Takhasi Hamazaki 
  
  
   
     
    
      
    
        
   
         
     
    
   
     
  
  
   
   
    
  
       
  
  
  
  
    
   
  
  
  
    
i n Star Tracker A Relay 
e . Antenna Launch Vehicle H-IIA 
igi bas S ft ^ Mass 4 
om | Generated Power 7KW 
Orbit 691.65km 
ks og Repeat Cycle 46 days 
25 Sub-C 2 da 
.20 
S 
Solar Array 
onal Trade PRISM AVNIRZ 
ased array 
n 10 to 51 Flight 
qnd ase Direccion Fig.4 ALOS On-Orbit Configuration 
width is 
  
  
  
3.3 Autonomous Position and Attitude Determination System 
ery High precision satellite position and attitude determination system enables users to locate exact position of any ground 
objects without any ground reference points. This capability is crucially important for cartography for unmapped 
region. This is achieved with accurate star trackers, dual-frequency carrier phase tracking GPS receivers, and jitter 
1z ^75 sensors on board. 
  
  
  
  
  
  
V/VH | In order to get sub arc-second accuracy with star trackers, 
e m list of target stars are carefully chosen (moving stars or 
des) adjacent stars are excluded) and stored in the on-board 
EE AOCS computer. Expected positions of target stars are 
m 
Ade sent to star trackers from AOCS computer every one 
TEE second and exact position is observed and calculated by 
km star trackers and this information is sent back to AOCS 
ts sl computer. 
ops — | Combining the data from dual-frequency carrier phase 
tracking GPS receiver on board ALOS and that of ground 
GPS reference stations, ALOS position is determined 
Within 0.2m accuracy 
3.4 Data Compression 
The PRISM generates 960Mbps data stream and data rate 
ghly 9m in is reduced to 240Mbps using Discrete Cosine 
r part and Transformation (DCT) and Huffman coding technology. 
russ, metal Similarly, AVNIR-2 data rate is reduced from 160Mbps 
S on-orbit to 120Mbps with Differential Pulse Code Modulation 
(DPCM) technology. 
3.5 Data Transmission 
B Inter-satellite communication capability allows real-time 
| stabilize data acquisition via Japanese and European data relay 
rom major satellites. This capability is of great importance for 
1rror drive disaster monitoring mission. The ALOS has a 
| technique conventional 120Mbps X-band direct down link capability 
Mega Gate for back up and additional services for foreign receiving 
Stations. Bit error rate is drastically reduced to the order 
of 10° with Reed-Solomon error correction code. Solid 
NU dot Ie Bes 768Gbits memory and Fig.5 ALOS Mechanical Test Model (MTM) 
recording at 240Mbps. 
a 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 139