Among other things, weightlessness affects the human cardiovascular system, the consequence being that astronauts who have just returned to Earth after a prolonged stay in space are able to stand upright only within limits. Similar changes occur in patients who have been confined to bedrest for a long time, in intensive care, for example. The reason is that our cardiovascular system has evolved under the continuous influence of gravity on Earth. Thus, it ensures that our blood does not rush entirely from the brain to the feet when we stand up after lying down. If it did, we would faint. DLR's join-in experiment illustrates this interaction, i.e. those mechanisms in our body that enable us to assume an upright position (orthostasis). On a parabolic flight, DLR scientists have examined orthostasis under the gravity conditions prevailing on Mars and the Moon.