25 research outputs found
Segmental dynamics in a blend of alkanes: Nuclear magnetic resonance experiments and molecular dynamics simulation
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Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE) mission overview
The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) is a joint US/UK mission consisting of two 6U CubeSats actively maintaining a lead-follow configuration in the same low Earth orbit with a launch planned for the 2020 timeframe. These nanosatellites will each feature multiple space weather payloads. From the US, the Naval Research Laboratory will provide two 1U Triple Tiny Ionospheric Photometers (Tri-TIPs) on each satellite, observing the ultraviolet 135.6 nm emission of atomic oxygen at nighttime. The primary objective is to characterize the twodimensional distribution of electrons in the Equatorial Ionization Anomaly (EIA). The methodology used to reconstruct the nighttime ionosphere employs continuous UV photometry from four distinct viewing angles in combination with an additional data source, such as in situ plasma density measurements, with advanced image space reconstruction algorithm tomography techniques. From the UK, the Defence Science and Technology Laboratory (Dstl) is providing the In-situ and Remote Ionospheric Sensing suite consisting of an Ion/Neutral Mass Spectrometer, a triple-frequency GPS receiver for ionospheric sensing, and a radiation environment monitor. We present our mission concept, simulations illustrating the imaging capability of the Tri-TIP sensor suite, and a range of science questions addressable via these measurements
CIRCE: Coordinated Ionospheric Reconstruction Cubesat Experiment
The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) is a collaborative space mission between the UK Defence Science and Technology Laboratory (Dstl), and the US Naval Research Laboratory (NRL) in developing small satellite ionospheric physics capability. CIRCE will characterise space weather effects on a regional scale in the ionosphere/thermosphere system. Properly characterising the dynamic ionosphere is important for a wide range of both civil and defence applications such as GPS, communications, and sensing technology.
Consisting of two near-identical 6U (2x3U) CubeSat buses, the CIRCE nanosatellites will fly in a lead-follow tandem configuration in co-planar near-polar orbits at 500km altitude. Provided by Blue Canyon Technologies (BCT), the two buses will use differential drag to achieve and maintain an in-track separation of between 250 and 500km, allowing short time-scale dynamics to be observed in-situ. These nanosatellites each carry a complement of 5 individual scientific instruments, contributed from academic, industrial, and government partners across the UK and US.
Scheduled to launch in 2021 via the US Department of Defence Space Test Program, the two CIRCE satellites will provide observations to enable a greater understanding of the driving processes of geophysical phenomena in the ionosphere/thermosphere system, distributed across a wide range of latitudes, and altitudes, as the mission progresses
Ultraviolet Spectroscopy of Comet 9P/Tempel 1 with Alice/Rosetta during the Deep Impact Encounter
We report on spectroscopic observations of periodic comet 9P/Tempel 1 by the
Alice ultraviolet spectrograph on the Rosetta spacecraft in conjunction with
NASA's Deep Impact mission. Our objectives were to measure an increase in
atomic and molecular emissions produced by the excavation of volatile
sub-surface material. We unambiguously detected atomic oxygen emission from the
quiescent coma but no enhancement at the 10% (1-sigma) level following the
impact. We derive a quiescent water production rate of 9 x 10^27 molecules per
second with an estimated uncertainty of 30%. Our upper limits to the volatiles
produced by the impact are consistent with other estimates.Comment: 11 pages, 4 postscript figures. Accepted for publication in Icarus
special issue on Deep Impac
Cometary water expansion velocity from OH line shapes
We retrieve the H_2O expansion velocity in a number of comets, using the
18-cm line shapes of the OH radical observed with the Nan\c{c}ay radio
telescope. The H_2O velocity is derived from the large base of a trapezium
fitted to the observed spectra. This method, which was previously applied to 9
comets, is now extended to 30 further comets. This allows us to study the
evolution of their water molecule outflow velocity over a large range of
heliocentric distances and gas production rates. Our analysis confirms and
extends previous analyses. The retrieved expansion velocities increases with
increasing gas production rates and decreasing heliocentric distances.
Heuristic laws are proposed, which could be used for the interpretation of
observations of cometary molecules and as a touchstone for hydrodynamical
models. The expansion velocities retrieved from 18 cm line shapes are larger
than those obtained from millimetric observations of parent molecules with
smaller fields of view, which demonstrates the acceleration of the gas with
cometocentric distance. Our results are in reasonable quantitative agreement
with current hydrodynamical models of cometary atmospheres.Comment: Accepted for publication in Astronomy & Astrophysic
Coordinated Ionospheric Reconstruction CubeSat Experiment (CIRCE), In situ and Remote Ionospheric Sensing (IRIS) suite
The UKâs Defence Science and Technology Laboratory (Dstl) is partnering with the US Naval Research Laboratory (NRL) on a joint mission to launch miniature sensors that will advance space weather measurement and modelling capabilities. The Coordinated Ionospheric Reconstruction Cubesat Experiment (CIRCE) comprises two 6U cube-satellites that will be launched into a near-polar low earth orbit (LEO), targeting 500 km altitude, in 2021. The UK contribution to CIRCE is the In situ and Remote Ionospheric Sensing (IRIS) suite, complementary to NRL sensors, and comprising three highly miniaturised payloads provided to Dstl by University College London (UCL), University of Bath, and University of Surrey/Surrey Satellite Technology Ltd (SSTL). One IRIS suite will be flown on each satellite, and incorporates an ion/neutral mass spectrometer, a tri-band global positioning system (GPS) receiver for ionospheric remote sensing, and a radiation environment monitor. From the US, NRL have provided two 1U Triple Tiny Ionospheric Photometers (Tri-TIPs) on each satellite (Nicholas et al., 2019), observing the ultraviolet 135.6 nm emission of atomic oxygen at night-time to characterize the two-dimensional distribution of electrons
FarâUV emissions from the SL9 impacts with Jupiter
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95348/1/grl8617.pd
Permanent set of cross-linking networks: Comparison of theory with molecular dynamics simulations
Modeled and observed N-2 Lyman-Birge-Hopfield band emissions: A comparison
A thorough understanding of how the N-2 Lyman-Birge-Hopfield (LBH) band emissions vary with altitude is essential to the use of this emission by space-based remote sensors. In this paper, model-to-model comparisons are first performed to elucidate the influence of the solar irradiance spectrum, intrasystem cascade excitation, and O-2 photoabsorption on the limb profile. Next, the observed LBH emissions measured by the High resolution Ionospheric and Thermospheric Spectrograph aboard the Advanced Research and Global Observation Satellite are compared with modeled LBH limb profiles to determine which combination of parameters provides the best agreement. The analysis concentrates on the altitude dependence of the LBH (1,1) band, the brightest LBH emission in the observations. In the analysis, satellite drag data are used to constrain the neutral densities used for the data-to-model comparisons. For the average limb profiles on two of the three days analyzed (28, 29, and 30 July 2001), calculations using direct excitation alone give slightly better agreement with the observations than did calculations with cascading between the singlet electronic N-2 states (a(1)Pi(g), a\u27Sigma(-)(u), and w(1)Delta(u)); however, the differences between the observed profiles and either model are possibly greater than the differences between the models. Nevertheless, both models give excellent agreement with the observations, indicating that current models provide an adequate description of the altitude variation of the N-2 LBH (1,1) band emissions. Consequently, when using the LBH bands to remotely sense thermospheric temperatures, which can be used to provide an unprecedented view of the thermosphere, the temperatures derived have a negligible dependence on the model used