During the transition between Act One and Act Two, 2001 displays a series of spacecraft demonstrating that by 2001, mankind had mastered space travel within the near regions around Earth.  Based on actual NASA designs and concepts introduced by the budding space science industry, the spacecraft revealed in this critical sequence laid the foundations for Gerry Anderson’s UFO and Space: 1999 series.  These, in turn, forced major films to move from the crude designs seen throughout science fiction films of the 1950s and 1960s to the more sophisticated models of films like Star Wars. 

When 2001 was made, NASA felt that deep space probes would be powered by the NERVA engine.  This small nuclear drive was under development by the United States Atomic Energy Commission until 1969, when it was dropped due to runaway development costs.  Stanley Kubrick paid tribute to their efforts by showing one of the early concept designs flying through space.
 

NERVA Space Probe