NASA’s Orion spacecraft, with its European service module, on top of the Space Launch System moon rocket. Credit: Stephen Clark / Spaceflight Now

The first unpiloted mission for NASA’s Artemis moon program aims to prove out the most powerful rocket to ever launch from U.S. soil, and test the function of a human-rated spacecraft traveling more than 40,000 miles beyond the far side of the moon before blazing back through Earth’s atmosphere at nearly 25,000 mph.

It’s all designed to gather data and build confidence for NASA’s new 322-foot-tall (98-meter) Space Launch System moon rocket and Orion moonship before astronauts strap in on the next Artemis test flight. The first Artemis mission, Artemis 1, is set for liftoff Saturday from the Kennedy Space Center in Florida during a two-hour launch window opening at 2:17 p.m. EDT (1817 GMT).

“We are stressing and testing this thing in a way that you would never do it if we had humans on board, and that’s the point,” said NASA Administrator Bill Nelson.

The first launch attempt for the Artemis 1 mission scrubbed Monday after teams at Kennedy ran into several technical problems, including a now-resolved hydrogen leak and data that showed one of the rocket’s main engines was not chilling down as designed. Engineers have concluded the engine cooling data came from a bad sensor, and approved another launch attempt for the Artemis 1 mission Saturday.

If the mission gets off the ground Saturday, the SLS moon rocket will propel the Orion spacecraft to a velocity of more than 22,500 mph (36,300 kilometers per hour) with a trans-lunar injection burn of its upper stage, fast enough to escape the bonds of Earth’s gravity and head for the moon. At that point, without its no-longer-needed launch abort tower and aeroshell, the moon-bound spaceship will comprise approximately 57,000 pounds (about 26 metric tons) — around 1% — of the 5.75-million pound total weight of the SLS moon rocket at liftoff.

The Orion spacecraft will separate from the moon rocket’s upper stage about two hours into the mission on a course to swing 60 miles (100 kilometers) over the lunar surface with its maneuvering engine firing. The outbound flyby five days after launch will guide the Orion spacecraft into a distant retrograde orbit with an average distance of more than 43,000 miles (70,000 kilometers) from the moon. At that distance from Earth, the spacecraft will be flying outside the magnetic field that shields the planet from solar and cosmic radiation.

Artemis 1 also carries a range of secondary payloads, including deployable subsatellites, or CubeSats, to pursue scientific and technology demonstration missions. There are experiments and payloads inside the Orion spacecraft, too. Three mannequins strapped into the crew module’s seat will help scientists gather data and test the performance of a new astronaut spacesuit and a vest to protect the human body against radiation.

Mission controllers at NASA’s Johnson Space Center in Houston will oversee the Artemis 1 flight from launch though splashdown. They will exercise the Orion capsule’s guidance and navigation, propulsion and cooling systems, computers, software, and communications equipment. Some elements of Orion’s life support system, and its cockpit crew displays, are not on the Artemis 1 flight.

After one-and-a-half laps around the moon, the Orion spacecraft will aim for another close flyby of the moon to steer onto a path back to Earth.

The SLS moon rocket on Launch Complex 39B. Credit: United Launch Alliance

Assuming Artemis 1 launches Saturday, the Orion capsule is scheduled to return to Earth on Oct. 11 for a re-entry and parachute-assisted splashdown in the Pacific Ocean west of San Diego. The capsule will plunge into the atmosphere traveling nearly 25,000 mph (more than 40,000 kilometers per hour), using a “skip re-entry” technique to bleed off speed. The re-entry velocity is about 30 percent faster than a spacecraft returning from a mission to the International Space Station.

The planned 38-day duration of the Artemis 1 mission is nearly double the 21-day design life of an Orion spacecraft on standalone mission. The Orion spacecraft can spend up to six months in space when docked to a space station.

NASA has assessed there is a 1-in-125 probability that the Orion spacecraft could be lost on the Artemis 1 mission. That’s more risk than the agency would accept on a mission with humans on-board.

“On Artemis 1, we have a lean forward strategy to get our high priority objective, which is to demonstrate the heat shield at lunar re-entry conditions,” said Mike Sarafin, NASA’s Artemis 1 mission manager. “We are going to thrust to the point of trans-lunar injection unless we’re sure that we’re going to lose the vehicle.”

Even if there’s a problem deploying the Orion spacecraft’s four power-generating solar array wings, or a failure that leaves the capsule without a critical back-up system, NASA will proceed with the mission, Sarafin said.

“We would be ‘go’ on this flight for conditions that we would normally be ‘no go’ for on a crewed flight in the interests of crew safety, but because we want to buy down risk across the manifest, and to understand this system and the system design and its margins, we are going to press through the point of trans-lunar injection if at all possible,” Sarafin said.

NASA officials assessed the risk of losing the Orion spacecraft due to a failure during the Artemis 1 launch is 1-in-260, and the risk of a catastrophic failure during entry, descent, and landing is 1-in-890. There’s a 1-in-314 probability that a failure of the SLS moon rocket itself will lead to the destruction or loss of the Orion spacecraft on Artemis 1, according to Kathryn Hambleton, a NASA spokesperson.

Sarafin said the risk calculations are part of a probabilistic risk assessment that take into account known failure modes of different components and systems, levels of redundancy in the rocket and spacecraft, and “common cause failures” during the launch, in-space, and re-entry phases of the flight.

Mike Sarafin, NASA’s Artemis 1 mission manager, participates in a press conference at the Kennedy Space Center in Florida. Credit: NASA/Kim Shiflett

One of the major risk drivers on the Artemis 1 mission is a hazard on every human spaceflight.

Collisions with tiny fragments of space junk or naturally-occurring dust grains or pebble-sized rock fragments — known as micrometeoroids and orbital debris, or MMOD — could damage part of the the Orion spaceship’s heat shield while it is traveling to and from the moon.

And the exposure to the MMOD risk goes up the longer the Orion spacecraft is in space. The heat shield itself is also a critical system on the Orion spacecraft that has to work for the capsule to be recovered.

Avionics and software on the SLS moon rocket, which provide guidance, navigation and health monitoring of its engines, are also a “key driver” of the risk on the Artemis 1 mission, Sarafin said, as is the Orion spacecraft’s propulsion system required for maneuvers to enter orbit around the moon

“Those are the top risk drivers,” Sarafin said. “And thats what drove that 1-in-125 number.”

The launch abort motor on top of the Orion spacecraft for the first three minutes of the launch sequence is not active for the Artemis 1. The launch abort system’s jettison motor will fire the escape tower away from the Orion capsule as soon as it reaches space, when the core stage of the SLS moon rocket is still firing.

On the Artemis 2 mission and later crew flights, the launch abort motor will be active and armed to pull the astronauts and their Orion spacecraft from a catastrophic failure of the rocket. That won’t be possible in the first three minutes of the Artemis 1 launch.

The addition of the launch abort capability, more conservative flight safety rules, and lessons learned from Artemis 1 will reduce the probability of a “loss of crew” on future astronaut missions, officials said.

For comparison, NASA calculated the loss of crew probability for SpaceX’s first astronaut test flight in 2020 at 1-in-276. NASA’s commercial crew program required SpaceX to meet a safety threshold of 1-in-270. The test flight with astronauts Doug Hurley and Bob Behnken was successful.

NASA pegged the overall risk of a loss of mission is 1-in-60 for the first human flight on SpaceX’s Crew Dragon spacecraft. That risk covered scenarios where the Crew Dragon couldn’t reach the International Space Station as planned, but the crew safely returned to Earth.

But probabilistic risk assessments for any given flight are tricky. The number hinges on a number of factors, including numerical and statistical inputs, many of which are grounded in assumptions.

Bill Gerstenmaier, who led NASA’s human spaceflight programs from 2005 until 2019, and is now a SpaceX executive, said in 2017 that at the time of the first space shuttle flight in 1981, engineers calculated the probability of a loss of crew on that mission between 1-in-500 and 1-in-5,000. After grounding the loss of crew model with flight data from shuttle missions, NASA determined the first space shuttle flight actually had a 1-in-12 chance of ending with the loss of the crew, Gerstenmaier said.

By the end of the shuttle program, after two fatal disasters, NASA calculated the risk of a loss of crew on any single mission was about 1-in-90.

Artist’s concept of the Orion spacecraft’s crew module and service module near the moon. Credit: Lockheed Martin

There are scenarios on the Artemis 1 mission where lower-than-expected performance from the SLS moon rocket, such as the early shutdown of a main engine, could prompt NASA’s mission control team to revert to an “alternate mission” for the Orion spacecraft. In some situations, the Orion could “down-mode” to a lunar flyby, without entering orbit around the moon, or deploy into a high orbit around Earth.

In those cases, the capsule could still re-enter Earth’s atmosphere at the velocity needed to test out Orion’s protective heat shield, the No. 1 goal of the Artemis 1 mission.

“It’s possible we may shorten some of the mission,” Kelso said. “The main objective of this test flight is to see that that heat shield works.”

When it blasts off, the SLS moon rocket will generate 8.8 million pounds of thrust, 15% more than NASA’s Saturn 5 moon rocket. Only the Soviet Union’s N1 moon rocket, which failed on all four of its test flights from 1969 through 1972, produced more power at liftoff.

SpaceX’s commercial Super Heavy booster — part of the reusable Starship rocket design — will generate nearly double the thrust of NASA’s SLS moon rocket with all of its 33 methane-fueled Raptor engines firing. SpaceX is preparing for the first Super Heavy/Starship test launch from Texas into a low-altitude Earth orbit as soon as later this year, but the company has not set a firm schedule for the flight.

The Space Launch System’s two solid-fueled boosters and four hydrogen-burning main engines are leftovers from the space shuttle program, but they’re upgraded for more power. The solid rocket boosters are taller than they were on the space shuttle, with the addition of a fifth motor segment, and will fire for two minutes and separate from the core stage to crash into the Atlantic Ocean downrange from Florida’s Space Coast.

The shuttle boosters had four segments connected together.

This diagram illustrates the major elements of the Space Launch System moon rocket. Credit: NASA

And the RS-25 main engines mounted to the bottom of the SLS core stage will fly at a throttle setting of 109%, up from the 104% power level used during shuttle missions. They will burn for eight minutes before the core stage jettisons to fall back into the atmosphere and disintegrate over the Pacific Ocean.

The upper stage of the SLS moon rocket was built by United Launch Alliance, and is based on that company’s Delta 4-Heavy rocket.

Aerojet Rocketdyne built the shuttle-era RS-25 core stage main engines and the RL10 engine flying on the launcher’s upper stage, officially known as the interim cryogenic propulsion stage. More than 500 RL10 engines have flown on Atlas, Delta, and Titan rockets since 1963, but the RL10’s trans-lunar injection burn required to send the Orion spacecraft toward the moon on the Artemis 1 launch will the longest-ever firing in space by the venerable engine type.

And the Orion service module’s main engine is also a flight-proven powerplant.

The service module has 33 engines and thrusters to control the Orion capsule’s orientation and adjust its trajectory after launch. The main engine for Artemis 1 is a refurbished Orbital Maneuvering System engine that flew on 19 space shuttle missions.

Despite the abundant use of flight-proven hardware on the SLS moon rocket and Orion spacecraft, and extensive ground testing over the last decade, there are still unknowns going into the Artemis 1 mission.

“We’ve gone through single engine tests, we had the green run test series (with all four main engines) … We’ve had full scale booster tests, several structural tests that we’ve had of the vehicle in structural test articles, and a dynamic rollout test,” said Chris Cianciola, NASA’s deputy program manager for the Space Launch System at the Marshall Space Flight Center in Alabama. “Now it’s time for the big test, the combined environments test and flight. It’s test that we can’t duplicate on the ground.”

Jim Free, who leads development for NASA’s Artemis program, said there are “staggering number” of requirements and tests planned for the Artemis 1 mission. Spaceflight Now requested an exact number of test objectives for Artemis 1, but a NASA spokesperson did not provide an answer.

“We are pushing the vehicle to its limits, really stressing it to get ready for crew,” Free said. “We’ve mitigated our risk as far as we can, and now it’s our time to get to launch, so that we get that data that we need to put crew on it.”

Boeing manufactured the SLS core stage at a factory in New Orleans. The solid rocket booster segments were fabricated and cast with propellant by Northrop Grumman in northern Utah. The Orion spacecraft’s pressurized crew module was built by Lockheed Martin in New Orleans and at the Kennedy Space Center in Florida, and the Orion service module — providing power and propulsion to the capsule — was assembled by Airbus in Bremen, Germany.

Suppliers and workers in all 50 U.S. states and 10 European continues worked on the Artemis 1 moon rocket and spacecraft.

NASA plans to launch the Artemis 2 mission with a crew of four astronauts on the second flight of the SLS moon rocket. That flight to carry a crew around the moon is scheduled for 2024, pending the results from Artemis 1. It will be the first time humans have traveled to the moon since the last Apollo lunar flight in 1972, and will set a record for the farthest distance people have ever traveled from Earth.

The Artemis 1 mission profile will carry the Orion spacecraft into a distant retrograde orbit around the moon, flying at an average 43,000 miles (70,000 kilometers) from the lunar surface. The Orion spacecraft will return to Earth for splashdown in the Pacific Ocean at the end of the mission. Credit: NASA

“The heat shield, the stressing of the system, the delivery and performance of SLS, and recovery of the vehicle are all critical things we need to do before we can talk about going to Artemis 2,” Free said. “If we don’t get all of those, we’ll have a discussion about the risk that remains before we would put crew onto Artemis 2.”

On the Artemis 2 mission, the Space Launch System will initially place the Orion crew capsule into orbit around Earth, where the astronauts will perform checkouts, test out the ship’s rendezvous and docking systems, and then fire Orion’s service module engine to fly to the moon a quarter-million miles away.

The Artemis 2 mission will follow a “hybrid free return trajectory” around the moon. The Orion crew capsule won’t enter orbit around the moon, but still instead loop around the far side and return directly to Earth for splashdown in the Pacific Ocean.

The Orion spacecraft will arc out to a distance of 4,600 miles (7,400 kilometers) beyond the far side of the moon, farther than any humans have ever traveled into space.

The Artemis 2 mission will last around 10 days, paving the way for future landing expeditions and longer-duration flights to the Gateway, a mini-space staton NASA plans to construct in orbit around the moon.

The Artemis program’s first attempt to land a crew on the moon is penciled in for the Artemis 3 mission, scheduled for 2025, with a derivative of the Starship vehicle SpaceX’s is developing in South Texas. The Orion spacecraft carrying astronauts from Earth with dock with the Starship lander near the moon to ferry the crew to the lunar south pole. The Starship will ascend back into space from the moon to link up with Orion to bring the astronauts back to Earth.

Future Artemis missions will utilize more commercially-developed lunar landing craft to deliver astronauts to the moon’s surface. NASA plans to debut a more powerful upper stage for the SLS moon rocket on the Artemis 4 mission, enabling assembly of the Gateway station in lunar orbit and hauling heavier cargo to the moon.

Artist’s concept of NASA’s Orion spacecraft during re-entry into Earth’s atmosphere. Credit: NASA

The Artemis program has its roots in a revamp of NASA’s human space exploration plans at the beginning of the Obama administration. The Obama White House in 2010 canceled the behind-schedule Constellation moon program, which started development of the Orion spacecraft with a different launch system than the SLS.

While President Obama ordered NASA to focus on developing commercial human-rated capsules to transport astronauts to and from the International Space Station — resulting in the commercial crew program with SpaceX and Boeing as contractors — Congress directed the Obama administration and NASA to accelerate work on a huge government-managed rocket program called the Space Launch System.

The Obama administration proposed NASA use the SLS rocket and Orion spacecraft for a crew mission to an asteroid, proving technology for an eventual human flight to Mars. Under President Trump, the effort was re-targeted for the moon and renamed the Artemis program — the twin sister of Apollo in Greek mythology — with a goal of landing astronauts at the lunar south pole by the end of 2024.

NASA has given up on the 2024 deadline, and the 2025 timetable for the human moon landing is in doubt. But President Biden has kept the Artemis program alive, and NASA last year selected SpaceX to build the first human-rated moon lander in more than 50 years.

The Artemis program’s ultimate objective, according to NASA, remains to test technology and practice for eventual human expeditions to Mars.

But the Artemis missions come with a hefty price tag.

NASA’s inspector general reported each of the first four Artemis missions will cost $4.1 billion apiece. None of the SLS moon rocket is reused, despite engines and boosters originally designed for multiple launches. NASA and Lockheed Martin eventually plan to refurbish and reuse Orion crew modules.

The agency watchdog also projected NASA will have spent $93 billion on the Artemis moon program by the end of 2025, including expenses for the SLS moon rocket, Orion spacecraft, ground systems, a human-rated moon lander, and the Gateway station.

So far, NASA has spent more than $48 billion to develop the Space Launch System, Orion spacecraft, and prepare ground systems at the Kennedy Space Center for the new-generation moon program.

NASA has committed $14.2 billion to develop the Orion spacecraft from 2012 through the end of this fiscal year Sept. 30, plus an additional $6.3 billion committed to the program in the prior decade under the Constellation program.

NASA has budgeted $22.4 billion for the SLS program from 2012 through the end of this fiscal year. Another $5.4 billion in the same period went toward readying Kennedy Space Center’s ground infrastructure for SLS and Orion missions.

This email address is being protected from spambots. You need JavaScript enabled to view it. the author.

Follow Stephen Clark on Twitter: @StephenClark1.