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.
Lunar Flashlight is an innovative NASA CubeSat mission dedicated to mapping water ice in the permanently shadowed regions of the Moon, which may act as cold traps for volatiles. To this end, a multi-band reflectometer will be sent to orbit the Moon. This instrument consists of an optical receiver aligned with four lasers, each of which emits sequentially at a different wavelength in the near-infrared between 1 μm and 2 μm. The receiver measures the laser light reflected from the lunar surface; continuum/absorption band ratios are then analyzed to quantify water ice in the illuminated spot. Here, we present the current state of the optical receiver design. To optimize the optical signal-to-noise ratio, we have designed the receiver so as to maximize the laser signal collected, while minimizing the stray light reaching the detector from solarilluminated areas of the lunar surface outside the field-of-view, taking into account the complex lunar topography. Characterization plans are also discussed. This highly mass- and volume-constrained mission will demonstrate several firsts, including being one of the first CubeSats performing science measurements beyond low Earth orbit.
The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer, funded by
NASA, as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the
Michelson Science Center. Since 2004, it has offered an H- and K-band fringe visibility mode through the Keck
TAC process. Recently this mode has been upgraded with the addition of a grism for higher spectral resolution.
The 10 um nulling mode, for which first nulling data were collected in 2005, completed the bulk of its engineering
development in 2007. At the end of 2007, three teams were chosen in response to a nuller key science call to
perform a survey of nearby stars for exozodiacal dust. This key science observation program began in Feb. 2008.
Under NSF funding, Keck Observatory is leading development of ASTRA, a project to add dual-star capability for
high sensitivity observations and dual-star astrometry. We review recent activity at the Keck Interferometer, with an
emphasis on the nuller development.
The Keck Interferometer combines the two 10m diameter Keck telescopes for near-infrared fringe visibility, and mid-infrared
nulling observations. We report on recent progress with an emphasis on new visibility observing capabilities,
operations improvements for visibility and nulling, and on recent visibility science. New visibility observing capabilities
include a grism spectrometer for higher spectral resolution. Recent improvements include a new AO output dichroic for
increased infrared light throughput, and the installation of new wave-front controllers on both Keck telescopes. We also
report on recent visibility results in several areas including (1) young stars and their circumstellar disks, (2) pre-main
sequence star masses, and (3) Circumstellar environment of evolved stars. Details on nuller instrument and nuller science
results, and the ASTRA phase referencing and astrometry upgrade, are presented in more detail elsewhere in this
CALISTO, the Cryogenic Aperture Large Infrared Space Telescope Observatory, will enable extraordinarily high
sensitivity far-infrared continuum and moderate (R ~ 1000) resolution spectroscopic observations at wavelengths from
~30µm to ~300 μm - the wavelengths between those accessible by JWST and future ground based facilities.
CALISTO's observations will provide vital information about a wide range of important astronomical questions
including (1) the first stars and initial heavy element production in the universe; (2) structures in the universe traced by
H2 emission; (3) the evolution of galaxies and the star formation within them (4) the formation of planetary systems
through observations of protostellar and debris disks; (5) the outermost portions of our solar system through observations
of Trans-Neptunian Objects (TNOs) and the Oort cloud. With optics cooled to below 5 K, the photon fluctuations from
the astronomical background (Zodiacal, Galactic, and extragalactic) exceed those from the telescope. Detectors with a
noise equivalent power below that set by the background will make possible astronomical-background-limited sensitivity
through the submillimeter/far-infrared region. CALISTO builds on studies for the SAFIR (Single Aperture Far Infrared)
telescope mission, employing a 4m x 6m off-axis Gregorian telescope which has a simple deployment using an Atlas V
launch vehicle. The unblocked telescope with a cold stop has minimal sidelobes and scattering. The clean beam will
allow astronomical background limited observations over a large fraction of the sky, which is what is required to achieve
CALISTO's exciting science goals. The maximum angular resolution varies from 1.2" at 30 µm to 12" at 300 μm. The
5σ 1 hr detectable fluxes are ▵S(dν/ν = 1.0) = 2.2x10-20 Wm-2, and ▵S(dν/ν = 0.001) = 6.2x10-22 Wm-2. The 8 beams per
source confusion limit at 70 μm is estimated to be 5 μJy. We discuss CALISTO optics, performance, instrument
complement, and mission design, and give an overview of key science goals and required technology development to
enable this promising far IR/submm mission.
We present a design for a cryogenically cooled large aperture telescope for far-infrared astronomy in the wavength
range 30 μm to 300 μm. The Cryogenic Aperture Large Infrared Space Telescope Observatory, or CALISTO, is
based on an off-axis Gregorian telesocope having a 4 m by 6 m primary reflector. This can be launched using an
Atlas V 511, with the only optical deployment required being a simple hinged rotation of the secondary reflector.
The off-axis design, which includes a cold stop, offers exceptionally good performance in terms of high efficiency
and minimum coupling of radiation incident from angles far off the direction of maximum response. This means
that strong astronomical sources, such as the Milky Way and zodiacal dust in the plane of the solar system,
add very little to the background. The entire optical system is cooled to 4 K to make its emission less than
even this low level of astronomical emission. Assuming that detector technology can be improved to the point
where detector noise is less than that of the astronomical background, we anticipate unprecedented low values
of system noise equivalent power, in the vicinity of 10-19 WHz-0.5, through CALISTO's operating range. This
will enable a variety of new astronomical investigations ranging from studies of objects in the outer solar system
to tracing the evolution of galaxies in the universe throughout cosmic time.
Proc. SPIE. 6265, Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter
KEYWORDS: Telescopes, Solar radiation models, Optical properties, Space telescopes, Black bodies, Space operations, Optical instrument design, Performance modeling, Thermal modeling, Radiative transfer
We have developed a thermal-optical-mechanical model of a representative sunshield and telescope assembly,
appropriate to 10-m class far-infrared large space telescopes such as SAFIR, SPECs, SPIRIT, and CMBPol. The model
provides a tool for sensitivity analysis for design parameters, including material properties and structural configuration,
provides performance predictions, and has been used to direct technology development for large space telescope
structures and materials.
The sunshield model incorporates a flight-like design support structure for the five-layer combined sunshield and V-groove
radiator, including temperature-dependent thermal, mechanical, and optical properties for the structure and
deployed sunshield layers. Heat lift from mechanical cryocoolers is included, in fixed-temperature or power-balance
conditions, at arbitrary points on the sunshields and support structure.
The model properly accounts the wavelength dependence of radiative transfer between surfaces of widely different
temperature, which capacity has not been available from commercial codes for the infrared thermal band (source
temperatures 300 K-15 K) until very recently. A simplified model of the zodiacal background to be experienced at the
Sun-Earth L2 point is used which, with the wavelength-dependent thermal transfer, improves the fidelity of temperature
and heat lift requirements predictions for the coldest sunshield layer and telescope assembly.
SAFIR, the Single Aperture Far Infra Red Observatory, is a very powerful space mission that will
achieve background-limited sensitivity in the far infrared-submillimeter spectral region. Many
processes of enormous interest to astronomers can best be studied in this wavelength range, but
require the demanding combination of high sensitivity, good angular resolution, and spectroscopic
capability. SAFIR is a 10m class telescope offering good angular resolution, cooled to below 5 K in
order to achieve background-limited sensitivity, and equipped with a complement of large-format
cameras and broadband spectrometers. Successful operation of such a facility is critically dependent
on achieving the level of sensitivity expected, but this is rendered difficult by potential pickup from
unwanted sources of radiation. This problem is exacerbated by the fact that the emission from the
optical system itself is minimal due to its low temperature, thus emphasizing the importance of
minimizing pickup from unwanted astronomical sources of radiation, including the emission from
dust in our solar system (analogous to the zodiacal light, hence "zodi"), and the emission from warm
dust in the Milky Way (Galactic "cirrus").
The extreme sensitivity of SAFIR to these unwanted sources of radiation makes it essential to
understand the relative sensitivity of the telescope/detector system to radiation coming from angles
far outside the main beam, and to develop designs which minimize this pickup. In this paper we
analyze in some detail the relative telescope sensitivity (referred to as the antenna pattern by
microwave engineers) for different designs of SAFIR. These calculations include edge diffraction
from the secondary and primary reflector, and also the effect of blockage by the secondary and
blockage and scattering by support legs in a symmetric system. By convolving the antenna pattern
with the brightness of the sky due to the zodi and cirrus, we can calculate the power received when
the antenna is pointed in any specified direction. We can also compare the undesired pickup for
different designs, in particular symmetric vs. asymmetric (off-axis or unblocked) antenna
configurations. These considerations are vital for achieving the most efficient SAFIR design
possible, in terms of achieving maximum sensitivity while being able to observe over a large fraction
of the sky.
The Keck Interferometer Nuller (KIN) will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. A successful pre-ship review was held for the KIN in June 2004, after which the KIN was shipped to the Keck Observatory. The integration of the KIN's many sub-systems on the summit of Mauna Kea, and initial on-sky testing of the system, has occupied the better part of the past year. This paper describes the KIN system-level configuration, from both the hardware and control points of view, as well as the current state of integration of the system and the measurement approach to be used. During the most recent on-sky engineering runs in May and July 2005, all of the sub-systems necessary to measure a narrowband null were installed and operational, and the full nulling measurement cycle was carried out on a star for the first time.
Mid-infrared (8-13μm) nulling is a key observing mode planned for the NASA-funded Keck Interferometer at the Keck Observatory on the summit of Mauna Kea in Hawaii. By destructively interfering and thereby canceling the on-axis light from nearby stars, this observing mode will enable the characterization of the faint emission from exo-zodiacal dust surrounding these stellar systems. We report here the null leakage error budget and pre-ship results obtained in the laboratory after integration of the nulling beam combiner with its mid-infrared camera and key components of the Keck Interferometer. The mid-infrared nuller utilizes a dual-polarization, modified Mach-Zehnder (MMZ) beam combiner in conjunction with an atmospheric dispersion corrector to achieve broadband achromatic nulling.
The first high-dynamic-range interferometric mode planned to come on line at the Keck Observatory is mid-infrared nulling. This observational mode, which is based on the cancellation of the on-axis starlight arriving at the twin Keck telescopes, will be used to examine nearby stellar systems for the presence of circumstellar exozodiacal emission. This paper describes the system level layout of the Keck Interferometer Nuller (KIN), as well as the final performance levels demonstrated in the laboratory integration and test phase at the Jet Propulsion Laboratory prior to shipment of the nuller hardware to the Keck Observatory in mid-June 2004. On-sky testing and observation with the mid-infrared nuller are slated to begin in August 2004.
SAFIR is a 10-meter, 4 K space telescope optimized for wavelengths between 20 microns and 1 mm. The combination of aperture diameter and telescope temperature will provide a raw sensitivity improvement of more than a factor of 1000 over presently-planned missions. The sensitivity will be comparable to that of the JWST and ALMA, but at the critical far infrared wavelengths, where much of the universe's radiative energy has emerged since the origin of stars and galaxies. We examine several of the critical technologies for SAFIR which enable the large cold aperture, and present results of studies examining the spacecraft thermal architecture. Both the method by which the aperture is filled, and the overall optical design for the telescope can impact the potential scientific return of SAFIR. Thermal architecture that goes far beyond the sunshades developed for the James Webb Space Telescope will be necessary to achieve the desired sensitivity of SAFIR. By optimizing a combination of active and passive cooling at critical points within the observatory, a significant reduction of the required level of active cooling can be obtained.
We report on the characterization of bolometers fabricated at the Jet Propulsion Laboratory for the High Frequency Instrument (HFI) of the joint ESA/NASA Herschel/Planck mission to be launched in 2007. The HFI is a multicolor focal plane which consists of 48 bolometers operated at 100mK. Each bolometer is mounted to a feedhorn-filter assembly which defines one of six frequency bands centered between 100-857GHz. Four detectors in each of six bands are coupled to both linear polarizations and thus measure the total intensity. In addition, eight detectors in each of 3 bands (143, 217, and 353GHz)couple only to a single linear polarization and thus provide measurements of the Stokes parameters, Q and U, as well the total intensity. The detectors are required to achieve a Noise Equivalent Power (NEP) at or below the background limit (formula available in paper)for the telescope and time constants of a few ms, short enough to resolve point sources as the 5 to 9 arc-minute beams move across the sky in great circles at 1 rpm. The bolometers are tested at 100mK in a commercial dilution refrigerator with a custom built thermal control system to regulate the heat sink with precision (formula available in paper). The 100mK tests include dark electrical characterization of the load curves, optical and electrical measurement of the thermal time constants and measurement of the noise spectral density from 0.01 to 10Hz for up to 24 bolometers simultaneously.