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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.

Looking for our policy perspective? Read The Planetary Society's Principles for Human Spaceflight.

Humans in deep space updates

NASA / Seán Doran

When Apollo 8 astronauts Bill Anders, Frank Borman, and Jim Lovell rounded the farside of the Moon, they became the first humans to witness an Earthrise above an alien surface. The iconic image was first published on 30 December 1968.

The current plan

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, a lunar landing system, and the start of a small station in lunar orbit called the Gateway. 

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.

Space Launch System


Space Launch System

Vehicle overview

SLS Block 1 expanded view


SLS Block 1 expanded view
Major components of the Space Launch System, block 1 version.

Core stage

SLS core stage components


SLS core stage components
A breakdown of SLS core stage components.

Solid rocket boosters

SLS Solid Rocket Boosters


SLS Solid Rocket Boosters

Other resources


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.

Orion beyond the Moon


Orion beyond the Moon
Orion beyond the Moon.

Vehicle overview

Orion components


Orion components
NASA's Orion spacecraft consists of three major parts. From left: the European Service Module, which has foldout solar arrays and three fairing panels that jettison during launch, the Command Module, and the Launch Abort System.

Crew module

Service module

Launch abort system

Other resources

Lunar Gateway

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. Prior to the Trump administration's March 2019 directive to return humans to the Moon by 2024, the Gateway would nominally have consisted of 3 pressurized modules, 2 unpressurized utility elements, and attachment points for crew and cargo vehicles.

Lunar Gateway components (March 2019)


Lunar Gateway components (March 2019)

NASA currently plans to have a minimal version of the Gateway operational for the first Artemis Moon landing in 2024, consisting of the Power and Propulsion Module (PPE) and a U.S. Utilization Module.

Lunar Gateway 2024 configuration (May 2019)


Lunar Gateway 2024 configuration (May 2019)
By the first Artemis Moon landing in 2024, the Lunar Gateway would consist of the Power and Propulsion Module (PPE) and a U.S. Utilization Module. Shown here are those 2 modules with a logistics resupply module, and a lunar lander, ascent vehicle, and transfer vehicle. Orion is approaching from the right.


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.

Power and Propulsion Element

Provides power for Gateway and uses a 50-kilowatt Solar-Electric Power (SEP) system to transfer between lunar orbits, as well as orbital maintenance and attitude control. Launches on a commercial rocket in late 2022. Contract awarded to Maxar Technologies on 23 May 2019.

U.S. Utilization Module (a.k.a. Minimal Habitation Module)

A general-purpose crew space to be built by Northrop Grumman.

Cargo Transportation

NASA is asking commercial companies to provide Gateway cargo transportation services, similar to the way it does for the International Space Station.


ESA-built (uncommitted). Unpressurized with small science airlock. Stores additional Gateway propellant and houses additional communications capabilities.

International Habitation Module

ESA or JAXA-built (uncommitted). General-purpose crew living space. Attachment point for CSA-provided Canadarm3 (committed 28 February 2019).

U.S. Habitation Module

NASA-built. Most artist's concepts include an inflatable module similar to BEAM aboard the International Space Station. General-purpose crew living space.

Multi-purpose Module

Roscosmos-built (uncommitted). May include airlock.

Other resources

Lunar landers

NASA is asking commercial companies to build a lunar lander system that would launch to and 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. The landing system is not required to be reusable in order to increase the chance it will be ready by 2024.

Program costs

NASA has spent roughly $50 billion on deep space exploration programs since 2004. Costs for current programs in 2019 dollars are:

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.

14 January 2004: In a speech at NASA headquarters, President Bush announces the Vision for Space Exploration, directing NASA to return to the Moon by 2020.

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.

October 2009: Augustine Committee finds Constellation is severely behind schedule, and that a lunar landing would not happen until the 2030s, if ever.

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).

11 December 2017: Trump signs Space Policy Directive 1, which maintains Mars as the agency's horizon goal, but mandates the lunar surface as an intermediary step.

12 February 2018: NASA FY19 budget begins referring to Deep Space Gateway as Lunar Orbital Platform-Gateway (LOP-G).

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.

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