellites.  Low cost mobile optical ground stations are now also being developed (Φ 200mm). Pointing error evaluation is planned using array of optical ground stations.

19 Thank you for your attention.