Warren Holmes

A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument

We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider, a polarization-sensitive balloon-borne telescope array that observed the cosmic microwave background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of ±0.1(∘). The system performed well in Spider during its successful 16 day flight.

Performance comparisons of space borne cryostats

Abstract We discuss the performance of liquid helium cryostats that have flown in space or are planned for space flight. Usual figures of merit are total cryostat mass or depletion rate of the cryogen. These often fail to accurately represent other important characteristics which affect cryostat performance such as the method used to survive launch lock-up or the temperature of the cryostat vacuum shell obtained by radiative cooling. To address these issues, we define the ratio, H/R in W day/l as metric to judge cryostat performance. The parameter H=σBAtank(T4shell−T4tank) is the Stefan Boltzmann law for energy transfer to the helium tank, where σB is the Stefan Boltzmann constant, Atank is the surface area of the cryogen tank and Tshell and Ttank are the vacuum shell and cryogen temperatures. The average cryogen depletion rate R=Vf/t is computed using the total cryogen volume, Vf, at the last fill before launch, including the volume of `booster tank cryogen if used and the cryogen lifetime, t, to depletion on-orbit. Cryostats launched on the Space Shuttle have the same H/R≈60 W day/l whether the cryogen was liquid helium or solid neon, and for a broad range of vacuum shell temperatures 113 shell K , cryogen volumes 2200>Vf>85 l, and mission times, 9 days to >2 years. Cryostats launched on unmanned rockets have a higher H/R≈300 W day/l. Only one, the X-Ray Spectrometer (XRS), out of the four solid neon and two solid hydrogen cryostats showed a clear advantage of using a cryogen other than liquid helium.

The fast alternative cryogenic experiment testbed

Abstract Subsystems for a “proof of concept” cryogenic payload have been developed to demonstrate the ability to accommodate low temperature science investigations within the constraints of the Hitchhiker siderail (HH-S) carrier on the Space Shuttle. These subsystems include: a hybrid solid neon – superfluid helium cryostat, a multi-channel Versa Modular European (VME) architecture Germanium Resistance Thermometer (GRT) readout and heater control servo system, and a multiple thermal isolation stage “probe” for thermal control of helium samples. The analysis and tests of these subsystems have proven the feasibility of a cryogenic HH-S carrier payload.

FUNDAMENTAL PHYSICS ON THE JEM-EF: THE Low TEMPERATURE MICROGRAVITY PHYSICS EXPERIMENTS FACILITY

The Low Temperature Microgravity Physics Experiments Facility (LTMPEF) takes advantage of the long-duration microgravity environment provided by the International Space Station and the payload accommodation of the Japanese Experiment Modules Exposed Facility (JEM-EF) to provide a NASA facility for fundamental physics research. Environmental factors influencing the quality of the experiments such as the vibration created within and by the Space Station, the charged-particle environment in low-Earth orbit, and the EMI environment will be discussed. Descriptions of the approved and candidate experiments will be presented as part of this presentation.

Safety requirements and process for attached payloads - The Low Temperature Microgravity Physics Facility

Introduction Payloads are required to provide assurances that all safety requirements have been met for flight prior to being installed on a launch vehicle. The design of the payload must be reviewed by the launch vehicle organization to confirm that appropriate safety features have been implemented. If the payload is launched on the Space Transportation System (STS), then several reviews will be held independently at the NASA Johnson Space Center (JSC) and the NASA Kennedy Space Center (KSC). As the launch vehicle operator, JSC assures the safety of the Space Shuttle in flight, and as the launch facility operator, KSC assures the safety of ground and launch operations, including Shuttle integration. If launching on a Japanese expendable rocket, then the payload and its GSE will be reviewed by NASDA at a facility such as Tanegashima Space Center (TNSC) to assure the safety of ground and launch operations for both the H-IIA rocket and its facilities.