The ODIN AOS was built by a consortium of three french laboratories: the LAS (Marseille) which is responsible for the qualification tests and the technical management of the whole instrument and is in charge of the AOS processor; the CESR (Toulouse) which built the digital interface and power supplies sub-systems; and the Paris-Meudon observatory (Laboratoire ARPÈGES) which built the I.F. sub-system and is in charge of the scientific management of the instrument.

AOS IF processor

It provides the following functions:

select one from five available channels (four sub-millimetre and one millimetre bands). The channel bandwidth is 1 GHz centred at 3.9 GHz with an input level of -60 dBm/MHz,
amplify and down convert the 3.9 GHz frequency band to 2.1 GHz, by frequency mixing with a phase-loop locked DRO at 6 GHz,
adjust the input level by 1 dB steps over a 15 dB range,
internally calibrate the AOS frequency response by using a 100 MHz Comb generator (stability of 10^-3 between -30° and 70 °C).

The utilised technology involves reliable, hyperfrequency components, including thin films on alimina substrates and underground lines.

AOS Acousto-Optical processor

The AOS processor is directly derived from an acousto-optical design made in Meudon Observatory for ground-based instrumentation (Lecacheux et al., 1993). The AO processor utilises a 780 nm laser diode (Hitachi HL 7851 G) driven by a constant current. The lithium niobate Bragg cell (from Thomson), after anisotropic diffraction of the light, provides about 1000 resolution elements over a bandwidth of 1 GHz. The photodetector is a 1728 pixels, linear CCD (Thomson TH 7803). The whole AO processor is stabilised in temperature over several, distinct functioning steps ranging between 10° and 30°C, in order to avoid variations due to short term (satellite platform) and long term (aging) temperature changes.

AOS data handling and interfaces

The CCD video output is readout every 5 ms and digitised over 12 bits, in order to keep the noise statistics of the signal unmodified over a dynamic range greater than 10 dB. A pre-adder delivers the sums of four consecutive readouts to transputer (Thomson T805), also performs the final double-buffer integration in synchronism with the radiometer and antenna pointing informations. The transputer also performs instrument monitoring and manages communication with the ODIN on-board computer.

AOS instrumental characteristics

All the involved components are reliable, space-qualified components at the exception of the laser diode and of the Bragg cell. These two parts have been extensively tested and space-qualified in the frame of two specific programs, undertaken by CNES.
The main electrical and environmental characteristics of the instrument are listed below:

The instrument has been extensively tested in laboratory: all the measured spectrometric parameters (bandwidth and flatness, spectral resolution, amplitude stability, frequency accuracy and stability, etc...) are well beyond the required specifications.