SLC-41 completes EES installation ahead of Starliner missions

by Chris Bergin

An Emergency Egress System (EES) has completed its installation into the Crew Access Tower (CAT) at Space Launch Complex -41 (SLC-41) in preparation for Atlas V launches with Boeing’s Starliner spacecraft. The EES is a vital element for all crew launch vehicles, with the SLC-41 EES working with the traditional “slide wire” concept.


The requirement to have an Emergency Egress System (EES) is not just for the astronauts set to ride uphill from the launch pad, but also for the engineering teams who’s role includes working up close and personal with the rocket in the final days of the pad flow.

2016-10-13-183511ULA began evaluating options for SLC-41 during a period Atlas V was catering for two crew-capable vehicles options, namely Starliner – or CST-100 as it was known – and Sierra Nevada Corporation’s (SNC) and their Dream Chaser spacecraft.

“Different options for emergency egress. Detailed hazard analysis of the launch operations is a key determinant,” noted the since-retired Dr. George Sowers, ULA VP for Human Launch Services, during a Q&A session with members in 2012. “We have the option of implementing a shuttle-like slide wire system if required.”

Although Atlas V is still hoping to launch Dream Chaser missions, the spacecraft’s role has been refocused on cargo missions. The EES option will still be employed for pad crews tending to the spacecraft. However, the highlighted role will be for astronauts riding on the Starliner.

The historical heritage of the EES hardware has mainly been based around utilizing a fairly simple, gravity-powered systems with a requirement to be passive/unpowered, in case the emergency cut power to the pad. However, each option had a different take on a similar theme.

The first EES for the Saturn V used the existing launch tower elevators to evacuate crew and/or engineers to the base of the Mobile Launch Platform, before transferring to a “slide tube” that led in an underground rubber room/sealed blast room – which remains in a preserved condition at Complex 39. (Large photo collection available on L2 – LINK).

A second system was added a few years later, adding the option of a single cab on a slide wire that egressed the astronauts outside of the pad perimeter – known as the Blast Danger Area (BDA) – 2,400 feet away from the pad. From there, they would enter a sealed bunker and await rescue.

This slide wire system was expanded by the time the Space Shuttle began its service for NASA, with extra emphasis on the pad EES, not least because a pad abort was not possible via the vehicle, due to the lack of a LAS.

Engineers installed five slide wires to the launch tower – later expanded to seven – with baskets that could hold up to four people each.

These slidewires ended at the same Apollo bunkers outside the BDA, where personnel could wait out the disaster or transfer to an armored vehicle (M-113) and drive to a triage site where they could be met by rescue personnel.

The slide wire option remained relatively unchanged throughout its career with the Space Shuttle Program (SSP) and was thankfully never required or used in anger.

It was used – mostly uncrewed – during emergency drills carried out on occasions such as the Terminal Countdown Demonstration Test (TCDT), allowing the crew to practice their evacuation plans.

With ULA working on SLC-41 during regular Atlas V missions, this week’s announcement that a final test of the pad’s EES has been conducted is another step towards seeing US astronauts launching from the Cape.

“ULA is absolutely focused on the safety of the crews we will be supporting and although we hope to never use it, we are excited to announce the Emergency Egress System is fully operational,” said Gary Wentz, Vice President of Human & Commercial Services.

“Through our partnership with Terra-Nova, a company that designs and builds zip lines for recreational use, a modified, off-the-shelf product has been designed and constructed to meet our needs and reduce costs, while maintaining reliability and safety.”

The egress cables are situated on level 12 of the Crew Access Tower (CAT), 172 feet above the Space Launch Complex 41 pad deck and will allow the crew to evacuate the CAT quickly to a landing zone more than 1,340 feet from the launch vehicle.

The EES can accommodate up to 20 personnel, including ground crew and flight crew.

ULA noted that Terra-Nova, LLC (makers of the ZipRider Hybrid) offered a commercially developed EES based on their “off-the-shelf,” patented designs.

The ZipRider was easily adaptable to ULA’s specific needs while offering an unmatched safety record, and providing the best overall value.

With Boeing’s Chris Ferguson – a former Shuttle commander – enjoying a test ride on the system ahead of its installation at SLC-41, it takes just 30 seconds for the rider to reach a top speed of 40 mph. The riders control their speed by releasing pressure on the handles, with the ability to glide to a gentle stop at the landing zone.

There are 30 feet of springs on each cable located in the landing area to gradually slow a rider down if they forget to brake. Terra-Nova will install a training system located north of the CAT for riders to practice on before final training on the operational EES.

“Crew safety is paramount, and the ULA emergency egress system hits the mark for an effective yet simple system that is adapted from other commercial applications,” said Commander Ferguson, Boeing director of Starliner Crew and Mission Systems.

“We look forward to spaceflight operations next year knowing that every measure to protect the flight and ground crew has been employed.”

There’s also been internal movement on the EES that will be employed for the Space Launch System (SLS) on Pad 39B, years after a trade study began to evaluate the best EES option for safely evacuating crew and engineers from the dizzy heights of the Mobile Launcher (ML). Teams have been told to accelerate options in light of the recent study into changing Exploration Mission -1 (EM-1) into a crewed mission.

Currently, only one patchy render of the system has been acquired (L2) – showing the use of a massive crane.

“Members of the Operations Integration and Analysis team developed, modeled, and created images of an Emergency Egress System concept in support of the Crewed SLS EM-1 Mission Study,” noted a memo via L2.

“The orange frame depicts the fixture with the four baskets lifted by a mobile crane and attached to the west side of the Mobile Launcher. The ground distance from the tower to the end of the slide wire is over 1100 feet, and the wire would be approximately 1300ft long. These images were used in the crewed EM-1 impact briefing to NASA Headquarters.”

The use of a massive crane will be far cheaper than the recommended option from the 2006 study for the since-cancelled Ares I launch vehicle EES, once again pitching several very different designs against each other – including a slide wire system.

The winner of the 2006 study was the spectacular Roller Coaster EES – a giant structure that would have been a permanent fixture out at Pad 39B, rising into the Florida skyline ready to be hooked up to the ML once it had rolled out to the pad with the vehicle.

The Roller Coaster EES included a multi-car high-speed rail system and used gravity to get personnel to a safe haven. It was deemed to be very accommodating to incapacitated crew members as well as limited 3G forces on the people riding the cars with a passive electromagnetic braking system.

It underwent a few redesigns during the life of the Constellation Program, including options to extend the rails to an area outside the BDA directly into a triage site.

For this system, NASA relied on many different areas of expertise: Safety, Medical, Operations Personnel, and the Astronaut Office. Engineers involved in Disney’s roller coaster systems were also part of the design project.

The 2006 trade study – (available on L2 LINK) – helped explain the requirements of the future EES, of which there are numerous considerations. These considerations will be playing into the SLS trade study discussions.

“The EES starts at the crew hatch of the Orion and terminates at the designated safe area. Once the crew access arm is extended, a maximum of 2 minutes for 15 able bodied personnel (six crew members, three closeout crew members, and six fire/rescue members) is allowed to move from the hatch to inside the safe area during vehicle processing at the pad up to T-0.

“The EES shall provide a safe area built to withstand possible blast, fire, and flying debris within the 5,000-ft blast danger area of the tower. The EES shall accommodate the following hazards at the pad: fire, propellant spills, tank overpressure, radioactive-material release, and toxic atmosphere.

“The EES shall provide a clear route from Orion hatch to the egress vehicles with provision for 0.25 gpm/sq ft of water spray and fire detection for the EES before entering the vehicles.”

The list continued for two pages, and despite being by far the most expensive, the Roller Coaster EES scored the highest in nearly all of the requirement categories.

The 2006 study design was refined again in 2008, mainly relating to the initial drop from the ML, in turn providing a CGI view from both onboard the coaster and viewing it drop from various viewpoints (L2 Link to Video).

However, the Constellation Program was then canceled.

Pad 39A’s EES will be mainly focused around the needs of the pad engineers, given astronauts onboard the Dragon 2 will find their spacecraft will be the fastest way of egressing the pad in the event of an emergency ahead of launch.

Dragon 2 will fire her SuperDraco thrusters in the event of a pad abort scenario, as has already been tested.

(Images: Via Boeing, ULA and L2’s specific sections. To join L2, click here: //

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