Future Pad Escape options – From Slidewires to Roller Coasters
Evaluations into pad escape options for the crewed vehicles of the future are currently taking place, with the Space Launch System (SLS) employing a trade study that includes the spectacular Roller Coaster Emergency Egress System (EES), while the United Launch Alliance (ULA) may opt for a Shuttle slide wire concept for their crewed Atlas V.
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.
Escape systems have existed since the early days of the space program. However, the Mercury and Gemini Programs did not have an official launch pad escape system, instead relying on ejection seats (Gemini) or a Launch Escape System (LES – for Mercury) – a separate solid rocket motor attached to the crew capsule that could pull the astronauts to safety in the event of an emergency.
Known as a Pad Abort, this option will continue to exist with vehicles such as Orion – atop of the SLS – using the Launch Abort System (LAS) motors to provide an emergency exit from a serious launch vehicle failure whilst still on the pad.
A rare example of a pad abort – some claim to be the only documented example – was observed during the final seconds of the Soyuz T-10-1 countdown, when the vehicle caught fire at ignition, resulting in the LAS firing and lofting the crew to relative safety.
Video footage captured the moment the vehicle began to fail on the pad, prior to the LAS firing the Soyuz capsule away, just seconds before the vehicle was engulfed by fire.
The video shows a line of Soviet military leaders witnessing the dramatic abort, acknowledged only by one General calmly adjusting his collar as the pad abort was initiated. It was reported that the crew landed safely, just four miles away.
However, a pad abort using the LAS only provided an option once the crew were secured into their vehicles, with the hatches closed. A serious problem during crew ingress, or when the vehicle still had engineers up at the pad, required the implementation of the EES.
Early versions of the EES hardware were fairly simple, gravity-powered systems with a requirement to be passive/unpowered, in case the emergency cut power to the pad.
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 still exists in good condition today (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 slidewire 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 slidewire 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.
Future EES Options:
The Slidewire option remained relatively unchanged throughout its 30 year 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 practise their evacuation plans.
The baskets were released for a final time from the 195 foot level of the Fixed Service Structure (FFS) at Pad 39A in March of this year, following the retirement of the Shuttle and the transition of 39A into mothball status.
However, another slidewire system may be used for the new generation of vehicles, with the United Launch Alliance (ULA) evaluating what they will need at their pad structure, as their Atlas V prepares to host Commercial Crew integrated Capability (CCiCap) initiative award winners, Sierra Nevada Corporation (SNC) and their Dream Chaser vehicle, along with Boeing’s CST-100.
Before both vehicles can be launched by the human-rated version of the Atlas V, modifications to the launch pad will be required, as the vehicle transitions from cargo to crew.
These modifications will include the installation of an elevator and ingress platforms, but also the potential for a full EES involving the slidewire option.
“We are still looking at different options for emergency egress. Detailed hazard analysis of the launch operations is a key determinant and is being refined,” noted Dr George Sowers, ULA VP for Human Launch Services, during a Q&A session with NASASpaceFlight.com members.
“We have the option of implementing a shuttle-like slide wire system, if required.”
For the much larger Space Launch System (SLS), a trade study is being carried out to evaluate the best EES option for safely evacuating crew and engineers from the dizzy heights of the Mobile Launcher (ML).
The trade study – ongoing at the Kennedy Space Center (KSC) – is following a similar path to the 2006 study for the since-cancelled Ares I launch vehicle EES, once again pitching several very different designs against each other – including a slidewire system.
Also under consideration is the winner of the 2006 study, the spectacular Roller Coaster EES – a giant structure that would be 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.
“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 continues 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.
“An unpowered fixed single-rail system from the access arm level of the ML tower to the existing bunker would be used. The rail cars could be enclosed to provide personnel protection. Each rail car can hold four to six people,” overviewed the presentation on the winning concept.
“The rail would follow the ML tower vertically down to the pad surface, then turn and continue close to the ground to the safety bunker. A passive magnetic and friction braking system will decelerate the cars at the track’s end as well as prevent the cars from hitting each other.”
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).
Should the Roller Coaster EES win the latest trade study, engineering teams will have a large database to drawn on via the Constellation Program’s evaluations.
(Images: Via L2’s specific sections, which include presentations, videos, graphics and internal updates. L2 Members, *Click Here* for L2’s full collection of EES resources. Other images via NASA.)
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