Stellar "GPS": Navigation in the Solar System

Chris Jacobs from NASA, JPL will present the NASSP colloquim with a talk entitled, "Stellar "GPS": Navigation in the Solar System

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!

Christopher Jacobs has worked for nearly 33 years in the Deep Space Tracking Systems group at NASA's Jet Propulsion Laboratory of the California Institute of Technology in Pasadena California.


Chris specializes in the use of the Very-Long-Baseline Interferometry (VLBI) technique to build reference systems used for space mission navigation. He recently chaired of a global group of 20 astronomers who are preparing the next generation international standard for celestial reference frames.

His team has supported numerous interplanetary missions, such as Galileo (Jupiter and its moons), Cassini (Saturn),  Magellan (Venus), and numerous NASA probes to Mars, such as the recent Mars Science Laboratory (MSL)  and its roving laboratory, Curiosity.

Chris as authored or co-authored over 200 scientific presentations and papers. In 2015 he was awarded the NASA medal for Exceptional Achievement in recognition of his innovations in the art of building reference frames.

He is also known for his efforts to bring astronomy to wider audiences around the globe through his public lectures on astronomy. He has been invited to speak in such diverse places as Spain, Argentina,  China, Azores, England, and South Africa.  He is looking forward to connecting with audiences in South Africa.


"It is an honor to be working with South Africans who have such a vital role to play in the international scientific community.  My last visit to South Africa was prompted by a gathering of more than 130 scientists from 22 nations and 5 continents. Out of this meeting many international collaboration were strengthened which will be essential for monitoring sea level rise and other issues of concern to society."

Date: 
Tuesday, August 16, 2016 - 16:15
Venue: 

MAM 304 Lecture Theatre, Mathematics Building, Upper Campus, UCT

TOP