Mittwoch, 10. Juli 2019 - 07:40
10.07.2019
NASA’s orbiting Lunar Gateway is either essential for a moon landing or a boondoggle in the making
When astronauts first landed on the moon a half century ago, they went there in a single shot: A Saturn V rocket launched the Apollo command and service module and the lunar lander, which entered into a low orbit around the moon. The lander then detached and descended to the surface. After 22 hours in the moondust, the Apollo 11 astronauts climbed into the lander’s ascent stage and returned to the command module for the trip back to Earth.
NASA’s current plan for sending astronauts back to the moon, which may happen as soon as 2024, goes a little differently. A series of commercial rockets will first launch the components of a small space station, which will self-assemble in high lunar orbit. Then another rocket will send up an unoccupied lunar lander. Finally, a giant Space Launch System (SLS) rocket will launch an Orion spacecraft (which looks a lot like an Apollo command module), with astronauts inside. Orion will dock with the space station, and some of the astronauts will transfer to the waiting lander. Finally, the astronauts will descend to the lunar surface. After their sortie on the moon, they’ll return to the orbital station, where the crew will board Orion for the trip home.
That lunar orbital space station is envisioned as a collection of modules, including habitats, an air lock, and a power and propulsion unit. NASA calls it the Gateway .
Its origins predate NASA’s current plan to return to the moon, which the agency recently rebranded as the Artemis program , and the proposed facility has grown and shrunk in response to changing policies and budgets. NASA argues that the Gateway is an essential part of its human space exploration plans. But others wonder if it’s necessary at all.
The Gateway’s origins can be traced back to President Barack Obama’s cancellation of NASA’s last plan to return humans to the moon (the Constellation program ). In an April 2010 speech announcing a new direction for NASA’s human spaceflight efforts, Obama called on the agency to develop vehicles for deep space missions, starting with a trip to a near-Earth asteroid in 2025. However, NASA quickly determined that this goal was too ambitious, as it would require a crewed mission lasting many months. So the agency suggested an alternative: Instead of sending astronauts to an asteroid, they would bring an asteroid to the astronauts.
That idea led to the Asteroid Redirect Mission (ARM) , announced in 2013. A robotic spacecraft would grab a small near-Earth asteroid—no more than 10 meters wide—and gradually shift it into a high, stable orbit around the moon, called a distant retrograde orbit, where it could be visited by astronauts on short-duration missions. But doubts about ARM’s feasibility and utility doomed the program when it came up for budget approval in the U.S. Congress.
In 2017, under the new administration of President Donald Trump, NASA pivoted again. The agency had long maintained that the space program would benefit from having a presence in cislunar space—the area between the Earth and the moon—to test technologies for future missions to Mars and beyond. NASA’s next proposal, revealed in March 2017, was a concept called the Deep Space Gateway : a collection of modules in a distant retrograde orbit around the moon. By the late 2020s, astronauts at this built-out Gateway could begin assembling a separate spacecraft, the Deep Space Transport, for long-duration missions to Mars.
That plan also fell by the wayside, though, after President Trump declared a new priority for NASA: sending astronauts back to the moon’s surface, and beginning to build a permanent presence in space.
“This time, we will not only plant our flag and leave our footprints,” President Trump said in December 2017. He had just signed a space policy directive that refocused the U.S. space program on human exploration, and most immediately on returning American astronauts to the moon. The “long-term exploration and use” of the moon, he said, was a step toward even grander projects. “We will establish a foundation for an eventual mission to Mars, and perhaps someday, to many worlds beyond.”
The directive called on NASA to return humans to the surface of the moon using commercial and international partnerships—but left it up to the agency to figure out the best way to do so. NASA’s approach was to repurpose the Gateway, formally renaming it the Lunar Orbital Platform–Gateway and presenting it as a staging area for lunar missions. The Gateway would be assembled in a different orbit, a highly elliptical one over the poles of the moon called a near-rectilinear halo orbit. Spacecraft from Earth can reach this orbit using minimal fuel, so supplies could be shipped up relatively easily and cheaply. With this setup, NASA said, astronauts would return to the lunar surface in 2028.
NASA also worked to bring in international partners, many of which were already involved with the International Space Station . By early 2019, the Gateway was taking form in a much grander configuration than ever before. The proposed configuration featured a power and propulsion element, which would use a solar-electric system to power the Gateway and move it around cislunar space, as well as two habitation modules, utilization and multipurpose modules, and a robotic arm. Canada promised to build the robotic arm; in February 2019 Canadian prime minister Justin Trudeau announced that the country would spend CAN $2 billion on the project. In the Gateway concept drawings, other modules were optimistically emblazoned with the logos from the European Space Agency (ESA), the Japanese Aerospace Exploration Agency (JAXA), and Roscosmos, the Russian space agency.
“This is an aspirational vision of the Gateway,” said NASA administrator Jim Bridenstine in a speech in mid-March. He was discussing NASA’s fiscal year 2020 budget proposal, which included US $821 million for Gateway development. But, he added, he had talked with the leaders of other space agencies, and “they are very excited about partnering with us on going to the moon.”
Two weeks later, the aspirational vision changed dramatically once again. In a speech at a meeting of the National Space Council on 26 March, Vice President Mike Pence ordered NASA to accelerate its plans for lunar return. “At the direction of the president of the United States, it is the stated policy of this administration and the United States of America to return American astronauts to the moon within the next five years,” Pence announced in the speech. The ambitious goal—a moon landing in 2024—took the world by surprise.
It also sent NASA scrambling to figure out how to reach that goal. In an April speech at the Space Symposium in Colorado Springs, Bridenstine said NASA would adjust its plans for lunar exploration, and would focus on only the basic elements required to get humans to the surface in five years. “The first phase is speed. We want to get those boots on the moon as soon as possible,” he said. “Anything that is a distraction from making that happen we’re getting rid of.” And much of the Gateway seemed to qualify as a distraction. Bridenstine suggested that the only parts of the Gateway needed for a lunar landing would be the propulsion module and a habitation node where the Orion spacecraft and lunar landers could dock.
NASA’s international partners were also shocked. The space agencies that had been considering building Gateway components suddenly didn’t know when, or even if, their potential contributions would be needed. Bridenstine acknowledged this confusion in his April speech. “It has been a concern to our international partners, and they have expressed that to me throughout this conference,” he said. But, he argued, these partners could still play roles in the second phase of NASA’s lunar exploration plans—after that initial 2024 landing. Then, he said, NASA will prioritize long-term sustainability in cislunar space, which will include building out the Gateway to something like the configuration discussed earlier.
In the weeks that followed, NASA increasingly talked about building a “minimal” Gateway to support a 2024 lunar landing. In May, NASA announced that the White House would seek an additional $1.6 billion in funding [PDF] in 2020 as a “down payment” toward meeting that deadline. The additional money is primarily intended to support commercial companies in their speedy development of lunar landers and to boost the lagging SLS rocket and Orion spacecraft programs, both of which are years behind schedule and billions of dollars over budget. The proposal also cut $321 million from the budget for the Gateway.
This revised budget “refocuses Gateway a little bit,” said NASA’s associate administrator for human exploration and operations, William Gerstenmaier , in a hastily arranged call with reporters. “Gateway was focused towards a little bit of a larger capability, more than we need just for the landing. This focused Gateway back to just the initial components that are needed to land on the moon.” At the end of May, Bridenstine announced that NASA had selected the Colorado-based company Maxar Technologies to build the Gateway’s power and propulsion element.
Critics of the Gateway argue that NASA shouldn’t just scale back the space station—it should cancel the project altogether . If you want to go to the surface of the moon, the refrain goes, go there directly, as the Apollo missions did a half century ago. Building an outpost in lunar orbit adds expense, delay, and complications to a task that is already hard enough.
Among those critics is former NASA administrator Michael Griffin . Last November, during a meeting with an advisory group of the National Space Council, he offered a devastating critique of the space station. “The architecture that has been put in play, putting a Gateway before boots on the moon, is, from a space systems engineer’s standpoint, a stupid architecture,” he said. NASA should instead go directly to the lunar surface, he argued, and only then set up something like the Gateway to support such missions, particularly once astronauts are able to tap into resources like water ice at the lunar poles. “Gateway is useful when, but not before, they’re manufacturing [rocket] propellant on the moon and shipping it up to a depot in lunar orbit.”
Another prominent critic is Robert Zubrin, founder and president of the Mars Society . He likens the Gateway to a tollbooth , arguing that it adds expense to any future missions to the moon or Mars. He has proposed an alternative plan called Moon Direct that would make use of existing commercial launch vehicles to gradually build up a base on the lunar surface.
Aware of such criticisms, NASA is defending the Gateway. In May, the agency quietly distributed a white paper titled “Why Gateway? ” [PDF] that makes the case for the space station. “NASA’s position, based on technical and programmatic analysis, is that the Gateway enables the most rapid landing of the next Americans on the moon,” it stated. Among the reasons it cited: Orion’s main engine is too weak to propel the spacecraft into a low orbit around the moon, requiring a staging area like the Gateway in its higher orbit.
“On balance, the near- and long-term benefits of pressing forward with the Gateway architecture far outweigh the risks of incurring substantial delays and inefficiencies that would inevitably result from a change to the architecture at this late date,” the white paper concluded. Such changes, like increasing the performance of the Orion’s propulsion system to enable it to reach low lunar orbit, might add billions to the roughly $30 billion spent to date on SLS and Orion and do nothing to achieve the 2024 deadline.
That reliance on SLS and Orion worries some moon enthusiasts, as both technologies are still under development—and both projects have encountered significant cost overruns and delays. Last October, NASA’s inspector general issued a scathing report [PDF] of the SLS program, which at that time was three years behind schedule and billions of dollars over budget. Yet NASA and its allies say there’s no other way to the moon.
“The elements that we have right now can’t do that [lunar landing] mission without Gateway,” said Mike Fuller, who handles business development for NASA programs at Northrop Grumman . He believes Orion’s limited propulsion is actually a design strength. The Apollo missions sent the control modules into an orbit about 100 kilometers above the moon, but “it was disadvantageous to go that deep” into the moon’s gravity well, he says. Having Orion come to rest at a higher orbit makes it easier to abort back to Earth, as less propulsion is required.
Would it be possible for NASA to abandon the Gateway and its mission architecture entirely? Critics say that technological alternatives are emerging in the commercial space sector. They look to Blue Origin , the space company founded by Amazon billionaire Jeff Bezos and based near Seattle. Blue Origin is building both a reusable heavy-lift rocket, called New Glenn , and a lunar lander known as Blue Moon . Another contender is Elon Musk’s SpaceX , based in Hawthorne, Calif., which is also working on a fully reusable rocket. It will carry an upper stage called Starship , which the company says could land directly on the moon and carry heavy cargo. “Having that vehicle on the moon can basically serve as the core of a pretty significant lunar outpost, growing with time,” said Paul Wooster, principal Mars development engineer at SpaceX.
However, the exciting spacecraft from these companies are still under development, and it may be years before they’re ready for lunar-landing missions. Moreover, any attempt to cancel SLS or Orion would likely face stiff opposition in Congress, particularly by influential members in states where work on those vehicles takes place. Perhaps it’s no surprise, then, that NASA is doubling down on its Gateway plan. In May, while discussing NASA’s revised budget proposal, Bridenstine said the Gateway is vital to achieving a 2024 lunar landing. “The Gateway is as important now as it was before,” he said. “We cannot overemphasize how important the Gateway is.”
If NASA, heedful of sunk costs and political realities, continues to march toward the Gateway, we may indeed witness a triumphant return of NASA astronauts to the moon’s surface in 2024. NASA has defied the odds and met grand challenges before. But it’s also possible that the plan won’t survive budgetary debates in Congress, or that the 2020 elections will bring a new administration that will change the course of the lunar exploration program yet again. In which case, the determined billionaires behind SpaceX and Blue Origin might not wait around for NASA, and the next moon boots in the regolith might stamp a corporate logo in the dust.
Quelle: IEEE
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