One year ago, In the early hours of November 16th, 2022, the skies of Florida were lit up by the first moon rocket to fly in over 48 years. This mission, the first of its kind to bring humanity back to the moon, represents the culmination of nearly a decade and a half of policy, engineering and development – all with the goal of sustainable long term exploration. The Space Launch System, a rocket a decade in the making, was finally in the air, lofting the Orion capsule on its first journey to the moon. While the thunderous roar of its twin solid rocket boosters echoed across Kennedy Space Center, engineers at NASA closely followed the vehicle’s performance through each phase of flight. Each milestone ticked away right on queue, from booster separation just over two minutes into flight, to the separation of Orion from the Interim Cryogenic Propulsion Stage. From the outside, it looked like a flawless debut for NASA’s new superheavy lifter. On the inside, the investigation into how the flight went had just begun.
The Artemis I mission was a test flight, meant to put each and every system through its paces before putting crew on board. Orion had flown once previously, on a four hour test flight called Exploration Flight Test 1 in 2014. Artemis I however would be the first time the capsule flew in a nearly fully outfitted configuration. Also flying for the first time would be the SLS rocket. This test flight would push it to its limit, hurling Orion out to the Moon, and then further than any human rated spacecraft had ever been.
The Block 1 SLS rocket is composed of 3 main propulsion systems, the Core Stage, Interim Cryogenic Propulsion Stage (ICPS), and the twin RSRMV Boosters. Each system had a team of engineers comb through the data, looking for any data that varied from predicted values, and identifying potential idiosyncrasies on the flight vehicle that were not seen on simulated vehicle performance. These data points will help refine the SLS rocket for future missions, increasing its precision and reliability as it evolves over time.
The Solid Rocket Boosters were the first part of the vehicle to complete their mission, burning for approximately two minutes and six seconds. Each booster performed nearly identically, reaching peak thrust within a tenth of a second of each other. Burnout of each booster, where the thrust begins tailing off sharply as they run out of fuel, was approximately four tenths of a second apart from each other. At this point in flight pressure begins to lower inside of the booster, and when it reaches 50 psi (as measured by three sensors inside of each booster) a separation command is issued, jettisoning the now spent SRBs. All six sensors hit the 50 psi mark within four hundredths of a second, separating the spent boosters right on time.
SLS’s core stage was next up, burning for approximately eight minutes, accelerating the vehicle up to 7,796.74 m/sec (17,441 mph), 2.01 m/sec (4.5 mph) short of a perfect injection. This underspeed resulted in the apogee, the highest point in its orbit, being 6km lower than intended, well within the allowable margin of error for the Core Stage performance. Data from the 999 sensors and 72 km of wiring, indicated that the structure of the stage performed as expected.
The four RS-25D main engines, all of which had previously flown during the Space Shuttle Program, also performed as expected. The thrust, and fuel mixture ratios, were within .5% of the pre launch predicted levels. Internal Pressures and Temperatures of the 4 engines were within 2% of expected values. The stage reached peak G-Loading right before MECO, topping out at approximately 3.25G, right on cue. This performance mirrored those of their combined 25 previous missions during their tenure with the Space Shuttle program.
After the core stage separated, Orion and the ICPS continued on their suborbital trajectory, before performing a short burn to raise its perigee, the lowest point in its orbit, to be outside of the atmosphere. The spacecraft then coasted, and after completing an orbit of Earth, fired up its RL10-B-2 engine for the Trans-Lunar Injection burn. After this burn, the Orion spacecraft was separated. The stage performed near flawlessly, only using 3% of its allowable margin of error.
Each and every component on the first SLS rocket performed at a level often only expected of well established launch vehicles, but for NASA, it was the expectation of this rocket from day one. It underwent one of the most comprehensive test campaigns for a launch vehicle in recent memory. The core stage alone spent over a year in its Mississippi test stand undergoing its “Green Run” test campaign, which culminated in a full duration static test of the vehicles four main engines.
NASA’s determination to ensure a successful flight of SLS, has continued into Artemis II. Agency leaders have stressed the need to not get complacent in the wake of the Artemis I’s roaring success, as while the engineering is the same, the vehicles are different. Another potential issue that NASA has been facing is retaining institutional knowledge. This was a factor in why SLS took so long to initially develop, as many engineers and technicians left NASA at the conclusion of the Shuttle program. Despite these difficulties however, the sheer volume of data gained from the Artemis I launch campaign will inform a number of decisions, ranging from upgrading the umbilical arm flanges that delayed the launch due to leaks, to refining performance values for the vehicles control software.
As Artemis II quickly approaches, NASA will continue to look back at Artemis I to inform their decisions leading up to flight. The incredible success was not only the fulfillment of a mission statement, but a testament to the monumental effort put in by each and every person working on the program. Thanks to their efforts and continual push for perfection, Artemis I has gone down as one of the most successful debut flights in NASA’s storied history.