Space motion sickness was effectively unknown during the earliest spaceflights because the very cramped conditions of the spacecraft allowed for only minimal bodily motion, especially head motion. Space motion sickness seems to be aggravated by being able to freely move around, and so is more common in larger spacecraft. Around 60% of Space Shuttle astronauts currently experience it on their first flight; the first case of space motion sickness is now thought to be the Soviet cosmonaut Gherman Titov, in August 1961 onboard "Vostok 2", who reported dizziness, nausea, and vomiting. The first severe cases were in early Apollo flights; Frank Borman on "Apollo 8" and Rusty Schweickart on "Apollo 9". Both experienced identifiable and quite unpleasant symptoms—in the latter case causing the mission plan to be modified.