Low Temperature Microgravity Physics Facility Experiments Chosen

Science Concept Reviews (SCRs) were held this week for three candidate experiments for the second mission M2 of the Low Temperature Microgravity Physics Facility (LTMPF), which is scheduled to launch in August 2005. The SCR requires the investigator team to show the value of the science to be obtained in their experiment, to demonstrate the need for the microgravity environment to accomplish the science objectives, and to present a preliminary version of the Science Requirements Document for their experiment. A panel composed mostly of peer scientists, but also containing engineers familiar with flight requirements, selected the Boundary Effects on the Superfluid Transition (BEST) experiment and the Superconducting Microwave Oscillator (SUMO) experiment to proceed to the Requirements Definition Review.

SUMO, proposed by Principal Investigator John Lipa of Stanford, intends to use the LTMPF on ISS to place two superconducting cavity-stabilized oscillators in orbit with a second type of clock (located elsewhere on ISS) to test several aspects of the Equivalence Principle of General Relativity. If SUMO can be flown concurrently with a laser-cooled atomic clock such as those presently being developed for flight experiments in our program, both the SUMO science goals and the LCAP clock experiment goals would be enhanced. Improvements in reducing the uncertainty in several relativistic effects are estimated to range from factors of 26 to 2500 in the stand-alone mode (no LCAP clock experiment on ISS), and from 50 to 240,000 if flown simultaneously with a LCAP clock.

The BEST experiment team of Principal Investigator Guenter Ahlers of the University of California at Santa Barbara will fly three samples of liquid helium on ISS to conduct a comprehensive set of studies of critical thermal transport of 4He confined in planar and cylindrical geometries. By flying an unconfined bulk sample of liquid helium, a sample confined in cylinders of 50-microns diameter, and a sample confined in planar channels having 50-micron gaps, the experiment will be able to observe the transitions from bulk (3-dimensional) behavior to both 1-dimensional heat flow and 2-dimensional heat flow as the liquid helium is brought closer to the critical temperature. The experiment will thereby be able to test the universal scaling functions that describe finite-size effects for the different dimensionalities.

The science and engineering panel unanimously endorsed the importance of the science of all three M2 experiments and encouraged the Experiments Along Coexistence near Tricriticality (EXACT) team (Principal Investigator Melora Larson of JPL) to continue their work to develop a microgravity experiment.