In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted.
In astronomy and spaceflight, a lunar orbit is an orbit of an object around Earth's Moon. In general these orbits are not circular. When farthest from the Moon a spacecraft is said to be at apolune, apocynthion, or aposelene. When closest to the Moon it is said to be at perilune, pericynthion, or periselene. These derive from names or epithets of the moon goddess.
In orbital mechanics, a Lissajous orbit, named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system with minimal propulsion. Lyapunov orbits around a Lagrangian point are curved paths that lie entirely in the plane of the two primary bodies. In contrast, Lissajous orbits include components in this plane and perpendicular to it, and follow a Lissajous curve. Halo orbits also include components perpendicular to the plane, but they are periodic, while Lissajous orbits are usually not.
A halo orbit is a periodic, three-dimensional orbit associated with one of the L1, L2 or L3 Lagrange points in the three-body problem of orbital mechanics. Although a Lagrange point is just a point in empty space, its peculiar characteristic is that it can be orbited by a Lissajous orbit or by a halo orbit. These can be thought of as resulting from an interaction between the gravitational pull of the two planetary bodies and the Coriolis and centrifugal force on a spacecraft. Halo orbits exist in any three-body system, e.g., a Sun–Earth–orbiting satellite system or an Earth–Moon–orbiting satellite system. Continuous "families" of both northern and southern halo orbits exist at each Lagrange point. Because halo orbits tend to be unstable, station-keeping using thrusters may be required to keep a satellite on the orbit.
A subsatellite, also known as a submoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet.
A distant retrograde orbit (DRO), as most commonly conceived, is a spacecraft orbit around a moon that is highly stable because of its interactions with two Lagrange points (L1 and L2) of the planet–moon system.
Lunar Flashlight was a low-cost CubeSat lunar orbiter mission to explore, locate, and estimate size and composition of water ice deposits on the Moon for future exploitation by robots or humans.
Artemis 3 is planned to be the first crewed Moon landing mission of the Artemis program and the first crewed flight of the Starship HLS lander. Artemis 3 is planned to be the second crewed Artemis mission and the first American crewed lunar landing since Apollo 17 in December 1972. In December 2023, the Government Accountability Office reported that the mission is not likely to occur before 2027; as of January 2024, NASA officially expects Artemis 3 to launch no earlier than September 2026.
The Lunar Gateway, or simply Gateway, is a space station which Artemis program participants plan to assemble in an orbit near the Moon. The Gateway is intended to serve as a communication hub, science laboratory, and habitation module for astronauts. It is a multinational collaborative project: participants include NASA, the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA), the Canadian Space Agency (CSA) and the Mohammed Bin Rashid Space Centre (MBRSC). The Gateway is planned to be the first space station beyond low Earth orbit.
Blue Moon is a family of lunar landers and their associated infrastructure, intended to carry humans and cargo to the Moon, currently under development by a consortium led by Blue Origin and including Lockheed Martin, Draper, Boeing, Astrobotic, and Honeybee Robotics. Two versions of Blue Moon are under development: a robotic lander planned to land on the Moon in 2024, and a larger human lander planned to land a crew of four astronauts on the lunar surface for the NASA Artemis V mission in 2029.
EQUULEUS is a nanosatellite of the 6U CubeSat format that will measure the distribution of plasma that surrounds the Earth (plasmasphere) to help scientists understand the radiation environment in that region. It will also demonstrate low-thrust trajectory control techniques, such as multiple lunar flybys, within the Earth-Moon region using water steam as propellant. The spacecraft was designed and developed jointly by the Japan Aerospace Exploration Agency (JAXA) and the University of Tokyo.
The Artemis program is a Moon exploration program that is led by the United States' NASA and was formally established in 2017 via Space Policy Directive 1. The Artemis program is intended to reestablish a human presence on the Moon for the first time since Apollo 17 in 1972. The program's stated long-term goal is to establish a permanent base on the Moon to facilitate human missions to Mars.
Artemis 4 is a planned mission of the NASA-led Artemis program. The mission will include the fourth use of a Space Launch System (SLS) launch vehicle, will send an Orion spacecraft with four astronauts to the Lunar Gateway space station, install a new module on the Gateway, and conduct the second lunar landing of the Artemis program.
Artemis 5 is the fifth planned mission of NASA's Artemis program and the first crewed flight of the Blue Moon lander. The mission will launch four astronauts on a Space Launch System rocket and an Orion to the Lunar Gateway and will be the third lunar landing of the Artemis program. In addition, Artemis V will also deliver two new elements to the Gateway Space Station.
CAPSTONE is a lunar orbiter that is testing and verifying the calculated orbital stability planned for the Lunar Gateway space station. The spacecraft is a 12-unit CubeSat that is also testing a navigation system that is measuring its position relative to NASA's Lunar Reconnaissance Orbiter (LRO) without relying on ground stations. It was launched on 28 June 2022, arrived in lunar orbit on 14 November 2022, and was scheduled to orbit for six months. On 18 May 2023, it completed its primary mission to orbit in the near-rectilinear halo orbit for six months, but will stay on this orbit, continuing to perform experiments during an enhanced mission phase.
Starship HLS is a lunar lander variant of the Starship spacecraft that is slated to transfer astronauts from a lunar orbit to the surface of the Moon and back. It is being designed and built by SpaceX under the Human Landing System contract to NASA as a critical element of NASA's Artemis program to land a crew on the Moon.
The Power and Propulsion Element (PPE), previously known as the Asteroid Redirect Vehicle propulsion system, is a planned solar electric ion propulsion module being developed by Maxar Technologies for NASA. It is one of the major components of the Lunar Gateway. The PPE will allow access to the entire lunar surface and a wide range of lunar orbits and double as a space tug for visiting craft.
