  Processing the data of lunar laser ranging (LLR) points to the effect of
anomalous increase in the lunar semimajor axis (with an excessive rate about
1.3 cm/yr), which cannot be attributed to the well-known tidal exchange of
angular momentum between the Earth and Moon. The nature of this phenomenon is
not quite clear yet, but one of the possible explanations is that it is a
manifestation of the "residual" Hubble expansion, caused by some forms of an
unclumped "dark matter" or "dark energy". If this is the case, a similar effect
will reveal itself also in operation of space-based interferometers with
sufficiently long arms (10^7 km or greater, e.g., LISA and ASTROD) and,
therefore, should be taken into account in processing the data on
gravitational-wave signals.
