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The workshop to define feasible concepts in the UV-optical 1R area for Astronomy Spacelab Payloads is reported. Payloads proposed include: high resolution spectrograph, Schmidt camera spectrograph, UV telescope, and small infrared cryogenic telescope.
The state of contaminant molecules, the deposition rate on key surfaces, and the heat transfer rate were estimated by the use of a zeroth-order approximation. Optical surfaces of infrared telescopes cooled to about 20 K should be considered to be covered with at least several deposition layers of condensible molecules without any contamination controls. The effectiveness of the purge gas method of contamination controls was discussed. This method attempts to drive condensible molecules from the telescope tube by impacts with a purge gas in the telescope tube. For this technique to be sufficiently effective, the pressure of the purge gas must be more than 2 x .000001 torr. The influence caused by interactions of the purged gas with the particulate contaminants was found to slightly increase the resident times of the particulate contaminants within the telescope field of view.
SIRTF will require new liquid helium cryogenics and optical technology at liquid helium temperatures to meet the scientific requirements. In particular, it will require a helium cryogenic system operating at 1.25 K with a lifetime of five years. The optical system will require a 1-m mirror operating at 2 K, which is diffraction limited at 3 microns. This paper describes the advances which will be needed and the approaches to be taken.
Systems considerations for the Shuttle Infrared Telescope Facility (SIRTF) are discussed, taking into account SIRTF telescope engineering and trade studies, implications of orbital inclination for SIRTF design and operations, the approaching of the natural background limit with the SIRTF, a long life feasibility study for SIRTF, and the impact of chopping on image quality in the SIRTF telescope. Cryogenic systems and coolers for space missions are considered, giving attention to the Infrared Astronomical Satellite (IRAS) hardware flight performance, the design of the superfluid helium dewar for the Cosmic Background Explorer (COBE), Infrared Telescope (IRT) system cryogenic performance, the solidification of a cryogen by pumping, the production of superfluid helium using a Joule-Thomson Expander, and open cycle He-3 cooling to 0.18 K for space operation. Other topics explored are related to cryogenic optical instruments, facilities, and components, and to supporting technology for cryogenic infrared telescopes in space.
A two axis optical gimbal mechanism for aligning 1 meter diameter telescope primaries and test flat mirrors at temperatures from 300 to 4.2 K is being constructed for use in the Cryogenic Telescope Test Facility.
The James Webb Space Telescope cryogenic testing requires measurement systems that both obtain a very high degree of accuracy and can function in that environment. Close-range photogrammetry was identified as meeting those criteria. Testing the capability of a close-range photogrammetric system prior to its existence is a challenging problem. Computer simulation was chosen over building a scaled mock-up to allow for increased flexibility in testing various configurations. Extensive validation work was done to ensure that the actual as-built system meet accuracy and repeatability requirements. The simulated image data predicted the uncertainty in measurement to be within specification and this prediction was borne out experimentally. Uncertainty at all levels was verified experimentally to be less than 0.1 millimeters.
The James Webb Space Telescope cryogenic testing requires measurement systems that both obtain a very high degree of accuracy and can function in that environment. Close-range photogrammetry was identified as meeting those criteria. Testing the capability of a close-range photogrammetric system prior to its existence is a challenging problem. Computer simulation was chosen over building a scaled mock-up to allow for increased flexibility in testing various configurations. Extensive validation work was done to ensure that the actual as-built system meet accuracy and repeatability requirements. The simulated image data predicted the uncertainty in measurement to be within specification and this prediction was borne out experimentally. Uncertainty at all levels was verified experimentally to be less than 0.1 millimeters.
The James Webb Space Telescope (JWST) Optical Telescope Element (OTE) is a segmented, cryogenic telescope scheduled for launch in 2011. In September of 2002, NASA selected prime contractor Northrop Grumman Space Technology (NGST) to build the observatory including management of the OTE. NGST is teamed with subcontractors Ball Aerospace, Alliant Techsystems (ATK). and Kodak. The team has completed several significant design, technology, architecture definition, and manufacturing milestones in the past year that are summarized in this paper.
The use of wavefront measurements to deduce the state of multiple optics in a telescope beam train - their misalignments and figure errors — can be confused by the fact that there are multiple potential sources for the same measured error. This talk applies Kalman filtering techniques as a tool for separating true telescope errors from artifactual testing errors in the alignment and testing of NASA’s James Webb Space Telescope, a large segmented-aperture cryogenic telescope to be launched after 2010.
The seminar focused on infrared systems, the space telescope, new design for space astronomy, future earth resources systems, and planetary systems. Papers were presented on infrared astronomy satellite, infrared telescope on Spacelab 2, design alternatives for the Shuttle Infrared Telescope Facility, Spacelab 2 infrared telescope cryogenic system, geometrical theory of diffraction and telescope stray-light analysis, Space Telescope scientific instruments, faint-object spectrograph for the Space Telescope, light scattering from multilayer optics, bidirectional reflectance distribution function measurements of stray light suppression coatings for the Space Telescope, optical fabrication of a 60-in. mirror, interferogram analysis for space optics, nuclear-pumped lasers for space application, geophysical fluid flow experiment, coherent rays for optical astronomy in space, optical system with fiber-optical elements, and Pioneer-Venus solar flux radiometer.
The Spitzer Space Telescope, formerly known as SIRTF, is a cryogenic telescope (85 cm diameter) operating in a heliocentric orbit trailing the Earth. Its three instruments provide capabilities for spectroscopy, wide-field and small-field imaging at many wavelengths in the range 3.5-160 microns. Observations to be executed in the first two years in programs defined by the Guaranteed Time Observer (GTO) group (the authors of this presentation) consist of photometry, spectroscopy, and radiometry of many Solar System objects, including Titan and other satellites of the outer planets, Pluto, Centaurs, trans-Neptunian objects, comers, asteroids, Uranus, and Neptune. At the time of the preparation of this abstract, some preliminary observations have been made, but the final calibration and reduction of the data are still in progress. The latest results of the Solar System investigations will be presented here.
High-performance, integrated spectrometers operating in the far-infrared and submillimeter ranges promise to be powerful tools for the exploration of the epochs of reionization and initial galaxy formation. These devices, using high-efficiency superconducting transmission lines, can achieve the performance of a meter-scale grating spectrometer in an instrument implemented on a 4 inch silicon wafer. Such a device, when combined with a cryogenic telescope in space, provides an enabling capability for studies of the early universe. Here, the optical design process for Micro-Spec (micron-Spec) is presented, with particular attention given to its two-dimensional diffractive region, where the light of different wavelengths is focused on the different detectors. The method is based on the stigmatization and minimization of the light path function in this bounded region, which results in an optimized geometrical configuration. A point design with an efficiency of (is) approximately 90% has been developed for initial demonstration and can serve as the basis for future instruments. Design variations on this implementation are also discussed, which can lead to lower efficiencies due to diffractive losses in the multimode region.
To address the scientific goals of NASA’s astrophysics division, the JPL and Caltech’s SPHEREx mission conducts the first near-infrared all-sky spectral survey in low-earth-orbit using a passively-cooled, cryogenic telescope. Several unique water contamination issues arise due to the combination of cryogenic operation temperatures and the limited temperature control authority of passive cooling. Because water molecules have adsorption bands within the wavelengths of interest for SPHEREx’s survey, it is imperative that water contamination be controlled and minimized. In this work, a model is developed for the SPHEREx mission to predict the transport and accumulation of outgassed water onto sensitive payload components. The model utilizes the time dependent thermal profiles of the individual payload components, initial water content, and spacecraft geometry to calculate the time dependent water diffusion, transport, and adsorption. This model is subsequently used to predict water contamination risks and design decontamination solutions for each risk. Two major water contamination risks were predicted, water accumulation during cooldown and on cryogenic surfaces during the mission. The first risk occurs during the cooldown of the payload to cryogenic temperatures, predicting water accumulation on optical surfaces in excess of the allowable levels. To mitigate this accumulation, the temperature of the optical surfaces is controlled during cooldown through a combination of heaters and spacecraft pointing. The second risk is that over the course of the mission, is unavoidable water accumulation onto the payload thermal system’s cryogenic surfaces, possibly jeopardizing thermal performance and temperature stability, both of which are required for science success. To decontaminate any water that had collected onto cryogenic thermal system surfaces, a decontamination maneuver was designed. In this decontamination maneuver, cryogenic surfaces of the thermal system are warmed to a temperature where water will desorb by spacecraft pointing while still meeting all avoidance constraints, and thereby avoiding undue risk to the observatory hardware. Through application of the developed analytical model and inclusion of the decontamination maneuver in the mission design, SPHEREx can confidently demonstrate that it is able to decontaminate, at the start of and during the mission as needed to meet its end of life science performance requirements.
Conceptual passive-cooling technique enables very large infrared telescope in vacuum of outer space cooled to below 20 K without using cryogen. Telescope orbiting Earth at high altitude of around 100,000 km. Scheme also offers very small gradient of temperature across primary telescope reflector, so thermal distortions smaller; accuracy of surface figure of reflector significantly enhanced. Passive-cooling technique also applied to building of very large cryostats and to development of very large sun shields in traditional manner, and some elements of technique adapted for current small observatories.
Comet observations are included in the programs of the Guaranteed Time Observers (GTO) on the Space Infrared Telescope Facility (SIRTF), scheduled to be in space and operational for five years beginning in late 2003. SIRTF is a cryogenic telescope with three basic instruments for imaging, photometry and spectroscopy from 3.6 m to 160 m. All of these capabilities will be used in studies of comets. The intent is to study the infrared radiation (emission) from comets (and dust tails, where relevant) in all stages of evolution, starting with Kuiper Belt objects and Centaurs (thermal emission at 24,70, and 160 m to derive dimensions and albedos). Active comets will be observed spectroscopically and in deep thermal images. Several known or suspected extinct comets will be observed spectroscopically (5-37 m) for information on their surface compositions. There are opportunities for Guest Observers (GO) to propose additional comet work. .
The Spitzer Space Telescope, NASA's Great Observatory for infrared astronomy, was launched 2003 August 25 and is returning excellent scientific data from its Earth-trailing solar orbit. Spitzer combines the intrinsic sensitivity achievable with a cryogenic telescope in space with the great imaging and spectroscopic power of modern detector arrays to provide the user community with huge gains in capability for exploration of the cosmos in the infrared. The observatory systems are largely performing as expected, and the projected cryogenic lifetime is about five years. Spitzer is thus both a scientific and a technical precursor to the infrared astronomy missions of the future. This very brief paper refers interested readers to several sets of recent publications which describe both the scientific and the technical features of Spitzer in detail. Note that, until 2003 December, Spitzer was known as the Space Infrared Telescope Facility (SIRTF).
Programs are now underway to develop and demonstrate the detector/array technology needed for the Space Infrared Telescope Facility (SIRTF), Large Deployable Reflector (LDR), and other future NASA missions. The development goal is to achieve focal plane sensitivities, at extended integration times over the 2 to 700 microns range, limited only by the low astrophysical backgrounds encountered in cryogenic telescopes such as SIRTF. Dramatic progress has been made in the last 2 to 3 years in integrated array and detector systems for low background astronomical applications. With the broadly based developments and lab characterizations now underway for SIRTF and similar space applications, coupled with the rapidly expanding art and science of ground based astronomical imagery with arrays, the potential for effective utilization of arrays with LDR appears to be very good.
The James Webb Space Telescope (JWST) launched on December 25th, 2021. During the first 120 days of the mission the telescope and mirrors were deployed and the 18 primary segments and secondary mirror were aligned from millimeters to nanometers. This process led to an optical system that is limited only by the laws of physics. JWST is the first segmented, large cryogenic telescope that has been in flown in space and its deployment was an incredible first step in the advancement of large space telescopes. This talk will discuss the origin of several key technologies as well as the commissioning process from the perspective of the telescope including launch, deployments, alignments. It will culminate with a summary of how well the telescope is performing.