NASA’s new technology to better measure Earth’s orientation

NASA has developed advanced technology for making precise measurements of Earth’s orientation and rotation — information that will help provide a foundation for navigation of all space missions and for geophysical studies.

The technology includes a new class of radio antenna and electronics that provide broadband capabilities for Very Long Baseline Interferometry (VLBI). This technique is used to make precise measurements of Earth in space and time, researchers said.

VLBI measurements have been conducted for decades using a worldwide network of stations that carry out coordinated observations of very distant astronomical objects called quasars.

To meet the demand for more precise measurements, a new global network of stations, called the VLBI Global Observing System (VGOS) is being rolled out to replace the legacy network.

NASA is participating in this next generation network and just completed the installation of a joint NASA-US Naval Observatory VGOS station at NASA’s Observatory in Hawaii.

On February 5, NASA conducted the first demonstration anywhere in the world of broadband observations for VLBI over a long baseline.

“The successful tests demonstrate the viability of the new broadband antenna technology for making the kinds of observations needed for improved accuracy in measurements of the very fine-scale shape of Earth,” said Benjamin R. Phillips, who leads NASA’s Earth Surface and Interior Focus Area.

The coordinated observation was verified by detection of fringes — an interference pattern indicating that all three stations were receiving and could combine the signals from the quasar they observed.

The broadband antenna and electronics provide improved sensitivity in a scaled-down package. With dish sizes of 12 to 13 metres, the next-generation antennas are designed to be smaller than most of the current system’s dishes, which are typically 20 to 30 metres.

The scaled-down size allows an antenna to move quickly, conducting up to 100 observations in an hour compared to about 12 observations in an hour for the current VLBI system. This type of antenna is also much less expensive than the larger antennas, making it more economical to deploy and operate a global network.

Broadband capability makes it possible to conduct observations in four bands — that is, at four frequencies — at the same time, whereas current VLBI systems operate in two bands.

Another new feature is that the four bands are selectable within a range of 2 gigahertz to roughly 14 gigahertz. This helps to avoid interference with other sources, such as radio and cellphone towers.

“The next-generation VLBI system will expand our ability to make the kinds of measurements that will be needed for geophysical studies and navigation applications, which demand more precision all the time,” said Stephen Merkowitz, manager of NASA’s Space Geodesy Project.

March 11, 2016

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