Modernizing and Expanding the NASA Space Geodesy Network to Meet Future Geodetic Requirements.

NASA maintains and operates a global network of Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System (GNSS) ground stations as part of the NASA Space Geodesy Program. The NASA Space Geodesy Network (NSGN) provides the geodetic products that support Earth observations and the related science requirements as outlined by the US National Research Council (NRC 2010, 2018). The Global Geodetic Observing System (GGOS) and the NRC have set an ambitious goal of improving the Terrestrial Reference Frame (TRF) to have an accuracy of 1 millimeter and stability of 0.1 millimeters per year, an order of magnitude beyond current capabilities. NASA and its partners within GGOS are addressing this challenge by planning and implementing modern geodetic stations co-located at existing and new sites around the world. In 2013, NASA demonstrated the performance of its next-generation systems at the prototype next-generation core site at NASA's Goddard Geophysical and Astronomical Observatory in Greenbelt, Maryland. Implementation of a new broadband VLBI station in Hawaii was completed in 2016. NASA is currently implementing new VLBI and SLR stations in Texas and is planning the replacement of its other aging domestic and international legacy stations. In this article, we describe critical gaps in the current global network and discuss how the new NSGN will expand the global geodetic coverage and ultimately improve the geodetic products. We also describe the characteristics of a modern NSGN site and the capabilities of the next-generation NASA SLR and VLBI systems. Finally, we outline the plans for efficiently operating the NSGN by centralizing and automating the operations of the new geodetic stations.

Adrenocortical hormones and lactation: metabolism of 3H-corticosterone and 3H-aldosterone by rat mammary gland minces and by the nuclear fraction of the homogenates.

3H-Corticosterone undergoes extensive metabolism on incubation with mammary acini and minced mammary glands from lactating rats; 3H-corticosterone-21-oleate was the major radiometabolite formed. In a similar study with 3H-aldosterone, 3H-aldosterone-21-oleate was one of the two major radiometabolites formed. In the present study, an enzyme system highly active in the biosynthesis of 21-acyl-3H-corticosterone was demonstrated to be present chiefly in the nuclear fraction of mammary gland homogenates. The enzyme system comprises: a fatty acid thiokinase (or fatty acyl-CoA synthetase); a fatty acyl transferase. The methods entailed incubation of 3H-corticosterone with the nuclear fraction in the presence and absence of: the cofactors, CoA, ATP, and Mg2+; oleoyl-CoA and other fatty acyl-CoA donors. The results of the present investigation support the view that the major cellular site for the acylation of adrenocortical hormones is the nucleus. It has been suggested that the acylation serves to modulate the biological action of the hormones on the mammary glands by interaction with the glucocorticoid receptor.

In vitro metabolism of adrenocortical hormones by mammary glands of lactating rats. A comparative study.

A comparative study was made of the metabolism of tritium-labeled corticosterone, cortisol and aldosterone on incubation with minced mammary glands of lactating rats. The yield of total nonpolar (acylated) radiometabolites was highest for [3H]corticosterone, lowest for [3H]cortisol and intermediate for [3H]aldosterone. Unlike [3H]corticosterone, [3H]aldosterone yielded two 21-acyl derivatives (Metabolites I and II) in comparable amounts. Metabolite I (39%) was identified as [3H]aldosterone 21-oleate by isotope dilution analysis. Metabolite II (54%) could not be identified: it is intermediate in polarity between corticosterone 21-oleate and the less polar, corticosterone 21-stearate, and is distinctly less polar than the 21-palmityl, linoleoyl (and presumably also less polar than the arachidonyl) derivatives of aldosterone. The [3H]cortisol metabolites were not further investigated.

In vitro metabolism of [3H] corticosterone by mammary glands from lactating rats. Isolation and identification of 21-acyl[3H]corticosterone.

[3H] Corticosterone undergoes extensive 21-acylation on incubation with minced mammary glands from lactating rats. A purified 21-acyl [3H] corticosterone fraction was obtained by subjecting extracts of the incubated tissues to Sephadex LH-20 column chromatography followed by partitioning between n-heptane/methanol. The methanol extracts were chromatographed consecutively on columns of silica gel and C18-silanized (reverse-phase) silica gel. The radioactive product was methoximated and re-chromatographed on the reverse-phase column. Mass spectral analysis of the 21-acyl [3H] corticosterone 3,20-dimethoxime and synthetic corticosterone 21-oleate 3,20-dimethoxime suggested identity. Confirmation of the precise nature of the 21-acyl moiety was obtained by isotope dilution analysis of the underivatized radiometabolite with corticosterone 21-oleate. The composition of the 21-acyl [3H] corticosterone fraction (i.e. before extensive purification) was ascertained by isotope dilution analysis with various corticosterone esters. It appears that [3H] corticosterone 21-oleate is a major component of this fraction, representing 80% of the radioactivity; [3H] corticosterone 21-linoleate is a minor component, i.e. 8.6%. [3H] Corticosterone 21-palmitate, [3H] corticosterone 21-arachidonate, and [3H] corticosterone 21-stearate, if indeed present, constitute considerably less than 14, 6, and 2%, respectively, of the radiometabolite fraction. It is suggested that bioacylation of corticosterone serves to modulate the biological action of the glucocorticoid hormone on the mammary glands during lactation.

Glucocorticoids and lactation. In vitro metabolism of glucocorticoids by rat mammary glands.

In view of: 1. the extensive in vitro 21-acylation of [3H]corticosterone by rat mammary glands, especially during lactation; 2. the accumulation of 21-acyl [3H]corticosterone as the predominant form of the hormone in the alveolar nuclear fraction with which it is strongly associated; 3. the results of a systematic study of the influence of acylation per se of corticosterone and dexamethasone on their binding affinities for specific glucocorticoid-binding proteins; and 4. the extensive metabolic acylation, similarly, of adrenocortical hormones other than corticosterone, it is suggested that the acylation of glucocorticoid by the mammary gland may serve to modulate the biological action of the hormone on this target organ, and indirectly influence the flow of glucocorticoid from plasma to milk.

In-vitro uptake and metabolism of [3H] corticosterone by mammary glands from pregnant, lactating, and post-lactational rats and by parametrial adipose tissue from lactating rats.

The study was designed to determine the influence of the physiological state on the in-vitro uptake and metabolism of glucocorticoid hormone by the mammary gland. [3H] Corticosterone was accordingly incubated with minced mammary glands from pregnant, lactating and post-lactational rats. The total uptake of [3H] corticosteroid was obtained from the concentration of radioactivity by the tissue and the specific activity of the steroid substrate. The extent of 21-acylation was determined as the percentage of the radioactivity in the chromatographed tissue extracts attributable to 21-acyl-[3H] corticosterone. The results indicated that the uptake of [3H] corticosteroid increased with advancing pregnancy, attained a high plateau level during lactation, and steadily declined during the post-lactational period. The extent of 21-acylation of [3H] corticosterone varied from 10 to 40%, fluctuating widely in all physiological states, particularly during the post-lactational period. It was inferred that the stromal elements, presumably the adipocytes, of the mammary gland can also acylate the corticosteroid hormone, a view which gained experimental support from similar studies with minced parametrial adipose tissue from lactating rats.

Transportable lunar-ranging system.

Ruby lasers in large, fixed installations are being used by groups in France, Japan, the Soviet Union, and the U.S. for measuring distances to retroreflectors on the moon. This paper describes a transportable transmitting unit that can be installed at any astronomical observatory where a large telescope is available to detect the received signal. The transmitter consists of a high radiance, frequency-doubled, neodymium-glass laser and a coudé optical system of moderate size. It has been installed, but is not yet in operation, at the Agassiz Observatory, Harvard, Massachusetts.