LA CAÑADA FLINTRIDGE, Calif.—At one end of the conference room, four large window panes framed a view of the San Gabriel Mountains. Outside, ribbons of greenery snaked across the hills, a vestige of spring before the dry summer season descends upon Los Angeles.

Inside, deep in discussion, a dozen men and women sat around a long, oval-shaped wooden conference table. They were debating how best to send a daring mission, known as Europa Clipper, to Jupiter’s mysterious, icy moon Europa. Although hundreds of scientists and engineers were already planning and designing this spacecraft, the key decisions were being made in this room on the top floor of the administrative building at NASA’s Jet Propulsion Laboratory.

It will not be cheap or easy to reach Europa, which lies within the complicated gravitational tangle of Jupiter and its dozens of moons, 600 million kilometers from Earth. But the payoff, scientists feel, is potentially incalculable. Beneath Europa’s ice, perhaps just a few kilometers down in some areas, lies the most vast ocean known to humans. With abundant energy emanating from the moon’s interior into the ocean, scientists speculate life might exist—probably just microbes, but why not something krill-like, too?

In recent years, scientists have locked down a set of nine scientific instruments to fly on the Europa Clipper probe, which will look, search, and sniff for signs of life during 47 flybys that will skim to within 25 kilometers of the moon's surface. But one big question remains, and it will probably determine whether the mission costs in the range of $2 billion or $3 billion dollars: how best to get the six-ton probe from Earth to the Jupiter system?

This was a key reason for the meeting held in early April outside the San Gabriel Mountains. Barry Goldstein, who is managing the ambitious Europa Clipper mission at the Jet Propulsion Laboratory, stood at the head of the conference table. “There’s been a lot of discussion about launch vehicles,” he said. “So we’ve prepared a chart.”

The physics of that chart displayed the capability of commercially available, lower-cost rockets to throw the Clipper to Jupiter; it also highlighted the capability of NASA’s more expensive Space Launch System. The latter rocket is more powerful than any booster flying today, but it has never launched, and when the titanic rocket will be ready for the launchpad is not certain.

Reaching Europa relies on more than physics, and invariably politics matter more when it comes to missions bound for the outer planets. This kind of exploration requires years of planning and development, as well as years of flight. In addition to costing billions of dollars, such missions must be managed across multiple presidential administrations and the comings and goings of Congress.

NASA

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/University of Arizona

NASA/JPL/DLR

For Europa, one Congressman matters more than all the rest. Since 2004, John Culberson has been on a quest to make a Europa mission happen. In the just-completed budget for fiscal year 2018, the Texas Republican pushed funding for planetary science missions to its highest-ever level, more than $2 billion. And of that, he had funneled $495 million to this NASA facility for Europa exploration.

So before the discussion of launch vehicles began, Goldstein had something he wanted to tell the politician who had flown in from Houston. “On behalf of the entire project, let me start with this,” Goldstein said. “Thank you, thank you, thank you, thank you, thank you. And I could go on for what, 60 minutes? We are in really good shape.”

Is Block 1 ready?

In a blue dress shirt, sans tie, Culberson shook off the compliment. First elected to Congress in 2001, he started agitating for a Europa mission only a few years later during the presidency of George W. Bush. The White House wasn’t having it. At the time, an already cash-strapped NASA was shoveling every spare dollar into the Constellation Program for human exploration, which would ultimately go nowhere.

By the time Barack Obama won his second term in the White House, Culberson’s seniority and membership on the House Committee on Appropriations allowed him to begin providing limited funding for a Europa mission. (Scientists have long had Europa atop their wish-list, but NASA leadership had been hesitant to take on such an ambitious, costly program). At the end of Obama’s presidency, Culberson had risen to chair of the Appropriations subcommittee that sets NASA’s budget, and the Europa Clipper had become an official NASA program.

Culberson loves space. He views planetary exploration and the potential for finding life elsewhere in the Solar System as the most enduring legacy he can leave behind for humanity. Since last summer, however, Culberson has focused on securing funding for victims of Hurricane Harvey, which dropped four feet of rain on Houston and ranks with Hurricane Katrina as the costliest storm to ever hit the United States. Some of his own family members had only just moved out of a trailer back into renovated housing. But on this Friday, he had come to California to see how the Clipper mission was doing, as well as a follow-on mission to land on Europa.

The missions are coming along nicely, but soon critical decisions about how to get Clipper to Jupiter must be made. The JPL scientists and engineers want to send the Clipper, which is so big that its solar panels have a wingspan as long as a basketball court from end to end, directly to Jupiter. They prefer this because a quicker trip to Jupiter will require less thermal protection, and, more importantly, they want the Clipper to reach Jupiter before the follow-on mission designed to land on and sample the moon’s icy surface. Ideally, the Clipper will scout Europa for several years and identify the most interesting, safest landing location.

A direct shot of a six-ton satellite to Jupiter requires a rocket with a lot of muscle. During the briefing, Culberson was told no commercial rocket can do this, even SpaceX’s Falcon Heavy rocket, which flew for the first time in February. (It is not clear whether NASA specifically asked SpaceX about the Falcon Heavy and Europa, as Goldstein said figures for all the commercial rockets were provided by a competitor to SpaceX, United Launch Alliance.) In the charts shown in the JPL conference room, engineers had modeled a Falcon Heavy with a small “kick stage,” but they had not considered alternatives, such as a Falcon Heavy with a more powerful Centaur upper stage for a direct-to-Jupiter mission.

Because the existing commercial rockets were not powerful enough, Goldstein said only NASA’s Space Launch System could get Clipper directly to Jupiter. The first version of this rocket, Block 1, can put 70 tons into low Earth orbit, and its Interim Cryogenic Propulsion upper stage has enough oomph to reach Jupiter in about three years. This is half the time of the commercial rockets, which will require more time to slingshot around inner Solar System planets to attain a Jupiter trajectory.

What Culberson really wanted to know is whether the big NASA rocket will be ready for a second launch in June 2022. This is a good question. Congress has patiently funded the SLS rocket’s development since 2011 and now spends more than $2 billion annually to fund work to design and build it. Even so, the SLS remains at least two years away from the launchpad for its maiden test flight. A few lawmakers have begun to ask questions about why it is taking so long.

Meanwhile, the engineers in California have told the Texas congressman that the Europa spacecraft can be ready for launch in just four years, thanks to his generous funding. Especially important, money has been front-loaded to arrive earlier in the project when development costs are highest.

If the spacecraft will be ready by mid-2022, Culberson wanted to make sure the booster was ready, too. “Block 1 is on time and on target?” he asked. “I want to make sure the SLS Block 1 is the rocket you need, and it’s on time.”