NASA Tests Mobile Launcher’s Slidewire Baskets


The SLS Mobile Launcher is illuminated by floodlights as preflight testing of Artemis 2’s ground support equipment continues. Credit: Jeff Seibert/AmericaSpace.

If you are an astronaut, the Emergency Egress System (EES) is the most fun ride which you hope you never need to take.  These systems have taken many forms over the 63-year saga of American human spaceflight, from cherry pickers to ejection seats to inflatable slides.  However, they all serve a common purpose: to rapidly transport astronauts to a safe distance from a fueled rocket in the event of an emergency on the launch pad.  To satisfy this requirement, the Artemis Program opted to install slidewire baskets on its Mobile Launcher.  NASA recently tested the system to verify that it is safe for human use.  The video of the demonstration showcases how the baskets will be an invaluable safety feature for the four Artemis 2 astronauts during their launch next September.

A camera mounted inside one of the SLS program’s slidewire baskets records a first-person view of a recent test of the system.

The testing of the slidewire system is the culmination of a nearly year-long test campaign at the Kennedy Space Center.  It is intended to demonstrate that the infrastructure at historic Launch Complex 39B is prepared to support a crewed launch of the Space Launch System (SLS), Artemis 2’s titanic launch vehicle.  Last August, the 40-story-tall Mobile Launcher (ML) was rolled to Pad 39B to begin a series of Integrated System Verification and Validation (ISVV) tests.  The ML’s stay on the pad was supposed to be relatively brief.  The tower was initially slated to roll back to the iconic Vehicle Assembly Building in December of last year.  

A remote survey reveals the damage to the Mobile Launcher’s elevator doors following the launch of Artemis 1. Credit: NASA.

The comprehensive demonstration was prolonged by two factors.  The first was the continuing repairs and upgrades to the ML, which sustained more damage than expected during the launch of Artemis 1.  Computer models underestimated the effects which low-frequency sound waves would have on some of the tubing and electrical boxes at the launch pad.  In addition, recent report by NASA’s Office of the Inspector General revealed that the tower was the victim of a very unfortunate miscommunication.  “According to an Agency official, going into the Artemis I mission it was not known that the elevator ‘blast doors’ were not in fact blast doors but rather fiberglass doors designed to keep wind out,” the watchdog wrote.  While many of the repairs were completed prior to the ML’s journey to the launch pad, some work spilled over into the test campaign.  

In addition, there was simply less urgency to complete the tests after NASA announced a 10-month delay to the Artemis 2 mission.  In January, the historic flight was officially postponed to September of 2025 due to persistent issues with the Orion crew capsule’s heat shield, life support system, and batteries.  As NASA has no need for the ML before the fall, the Exploration Ground Systems team was able to devote additional time to fixing problems which arose during testing.  

The Artemis 2 crew poses for a photo inside the SLS Mobile Launcher’s Crew Access Arm. Left to right: Victor Glover, Jeremy Hansen, Christina Koch, and Reid Wiseman. Credit: NASA/Frank Michaux.

Over the past nine months, the Artemis team has methodically worked their way through the campaign, putting their engineers and equipment though several new procedures for the first time.  The most visible was a simulated launch countdown.  The four Artemis 2 crewmembers donned their bright orange pressure suits, boarded three new “Astrovans” developed by the electric vehicle start-up Canoo Technologies, and walked down the Mobile Launcher’s Crew Access Arm.  Commander Reid Wiseman told AmericaSpace, “They have the video of the whole test, and I am still trying to find a moment when we are not smiling.  It was awesome.  We had the convoy, and we had the Mobile Launcher at Pad 39B.  The only thing we were missing was a rocket (…) You just had that visceral feel – it felt so real, it felt so good.”

Launch Complex 39B’s water deluge system releases a torrent of 450,000 gallons of water onto the base of the Mobile Launcher. Credit: NASA/Kim Shiflett.

NASA also tested new “rainbird” nozzles for the Mobile Launcher’s Sound Suppression System.  This labyrinth of plumbing releases 450,000 gallons (1,700,000 liters) of water in a matter of seconds to blunt the pressure waves from SLS’ twin Solid Rocket Boosters.  It is hoped that the new nozzles will help alleviate some of the damage which was seen during Artemis 1.  

Simultaneously, the high-speed cameras on the tower were put through their paces.  According to NASA’s Inspector General, NASA was disappointed with the quality of the Artemis 1 launch videos.  Persistent hydrogen leaks and severe weather delayed the launch of Artemis 1 to mid-November, at which point the only available launch windows were at night.  Faced with a choice between a night launch or a multi-month delay, NASA concluded that the former posed fewer risks to Artemis as a whole.  The drawback is that the settings for the cameras at the launch pad were optimized for a daytime liftoff.  The videos from all but one of the 33 high-speed cameras were underexposed.  Additional camera tests should prevent this issue from reoccurring if Artemis 2 does launch at night. 

Short-exposure photographs can capture the spectacular billowing exhaust plume from SLS’ Solid Rocket Boosters, while longer exposures are better for documenting details on the rocket itself. Credit: Mike Killian/AmericaSpace.

All of these activities built up to the inaugural test of the new Artemis slidewire baskets.  The sole purpose of the baskets is to evacuate an Artemis crew and their support team from the launch pad in the event of an emergency.  In the unlikely event of a pad explosion, Orion will be whisked to safety by its Launch Abort System, a set of four powerful solid rocket motors which crown the SLS stack.  However, there are a number of other scenarios where remaining inside the capsule is not the best approach to survival.  These include a fire in the cabin, a toxic gas leak from the propulsion system, a loss of electrical power at the launch pad, and a medical emergency.  In these situations, the crew will quickly exit Orion and board the baskets.  NASA requires this entire operation, from opening the hatch to arriving in a bunker at the perimeter of the launch pad, to be completed in less than two minutes.

One of the SLS Mobile Launcher’s emergency egress baskets is hoisted up a cable. In the event of an emergency on the launch pad, the baskets will rapidly carry the Artemis 2 crew and their support team to the safety of a bunker (the blue area at top left). Credit: NASA/Isaac Watson.

The baskets vaguely resemble a large zipline or a ski lift.  During a launch campaign, four of them will be anchored to a platform which is located on the same level as the Crew Access Arm.  If Wiseman, Glover, Koch, and Hansen need to exit Orion for any reason, a set of bright yellow arrows painted onto the floor of the arm and the Mobile Launcher will direct them to the baskets.  Each rectangular basket seats five people and can be released with the simple push of a button.  The unpowered baskets slide down a cable solely under the influence of gravity until they are caught by a net at ground level.  Once they exit the baskets, the astronauts can elect to wait out the crisis in a reinforced bunker or to drive away from the launch pad in a Mine-Resistant Ambush Protected (MRAP) armored vehicle.  

Artemis 2 astronauts (left to right) Victor Glover, Reid Wiseman, and Jeremy Hansen pose for a photo with NASA’s Exploration Ground Systems team underneath the Mobile Launcher. Credit: NASA/Kim Shiflett.

One unique challenge associated with SLS is the 402-foot-tall umbilical tower’s eponymous mobile nature.  It makes the journey to and from the launch pad alongside the rocket itself.  This reduces its exposure to the humid, salty air of the Florida coastline, which reacts with metal components to produce severe corrosion over long periods of time.  Because of this approach, the launch team must install the baskets at the beginning of every launch campaign and disassemble them after the launch.  A system of pilot lines is used to winch the four main slidewire cables to the top of the Mobile Launcher.  After the cables are anchored in place, engineers carefully adjust their tension so that the baskets accelerate at a safe rate.  

NASA tested the slidewire baskets several times in April.  To avoid risking the lives of engineers in an unproven system, large jugs of water were used to simulate the weight of the astronauts and their support team.  The data from the test will be used to certify that the baskets are safe for human occupancy.  The Artemis 2 astronauts are scheduled to visit the Kennedy Space Center in the coming weeks, where they will receive an orientation on how to operate the system.  The Mobile Launcher will be rolled back to the Vehicle Assembly Building in mid-summer.

Alan Shepard’s Mercury Redstone-3 rocket is seen on the launch pad prior to America’s first human spaceflight. The cherry picker is being raised towards the hatch of the capsule. Credit: NASA.

The Artemis slidewire baskets are just the latest in a long line of creative, and sometimes bizarre, crew egress systems.  The concept originated with astronaut Gordon Cooper during the lead-up to Alan Shepard’s historic Mercury flight.  As the chair of Project Mercury’s Emergency Egress Committee, Cooper was charged with determining how to quickly extricate an astronaut from a capsule without the support of technicians on the ground.  His team devised a modified cherry picker which could be remotely commanded to swing into position next to the capsule.  This device had its limitations; most notably, it could not be rapidly deployed to save an astronaut from a dire emergency inside the cockpit.  Rather, it was primarily intended to provide an alternate exit pathway if the Mobile Service Structure could not roll back into position following a launch scrub.

Left to right: Gemini 3 Pilot John Young, backup crewmembers Wally Schirra and Tom Stafford, and Commander Gus Grissom walk out to the launch pad. Credit: NASA.

The cherry picker remained in use throughout the Gemini program, and fittingly, it was used to extract Cooper and his crewmate Pete Conrad from their Gemini 5 capsule following a launch countdown simulation.  The Gemini service structure rotated into place from a horizontal resting position, and on that day, it was unable to deploy.  A more rapid exit was also possible thanks to two ejection seats.  In hindsight, the seats might have been as dangerous as the hazards which they supposedly mitigated.  Gemini 6 Pilot Tom Stafford expressed relief when his commander, Wally Schirra, did not fire the ejection seats after a hair-raising launch abort.  “Given that we’d been soaking in pure oxygen for two hours, any spark, especially the ignition of an ejection-seat rocket, would have set us on fire.  We’d have been two Roman candles shooting off into the sand and palmetto trees,” Stafford wrote in his autobiography.

The bunker inside the “Rubber Room” served as an impregnable haven for Apollo crews in the event of a pad explosion. Credit: NASA.

Following the Apollo 1 tragedy, NASA began building more elaborate and robust egress systems at its launch pads.  To protect astronauts from the detonation of a gargantuan Saturn V rocket, Pads 39A and 39B featured identical bunkers situated 40 feet below ground.  In the event of an emergency, the crew would ride the umbilical tower’s elevator to ground level and slide down a 200-foot-long chute to access the bunker.  Because the exit to the tunnel was padded with rubber to cushion their fall, the bunker was universally known as the “Rubber Room.”

Left to right: STS-131 astronauts Clay Anderson, Naoko Yamazaki, and Stephanie Wilson practice boarding a slidewire basket. Credit: NASA/Kim Shiflett.

The now-familiar slidewire system made its first appearance midway through the Apollo era as a backup to the Rubber Room.  The Saturn V umbilical tower featured just one basket for the crew to use after the closeout team had already evacuated the launch pad.  However, it worked well enough for NASA to adopt it as the primary evacuation system at the Space Shuttle launch pads.  When compared to the Rubber Room, it had the obvious advantage of cutting out the 30-second elevator ride, which could be the difference between life and death in a crisis.  During the Shuttle era, Pads 39A and 39B incorporated seven small slidewire baskets, each of which could accommodate three people.  Over the entire thirty-year history of the program, only one man rode in the baskets: the legendary mission commander Charlie Bolden.  Following the Challenger tragedy, a new set of requirements mandated that the baskets be certified with a human passenger.  Bolden was assigned to complete this task.  Military astronauts frequently tease each other over interservice rivalries, so Bolden’s Air Force and Navy colleagues joked that “We sent a Marine to confirm that the baskets were safe for sandbags.”

A first responder practices exiting SpaceX’s new egress slide at Space Launch Complex 40. Credit: SpaceX.

Launch Complex 39A still features the original slidewire baskets, though they have been refurnished to match the striking black-and-white aesthetic of their new owner.  SpaceX uses them as the primary pad egress system for Crew Dragon astronauts.  For redundancy, the company recently commissioned a second crew access tower at Space Launch Complex 40.  This launch pad features a completely different approach to crew safety: an inflatable slide.  This neon orange chute can deploy within seven seconds, and the crew can then slide to safety.  For its part, Boeing has built a zipline-like system for its Starliner spacecraft.  Astronauts sit in personal seats for support, grasp onto two vertical bars attached to the armrests, and then glide down a slidewire-like cable.

The Ares I program’s “Roller Coaster” (yellow structure) was the most capable, yet most expensive and high-maintenance, Emergency Egress System ever devised. Credit: NASA.

NASA considered several candidate Emergency Egress System designs for SLS and its ill-fated predecessor, the Ares I rocket.  Initially, the Ares I Mobile Launcher was supposed to feature a “roller coaster” system designed in collaboration with a handful of Walt Disney World’s engineers.  The “roller coaster” would feature several enclosed cars which would roll down a track and directly into a blast-proof bunker.  In theory, the system would have provided a faster and gentler ride than the slidewire baskets.  However, the baskets were well-tested and comparatively inexpensive, so NASA switched to the more traditional system when Ares I morphed into SLS.  It is that system which will build on the diverse heritage built over six decades of human spaceflight as it protects crews throughout what will hopefully be a long and productive Artemis era.

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