The Lunar Orbital Platform – Gateway (LOP-G) is a future space station in lunar orbit intended to serve as a solar-powered communications hub, science laboratory, short-term habitation module, and holding area for rovers and other robots. While the project is led by NASA, the Gateway is meant to be developed, serviced, and utilized in collaboration with commercial and international partners. It will serve as the staging point for robotic and crewed exploration of the lunar south pole, and is the proposed staging point for NASA's Deep Space Transport concept. The science disciplines to be studied on the Gateway are expected to include planetary science, astrophysics, Earth observations, heliophysics, fundamental space biology, and human health and performance. Under current plans, this scientific activity will start after the first crewed landing (Artemis 3). Gateway development includes all of the International Space Station partners: ESA, NASA, Roscosmos, JAXA, and CSA. Construction is planned to take place in the 2020s. The International Space Exploration Coordination Group (ISECG), which is composed of 14 space agencies including NASA, has concluded that LOP-G will be critical in expanding a human presence to the Moon, Mars, and deeper into the Solar System. Formerly known as the Deep Space Gateway, the station was renamed in NASA's 2018 proposal for the 2019 United States federal budget. When the budgeting process was complete, US$450 million had been committed by Congress to preliminary studies.
The LOP-G is currently intended to be placed in a highly elliptical six-day near-rectilinear halo orbit (NRHO) around the Moon, which would bring the station within 1,500 km (930 mi) of the lunar surface at closest approach and as far away as 70,000 km (43,000 mi). Traveling to and from cislunar space (lunar orbit) is intended to develop the knowledge and experience necessary to venture beyond the Moon and into deep space.
The proposed NRHO orbit would allow lunar expeditions from the Gateway to reach a polar low lunar orbit with a delta-v of 730 m/s and a half a day of transit time. Orbital station-keeping would require less than 10 m/s of delta-v per year, and the orbital inclination could be shifted with a relatively small delta-v expenditure, allowing access to most of the lunar surface.
The Gateway could conceivably also support in-situ resource utilization (ISRU) development and testing from lunar and asteroid sources, and would offer the opportunity for gradual buildup of capabilities for more complex missions over time. Various components of the Gateway would be launched on commercial launch vehicles and on the Space Launch System as Orion co-manifested payloads on the Artemis 4 through Artemis 8 missions. According to Roscosmos, they may also use Proton-M and Angara-A5M heavy launchers to fly payloads or crew.
All modules will be connected using the International Docking System Standard.
The concept for the lunar Gateway is still evolving, and is currently intended to include the following modules:
|Year||Vehicle assembly objective||Mission name||Launch vehicle||Human/robotic elements|
|Q4 2022||Launch of the Power and Propulsion Element (PPE)||TBA||Commercial launch vehicle||Uncrewed|
|2023||ESPRIT and US Utilization Module||TBA||Commercial launch vehicle||Uncrewed|
|2023||Three components of an expendable lunar lander||TBA||Commercial launch vehicles||Uncrewed|
|2024||Orion docking to the Gateway, followed by a lunar landing and return to the Gateway||Artemis 3||Space Launch System, Block 1B||Crewed|
|2025||Orion will deliver the U.S. Habitation module; lunar landing.||Artemis 4||Space Launch System, Block 1B||Crewed|
|2026||Orion will deliver U.S. Habitat; lunar landing||Artemis 5||Space Launch System, Block 1B||Crewed|
|2027||Orion will deliver the first logistics module and the robotic arm||Artemis 6||Space Launch System, Block 1B||Crewed|
|2028||Deliver a logistics module||Artemis 8||Space Launch System, Block 1B||Uncrewed|
An earlier NASA proposal for a cislunar station had been made public in 2012 and was dubbed the Deep Space Habitat. That proposal had led to funding in 2015 under the NextSTEP program to study the requirements of deep space habitats. In February 2018, it was announced that the NextSTEP studies and other ISS partner studies would help to guide the capabilities required of the Gateway's habitation modules.
On 27 September 2017, an informal joint statement on cooperation between NASA and Russia's Roscosmos was announced. The solar electric Power and Propulsion Element (PPE) of the Gateway was originally a part of the now cancelled Asteroid Redirect Mission.
On 7 November 2017, NASA asked the global science community to submit concepts for scientific studies that could take advantage of the Gateway's location in cislunar space. The Deep Space Gateway Concept Science Workshop was held in Denver, Colorado from February 27 to March 1, 2018. This three-day conference was a workshop where 196 presentations were given for possible scientific studies that could be advanced through the use of the Gateway.
In 2018, NASA initiated a Revolutionary Aerospace Systems Concepts Academic Linkage (RASC-AL) competition for universities to develop concepts and capabilities for the Gateway. The competitors are asked to employ original engineering and analysis in one of the following areas:
Teams of undergraduate and graduate students were asked to submit a response by 17 January 2019 addressing one of these four themes. NASA will select 20 teams to continue developing proposed concepts. Fourteen of the teams presented their projects in person in June 2019 at the RASC-AL Forum in Cocoa Beach, Florida, receiving a $6,000 stipend to participate in the Forum. "Lunar Exploration and Access to Polar Regions" from the University of Puerto Rico at Mayagüez was the winning concept.
On 1 November 2017, NASA commissioned 5 studies lasting four months into affordable ways to develop the Power and Propulsion Element (PPE), hopefully leveraging private companies' plans. These studies had a combined budget of $2.4 million. The companies performing the PPE studies are Boeing, Lockheed Martin, Orbital ATK, Sierra Nevada and Space Systems/Loral. These awards are in addition to the ongoing set of NextSTEP-2 awards made in 2016 to study development and make ground prototypes of habitat modules that could be used on the Lunar Orbital Platform – Gateway as well as other commercial applications, so the LOP-G is likely to incorporate components developed under NextSTEP as well.
NASA officials stated that the most likely ion engine to be used on the PPE is the 14 kW Hall thruster called Advanced Electric Propulsion System (AEPS) which has an Isp of up to 2,600 s. The engine is being developed by Glenn Research Center, the Jet Propulsion Laboratory, and Aerojet Rocketdyne. Four identical AEPS engines would consume the 50 kW generated.
In 2019, the contract to manufacture the PPE was awarded to a division of Maxar Technologies (formerly SSL). After a one-year demonstration period, NASA would then "exercise a contract option to take over control of the spacecraft."
The lunar Gateway has received criticisms from several space professionals as lacking a proper, focused scientific goal. NASA officials promote the Gateway as a "reusable command module" that could direct activities on the lunar surface.
In May 2018, three major criticisms were aired. Former NASA Astronaut Terry W. Virts, who was a pilot of STS-130 aboard Space Shuttle Endeavour and Commander of the International Space Station on Expedition 43, wrote in an Op-ed on Ars Technica that the lunar Gateway would "shackle human exploration, not enable it". Terry stated that there is no concrete human spaceflight goal with the Gateway and that he cannot envision a new technology that would be developed or validated by building another modular space station. Terry further criticized NASA for abandoning its planned goal of separating crew from cargo, which was put in place following the Space Shuttle Columbia disaster in 2003. Mars Society founder Robert Zubrin, who has consistently advocated a human mission to Mars, called the lunar Gateway "NASA's worst plan yet" in an article in the National Review. Zubrin went on to state that, in his opinion, the proposed Gateway would not be useful to go to the Moon, Mars, near-Earth asteroids, or any other possible destination. He also stated that the ISS could accomplish many of the goals for the Gateway, and that "there is nothing at all in lunar orbit". Zubrin also stated that "If the goal is to build a Moon base, it should be built on the surface of the Moon. That is where the science is, that is where the shielding material is, and that is where the resources to make propellant and other useful things are to be found." Retired aerospace engineer Gerald Black stated that the "LOP-G is useless for supporting human return to the lunar surface and a lunar base." He added that it was not planned to be used as a rocket fuel depot and that stopping at LOP-G on the way to or from the Moon would serve no useful purpose and cost propellant.
In July 2018, Pei Zhaoyu, deputy director of the Lunar Exploration and Space Program Center of the China National Space Administration, concluded that, from a cost-benefit standpoint, the gateway would have "lost cost-effectiveness." Pei said the Chinese plan is to focus on a research station on the surface.
In December 2018, four major criticisms were aired. Michael D. Griffin, a former NASA administrator, said that in his opinion, the Gateway can be useful only after there are facilities on the Moon producing propellant that could be transported to the Gateway. Griffin thinks that after that is achieved, the Gateway would then best serve as a fuel depot. Former Apollo 11 astronaut Buzz Aldrin stated that he is "quite opposed to the Gateway" and that "using the Gateway as a staging area for robotic or human missions to the lunar surface is absurd." Aldrin also questioned the benefit of "send[ing] a crew to an intermediate point in space, pick[ing] up a lander there and go[ing] down" On the other hand, Aldrin expressed support for Robert Zubrin's Moon Direct concept which involves lunar landers traveling from Earth orbit to the lunar surface and back. Former NASA Astronauts Eileen Collins, who was a Space Shuttle pilot and commander, and Harrison Schmitt, who was Lunar Module pilot aboard Apollo 17, criticized NASA's plans for not being ambitious enough. Although they did not mention the Gateway directly, Collins stated that "2028 for humans on the moon seems like it's so far off" and that "we can do it sooner", while Schmitt stated that "the pace of the proposed program didn't match what took place under Apollo." Mark Whittington, who is a contributor to The Hill newspaper and an author of several space exploration studies, stated in an article that the "lunar orbit project doesn’t help us get back to the Moon". Whittington also pointed out that a lunar orbiting space station was not utilized during the Apollo program and that a "reusable lunar lander could be refueled from a depot on the lunar surface and left in a parking orbit between missions without the need for a big, complex space station."
In February 2019, the astrophysicist Ethan Siegel wrote an article in Forbes titled "NASA's Idea For A Space Station In Lunar Orbit Takes Humanity Nowhere". Siegel stated that "Orbiting the Moon represents barely incremental progress; the only scientific 'advantages' to being in lunar orbit as opposed to low-Earth orbit are twofold: 1. You're outside of the Van Allen belts. 2. You're closer to the lunar surface," reducing the time delay. His final opinion was that the Lunar Gateway is "a great way to spend a great deal of money, advancing science and humanity in no appreciable way."