D-CIXS instrument

D-CIXS

D-CIXS (Demonstration of a Compact Imaging X-ray Spectrometer), built within RAL Space, was an instrument that flew as part of the science payload for ESA's SMART-1 mission to the Moon. SMART-1 aimed to flight test electric propulsion and other deep-space technologies for the first time, while at the same time performing scientific observations of the Moon.

D-CIXS was a miniature X-ray Spectrometer that used new technology to reduce the mass and volume of the instrument. Its main innovation was a purpose-designed matrix of Swept Charge Device (SCD) X-ray sensors mounted behind collimators and filters.

The SCDs were designed by e2v specifically as an energy resolving X-ray detector that was capable of working with only passive cooling. To do this, they incorporated a number of novel design features to maximise the X-ray energy determination and reduce the impact of radiation damage.

First light on D-CIXS
Credit: STFC (Barry Kellett)

An SCD works in a similar fashion to that of a conventional X-ray CCD; the charge packets generated from the absorbed X-rays are transferred to an output amplifier by voltages applied to clock lines, the clocking moves the charge diagonally across the device so that the active area can be clocked continuously and read out by a single readout channel.

D-CIXS's primary aim was to demonstrate that the SCD and collimation techniques could be used to produce a small X-ray spectrometer that would operate using passive cooling for the detectors. This was the first time that any mission had flown SCD detectors into space. The science goal was to detect X-rays from the lunar surface and to then establish the elemental abundances of the main rock forming elements – in particular Al, Mg and Si.

Although insufficient data was obtained to generate abundance maps the instrument did achieve the following ‘firsts’:-

• First direct detection of Ca on the lunar surface
• First direct detection of Ti on the lunar surface