  We have studied solar activity and space weather conditions during multiple
planetary conjunction periods ( MPC) as observed from Earth during the years
1850-2000 AD. Significant decreases in sunspot activity and solar 10.7 cm radio
flux and absence of severe space weather conditions is found during most of
these MPC . Possible planetary influences in longitudinal organisation of
sunspot activity is suggested by these results. The success of major space
missions ( lunar and human) during MPC is also noticed during 1957-2000 AD. The
applications of the above results include: short term space mission planning
and inference/prediction of solar-terrestrial conditions during multiple
planetary conjunction periods.
