Ptolemy (link opens in a new window) is an evolved gas analyser instrument on the lander of ESA's Rosetta mission (link opens in a new window) to comet 67 P/Churyumov-Gerasimenko.
The spacecraft will be the first to undertake a long-term exploration of a comet at close quarters and is scheduled to arrive in 2014. The mission consists of an orbiter and a small lander from which a suite of instruments will analyse the comet's surface and sub-surface.
Rosetta aims to investigate the origin of comets and the relationship between cometary and interstellar matter, and establish the implications from these with regard to the origins of the Solar System.
Ptolemy seeks to explore the relationship between water ice on comets and the Earth's oceans and to study the nature of organic material on the comet and thus investigate the relationship with similar materials from other Solar System bodies.
The instrument combines gas chromatography and mass spectrometry to measure the isotope ratios of Hydrogen, Carbon, Nitrogen and Oxygen. The ratios of heavy to light isotopes (e.g. 18O/16O in H2O) act as fingerprints to determine where a sample of water came from. Ptolemy was designed and built by teams from RAL and the Open University.
Once on the comet's surface, Ptolemy will be provided with sub-surface samples which are then heated in miniature ovens. Once gaseous, the samples are fed into a sophisticated chemical analysis system and from here into an ion trap mass spectrometer. The gas is ionised by an electron-source and then a controlling high-voltage field is used to selectively eject ions of differing mass into a counter, enabling isotope ratios to be measured to very high precision.
The challenges for the project were the miniaturisation of the mass spectrometer with its high-voltage control electronics, the many gas valves and high temperature reactors of the complex chemical analysis system, and the supply of ultra-high purity helium to flush the evolved gases through the instrument.
The instrument control and data processing electronics required the design of several ASICs. Overall, the severe constrains on the size, mass and power available for Ptolemy required the miniaturisation and space-qualification of every component –either with significant evolution and modifications of existing components or the development of completely new technologies.
For more information please contact: RAL Space Enquiries