Laboratory mice and other rodents have provided valuable information since the dawn of the space age. The mice on SpaceX-4 travel in a specially designed space rat habitat, and they will be used to study the effects of long-duration spaceflight on the senses, muscles, nerves, heart and other body systems.
The space station's first X-ray machine, a bone densitometer, will be used to study bone loss in the rodents due to weightlessness.
If they work in space, 3D printers could be used to quickly make repair parts and tools that would otherwise have to be sent up from Earth. The experimental printer is made by the California-based company Made In Space and will work by heating and extruding plastic.
SpaceX has a $1.6 billion contract with NASA to provide at least 12 cargo delivery flights to the International Space Station using its unmanned Dragon spacecraft and Falcon 9 rockets. The Dragon spacecraft is equipped with a heat shield, allowing SpaceX to return science gear and experiment samples back to Earth.
Dragon capsules currently make water landings in the Pacific Ocean and are recovered by SpaceX, which is based in Hawthorne, California. SpaceX is also designing a manned version of the Dragon capsule to launch astronauts to and from the space station. That capsule, the Dragon Version 2, will be able to land on the ground.