... Spacecraft . ... To space by cannon? Finally, the deep space explorers --spacecraft which break away from the Earth's gravity . ... The "Luna" series of the USSR conducted 7 soft landing of unmanned probes, two of them with wheeled robotic "Lunokhods," and two of those missions returned samples to Earth. Others spacecraft have visited the major planets of the Solar system. ... The Mariner series have explored Venus and Mars--and Mariner 10 even reached Mercury, for three separate encounters! ...

An astronaut in low Earth orbit moves in (approximately) a big circle extending around the Earth. ... That can be interpreted as stating that in the astronaut's frame of reference, all bodies are subject to two forces, gravity and the centrifugal force, and the two are in perfect balance, adding up to zero. ... Wheel-shaped space . ... The science-fiction film "2001: A Space Odyssey" featured spinning space station, whose rotation provided the crew with "artificial gravity." ...

Luna and Io - A Comparison Study . ... They will construct paper scale models of Io , Luna , Earth and Jupiter and use these models to explain the differences between the two moons. ... Explain to the students that the picture is not to scale, but that it represents Jupiter and one of its moons. ... Have the students divide into groups of three or four and construct scale models of the Earth/Luna system, and the Jupiter/Io system, using the facts on the data sheets. ... Jupiter, Io, Earth, and Luna . ...