The Solar System formed 4. 6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
Mars One’s original concept includes launching a robotic Mars lander and Mars orbiter as early as 2020, to be followed by a human crew of four in 2024, and one in 2026 which would not be returning to Earth. Although the announcement garnered much international publicity, the concept has been criticized by scientists, engineers, and those in the aerospace industry. Mars One is noted as being very short on funding, lacking critical concepts about hardware, life support, electrical power supply, and has been criticized as glossing over logistics, medical concerns, and protection against space radiation. The concept has been called a suicide mission in academia, spaceflight, and international news.
Players can create rockets, aircraft, spaceplanes, rovers, and other craft from a provided set of components. Once built, the craft can be launched by players from the KSC launch pad or runway, or other launch pads and runways around Kerbin, in an attempt to complete player-set or game-directed missions while avoiding partial or catastrophic failure (such as lack of fuel or structural failure). Players control their spacecraft in three dimensions with little assistance other than a stability system called “SAS” to keep their rocket oriented. Provided it maintains sufficient thrust and fuel, a spacecraft can enter orbit or even travel to other celestial bodies. To visualize vehicle trajectory, the player must switch into map mode; this displays the orbit or trajectory of the player vehicle, as well as the position and trajectory of other spacecraft and planetary bodies. These planets and other vehicles can be targeted to view information needed for rendezvous and docking, such as ascending and descending nodes, target direction, and relative velocity to the target. While in map mode, players can also access maneuver nodes to plan out trajectory changes in advance.