Spacecraft engineers are hard at work bending metal, testing and refining designs for the launch vehicle and crew capsule chosen by the U.S. government to take humans all the way to Mars. The spaceships are starting to take shape, but the path ahead is far from certain.

Like development of the space shuttle for operations in low Earth orbit, the U.S. effort to send humans into the Solar System brings together NASA and top U.S. aerospace primes—specifically Boeing and Lockheed Martin, for the heavy-lift Space Launch System (SLS) and Orion crew capsule, respectively.

But this time new players are in the arena—SpaceX, Blue Origin, Bigelow, to name a few—and are making their presence felt.

The route NASA is following as principal exploration customer for the private sector has plenty of critics. Among them are decision makers in other spacefaring nations that depend on NASA’s leadership—and the relatively rich funding that sometimes buys it—and the authors of a new congressionally mandated National Research Council (NRC) report on U.S. human spaceflight prospects (AW&ST June 9, p. 23).

As the debate goes on, the metal-bending work advances at Kennedy Space Center in Florida and the Michoud Assembly Facility in New Orleans. First flight of an Orion prototype atop a modified Delta IV Heavy is set for December. The first SLS is scheduled to fly in 2017, carrying an Orion but no crew. That flight—Exploration Mission-1 (EM-1)—will take an Orion, with a design based in part on results from the December flight test, into the distant retrograde orbit (DRO) around the Moon that has been designated, for now, as the next area of operations in space for U.S. astronauts.

“We can stay in that orbit for an extended period of time, maybe 100 years, a century, and not have to do any attitude control at all,” says William Gerstenmaier, associate NASA Administrator for human exploration and operations. “If we go anyplace else—to L-1 or L-2, the Lagrangian points around the Moon—there is some small attitude maneuver that needs to occur, probably every two weeks. We also see that once you get into the vicinity around the Moon, it is fairly easy to move from this distant retrograde orbit to either L-1 or to L-2. You can go from L-1 to L-2 with very little change in velocity to your spacecraft.”

Sometimes called cislunar space, NASA sees the region around the Moon as a “proving ground” for Orion, SLS and the astronauts and mission controllers who will operate them. A prime objective of the December flight test—designated EFT-1, the first exploration flight test—is to trial run the Orion thermal protection system (TPS) in atmospheric reentry conditions approaching those the capsule will experience returning from the Moon.

That heat shield, made of the same ablative Avcoat material that protected the Apollo command modules, was attached to the EFT-1 capsule this month (see photo, page 42), and then stacked on a test article representing the service module that will carry power and propulsion systems based on the European Space Agency Automated Transfer Vehicle (ATV). In EFT-1, the Delta IV will take the heavily instrumented Orion capsule on a 4.5-hr. two-orbit swing around Earth, boosting it to an altitude of 3,600 mi. for a plunge back into the atmosphere at more than 20,000 mph—80-85% of the speed it would have coming back from the Moon.

In addition to the Avcoat heat shield—the largest ever built—the test will help engineers evaluate the load-bearing fairings that will enshroud the service module, and exercise the parachute and ocean-recovery systems after it splashes down in the Pacific Ocean off the coast of California.

“We’ll be able to do the aerodynamic performance, the fairings, separation of the fairings, separation of the crew module and service module, and then reorientation of the crew module and entry,” says Larry Price, Lockheed Martin’s deputy Orion program manager. He says most of the items being developed will be addressed on this flight, “virtually everything except crew interfaces and deep space sorts of things—lunar navigation and communication.”

The TPS instrumentation may let Orion designers pare the weight of the heat shield, if the data they generate show the initial design was overly conservative. The same holds for how well the capsule handles the water-landing impact, and other factors EFT-1 will monitor. All will help engineers on both Orion and SLS as they work toward the best combination of capsule weight and launch vehicle performance for the missions that are planned.

“We will learn things from the flight test which we can then apply to refinement of the design of the vehicle,” Price says. “We have a target of removing 4,000 pounds out of the crew module/service module combination.”

As was the case with the Apollo vehicles that last took men to the Moon, Orion is a small tip at the end of a very large spear. Tools built to manufacture the SLS at NASA’s Michoud site clearly illustrate the other end of the size scale.

At 170 ft. tall, the friction stir welder that will assemble SLS core stages is the largest in the world (see photo, page 43). Designed, delivered and installed by Sweden’s ESAB, the tool is highly automated to hold down cost, even on a low-production piece like the SLS.

“We’ll take the domes, the teacup upside down, weld it to a barrel [with a] circumferential weld,” says Virginia “Ginger” Barnes, Boeing’s SLS program manager. “Then the tool lifts that, and you slide another barrel under it, do another circumferential weld, and however many you need, and then you put the teacup right side up [at the bottom]. It’s like a reverse Pez dispenser.”

The finished core stage will measure more than 200 ft. tall, with a diameter of  27.6-ft., five barrel sections for the liquid hydrogen tank, and two more for liquid oxygen to feed the vehicle’s four RS-25 space shuttle main engines. Initially those engines will be surplus from the shuttle program, although work is set to begin this summer on a throw-away version of the reusable shuttle hardware, according to Dan Dumbacher, Gerstenmaier’s deputy for exploration systems development.

For EM-1—the first, unmanned flight of SLS to the lunar distant retrograde orbit—NASA intends to use the core stage Barnes’s crew is building with the Delta IV Heavy upper stage that will also fly on the test flight this year. That same configuration, which can lift 70 metric tons to low Earth orbit, will also work on the first manned Orion flight—EM-2—to DRO.

But Congress ordered an SLS able to deliver at least 130 metric tons to LEO. That requires a new upper stage and a more powerful pair of strap-on boosters than the five-segment solid-fuel versions—descended from the four-segment version used by the shuttle—that will go on EM-1 and EM-2.

Since Congress did not include enough funding to develop both the upper stage and the advanced booster simultaneously, NASA has tentatively decided to start developing an “Exploration Upper Stage” (EUS) that will provide the SLS with a 105-metric-ton capability off the pad, and better in-space performance for work in the proving ground around the Moon.

“In a cost-constrained environment, if we do the upper stage first, it actually gives the agency more capability to do more missions on the way to Mars, recognizing that I am still going to have to do the advanced boosters for the 130-metric-ton Mars case,” says Dumbacher.

The SLS program office at Marshall Space Flight Center calculates that the EUS will need a total engine performance in the 120,000-lb.-thrust range, with in-space restart, and is studying possible engine options. These include the J-2X derivative of the Saturn V upper-stage engine originally baselined for the defunct Ares V upper stage and now nearing completion, the venerable RL-10 built by Aerojet Rocketdyne, Europe’s Vinci and Japan’s MB-60.

The J-2X is a heavy engine, and would need to be throttled back to qualify, while business arrangements for the MB-60 are problematic, making the RL-10 in a gang of four the likely EUS engine. However, on May 15 Dumbacher emphasized that the trade study at Marshall was not finished.

“We’re trying to be objective about all of the engines out there,” he says. “We are even looking at some of the LOX-methane work that Blue Origin and others are doing.”

The Orion and SLS vehicles in development now, even with the capsule at its EFT-1 weight, can handle EM-1 and EM-2, although it is unclear whether the Exploration Upper Stage would replace the Delta IV upper stage on EM-2.

While Price says of Orion: “The lighter it is, the more we can do with it,” he notes that the vehicle’s official name is the Multi-Purpose Crew Vehicle, and that its weight will fluctuate with the mission requirements. “We are designed to be a multi-purpose vehicle, so there is a lot of flexibility in what the configuration would be, sort of unique configuration in the form of kits for each flight,” he says. “So we can accommodate different objectives.”

That kind of flexibility did not necessarily sit well with the NRC panel that reviewed U.S. human-spaceflight options over a period of 18 months. Instead, the panel recommended more focus and more money, from both NASA and its international partners. John C. Sommerer, a retired senior engineer from the Johns Hopkins University Applied Physics Laboratory who headed the study’s technical panel, suggests the agency’s “capabilities-driven” approach will unnecessarily add to the cost of landing humans on Mars.

“Capabilities-based, you are deciding where you can go based on what you have on hand,” Sommerer says. “You may be following multiple pathways at once.”

After EM-2 in 2021, NASA plans to use its proposed “Asteroid Redirect Mission” as a focus for developing technologies—capabilities—that will be needed over the long haul to Mars. These include solar-electric propulsion and sensors and other gear for rendezvous and proximity operations beyond low Earth orbit. Drafted in part at the White House Office of Science and Technology Policy as a way to accomplish President Barack Obama’s vow of a manned mission to an astroid by 2025, the concept of building a spacecraft to capture a small Earth-crossing asteroid and nudge it into lunar distant retrograde orbit has met an unenthusiastic response on Capitol Hill, and with the NRC panel as well.

NASA is evaluating the 108 responses to its call for outside input on technical and partnership arrangements for an asteroid redirect mission. Follow-on 180-day studies from those selected next month will feed into a mission concept review in February 2015, Gerstenmaier says.

The NRC panel included the asteroid-capture in its “pathways” to Mars, along with a lunar landing and a visit to the second Earth-Moon Lagrangian point, beyond the far side. “A pathways-based approach will set specific engineering requirements as a function of progress through the pathways, allowing NASA to focus investment essentially on burning down the major technological challenges required for deep-space exploration,” said Sommerer.

The NRC panel also recommends early consultation with NASA’s international partners, before a decision “soon” on which path to follow, as a way to infuse realism into a global effort toward a human mission to Mars in the next two to three decades. And it joins most of those partners in viewing the lunar surface as a more productive way station on the path to Mars than NASA’s approach.

“There are some compelling reasons for including the lunar surface as a stepping stone in any particular pathway that would ultimately be chosen,” the panel states.

Gerstenmaier calls the NRC report “well-written,” but says it is not realistic. “The problem is when folks look at us, they would like to have—from the beginning all the way to the end—a concrete plan with every milestone and a work breakdown structure, cost, line item, and I can’t get there because it is really too complex a problem.”

Among the decisions that cannot be made today because not enough is known, Gerstenmaier mentions the in-situ resource utilization experiment, which “dramatically changes what we have to take”; use of a high-elliptical Earth orbit as a transfer point for prepositioning supplies at Mars; use of a human-tended “exploration accommodation module” under consideration for lunar orbit as a way station in Mars orbit for landings there; and using the Martian moons Phobos and Deimos for the same purpose.

“There’s tons of branches and permutations of this thing going forward,” Gerstenmaier says. So technology and funding levels will determine the goals pursued and how quickly NASA can pursue them, he notes. 

 

Tap the icon in the digital edition of AW&ST for an interactive look at human exploration targets in the Solar System, or go to AviationWeek.com/exploration