Kerbal Space Program
Kerbal Space Program is a 2015 space flight simulation video game developed by Mexican studio Squad for Linux, macOS, Windows, PlayStation 4, PlayStation 5, Xbox Series X/S and Xbox One. In the game, players direct the space program of a species of green humanoid aliens known as Kerbals. The game features a pseudorealistic orbital physics engine, allowing for various real-life orbital maneuvers such as Hohmann transfer orbits and orbital rendezvous.
The first public version was released digitally on Squad's Kerbal Space Program storefront on 24 June 2011, and joined Steam's early access program on 20 March 2013. The game was released out of beta on 27 April 2015. Kerbal Space Program has support for user-created mods that add new features, such as interstellar travel, improved physics, new parts, and multiplayer. Popular mods have received support and inclusion in the game by Squad. The game has garnered commendation from spaceflight industry figures such as NASA, ESA, science communicator Scott Manley, ULA CEO Tory Bruno, SpaceX CEO Elon Musk, and Rocket Lab CEO Peter Beck.
In May 2017, Squad announced that the game had been purchased by video game company Take-Two Interactive, who would help support Squad in keeping the console versions up-to-date alongside the personal computer versions. An Enhanced Edition was released for Xbox One and PlayStation 4 in January 2018, and for PlayStation 5 and Xbox Series X/S in September 2021 by Private Division, a publishing subsidiary of Take-Two Interactive. Two expansions for the game have been released as downloadable content: Making History in March 2018 and Breaking Ground in May 2019. A sequel, Kerbal Space Program 2, was released in early access on 24 February 2023.
Gameplay
The player operates a space program operated by Kerbals, a species of small green humanoids, who have constructed a spaceport on their home planet, Kerbin. From the space center players can build various vehicles such as rockets, aircraft, spaceplanes, and rovers from a provided set of components. Constructed craft can be launched from the space center's launch pad or runway to accomplish various tasks while avoiding partial or catastrophic failure. Players control flight with little assistance other than a Stability Assist System to keep their vehicle oriented. Provided it maintains sufficient thrust and fuel, a spacecraft can enter orbit around Kerbin, or travel to other celestial bodies. To visualize vehicle trajectories, the player is provided with a 'map' that displays the vehicle's trajectory as well as that of celestial bodies and other spacecraft, as well as their orbital parameters. Spacecraft maneuver 'nodes' can be plotted, timed, and executed, and objects can be selected and 'targeted' to facilitate flybys, rendezvous, and docking.Missions involve goals such as reaching a certain altitude, escaping the atmosphere, reaching a stable orbit, landing on a certain planetary body, rescuing stranded astronauts, capturing asteroids, and creating space stations and surface bases. Players may also set challenges for each other on the game's forums, such as landing on all five moons of the gas giant Jool. In addition, the game has many user-created mods, dealing with gameplay and visuals.
Players can control in-game Kerbal astronauts, who can exit spacecraft on extravehicular activities. While on EVA, Kerbals may use their EVA suit to maneuver in space, similar to the use of NASA's Manned Maneuvering Unit. Kerbals on EVA can collect and cache science experiments, plant flags on the surfaces of planets and moons, and repair spacecraft.
Historical space missions can be implemented and flown in the game, such as an Apollo Moon landing, the Curiosity rover, and the International Space Station. Certain parts in the game are based on real-life hardware, such as the Probodobodyne Stayputnik, the Mk1-3 Command Pod, and the KS-25 'Vector'. Various community-developed mods can add features such as additional parts, informational displays detailing orbital characteristics, and autopilot functionalities. Some mods have been incorporated into the core game, due to popularity. For example, resource mining, or extracting ore for refinement into rocket fuel, has been implemented into the main game from a popular mod.
The game's planetary system is loosely based on the real-world Solar System, consisting of the planets Moho, Eve, Kerbin, Duna, Dres, Jool, and Eeloo, which are respectively analogues of Mercury, Venus, Earth, Mars, Ceres, Jupiter, and Pluto. Eve is orbited by Gilly, a small captured asteroid; Kerbin is orbited by two moons, the larger Mun and the smaller, more distant Minmus; and Duna is orbited by Ike, a large rocky moon, both of which are tidally locked to each other. Jool possesses 5 moons: Laythe, an ocean world with a breathable atmosphere; Vall, an icy moon; Tylo, a rocky moon the size of Kerbin; and Bop and Pol, two small irregular moons. Various community mods implement extended or alternative planetary systems, including an exact-size real-world Solar System.
Game modes
Three game modes are available: sandbox, science, and career. Sandbox mode imposes no limitations, with unlimited parts available for any player-directed project. Many players have used Sandbox mode to implement replicas of historical real-life vehicles, as well as create impractically large or complex spacecraft.Science mode presents a limited selection of parts at the beginning of the game. Players must travel to and perform experiments at various sites around Kerbin, outer space, and on other celestial bodies to gain 'science', which can be used to unlock additional parts. This mode was designed to ease new players into the game and prevent them from getting overwhelmed.
Career mode extends science mode by adding funds, reputation, and contracts. Parts and fuel must be purchased with funds. Completing contracts on time will pay out funds and increase reputation, while unsatisfactory outcomes result in penalties to funding and reputation. Greater reputation results in more difficult and prestigious contracts. Players must spend funds to purchase parts and upgrade buildings to unlock new features such as larger rocket build size and improved tracking.
Physics
While the game's physics engine is not a perfect simulation of reality, it has been praised for its largely accurate orbital mechanics; all objects in the game except the celestial bodies are simulated using Newtonian dynamics. Rocket thrust is applied to a vehicle's frame based on the placement of engines, and joints between parts have limited strength — too much force will break a vehicle apart. The stock, unmodded game simulates orbits using patched conic approximation instead of a full n-body simulation; thus, it does not support Lagrange points, perturbations, Lissajous orbits, halo orbits or tidal forces.The in-game astronauts, Kerbals, are physically simulated. Sufficiently forceful collisions with objects or terrain will cause Kerbals to tumble until they can regain their balance.
Some celestial bodies have atmospheres of varying heights and densities, affecting the impact of drag on wings and parachutes. The simulations are accurate enough that real-world techniques such as aerobraking are viable methods of navigating the solar system. Flight through an atmosphere at excessive speeds results in aerodynamic heating; high enough temperatures will cause components to fail or explode, necessitating the use of heat shields or more careful flight profiles. In-game atmospheres thin out into space but have finite heights, unlike real atmospheres.
Kerbal Space Program alters the scale of its solar system for gameplay purposes. For example, Kerbin has a radius of only, approximately that of Earth's. To compensate for the gravitational consequences of this size difference, Kerbin's density is over 10 times that of Earth's. The planets themselves are also significantly closer together than the planets in the real-life Solar System.