  LISA may make it possible to test the black-hole uniqueness theorems of
general relativity, also called the no-hair theorems, by Ryan's method of
detecting the quadrupole moment of a black hole using high-mass-ratio
inspirals. This test can be performed more robustly by observing inspirals in
earlier stages, where the simplifications used in making inspiral predictions
by the perturbative and post-Newtonian methods are more nearly correct. Current
concepts for future missions such as DECIGO and BBO would allow even more
stringent tests by this same method. Recently discovered evidence supports the
existence of intermediate-mass black holes (IMBHs). Inspirals of binary systems
with one IMBH and one stellar-mass black hole would fall into the frequency
band of proposed maximum sensitivity for DECIGO and BBO. This would enable us
to perform the Ryan test more precisely and more robustly. We explain why tests
based on observations earlier in the inspiral are more robust and provide
preliminary estimates of possible optimal future observations.
