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When Good Rockets Go Bad: Orion's Launch Abort System

Posted by Jason Davis

20-10-2014 13:30 CDT

Topics: Orion, human spaceflight

One of the tricky parts of launching humans into space is deciding what to do if something goes wrong. No matter the launch vehicle, getting from the ground to orbit requires riding a controlled explosion for about nine minutes. It stands to reason that if the controlled explosion suddenly becomes uncontrolled—or stops altogether—it would be nice to have a backup plan.

On conventional rockets, where a capsule full of humans sits at the very tip of the launch vehicle, it makes sense to have a second controlled explosion at the ready that can pull the capsule away from whatever went wrong. This second rocket motor is usually built into a tower attached to the capsule, which, under normal launch conditions, gets thrown away once the capsule makes it through most of Earth's atmosphere. Future capsule designs by companies like SpaceX plan to forgo the tower and use thrusters built into the capsule. These thrusters could also be used to land the capsule in lieu of parachutes, which normally bring spacecraft home under both normal and abort scenarios.

NASA has a lot of experience with the tower system—it's been used on every American human spaceflight program except Gemini and the space shuttle. Gemini relied solely on ejection seats, but the shuttle's abort scenarios were altogether different beasts. They involved wild acrobatics that fortunately never had to be used, except for the time one of Challenger's main engines failed, and the shuttle hobbled into low-Earth orbit without much of a problem. The trouble with the shuttle's abort modes was highlighted in 1986, when Challenger's external fuel tank disintegrated, throwing the orbiter into the local airflow at forces way above design tolerances. It ripped apart, claiming the lives of seven astronauts. For the shuttle, there wasn't much you could do if the entire rocket stack suddenly fell apart around the orbiter.

So for Orion, NASA's new spacecraft, the capsule and tower system are back. Critics have questioned why NASA didn't try out next-generation abort systems like built-in thrusters or powered landings. They argue Orion is simply an Apollo redux—and that other NewSpace capsules are, as one prominent journalist once told me, "still f—ing capsules." But other considerations aside, capsules and launch abort towers are a safe bet for a government agency trying to please a long list of bureaucrats, politicians and industry leaders. Especially when Orion's end goal—humans on Mars—is far from a safe bet.

Orion's first test flight happens this December, when a Delta IV Heavy rocket will send the spacecraft on a two-orbit shakedown cruise. The spacecraft is currently sitting in the aptly-named Launch Abort System Facility, and won't roll out to the pad until November. At the LAS Facility, Orion's abort tower was gingerly installed by engineers wearing lab coats and hair nets. A hand-written sign taped to scaffolding around the capsule read "MAN LOAD, 2 Persons Total, 1 on Top Deck at a Time," serving as a reminder that people are the heart and soul of spacecraft engineering—a field that occasionally still uses Apollo-era terms like "man load."

Orion integrated with Launch Abort System


Orion integrated with Launch Abort System
Orion sits all buttoned up for its December 2014 test flight following the integration of its Launch Abort System.

The solid-fuel abort motor won't be active for Exploration Flight Test 1—if the Delta IV Heavy goes up in flames, so will Orion. The attitude control motor, which consists of eight gas generator-driven valves ringing the top of the LAS, won't be armed, either. The only functional rocket motor will be the jettison motor, which fires a few minutes into flight, pulling the LAS tower away from Orion, leaving the capsule exposed to space.

When actual astronauts go for a ride in Orion—by current timelines, at least seven years from now—they'll have the entire might of the LAS at their disposal. Should they need to abort, they'll be subjected to extreme forces. The launch abort motor provides 400,000 pounds of thrust, enough to accelerate the capsule from zero to 800 kilometers per hour in three seconds—and that's on top of whatever speed the launch vehicle is already going. The published numbers on how many Gs this produces varies, but it's somewhere north of 11. Eleven Gs are survivable, and the astronauts should stay cognizant enough to flip switches inside Orion while they travel a mile uphill and a mile downrange of whatever calamity is engulfing the Space Launch System, the rocket slated to carry Orion. Eleven Gs are easier to take when they push you back into your seat, as opposed to the opposite direction, where you have to start worrying abut your retinas detaching from the tissue inside your eyeballs.

Like Orion, the LAS was developed and built when NASA's human spaceflight program was still called Constellation, and the rocket system was called Ares. The first and only full test of the integrated capsule and abort system took place in May 2010. On that day, at New Mexico's White Sands Missile Range, Orion left the pad so fast that one of the video cameras trained on the pad hardly saw a thing, quickly panning upward into a trail of smoke, with a "TILT LIMIT" message flashing on the screen. Later high-frame video revealed the full magnificence of the test. As the capsule ascends, its attitude control motor fires continuously, keeping the stack upright. On its own, the LAS is aerodynamically unstable—it wants to flip 180 degrees. If you've ever chucked a dart fins-first at a dartboard, you've seen this effect in action—the dart immediately begins to reorient itself into the proper alignment. Providing you do this delicately enough, the dart will stick in the board tip-first, making you look like a carnival knife-throwing expert.


Orion Pad Abort 1 Highlights
The first and only end-to-end test of Orion's Launch Abort System was conducted on May 6, 2010 at White Sands Missile Range in New Mexico.

When Orion reaches the apex of its abort flight, it is allowed to make its 180-degree flip. The capsule of astronauts, who have already realized they will not go to space today, experience a brief moment of weightlessness before the capsule starts falling back to Earth, heat shield down. The jettison motor fires, pulling the LAS away from Orion. At White Sands, the LAS landed back on the desert floor in a smoldering crater.

Orion, meanwhile, sheds its Forward Bay Cover, a ring at the top of the capsule protecting the parachutes. Two drogue chutes deploy, stabilizing the wobbling capsule. The drogues pull out Orion's three main chutes, no doubt eliciting a sigh of relief from the spacecraft's occupants. During the pad abort test, Orion came to a rest among some creosote bushes, hardly scathed from the fire and fury of the abort motors that engulfed it in smoke a couple minutes earlier. 

If the LAS ever gets used with astronauts aboard, it will be for just the second time in the history of spaceflight. In 1983, two cosmonauts aboard a Soyuz capsule were safely pulled away from an exploding rocket, coming to rest on the Kazakhstan steppe a few kilometers downrange. Hopefully, the incident will continue to stand alone in the annals of human spaceflight. One of many compelling reasons for sending people to Mars is making humanity a multi-planet species. But the first step to is getting off Earth safely in the first place, and that starts with a good backup plan.

Orion discards its Launch Abort System


Orion discards its Launch Abort System
In this artist's concept, Orion's Launch Abort System fires its jettison motor, pulling the abort tower away from the spacecraft.
See other posts from October 2014


Or read more blog entries about: Orion, human spaceflight


Brian: 10/20/2014 02:16 CDT

"NASA has a lot of experience with the tower system—it's been used on every American human spaceflight program except the space shuttle." Does Project Gemini not count as an American human spaceflight program?

Messyq: 10/20/2014 03:05 CDT

The first manned flight is SEVEN years from now? No test flights? No Apollo 8 reruns to make sure the thing works? So it' just the Asteroid walk in lunar orbit and that's the end of it? Why are we wasting all this money?

CJ: 10/20/2014 03:25 CDT

I think it's a mistake to not have a fully loaded and armed LAS on EFT-1. Should the rocket explode ('s very proven), at least you get live LAS test data. It's reminiscent of the test of the Apollo LAS. It was launched on a Little Joe, but the vehicle's roll controls were mis-wired. As a result, the rocket entered a critical roll condition and started to break apart -- at which time the LAS did what it was designed to do. The failed test turned out to be the best test.

ethanol: 10/20/2014 07:09 CDT

It's a beast, no doubt. However, weighing in at 7 metric tons!! Orion's launch abort system alone is 1500kg heavier than an entire dragon capsule, fully fueled. And this is where I have trouble seeing how Orion fits in to a deep space program. Its HUUUUUGE, but when it comes down to long, multi-month missions, there still isn't enough space, life support, or storage capacity in this capsule alone. So you need a separate habitat module. But then the only real point of the capsule is to safely launch/land the crew. So why bring this massive heavy capsule along for the whole trip? It totally makes sense for a more muscular trans-lunar program (what it was designed for in the first place), where you are better off sticking with a single craft. But if you need a separate habitat module in the first place, it makes no sense to launch a this beast with its 5m heat shield, let alone bring it all the way to mars and back, when you all you really need is a small re-entry capsule. Ok sorry for rambling on like this about Orion, and almost entirely ignoring your excellent article on its badass LAS, I just get so AAAANGRY.

Dougforworldsexplr: 10/20/2014 08:30 CDT

I too think there might be a problem with not having enough living quarters on Orion to get to Mars and I would suggest that at least after Obama leaves office if not before that the president and NASA make the Moon instead of an asteroid the initial destination for the Space Launch System. The Moon still is a good destination in terms of strategic location, resources, accessibility, science objectives and inspiration certainly to me much more than any asteroid or moon of Mars although I would like to see a manned mission to Mars as soon as possible too. However it is good to remember that Robert Zubrin who of course is an informed engineer familiar with space flight didn't envision using very large capsules with manned missions to Mars even using chemical rockets like SLS but was focused on astronauts living off the land. Maybe his Mars Direct plan could use the Space Launch System if it incorporated Mars landers.

Jason Davis: 10/20/2014 09:58 CDT

Thanks all, as always, for your comments. Brian: Fascinating, I didn’t know that about Gemini — My brain linked the black capsule with Mercury and my mind pictured a tower. Here’s a neat technical article for anyone else that’s interested (h/t ethanol: I think in order to determine whether the LAS weight is reasonable compared to existing and past rocket systems, we’d need to compile a lot more information, including safety requirements, the amount of force produced, capsule weights (which could vary depending on the type of mission), wet and dry mass (armed vs. inert?), etc. Messyq: Yep, EM-2 is scheduled for 2021 (though I guess if it launches early that year it could be closer to six years, not seven). CJ: That same thought occurred to me as I was writing this, but I didn't have any extra time to spend looking for the reason. As I was searching for a couple of these answers, I noticed recently did a technical review of the LAS, including details about the upcoming tests. The in-flight abort test atop a Peacekeeper missile should be fun to see.

porkfight: 10/21/2014 07:40 CDT

ethanol: Orion was sized to support 4-6 crew on multi-week missions beyond the van allen belts in cis-lunar space. You can't fit all the equipment, radiation protection, and supplies necessary to do that in a smaller spacecraft. As for mars, that capability lets you take advantage of better transfer orbits, mars cycler orbits, and good staging points such as earth-moon or earth-sun Lagrange points. Jason: An abort system that can be jettisoned was selected not for conservatism, but because it's inefficient to carry all that propellant and engine hardware with you to escape velocity and back. A removable system and parachutes is a far more efficient approach for BEO missions. On a side note, a sidewall abort engine system (MLAS) was developed for Orion and a prototype flown from wallops back in 2009. It looked like the approach SpaceX decided to pursue, except it was ejectable and not carried all the way to orbit.

Arbitrary: 10/23/2014 05:07 CDT

@porkfight Dragon uses (*will use* if all goes well) the same fuel to land anyway, whether during launch abort or as intended. Fuel mass and rocket size is not important if one can reuse the hardware. SLS/Orion is neither rational nor innovative. But I'm not complaining about it, because I know that government can only do things extremely inefficiently and absurdly expensive and that its chaotic nature prevents it from having any foresight in planning. Rather going back to the 1960's with SLS/Orion, than having nothing. Once it exists an idea of what to use it for may turn up.

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