C. Paine

Initial test results on bolometers for the Planck high frequency instrument

We summarize the fabrication, flight qualification, and dark performance of bolometers completed at the Jet Propulsion Laboratory for the High Frequency Instrument (HFI) of the joint ESA/NASA Herschel/Planck mission to be launched in 2009. The HFI is a multicolor focal plane which consists of 52 bolometers operated at 100 mK. Each bolometer is mounted to a feedhorn-filter assembly which defines one of six frequency bands centered between 100-857 GHz. Four detectors in each of five bands from 143-857 GHz are coupled to both linear polarizations and thus measure the total intensity. In addition, eight detectors in each of four bands (100, 143, 217, and 353 GHz) couple only to a single linear polarization and thus provide measurements of the Stokes parameters, Q and U, as well as the total intensity. The measured noise equivalent power (NEP) of all detectors is at or below the background limit for the telescope and time constants are a few ms, short enough to resolve point sources as the 5 to 9 arc min beams move across the sky at 1 rpm.

Space-quality data from balloon-borne telescopes: the High Altitude Lensing Observatory (HALO)

We present a method for attaining sub-arcsecond pointing stability during sub-orbital balloon flights, as designed for in the High Altitude Lensing Observatory (HALO) concept. The pointing method presented here has the potential to perform near-space quality optical astronomical imaging at similar to 1-2% of the cost of space-based missions. We also discuss an architecture that can achieve sufficient thermo-mechanical stability to match the pointing stability. This concept is motivated by advances in the development and testing of Ultra Long Duration Balloon (ULDB) flights which promise to allow observation campaigns lasting more than three months. The design incorporates a multi-stage pointing architecture comprising: a gondola coarse azimuth control system, a multi-axis nested gimbal frame structure with arcsecond stability, a telescope de-rotator to eliminate field rotation, and a fine guidance stage consisting of both a telescope mounted angular rate sensor and guide CCDs in the focal plane to drive a Fast-Steering Mirror. We discuss the results of pointing tests together with a preliminary thermo-mechanical analysis required for sub-arcsecond pointing at high altitude. Possible future applications in the areas of wide-field surveys and exoplanet searches are also discussed

He II liquid/vapour phase separator for large dynamic range operation

A phase separator, which separates helium vapour from liquid superfluid helium (He II), is an indispensable device for space cryogenics. The most recent approach to the Space Infrared Telescope Facility (SIRTF) uses a new design concept in which only the detector package is cold at launch, the remainder of the telescope being subsequently cooled to operating temperature on orbit. Therefore, a large dynamic operational range is required of the cryogen system. This is a report of initial laboratory test results with candidate porous plugs as phase separators. Mass flow rates and pressure and temperature differences across a porous plug were measured in this experiment. Relatively large mass flow rates were observed even at small pressure differences. In the high mass flow rate region, hysteresis was observed with increases and decreases in the pressure difference. A linear theory is proposed and compared with experimental data to explain several phenomena observed in this system.

Characterization and lifecycle testing of hydride compressor elements for the Planck sorption cryocooler

Continuous 20 K sorption-based coolers are being developed for the European Space Agency (ESA) Planck mission. Sorbent beds containing the hydrogen absorbing Lanthanum-Nickel-Tin alloy LaNi4.78Sn0.22 are being tested to evaluate their performance as compressor elements for unprecedented two years of flight operation thus demonstrating the basic performances of the cooler: namely cold end temperature, input power and cooling power. To provide basic characterization and life cycling data, a test facility was developed to test three prototype compressor elements under all conditions expected for the flight cooler operation. Each compressor element is continuously cycled in concentration and temperature to follow the absorption and desorption process assumed for the flight cooler. We present data on the hydrogen mass flow rates and thermal characteristics for all phases of the compressor cycle, with an emphasis on the controlled absorption of hydrogen. This function of the compressor element is the major driv...

PLANCK Sorption Cooler Initial Compressor Element Performance

PLANCK is an ESA-led mission to map the cosmic microwave background using bolometric and heterodyne instruments; both instruments require cooling, one to ∼20K, the other to 0.1K. JPL is developing a sorption-based hydrogen cooler to provide 18–20 K cooling to the two instruments. The system mass and power limitations require tradeoffs in thermal design.

Investigation of large dynamic range helium II liquid/vapor phase separator for SIRTF

Abstract A large dynamic range superfluid helium, helium II, liquid–vapor phase separator is required for the thermal design of the Space Infrared Telescope Facility (SIRTF). A porous plug type phase separator is adopted for SIRTF mission. A candidate porous plug was tested using two different types of experimental apparatus to obtain the exact flow characteristics. Mass flow rate, pressure and temperature differences across the porous plug were measured in this experiment. The experimental data are compared with the theoretical predictions. The fundamental feature of the flow phenomena through the tested porous plug provides valuable data for the practical design of a phase separator for SIRTF needs.

20 K continuous cycle sorption coolers for the Planck flight mission

Two sorption coolers using Hydrogen as the working fluid are currently being fabricated and assembled for flight delivery by the Jet Propulsion Laboratory (JPL). These systems have been designed to provide a total cooling capacity (per cooler) of 1 W at a cold end temperature less than 19 K with a temperature stability of 100–450 mK over a cooler cycle. Being vibration free, scalable and with the capability for the cold end to be remotely located from the warm spacecraft are the major advantages of this class of cryocoolers. This sorption cooler design has been validated by tests on components, subsystems and a fully integrated breadboard cooler (including electronics) at JPL where the two flight units are now being assembled for delivery to Europe in 2005. They will be used for the Planck Surveyor mission, which will perform high‐resolution measurements of the cosmic microwave background anisotropy. In this paper we present the level of maturity of the hydrogen sorption cooler technology at JPL by descri...

A low noise, high thermal stability, 0.1 K test facility for the Planck HFI bolometers

We are developing a facility which will be used to characterize the bolometric detectors for Planck, an ESA mission to investigate the Cosmic Microwave Background. The bolometers operate at 0.1 K, employing neutron-transmutation doped (NTD) Ge thermistors with resistances of several megohms to achieve NEPs~1×10^(–17) W Hz^(–1/2). Characterization of the intrinsic noise of the bolometers at frequencies as low as 0.010 Hz dictates a test apparatus thermal stability of 40 nK Hz^(–1/2) to that frequency. This temperature stability is achieved via a multi-stage isolation and control geometry with high resolution thermometry implemented with NTD Ge thermistors, JFET source followers, and dedicated lock-in amplifiers. The test facility accommodates 24 channels of differential signal readout, for measurement of bolometer V(I) characteristics and intrinsic noise. The test facility also provides for modulated radiation in the submillimeter band incident on the bolometers, for measurement of the optical speed-of-response; this illumination can be reduced below detectable limits without interrupting cryogenic operation. A commercial Oxford Instruments dilution refrigerator provides the cryogenic environment for the test facility.

PICO - the probe of inflation and cosmic origins

The Probe of Inflation and Cosmic Origins (PICO) is a NASA-funded study of a Probe-class mission concept. The toplevel science objectives are to probe the physics of the Big Bang by measuring or constraining the energy scale of inflation, probe fundamental physics by measuring the number of light particles in the Universe and the sum of neutrino masses, to measure the reionization history of the Universe, and to understand the mechanisms driving the cosmic star formation history, and the physics of the galactic magnetic field. PICO would have multiple frequency bands between 21 and 799 GHz, and would survey the entire sky, producing maps of the polarization of the cosmic microwave background radiation, of galactic dust, of synchrotron radiation, and of various populations of point sources. Several instrument configurations, optical systems, cooling architectures, and detector and readout technologies have been and continue to be considered in the development of the mission concept. We will present a snapshot of the baseline mission concept currently under development.