Description: To accurately determine endogenic heat flow, both thermal gradient and thermal conductivity measurements are needed. The thermal gradient measurement can be achieved by using several temperature sensors equally spaced along the length of the probe. Thermal conductivity can be measured by one of two methods: the 'steady state' method or the 'transient with a variant' or 'pulse heating' method. The steady state method was used by the Apollo 15-17 missions , whereas the pulse heating method was developed by Lister (1979) after the Apollo period In the steady state heating method, heat is applied to the regolith around the probe for a long period of time and thermal conductivity is derived from the rate at which temperature rises. This will affect the measurement associated with the diurnal and annual wave as it adds a significant amount of heat to the regolith, which will take a very long time to dissipate. In the pulse heating method, more heat is applied for a short duration of time. The temperature of the probe increases instantaneously and slowly falls off as the heat dissipates into the regolith after the heater is turned off. In this case, the thermal conductivity is derived from the cooling rate. In the pulse heating method, less heat is required and less time is required for a measurement. For the most accurate results, sensors must extend below the depth of the multi-year thermal fluctuation detected during the Apollo missions (>3 m). If the hole is deep enough to avoid the effects of the insolation, the geothermal gradient obtained in a lower portion of the hole should accurately reflect the endogenic heat flow. The spacing between sensors should be small (approximately 30 cm), because thermal conductivity of the regolith is heavily affected by its texture, which varies with depth. Determining the in situ heat flow, as well as the site-specific thermal wave depths, requires that measurements be taken over long durations (6-8 years).

Benefits: The National Research Council's 2011 Decadal Survey on planetary sciences recommended performing heat flow measurements on network geophysical missions to the Moon. The heat flow probe therefore meets payload requirements for the International Lunar Networks. In addition to measuring heat flow on the Moon, the probe can be deployed on the future Discovery- and New Frontier-class robotic missions to Mars, and other planetary bodies. The instrument may be used by astronauts on Sortie human lunar missions. The percussive penetrometer can also be used to deploy other sensors, such as Neutron and Gamma spectrometer and Electrical Properties probe. Since the penetration rate relates to soil's bearing strength, the tool could also provide geotechnical measurements (incl. in situ density) of lunar subsurface to a depth of 3 m.

Non-NASA applications include measuring of heat flow in areas on earth, where optimal thermal isolation of heaters/temperature sensors is of paramount importance. These for example include areas with hydrocarbon potential. Therefore exploration companies, such as Shell or Chevron, would in particular be interested in this technology. Since these heat probes are small and can be made relatively cheaply, they can be left in earth forever. Thus, the heat flow data can be accumulated indefinitely. This in particular would be important for tracking global climate change and to understand the nature and causes of climate change. Thus, proposed heat flow deployment method, because of potential cost savings, may allow more heat flow probes being deployed around the earth. The possible 'customer' may for example be the International Heat Flow Commission of IASPEI, who initiated the project "Global Database of Borehole Temperatures and Climate Reconstructions". Prof Nagihara is working with Oil and Gas companies in the Gulf of Mexico in the area of heat flow measurements and he will be the best segue for identifying commercialization opportunities.