NASA Finds Weight Savings With Fewer Backup Systems In Next Spaceship
NASA is shaving weight on the next-generation U.S. spaceship, the Orion crew exploration vehicle (CEV), by cutting back on backup systems, according to Skip Hatfield, project manager for the CEV in the Constellation Program.
But reducing some of the backup systems that normally would be included won’t lessen safety for the ship and its crew, Hatfield said.
He spoke with reporters after a Space Transportation Association breakfast at a restaurant near the Capitol building.
It is critical to reduce some of the excess weight on the CEV, because every pound that has to be hauled into space, to the moon or farther is highly expensive, he said.
At the same time, these efficiency moves require a change in the long-enduring mindset of NASA and contractors, he said.
"It’s almost a dogma, that in order to have a safe system, thou shalt have two redundant strains of every [system] we do, you know, for safety critical items, and similarly for mission critical" systems, Hatfield said.
"That’s not always what you want, especially in a spacecraft like this, where you’re weight constrained. You can’t have — it’s just like a car," you can’t go to extremes such as providing two engines, one as a backup in case the other one fails.
"The systems designers tend to say, you want [duplicating backup systems] in every single system," he said. But NASA leaders "told the teams on a ground rule point of view, is, look, we’re going to give you this assumption going in that you only get, you know, one redundant system, one fault tolerance."
In other words, instead of multiple backup systems, there might be just one backup.
After that change in approach, he said, the NASA leaders said, "Now go tell us what your system weighs."
This has to be done carefully, to ensure that safety is maintained, Hatfield said.
"We’ve been doing in parallel with that, we’ve been doing probabilistic risk assessments, fault tree analyses and other analytical tools to look at the whole system, and say, okay, where are the places that we now feel like we’re weak, from an analytical point of view in terms of having a system that we’re comfortable with from a safety and mission success point of view."
Sometimes, he said, it turns out that the new efficiency moves to get by with fewer backup systems won’t work, and the old approach still must be followed.
"In some cases, that causes us to go back, okay, yeah, we really did need [more backup] for this particular thing, yes," he said.
"In most cases, though, we find, we didn’t necessarily need that, but there’s another way that’s maybe not a complete redundant system, but provides a simpler capability to do that function in an emergency, that’s much lighter, and therefore allows you to get the same net effect" of being able to survive a primary system failure.
In any event, though, Hatfield said there is no diminution of safety for the ship and crew, "absolutely not. That’s one of our critical ground rules in this whole effort, is the overall system safety. We want to keep it within the same targets we’ve been trying to achieve all along."
Using this approach of cutting back on backup redundancies has yielded some weight savings, Hatfield said. But those moves often, in turn, yield further weight reductions.
It works this way, he said: "Some of the things have cascading effects." After removing a given redundant or unneeded system, "you start finding, then, okay, gee, I don’t need as many boxes as I once had, electronic boxes. Well, now I need less power. Okay, so now the radiators don’t have to be as big. The solar arrays don’t have to be as big. The power distribution boxes don’t have to be as heavy to switch all that power. You know, so it cascades to a lot of things in the vehicle."
Ultimately, the CEV spacecraft is likely to tip off at a total weight about equal to five or six average-sized cars.?"The capsule itself, our target’s about 19,000 pounds," Hatfield said. "We’ll probably be a little heavier than that in the capsule when the smoke clears," including management reserves and margins.
Earlier in the breakfast, the audience heard from Jeff Hanley, the NASA program manager for the overall Constellation Program (including the CEV and Ares lifter).
"Every pound we send [to the moon] is very expensive," Hanley said.
He also said that another efficiency is that much of the money, time and effort invested in the smaller Ares I lifter will be useful for developing the bigger Ares V.
Hanley said there is a 65 percent probability, or "two-thirds likelihood of success," that Constellation will achieve its scheduled March 2015 initial operational capability for lifting crews into orbit.
Before that, there will be a half-decade period after retirement of the space shuttle fleet when the United States won’t be able to send even one astronaut into low Earth orbit.
Hanley said pouring more money into the Constellation Program might not mean that Orion-Ares would be operational much sooner, but more money might increase confidence in chances of success for the program.
In June 2019, the United States should send humans back to the moon, he said.
Once there, astronauts will use some unusual vehicles for exploration, such as rovers that could range out more than 100 miles from the landing site, and a six-wheeled explorer that can walk over obstacles or up over boulders, and drill into the lunar surface.
Eventually, even longer-range vehicles might be possible, perhaps solar powered, or, later, nuclear-powered.
The lunar missions will involve many new systems and technologies.
For example, the NASA Lunar Architecture Team is examining concepts for habitation, rovers, and space suits.
Astronauts will set up a lunar outpost — possibly near a south pole site called Shackleton Crater — where they’ll conduct scientific research, and test technologies and techniques for possible exploration of Mars and other destinations.
Even though Shackleton Crater entices NASA scientists and engineers, they don’t want to limit their options, according to NASA. To provide for maximum flexibility, the space agency is designing hardware that would work at any number of sites on the moon.
Data from the Lunar Reconnaissance Orbiter mission, a moon-mapping mission set to launch in October next year, might suggest that another lunar site would be best suited for the outpost.
First, astronauts on the moon will need someplace to live. NASA officials had been looking at having future moonwalkers bring smaller elements to the moon and assemble them on site.
But the Lunar Architecture Team found that sending larger modules ahead of time on a cargo lander would help the outpost get up and running more quickly. The team also is discussing the possibility of a mobile habitat module that would allow one module of the outpost to relocate to other lunar destinations as mission needs dictate.
NASA also is considering small, pressurized rovers that could be key to productive operations on the lunar surface. Engineers envision rovers that would travel in pairs — two astronauts in each rover — and could be driven nearly 125 miles away from the outpost to conduct science or other activities. If one rover had mechanical problems, the astronauts could ride home in the other.
Astronauts inside the rovers wouldn’t need special clothing because the pressurized rovers would have what’s called a "shirt-sleeve environment." Spacesuits would be attached to the exterior of the rover. NASA’s lunar architects are calling them "step in’ spacesuits because astronauts could crawl directly from the rovers into the suits to begin a moonwalk.
NASA also is asking industry for proposals for a next-generation spacesuit. The agency hopes to have a contractor on board by the middle of next year.
The space agency will spend the next several months communicating the work of the Lunar Architecture Team to potential partners — the aerospace community, industry, and international space agencies — to get feedback that will help NASA further refine plans for the moon outpost.
The goal is to have finalized plans by 2012 to get "boots on the moon" by 2020.