Solar System Ephemerides, Pulsar Timing, Gravitational Waves, & Navigation

In-spiraling supermassive black holes should emit gravitational waves, which would
produce characteristic distortions in the pulse time of arrival residuals from millisecond pulsars.
There are multiple national and regional consortia that have constructed pulsar timing arrays
by precise timing of different sets of millisecond pulsars. An essential aspect of precision timing
is the transfer of the pulsar times of arrival to a (quasi-)inertial reference frame, conventionally
taken to be the solar system barycenter. The solar system barycenter is determined from the
knowledge of the planetary masses and orbits, which has been re ned over the course of the past
50 years by multiple spacecraft missions. Within the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav), uncertainties on the solar system barycenter are emerging
as an important element of the overall NANOGrav noise budget. We describe what is known
about the solar system barycenter, touch upon how uncertainties in it affect gravitational wave
studies with pulsar timing arrays, and consider future trends in spacecraft navigation.