Irwin Allen 
One Way To The Moon [EPUB ebook] 

Tony and Doug are transported through the Time Tunnel into the service module of a spaceship just before liftoff. The spacecraft, part of the M.E.M. (Mars Excursion Module) ten years into Tony and Doug s future, it will be the first manned US spaceflight to Mars. Tony and Doug s added weight (335 pounds) makes it impossible for the spacecraft to reach escape velocity to escape Earth s gravitational pull. Unbeknownst to the stowaways, the astronauts on board decide to eject the service module.