Posted: October 15, 2008
A UK-built X-ray camera that will chart the mineral inventory of the Moon is set to launch into space on 22 October aboard the Chandrayaan-1 spacecraft, India’s first mission to the Moon.
Chandrayaan-1 will spend two years performing high resolution mapping of the lunar surface in visible light, near infrared, low energy and high energy X-rays. Its scientific payload contains two NASA, three European and seven Indian instruments. The UK’s contribution is the X-ray spectrometer C1XS, which builds on the legacy of the D-CIXS instrument (Demonstration of a Compact Imaging X-ray Spectrometer) that flew aboard ESA’s SMART-1 mission between 2003 and 2006, and was built by scientists and engineers from the Rutherford Appleton Laboratory (RAL) in Didcot, near Oxford.
The Chandrayaan-1 spacecraft before the majority of instruments had been mounted. In this orientation, the Moon will be at the bottom of the spacecraft during observations. Image: ISRO/ISAC.
C1XS will quantify the Moon’s mineral resources and is expected to unearth clues regarding the origin of the Earth-Moon system. "There is still a lot we don't know about the Moon," says C1XS Science Team chair Dr Ian Crawford of Birkbeck College, London. "Accurate maps of the surface composition will help us unravel its internal structure and geological history. Among other things this will help us better understand the origin of the Earth-Moon system. We will also be able to learn more about what happened on the Moon since it formed and how and when it cooled. By peering into its craters, we may even be able to see below its crust to the material underneath."
X-ray spectrometers work by detecting X-rays from the Sun which have been absorbed by atoms in the lunar soil, then re-emitted in such a way as to reveal the chemistry of the surface in that location, since each element has its own signature in X-rays. The sensitivity of the instrument is related to the activity of the Sun, for example, under ‘normal’ conditions, C1XS will be able to detect magnesium, aluminium and silicon X-rays. But during a solar flare, it may also be able to ‘see’ higher energy elements such as iron, titanium and calcium. The X-rays produced by the Sun are measured by a separate detector system, the X-ray Solar Monitor (XSM), supplied by the University of Helsinki, in order to accurately calibrate the X-rays detected at the Moon’s surface.
Animations of the Chandrayaan-1 spacecraft in action around the Moon are available here. Comissioned by RAL (STFC) and produced by Doug Ellison to help promote British involvement in space science.
"C1XS uses an advanced version of conventional CCD sensors such as you might find in a digital camera, called swept charge devices,” explains C1XS Chief Engineer Chris Howe. “These are mounted behind a gold/copper 'collimator', which limits the field of view of the X-ray detectors to a narrow beam. Together these two innovations form an X-ray camera that has high resolution allowing identification of the surface elements, yet is far more compact and lower mass than other spacecraft's X-ray spectrometers."
C1XS is one of three instruments funded by ESA for the Chandrayaan-1 mission. SIR-2, a near infrared spectrometer led by the Max-Planck Institute for Solar System Science, will survey the Moon's mineral composition and the effect of space weathering, since in the absence of an atmosphere, the Moon’s barren surface is exposed directly to the harsh environment of space. Like C1XS and XSM, the SIR prototype also flew on Europe’s SMART-1 mission. SARA (Sub-kilo electron volt Atom Reflecting Analyser), led by the Swedish Institute of Space Physics and developed with hardware contributions from India, will investigate the space environment around the Moon, and the interactions of the solar wind with the Moon's surface.
NASA is providing the Moon Mineralogy Mapper (M3) and the Miniature Synthetic Aperture Radar (MiniSAR), which will be able to detect water ice up to a depth of several metres. The presence of water ice in permanently shadowed craters in the Moon's polar regions has long been debated. The Indian contributions include the Terrain Mapping Camera (TMC) which has a five metre resolution, the Lunar Laser Ranging Instrument (LLRI) which will accurately map the lunar topography, and the Moon Impact Probe (MIP), a 30 kilogram device that will be ejected towards the Moon once Chandrayaan reaches a polar orbit of 100 kilometres altitude. Initially the spacecraft will enter orbit around the Moon at a distance of 1,000 kilometres. The MIP will demonstrate the technologies required for impacting a probe at a desired location on the Moon as well as making scientific measurements and taking video images during the probe’s descent.
A small fraction of the lunar surface was investigated by the Apollo X-ray experiment. C1XS will provide much greater coverage at a high resolution of 20-25 kilometres. Image: USRA/LPI.
"There is currently a renaissance in lunar exploration, with many international lunar missions either underway or planned for the next few years, leading up to the planned return of astronauts to the lunar surface by 2020,” says Crawford. “Through its involvement in C1XS, the UK is playing an important role in this international activity."
Chandrayaan-1 is expected to launch from the Satish Dhawan Space Centre at Sriharikota in India at around 1:58am BST on 22 October, and will reach the Moon around eight days later. "Launches are always an incredibly nail-biting and exciting time in a mission," adds Howe. "After all our hard work, we're all eager to see C1XS safely on its way so that it can get to work uncovering more of the Moon's secrets."
Further launch information and details of the UK contribution to Chandraayan-1 can be found on the C1XS homepage.