Estimating Drag and Heating Coefficients for Hollow Reentry Objects in Transitional Flow Using DSMC

In NASAs Object Reentry Survival Analysis Tool (ORSAT), aerodynamic drag and aerothermal heating coefficients are computed for each of the free-molecular, continuum, and transitional flow regimes using analytical and semi-analytical methods. These methods are typically limited to convex, blunt objects (such as spheres) and are applied to other objects such as boxes and cylinders using multiplicative shape factors to account for the different behavior. Previous literature has analyzed the aerodynamic and aerothermodynamic properties of flow around sharp-edged objects like boxes and cylinders in transitional flow, though only those objects with solid external boundaries. However, many reentry objects we have encountered in real spacecraft have been hollow (i.e., with the potential to allow flow through them). We present here preliminary results from analyses performed using the NASA Direct Simulation Monte Carlo (DSMC) Analysis Code (DAC) on hollow cylinders and boxes (with varying wall thickness-diameter ratio)

The Distribution of Recent Foraminifera in Timbalier Bay, Louisiana

Paper by Christopher L. Ostro

Improving Estimation of Ground Casualty Risk From Reentering Space Objects

A recent improvement to the long-term estimation of ground casualties from reentering space debris is the further refinement and update to the human population distribution. Previous human population distributions were based on global totals with simple scaling factors for future years, or a coarse grid of population counts in a subset of the world's countries, each cell having its own projected growth rate. The newest population model includes a 5-fold refinement in both latitude and longitude resolution. All areas along a single latitude are combined to form a global population distribution as a function of latitude, creating a more accurate population estimation based on non-uniform growth at the country and area levels. Previous risk probability calculations used simplifying assumptions that did not account for the ellipsoidal nature of the Earth. The new method uses first, a simple analytical method to estimate the amount of time spent above each latitude band for a debris object with a given orbit inclination and second, a more complex numerical method that incorporates the effects of a non-spherical Earth. These new results are compared with the prior models to assess the magnitude of the effects on reentry casualty risk

Effect of Latitude Bias in Entry Angle on Ground Casualty Risk from Naturally Decaying Space Objects

An improvement to the long-term estimation of ground casualties from naturally decaying space objects is the refinement to the distribution of entry angle at the entry interface as a function of latitude. Previous analyses were based on an assumed "small angle," typically -0.1, and entry interface at the equator. This study expands on work by Bacon and Matney that indicated there is significant latitude bias in the location of reentries, compared to prior assumptions of equal temporal probability. A new model has been developed, which describes the distribution of entry angle as a function of orbital inclination and argument of latitude. This model has been used to generate inputs for ODPOs certified reentry survivability software, Object Reentry Survival Analysis Tool (ORSAT). These new results are compared with the prior standard model to assess the magnitude of the effects on reentry casualty risk

Snowy Plover Activity in the Central Platte River Valley in May 2019

During five of eight site visits between 14 and 27 May 2019 we detected up to four Snowy Plovers (Charadrius nivosus nivosus) in the Central Platte River Valley (CPRV) near Mormon Island, Hall County, Nebraska, and recorded their behavior using an instantaneous scan sampling approach. We recorded loafing (47%), foraging (43%), mating (4%), flying (4%), and external threat (1%) related behavior. Most notably, we documented a copulation event on 23 May. During the 10-day span from 14 to 23 May when Snowy Plovers were detected, river stage and discharge were near median levels, but from 23 to 27 May river discharge more than doubled and gage height increased by over 20%. This resulted in sandbar habitat becoming submerged and the Snowy Plovers vacating the site. This observation illustrates how wide variation in late spring flows can preclude potential breeding by ground nesting waterbirds in the CPRV given the current limited availability of unvegetated sandbars significantly exceeding flood stage. This represents a notable late-spring stay length in the CPRV with behavior suggestive of the potential for local breeding