  There are very few direct experimental tests of the inverse square law of
gravity at distances comparable to the scale of the Solar System and beyond.
Here we describe a possible space mission optimized to test the inverse square
law at a scale of up to 100 AU. For example, sensitivity to a Yukawa correction
with a strength of $10^{-7}$ times gravity and length scale of 100 AU is within
reach, improving the current state of the art by over two orders of magnitude.
This experiment would extend our understanding of gravity to the largest scale
that can be reached with a direct probe using known technology. This would
provide a powerful test of long-distance modifications of gravity including
many theories motivated by dark matter or dark energy.
