Nominal Mission Lifetime Research Articles

A New GRACE Filtering Approach Based on Iterative Image Convolution

AbstractThe Gravity Recovery and Climate Experiment (GRACE) mission and its successor GRACE Follow‐On (GRACE‐FO) mission provide humans with a unique perspective on mass distribution through accurate temporal gravity field models. However, these models suffer from unavoidable stripe errors in the spatial domain. A new approach based on image processing has been developed for filtering GRACE and GRACE‐FO spherical harmonic solutions. In this approach, the gravity fields are treated as noise‐contaminated images, and the stripe errors are expected to be suppressed by convolving the input with an appropriate kernel. To verify the effectiveness of the proposed approach, a closed‐loop simulation environment over the nominal mission lifetime of 5 years is designed. Image processing indicators and geophysical information evaluation results demonstrate the superior performance of the new approach in suppressing stripe errors. In the context of real GRACE data processing, our new approach still yields better results as follows: (a) The comprehensive ability of de‐striping and retaining details has slight advantages over some commonly used filters, as demonstrated through spatial distributions, amplitude spectra, and coefficient spectra. (b) The equivalent water height time series at the basin scale is comparable to the results derived from other filters or Level‐3 products. (c) The estimated signal amplitude of the Mw9.1 2004 Sumatra earthquake co‐seismic gravity change is 52.7% larger than that derived from the Gaussian 300 km filter, which is much closer to the theoretical value derived from the dislocation theory.

Differentiating modern and prebiotic Earth scenarios for TRAPPIST-1e: high-resolution transmission spectra and predictions for JWST

ABSTRACT The TRAPPIST-1 system is a priority target for terrestrial exoplanet characterization. TRAPPIST-1e, residing in the habitable zone, will be observed during the James Webb Space Telescope (JWST) GTO Program. Here, we assess the prospects of differentiating between prebiotic and modern Earth scenarios for TRAPPIST-1e via transmission spectroscopy. Using updated TRAPPIST-1 stellar models from the Mega-MUSCLES survey, we compute self-consistent model atmospheres for a 1 bar prebiotic Earth scenario and two modern Earth scenarios (1 and 0.5 bar eroded atmosphere). Our modern and prebiotic high-resolution transmission spectra ($0.4\!-\! 20\, \rm{\mu m}$ at R ∼100 000) are made available online. We conduct a Bayesian atmospheric retrieval analysis to ascertain the molecular detectability, abundance measurements, and temperature constraints achievable for both scenarios with JWST. We demonstrate that JWST can differentiate between our prebiotic and modern Earth scenarios within 20 NIRSpec Prism transits via CH4 abundance measurements. However, JWST will struggle to detect O3 for our modern Earth scenario to $\gt 2\, \sigma$ confidence within the nominal mission lifetime (∼ 80 transits over 5 yr). The agnostic combination of N2O and/or O3 offers better prospects, with a predicted detection significance of $2.7\, \sigma$ with 100 Prism transits. We show that combining MIRI LRS transits with Prism data provides little improvement to atmospheric constraints compared to observing additional Prism transits. Though biosignatures will be challenging to detect for TRAPPIST-1e with JWST, the abundances for several important molecules – CO2, CH4, and H2O – can be measured to a precision of ≲ 0.7 dex (a factor of 5) within a 20 Prism transit JWST program.

The wide-field multiband imaging and slitless spectroscopy survey to be carried out by the Survey Space Telescope of China Manned Space Program

<p indent=0mm>The 2 m-aperture Survey Space Telescope (also known as the China Space Station Telescope, CSST) is a major science project of China Manned Space Program. It is expected to start science operations around 2024 and has a nominal mission lifetime of <sc>10 years.</sc> During observations, CSST will fly independently in the same orbit as the space station while maintaining a large distance apart. It can dock with the space station for refueling and servicing as scheduled or as needed. With a Cook-type three-mirror anastigmat design, CSST can achieve superior image quality within a large field of view (FoV), which gives it an advantage for survey observations. Being an off-axis telescope without any obstruction, its point spread function (PSF) is not affected by diffraction of mirror support structures and is thus helpful for weak-lensing shear measurements. The radius encircling 80% energy of the PSF within CSST’s central 1.1 square degrees of FoV is required to be no more than 0.15″, including all wavefront errors in the optics and instruments and dynamical effects such as the telescope’s attitude control and vibration. CSST will be launched with 5 first-generation instruments including a survey camera, a terahertz receiver, a multichannel imager, an integral field spectrograph, and a cool planet imaging coronagraph. The survey camera is equipped with 30 9k×9k detectors for science observations, each with a filter or grating mounted above, a defocused 9k×9k detector for flux calibration in r band, 8 640×512 near-infrared detectors, fine guide sensors, and wavefront sensors. The primary task of CSST is to carry out a high-resolution large-area multiband imaging and slitless spectroscopy survey covering the wavelength range of <sc>255–1000 nm.</sc> Precision cosmology is the main science driver of the survey, and, therefore, the main area of sky selected for observation is at median-to-high galactic latitude and median-to-high ecliptic latitude. It will take the survey camera roughly <sc>7 years</sc> of operation accumulated over <sc>10 years</sc> of orbital time to image roughly 17500 square degrees of the sky in NUV, u, g, r, i, z, and y bands and take slitless spectroscopy of the same sky in 3 bands. The point-source 5σ limiting magnitudes in g and r bands can reach 26 (AB mag) or higher. The spectral resolution (<italic>R</italic>=<italic>λ</italic>/Δ<italic>λ</italic>) of the slitless spectrograph is specified to be on average no less than 200, and the wide-band-equivalent limiting magnitudes in GV <sc>(400–620 nm)</sc> and GI <sc>(620–1000 nm)</sc> bands will reach 23 or higher. In addition, a number of deep fields will be selected for more observations to reach at least one magnitude deeper than the wide-area survey. The combined advantage of its angular resolution, depth, wavelength range, capability of both imaging and spectroscopy and large-area sky coverage makes the CSST survey highly competitive, and, at the same time, its observations are also highly complementary with other large projects of its time, such as Vera Rubin Observatory, Euclid, and Roman Space Telescope. These projects will provide extremely rich datasets for potential breakthroughs in studies from the solar system to cosmology and beyond.

High-redshift galaxy groups as seen by ATHENA/WFI

Context. The first massive galaxy groups in the Universe are predicted to have formed at redshifts well beyond two. Baryonic physics, like stellar and active galactic nuclei (AGN) feedback in this very active epoch, are expected to have left a strong imprint on the thermo-dynamic properties of these early galaxy groups. Therefore, observations of these groups are key to constrain the relative importance of these physical processes. However, current instruments are not sensitive enough to detect them easily and characterize their hot gas content. Aims. In this work, we quantify the observing power of the Advanced Telescope for High ENergy Astrophysics (ATHENA), the future large X-ray observatory of the European Space Agency, for discovering and characterizing early galaxy groups at high redshifts. We also investigate how well ATHENA will constrain different feedback mechanisms. Methods. We used the SImulation of X-ray TElescopes simulator to mimic ATHENA observations, and a custom-made wavelet-based algorithm to detect galaxy groups and clusters in the redshift range 0.5 ≤ z ≤ 4. We performed extensive X-ray spectral fitting in order to characterize their gas temperature and X-ray luminosity. In the simulations and their analysis, we took into account the main ATHENA instrumental features: background, vignetting, and point spread function degradation with off-axis angle, as well as all X-ray foreground and background components including a realistic AGN flux distribution. Different physically motivated thermo-dynamical states of galaxy groups were simulated and tested, including central AGN contamination, different scaling relation models (luminosity evolution), and distinct surface brightness profiles. Also, different ATHENA instrumental setups were tested, including both 15 and 19 mirror rows and the applied optical blocking filter. Results. In the deep Wide Field Imager survey expected to be carried out during part of ATHENA’s first four years (the nominal mission lifetime) more than 10 000 galaxy groups and clusters at z ≥ 0.5 will be discovered. We find that ATHENA can detect ∼20 high-redshift galaxy groups with masses of M500 ≥ 5 × 1013 M⊙ and z ≥ 2, and almost half of them will have a gas temperature determined to a precision of ΔT/T ≤ 25%. Conclusions. We demonstrate that high-redshift galaxy groups can be detected very efficiently as extended sources by ATHENA and that a key parameter determining the total number of such newly discovered sources is the area on the sky surveyed by ATHENA. We show that these observations have a very good potential to constrain the importance of different feedback processes in the early universe because of ATHENA’s ability not only to find the early groups but also to characterize their hot gas properties at the same time.

The OCO-3 mission: measurement objectives and expected performance based on 1 year of simulated data

Abstract. The Orbiting Carbon Observatory-3 (OCO-3) is NASA's next instrument dedicated to extending the record of the dry-air mole fraction of column carbon dioxide (XCO2) and solar-induced fluorescence (SIF) measurements from space. The current schedule calls for a launch from the Kennedy Space Center no earlier than April 2019 via a Space-X Falcon 9 and Dragon capsule. The instrument will be installed as an external payload on the Japanese Experimental Module Exposed Facility (JEM-EF) of the International Space Station (ISS) with a nominal mission lifetime of 3 years. The precessing orbit of the ISS will allow for viewing of the Earth at all latitudes less than approximately 52∘, with a ground repeat cycle that is much more complicated than the polar-orbiting satellites that so far have carried all of the instruments capable of measuring carbon dioxide from space. The grating spectrometer at the core of OCO-3 is a direct copy of the OCO-2 spectrometer, which was launched into a polar orbit in July 2014. As such, OCO-3 is expected to have similar instrument sensitivity and performance characteristics to OCO-2, which provides measurements of XCO2 with precision better than 1 ppm at 3 Hz, with each viewing frame containing eight footprints approximately 1.6 km by 2.2 km in size. However, the physical configuration of the instrument aboard the ISS, as well as the use of a new pointing mirror assembly (PMA), will alter some of the characteristics of the OCO-3 data compared to OCO-2. Specifically, there will be significant differences from day to day in the sampling locations and time of day. In addition, the flexible PMA system allows for a much more dynamic observation-mode schedule. This paper outlines the science objectives of the OCO-3 mission and, using a simulation of 1 year of global observations, characterizes the spatial sampling, time-of-day coverage, and anticipated data quality of the simulated L1b. After application of cloud and aerosol prescreening, the L1b radiances are run through the operational L2 full physics retrieval algorithm, as well as post-retrieval filtering and bias correction, to examine the expected coverage and quality of the retrieved XCO2 and to show how the measurement objectives are met. In addition, results of the SIF from the IMAP–DOAS algorithm are analyzed. This paper focuses only on the nominal nadir–land and glint–water observation modes, although on-orbit measurements will also be made in transition and target modes, similar to OCO-2, as well as the new snapshot area mapping (SAM) mode.

Low-energy particle experiments\u2013electron analyzer (LEPe) onboard the Arase spacecraft

In this report, we describe the low-energy electron instrument LEPe (low-energy particle experiments–electron analyzer) onboard the Arase (ERG) spacecraft. The instrument measures a three-dimensional distribution function of electrons with energies of sim 19 eV–19 keV. Electrons in this energy range dominate in the inner magnetosphere, and measurement of such electrons is important in terms of understanding the magnetospheric dynamics and wave–particle interaction. The instrument employs a toroidal tophat electrostatic energy analyzer with a passive 6-mm aluminum shield. To minimize background radiation effects, the analyzer has a background channel, which monitors counts produced by background radiation. Background counts are then subtracted from measured counts. Electronic components are radiation tolerant, and 5-mm-thick shielding of the electronics housing ensures that the total dose is less than 100 kRad for the one-year nominal mission lifetime. The first in-space measurement test was done on February 12, 2017, showing that the instrument functions well. On February 27, the first all-instrument run test was done, and the LEPe instrument measured an energy dispersion event probably related to a substorm injection occurring immediately before the instrument turn-on. These initial results indicate that the instrument works fine in space, and the measurement performance is good for science purposes.

What Can be Expected from the GRACE-FO Laser Ranging Interferometer for Earth Science Applications?

The primary objective of the gravity recovery and climate experiment followon (GRACE-FO) satellite mission, due for launch in August 2017, is to continue the GRACE time series of global monthly gravity field models. For this, evolved versions of the GRACE microwave instrument, GPS receiver, and accelerometer will be used. A secondary objective is to demonstrate the effectiveness of a laser ranging interferometer (LRI) in improving the satellite-to-satellite tracking measurement performance. In order to investigate the expected enhancement for Earth science applications, we have performed a full-scale simulation over the nominal mission lifetime of 5 years using a realistic orbit scenario and error assumptions both for instrument and background model errors. Unfiltered differences between the synthetic input and the finally recovered time-variable monthly gravity models show notable improvements with the LRI, on a global scale, of the order of 23 %. The gain is realized for wavelengths smaller than 240 km in case of Gaussian filtering but decreases to just a few percent when anisotropic filtering is applied. This is also confirmed for some typical regional Earth science applications which show randomly distributed patterns of small improvements but also degradations when using DDK4-filtered LRI-based models. Analysis of applied error models indicates that accelerometer noise followed by ocean tide and non-tidal mass variation errors are the main contributors to the overall GRACE-FO gravity model error. Improvements in these fields are therefore necessary, besides optimized constellations, to make use of the increased LRI accuracy and to significantly improve gravity field models from next-generation gravity missions.

The PROBA-V mission: the space segment

PROBA-V (Project for On-Board Autonomy – Vegetation) is an ESA (European Space Agency) mission developed within the framework of the Agency’s General Support Technology Programme (GSTP) devoted to the observation of the Earth’s vegetation, providing data continuity with the SPOT (Satellite pour l’Observation de la Terre) 4 and 5 VEGETATION payloads as a gap-filler to the ESA Sentinel-3 mission. The PROBA-V space segment is based on a three-axis stabilized PROBA small-satellite platform of about 140 kg equipped with a state-of-the-art compact 4-band multi-spectral imager with a large field of view. The instrument’s optomechanics is based on three very compact TMA (three mirror anastigmat) telescopes placed on an optical bench. At an altitude of 820 km, the instrument is able to provide daily coverage of the Earth in three VNIR (visible and near-infrared) bands and one SWIR (short-wave infrared) spectral band, with a spatial resolution of up to 100 m × 100 m at nadir for the VNIR. The instrument raw data will be downlinked with an X-band transmitter to the ground reception station in Kiruna, Sweden. The mission control centre is located in Redu, Belgium. The image processing centre, the so-called ‘user segment’, automatically accesses the raw data and is responsible for the processing and the dissemination of the data products towards the user community. The PROBA-V spacecraft was launched on board the new European launcher Vega on 7 May 2013. It is designed for a nominal mission lifetime of 2.5 years with a possible extension to 5 years.

B-mode detection with an extended planck mission

The Planck satellite has a nominal mission lifetime of 14 months allowing two complete surveys of the sky. Here we investigate the potential of an extended Planck mission of four sky surveys to constrain primordial B-mode anisotropies in the presence of dominant Galactic polarized foreground emission. An extended Planck mission is capable of powerful constraints on primordial B-modes at low multipoles, which cannot be probed by ground based or sub-orbital experiments. A tensor-scalar ratio of r = 0.05 can be detected at a high significance level by an extended Planck mission and it should be possible to set a 95% upper limit of r ≲ 0.03 if the tensor-scalar ratio is vanishingly small. Furthermore, extending the Planck mission to four sky surveys offers better control of polarized Galactic dust emission, since the 217 GHz frequency band can be used as an effective dust template in addition to the 353 GHz channel.

Radiation Belt Storm Probes: A New Mission for Space Weather Forecasting

Radiation Belt Storm Probes: A New Mission for Space Weather Forecasting

The NASA-ESA MiniSTEP payload

The Equivalence Principle, which states that gravitational mass and inertial mass are different ways of measuring the same property, is the experimental foundation for modern gravitational theory. Modern theory cannot reconcile gravity with the other fundamental forces. One possibility is that the present theory of gravity, general relativity, is incomplete or incorrect. If this is the case, the Equivalence Principle may be violated at some level beyond the one part in 10 12 that has been experimentally verified. The goal of the Satellite Test of the Equivalence Principle (STEP) is to improve this result to better than one part in 10 18. In STEP two or more concentric, cylindrical test masses “fall” around the Earth in a drag-free satellite. The masses are cooled to < 2K and supported by frictionless, superconducting, linear bearings. Ultra-sensitive SQUID position detectors measure their relative motion. A confirmed violation could provide key information toward the possible unification of the four fundamental forces; conversely, a null result can rule out competing theories or constrain new theories. MiniSTEP is the least expensive mission proposed to date that still achieves STEP's basic scientific goal. It compares four different materials in four differential accelerometers. Cost saving is achieved by operating the accelerometers sequentially, thereby avoiding duplicated equipment. The drag-free satellite will be built around an existing superfluid helium dewar and a small, semi-production spacecraft. A small commercial launch vehicle will place the satellite in a 400 km, sun-synchronous, polar, Earth orbit. Nominal mission lifetime is four months - but a six to eight month life is expected.

The NASA/ESA MiniSTEP project

The Equivalence Principle states that gravitational mass and inertial mass are identical quantities. However, modern theory cannot reconcile gravity with the other three fundamental forces found in nature. One possibility is that the present theory of gravity, rooted in general relativity, is incomplete or incorrect. As a consequence of this, the Equivalence Principle may be violated at some level beyond the one part in ∼10 12 that has been experimentally verified. The objective of the Satellite Test of the Equivalence Principle (STEP) is to extend the range of experiment to one part in 10 18. This is accomplished by allowing two concentric, cylindrical test masses to “fall” around the Earth in a drag-free satellite. The test masses are cooled to < 2K and are supported by frictionless, superconducting, linear bearings. Relative motion between the test masses is measured by ultra-sensitive SQUID position detectors. The consequences of a confirmed violation will be to provide key information toward the possible unification of the four fundamental forces. A null result may rule out several competing theories and set better limits for new theories. Of the several STEP missions studied, MiniSTEP is the least expensive mission to date that still achieves the basic scientific goals. It uses four pairs of test masses (four differential accelerometers) to compare at least four different materials. An existing superfluid helium dewar, containing the four differential accelerometers, will be used along with a small, semi-production spacecraft to form the drag free satellite. The satellite will be placed in a 400 km, sun-synchronous, Earth orbit by a small commercial launch vehicle early in 2002. The nominal mission lifetime is four months.

Narrow‐Angle Astrometry with the Space Interferometry Mission: The Search for Extrasolar Planets. I. Detection and Characterization of Single Planets

ABSTRACTA decade after the publication of the Hipparcos Catalogue, the Space Interferometry Mission (SIM) will be capable of making selected high‐precision astrometric measurements about 3 orders of magnitude more accurate than the Hipparcos survey.We present results from a detailed set of end‐to‐end numerical simulations of SIM narrow‐angle astrometric measurements and data analysis to illustrate the enormous potential that SIM has for the discovery and characterization of planets outside the solar system. Utilizing a template observing scenario, we quantify SIM sensitivity to single planets orbiting single normal nearby stars as a function of measurement errors and properties of the planet: SIM will detect over 95% of the planets with periods between a few days and the 5 yr nominal mission lifetime that produces astrometric signatures ∼2.2 times larger than the single‐measurement accuracy. We provide accuracy estimates of full‐orbit reconstruction and planet mass determination: at twice the discovery limit, orbital elements will be determined with a typical accuracy of 20%–30%; the astrometric signature must be ∼10 and ∼15 times the minimum signal required for detection to derive mass and inclination‐angle estimates accurate to 10%. We quantify the impact of different observing strategies on the boundaries for secure detection and accurate orbit estimation: the results scale with the square root of both the number of observations and the number of reference stars. We investigate SIM discovery space, to gauge the instrument ability in detecting very low mass planets: around the nearest stars, SIM will find planets as small as Earth, if they are present. Some of these might be orbiting inside the parent star’s habitable zone.Extrasolar planets figure prominently among SIM scientific goals: our results reaffirm the importance of high‐precision astrometric measurements as a unique complement to spectroscopic surveys based on radial velocity. For example, establishing the existence of rocky, perhaps habitable planets would constitute both a fundamental test of theoretical models and progress toward the understanding of formation and evolution processes of planetary systems. Such discoveries would also provide the Terrestrial Planet Finder with prime targets to investigate with direct spectroscopy in terms of the potential for life.

The step payload and experiment

The foundation of modern gravitational theory is the Equivalence Principle. General Relativity is incompatible with theories of other fundamental forces such as QED, suggesting that it is incomplete. For example, there may be additional forces coupled to baryon number or spin. In this case the Equivalence Principle may be violated below the experimentally verified level of one part in 10 12. A violation could provide crucial information for new theories. A team of US and European scientists has assembled to do the Satellite Test of the Equivalence Principle (STEP) with the goal of improving this measurement to 1 part in 10 18. In STEP two or more test masses “fall” around the earth in a drag free satellite. A difference in the rate of fall appears as a periodic difference in their acceleration. The test masses are cooled to less than 2K and are supported by frictionless superconducting bearings. Ultra-sensitive SQUID position sensors measure their relative motion and their common motion is removed by adjustments during acceleration maneuvers. Any Equivalence Principle signal is separated from major disturbances by rotation of the spacecraft. STEP is planned to be launched by 2004, with nominal mission lifetime of 6 months.

Mars '94

U.S. planetary scientists have been invited to participate in the Mars '94 mission of the U.S.S.R. Up to 10 will be selected as Participating Scientists, to do Mars research with Soviet mission scientists using information obtained by instruments on the spacecraft. Of U.S. scientists invited by non‐U.S. principal investigators to participate as co‐investigators, fewer than 10 can be supported. The U.S. program will be directed and managed by the National Aeronautics and Space Administration.In October 1994 the Soviet Union will launch the two Mars '94 probes, which will reach Mars in 315 days. The nominal mission lifetime is 12 months, or half a Mars year, starting at orbit insertion. Each probe will consist of a 3‐axis stabilized PHOBOS‐type spacecraft and a descent module containing a balloon, two or three small stations, and two or three penetrators. Instruments on the spacecraft will do planetary, plasma and trajectory studies.