NASA is helping to lead an international effort to upgrade the systems that supply crucial location information and earth science measurements. Stephen Merkowitz, the project manager of NASA's space geodesy initiative at NASA Goddard Space Flight Center in Greenbelt, Maryland, manages the budget and schedule for the upgraded ground station that will help serve satellites of the future.

NASA Tech Briefs: What is NASA's international geodesy initiative?

Stephen Merkowitz: NASA currently offers a network of space geodetic ground stations that do Very Long Baseline Interferometry (VLBI), satellite laser ranging (SLR), and [global navigation satellite system] GNSS or GPS tracking. The new space geodesy project will develop and implement the next-generation systems. The current systems are 20-30 years old. One of the primary drivers for upgrading the system is sea-level measurement, where you would like to be able to make those measurements at the millimeter level and have them be stable over the years, so you can do repeated measurements.

NTB: What is Very Long Baseline Interferometry (VLBI)?

Merkowitz: VLBI is a system of radio telescopes that observe distant quasars, astronomical bodies that are very far away from Earth. They’re so far away that their position in the sky is relatively stable. We can use them as a stable reference system, and we do this by observing these quasars with a number of radio telescopes all over the globe. NASA operates a few, but we do need the global community to do this, and they’ll observe the same quasar simultaneously. So in a sense you can think of all of these little telescopes acting together as one big telescope. You also get baseline information between the telescopes when you’re doing the same observation, which allows you to determine the orientation of the Earth in space.

NTB: How does the satellite ranging system work?

Merkowitz: We can determine the distance to the satellites that we observe to roughly a centimeter, sometimes slightly better than that. The newer systems will be about an order magnitude better, doing millimeter-level tracking. They’ll be able to [work with] many more sources: different satellites and satellites at higher altitudes and during the daytime. Probably most importantly, from a cost perspective, is that these systems will be much more autonomous than the current system.

NTB: What is your favorite part of the job?

Merkowitz: I come from a background of precision measurement, and I really enjoy when I go out to the prototype station—particularly at night when the satellite ranging system is operating. You can see the laser going up to the satellites, and you see the telescope moving and the laser moving with it, and while you can’t see the return light coming back from the satellite, you imagine this light is going up into space, bouncing off a satellite, and coming back. We’re receiving it and measuring the position of that satellite to millimeters, and that is a very impressive thing. I always enjoy going out to the site and seeing the hardware operating.

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