  A Micro-Channel Plate (MCP) is a widely used component for counting particles
in space. Using the background counts of MCPs on Mars Express and Venus Express
orbiters operated over 17 years and 8 years, respectively, we investigate the
galactic cosmic ray (GCR) characteristics in the inner solar system. The MCP
background counts at Mars and Venus on a solar cycle time scale exhibit clear
anti-correlation to the sunspot number. We conclude that the measured MCP
background contain the GCR information. The GCR characteristics measured using
the MCP background at Mars show features that are consistent with the
ground-based measurement in solar cycle 24. The time lag between the sunspot
number and the MCP background at Mars is found ~9 months. The shorter-term
background data recorded along the orbits (with a time scale of several hours)
also show evident depletion of the background counts due to the absorption of
the GCR particles by the planets. Thanks to the visible planetary size change
along an orbit, the GCR contribution to the MCP background can be separated
from the internal contribution due to the \b{eta}-decay. Our statistical
analysis of the GCR absorption signatures at Mars implies that the effective
absorption size of Mars for the GCR particles have a >100 km larger radius than
the solid Martian body.
