Starship HLS

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 mission plan calls for a Starship launch vehicle to launch a Starship HLS into Earth orbit, where it will be refueled by multiple Starship tanker spacecraft before boosting itself into a lunar near-rectilinear halo orbit (NRHO). There, it will rendezvous with a crewed Orion spacecraft that will be launched from Earth by a NASA Space Launch System (SLS) launcher. A crew of two astronauts will transfer from Orion to HLS, which will then descend to the lunar surface for a stay of approximately 7 days, including at least five EVAs. It will then return the crew to Orion in NRHO.

In the third phase of its HLS procurement process, NASA awarded SpaceX a contract in April 2021 to develop, produce, and demonstrate Starship HLS. An uncrewed test flight is planned for 2025 to demonstrate a successful landing on the Moon. Following that test, a crewed flight is expected to occur as part of the Artemis 3 mission, no earlier than September 2026. NASA later contracted for an upgraded version of Starship HLS to be used on the Artemis 4 mission.

Design
Starship HLS is a variant of SpaceX's Starship spacecraft optimized to operate on and around the Moon. Unlike the standard Starship Spacecraft, Starship HLS will never re-enter an atmosphere, so it does not have a heat shield or flight control surfaces. This reduces its mass, as well as the number of tanker Starship launches needed for refueling. In contrast to earlier HLS designs that proposed multiple stages, the entire spacecraft functions as both an ascent and descent stage. Like other Starship variants, Starship HLS has six Raptor engines mounted at the tail, which are used during launch and the majority of landing and ascent. When within 100 meters of the lunar surface, the variant will use high‑thrust RCS thrusters located mid‑body to avoid plume impingement with the lunar regolith, though these thrusters may not be needed. The thrusters burn gaseous oxygen and methane instead of the liquid oxygen and methane used by the Raptors. Electrical power is supplied by a band of solar panels around the circumference of the vehicle. HLS has the capability to loiter in lunar orbit for 100 days.

According to NASA, minimizing changes in vehicle configuration and making the design and development of Starship HLS as common as possible will benefit future Starship HLS builds by eliminating the need for additional testing, evaluation, and verification of different vehicle designs. NASA added this will also allow SpaceX to accelerate vehicle builds to help ensure availability and on time delivery for mission integration.

Development
NASA astronauts tested the elevator concept (crew transfer between the cabin of Starship HLS and the lunar surface) in December 2023. In February 2024, SpaceX had fully tested the life support system, and NASA performed a full-scale test of the Starship HLS to Orion – and later Gateway – docking transfer system. The same month, NASA said SpaceX had accomplished over 30 HLS-specific milestones by defining and testing hardware needed for power generation, communications, guidance and navigation, propulsion, life support, and space environments protection.

On March 14, 2024, SpaceX successfully tested cryogenic propellant transfer on Integrated Flight Test 3. In April 2024, NASA reported that work was underway on the cargo specific variant of the lander. NASA expects this variant to be ready and in service by Artemis VII.

Mission profile
Prior to the launch of the HLS vehicle from Earth, a Starship configured as a propellant depot would be launched into an Earth orbit and then partially or fully filled by between four and fourteen Starship tanker flights carrying propellant.

Musk said in 2021 that between "four and eight" tanker launches would be required. The same year, the Government Accountability Office said that SpaceX would "require 16 launches overall", and in 2023, a NASA official estimated the number of Starship launches required for one lunar landing to be "in the high teens". In 2024, SpaceX vice president of customer operations estimated that the number of tanker launches would be "10-ish", though this number is subject to change. The launches will need to be in rapid succession in order to maintain schedule constraints and the loss of liquid cryogenic propellants due to boiloff.

The Starship HLS vehicle would then launch and rendezvous with the already-loaded propellant depot and refuel before transiting from Earth orbit to Lunar orbit.

Once HLS is in a near-rectilinear halo orbit around the moon, an Orion spacecraft would be launched by a Space Launch System rocket and dock with the waiting Starship HLS lander. After two to four of the crew had transferred into the HLS, it would depart and descend to the lunar surface. After lunar surface operations, Starship HLS will lift-off from the Moon and return to lunar orbit to rendezvous with Orion. The crew then transfers back to Orion and departs for Earth. Although not confirmed yet, Starship HLS could, in theory, be refueled in orbit to carry more crews and cargo to the surface.

History
Starship HLS builds on the SpaceX Starship system by adding a new spacecraft variant called Starship HLS. This spacecraft will be used in conjunction with the Starship booster (called Super Heavy) and two additional Starship spacecraft variants, "tanker" and "depot", that were already planned prior to the NASA HLS contract.

Prior Starship system history
The SpaceX Starship concept was initially conceived in the early 2010s as a spacecraft that would be principally built for the Mars colonization effort that Musk has advocated since 2011, with the first colonists arriving no earlier than the middle of the 2020s.

By 2016, the scope became somewhat broader, enabling landings on planets with and without an atmosphere. Lunar destination flights, however, were not generally emphasized by Musk, and he specifically stated that the Moon was not a necessary step on the path to Mars.

By late 2018, SpaceX had specified the primary construction material for Starship to be stainless steel – after approximately a year of building manufacturing pathfinder hardware out of carbon composite materials—and manufacture of the initial test article including pressure vessel construction for the liquid methane and liquid oxygen tanks began in early 2019.

Between July 2019 and July 2021, seven Starship prototype vehicles, each with different vehicle design configurations and varied test objectives, flew a total of eight atmospheric test flights, all launched from the SpaceX South Texas launch site at Boca Chica, Texas. In 2023, flight testing of complete Starship vehicles began. As of 2024, the first two test flights have ended in failure, with a third test flight successfully reaching the desired trajectory on March 14, 2024. The fourth flight test was also successful, ending with both the booster and second stage completing a soft landing in the ocean.

Initial Artemis 3 contract ("Option A")
Starship itself has been in privately funded development by SpaceX since the mid-2010s, but the HLS variant is being developed under NASA's Human Landing System contracts. The initial contracted design work started in May 2020, with selection and funding for full-development occurring in April 2021, when Starship HLS was selected by NASA to land "the first woman and the next man" on the Moon for the Artemis 3 mission.

Selection of the Starship lunar lander
In 2021, NASA entered into a fixed-price contract with SpaceX valued at US$2.89 billion. The contract involves the development and manufacturing of Starship HLS, as well as the execution of two flights: an uncrewed demonstration mission and a crewed lunar landing.

Starship HLS is intended to dock in a lunar near-rectilinear halo orbit with either the NASA Orion spacecraft or NASA lunar Gateway space station, in order to take on passengers before descending to the lunar surface and return them after ascent.

Starship HLS was first made public when it was initially selected by NASA in April 2020 for a design study as part of their Artemis program, which aims to land humans on the Moon. SpaceX was one of three teams selected to develop competing lunar lander designs for the Artemis program over a year-long period starting in May 2020. The other landers in consideration were Dynetics HLS, proposed by aerospace manufacturer Dynetics, and the Integrated Lander Vehicle, proposed by a team led by Blue Origin. NASA intended to later select and fund at most two of these landers to continue to perform initial demonstration flights.

On 16 April 2021, NASA selected only Starship HLS for crewed lunar lander development plus two lunar demonstration flights – one uncrewed and one crewed – no earlier than 2024. The contract is valued at US$2.89 billion over a number of years. Two NASA Artemis astronauts are to land on the first crewed Starship HLS landing. NASA had previously stated that it preferred to fund development of multiple Human Landing System proposals with dissimilar capabilities; however, "only one design was selected for an initial uncrewed demonstration and the first crewed landing, due to significant budget constraints" for the human landing system program imposed by the US Congress. NASA stated that the unselected proposals – Dynetics HLS and Blue Origin Integrated Lander Vehicle – as well as landers from other companies would be eligible for later lunar landing contracts.

Opposition by competing companies
On 26 April 2021, Blue Origin and Dynetics separately protested the award to SpaceX at the US Government Accountability Office (GAO). On 30 July 2021, the GAO rejected the protests and found that "NASA did not violate procurement law" in awarding the contract to SpaceX, who bid a much lower cost and more capable human and cargo lunar landing capability for NASA Artemis. Soon after GAO rejected the appeal, NASA made the initial $300 million contract payment to SpaceX. The protest action delayed NASA from authorizing work on the contract, and thus delayed the start of work by SpaceX for 95 days. Blue Origin produced infographic posters that highlight the complexity of Starship HLS, for example the fact that on orbit refuelling with cryogenic fuels like that Starship HLS uses has never been demonstrated, while stating that its design uses "proven technology".

On 13 August 2021, Blue Origin filed a lawsuit in the US Court of Federal Claims challenging "NASA's unlawful and improper evaluation of proposals". Blue Origin asked the court for an injunction to halt further spending by NASA on the existing contract with SpaceX, and NASA stopped work on the contract on 19 August, after SpaceX had been allowed to work on the NASA-specific parts of Starship HLS for just three weeks since the work had been previously halted in April. Reactions to the lawsuit were negative, with many criticizing Blue Origin for causing unnecessary delays to the Artemis program.

On 4 November 2021, the court granted the federal government's motion to dismiss the case, and NASA announced that it would resume work with SpaceX as soon as possible.

Artemis 4 contract ("Option B")
On 23 March 2022, NASA announced it would be exercising an option under the initial SpaceX HLS contract, known as Option B, that would allow a second-generation Starship HLS design to conduct a demonstration mission after Artemis 3.

On 15 November 2022, NASA announced the Option B award of US$1.15 billion, and announced that this crewed landing is to occur as part of Artemis 4. The flight will include docking with the Lunar Gateway. The Option B HLS will meet NASA's requirements for a "sustainable" HLS. These include the ability to support four crew members and delivering more mass to the surface.

Subsequent contracts
After NASA awarded the Option A contract to SpaceX, Congress directed NASA to award a second HLS contract. NASA responded by creating "Appendix P" for a non-SpaceX sustainable HLS. This lander will be used for Artemis 5 as its crewed demonstration flight. In May 2023, Blue Origin was awarded $3.4 billion by NASA to develop their Blue Moon lunar lander. NASA intends to allow Starship HLS option B and the Blue Moon lander to compete for Artemis missions after Artemis 5.

Schedule delays
In 2021, the NASA Office of Inspector General (OIG) warned that the HLS development schedule was unrealistic when compared to other major NASA space flight programs. Stating that space flight programs in the prior 15 years had taken on average 8.5 years from contract award to first operational flight, while the HLS Program was attempting to do so in about half that time. By contrast, NASA OIG noted that the Apollo Lunar Lander took approximately 6 years from contract award to its launch on the Apollo 11 mission while receiving "substantially higher levels of funding" adjusted for inflation. Based on the HLS base period contract award date (May 2020) and the average delay for recent major NASA space flight programs, they estimated that the HLS Program could face up to 3.4 years of delays before operational flights.

In November 2023 the United States Government Accountability Office, in their report to Congress, outlined several challenges that Starship HLS is facing in development. As of September 2023 the "HLS program has delayed 8 out of 13 key events by at least 6 months", with 2 events being delayed to 2025, "the year the lander is planned to launch".

The GAO also noted that SpaceX had made limited progress maturing the technologies needed for in-orbit refueling and cryogenic propellant storage, a "critical aspect of SpaceX’s plan for landing astronauts on the moon". In 2023, NASA delayed Starship HLS's critical design review until after SpaceX performs a mission demonstrating in-orbit transfer of cryogenic propellants. The GAO concluded in their report to Congress that the Artemis 3 crewed lunar landing is unlikely to occur in 2025, and that a launch date in early 2027 is more likely. Although SpaceX considers the technology behind the Raptor engine to be "relatively mature", the HLS development office identified its development as a "top risk" for the program and its 2025 timeline.

In June 2023, NASA's chief of exploration systems development, Jim Free, said that the planned December 2025 launch date for Artemis 3 was "really concerning" and would likely slip to 2026. He said that the Starship HLS's critical design review, required before further funds from the contract could be released to SpaceX, had been delayed until SpaceX completes an in orbital refueling demonstration mission. The head of NASA's moon and Mars exploration strategy said that the delay of Artemis 3 from 2025 to 2026 was partly due to "development challenges" with Starship HLS.

In January 2024, NASA and SpaceX said that the uncrewed Starship HLS lunar landing and ascent test was expected to take place in 2025, with Artemis 3 being delayed to no earlier than September 2026. The delay was in part due to issues with Orion's heatshield during Artemis I.

Cargo variant
In April 2024, NASA reported that work was underway on the cargo specific variant of the lander. NASA expects this variant to be ready and in service by Artemis VII. The cargo variant will be referred to by NASA as Human-class Delivery Landers (HDL) and represent, as of June 2024, the highest capacity landers available to NASA under the current lunar exploration push.