KENNEDY SPACE CENTER, Fla. – NASA is heading back to the Moon.
But despite advances in computing and manufacturing, America’s space agency is still relying – in some key areas – on decades-old hardware and tech.
What to know:
- NASA is sending astronauts around the moon this spring – but no landing this time
- NASA’s newest Moon rocket uses four RS-25 engines – refurbished from the Space Shuttle program – and two solid rocket boosters
- Each launch discards the RS-25 engines and solid rocket boosters – together worth on the order of roughly $1 billion in propulsion hardware (based on public cost estimates)
- In 2021, NASA’s Inspector General estimated Artemis launches at a cost of about $4.1 billion each
More than 50 years ago, America’s Moon program was called Apollo; in 2026 the next step in space exploration is called Artemis.
America’s space agency has identified launch windows in early April 2026 for Artemis II, a mission that will send four astronauts to the Moon for the first time since 1972.
As of March 12, 2026, available launch windows for all of April are as follows:
- Wed. April 1: 120-minute window opens at 6:24 p.m. Mission duration is 10.0 days. Return on Sat. April 11 at approximately 6:24 p.m.
- Thu. April 2: 120-minute window opens at 7:22 p.m. Mission duration is 10.1 days. Return on Sun. April 12 at approximately 9:46 p.m.
- Fri. April 3: 120-minute window opens at 8 p.m. Mission duration is 10.2 days. Return on Tue. April 14 at approximately 12:48 a.m.
- Sat. April 4: 120-minute window opens at 8:53 p.m. Mission duration is 10.3 days. Return on Wed. April 15 at approximately 4:05 a.m.
- Sun. April 5: 120-minute window opens at 9:40 p.m. Mission duration is 10.4 days. Return on Thu. April 16 at approximately 7:16 a.m.
- Mon. April 6: 120-minute window opens at 10:36 p.m. Mission duration is 10.5 days. Return on Fri. April 17 at approximately 10:36 a.m.
- Thu. April 30: 120-minute window opens at 6:06 p.m. Mission duration is 10.0 days. Return on Sun. May 10 at approximately 6:06 p.m.
Although NASA’s next chapter for Moon exploration could be considered Apollo 2.0, the fact is, this is not the same space program or the same kind of rocket first used over 50 years ago. While Artemis II represents the future of space exploration, physical parts of the rocket powering the mission date back to the Space Shuttle era. And some of the technology used for the mission dates back to Apollo – and beyond.
The Artemis Program
First let’s start with some clarification: NASA may be sending astronauts back to the vicinity of the Moon this spring, but NASA won’t be landing on the surface.
NASA has identified launch opportunities for Artemis II beginning April 1, 2026 – a mission that will send four astronauts to orbit the Moon, but for this time out, no landing. Putting astronauts physically back on the Moon will come with Artemis III.
Let’s also lay out the new playbook: as mentioned, Apollo was NASA’s program identifier for Moon exploration in the 1960s and 1970s. It was preceded by Gemini (orbital operations, rendezvous) and Mercury (first human spaceflights). Today, Artemis is the name of NASA’s 21st-century program to get back to the Moon, and at some point, eventually to send humans to Mars. Artemis is focused on returning humans to the Moon, but a future mission to Mars would likely carry a new name – just as Apollo followed Mercury and Gemini.
Another change: Apollo astronauts went to the Moon on the legendary Saturn V rocket (first used on November 9, 1967 for the unmanned Apollo 4 mission) – Artemis astronauts will ride to space on the new Space Launch System (SLS).
[WATCH: Artemis II’s launch may be heard from miles away. Here’s how far]
And finally, Apollo’s astronauts rode atop Saturn V rockets nine times in individually named Command Modules (Columbia, Odyssey, America, etc.). Artemis astronauts will be inside new Orion capsules, first flown in test missions beginning in 2017. The capsule for Artemis II is officially designated CM-003, but the four person crew nicknamed it Integrity.
To recap: three big updates for the different space missions separated by over 50 years: program names, rockets, and capsules.
Artemis I and II
Artemis I launched on November 16, 2022 – about three and half years ago – and splashed down in the Pacific Ocean on December 11, 2022. That launch was a proof of concept for NASA’s newest rocket and space capsule – get SLS off the ground, get the new Orion capsule into space, have it circle the Earth, have it perform two lunar flybys, get it down safely.
While the unmanned Artemis I proved NASA could get to the Moon and back, the mission also revealed surprises – especially in the one system astronauts will rely on most to survive the journey home on Artemis II.
[WATCH: NASA launches mega moon rocket from Florida’s Space Coast (from 2022)]
Orion’s heat shield
The big surprise centered on Orion’s heat shield, the protective layer designed to withstand the extreme temperatures of re-entry. When Orion re-enters the Earth’s atmosphere, it travels at about 27,000 miles per hour. As the spacecraft encounters friction from the atmosphere, it slows down dramatically before parachutes get it to a final descent speed of about 20 mph.
Post-Artemis I, engineers observed that portions of Orion’s thermal blocks (blocks that make up the heat shield) had charred, cracked, and in some cases broken away.
While some erosion is expected in any re-entry, NASA found the pattern and extent of the material loss did not fully match pre-flight models. Part of the problem is the way an Orion capsule returns to Earth and the way NASA tested the material on the ground.
Unlike Apollo-era missions, on Artemis I, Orion used what is known as a “skip re-entry” trajectory – briefly dipping into the atmosphere, then back out again a number of times before a final descent. Lockheed Martin, the manufacturer of Orion, sums up the skip maneuver like this: “Ever skip stones across a pond? Imagine doing it with a spacecraft.”
While that maneuver helps control speed and landing location, it also exposes the heat shield to multiple waves of extreme heating and cooling – conditions that are difficult to fully replicate in testing.
[WATCH: Orion flies around moon for last time before heading back to Earth (from 2022)]
The material used for the thermal blocks is based on Avcoat (the heat shield material) and Novolac (the resin inside Avcoat). The Avcoat system for the heat shield was developed during the Apollo program and updated for modern use. Novolac has been around since the early 1900s!
This is where NASA was caught off guard: tests focused on extreme heat but didn’t fully anticipate how Orion would react to lower temps during the skip re-entry. When exposed to those temperature fluctuations, the heat shield allowed gases inside the material to expand and push outward, causing the surface to crack and shed pieces.
In simple terms: the heat shield didn’t fail, but it didn’t behave exactly as expected either.
After Artemis I, NASA went back to the drawing board for Artemis II – and didn’t change the design. But… to ensure the safety of the astronauts, NASA did decide to change how Orion will re-enter the atmosphere. The skip re-entry maneuver has been modified to a trajectory with a steeper angle to reduce the conditions that caused the damage.
For Artemis III and beyond, NASA plans on new manufacturing techniques that will prevent the gas build-up and allow gases to escape.
Space shuttle-era engines
The heat shield isn’t the only place where Artemis relies on legacy technology. Powering the new SLS rockets are sets of sleek hardware with long – and surprising histories.
First thing to know: SLS uses two different kinds of propulsion devices. The first ones are known as RS-25 engines. SLS uses four of them – they are part of the core stage of the rocket and are the first to ignite to provide the initial thrust to get off the pad.
Next, there are two side units known as solid rocket boosters. If these look familiar, your instincts are on target – the design comes straight from the SRBs (solid rocket boosters) used for the Space Shuttle program.
We’ll talk more about the SRBs in a bit.
SLS uses RS-25 engines from the Space Shuttle era. These engines are not just inspired by shuttle-era technology – they are the same engines, refurbished and repurposed for a new mission.
One Artemis I engine (Engine E2045) first flew on Space Shuttle Discovery on STS-41D on August 30, 1984, more than four decades ago. The “newest” SLS engine is Engine E2062 (built from spare parts of other engines and re-certified for SLS use in 2017).
[WATCH: Artemis II astronauts to pave way for moon landing]
L3 Harris is under contract to manufacture 24 new RS-25 engines; the first ones will make their debut on Artemis V. You can tell the difference by the serial numbers: newer engines begin with “E5,” while the legacy shuttle engines used today begin with “E2.”
In other words, some of the engines sending astronauts back to the Moon first flew when the Space Shuttle program was just getting started.
In the Space Shuttle configuration, engines were re-used after missions – for SLS launches, RS-25 engines aren’t reusable. Once they go up, they fall back into the atmosphere and are destroyed during descent and not recovered. At roughly $100 million a pop, that means each launch discards $400 million in rocket engines alone.
And then there are the SRBs.
Solid rocket boosters aren’t reusable either
The solid rocket boosters – or SRBs – are the largest and most powerful pieces of the SLS rocket. At ignition, they provide the majority of the thrust needed to lift the vehicle off the launch pad, working alongside the four RS-25 engines to send Artemis skyward.
And like the engines, their roots go back decades.
The boosters used on SLS are based directly on the design of the Space Shuttle’s SRBs, which first flew in the early 1980s. For Artemis, the boosters have been upgraded – incorporating improvements first developed for NASA’s cancelled Constellation program and Ares rockets – making them larger and more powerful than their shuttle-era predecessors.
The underlying design remains largely the same – the same but with one major difference.
During the Space Shuttle program, SRBs were recovered after launch – once separated from the shuttle, they parachuted into the ocean, were retrieved by ships, and refurbished for future missions. For Artemis, SRBs are destined for the same fate as the RS-25s – roughly two minutes after liftoff, once the boosters separate from the rocket, they fall back into the ocean and are not recovered.
They are also used once and then discarded.
This change was intentional for Artemis; to streamline the overall program, NASA opted for simplicity to enhance performance.
With the end-goal being to discard the SRBs, the space agency was able to remove the parachutes and recovery systems used during the shuttle era. With nothing to recover, the task of refurbishment between flights was also eliminated.
But it also means that each launch throws away not just the engines, but the boosters as well – massive pieces of hardware that took years to design and build. Independent estimates put the cost of each solid rocket booster at roughly $200 to $300 million.
The two SRBs plus the four RS-25 engines total roughly $1 billion in propulsion hardware per launch.
At an estimated total cost of $4.1 billion per launch, the RS-25 engines and solid rocket boosters represent a significant portion of the propulsion system – all of it one and done.
Tyranny of the rocket equation and final thoughts
Ever heard of the tyranny of the rocket equation?
In simple terms, it’s a kind of catch-22: the farther you want to go in space, the more fuel you need. But adding fuel adds weight – and that extra weight requires even more fuel.
Engineers are left with a difficult tradeoff: carry more fuel or find ways to reduce mass. That tradeoff helps explain some of the design choices behind Artemis.
To generate the thrust needed to send Orion to the Moon and back, engineers added fuel, built larger and more powerful engines, and looked for ways to reduce weight wherever possible. By discarding the engines and boosters after launch, NASA eliminated the need for parachutes, recovery systems, and refurbishment hardware.
Commercial companies like SpaceX are taking a different approach – designing rockets to be reused, but reuse comes with tradeoffs of its own including the need to reserve fuel for landing and recovery.
NASA, on the other hand, designed the Space Launch System to maximize performance for deep space missions, relying on proven technology, and accepting that key components would be used only once.
In 2022, the agency’s Associate Administrator for Exploration Systems, Jim Free, put it this way in an interview with Time magazine: “The architecture we’ve chosen doesn’t allow for reusability… Disposing of it is the best way to go, and that’s what we’ve chosen.” Free retired from NASA in 2025.
Artemis is meant to take us back to the Moon – and is the first step toward human exploration of Mars. But as NASA looks ahead, a big part of its future is still being powered by the past – and for this role, now designed to be thrown away.