A proposal to measure G in the deep space

Michael R Feldman, John D Anderson, Gerald Schubert, Virginia Trimble, Sergei M Kopeikin and Claus Lämmerzahl, Deep space experiment to measure G, IOP Publishing Ltd Classical and Quantum Gravity, Volume 33, Number 12, Published 17 May 2016.
https://iopscience.iop.org/article/10.1088/0264-9381/33/12/125013

Abstract:
Responding to calls from the National Science Foundation (NSF) for new
proposals to measure the gravitational constant G, we offer an interesting experiment
in deep space employing the classic gravity train mechanism. Our setup requires
three bodies: a larger layered solid sphere with a cylindrical hole through its center,
a much smaller retroreflector which will undergo harmonic motion within the hole
and a host spacecraft with laser ranging capabilities to measure round trip lighttimes
to the retroreflector but ultimately separated a significant distance away from
the sphere-retroreflector apparatus. Measurements of the period of oscillation of the
retroreflector in terms of host spacecraft clock time using existing technology could
give determinations of G nearly three orders of magnitude more accurate than current
measurements here on Earth. However, significant engineering advances in the release
mechanism of the apparatus from the host spacecraft will likely be necessary. Issues
with regard to the stability of the system are briefly addressed.