Starship Block 3 and HLS: The path to get back to the Moon

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Amid numerous questions about whether SpaceX can have the Human Landing System (HLS) variant of Starship ready in time for Artemis 3, the company released a significant amount of information on its progress with HLS and Starship in relation to the Artemis Program.

Starship Human Landing System (HLS)

SpaceX recently released an update regarding Starship and its Human Landing System variant. This variant of the Starship is set to be one of the landers for the National Aeronautics and Space Administration’s (NASA) Artemis program, which aims to land on the moon and establish a sustainable presence.

Starship HLS is expected to be a variant of the Starship Program’s Block 3 design, which is currently under development and is scheduled to fly sometime in Quarter 1 of 2026. This ship will operate alongside tankers and depots to refuel, enabling it to deliver not only people but also approximately 100 tons of cargo to the lunar surface.

Render of HLS stacked on a Block 3 Booster for Launch (Credit: SpaceX)

Since the HLS contract was awarded in April 2021, SpaceX has made significant strides in developing this variant, which includes interior systems and other key subsystems. After years of development, the design is becoming finalized enough for SpaceX to start building flight hardware for HLS. Currently, the Ship is set to have two airlocks, each with a volume of 13 cubic meters, which is double the internal volume of the Lunar Excursion Module (LEM), the lander used in the Apollo program.

The overall internal volume is set to be approximately 600 cubic meters; in comparison, the International Space Station (ISS) has an internal volume of around 1,000 cubic meters. This will allow for space to store supplies, beds, a command and control area, and many other things with room to spare. Since this ship will land vertically, the crew will have to use an elevator to travel from the airlock to the surface of the Moon.

Render of the HLS interior (Credit: SpaceX)

In addition to the six main Raptor engines for Starship, HLS is set to be equipped with a set of multiple smaller landing thrusters higher up on the ship’s structure. These will be used to prevent kicking up a large amount of lunar regolith during vertical landing.

As for specific progress, SpaceX has stated that its teams have completed a total of 49 milestones so far in the development of HLS. Docking adapter qualification has been achieved in conjunction with NASA and Lockheed, utilizing an androgynous docking system that will be used to dock with the Orion Capsule and the Lunar Gateway in lunar orbit. This docking system is based on Dragon 2’s flight-proven design for docking with the ISS.

Astronauts Suited up In Axiom EVA Suits practicing inside a HLS Airlock Mockup (Credit: NASA)

Life support and environmental control systems have been tested using a full-scale cabin inhabited by multiple people to test the systems on board. A full demonstration of the elevator using the Axiom Extra Vehicular Activity (EVA) suits, which will be used during the Artemis missions, has also been completed. And landing leg testing, which included the dropping of a full-scale article at flight energies onto simulated lunar regolith. This was to test how the landing leg and lunar regolith would interact on the moon.

Many other milestones have been completed, and SpaceX still has many more to get through to make HLS a reality.

Next Objectives in the Program, Block 3: The Core System of Starship

It’s nice to hear about all of the progress SpaceX is making on Starship’s HLS variant, but HLS won’t be going to the moon until Block 3 and the core system are online. Because Starship is not just HLS, it’s an entire rocket system with several variants and other objectives that need to be achieved. To that end, SpaceX has flown 11 Full Stack Flight tests so far, and while there have certainly been ups and downs, SpaceX ended the Block 2 era on a high note.

So far, SpaceX has been able to prove they can get a booster back at the launch site and reuse it, get a Ship into space, relight a Raptor 2 engine in space, perform a five metric ton propellant transfer, control the ship in space, and reenter Earth’s atmosphere in one piece, which sets up for reuse of the ship. These milestones are merely the opening act of a program with high aspirations.

Booster 15 about to be caught by Pad 1 (Credit: BocaChicaGal for NSF)

The next set of objectives is crucial to proving that Starship can function as SpaceX intends it to. This process begins with testing the new designs for the Block 3 ship and booster, as well as the new launch pad design. It also involves getting a ship into orbit and maintaining that orbit for an extended duration. The significant milestones that will truly propel this program forward are catching a ship, then reusing a ship, and performing a ship-to-ship docking and cryogenic propellant transfer. 

Without ship reuse and propellant transfer, Starship isn’t going anywhere quickly. SpaceX also needs to test out the Tanker variant, Depot variant, Cargo variant, and eventually test the HLS variant itself. Once these objectives and vehicles are proven, SpaceX will have the tools to transport humans from Earth to the Moon and send hundreds of tons of material to build a lunar base. As a fun addition, that framework will enable SpaceX to send cargo and eventually people to Mars, which is their ultimate goal, making life multiplanetary.

Render of a Depot Variant for Starship (Credit SpaceX)

As for Block 3 and Raptor 3 testing, which will help accomplish this goal, SpaceX has performed over 40,000 seconds of Raptor 3 Engine firings and continues to fire them every day. This upgraded Raptor engine has increased thrust and requires significantly less shielding on the vehicle, resulting in a reduction in dry mass from the engines.

Booster-wise, SpaceX currently has two test tanks at their Masseys test area, B18.1, which is for testing the newly designed Booster aft section and part of the new landing tank, and B18.3, which is designed to test the new integrated hotstage truss and grid fin sockets.

So far, B18.1 has been at Masseys since May 10 and has performed 10 cryogenic proof tests. SpaceX even stated that using the thrust rams in the cage, teams subjected the new aft design to 13,400 tons of thrust, compared to the 10,000 tons that SpaceX hopes to achieve on a booster in the future with 33 Raptor 3 engines.

B18.1 in the cage and B18.3 to the right at Masseys (Credit Jack Beyer for NSF)

B18.3 has been at Masseys since Sept 20 and has performed a couple of cryogenic proof tests so far. Currently, SpaceX is building a second can crusher cap and will likely place it on B18.3 to thoroughly test the new truss design. SpaceX has also been testing the new, larger transfer tube design with at least three separate test tanks. This new transfer tube is designed to enable them to perform the booster flip more effectively, as well as offer other improvements.

As for the Ship, SpaceX does not yet have a completed Block 3 ship test tank. There was a test tank that was partially stacked inside Mega Bay 2 for a while, but it has since been rolled into the Starfactory, possibly awaiting a Block 3 ship aft for testing.

Alongside all the vehicle test tanks and engine testing, SpaceX is nearing completion of the new launch pad design at Pad 2(B) in Starbase. This new pad design features a flame trench, a water-cooled steel deck, a redesigned tank farm, and a significantly more robust overall design. This new pad design is also being built at LC-39A; two more will be built at SLC-37, once the approval comes through, and Pad 1(A) at Starbase is currently in the process of being converted.

Pad 2 at Starbase getting close to Completion (Credit: Gage (Rough Riders Show) for NSF)

Flight 12, Booster 18, and Ship 39

The first full flight test of Block 3 is scheduled to involve Booster 18 and Ship 39 and is expected to launch sometime in Quarter 1 of 2026. Currently, neither vehicle is complete in construction, and, based on the best timelines using past boosters and ships as reference points, neither will likely begin cryogenic proof testing until December. Once cryogenic proof testing is completed, Booster 18 will need to use the new launch pad for engine testing.

As for Ship 39, it will have to commission the new Masseys static fire tank farm and repaired stand following Ship 36’s untimely demise at the hand of a Composite Overwrapped Pressure Vessel (COPV). Once each vehicle has completed its individual testing, a full stack wet dress rehearsal will likely be required to test the new countdown and new pad systems.

These vehicles come with numerous changes that will enable the testing of critical objectives to support HLS’s mission to land on the moon. Booster 18 is nearly a clean-sheet design, with the aft section and forward section being completely redesigned. The Block 3 booster aft now has all of the high-pressure piping, engine controls, and gas distribution on the outside of the booster rather than inside of a ton of shielding on the aft dome.

With the massive reduction in shielding around Raptor 3, SpaceX has added metallic tiles to protect the aft plate of the booster on reentry. This also helps shave a significant amount of weight off the booster, thereby helping to improve performance.

The forward section now features the integrated hot stage truss, as previously stated. With this design change, the grid fins are mounted inside cavities located within the liquid methane (LCH4) tank, and there are now three larger fins instead of four. This is due to the higher angle of attack that Block 3 boosters are likely to experience during the glide; the grid fin on top of the booster during the glide would be of little use due to the lack of airflow, so SpaceX deleted it.

Ship 39 already has a few noticeable changes, even though it is only a couple of sections into stacking. SpaceX has refined the design of the ship catch pins and relocated them to the nosecone. The Starlink antennas have once again changed positions, but there are still four of them in total.

Ship 39 in Mega Bay 2 with Just the Nose Cone and Payload Bay (Credit: Jack Beyer for NSF)

The common dome has moved down slightly, which means SpaceX will be able to load more LCH4 into the tank. And due to this, the aft dome is likely set to move down as well to maintain the ratio of liquid oxygen (LOX) to LCH4. 

The heat shield has also been refined, with SpaceX relocating the smaller tile strips over the dome welds to improve gap closure between the tiles on the tank wall. The ramps that were over the chopstick pin sockets and the stabilizer sockets have been deleted. Teams achieved this by integrating the stabilizer socket into the structure more effectively and removing the lifting pin socket, as the catch pins are now the primary lifting point.

Render of two Starships docking in Space (Credit: SpaceX)

Another significant addition is a probe-and-drogue docking system, which will enable ships to dock with each other in orbit. This system has a passive side and an active side. Currently, Ship 39 has the passive drogue system installed on its payload bay.

With all these changes, Flight 12 is set to usher in a new era of the Starship program. Considering the number of milestones SpaceX still needs to complete, it is unclear whether teams can have HLS ready by mid-2027 for Artemis 3, assuming every other aspect of Artemis will be ready as well.

However, a string of several excellent flight tests could propel the Starship program ahead and enable it to meet the current Artemis 3 launch timeline. One way or another, SpaceX still has a lot of work to do to reach the Moon with HLS and eventually Mars.

Lead Image: SpaceX HLS Render.

The post Starship Block 3 and HLS: The path to get back to the Moon appeared first on NASASpaceFlight.com.



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