SLS mobile launcher moves to pad 39B for final exams

The Space Launch System’s Mobile Launcher rolls down the crawlerway Thursday at NASA’s Kennedy Space Center in Florida toward pad 39B. Credit: Stephen Clark/Spaceflight Now

A towering mobile platform for the agency’s Space Launch System arrived at launch pad 39B Friday at the Kennedy Space Center in Florida for a sequence of water and propellant flow tests, swing arm checkouts and other rehearsals that should conclude with managers declaring the spaceport’s ground systems ready to support the first SLS launch campaign by the end of the year.

The Mobile Launcher is a moving platform that will transfer the 322-foot-tall (98-meter) Space Launch System from the Vehicle Assembly Building to the launch pad. The tower is one of the tallest structures in the Cape Canaveral area, and NASA originally built it for the Ares 1 rocket, a single-booster launcher that was cancelled in 2010 before it ever flew on an orbital mission.

The rollout of the Mobile Launcher to pad 39B this week caps nine months of electrical and mechanical testing inside the Vehicle Assembly Building. After checking the platform and tower’s compatibility with the VAB, where the Space Launch System will be stacked, engineers now want to ensure it will work at the launch pad.

“It’s that next big step right before the final exam, before we’re done,” said Cliff Lanham, NASA’s senior project manager for the Mobile Launcher. “So we’re all very excited. I know our operations group is ready to get ahold of it, so they can operating it with the rocket. Everybody’s pumped about this.”

But exactly when NASA can finally put the Mobile Launcher to use is hard to predict, officials said Thursday. Difficulties with the assembly of the Space Launch System’s Boeing-built core stage in Louisiana have put in doubt a first launch of the new rocket in 2020, three years later than originally envisioned.

This illustration shows the components of the Space Launch System’s Block 1 configuration, which is the version scheduled to fly on the rocket’s first mission, designated Exploration Mission-1. Credit: NASA

NASA is developing the Space Launch System to send astronauts on voyages to the moon — with a goal of a human landing there within five years — by way of a mini-space station the space agency plans to assemble in a high lunar orbit.

The space agency says the first SLS launch, without a crew on-board, could still happen before the end of 2020, but any technical problems discovered in several critical upcoming ground tests could delay the launch as late as June 2021, according to a Government Accountability Office report released earlier this month.

NASA officials said the rollout of the Mobile Launcher to pad 39B should be the last time the mammoth structure makes the trip to the launch pad before ground crews stack the Space Launch System on the platform in preparation for the first flight.

The SLS core stage will be powered by four RS-25 main engines, two solid rocket boosters and an RL10 upper stage engine. At liftoff, the rocket will generate up to 8.8 million pounds of thrust, more than any launcher in history.

The first SLS launch, designated Artemis 1, will send an unpiloted Orion crew capsule on a shakedown cruise to the moon and back. The Orion spacecraft and its service module will swing as close as 62 miles (100 kilometers) from the lunar surface, then loop into a more distant orbit around 40,000 miles (70,000 kilometers) from the moon before returning to Earth.

The second SLS/Orion flight, in 2022 or 2023, will carry astronauts on a looping trajectory around the moon and back to Earth, followed by the Artemis 3 mission in 2024, which could attempt the first landing on the moon by astronauts since 1972.

Workers at the Michoud Assembly Facility in New Orleans recently joined four of the five major sections of the SLS core stage. Technicians continue outfitting the core stage’s engine section before it is ready to join the rest of the rocket. Credit: NASA

One of NASA’s Apollo-era diesel-powered crawler-transporters carried the 10.5-million-pound Mobile Launcher from the cavernous Vehicle Assembly Building to pad 39B, facilities at the Florida spaceport that built in the 1960s for the Apollo moon program, and later modified for the space shuttle and the Space Launch System.

The crawler crew divided the 4.2-mile (6.8-kilometer) journey over two days, beginning around 12 a.m. EDT (0400 GMT) Thursday with rollout from High Bay 3 in the Vehicle Assembly Building, where the tower has resided since last September. The Mobile Launcher trekked down the rock-covered crawlerway at a top speed of 0.8 mph — about 1.3 kilometers per hour, or 70 feet per minute — and arrived at the gate to pad 39B by late morning Thursday.

The Mobile Launcher finished the trip up the ramp to pad 39B on Friday morning. A laser alignment system helped the crawler crew guide the Mobile Launcher to the correct position, then lower it over six pedestals at the launch pad.

NASA plans to keep the Mobile Launcher at pad 39B until around the end of September. During the three-month campaign, engineers will run a series of tests, including swing arm retractions to mimic their function during a launch countdown, and pumping cryogenic liquid hydrogen and liquid oxygen propellants through the structure’s plumbing for the first time.

“What we’ll do is we’ll hook all our systems to the pad systems, and we’ll test to make sure the Mobile Launcher and the pad work together properly,” Lanham said. “We’ll be testing, for instance, water flows, sound suppression, IOP (Ignition Overpressure) systems. We’ll be doing cryo flows as well out there.

“We will be doing the crew access arm swings because in the VAB we can’t fully test the swings of the arm, so we’ll be testing those out there. We’ll also be doing some end-to-end testing on the electrical systems. We’ll make sure we can command from the LCC (Launch Control Center) all the way out to the pad,” Lanham said. “We do have a simultaneous arm swing planned, where we’ll swing three of the arms together and make sure the hydraulic system can handle that.”

Unlike the moving launch tables used by the space shuttle, the SLS mobile launcher includes a gigantic skyscraper-like structure on the platform itself. The 380-foot-tall (115-meter) mobile launcher features a metal tower with six swing arms that will retract away from the rocket before launch.

In the shuttle era, pads 39A and 39B had fixed umbilical towers to provide astronauts, ground crews and swing arms access to the vehicle. The Apollo program’s Saturn 5 moon rocket used a similar pad setup as the SLS, but the Saturn 5’s mobile tower had nine swing arms.

Once engineers finish the the tests at the launch pad this summer, the Mobile Launcher will return to High Bay 3 inside the Vehicle Assembly Building for a few final checkouts, including a demonstration in which cranes will stack dummy segments of an SLS booster on the platform for the first time.

“This is a big day for us,” said Darrell Foster, exploration ground systems integration manager at KSC. “From my perspective, this is our launch day … From a hardware development standpoint, this is what we live for, these big milestones, and putting the pieces together. It’s like a puzzle.”

At launch pad 39B, workers have installed new heat-resistant bricks inside the flame trench, and put in a new flame director to shunt exhaust from the SLS main engines and solid rocket boosters toward the north at liftoff. NASA added new work platforms inside the VAB high bay to allow workers to reach the SLS during stacking and test operations.

NASA officials said the Mobile Launcher, along with newly-installed hardware at pad 39B and inside the VAB, should be ready to start the first SLS launch campaign by the end of the year.

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