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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1995

Anticipated uncertainty budgets of PRARETIME and T2L2 techniques as applied to ExTRAS

The Experiment on Timing Ranging and Atmospheric Soundings, ExTRAS, was conceived jointly by the European Space Agency, ESA, and the Russian Space Agency, RSA. It is also designated the 'Hydrogen-maser in Space/Meteor-3M project'. The launch of the satellite is scheduled for early 1997. The package, to be flown on board a Russian meteorological satellite includes ultra-stable frequency and time sources, namely two active and auto-tuned hydrogen masers. Communication between the on-board hydrogen masers and the ground station clocks is effected by means of a microwave link using the modified version for time transfer of the Precise Range And Range-rate Equipment, PRARETIME, technique, and an optical link which uses the Time Transfer by Laser Link, T2L2, method. Both the PRARETIME and T2L2 techniques operate in a two-directional mode, which makes it possible to carry out accurate transmissions without precise knowledge of the satellite and station positions. Due to the exceptional quality of the on-board clocks and to the high performance of the communication techniques with the satellite, satellite clock monitoring and ground clocks synchronization are anticipated to be performed with uncertainties below 0.5 ns (1 sigma). Uncertainty budgets and related comments are presented.

Thomas, Claudine↗

NASA NTRS2018

Small Spacecraft for Planetary Atmospheric, Surface, and Interior Structure Using Radio Links

Scientific studies using spacecraft radio links have been conducted on almost every Solar System exploration mission in the past five decades and have led to numerous discoveries. Radio Science experiments have elucidated the thermal history of the Moon from high resolution gravitational field measurements, unveiled the interiors of Titan, Enceladus, Mercury, Phobos, Vesta and Ceres providing key evidence for identifying subsurface oceans on icy moons; sounded Titan, Saturn, and Pluto’s atmospheres, and refined models for the atmospheres, surfaces, and interior structure of Mars and Venus. A Juno experiment is in progress measuring the gravitational field of Jupiter to reveal its interior structures, as did a similar recent Cassini experiment with Saturn. Experiments at Mercury, the Jovian system, and other targets, are in development or planning phases. Over the next 30 years, significant advances in radio and laser link-science technologies, including nearly one order of magnitude improvement achievable in range-rate and range accuracy, could enable many new scientific breakthroughs. Future exploration concepts in many cases focus on applications of small spacecraft and can include spacecraft constellations for studies of atmospheric dynamics, interior structures, and surface properties. A set of science-enabling radio link technologies specific to small spacecraft instrumentation on future solar system missions are under study and development. Examples include field tests of radio scattering to determine soil properties, smallsat constellations for dense geographic and temporal atmospheric probing, small science-quality software-defined transponders, miniature ultra-stable oscillators, and advanced radio-metric calibrations at the Deep Space Network. This paper describes many of these technologies and their scientific applications.

Elliott, Harvey↗

NASA NTRS2011

Flight-Like Optical Reference Cavity for GRACE Follow-On Laser Frequency Stabilization

We describe a prototype optical cavity and associated optics that has been developed to provide a stable frequency reference for a future space-based laser ranging system. This instrument is being considered for inclusion as a technology demonstration on the recently announced GRACE follow-on mission, which will monitor variations in the Earth's gravity field.

Gravity Recovery and Climate Experiment (GRACE)↗

NASA NTRS2020

Impact of Jason-2/T2L2 Ultra-Stable-Oscillator Frequency Model on DORIS stations coordinates and Earth Orientation Parameters

Doppler Orbitography and Radiopositioning Integrated on Satellite (DORIS)is a tracking technique based on a one-way ground to space Doppler link.For Low Earth Orbit (LEO) satellites, DORIS shows a robust capability interms of data coverage and availability, due to a wide and well-distributedground network, where data are made available by the International DorisService (IDS). However, systematic errors remain in the DORIS data, suchas instabilities of the on-board clock due to radiation encountered in space,which limit the accurate determination of station positions.The DORIS on-board clock frequency stability is degraded by the increased radiation found in the region of the South Atlantic Anomaly (SAA)and has been shown to degrade station position estimation. This paper in-troduces a new model correction to the DORIS data for the frequency ofthe Jason-2 Ultra Stable Oscillator (USO), derived from the Time Transferby Laser Link (T2L2) experiment (Belli and Exertier, 2018). We show thata multi-satellite DORIS solution including this T2L2-corrected data appliedto the frequency modelling for The DORIS data, improves the estimationof station coordinates. We show the tie residuals with respect to collocatedGPS stations are improved by several millimeters. We also demonstratethat the 117-day (Jason-2) draconitic signal in the geophysical parametersis reduced, implying that the origin of this signal is not just solar radiationpressure mis-modeling, but also radiation-induced clock perturbations onthe Jason-2 DORIS Ultra-Stable-Oscillator (USO). Finally we demonstratethrough comparisons with the International Earth Rotations and ReferenceSystems Service (IERS) C04 series for Earth Orientation Parameters (EOP),that the estimation of EOP is improved in both a Jason-2 DORIS-only anda multi-satellite DORIS solution for EOP.

DORIS↗