The lunar regolith exhibits extremely low conductivity. Penetrating the regolith presents problems if the geo-technical properties of the regolith are not well understood and accounted for.

Measuring heat flow requires two measurements to be made: the thermal gradient and thermal conductivity of the subsurface. Measurements must be made at various depths. The gradient is a comparison of the subsurface temperature as a function of depth. Conductivity measurement is made by applying heat to a specific point and measuring the temperature response.

This innovation provides:

  • A method to deploy heat-flow sensors that press firmly against the borehole and offer good thermal conduction with the regolith.
  • A method to decouple the heat-flow sensors from the spacecraft with the exception of an electrical tether to carry signals to the avionics. The penetration rod is removed completely from the borehole, increasing the sensitivity of the measurement.
  • A low-mass, low-power method of reaching 3-meter depths in lunar regolith. The method uses energy stored in compressed gas and exhibits a very high deployed-to-stowed packing ratio, critical for reaching 3-meter depths within a small lander payload.
  • A method of reaching 3-meter depths and beyond utilizing a high-frequency percussive penetrometer.

This innovation:

  • Offers conductive coupling to the regolith.
  • Minimizes the effect of the spacecraft on the heat-flow measurement.
  • Uses very low power and mass to penetrate to 3-meter depths and beyond.
  • Provides rapid penetration and stable borehole for deployment of sensors.

Non-NASA applications include measuring of heat flow in areas on Earth, where optimal thermal isolation of heaters and temperature sensors is of paramount importance. These include areas with hydrocarbon potential. 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 would be important for tracking global climate change and to understand the nature and causes of climate change.

This work was done by Erik Mumm and Kris Zacny of Honeybee Robotics for Marshall Space Flight Center. For more information, contact Ronald C. Darty, Licensing Executive in the MSFC Technology Transfer Office, at This email address is being protected from spambots. You need JavaScript enabled to view it.. Refer to MFS-32792-1.

NASA Tech Briefs Magazine

This article first appeared in the September, 2014 issue of NASA Tech Briefs Magazine.

Read more articles from this issue here.

Read more articles from the archives here.