Devices in low Earth orbit are particularly susceptible to the cumulative effects of radiation damage and the Hubble
Space Telescope Wide Field Camera 3 (HST/WFC3) UVIS detectors, installed on HST in May 2009, are no exception.
Such damage not only generates new hot pixels but also generates charge traps which degrade the charge transfer
efficiency (CTE), causing a loss in source flux as well as a systematic shift in the object centroid as the trapped charge is
slowly released during readout. Based on an analysis of internal and external monitoring data, we provide an overview
of the consequences of the ~3 years of radiation damage to the WFC3 CCD cameras. The advantages and disadvantages
of available mitigation options are discussed, including use of the WFC3 post-flash and charge injection modes now
available to observers, and the status of an empirical pixel-based correction similar to the one adopted for the HST
Advanced Camera for Surveys (ACS).
We now know that the flux of a source measured with HgCdTe arrays is not a simple, linear function, but depends on the
count-rate as well as the total number of counts. In addition to the count-rate non-linearity (and probably related to the
same physical mechanism), HgCdTe detectors are also susceptible to image persistence. Most of the persistence image
fades in a few minutes, but there is a longer-term component that can result in faint afterimages in the next orbit,
approximately 45 minutes later. For sources saturated at ~100 times full-well, the afterimages can persist for hours
afterwards. This report describes results from ground and on-orbit tests to characterize the persistence and the count-rate
non-linearity in the WFC3 IR detector during its first year of operation.
We evaluate the feasibility of a balloon-borne nulling interferometer to detect and characterize an exosolar planet and the
surrounding debris disk. The existing instrument consists of a three-telescope Fizeau imaging interferometer with thre
fast steering mirrors and three delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine
pointing. A compact visible nulling interferometer would be coupled to the imaging interferometer and in principle,
allows deep starlight suppression. Atmospheric simulations of the environment above 100,000 feet show that balloonborne
payloads are a possible path towards the direct detection and characterization of a limited set of exoplanets and
debris disks. Furthermore, rapid development of lower cost balloon payloads provide a path towards advancement of
NASA technology readiness levels for future space-based exoplanet missions. Discussed are the BENI mission and
instrument, the balloon environment and the feasibility of such a balloon-borne mission.
The Wide-field Camera 3 (WFC3) is a fourth-generation instrument planned for installation in Hubble Space Telescope
(HST). Designed as a panchromatic camera, WFC3's UVIS and IR channels will complement the other instruments onboard
HST and enhance the observatory's scientific performance. UVIS images are obtained via two 4096×2051 pixel
e2v CCDs while the IR images are taken with a 1024×1024 pixel HgCdTe focal plane array from Teledyne Imaging
Sensors. Based upon characterization tests performed at NASA/GSFC, the final flight detectors have been chosen and
installed in the instrument. This paper summarizes the performance characteristics of the WFC3 flight detectors based
upon component and instrument-level testing in ambient and thermal vacuum environments.
Wide Field Camera 3 (WFC3), a panchromatic imager developed for the Hubble Space Telescope (HST), is fully
integrated with its flight detectors and has undergone several rounds of ground testing and calibration at Goddard Space
Flight Center (GSFC). The testing processes are highly automated, with WFC3 and the optical stimulus, which is used to
provide external targets and illumination, being commanded by coordinated computer scripts. All test data are captured
and stored in the long-term Hubble Data Archive. A full suite of instrument characterization and calibration tests has
been performed, including the measurement of key detector properties such as dark current, read noise, flat field
response, gain, linearity, and persistence, as well as instrument-level properties like total system throughput, imaging
quality and encircled energy, grism dispersions, IR thermal background, and image stability. Nearly all instrument
characteristics have been shown to meet or exceed expectations and requirements.
The Extrasolar Planetary Imaging Coronagraph (EPIC) is a proposed NASA Discovery mission to image
and characterize extrasolar giant planets in orbits with semi-major axes between 2 and 10 AU. EPIC will
provide insights into the physical nature of a variety of planets in other solar systems complimenting radial
velocity (RV) and astrometric planet searches. It will detect and characterize the atmospheres of planets
identified by radial velocity surveys, determine orbital inclinations and masses, characterize the
atmospheres around A and F type stars which cannot be found with RV techniques, and observe the inner
spatial structure and colors of debris disks. EPIC has a proposed launch date of 2012 to heliocentric Earth
trailing drift-away orbit, with a 3 year mission lifetime (5 year goal), and will revisit planets at least three
times at intervals of 9 months. The robust mission design is simple and flexible ensuring mission success
while minimizing cost and risk. The science payload consists of a heritage optical telescope assembly
(OTA), and visible nulling coronagraph (VNC) instrument. The instrument achieves a contrast ratio of 109
over a 4.84 arcsecond field-of-view with an unprecedented inner working angle of 0.14 arcseconds over the
spectral range of 440-880 nm, with spectral resolutions from 10 - 150. The telescope is a 1.5 meter offaxis
Cassegrain with an OTA wavefront error of λ/9, which when coupled to the VNC greatly reduces the
requirements on the large scale optics, compressing them to stability requirements within the relatively
compact VNC optical chain. The VNC features two integrated modular nullers, a spatial filter array (SFA),
and an E2V-L3 photon counting CCD. Direct null control is accomplished from the science focal
mitigating against complex wavefront and amplitude sensing and control strategies.
The CorECam Instrument Concept Study (ICS) addressed the requirements and science program for the
Terrestrial Planet Finder Coronagraph's (TPF-C) primary camera. CorECam provides a simple interface to
TPF-C's Starlight Suppression System (SSS) which would be provided by the TPF-C Program, and
comprises camera modules providing visible, and near-infrared (NIR) camera focal plane imaging. In its
primary operating mode, CorECam will conduct the core science program of TPF-C, detecting terrestrial
planets at visible wavelengths. CorECam additionally provides the imaging capabilities to characterize
terrestrial planets, and conduct an extended science program focused on investigating the nature of the
exosolar systems in which terrestrial planets are detected. In order to evaluate the performance of CorECam
we developed a comprehensive, end-to-end model using OSCAR which has provided a number of key
conclusions on the robustness of the TPF-C baseline design, and allows investigation of alternative
techniques for wavefront sensing and control. CorECam recommends photon counting detectors be
baselined for imaging with TPF-C since they provide mitigations against the background radiation
environment, improved sensitivity and facilitate alternative WFSC approaches.
The Extrasolar Planetary Imaging Coronagraph (EPIC) will provide the first direct measurements of a broad range of fundamental physical characteristics of giant planets in other solar systems. These characteristics include orbital inclination, mass, brightness, color, the presence (or absence) of CH4 and H2O, and orbital or rotational-driven variability. EPIC utilizes a 1.5 meter telescope coupled to a Visible Nulling Coronagraph to achieve these science goals. EPIC has been proposed as a Discovery Mission.
This paper presents a description of the Hubble Space Telescope (HST) Near Infrared Camera and Multi Object Spectrometer (NICMOS) Cooling System (NCS), the cutting edge technology involved, a comparison of predicted versus on-orbit thermal performance, as well as possible future space applications. The NCS hardware consists of the NICMOS Cryogenic Cooler (NCC), an Electronics Support Module (ESM), a Capillary Pumped Loop (CPL)/Radiator assembly, and associated interface harnessing. The NCC is a state-of-the-art reverse Turbo-Brayton cycle mechanical cooler employing micro turbo machinery, driven by advanced power conversion electronics, operating at speeds up to 450,000 revolutions per minute to remove heat from the NICMOS instrument. The ESM provides command, control, and power distribution to the NCS, as well as providing the primary interface to the existing HST electronics. A two-phase CPL system removes heat from the NCC and transfers it to the radiator mounted externally on the HST aft shroud. The system was installed during Servicing Mission 3B via extravehicular activities in March 2002. The NCS revived the NICMOS instrument, which experienced a reduced operational lifetime due to an internal thermal short in its dewar structure, and restored HST scientific infrared capability to operational status.
The Jovian Planet Finder (JPF) is a proposed NASA MIDEX mission to place a highly optimized coronagraphic telescope on the International Space Station (ISS) to image Jupiter-like planets around nearby stars. The optical system is an off-axis, unobscured telescope with a 1.5 m primary mirror. A classical Lyot coronagraph with apodized occulting spots is used to reduce diffracted light from the central star. In order to provide the necessary contrast for detection of a planet, scattered light from mid-spatial-frequency errors is reduced by using super-smooth optics. Recent advances in polishing optics for extreme-ultraviolet lithography have shown that a factor of >30 reduction in midfrequency errors relative to those in the Hubble Space Telescope is possible (corresponding to a reduction in scattered light of nearly 1000x). The low level of scattered and diffracted light, together with a novel utilization of field rotation introduced by the alt-azimuth ISS telescope mounting, will provide a relatively low-cost facility for not only imaging extrasolar planets, but also circumstellar disks, host galaxies of quasars, and low-mass substellar companions such as brown dwarfs.
Detecting life-bearing Earth-like planets (ELPs) is one of NASA's highest priority goals. In this paper we derive the wave-front requirements for optical detection of ELPs with an 8-m space telescope and coronagraph. We will present detailed simulations that show that an 8-m coronagraphic space telescope can detect Earth-sized planets around nearby stars, provided that the wavefront at the detector is corrected to an RMS error of ~λ/3000. We use the derived wavefront error to set requirements for a deformable mirror based on micro-electro-mechanical systems technology.
We report on first observation run with the Achromatic Interfero Coronagraph (AIC) developed at Observatoire de la Cote d'Azure, France. Observations took place last Fall at Observatoire de Haute Provence with the 1.52 m telescope equipped at that time with adaptive optics. The AIC is an imaging device providing the nulling of a star without nulling the close environment of this star. Nulling results from a destructive interference process. Morphological features located as close to the star as the first angular Airy ring can be detected, thus breaking a limitation of the classical Lyot coronagraphs. The objectives of the observation run is to demonstrate that the AIC can image faint companions very close to the diffraction limit with ground-based telescope. After a short reminding of the principle of the AIC, conditions of observations are reported and first coronagraphed-images are shown. Finally limitations are discussed and improvements to carry on are described.
Current concepts for the NGST call for an 'open' telescope design in order to passively cool the telescope and instrument to cryogenic temperatures. We show that, in spite of the lack of an external baffle, straylight due to off- axis sources is negligible compared to the zodiac light. We also show that the instrumental thermal emission is in general dominated by scatter from the sunshield and not by emission from the optics. The back surface of the sunshield needs to be at about 180 K or less to reduce the self emission of the observatory to a negligible level in the near-IR, and at about 90 K or less in the case of the mid- IR.
The detection of exo-Zodiacal discs is an important step in the NASA program for the detection of exo-solar planets, in particular, the detection of earth-like planets. We show that by incorporating a nulling interferometer NGST would be very well suited to study exo-zodiacal disks in nearby stars. Over 400 stars could be surveyed and at least 40 could be resolved such that structural parameters on the 2-3 AU scale could be measured. This can be done within the existing optical NGST design but demands a wavefront RMS error less than (lambda) /100 at 10 micron in order to assure a wavefront cancellation of 1000. In addition, a new concept for an off-axis NGST design is discussed.
We propose a concept for a space mission designed to make a survey of potential zodiacal dust disks around nearby stars in the mid-IR. We show that a 10-meter baseline nulling interferometer with two 0.6-meter apertures located in a 1 X 1 AU heliocentric orbit would allow for the survey of about 400 stars in the solar neighborhood and permit a first order determination of the disk inclination and of the dust density and temperature radius dependence. The high dynamic range of the instrument may also be used to study an additional astrophysical phenomena. Beyond its own scientific merit, such a mission would also serve as a technological precursor to a larger interferometer of the type being considered for the detection of earth-like planets.