Donald M. Strayer

Short-Range Inverse-Square Law Experiment in Space

The objective of ISLES (Inverse-Square Law Experiment in Space) is to perform a null test of Newtons law in space with a resolution of one part in 105 or better at 100 μm. ISLES will be sensitive enough to detect axions with the strongest allowed coupling and probe large extra dimensions of string theory down to a few μm. The experiment will be cooled to ≤2 K, which permits superconducting magnetic levitation of the test masses. This soft, low-loss suspension, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a nominal distance of 100 μm. The signal is detected by a superconducting differential accelerometer.

Superconducting-cavity-stabilized oscillators (SCSO) for precise frequency measurements

We report our progress in achieving precise frequency measurements by integrating high-Q superconducting-cavitystabilized oscillators (SCSO) with high-resolution thermometry and phase-locked-loop (PLL) techniques. The relevant e!ects that in#uence the ultimate frequency stability of SCSO (10~17}10~18) are described, and applications of this technique to precise measurements of the liquid helium critical phenomena are discussed. ( 2000 Elsevier Science B.V. All rights reserved.

Low Temperature Research in Microgravity

Abstract The recent flight of the Lambda Point Experiment has demonstrated the potential for performing precise tests of fundamental theories using low temperature techniques in Earth orbit. NASAs Microgravity Science and Applications Division has established a program of successor experiments to investigate other aspects of condensed matter physics using the same low temperature flight facility. This paper will describe the new investigations that have been chosen for flight experiments, and those selected for ground-based studies that could lead to flight experiments later. The flight facility, which has now flown twice on the shuttle orbiter, will also be described. We shall also describe opportunities for investigators to apply for support of scientific studies that could gain significantly by being performed in a low gravity environment.

Space infrared telescope facility mission and cryogenic design

Abstract The Space Infrared Telescope Facility (SIRTF) is the last of the Great Observatory missions. It is presently scheduled for launch in 2001. The mission will study the infrared spectrum from 2 to 1200 μm with three imaging and spectral instruments. The observatory will have a 5 year lifetime and will be placed in a 100 000 km earth orbit. The cryogenic system is based on a 4000 I superfluid helium cryostat. The mission and the cryogenic system are described, and the cryogenic technology issues are discussed.

Cryogenic design of the liquid helium experiment Critical Dynamics in Microgravity

Although many well-controlled experiments have been conducted to measure the static properties of systems near criticality, few experiments have explored the transport properties in systems driven far away from equilibrium as a phase transition occurs. The cryogenic design of an experiment to study the dynamic aspect of critical phenomena is reported here. Measurements of the thermal gradient across the superfluid (He II)-normal fluid (He I) interface in helium under microgravity conditions will be performed as a heat flux holds the system away from equilibrium. New technologies are under development for this experiment, which is in the definition phase for a space shuttle flight.

Dynamic measurements near the lambda-point in a low-gravity simulator on the ground

Abstract The properties of liquid helium very near the lambda-transition in the presence of a heat current has received recent theoretical and experimental attention. In this regime, gravity induced pressure effects place severe constraints on the types of experiments that can be performed. A new experiment is described which largely overcomes these difficulties by magnetostrictively cancelling gravity influences in the helium sample with a suitable magnetic coil. Design limitations of the technique and a discussion of proposed experiments is presented.

Microwave applications and characterization of the microwave properties of high-temperature superconducting films

The development by NASA JPL of high-temperature superconductors (HTSs) for use in microwave circuit elements is discussed. The synthesis of HTS films and characterization of their microwave absorption are reviewed. Applications to cryogenic low-noise receivers, spacecraft microwave systems, and low-noise oscillators are considered.

Short-range inverse-square law experiment in space

The objective of ISLES (inverse-square law experiment in space) is to perform a null test of Newton’s law on the ISS with a resolution of one part in 105 at ranges from 100 μm to 1 mm. ISLES will be sensitive enough to detect axions with the strongest allowed coupling and to test the string-theory prediction with R⩾5 μm. To accomplish these goals on the rather noisy International Space Station, the experiment is set up to provide immunity from the vibrations and other common-mode accelerations. The measures to be applied for reducing the effects of disturbances will be described in this presentation. As designed, the experiment will be cooled to less than 2 K in NASA’s low temperature facility the LTMPF, allowing superconducting magnetic levitation in microgravity to obtain very soft, low-loss suspension of the test masses. The low-damping magnetic levitation, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near-null so...

The Control of Liquid Helium in Space by Electrostatics for the Satellite Test of Equivalence Principle Experiment

The equivalence of gravitational and inertial mass has been advanced to a basic postulate of the Einstein view of gravity. As such it deserves the most rigorous testing possible. Recent advances in technology (SQUIDS, superconducting bearings, space-operable liquid helium cryogenics) have made it possible to test this equivalence to one part in 1017, an advance of a factor of a million. The Satellite Test of the Equivalence Principle has been proposed to NASA and ESA for flight in about 2000. It will incorporate an extremely sensitive accelerometer in a liquid helium cryostat in Earth orbit at 550 km.

A Test of Commercial Squid Systems for Response to EMI and Temperature Changes

Tests of interface electronics for thermal response and electromagnetic interference (EMI) susceptibility were conducted on two unmodified commercial SQUID systems to determine their suitability for use on NASA space missions. The zero offset and open loop gain were measured as a function of preamplifier temperature for one RF and one DC SQUID system while the electronics were in vacuum. Suitable performance can be obtained from these systems operating from 0 to 40°C if the preamplifier temperature is controlled. Measurements of EMI susceptibility were performed on one RF and several DC SQUID systems by exposing the preamplifiers to fields up to 2 V/m at frequencies from 10 KHz to 250 MHz. The RF SQUID system was sensitive at narrow bands near the 200 Mhz modulation frequency. The DC SQUID systems were very sensitive to EMI in broad bands over the frequency range studied, at field intensities as low as 0.5 V/m. These preliminary tests show that the DC SQUID systems tested will need extensive modifications in order to reduce their EMI susceptibility to acceptable levels.