Kerbal Space Program is a 2015 space flight simulation video game created by the Mexican studio Squad. It is available for Linux, macOS, Windows, PlayStation 4, PlayStation 5, Xbox Series X/S, and Xbox One. In the game, players manage the space program of a species of green, human-like aliens called Kerbals. The game includes a realistic orbital physics engine that allows players to perform real-life space maneuvers, such as Hohmann transfer orbits and orbital rendezvous.
The first public version of the game was released on Squad’s website on June 24, 2011. It joined Steam’s early access program on March 20, 2013, and was officially released on April 27, 2015. The game supports player-made additions that add new features, such as interstellar travel, improved physics, new parts, and multiplayer. Some popular mods have been included in the game by Squad. The game has received praise from spaceflight experts, including NASA, ESA, science communicator Scott Manley, former ULA CEO Tory Bruno, SpaceX CEO Elon Musk, and Rocket Lab CEO Peter Beck.
In May 2017, Squad announced that Take-Two Interactive had purchased the game. Take-Two helped Squad keep the console versions updated alongside the 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 subsidiary of Take-Two Interactive. Two expansions were 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 February 24, 2023. However, the developer has since closed, and no major updates have been released since June 2024.
Gameplay
The player manages a space program run by Kerbals, small green humanoids who built a spaceport on their home planet, Kerbin. From the space center, players can build vehicles like rockets, airplanes, spaceplanes, and rovers using provided parts. These vehicles can be launched from the space center's launch pad or runway to complete tasks while avoiding problems like running out of fuel or structural failure. Players control flight with limited help, using a Stability Assist System (SAS) to keep their vehicle steady. If a spacecraft has enough thrust and fuel, it can orbit Kerbin or travel to other celestial bodies. A map shows the vehicle's path, the positions of celestial bodies, and orbital details. Players can plan and adjust spacecraft movements and select targets to perform tasks like flybys, rendezvous, and docking.
Missions, which can be set by the player or assigned as contracts, include goals like reaching a certain altitude, escaping the atmosphere, achieving orbit, landing on a planet, rescuing astronauts, capturing asteroids, and building space stations or bases. Players can also challenge each other on forums, such as landing on all five moons of the gas giant Jool. The game includes many user-created mods that add new features, parts, or visual effects.
Players can control Kerbal astronauts during extravehicular activities (EVAs). While outside their spacecraft, Kerbals can move in space using their EVA suits, collect science experiments, plant flags, and repair spacecraft. Historical missions, such as an Apollo Moon landing or the Curiosity rover, can be recreated in the game. Some parts are based on real-life hardware, like the Probodobodyne Stayputnik (similar to Sputnik 1) or the Mk1-3 Command Pod (like the Apollo command module). Community-developed mods can add features like detailed orbital displays or autopilot systems. Some mods, such as resource mining, have been added to the main game due to popularity.
The game’s planetary system is inspired by the real Solar System, with planets named Moho, Eve, Kerbin, Duna, Dres, Jool, and Eeloo, which represent Mercury, Venus, Earth, Mars, Ceres, Jupiter, and Pluto. Eve has a moon called Gilly, Kerbin has two moons (Mun and Minmus), and Duna has a moon called Ike. Jool has five moons: Laythe, Vall, Tylo, Bop, and Pol. Players can use community-created mods to explore alternate planetary systems, including a real-size Solar System.
Three game modes are available: sandbox, science, and career. In sandbox mode, players have unlimited parts and can build any project. Science mode starts with limited parts and requires players to collect science by exploring Kerbin, space, and other planets to unlock new parts. Career mode adds funds, reputation, and contracts. Players must buy parts and fuel with money, complete contracts to earn rewards, and manage reputation. Higher reputation unlocks more challenging missions and upgrades.
The game’s physics engine uses Newtonian dynamics for most objects, but it does not simulate real-world complexities like Lagrange points or tidal forces. Instead, it uses a simplified method called patched conic approximation. Kerbals are physically simulated, so collisions can cause them to tumble until they recover. Atmospheres on some planets affect flight, with drag impacting wings and parachutes. Real-world techniques like aerobraking are possible, but flying too fast can cause overheating, requiring heat shields. In-game atmospheres have limited heights, unlike real ones.
Kerbin is smaller than Earth, with a radius of 600 kilometers (370 miles), but it is much denser to match Earth’s gravity. Planets in the game are closer together than in the real Solar System.
Two downloadable content (DLC) expansions are available: Making History and Breaking Ground. Making History adds parts from the Space Race, such as the Apollo Lunar Module and Soviet R7 fuel tanks, along with a level editor and new missions. Breaking Ground introduces robotic parts for building helicopters, propeller planes, and robots, as well as new science experiments like seismometers and weather stations. A retro-futuristic spacesuit and surface features are also included.
Development
Director Felipe Falanghe was hired by Squad in April 2010. At that time, the company did not create software. Falanghe explained that the name "Kerbal" came from the names he gave small tin figurines he placed in modified fireworks as a teenager. In October 2010, co-founder Adrian Goya approved the development of Kerbal Space Program but delayed it until Falanghe finished his other projects. The game was first created on 17 January 2011. The first public release, version 0.7.3, was on 24 June 2011. The game entered beta testing on 15 December 2014 with version 0.90 and was released from beta on 27 April 2015.
Version 0.7.3 was the first public release of Kerbal Space Program and was released on 24 June 2011. It was downloaded more than 5,000 times. Compared to later versions, 0.7.3 was very basic. It did not include stability assist mode, Kerbin did not rotate, and the Sun was only a directional light source. There were no fuel flow mechanics, no control surfaces, and no other celestial bodies. Later versions added more planets and moons, the ability to save and load part collections called "subassemblies," and tutorials.
On 20 March 2013, Steam’s early access program began, with Kerbal Space Program being one of twelve games available from the start.
Version 0.24, titled "First Contract," was released on 17 July 2014. It added contracts and a reputation system to the game’s career mode. However, players could still play career mode without these features in the new science mode. The final alpha release, version 0.25, improved career mode and redesigned aircraft components.
Version 0.90, nicknamed "Beta Than Ever," was released on 15 December 2014. This was the only beta update for the game. It included a major change to the rocket creation editor, allowing players to sort parts by characteristics and assign them to custom categories. Players could now place parts in space. Career mode also added building upgrades. Initially, only small rockets with low mass and part counts could be built, but upgrades later allowed larger rockets and new capabilities.
Version 1.0, the first full release of Kerbal Space Program (nicknamed "We Have Liftoff!"), was released on 27 April 2015. This version improved the flight and drag model for more realistic simulation, ignoring drag on parts blocked from airflow. It also allowed body lift, so parts like structural panels could generate lift. Version 1.0 added shock heating and heat shields, making atmospheric entry more dangerous, as well as air brakes and procedurally generated fairings. All parts received internal modeling. Resource mining was added to create fuel or monopropellant. Kerbals could now have specializations, such as "Engineer" Kerbals who can repair wheels and landing legs. Female Kerbals were also added.
Version 1.1, nicknamed "Turbo Charged," was released on 19 April 2016, nearly a year after the last major update. The game engine was upgraded from Unity 4 to Unity 5, improving performance and allowing a stable 64-bit client. This change removed memory limits caused by too many mods. Much of the game was rewritten to support these updates.
Squad released Version 1.2, nicknamed "Loud And Clear," to upgrade the game from Unity 5 to 5.4 and add performance and minor gameplay improvements. The patch entered experimental testing on 6 September 2016 and was officially released on 11 October 2016. Its main new features included communication satellites, relay systems, and KerbNet. Several updates have been released since.
On 10 June 2021, Squad announced that update 1.12 "On Final Approach" would be the last major planned release. Squad developers would join the Intercept Games team working on KSP 2.
On 27 January 2014, it was revealed that Squad was working on an education-themed version of the game, called KerbalEdu, in collaboration with TeacherGaming LLC, creators of MinecraftEdu. It was later released and includes an improved user interface for data gathering, pre-made lessons, metric system support, and a "robust pedagogy" that connects game content to educational materials outside the game.
Squad also created an Asteroid Mission Pack with full support from NASA. Released on 1 April 2014, it is based on real-life efforts to study asteroids.
Most of the game’s music was provided by royalty-free composer Kevin MacLeod, with the rest written by Squad’s in-house composer Victor Machado. The game’s main theme was composed by lead designer Felipe Falanghe and arranged by Machado.
On 5 June 2015, it was announced that Kerbal Space Program was being ported to the PlayStation 4 by Flying Tiger Entertainment. In August 2015, it was also announced that Xbox One and Wii U ports were in development by the same company.
The game has since been released on PlayStation 4 and Xbox One, but Squad has not shared details about the Wii U port. In January 2017, a Squad developer mentioned on official forums that external factors had forced them to reconsider supporting the Wii U. More details were promised later.
On 17 March 2017, Squad announced a full expansion called "Making History," which would be paid and include new features. These features included Mission Builder, allowing players to create and edit missions, and History Pack, which simulates real-life historical space missions. The expansion was released on 13 March 2018 and included parts inspired by rockets like the Soyuz spacecraft and Saturn V.
In May 2017, Squad announced that Kerbal Space Program had been acquired by publisher Take-Two Interactive. This acquisition did not change Squad’s development plans or free DLC for early backers. Take-Two’s support helped improve console versions to stay updated with the PC version. Kerbal Space Program was one of the first titles published under Take-Two’s 2017-launched Private Division label.
In late May 2019, Squad released the "Breaking Ground" expansion, which included servos, pistons, redesigned space suits, and experiments that earn science over time.
On 24 June 2021, the last major version of Kerbal Space Program, version 1.12, was released. It was named "On Final Approach."
Reception
The public alpha and beta versions of the game were very well received. Many publications, including Kotaku, Rock, Paper, Shotgun, IGN, GameSpy, Eurogamer, Polygon, and Destructoid, praised the game for its replay value and creative features.
In May 2015, PC Gamer gave Kerbal Space Program 1.0 a score of 96 out of 100, which was the highest score they gave to any game in 2015. They praised the game for combining science with humor and for making players feel proud when they achieved goals, such as reaching other planets. IGN’s Seth G. Macy noted that the game helps players learn from failure, saying that the joy of finally building a successful rocket was made greater by the many failures that came before.
Edge magazine wrote that the magic of Kerbal Space Program lies in its ability to be both a game and a simulation, as well as an educational tool and a fun experience. They highlighted how the game connects players to real history and human achievements by challenging them to solve problems based on real-life situations.
At the 19th Annual D.I.C.E. Awards, the Academy of Interactive Arts & Sciences nominated Kerbal Space Program for "Strategy/Simulation Game of the Year" and the "D.I.C.E. Sprite Award."
After its Steam early access release on March 20, 2013, Kerbal Space Program became one of the top five best-selling games on Steam and the top-selling game for Linux users.
Squad, the game’s developers, released physical merchandise such as clothing and plush toys. In March 2015, Squad partnered with a 3D printing service called Eucl3D to allow players to order custom models of their spacecraft.
Scientists and members of the space industry, including NASA, ESA, ULA’s Tory Bruno, Rocket Lab’s Peter Beck, and SpaceX’s Elon Musk, have shown interest in the game. Squad added a NASA-based Asteroid Redirect Mission pack to the game, letting players track and capture asteroids for study. They also created an official mod called "Asteroid Day" in partnership with the B612 Foundation to help players observe threatening asteroids. Parts from this mod were later included in the game’s 1.1 update, with full integration in version 1.3. In version 1.10, Squad added components for the BepiColombo and Rosetta spacecraft and ESA-themed textures for in-game parts.
During the second orbital test flight of the Boeing Starliner on May 21, 2022, the crew placed a Kerbal plush toy in the spacecraft to serve as a zero gravity indicator. A Boeing spokesperson explained that "Jeb," the toy’s name, was chosen to honor the enthusiasm the Starliner engineering team has for the game and to recognize the science, technology, engineering, and mathematics (STEM) lessons it teaches.
Sequel
Kerbal Space Program 2, a sequel to the original game, was released in early access on February 24, 2023. The game aimed to add new features to the original, such as new propulsion methods (e.g., the Orion drive), modules for building on the surface of planets, orbital and planetary colonies, a multiplayer mode, and the ability to travel between stars. However, many of these features were not completed or missing, which upset many players.
In June 2024, Intercept Games, the company that created the game, closed its doors after laying off its development team. No updates to the game have been made since that time.
Because of these issues and the game’s poor performance, its Steam page received many negative reviews. As a result, the game’s average rating dropped to "Overwhelmingly Negative."