The world won't be so close-fisted in sharing the information collected by the tens of satellites floating around the Globe.

ESA's Envisat satellite and the Japan Aerospace Exploration Agency's (JAXA) data relay test satellite Kodama (photo) have successfully showed that scientific data from Envisat can be sent to Kodama and from there transmitted to the Japanese ground receiving station in Tsukuba.

More than 50 environmental satellites are orbiting around the earth and interoperability is an important topic among space agencies because compatibility between the systems would permit more efficiency and flexibility in operations and the integrated analyses of the millions of created data sets.

Envisat has been successfully gathering data from the European data-relay spacecraft Artemis, in geostationary orbit, since 2003 in order to fasten acquiring, downlinking, processing and delivering data. Envisat can do it because it has an antenna terminal that transmits on two channels of 100 Mbp/second each in the 27 GHz radio-frequency bandwidth, referred as Ka-band.

Kodama is also a 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 specialized equipment configured specifically for handling Envisat science data.

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

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. 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.

ESA specialists 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), provided the 'end product' (images) by which the overall success of the test was evaluated.

The data produced by Envisat is in so much demand by the scientific community that routine communication with Artemis is required in nearly all of Envisat's fourteen daily orbits. Likewise, Kodama supports a number of Japanese EO (Earth Observation) satellites in low Earth orbit. 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 operations for either satellite. This success required a lot of effort, time and close cooperation between ESA and JAXA.