African VLBI Network Training Site

Title: Stellar GPS: Navigating the Solar System

Authors: Mr Christopher Jacobs
                JPL, Caltech / NASA

                Mrs Cristina Garcia-Miro
                Madrid Deep Space Communications Complex / NASA

Abstract:
How does one navigate to a planet such as Mars?     Will GPS work?

Since ancient times sailors have navigated by following a path guided by markers with known locations: bottom sounding, landmarks such as mountain peaks, and of course stars overhead in the sky. In modern times the GPS satellites in the sky are providing the needed markers. However, when our spacecraft travel to the planets they go beyond the reach of GPS signals. What then can the navigator do?

Needing markers which are very, very stable in position and very far away, the modern navigator chooses beacons powered by supermassive black holes: quasars! Yet even super-powerful quasar signals are very diluted by the time they travel billions of light years to Earth. So we need large antennas (~30-meters) and super-cooled electronics (-270 deg C) and averaging over billions of bits of data in order to detect the quasar signals—and even that is not enough. Next we need to link antennas from around the world into a super-antenna we call an "interferometer." Only then, with these super-antennas and their lever arms the size of the Earth, can we pinpoint the location of the spacecraft to within about the 100 meters accuracy needed to initiate the landing sequence from the top of the Martian atmosphere.

The last part of the trip is the most exciting. First, a parachute slows the lander down enough to fly on auto-pilot (because round trip light time is ~10 minutes) using radar to guide us almost to the ground. Lastly, in the case of MSL, the Curiosity Rover is lowered from a sky crane”. Mission accomplished!

More about the author:

Christopher Jacobs is a senior deep space navigation engineer at NASA's Jet Propulsion Laboratory (JPL) of the California Institute of Technology. Jacobs holds a degree in Applied Physics from Caltech. He joined JPL in 1983 and has taken on roles of increasing responsibility in the area of deep space tracking specializing in the area of celestial and terrestrial reference frames. He has served as the Reference Frame Calibration task manager for 25 years in which role he has been responsible for delivering the reference frames used to navigate NASA missions such as MSL to planetary targets.

Jacobs is a member of the American Astronomical Society (AAS), the International VLBI Service (IVS) including its education committee, and the International Astronomical Union (IAU) where he has served on the working group for the International Celestial Reference Frame for over 20 years. Recently he chaired the working group responsible for the next generation international celestial reference frame (ICRF-3).

Jacobs has spoken professionally in numerous countries spanning six continents, has authored or co-authored over 200 papers (both refereed, conference). He has founded several international collaborations for the development of reference
frames.

He has an active interest in professional education having taught at professional training schools sponsored by the IVS, the association for European VLBI for Geodesy and Astrometry (EVGA). He is also active in public education and outreach having given public lectures in a diverse range of places spanning from Spain to the Azores, England and South Africa and covering a diverse range of levels from primary schools to universities and public planetariums.

His publication history has focussed on developing international standard reference frames for global use including the famous International Celestial Reference Frame (ICRF) papers which initiated a new era in measuring positions on the sky. He was recently awarded the NASA Medal for Exceptional Achievement in recognition of his work.