The ESA PROSPECT Payload: Status and Operations Planning

PROSPECT Overview: The Package for Resource Observation and in-Situ Prospecting for Exploration, Commercial Characterisation and Testing (PROSPECT) is a payload in development by ESA for use at the lunar surface.  PROSPECT is being prepared for flight to the lunar south polar region as part of the NASA CLPS program.

PROSPECT will perform an assessment of the volatile inventory in the near surface lunar regolith (down to ~1 m), and complete elemental and isotopic analyses to determine the abundance and origin of any volatiles discovered. PROSPECT also has ISRU capabilities and will aim to complete in-situ extraction of oxygen (and solar wind implanted volatiles) from lunar minerals, which will constitute potential science return from anywhere on the Moon.

PROSPECT is comprised of the ProSEED drill module and the ProSPA analytical laboratory plus the Solids Inlet System (SIS), a carousel of sealable ovens for evolving volatiles from regolith.  The ProSEED drill is capable of collecting two icy samples of different sizes and mechanical properties in a single sampling operation, one of up to 45 mm³ and a second up to 8 cm³, with the smaller sample delivered to ProSPA for analyses.  The drill rod also has integrated temperature sensors and a sensor to measure the electrical permittivity of the lunar soil along the borehole to give an indication of the presence of water ice and small subsurface structures in the surrounding regolith.

The ProSPA laboratory will receive samples from the drill, seal them in miniaturized ovens, and process them via ramped (EGA), stepped (isotopic) or single step (ISRU) heating up to ~1000 °C, completing physical and chemical processing of released volatiles, and analyzing the obtained constituents via Ion Trap (ITMS) or Magnetic Sector (MS) mass spectroscopy.

ProSEED and ProSPA will also each carry small cameras.  The ProSEED Imaging System (IS) has multispectral capabilities via 6 LEDs, which can illuminate the surface with wavelengths ranging from 451 to 970nm.  This will provide images and ‘video’ of the drill working area to monitor activities and deliver contextual scientific information.  ProSPA’s Sample Camera (SamCam) has its own specific illumination unit with similar capabilities to the ProSEED IS and will image the samples before they are sealed in the ovens, providing information on their morphology, grain size, volume and mineralogy.

Operations Planning: PROSPECT Science Team (ST), led by the ESA Project Scientist, comprises ~40 experts within Europe, including 8 ‘Investigation Leads’.  Together, the ST is responsible for supporting all activities related to the scientific exploitation of PROSPECT instrumentation.  Recent focus has been on developing nominal operational scenarios that will allow PROSPECT to achieve its high priority science objectives and maximise science return within the tight operational constraints available.  Two fundamental operational scenarios have been defined, depending upon whether regolith at the landing site is found to be icy or dry.

Conceptually, operations for PROSPECT will be ‘front-loaded’ for science, pushing for high impact science activities and the highest priority science objectives as early as possible rather than building up towards them.  This is mainly driven by the limited operational lifetime on the lunar surface, which will also mean that there will be very little operator interaction and limited tactical planning available.

The baseline plan includes two ‘vertical surveys’, each of which includes the acquisition and analysis of 4 subsurface samples.  The general pattern of activities would be to run an ‘Evolved Gas Analysis’ on the first sample using the ion trap (ITMS), and then a magnetic sector (MS) analysis on the second sample which is taken from a similar depth.  In combination, this would provide a complete chemical analysis with abundance and isotopic measurements for key species at that depth in the borehole.  For the very first sample, the ISRU demonstration would also be attempted after the EGA, in order to maximise the use of that sample.

Samples 3 and 4 would follow a similar pattern with an EGA followed by MS, but they would be acquired deeper than the initial samples.  The permittivity sensor is embedded in the drill ~40cm from the drill tip, and will be used regularly as the drill descends below 40cm.  This sampling pattern will allow PROSPECT to explore the vertical distribution of various species within the borehole, which is one of the payload’s primary objectives.  With these 4 sampling and analysis sequences, the first ‘vertical survey’ is complete.

A second borehole would follow a similar operational pattern but with different sampling depths, and provide lateral profiling for any ices, volatiles and species of interest.  In combination, the two vertical surveys would allow for PROSPECT to meet its priority objectives.  An additional ISRU demonstration may be attempted in the second borehole at a different depth to the original in order to explore the impact of grain size on the process.

The differences between the icy and dry scenarios will primarily be in the various parameters and instrument modes used.  The dry scenario may also allow for ‘hot’ operations, with fewer cooling periods required to manage icy volatile loss.

The high level plan will be further detailed as PROSPECT builds towards operations, defining the parameters to use for sampling depths, oven heating profiles, gas processing etc.  This will also allow for more fine tuning of the priorities. 

Additional Science Team Activities: The Science Team will also be completing several activities in support of the operations planning and to prepare for data calibration and interpretation.  These efforts are needed to support PROSPECT all the way from now through launch, operations, data exploitation, and data archive delivery.  Work will include aspects of ground calibrations, testing of command sequences, and end-to-end testing to understand how each aspect of the payload is expected to perform.  In addition, data pipelines will be developed to manage the data returned as quickly and effectively as possible, processing the data from telemetry through to a calibrated level.