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May 2, 2003
National Space Development Agency of Japan

                  NASDA REPORT NO.130

Part 1 of 3

C O N T E N T S

* First Images Successfully Transmitted in DRTS-ADEOS-II
  Inter-satellite Communications Experiment
* Front Line of Advanced and Common Technology Research 12
* Let Us Talk to Space Challengers


First Images Successfully Transmitted in DRTS-ADEOS-II Inter-
satellite Communications Experiment 

Establishing a "Space Network" for drastic expansion of communication
coverage
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Communication Test with Midori-II via Inter-satellite Link

NASDA successfully conducted its first inter-satellite communications
experiment between Midori-II and the Data Relay Test Satellite
(Kodama), in geostationary orbit on February 20, 2003.

In this experiment, Kodama relayed the real time image to the Earth
Observation Center (Hatoyama-cho, Saitama Pref.) from Midori-II,
which was at a location where it could not make a direct
communication link with Japan's ground stations. 


Kodama Serving as a Data Relay Station in Space

The data relay satellite is a type of communications satellite.
Placed in geostationary orbit, it relays data from spacecraft in mid
or low earth orbit (300 -1000 km) to the ground station. This relay
operation greatly expands the coverage area and time available to
communicate with mid or low earth orbit satellites on a real-time
basis. 

In the West, NASA's six TDRSs and ESA's ARTEMIS are categorized as
data relay satellites. 

Kodama, Japan's first-ever data relay test satellite, was launched
atop the third H-IIA launch vehicle on September 10, 2002. Since
being put into geostationary orbit over the Indian Ocean (90 degrees
west longitude) on October 11, Kodama has been well prepared for use
in a variety of experiments. It is capable of transmitting data at a
rate of up to 240 Mbps, which is equivalent to simultaneous
broadcasting of 11 digital BS (Japan's broadcasting satellite)
channels or 60 digital CS (JapanIs communications satellite)
channels.


Inter-Satellite Communications Experiment Taking Advantage of the
Space Network

Historically, satellites have communicated directly with ground
stations. On the other hand, Midori-II communicates with Kodama in
geostationary orbit, and Kodama then downlinks the data to the feeder
link stations located at Tsukuba and Hatoyama. We call this
communication method the Space Network. 

NASDA conducted the experiment as follows: 

    (1) Kodama's inter-satellite communication antenna is oriented to
        Midori-II with its program tracking function and vice versa.
        (Each satellite is provided with the other's positional
        information in advance.) 

    (2) Receiving Ka-band forward beacon beams (23 GHz) transmitted
        from Kodama, Midori-II's inter-satellite communication
        antenna starts to track Kodama automatically. 

    (3) Midori-II uses the Ka-band (26 GHz) return channel to
        transmit signals containing a pseudo-noise (PN) code to
        Kodama. Once receiving the signals, Kodama's inter-satellite
        communciation antenna switches to the autotracking mode. This
        operation is called "establishing a link". 

    (4) Midori-II changes the signal content from PN code to image
        data, and then starts trasmitting the signals to Kodama.

    (5) Kodama relays the received image signals to the relevant
        ground feederlink stations.

    (6) The Hatoyama and Tsukuba feererlink stations receive the
        image signals in real-time. The Earth Observation Center
        (Hatoyama) analyzes and processes the data to create an
        image.
 
By this procedure, NASDA success fully acquired the first images from
Midori-II through the inter-satellite communications experiment. 


Future Applications of the Space Network

NASDA is planning to conduct various data transmission experiments
using the space network after establishing primary procedures for
communication experiments. 

The Tsukuba feederlink station can transmit command signals to Kodama
and experimental target spacecraft such as Midori-II via Kodama, as
well as receive observation data from spacecraft. 

The space network is expected to be used for relaying data from
future satellites such as the Advanced Land Observing Satellite
(ALOS) and Optical Inter-orbit Communications Engineering Satellite
(OICETS), It will also be used for communication between Kibo
laboratory module on the International Space Station(ISS) and the
ground stations, and for live broadcasting activities of astronauts
on television. 

Note: 

In this document, "forward" signals" denotes radiowaves trasmitted
from Kodama to Midori-II, while "return" signals" indicates that from
Midori-II to Kodama. "Ka-band" is a term to represent a frequency
bandwidth. 


Development Research on Space Software Technologies Aboard Rockets
and Satellites 

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Both hardware and software play an important role in confirming the
status of rockets or satellites through the relevant inflight data.
Software technology is also an essential element in the design of
spacecraft. This month's issue presents an outline of research being
conducted on a visualization technology for data of a spacecraft's
attitude and health, as well as approaches to shortening the
development period of spacecraft and to developing highly reliable
software.

 - Continued -

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