Humans have not left Earth orbit since Apollo 17 returned from the Moon in 1972. NASA has been trying to change that since 14 January 2004, when then-president George W. Bush announced the Vision for Space Exploration, an initiative to send humans back to the Moon and eventually to land on Mars. Since then, NASA's deep space efforts have had a number of names: Constellation (2004-2010, targeted lunar surface and Mars), Journey to Mars (2015-2018, targeted cislunar space, asteroid and Mars), and Moon to Mars (2018 to present, targeting lunar surface and Mars).
Through its current Artemis program, NASA envisions sending astronauts to the lunar south pole by 2024 and eventually establishing a permanent presence on the Moon. The program is a result of the Trump administration's Space Policy Directive 1 and a 26 March 2019 speech by Vice President Mike Pence directing NASA to reach the Moon by 2024, 4 years earlier than its previous goal.
Artemis is designed to land humans on the Moon quickly, by 2024, and focus on Mars as a long-term human spaceflight goal after that. The preliminary short-term plan involves using both commercial rockets and NASA's Space Launch System, the Orion crew capsule, and a lunar landing system. A small space station in lunar orbit called the Gateway would serve future surface missions.
Light and Shadow at the Moon's South Pole The Moon's north and south poles have high points that are almost always in sunlight, and low spots that are permanently dark. This NASA visualization starts on the side of the Moon we see from Earth—with the Apollo landing sites labeled—and moves down to the south pole, where a timelapse shows changing illumination conditions for an entire year. The large crater in the center, Shackleton crater, lies in permanent darkness, but its raised rims are nearly constantly illuminated. High-sunlight areas are good locations for human habitats because they stay warm and can draw near-continuous power from solar panels, while nearby permanently dark areas harbor water ice that could be mined for air, water, and rocket propellant. NASA's Scientific Visualization Studio
The Space Launch System
The Space Launch System, or SLS, is a massive rocket based on Space Shuttle-derived technology. It is essentially a larger version of the Shuttle stack that trades out the winged orbiter for either cargo or the the Orion crew capsule on top. The vehicle's core stage is a stretched Shuttle external fuel tank powered by 4 Space Shuttle (RS-25) main engines. (During the Shuttle program these engines were refurbished and reused; for SLS they will be ditched in the ocean.) Assisting the core stage during the initial phase of flight are a pair of 5-segment Space Shuttle solid rocket boosters.
Orion is a crew vehicle capable of supporting up to 4 astronauts on deep-space journeys, similar in concept but having a larger interior than the gumdrop-shaped Apollo capsules. Unlike capsules designed solely for transportation to low-Earth orbit, Orion’s heat shield can withstand the high-velocity reentry necessary when returning from deep space. The Orion spacecraft consists of three major components: a pressurized crew capsule, a service module, and a launch abort tower, which is nominally jettisoned during ascent.
The Lunar Gateway is a small space station in lunar orbit that would function as a fuel and supply depot, a science outpost, and a waypoint for missions to and from the lunar surface. The Gateway is currently not required to be operational for the initial 2024 Moon landing. NASA is asking commercial companies to provide Gateway cargo transportation services, similar to the way it does for the International Space Station.
NASA will send a small spacecraft called CAPSTONE (Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment) to the same lunar orbit Gateway will occupy. The microwave oven-sized CubeSat will test out a number of key technologies critical for Artemis, including spacecraft-to-spacecraft communication using the Lunar Reconnaissance Orbiter.
NASA is asking commercial companies to build lunar lander systems that would eventually dock with the Gateway. A visiting Orion crew
would board the lander, take it to the surface, and return in either an
ascent module or the entire vehicle. Early landers would only be capable
of short surface stays, while future vehicles would be able to house
crews through the lunar night.
A short history of recent deep space exploration programs
After the Apollo Moon landings from 1969 to 1972, both political interest and funding for NASA’s human exploration program waned, and the agency turned to projects closer to home: Skylab, the Space Shuttle and the International Space Station. In 1989, President George H. W. Bush proposed a Mars initiative that quickly lost support after a preliminary study estimated it could cost as much as $500 billion.
1 February 2003: Space Shuttle Columbia breaks apart during reentry, killing all 7 crew members.
1 November 2004: NASA christens the Constellation program, which includes an Apollo-style crew capsule launched on commercial rockets (likely the Atlas V and/or Delta IV).
November 2005: New NASA administrator Michael Griffin releases agency-commissioned Exploration Systems Architecture Study, which concludes Moon missions require a heavy lift rocket.
June 2006: NASA names Constellation launch systems Ares I and Ares V.
22 August 2006: NASA names Constellation crew vehicle Orion.
31 August 2006: NASA selects Lockheed Martin as Orion prime contractor. The first crewed launch is set for 2014.
4 November 2008: Barack Obama elected president.
1 June 2009: Obama administration forms Review of U.S. Human Spaceflight Plans Committee, informally known as Augustine Committee.
28 October 2009: Ares I-X test flight.
1 February 2010: Obama administration cancels Constellation, shifts lunar funding to deep-space technology development programs.
Journey to Mars
15 April 2010: Facing congressional backlash, Obama pledges NASA will keep Orion, develop heavy lift engine technology, send humans to a near-Earth asteroid by 2025, and a press on to Mars after that.
11 October 2010: President Obama signs the NASA Authorization Act of 2010, which mandates the creation of the Space Launch System with an operational due date of 31 December 2016. The bill specifies the rocket must use Space Shuttle technology and its existing workforce, and be used to launch Orion.
14 September 2011: Members of Congress and NASA unveil the final design of the Space Launch System. A test flight with Orion is set for 2017. Internal and external audits estimate SLS, Orion and ground systems costs through that mission will be $18 billion.
16 January 2013: NASA announces the European Space Agency will provide Orion's service module, which provides the capsule with power and propulsion.
April 2013: After studies of how to visit a near-Earth asteroid conclude that the mission would be just as complex, if not more complex, NASA proposes the Asteroid Redirect Mission (ARM), a plan to tow either an entire, small asteroid or a piece of a larger asteroid back to lunar space, where it would be visited by a crewed Orion capsule.
27 August 2014: SLS passes its KDP-C milestone, and the baseline launch date moves to November 2018.
5 December 5 2014: The first Orion spacecraft completes a successful four-and-a-half hour test flight atop a Delta IV Heavy rocket. Around the same time, NASA and ESA officials report continuing challenges with the Orion service module mean the capsule will not be ready in 2017 as previously hoped.
16 September 2015: NASA announces Orion has passed KDP-C, which locks in a baseline crewed flight test date of no later than April 2023.
8 November 2016: Donald Trump elected president.
7 February 2017: A tornado hits the Michoud Assembly Facility, damaging an estimated half of NASA's facilities. SLS hardware is unharmed, but operations are disrupted.
15 February 2017: NASA announces it is studying adding crew to the first SLS-Orion flight.
16 March 2017: Following mixed political and scientific reactions to ARM, newly inaugurated President Trump's first budget canceled the program.
28 March 2017: NASA announces initial designs for the Deep Space Gateway.
27 April 2017: A GAO report says the first SLS-Orion flight will be delayed again, regardless of whether or not a crew is added. In the report, NASA concurs with the finding.
12 May 2017: During a press call with reporters, NASA says it will not place crew aboard the first SLS-Orion mission, but nevertheless, the first flight has slipped to 2019.
1 November 2017: NASA selects five companies to study Deep Space Gateway Power and Propulsion Element (PPE).
16 April 2018: NASA Exploration Campaign materials begin referring to LOP-G as Lunar Gateway.
10 October 2018: An OIG report says internal NASA schedules are now showing a launch date of mid-2020 for SLS.
Moon to Mars
26 September 2018: NASA's unveils Moon to Mars campaign, an initiative to land humans on the Moon by 2028 using a sustainable, government-led program that includes commercial and international partners.
28 February 2019: Canada signs on as first Gateway partner, will provide Canadarm3
11 March 2019: NASA's FY2020 budget defers funding for the vehicle's Exploration Upper Stage, meaning SLS will stay in its initial Block 1 configuration for the foreseeable future.
13 March 2019: NASA administrator Jim Bridenstine says NASA is considering using commercial rockets to launch Orion on its first test flight to the Moon, which is in danger of slipping to 2021.
26 March 2019: At a National Space Council meeting, Vice President Mike Pence directs NASA to land humans on the Moon by 2024, using "all means necessary." NASA recommits to a 2020 test flight for the Space Launch System and Orion, followed by a crewed test flight in 2022.
13 May 2019: NASA releases a supplemental budget request for fiscal year 2020 for Moon to Mars initiatives. Administrator Jim Bridenstine announced that NASA's lunar exploration program would be named Artemis. In Roman and Greek mythology, Artemis was Apollo's twin sister and the goddess of the Moon.
16 May 2019: NASA chooses 11 companies for 6-month studies of lunar lander descent, transfer and refueling elements.
23 May 2019: NASA chooses Maxar Technologies (formerly SSL) to build Lunar Gateway Power and Propulsion Element, launching on a commercial rocket in 2022.
02 July 2019: Orion completes in-flight abort test to show it can blast itself away from SLS in the event of an emergency.
19 July 2019: NASA announces intent to choose a single provider (Northrop Grumman) to build the Gateway habitation module.
22 July 2019: NASA publishes draft solicitation for companies to provide input on fully integrated lander systems.