Mapping and quantifying lunar water ice addresses one of NASA’s Strategic Knowledge Gaps to understand the lunar resource potential for future human exploration of the Moon. Lunar Flashlight is an innovative NASA CubeSat mission dedicated to mapping water ice in the permanently-shadowed and occasionally-sunlit regions in the vicinity of the lunar South Pole. Lunar Flashlight will acquire these measurements from lunar orbit using a multi-band laser reflectometer composed of an optical receiver aligned with four lasers emitting different wavelengths in the shortwave infrared spectral region between 1 μm and 2 μm. The receiver measures the laser radiance reflected from the lunar surface in each spectral band and continuum/absorption reflectance band ratios are then analyzed to quantify water ice concentration in the illuminated spot. The receiver utilizes a 70×70-mm, aluminum, off-axis paraboloidal mirror with a focal length of 70 mm, which collects the incoming light onto a single, 2 mm diameter InGaAs detector with a cutoff wavelength of 2.4 μm. We present the optical and mechanical designs of the receiver, including its optimization for rejection of solar stray-light from outside its intended field of view. This highly mass- and volume-constrained instrument payload will demonstrate several firsts, including being one of the first instruments onboard a CubeSat performing science measurements beyond low Earth orbit and the first planetary mission to use multi-band active reflectometry from orbit.
We report on the final design and current status of a 1-5 micron infrared test bench at the ETH Zurich Institute for
Astronomy. This facility will enable us to characterize infrared optics, both reflective and transmissive, at cryogenic
operating temperatures for both ground- and space-based applications. A focus of our lab is to facilitate the detection and characterization of extra-solar planets. The test bench is designed to characterize a range of spectrally dispersive and diffraction suppression optics such as filters, grisms, gratings, as well as both focal and pupil plane coronagraphs. The test bench is built around a 2048x2048 HAWAII-2RG detector from Teledyne Imaging Systems. The optical bench is envisioned to operate down to 30 K. “First light” is expected in the second half of 2012. We outline the status of the project, and describe the capabilities of the test bench in detail in order to alert potential collaborators to this new capability.
The Exoplanet Characterisation Observatory (EChO) is a medium class mission candidate within ESA's Cosmic Vision
2015-2025 program on space science. EChO will be equipped with a visible to infrared spectrometer covering the
wavelength range from 0.4 - 11 μm (goal: 16 μm) at a spectral resolving power between 30 and 300 in order to
characterize the atmospheres of known transiting extrasolar planets ranging from Hot Jupiters to Super Earths. In this
paper we will present first results from the dedicated study of the EChO science payload carried out by our EChO
Instrument Consortium during the assessment phase of the mission.
We present a conceptual design for a cryogenic optical mechanism for the SAFARI instrument. SAFARI is a long
wavelength (34-210 micron) Imaging Fourier Transform Spectrometer (FTS) to fly as an ESA instrument on the JAXA
SPICA mission projected to launch in 2021. SPICA is a large 3m class space telescope which will have an operating
temperature of less than 7K. The SAFARI shutter is a single point of failure flight mechanism designed to operate in
space at a temperature of 4K which meets redundancy and reliability requirements of this challenging mission. The
conceptual design is part of a phase A study led by ETH Institute for Astronomy and conducted by RUAG Space AG.
SIM Lite is a space-borne stellar interferometer capable of searching for Earth-size planets in the habitable zones of
nearby stars. This search will require measurement of astrometric angles with sub micro-arcsecond accuracy and optical
pathlength differences to 1 picometer by the end of the five-year mission. One of the most significant technical risks in
achieving this level of accuracy is from systematic errors that arise from spectral differences between candidate stars and
nearby reference stars. The Spectral Calibration Development Unit (SCDU), in operation since 2007, has been used to
explore this effect and demonstrate performance meeting SIM goals. In this paper we present the status of this testbed
and recent results.
The most stringent astrometric performance requirements on NASA's SIM(Space Interferometer
Mission)-Lite mission will come from the so-called Narrow-Angle (NA) observing scenario,
aimed at finding Earth-like exoplanets, where the interferometer chops between the target star
and several nearby reference stars multiple times over the course of a single visit. Previously,
about 20 pm NA error with various shifts was reported1. Since then, investigation has been under
way to understand the mechanisms that give rise to these shifts. In this paper we report our
findings, the adopted mitigation strategies, and the resulting testbed performance.
The SIM-Lite astrometric interferometer will search for Earth-size planets in the habitable zones of nearby stars. In this
search the interferometer will monitor the astrometric position of candidate stars relative to nearby reference stars over
the course of a 5 year mission. The elemental measurement is the angle between a target star and a reference star. This is
a two-step process, in which the interferometer will each time need to use its controllable optics to align the starlight in
the two arms with each other and with the metrology beams. The sensor for this alignment is an angle tracking CCD
camera. Various constraints in the design of the camera subject it to systematic alignment errors when observing a star of
one spectrum compared with a start of a different spectrum. This effect is called a Color Dependent Centroid Shift
(CDCS) and has been studied extensively with SIM-Lite's SCDU testbed. Here we describe results from the simulation
and testing of this error in the SCDU testbed, as well as effective ways that it can be reduced to acceptable levels.
In the course of fulfilling its mandate, the Spectral Calibration Development Unit (SCDU) testbed for SIM-Lite produces
copious amounts of raw data. To effectively spend time attempting to understand the science driving the data, the team
devised computerized automations to limit the time spent bringing the testbed to a healthy state and commanding it,
and instead focus on analyzing the processed results. We developed a multi-layered scripting language that emphasized
the scientific experiments we conducted, which drastically shortened our experiment scripts, improved their readability,
and all-but-eliminated testbed operator errors. In addition to scientific experiment functions, we also developed a set of
automated alignments that bring the testbed up to a well-aligned state with little more than the push of a button. These
scripts were written in the scripting language, and in Matlab via an interface library, allowing all members of the team to
augment the existing scripting language with complex analysis scripts. To keep track of these results, we created an easilyparseable
state log in which we logged both the state of the testbed and relevant metadata. Finally, we designed a distributed
processing system that allowed us to farm lengthy analyses to a collection of client computers which reported their results
in a central log. Since these logs were parseable, we wrote query scripts that gave us an effortless way to compare results
collected under different conditions. This paper serves as a case-study, detailing the motivating requirements for the
decisions we made and explaining the implementation process.
SIM-Lite missions will perform astrometry at microarcsecond accuracy using star light interferometry. For typical
baselines that are shorter than 10 meters, this requires to measure optical path difference (OPD) accurate to tens of
picometers calling for highly accurate calibration. A major challenge is to calibrate the star spectral dependency
in fringe measurements - the spectral calibration. Previously, we have developed a spectral calibration and
estimation scheme achieving picometer level accuracy. In this paper, we present the improvements regarding the
application of this scheme from sensitivity studies. Data from the SIM Spectral Calibration Development Unit
(SCDU) test facility shows that the fringe OPD is very sensitive to pointings of both beams from the two arms of
the interferometer. This sensitivity coupled with a systematic pointing error provides a mechanism to explain the
bias changes in 2007. Improving system alignment can effectively reduce this sensitivity and thus errors due to
pointing errors. Modeling this sensitivity can lead to further improvement in data processing. We then investigate
the sensitivity to a model parameter, the bandwidth used in the fringe model, which presents an interesting trade
between systematic and random errors. Finally we show the mitigation of calibration errors due to system drifts
by interpolating instrument calibrations. These improvements enable us to use SCDU data to demonstrate that SIM-Lite missions can meet the 1pm noise floor requirement for detecting earth-like exoplanets.
We report on a novel approach for implementing a dual Bracewell nulling interferometric beam combiner using miniature conductive waveguides contained in a single monolithic structure. We present modeling results for these devices at mid-infrared wavelengths. Potential applications for these devices in the Terrestrial Planet Finder mission are discussed.
StarLight, a NASA/JPL mission originally scheduled for launch in 2006, proposed to fly a two spacecraft visible light stellar interferometer. The Formation Interferometer Testbed (FIT) is a ground laboratory at JPL dedicated to validating technologies for StarLight and future formation flying spacecraft such as Terrestrial Planet Finder. The FIT interferometer achieved first fringes in February 2002. In this paper we present our status and review progress towards fringe tracking on a moving collector target.
Separated spacecraft interferometry is a candidate architecture
for several future NASA missions. The Formation Interferometer
Testbed (FIT) is a ground based testbed dedicated to the
validation of this key technology for a formation of two
spacecraft. In separated spacecraft interferometry, the residual
relative motion of the component spacecraft must be compensated
for by articulation of the optical components. In this paper, the design of the FIT interferometer pointing control system is described. This control system is composed of a metrology pointing loop that maintains an optical link between the two spacecraft and two stellar pointing loops for stabilizing the stellar wavefront at both the right and left apertures of the instrument. A novel feedforward algorithm is used to decouple the metrology loop from the left side stellar loop. Experimental results from the testbed are presented that verify this approach and that fully demonstrate the performance of the algorithm.