The Far Infrared Spectroscopic Explorer (FIRSPEX) is a novel European-led astronomy mission concept developed to enable large area ultra high spectroscopic resolution surveys in the THz regime. FIRSPEX opens up a relatively unexplored spectral and spatial parameter space that will produce an enormously significant scientific legacy by focusing on the properties of the multi-phase ISM, the assembly of molecular clouds in our Galaxy and the onset of star formation; topics which are fundamental to our understanding of galaxy evolution. The mission uses a heterodyne instrument and a ~1.2 m primary antenna to scan large areas of the sky in a number of discreet spectroscopic channels from L2. The FIRSPEX bands centered at [CI] 809 GHz, [NII]1460 GHz, [CII]1900 GHz and [OI]4700 GHz have been carefully selected to target key atomic and ionic fine structure transitions difficult or impossible to access from the ground but fundamental to the study of the multi-phase ISM in the Universe. The need for state-of-the-art sensitivity dictates the use of superconducting mixers configured either as tunnel junctions or hot electron bolometers. This technology requires cooling to low temperatures, approaching 4K, in order to operate. The receivers will operate in double sideband configuration providing a total of 7 pixels on the sky. FIRSPEX will operate from L2 in both survey and pointed mode enabling velocity resolved spectroscopy of large areas of sky as well as targeted observations.
We present the details of the optical design, corrector system, mechanical layout, tolerances, pointing requirements, and overall performance of the sub-millimeter wavelength Large Balloon Reflector telescope (LBR).
We report on the first room-temperature modular multi-pixel Schottky diode-based, tunable, frequency-multiplied local
oscillator sub-system at 1.9 THz. This source has been developed to enable efficient high-resolution mapping of the C+
line using suborbital platforms such as the SOFIA aircraft and balloons, as well as space instruments. This compact LO
source features four multipliers (X3X2X3X3) to up-convert Ka-band power to 1.9 THz. Preliminary results at 300 K
demonstrate more than 5 μW per pixel at 1.9 THz. The source is designed to provide a large output power dynamic
range and can be expanded to larger array receivers.
We report on the development of Argus, a 16-pixel spectrometer, which will enable fast astronomical imaging over the 85–116 GHz band. Each pixel includes a compact heterodyne receiver module, which integrates two InP MMIC low-noise amplifiers, a coupled-line bandpass filter and a sub-harmonic Schottky diode mixer. The receiver signals are routed to and from the multi-chip MMIC modules with multilayer high frequency printed circuit boards, which includes LO splitters and IF amplifiers. Microstrip lines on flexible circuitry are used to transport signals between temperature stages. The spectrometer frontend is designed to be scalable, so that the array design can be reconfigured for future instruments with hundreds of pixels. Argus is scheduled to be commissioned at the Robert C. Byrd Green Bank Telescope in late 2014. Preliminary data for the first Argus pixels are presented.
The Stratospheric TeraHertz Observatory (STO) is a NASA funded, Long Duration Balloon (LDB) experiment designed to
address a key problem in modern astrophysics: understanding the Life Cycle of the Interstellar Medium (ISM). STO will
survey a section of the Galactic plane in the dominant interstellar cooling line [C II] (1.9 THz) and the important star
formation tracer [N II] (1.46 THz) at ~1 arc minute angular resolution, sufficient to spatially resolve atomic, ionic and
molecular clouds at 10 kpc. STO itself has three main components; 1) an 80 cm optical telescope, 2) a THz instrument
package, and 3) a gondola . Both the telescope and gondola have flown on previous experiments [2,3]. They have been reoptimized
for the current mission. The science flight receiver package will contain four [CII] and four [NII] HEB mixers,
coupled to a digital spectrometer. The first engineering test flight of STO was from Ft. Sumner, NM on October 15, 2009.
The ~30 day science flight is scheduled for December 2011.
In the wavelength regime between 60 and 300 microns there are a number of atomic and molecular emission lines that
are key diagnostic probes of the interstellar medium. These include transitions of [CII], [NII], [OI], HD, H2D+, OH, CO,
and H2O, some of which are among the brightest global and local far-infrared lines in the Galaxy. In Giant Molecular
Clouds (GMCs), evolved star envelopes, and planetary nebulae, these emission lines can be extended over many arc
minutes and possess complicated, often self absorbed, line profiles. High spectral resolution (R> 105) observations of
these lines at sub-arcminute angular resolution are crucial to understanding the complicated interplay between the
interstellar medium and the stars that form from it. This feedback is central to all theories of galactic evolution. Large
format heterodyne array receivers can provide the spectral resolution and spatial coverage to probe these lines over
The advent of large format (~100 pixel) spectroscopic imaging cameras in the far-infrared (FIR) will fundamentally
change the way astronomy is performed in this important wavelength regime. While the possibility of such instruments
has been discussed for more than two decades, only recently have advances in mixer and local oscillator technology,
device fabrication, micromachining, and digital signal processing made the construction of such instruments tractable.
These technologies can be implemented to construct a sensitive, flexible, heterodyne array facility instrument for
SOFIA. The instrument concept for StratoSTAR: Stratospheric Submm/THz Array Receiver includes a common user
mounting, control system, IF processor, spectrometer, and cryogenic system. The cryogenic system will be designed to
accept a frontend insert. The frontend insert and associated local oscillator system/relay optics would be provided by
individual user groups and reflect their scientific interests. Rapid technology development in this field makes SOFIA the
ideal platform to operate such a modular, continuously evolving instrument.
The Cornell Caltech Atacama Telescope (CCAT) is a 25 m diameter telescope that will operate at wavelengths as short
as 200 microns. CCAT will have active surface control to correct for gravitational and thermal distortions in the
reflector support structure. The accuracy and stability of the reflector panels are critical to meeting the 10 micron
HWFE (half wave front error) for the whole system. A system analysis based upon a versatile generic panel design has
been developed and applied to numerous possible panel configurations. The error analysis includes the manufacturing
errors plus the distortions from gravity, wind and thermal environment. The system performance as a function of panel
size and construction material is presented. A compound panel approach is also described in which the reflecting surface
is provided by tiles mounted on thermally stable and stiff sub-frames. This approach separates the function of providing
an accurate reflecting surface from the requirement for a stable structure that is attached to the reflector support structure
on three computer controlled actuators. The analysis indicates that there are several compound panel configurations that
will easily meet the stringent CCAT requirements.
To meet the 10 µm RMS half wavefront error requirement for the 25 m diameter Cornell Caltech Atacama Telescope
(CCAT), active control of the approximately 200 primary mirror panels is required. The CCAT baseline design includes
carbon fiber aluminum honeycomb sandwich mirror panels. Distortions of the panels due to thermal gradients, gravity
and the mounting scheme need to be taken into consideration in the control system design. We have modeled the
primary mirror surface as both flat and curved surfaces and have investigated mirror controllability with a variety of
sensor types and positions.
To study different mirror segmentation schemes and find acceptable sensor configurations, we have created a software
package that supports multiple segment shapes and reconfigurable panel sizing and orientation. It includes extensible
sensor types and flexible positioning. Inclusion of panel and truss deformations allows modeling the effects of thermal
and gravity distortions on mirror controllability.
Flat mirrors and curved mirrors with the correct prescription give similar results for controlled modes, but show
significant differences in the unsensed flat mirror modes. Both flat and curved mirror models show that sensing
schemes that work well with rigid, thermally stable panels will not control a mirror with deformable panels. Sensors
external to the mirror surface such as absolute distance measurement systems or Shack-Hartmann type sensors are
required to deal with panel deformations. Using a combination of segment based sensors and external sensors we have
created a promising prototype control system for the CCAT telescope.
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 scientific rationale, concepts and technologies for far-IR (λ=35-600 μm) instrumentation for the
cryogenic single-dish space telescopes envisioned for the next two decades. With the tremendous success of
Spitzer, the stage is set for larger (3-10 meter) actively-cooled telescopes and several are under consideration
including SPICA in Japan, and CALISTO/SAFIR in the US. The cold platforms offer the potential for far-IR
observations limited only by the zodiacal dust emission and other diffuse astrophysical foregrounds. Optimal
instrumentation for these missions includes large-format direct-detector arrays with sensitivity matched to the
low photon backgrounds. This will require major improvements relative to the current state of the art, especially
for wavelengths beyond the 38-micron silicon BIB cutoff, We review options and present progress with one
approach: superconducting bolometers.
We highlight in particular the scientific potential for moderate-resolution broadband spectroscopy. The large
cold telescopes can provide line sensitivities below 10-20 W m-2, enabling the first routine survey spectroscopy
of the redshift 0.5 to 5 galaxies that produced the cosmic far-IR background. These far-IR-bright dusty galaxies
account for half of the photon energy released since stars and galaxies began forming, and the new far-IR
spectroscopic capability will reveal their energy sources and chart their history. We describe concepts for the
background-limited IR-Submillimeter Spectrograph (BLISS) designed for this purpose. BLISS is a suite of
R~1000 spectrometer modules spanning the far-IR range, and is under study for SPICA; a similar but more
capable instrument can be scaled for CALISTO/SAFIR.
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.
We present a first cut instrument design package for the proposed 25 meter Cornell-Caltech Atacama Telescope (CCAT). The primary science for CCAT can be achieved through wide field photometric imaging in the short submillimeter through millimeter (200 μm to 2 mm) telluric windows. We present strawman designs for two cameras: a 32,000 pixel short submillimeter (200 to 650 μm) camera using transition edge sensed bare bolometer arrays that Nyquist samples (@ 350 μm) a 5'×5' field of view (FoV), and a 45,000 pixel long wavelength camera (850 μm to 2 mm) that uses slot dipole antennae coupled bolometer arrays with wavelength dependent sampling that covers up to a 20' square FoV. These are our first light instruments. We also anticipate "borrowed" instruments such as direct detection and heterodyne detection spectrometers will be available at, or nearly at first light.
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 Submillimeter Wave Astronomy Satellite (SWAS) mission will study galactic star formation and interstellar chemistry. To carry out this mission, SWAS will survey dense (nH2 > 103 cm-3) molecular clouds within our galaxy in either the ground-state or a low- lying transition of five astrophysically important species: H2O, H218O, O2, CI, and 13CO. By observing these lines SWAS will: (1) test long-standing theories that predict that these species are the dominate coolants of molecular clouds during the early stages of their collapse to form stars and planets and (2) supply heretofore missing information about the abundance of key species central to the chemical models of dense interstellar gas. During its two-year mission, SWAS will observe giant and dark cloud cores with the goal of detecting to setting an upper limit on the water abundance of 3 X 10-6 (relative to H2) and on the molecular oxygen abundance of 2 X 10-6 (relative to H2). SWAS is designed to carry all elements of a ground based radiotelescope. The telescope is a highly efficient 54 X 68-cm off-axis Cassegrain antenna with an aggregate surface error less than or equal to 11 micrometers rms. The receiver system consists of two independent heterodyne receivers with second harmonic Schottky diode mixers, passively cooled to approximately equals 150 K. The spectrometer is a single acousto-optical spectrometer (AOS) with 1400 1-MHz channels enabling simultaneous observations of the H2O, O2, CI, and 13CO lines.
A new approach to rewritable optical data storage is under development which has the potential for satisfying all of the key requirements for a dynamic on-line data storage system including removability, high data density, high speed and long cycle life. The storage media consists of alkaline earth crystals doped with rare-earth elements. Thin crystalline films of these media deposited on disk substrates can store information in the form of trapped electrons. The information is written, read, and erased entirely by optical signals in this purely electronic process. Electrons are raised to a higher energy state by the absorption of visible light photons, filling available trap sites. An electron in the elevated energy state can be released from its trap site by imputing sufficient energy to the electron to permit it to escape from the well. When this occurs, the electron falls back to its ground state and emits a corresponding photon, indicating the existence of a binary ''1'' at the storage location site. The basic advantages of the ET media arise from the physical process which is purely photoelectronic. Read and write data transfer rates are very high because the process in the ET media is electronic rather than thermal in nature. The writing sensitivity of ET is approximately 100 times better than other optical media. This implies that the data recording rate can be made 10 times higher while using only 1/10 of the optical power of other systems. In addition, thermal cycling performance degradation is not a factor in contrast to the heat induced changes wrought by the write/erase laser beam in other optical storage media.
A new approach to rewritable optical data storage is under development which has the potential for satisfying all of the key requirements for a dynamic on-line data storage system including removability, high data density, high speed and long cycle life. The approach utilizes an electron-trapping (ETTM) storage media consisting of alkaline earth crystals doped with rare-earth elements. Thin crystalline films of these media deposited on disk substrates can store information in the form of trapped electrons. The information is written, read, and erased entirely.
A new photo-electronic optical data storage system is described which has the potential for exceeding key performance characteristics of current magnetic systems and other optical systems currently in development and production.