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Arraying Technique for Enhanced
Multiplexing of Interferometric Signals
(ARTEMIS) incorporates the techniques used for very long baseline
interferometry (VLBI), baseband correlation, and spread spectrum
communications to establish an inexpensive alternative to
the Deep Space Network (DSN) to provide terrestrial ground
support for communicating with low-power spacecraft at interplanetary
ranges using an array of several low-cost, small aperture
ground stations.
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Using
VLBI in ARTEMIS allows for the creation of an array that can
be made up of new and/or existing ground stations from all over
the world, each with its own independent local oscillator. Unlike
traditional VLBI, correlation will be done at baseband (modem)
frequencies rather than at the higher radio frequencies because
this obviates the need for expensive, stringent clocking at
each individual ground station. Several baseband correlation
techniques exist. The one that can best extract a signal greatly
eclipsed by noise is Full Spectrum Combining, which does an
open-loop down conversion to baseband of the entire received
spectrum.
The
low-cost local oscillators of each ARTEMIS ground station
will tend to drift in phase & frequency, causing the baseband
signals to likewise drift with respect to each other. This
places a maximum on the data rate the correlator can decode
due to time-domain alignment requirements and
requires that the signal have a very wide bandwidth so that
frequency spectrum correlation and correction can be performed.
ARTEMIS solves both problems through the application of spread
spectrum techniques.
As part of an initial feasibility study funded by the European
Space Agency in 2002, scenarios for communicating with the Moon, Mars,
and at very high data rates in low Earth orbit were investigated with a
low-power micro spacecraft transceiver equipped with an
omni-directional antenna. With subsequent funding from ETech,
an ARTEMIS breadboard prototype was constructed. Experiments with the
hardware prototype were completed in 2004, demonstrating the
ARTEMIS approach. UTIAS/SFL is aiming to fly an ARTEMIS transceiver
in space in the near future to test the communications technique
using an actual satellite.
Funding Partners
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![[ARTEMIS Funding Partners - ESA, ETech]](artemis_funding.jpg)