38 research outputs found
How to process radio occultation data: 1. From time series of frequency residuals to vertical profiles of atmospheric and ionospheric properties
Expertise in processing radio occultation observations, which provide vertical profiles of atmospheric and ionospheric properties from measurements of the frequency of radio signals, is not widespread amongst the planetary science community. In order to increase the population of radio occultation processing experts, which will have positive consequences for this field, here we provide detailed instructions for one critical aspect of radio occultation data processing: how to obtain a series of bending angles as a function of the ray impact parameter from a time series of frequency residuals. As developed, this tool is valid only for one-way, single frequency occultations at spherically symmetric objects, and is thus not immediately applicable to either two-way occultations, such as those of Mars Express, or occultations at oblate objects, such as Jupiter or Saturn. This tool is demonstrated successfully on frequency residuals from a Mars Global Surveyor occultation at Mars, and the resultant set of bending angles and impact parameters are used to obtain vertical profiles of ionospheric electron density, neutral atmospheric number density, mass density, pressure, and temperature via the usual Abel transform. The root-mean-square difference between electron densities in the ionospheric profile derived herein and archived electron densities is 7×10[superscript 8] m[superscript −3]. At the lowest altitudes, temperatures in the neutral atmospheric profile derived herein differ from archived neutral temperatures by less than 0.1 K. Software programs that implement these procedures accompany this paper and may be used to extract scientifically useful data products from lower-level data sets
CubeSat Laser Infrared CrosslinK
The CubeSat Laser Infrared CrosslinK (CLICK) mission will demonstrate technology to advance the state of the art in communications between small spacecraft as well as the capability to gauge their relative distance and location. CLICK is comprised of two sequential missions. The first mission, CLICK A, is a risk reduction mission that will test out elements of the optical (laser) communications with a single 3-unit (3U) spacecraft. The key objective of this risk reduction testing is to demonstrate the fine steering mirror control system's high precision pointing performance which enables the use of a lower power laser in CLICK B/C. The goal of CLICK B/C, the second mission, is to demonstrate full-duplex (send and receive) optical communication crosslink between two 3U small spacecraft, in low-Earth-orbit, at distances between 15 and 360 miles (25 - 580 kilometres) apart at data rates greater than 20 Mbps
WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach
The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey
Telescope (WFIRST) will demonstrate technologies and methods for high-contrast
direct imaging and spectroscopy of exoplanet systems in reflected light,
including polarimetry of circumstellar disks. The WFIRST management and CGI
engineering and science investigation teams have developed requirements for the
instrument, motivated by the objectives and technology development needs of
potential future flagship exoplanet characterization missions such as the NASA
Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR
Surveyor (LUVOIR). The requirements have been refined to support
recommendations from the WFIRST Independent External Technical/Management/Cost
Review (WIETR) that the WFIRST CGI be classified as a technology demonstration
instrument instead of a science instrument. This paper provides a description
of how the CGI requirements flow from the top of the overall WFIRST mission
structure through the Level 2 requirements, where the focus here is on
capturing the detailed context and rationales for the CGI Level 2 requirements.
The WFIRST requirements flow starts with the top Program Level Requirements
Appendix (PLRA), which contains both high-level mission objectives as well as
the CGI-specific baseline technical and data requirements (BTR and BDR,
respectively)... We also present the process and collaborative tools used in
the L2 requirements development and management, including the collection and
organization of science inputs, an open-source approach to managing the
requirements database, and automating documentation. The tools created for the
CGI L2 requirements have the potential to improve the design and planning of
other projects, streamlining requirement management and maintenance. [Abstract
Abbreviated]Comment: 16 pages, 4 figure
Laser Guide Star for Large Segmented-Aperture Space Telescopes, Part I: Implications for Terrestrial Exoplanet Detection and Observatory Stability
Precision wavefront control on future segmented-aperture space telescopes
presents significant challenges, particularly in the context of high-contrast
exoplanet direct imaging. We present a new wavefront control architecture that
translates the ground-based artificial guide star concept to space with a laser
source aboard a second spacecraft, formation flying within the telescope
field-of-view. We describe the motivating problem of mirror segment motion and
develop wavefront sensing requirements as a function of guide star magnitude
and segment motion power spectrum. Several sample cases with different values
for transmitter power, pointing jitter, and wavelength are presented to
illustrate the advantages and challenges of having a non-stellar-magnitude
noise limited wavefront sensor for space telescopes. These notional designs
allow increased control authority, potentially relaxing spacecraft stability
requirements by two orders of magnitude, and increasing terrestrial exoplanet
discovery space by allowing high-contrast observations of stars of arbitrary
brightness.Comment: Submitted to A
The Global Impact of ITAR on the For-Profit and Non-Profit Space Communities
Under the United States Arms Export Control Act, the International Traffic in Arms Regulations (ITAR) control the export of technologies that are specified as defense articles on the United States Munitions List (USML). The Directorate of Defense Trade Controls (DDTC) within the Department of State (DoS) interprets and enforces these regulations in an effort to safeguard national security by denying advanced military technology to potential competitors
The Deformable Mirror Demonstration Mission (DeMi) CubeSat: optomechanical design validation and laboratory calibration
Coronagraphs on future space telescopes will require precise wavefront
correction to detect Earth-like exoplanets near their host stars. High-actuator
count microelectromechanical system (MEMS) deformable mirrors provide wavefront
control with low size, weight, and power. The Deformable Mirror Demonstration
Mission (DeMi) payload will demonstrate a 140 actuator MEMS deformable mirror
(DM) with \SI{5.5}{\micro\meter} maximum stroke. We present the flight
optomechanical design, lab tests of the flight wavefront sensor and wavefront
reconstructor, and simulations of closed-loop control of wavefront aberrations.
We also present the compact flight DM controller, capable of driving up to 192
actuator channels at 0-250V with 14-bit resolution. Two embedded Raspberry Pi 3
compute modules are used for task management and wavefront reconstruction. The
spacecraft is a 6U CubeSat (30 cm x 20 cm x 10 cm) and launch is planned for
2019.Comment: 15 pages, 10 figues. Presented at SPIE Astronomical Telescopes +
Instrumentation, Austin, Texas, US
The low-order wavefront sensor for the PICTURE-C mission
The PICTURE-C mission will fly a 60 cm off-axis unobscured telescope and two high-contrast coronagraphs in successive high-altitude balloon flights with the goal of directly imaging and spectrally characterizing visible scattered light from exozodiacal dust in the interior 1-10 AU of nearby exoplanetary systems. The first flight in 2017 will use a 10^(-4) visible nulling coronagraph (previously flown on the PICTURE sounding rocket) and the second flight in 2019 will use a 10^(-7) vector vortex coronagraph. A low-order wavefront corrector (LOWC) will be used in both flights to remove time-varying aberrations from the coronagraph wavefront. The LOWC actuator is a 76-channel high-stroke deformable mirror packaged on top of a tip-tilt stage. This paper will detail the selection of a complementary high-speed, low-order wavefront sensor (LOWFS) for the mission. The relative performance and feasibility of several LOWFS designs will be compared including the Shack-Hartmann, Lyot LOWFS, and the curvature sensor. To test the different sensors, a model of the time-varying wavefront is constructed using measured pointing data and inertial dynamics models to simulate optical alignment perturbations and surface deformation in the balloon environment
Exoplanet albedo spectra and colors as a function of planet phase, separation, and metallicity
First generation optical coronagraphic telescopes will obtain images of cool
gas and ice giant exoplanets around nearby stars. The albedo spectra of
exoplanets at planet-star separations larger than about 1 AU are dominated by
reflected light to beyond 1 {\mu}m and are punctuated by molecular absorption
features. We consider how exoplanet albedo spectra and colors vary as a
function of planet-star separation, metallicity, mass, and observed phase for
Jupiter and Neptune analogs from 0.35 to 1 {\mu}m. We model Jupiter analogs
with 1x and 3x the solar abundance of heavy elements, and Neptune analogs with
10x and 30x. Our model planets orbit a solar analog parent star at separations
of 0.8 AU, 2 AU, 5 AU, and 10 AU. We use a radiative-convective model to
compute temperature-pressure profiles. The giant exoplanets are cloud-free at
0.8 AU, have H2O clouds at 2 AU, and have both NH3 and H2O clouds at 5 AU and
10 AU. For each model planet we compute moderate resolution spectra as a
function of phase. The presence and structure of clouds strongly influence the
spectra. Since the planet images will be unresolved, their phase may not be
obvious, and multiple observations will be needed to discriminate between the
effects of planet-star separation, metallicity, and phase. We consider the
range of these combined effects on spectra and colors. For example, we find
that the spectral influence of clouds depends more on planet-star separation
and hence temperature than metallicity, and it is easier to discriminate
between cloudy 1x and 3x Jupiters than between 10x and 30x Neptunes. In
addition to alkalis and methane, our Jupiter models show H2O absorption
features near 0.94 {\mu}m. We also predict that giant exoplanets receiving
greater insolation than Jupiter will exhibit higher equator to pole temperature
gradients than are found on Jupiter and thus may have differing atmospheric
dynamics.Comment: 62 pages, 19 figures, 6 tables Accepted for publication in Ap
MEMS Deformable Mirrors for Space-Based High-Contrast Imaging
Micro-Electro-Mechanical Systems (MEMS) Deformable Mirrors (DMs) enable precise wavefront control for optical systems. This technology can be used to meet the extreme wavefront control requirements for high contrast imaging of exoplanets with coronagraph instruments. MEMS DM technology is being demonstrated and developed in preparation for future exoplanet high contrast imaging space telescopes, including the Wide Field Infrared Survey Telescope (WFIRST) mission which supported the development of a 2040 actuator MEMS DM. In this paper, we discuss ground testing results and several projects which demonstrate the operation of MEMS DMs in the space environment. The missions include the Planet Imaging Concept Testbed Using a Recoverable Experiment (PICTURE) sounding rocket (launched 2011), the Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B) sounding rocket (launched 2015), the Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) high altitude balloon (expected launch 2019), the High Contrast Imaging Balloon System (HiCIBaS) high altitude balloon (launched 2018), and the Deformable Mirror Demonstration Mission (DeMi) CubeSat mission (expected launch late 2019). We summarize results from the previously flown missions and objectives for the missions that are next on the pad. PICTURE had technical difficulties with the sounding rocket telemetry system. PICTURE-B demonstrated functionality at >100 km altitude after the payload experienced 12-g RMS (Vehicle Level 2) test and sounding rocket launch loads. The PICTURE-C balloon aims to demonstrate 10(-7) contrast using a vector vortex coronagraph, image plane wavefront sensor, and a 952 actuator MEMS DM. The HiClBaS flight experienced a DM cabling issue, but the 37-segment hexagonal piston-tip-tilt DM is operational post-flight. The DeMi mission aims to demonstrate wavefront control to a precision of less than 100 nm RMS in space with a 140 actuator MEMS DM.DARPA; NASA Space Technology Research FellowshipOpen Access JournalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]