Analysis of navigation performance for the Earth Observing System (EOS) using the TDRSS Onboard Navigation System (TONS)

Use of the Tracking and Data Relay Satellite System (TDRSS) Onboard Navigation System (TONS) was proposed as an alternative to the Global Positioning System (GPS) for supporting the Earth Observing System (EOS) mission. The results are presented of EOS navigation performance evaluation with respect to TONS based orbit, time, and frequency determination (OD/TD/FD). Two TONS modes are considered: one uses scheduled TDRSS forward link service to derive one way Doppler tracking data for OD/FD support (TONS-I); the other uses an unscheduled navigation beacon service (proposed for Advanced TDRSS) to obtain pseudorange and Doppler data for OD/TD/FD support (TONS-II). Key objectives of the analysis were to evaluate nominal performance and potential sensitivities, such as suboptimal tracking geometry, tracking contact scheduling, and modeling parameter selection. OD/TD/FD performance predictions are presented based on covariance and simulation analyses. EOS navigation scenarios and the contributions of principal error sources impacting performance are also described. The results indicate that a TONS mode can be configured to meet current and proposed EOS position accuracy requirements of 100 and 50 m, respectively

Structural and Compositional Changes in the Upper Atmosphere Related to the PEDE‐2018 Dust Event on Mars as Observed by MAVEN NGIMS

The onset of the planet encircling dust event (PEDE‐2018) started around 1 June 2018 as observed by Mars Reconnaissance Orbiter/Mars Color Imager, peaking around 7–10 July and persisting through mid‐October 2018. After the onset of the event, the upper atmosphere underwent significant changes in density and thermal structures. Mars Atmosphere and Volatile Evolution‐Neutral Gas and Ion Mass Spectrometer (MAVEN NGIMS) had a good opportunity to observe these changes from the first detection in the upper atmosphere and throughout the duration of the PEDE. The compositional changes included increased density at a constant altitude for CO2 and Ar, while the O decreased from the peak throughout the decay of the bulk of the PEDE.Plain Language SummaryFrom June through October 2018 Mars experienced a planet encircling dust event (PEDE‐2018), a fairly rare event last observed in 2007. The dust storm grew from a local event to cover the entire planet and was opaque enough that so little sunlight reached the surface that the solar‐powered opportunity rover ceased operations and all attempts to re‐establish contact with it were unsuccessful. Meanwhile, the orbiter Mars Atmosphere and Volatile Evolution (MAVEN) was able to observe changes in the upper atmosphere in the composition as a result of this globally extensive PEDE. MAVEN observed increases in both the CO2 and Ar while also observing an unexpected reduction in the O densities.Key PointsMAVEN/NGIMS observed increased of CO2 and Ar densities observed in the upper atmosphere corresponding to the peak of the dust eventUnexpected decrease in O densities in the upper atmosphere (160–250 km) was simultaneously observedComparisons between model and data results show good agreement with scale height and temperatures, further M‐GITM model revisions needed to capture circulation effectsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154472/1/grl59716_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154472/2/grl59716.pd

The Value Of Graduate Certificate Programs In Engineering Education: A Strategic Assessment

There has been a significant increase in the popularity of non-degree graduate certificates throughout the past decade. This increase has raised questions about the value of engineering graduate certificate programs from students, alumni, and employers. Do engineering certificate programs provide real world skills and knowledge? Do they serve as effective recruiting tools for universities? Do they provide opportunities for students to meet their professional goals in terms of salary increase and promotions? This study explores these questions. Eighty-three current and former engineering certificate students, as well as forty professionals from industry, were surveyed about their value perception of graduate certificate programs. Guidance for engineering educators and other professionals concerned with development and marketing of engineering graduate certificate programs is also presented.

First Evidence of Persistent Nighttime Temperature Structures in the Neutral Thermosphere of Mars

Using two Mars years of data collected by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatiles EvolutioN spacecraft, we reconstruct the local solar time structure of the Martian equatorial thermosphere for the dawn and dusk sectors. The results indicate the presence of several persistent features near the dusk and dawn terminators appearing in the neutral temperature and in the O, Ar, N2, and CO2 densities. The dusk temperature features include a minimum at the terminator surrounded by two local maxima with amplitudes between 20 and 40 K. A nighttime temperature enhancement occurs at a local solar time of 4–5 hr and has an amplitude between 50 and 100 K relative to the surrounding temperatures. The observed enhancements are interpreted to be a result of either nighttime dynamical heating caused by converging and downwelling winds or of a terminator wave originating in the lower atmosphere.Plain Language SummaryNASA’s Mars Atmosphere and Volatiles EvolutioN (MAVEN) spacecraft has been collecting information about the Mars’ upper atmosphere since November 2014. In our study we examined the temperature in the upper atmosphere measured by a gas analyzer on MAVEN that periodically sniffs the air around it. By combining several years of data, we reconstructed a map of atmospheric temperatures dividing it into equatorial daytime, morning, evening, and nighttime regions. The results indicate that local patches of warm atmosphere extend about 300–600 km along the Martian equator (3–6 hr driving distance at highway speeds) on the nightside near morning and evening. One possible reason for these nighttime warm spots is the air currents in the Martian upper atmosphere. As the sun heats the dayside atmosphere, it expands and causes wind currents to blow away from the dayside region. These wind currents can extend away from the equator then return on the nightside colliding in the morning and evening regions. The resulting meeting of wind currents can heat the upper atmosphere. Warmer air escapes from the upper atmosphere faster. Because of this, these nighttime patches of warm air could have contributed to a faster escape of Martian atmospheric gases than previously believed.Key PointsPersistent neutral density and temperature enhancements are observed within 30 min of the dusk terminatorA persistent neutral density enhancement is also observed prior to the dawn terminator at around 4–5 local timeThe neutral density features are observed in all species and appear to be associated with enhancements in neutral temperaturePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146482/1/grl57932.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146482/2/grl57932_am.pd

Theory versus experiment for the rotordynamic coefficients of annular gas seals. Part 1: Test facility and apparatus

A facility and apparatus are described for determining the rotordynamic coefficients and leakage characteristics of annular gas seals. The apparatus has a current top speed of 8000 cpm with a nominal seal diameter of 15.24 cmn (6 in). The air supply unit yields a seal pressure ratio of approximately 7. An external shaker is used to excite the test rotor. The capability to independently calculate all rotordynamic coefficients at a given operating condition with one excitation frequency are discussed

He bulge revealed: He and CO2 diurnal and seasonal variations in the upper atmosphere of Mars as detected by MAVEN NGIMS

Analysis of the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere Volatiles and EvolutioN (MAVEN) spacecraft closed source data from all orbits with good pointing revealed an enhanced Helium [He] density on the nightside orbits and a depressed He density on the dayside by about a factor of 10–20. He was also found to be larger in the polar regions than in the equatorial regions. The northern polar winter nightside He bulge was approximately twice that of the northern polar summer nightside bulge. The first 6 weeks of the MAVEN prime mission had periapsis at high latitudes on the nightside during northern winter, followed by the midlatitudes on the dayside moving to low latitudes on the nightside returning to the high latitudes during northern summer. In this study we examined the NGIMS data not only in the different latitudes but sorted by solar longitude (Ls) in order to separate the diurnal or local solar time (LST) effects from the seasonal effects. The Mars Global Ionosphere‐Thermosphere Model (M‐GITM) has predicted the formation of a He bulge in the upper atmosphere of Mars on the nightside early morning hours (Ls = 2–5 h) with more He collecting around the poles. Taking a slice at constant altitude across all orbits indicates corresponding variations in He and CO2 with respect to LST and Ls and a diurnal and seasonal dependence.Key PointsData using MAVEN NGIMS for 1 Martian year reveal diurnal and seasonal variations in He and CO2 indicating a changing He bulge in upper atmosphereObserved He bulge is found to agree preliminarily with M‐GITM modeling effortsHe bulge found at Mars is similar to those found at Earth and VenusPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136361/1/jgra53312_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136361/2/jgra53312.pd

Modeling the seasonal variability of the plasma environment in Saturn's magnetosphere between main rings and Mimas

a b s t r a c t The detection of O 2 þ and O þ ions over Saturn's main rings by the Cassini INMS and CAPS instruments at Saturn orbit insertion (SOI) in 2004 confirmed the existence of the ring atmosphere and ionosphere. The source mechanism was suggested to be primarily photolytic decomposition of water ice producing neutral O 2 and H 2 Published by Elsevier Ltd