  Data from the power output of the radioisotope thermoelectric generators
aboard the Cassini spacecraft are used to test the conjecture that small
deviations observed in terrestrial measurements of the exponential radioactive
decay law are correlated with the Earth-Sun distance. No significant deviations
from exponential decay are observed over a range of 0.7 - 1.6 A.U. A 90% Cl
upper limit of 0.84 x 10^-4 is set on a term in the decay rate of Pu-238
proportional to 1/R^2 and 0.99 x 10^-4 for a term proportional to 1/R.
