Artemis

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ESA and JAXA satellites ‘talk’ to each other

This image of Mt. Fuji – Japan’s highest mountain (3 776 metres) –
was acquired on 23 September 2006 with Envisat’s ASAR (Advanced
Synthetic Aperture Radar) instrument and transmitted via Kodama to
Tsukuba where it was recorded and pre-processed by the Envisat
data-processing equipment. This pre-processed data was then transmitted
via a data link to ESRIN - ESA’s Earth Observation Centre in Italy – for
final processing into data ‘products’ and data quality checks.

Credits: ESA

1 December 2006
ESA’s Envisat satellite and the Japan Aerospace Exploration Agency’s (JAXA) data relay test satellite Kodama have successfully completed an interoperability test demonstrating that scientific data from Envisat can be transmitted to Kodama and from there transmitted to the Japanese ground receiving station in Tsukuba.

With more than 50 environmental satellites orbiting in space, interoperability and cross-support are important topics among space agencies because compatibility between the systems would allow for more efficiency and flexibility in the mission operations and the integrated analyses of the millions of data sets being created.

Envisat has been successfully relaying data to the European data-relay spacecraft Artemis, in geostationary orbit, since 2003 in order to allow data to be acquired, downlinked, processed and delivered to end users much faster. Envisat is able to do this because it is equipped with an antenna terminal that allows data to be transmitted on two channels of 100 Mbp/second each in the 27 GHz radio-frequency bandwidth, normally referred to as Ka-band.


Artist's impression of ESA's Envisat satellite transmitting scientific data to JAXA's
Kodama satellite and Kodama retransmitting to the Japanese ground receiving station in
Tsukuba.

Credits: JAXA

Like Artemis, Kodama is in geostationary orbit at an altitude of approximately 36 000 km, making it possible to use the same Envisat functions used for communicating with Artemis. However, in order to store and process the Envisat data downlinked by Kodama to Tsukuba, it was necessary for ESA to provide JAXA with spe*spam filter*ed equipment configured specifically for handling Envisat science data.

The objectives of the test were to demonstrate:

• Kodama could receive a single Ka-band return signal from Envisat and continuously track the signal for a predefined period
  
• Kodama could receive a single Ka-band transmission from Envisat without interference, while Envisat was transmitting on a second Ka-band frequency
  
• Kodama could receive data from Envisat via a Ka-band return signal and downlink it to ground for storage and low-level processing
  
• The down-linked data could be processed into products with an error level commensurate with similar data processed after downlink via Artemis.

The interoperability technology demonstration between ESA and JAXA was conducted in two stages.

In the first stage, an Envisat Ka-band signal was transmitted to Kodama to demonstrate correct pointing of antenna terminals on the two satellites and the radio-frequency compatibility of the two systems. This stage, which consisted of several inter-satellite link segments performed over a period of three days, was conducted successfully in April 2006 and gave the green light to prepare for stage two.


The Japan Aerospace Exploration Agency’s (JAXA) data relay test satellite Kodama.

Credits: JAXA

In the second stage, Envisat science data was transmitted via Kodama to Tsukuba where it was recorded and pre-processed by the Envisat data-processing equipment. This pre-processed data was then transmitted via a data link to ESRIN - ESA’s Earth Observation Centre in Italy – for final processing into science data ‘products’ and data quality checks. This stage, performed over a period of two weeks, was completed successfully in September 2006. ESA, supported by European industry, travelled to Tsukuba to monitor and control the data capture equipment and to perform real-time analysis of the acquired data.

Two of Envisat’s instruments, ASAR (Advanced Synthetic Aperture Radar) and MERIS (Medium Resolution Imaging Spectrometer), were used for the test and provided the ‘end product’ (images) by which the overall success of the test was assessed.

Engineers from ESA’s establishments, ESTEC in The Netherlands, ESRIN in Italy and ESOC in Germany, were supported by the European industry and collaborated with their counterparts in JAXA and the Japanese industry to make the test a reality.


Hokkaido, the northernmost and second largest island of Japan’s four main islands, was
captured on 26 September 2006 by Envisat’s MERIS (Medium Resolution Imaging
Spectrometer) instrument and transmitted via Kodama to Tsukuba where it was
recorded and pre-processed by the Envisat data-processing equipment. This
pre-processed data was then transmitted via a data link to ESRIN - ESA’s Earth
Observation Centre in Italy – for final processing into data ‘products’ and data
quality checks.

Credits: ESA

The Earth observation (EO) data produced by Envisat is in so much demand by the scientific community that routine communication, in addition to direct-to-ground links, with Artemis is required in nearly all of Envisat’s fourteen daily orbits. Sometimes communication is required more than once per orbit in order to transmit the acquired data to the ground. Likewise, Kodama supports a number of Japanese EO satellites in low Earth orbit, which communicate with it on a regular basis.

The engineers were therefore not only tasked with getting the satellites to speak to each other and interfacing Envisat data processing equipment with JAXA’s ground station, but they also had to ensure there was no impact on the nominal operations for either satellite.

A typical example of this is the generation of the Envisat commanding for the test. Normally, all Envisat commanding is generated automatically by mission planning software. However, for this test commands had to be generated semi-automatically and manually checked before being merged with the command schedule generated for nominal operations.

Achieving this level of success required a lot of effort, time and close cooperation by all team members involved at ESA and JAXA, demonstrating not only the inter-operability of Envisat and Kodama, but also the excellent cooperation between the two agencies.

Source: ESA - News

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"KODAMA" Data Relay Test Satellite (DRTS)

December 1, 2006 Update

Data relay experiments with ESA satellite

The Data Relay Test Satellite "Kodama" successfully carried out data relay experiments with the earth observation satellite "Envisat" of the European Space Agency (ESA). The experiments were performed in April and September, 2006, by coordinating the regular operation schedules of the two satellites.

In April, we confirmed that the "Envisat" at 800 km altitude, and the "Kodama" at 36,000 km altitude, were able to accurately face each other. In September, data was sent from the "Envisat" to the Tsukuba Space Center via the "Kodama", then it was further transmitted to the European Space Research Institute of the ESA in Italy. The quality of the data was verified to be high there.

The "Envisat" usually carries out operations using the ESA data relay satellite "Artemis" in a geostationary orbit at 21.5 degrees east longitude over the equator. We have already successfully performed communication experiments with the "Artemis" using two of our satellites, the "Midori II (S-band and Ka-band)" and the "Kirari (S-band and laser beams)". We have been making big progress in one of the challenges facing space agencies around the globe, namely "Interoperability and mutual support".

Source: JAXA Missions - DRTS

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Another world first for Artemis: a laser link with an aircraft

LOLA telescope assembly, as fitted to aircraft used in the Artemis laser link trials

Credits: Astrium

18 December 2006
Artemis, the European Space Agency Advanced Relay and Technology Mission Satellite, successfully relayed optical laser links from an aircraft in early December. These airborne laser links, established over a distance of 40 000 km during two flights at altitudes of 6000 and 10 000 metres, represent a world first.

The relay was set up through six two-way optical links between a Mystère 20 equipped with the airborne laser optical link LOLA (Liaison Optique Laser Aéroportée) and the SILEX laser link payload on board ARTEMIS in its geostationary orbital position at 36 000 kilometres altitude: a feat equivalent to targeting a golf ball over the distance between Paris and Brussels.

These tests were made by Astrium SAS (France), the prime constructor for both LOLA and SILEX, as part of the airborne laser optical link programme conducted by the DGA (French MoD procurement agency) from its Flight Test Centre at Istres, in the south of France. The ESA ground station of Redu, Belgium, also contributed to this success by managing the Artemis SILEX payload operations.

This clearly demonstrates the feasibility of an optical link between an airborne carrier and a geostationary satellite.


Carrying three payloads plus a number of experiments, Artemis (Advanced Relay and
Technology Mission Satellite) has been designed to test and operate new
telecommunications techniques.
The L-band mobile payload allows two-way voice and data communications, via satellite,
between fixed Earth stations and land mobiles - trucks, trains or cars - anywhere in
Europe and North Africa.
Artemis carries two payloads for communications directly between satellites, which
receive data from low-Earth-orbiting satellites and transmit them directly to Europe:
-a laser-optical relay terminal called SILEX
-a double S/Ka-band terminal called SKDR.
ARTEMIS was launched 12 July 2001 by Ariane 5. It was initially placed in the wrong
orbit and recovery operations have been underway since then to bring it to its final
position.

Credits: ESA-J.Huart

Previously, in November 2001, Artemis made a world premiere by establishing a laser link with the French Earth Observation satellite SPOT-4: imaging data was sent by SPOT-4 using a laser beam as signal carrier to Artemis and from there by radio waves to the ground. This unprecedented link-up between satellites in space was done in the framework of the SILEX development, an innovative payload which provides a laser beam as a data signal carrier.

More recently, since November 2005, Artemis has been relaying optical signals from KIRARI, the Japanese Optical Intersatellite Communications Engineering Test Satellite. This first ever two-way optical communication illustrated the value of this technology for the development of future Earth observation systems.

Optical technology has several advantages for data relay applications, including the capability to provide high data rates with low mass, low power terminals, combined with secure, interference-free communications. Earth observation can truly benefit from this new way of transmitting data around our planet.

On a daily basis Artemis is also relaying data in the Ka-band from Envisat, the ESA earth observation satellite, providing, since 2002, a comprehensive view of the Earth's oceans, land, atmosphere and ice caps.

This new world first between a satellite and an aircraft is another demonstration of what can be achieved in Europe thanks to the ESA ARTES technology programme.

Source: ESA - News