Historic Pad 39B at the Kennedy Space Center (KSC) in Florida—first used way back in May 1969 to send three humans to the Moon—is less than four weeks away from the 60th launch of its career, when it sees off the ambitious Artemis-1 mission to our nearest celestial neighbor. Liftoff of the mighty Space Launch System (SLS) rocket on its maiden voyage may occur as soon as 8:33 a.m. EDT on Monday, 29 August.
Earlier Wednesday, NASA Administrator Bill Nelson and senior staff from the agency’s headquarters in Washington, D.C., the Kennedy Space Center (KSC) in Florida, the Johnson Space Center (JSC) in Houston, Texas, and the Marshall Space Flight Center (MSFC) in Huntsville, Ala., provided comments and personal insights for a mission which will see the first human-capable spacecraft travel to lunar distance in almost a half-century. The success of Artemis-1 in its six-week voyage around the Moon will permit advanced planning for the crewed Artemis-2, provisionally targeted for no earlier than mid-2024.
“Just 26 days,” gushed Mr. Nelson, as he counted down to the end-of-August launch date for a rocket that has been more than a decade in the making. He drew attention to Pad 39B’s illustrious past and noted that the complex is “no stranger to monster rockets”.
And the SLS, of course, is a monster rocket on steroids. When it takes flight, it will generate 8.8 million pounds (3.9 million kilograms) of thrust from the four shuttle-heritage RS-25 engines of its Core Stage and a pair of five-segment Solid Rocket Boosters (SRBs).
That represents about 1.1 million pounds (500,000 kilograms) more liftoff thrust even than the behemoth Saturn V. And the mighty Saturn remains the largest and most powerful rocket ever brought to operational status.
Preparations for Artemis-1 have been ongoing on multiple fronts for more than two years. The 212-foot-tall (64.6-meter) Core Stage of the SLS underwent a year-long “Green Run” test campaign at NASA’s Stennis Space Center (SSC) in Bay St. Louis, Miss., throughout the entirety of 2020, ahead of a full-flight-duration “hot-fire” of its RS-25 engine suite in March of last year.
Its SRBs were delivered via rail to the Space Coast by prime contractor Northrop Grumman Corp. in June 2020. They were subsequently stacked inside High Bay 3 of KSC’s iconic Vehicle Assembly Building (VAB) between November 2020 and March 2021.
The Core Stage arrived in Florida a few weeks later and was lowered into position between the SRBs in June. Next, the tapering Launch Vehicle Stage Adapter (LVSA) was mounted atop the Core Stage, raising the height of the rocket to 25 stories.
By early July 2021, the Interim Cryogenic Propulsion Stage (ICPS)—whose RL-10 engine, built by Aerojet Rocketdyne, will conduct the Translunar Injection (TLI) “burn” to deliver Orion out of Earth orbit and on course for the Moon—was added to the stack. And the Orion Stage Adapter (OSA) was set in place last October.
All that remained was Orion itself and its Launch Abort System (LAS). Having attached the LAS and four protective “ogive” fairing panels onto Orion last summer, the finishing piece of Artemis-1 was in place last 20 October, topping-off the very first SLS at an impressive 322 feet (98 meters), taller than the Statue of Liberty.
Integrated testing followed over the winter and the SLS was rolled out of the VAB for an 11-hour crawl to Pad 39B on St. Patrick’s Day, 17 March. But hopes of having the luck of the Irish on its side were ominously absent, for the two-day Wet Dress Rehearsal (WDR) at the pad—which aimed to fuel the giant rocket with over 700,000 gallons (3.2 million liters) of cryogenic oxygen and hydrogen—seemed jinxed from the outset.
Four lightning strikes and multiple technical difficulties prompted managers to call off the first WDR in mid-April and return the stack to the VAB for repairs. The giant rocket was back inside the cavernous interior of the assembly building on 26 April.
Returning to Pad 39B in the first week of June, efforts to “tank” the rocket with cryogens hit an early obstacle in the form of a hydrogen leak in the quick-disconnect umbilical at the mobile launcher’s Tail Service Mast (TSM). For a second time, the SLS returned to the VAB on 2 July, where teams replaced a pair of seals on the quick-disconnect assembly, repaired a fist-sized collet which had worked its way loose and installed flight batteries for the SRBs, ICPS and Core Stage.
Speaking from KSC during Wednesday’s event, Artemis-1 Launch Director Charlie Blackwell-Thompson declared that NASA is now well inside “the final stretch” of preparedness for the mission. Orion was powered-up last weekend and teams are currently working nominal payload stowage operations, with closure of the spacecraft’s hatch anticipated about ten days from now.
Much of the SLS—including a good portion of the Core Stage and the LVSA—has already been closed out for flight, with the inter-tank section still open for planned engineering tests early next week. The left-hand SRB has no outstanding tasks, although a little more work remains to be done on its right-hand counterpart.
Three of the ten work platforms in the VAB have been retracted from the rocket and the Artemis-1 Launch Team will perform its final countdown simulation tomorrow. Ms. Blackwell-Thompson anticipates rollout from the VAB to Pad 39B on 18 August, allowing for a relatively spacious 11-day pad processing campaign.
Launch controllers will receive their formal “Call to Stations” at 9:53 a.m. EDT on the 27th. And the loading of cryogens aboard the giant rocket will pick up with liquid oxygen and liquid hydrogen tanking in the Core Stage, followed by fueling of the ICPS.
Last week, NASA officially unveiled three possible No Earlier Than (NET) launch opportunities for Artemis-1. The first would enjoy a spacious two-hour “window”, opening at 8:33 a.m. EDT on 29 August, producing a nominal 42-day flight for Orion and a return to Earth and splashdown on 10 October.
The second, also with a two-hour window, would shake the Florida ground at 12:48 p.m. EDT on 2 September, would see Orion return home on 11 October. And the third, launching at 5:12 p.m. EDT on 5 September, at the start of a slightly truncated 90-minute window, would envisage a mission duration extending through 17 October.
Following liftoff, the four RS-25 engines of the Core Stage and the twin SRBs will power the SLS uphill for the first two minutes of the flight. Then, in a fashion not unlike a shuttle launch of yesteryear, the boosters will be jettisoned, parachuting their way back into the Atlantic Ocean for recovery and refurbishment.
The Core Stage engines will continue to burn for a further six minutes—again, not unlike a shuttle ascent profile, in this regard—until they burn out and shut down about 8.5 minutes after launch. The ICPS will then execute the TLI “burn”, which will send Orion to the Moon, making Artemis-1 the first time since Apollo 17 that a human-capable machine has departed Earth orbit.
Orion’s outbound trip to the Moon will take several days, noted the Artemis-1 Press Kit, before it enters a Distant Retrograde Orbit (DRO). This looping ellipse will carry the spacecraft about 40,000 miles (64,000 kilometers) beyond the Moon, making it the farthest distance a vehicle built for humans has ever traveled.
After spending between six and 19 days in the DRO, Orion will commence its return to Earth, which could take up to two weeks. Significantly, the spacecraft is expected to reach a peak distance from home of 280,000 miles (450,000 kilometers), surpassing Apollo 13’s record of 248,654 miles (400,170 kilometers).
According to Artemis-1 Mission Manager Mike Sarafin, speaking from NASA Headquarters, the uncrewed nature of this flight permits a particularly aggressive push to get four “priority objectives” done. In order, these priorities are (1) the capability of Orion to re-enter Earth’s atmosphere at a blistering lunar-return velocity of Mach 32, equivalent to 25,000 mph (40,000 km/h), (2) an all-up demonstration of the complete vehicle at all stages of the real flight environment, (3) the satisfactory retrieval of Orion for post-mission testing and inspection and (4) the performance of payload and outreach activities, including on-board imagery of Earth and the Moon.
Mr. Sarafin stressed that the lack of astronauts aboard Artemis-1 has allowed a “lean-forward strategy” to be adopted, with controllers expected to declare themselves “Go” for some issues and in some circumstances, which—with a crew on board—might otherwise be “No-Go”. Clearly, Artemis-1 is expected to be a mission of firsts and a real presser of envelopes.
Data from a Mach 32 plunge into the atmosphere, Mr. Nelson added, could aid preparations for future Mars-return mission architectures. Re-entry velocities from a Mars mission may rise as high as Mach 36, some 27,600 mph (44,400 km/h).
Assuming all goes well, Artemis-1 will conclude with a parachute-assisted splashdown of Orion in the Pacific Ocean, off the coast of San Diego, Calif., after 42 days and three hours in flight and some 1.3 million miles (2.1 million kilometers) traveled. It promises to be a mission for the history books.
And for those of us—including this author—who were not yet born when humans last walked on the Moon, it will a poignant moment indeed. After a half-century, humanity stands on the brink of returning to deep space.
“Folks, we’re here,” said Mr. Nelson, with a characteristically dramatic flourish. “We are going back.”Missions » SLS » Missions » SLS » Artemis »