We report the results of an extensive set of simulations exploring the sensitivity of the BlackCAT CubeSat to long-duration gamma-ray bursts (GRBs). BlackCAT is a NASA APRA-funded CubeSat mission for the detection and real-time subarcminute localization of high-redshift ( z ≳ 3.5) GRBs. Thanks to their luminous and long-lived afterglow emissions, GRBs are uniquely valuable probes of high-redshift star-forming galaxies and the intergalactic medium. In addition, each detected GRB with a known redshift serves to localize a region of high-redshift star formation in three dimensions, enabling deep follow-on searches for host galaxies and associated local and large-scale structures. We explore two distinct models for the GRB redshift distribution and luminosity function, both consistent with Swift observations. We find that, for either model, BlackCAT is expected to detect a mean of 42 bursts per year on orbit, with 6.7% to 10% of these at z > 3.5. BlackCAT bursts will be localized to an r _90 ≲ 55″ precision and reported to the community within seconds. Due to the mission orbit and pointing scheme, bursts will be located in the night sky and well placed for deep multiwavelength follow-up observations. BlackCAT is on schedule to achieve launch readiness in 2025.

BlackCAT is a NASA-funded 6U CubeSat mission planned to be launch-ready in 2025. BlackCAT will use its wide field-of-view and arcminute-scale localization to identify gamma-ray bursts (GRBs), gravitational-wave counterparts, and other high-energy transient events. The mission will send rapid alerts after detection of a transient event, enabling prompt follow-up from other ground- and space-based observatories. The science instrument is a coded aperture telescope, using a focal plane with four Speedster-EXD550 event-driven X-ray hybrid CMOS detectors (HCDs) and a gold-plated nickel coded mask to localize source positions. We describe methods for the calibration of the detectors and the assembled coded-aperture instrument. We also briefly discuss plans for in-flight commissioning and calibration.

The number of planetary satellites around solid objects in the inner solar system is small either because they are difficult or unlikely to form or because they do not survive for astronomical timescales. Here we conduct a pilot study on the possibility of satellite capture from the process of collision-less binary exchange and show that massive satellites in the range 0.01-0.1 M circle plus can be captured by Earth-sized terrestrial planets in a way already demonstrated for larger planets in the solar system and possibly beyond. In this process, one of the binary objects is ejected, leaving the other object as a satellite in orbit around the planet. We specifically consider satellite capture by an "Earth" in an assortment of hypothetical encounters with large terrestrial binaries at 1 au around the Sun. In addition, we examine the tidal evolution of captured objects and show that orbit circularization and long-term stability are possible for cases resembling the Earth-Moon system.

The BlackCAT CubeSat is an X-ray coded-aperture-telescope observatory that is expected to launch in 2025. It is designed for observations of bright X-ray sources in the 0.5-20 keV band. The instrument will have a wide field of view (0.85 steradian) and be capable of catching gamma ray bursts (GRBs) from the distant universe, galactic transients, and flares from blazars, while monitoring the X-ray sky. In addition to the primary high-redshift GRB science, BlackCAT can monitor known source variability and search for rare and exciting events including gravitational-wave X-ray counterparts, magnetar flares, supernova shock breakouts, and tidal disruption events. The mission will thus function as a multi-wavelength and multi-messenger complement to present and future facilities including LIGO, VIRGO, KAGRA, IceCube, KM3NET, LSST, LOFAR, SKA, and CTA. Rapid notifications of burst positions will be transmitted to the ground via satellite network and then relayed to the GCN. The name BlackCAT is derived from its scientific emphasis on black-hole-related transient events being observed with a coded aperture telescope (CAT). BlackCAT will serve as the scientific payload aboard a commercial 6U CubeSat spacecraft provided by NanoAvionics US. Novel event-driven X-ray hybrid CMOS detectors will form the focal plane array. In addition to carrying out science programs related to distant GRBs, transients, and X-ray sky monitoring, BlackCAT will also serve as a pathfinder for future economical missions combining multiple BlackCAT modules on either a single small satellite or on multiple CubeSats. BlackCAT will also serve as a platform for new X-ray hybrid CMOS detector development. An overview of BlackCAT in its current development state and its current status will be presented.

BlackCAT is a NASA CubeSat mission planned to be launch-ready in early 2025. Using a wide-field telescope, this 6U CubeSat will monitor the soft x-ray sky, searching for high-redshift Gamma-Ray Bursts (GRBs), gravitational-wave counterparts, and other transient events. After detecting burst events, BlackCAT will be capable of transmitting rapid alerts to enable prompt follow-up observations. The instrument is composed of a coded-aperture telescope using an array of event-driven x-ray Hybrid CMOS Detectors (HCDs) in its focal plane. In this paper, we provide a brief update on the design and status of the mission.

Optical limiters (OLs) are systems designed to protect objects from high intensity irradiance above a set threshold. Often times, these OL systems are in the form of coatings and can be used to protect objects such as sensors, critical components, or human eyes. In this work, we report the successful development of a multilayer reflective OL coating system based on a non-linear Fabry-Perot resonator structure. The structure utilized distributed Bragg reflectors (DBRs) composed of silicon/ silicon nitride and a boron nitride non-linear layer embedded in the resonant cavity. The coatings were fabricated via DC and RF magnetron sputtering and exhibited high reflectance (-99%) over a 525 nm bandwidth with a single resonant transmission peak (-7%). The optical limiters fabricated in this study exhibited a transmission drop-off when exposed to irradiances above-1000 kW/cm2 from a 1064 nm Nd:YAG laser, demonstrating an abrupt reduction in resonant trans-mission. Fabricated optical limiters also demonstrated multi-hit survivability, maintaining low transmittance (< 0.4%) after numerous 3.6 ns laser pulse exposures. This multi-hit survivability and high reflectivity offers promising opportunities for improved protection against directed energy weapons. This study lays groundwork for future evaluation of the observed on/off mechanism, as well as further development of high laser damage threshold optical limiting thin films.

In this paper, we consider a combination of traditional and modern methods to perform data-driven system identification (SysID) of a prototype lighter-than-air vehicle. We explore the methods of linear least squares (LS), subsampling based threshold sparse Bayesian regression (SubTSBR), and a novel implementation using both methods to form a constrained optimization problem. Notably, linear LS system identification is used to solve for parameters that are defined by a proposed dynamic model and SubTSBR is used to discover remaining unmodeled dynamics given the error in the LS model. This allows for a high fidelity model of the prototype LTAV from flight test data that outperforms the LS method and reduces negative effects of sparse SysID.

The world's premier X-ray astronomical observatories, Chandra and XMM-Newton, have been operating for about 20 years. The next flagship X-ray observatory launched will be ESA's Athena mission. We discuss planned US contributions to the Athena Wide Field Imager instrument, which encompass transient source detection, background characterization and reduction, and detector electronics design and testing, in addition to scientific contributions.

During Snowball Earth episodes of the Neoproterozoic and Paleoproterozoic, limited amounts of tropical open ocean (Jormungand), or tropical ocean with thin ice cover, would help to explain (1) vigorous glacial activity in low latitudes, (2) survival of photosynthetic life, and (3) deglacial recovery without excessive buildup of atmospheric CO2. Some previous models have suggested that tropical open ocean or thin-ice cover is possible; however, its viability in the presence of kilometer-thick sea glaciers flowing from higher latitudes has not been demonstrated conclusively. Here we describe a new method of asynchronously coupling a zonal sea-glacier model with a 3-D global climate model and apply it to Snowball Earth. Equilibrium curves of ice line versus CO2 are mapped out, as well as their dependence on ocean heat transport efficiency, sea-glacier flow, and other model parameters. No climate states with limited tropical open ocean or thin ice are found in any of our model runs, including those with sea glaciers. If this result is correct, then other refugia such as cryoconite pans would have been required for life to survive. However, the reasons for the differences between our results and others should first be resolved. It is suggested that small-scale convective dynamics, affecting fractional snow cover in low latitudes, may be a critical factor accounting for these differences.

Ancient valleys suggest a warm early Mars where liquid water flowed, but a greenhouse effect strong enough to offset a dim early Sun has been difficult to explain. Climate simulations suggest that sufficient concentrations of the greenhouse gases CO2 and H2 — outgassed during volcanic eruptions — could have warmed Mars above water’s freezing point.

The presence of valleys on ancient terrains of Mars suggests that liquid water flowed on the martian surface 3.8 Gyr ago or before. The above-freezing temperatures required to explain valley formation could have been transient, in response to the frequent large meteorite impacts on early Mars, or they could have been caused by long-lived greenhouse warming. Climate models that consider only the greenhouse gases carbon dioxide and water have been unable to recreate warm surface conditions, given the lower solar luminosity at that time. Here we use a one-dimensional climate model to demonstrate that an atmosphere containing 1.3–4 bar of CO2 and water, in addition to 5–20% H2, could have raised the mean surface temperature of early Mars above the freezing point of water. Vigorous volcanic outgassing from a highly reduced early martian mantle is expected to provide sufficient atmospheric H2 and CO2—the latter from the photochemical oxidation of outgassed CH4 and CO—to form a CO2 and H2 greenhouse. Such a dense early martian atmosphere is consistent with independent estimates of surface pressure based on cratering data. Ancient valleys suggest a warm early Mars where liquid water flowed, but a greenhouse effect strong enough to offset a dim early Sun has been difficult to explain. Climate simulations suggest that sufficient concentrations of the greenhouse gases CO2 and H2 — outgassed during volcanic eruptions — could have warmed Mars above water’s freezing point.

Over 500 extrasolar planets (exoplanets) have now been discovered, but only a handful are small enough that they might be rocky terrestrial planets like Venus, Earth, and Mars. Recently, it has been proposed that observations of variability in scattered light (both polarized and total flux) from such terrestrial-sized exoplanets could be used to determine if they possess large surface oceans, an important indicator of potential habitability. Observing such oceans at visible wavelengths would be difficult, however, in part because of obscuration by atmospheric scattering. Here, we investigate whether observations performed in the near-infrared (NIR), where Rayleigh scattering is reduced, could improve the detectability of exoplanet oceans. We model two wavebands of the NIR which are "window regions" for an Earth-like atmosphere: 1.55-1.75 mu m and 2.1-2.3 mu m. Our model confirms that obscuration in these bands from Rayleigh scattering is very low, but aerosols are generally the limiting factor throughout the wavelength range for Earth-like atmospheres. As a result, observations at NIR wavelengths are significantly better at detecting oceans than those at visible wavelengths only when aerosols are very thin by Earth standards. Clouds further dilute the ocean reflection signature. Hence, other techniques, e. g., time-resolved color photometry, may be more effective in the search for liquid water on exoplanet surfaces. Observing an exo-Earth at NIR wavelengths does open the possibility of detecting water vapor or other absorbers in the atmosphere, by comparing scattered light in window regions to that in absorption bands.