Spacecraft can travel at above 800 MPH or the speed of sound, so I am unsure what you are asking. Things can typically travel faster in a vacuum because there is nothing to slow it down. A vacuum is supposed to be devoid of all atoms, providing no friction or resistance. Also, moons and asteroids can have atmospheres. For the sake of argument, you probably could create a small atmosphere around a ship, but it would not allow you to move faster. If anything this means that when something enters the atmosphere the effects could be interesting as it could work to push some things out of the way or lower kinetic every transfer. For your consideration The Apollo 10
crew (Thomas Stafford
, John W. Young
and Eugene Cernan
) achieved the highest speed relative to Earth ever attained by humans: 39,897 kilometers per hour (11.082 kilometers per second or 24,791 miles per hour, approximately 32 times the speed of sound
and 0.00037% of the speed of light
The record was set 26 May 1969.