WASHINGTON — Building a new mobile launch platform for later Space Launch System missions could cost NASA $300 million but allow for more frequent launches, agency officials said.

Bill Hill, NASA deputy associate administrator for exploration systems development, discussed the tradeoffs regarding building a new mobile launcher during a Nov. 29 meeting of the human exploration and operations committee of the NASA Advisory Council at the Kennedy Space Center.

The current mobile launcher, originally built during the Constellation program for the since-cancelled Ares 1, is finishing modifications to support the first SLS launch, which will use the Interim Cryogenic Propulsion Stage (ICPS). Future SLS missions, though, will involve the Block 1B version of the rocket with the larger Exploration Upper Stage, which will require further modifications to the launcher.

“The Exploration Upper Stage is 44 feet [13.4 meters] taller,” Hill said, which will require changes to the launcher structure and all its elements. “All the plumbing, elevators, cryos, everything you have to go back and redo. All the cabling that goes from the base to the top you basically have to pull out and reinstall it for the extra 44 feet. There’s just a lot to do.”

Those modifications mean there is what Hill called an “iron bar” in the schedule between Exploration Missions (EM) 1 and 2. Those modifications to the launcher can’t begin until after the EM-1 launch, which means EM-2 can’t take place until at least 33 months after EM-1, he said.

Building a new mobile launcher, with construction starting in the near future, could shorten that gap to some degree. It would also allow for additional SLS launches between EM-1 and EM-2, provided they use the ICPS, since the first mobile launcher would remain available. “That’s in my mind, the biggest benefit,” Hill said. “We’re not stuck on the ground until we get finished with the modifications. That’s one of the things we’re taking a look at.”

NASA has considered using the SLS for the Europa Clipper mission to Jupiter, with some notional schedules for future SLS launches placing that launch between EM-1 and EM-2, depending on the schedule for that mission and the availability of the SLS.

A faster cadence of SLS launches was a key reason why NASA’s Aerospace Safety Advisory Panel endorsed the development of a new mobile launcher at an October meeting. The current gap between EM-1 and EM-2 “represents a pause in the Program that the Panel thinks could involve safety difficulties,” the minutes of that meeting state. “It would be much more efficient for the continuation of the Program if it were possible to construct a second ML [mobile launcher] — starting that construction now — so the appropriate ML would be ready for the transition from EM-1 to EM-2.”

Bob Cabana, director of the Kennedy Space Center, also supports building a new mobile launcher rather than modifying the existing one. He said earlier at the NASA Advisory Council committee meeting that he took Bill Gerstenmaier, NASA associate administrator for human exploration and operations, on a tour of the current launcher “so he could appreciate the complexity of this thing and why I believe we need a second mobile launcher rather than modifying this one.”

Cabana offered an analogy for the work needed to modify the mobile launcher for the SLS Block 1B. “I’m going to cut off my head and add six inches to my body,” he said. “That’s essentially what you’re doing. You’re taking a very complex system — all the wire systems and everything else that is on that thing — and raising it up to extend it for the larger vehicle.”

Building a second mobile launcher, Hill said, would involve a net cost to NASA of about $300 million. That includes the cost of the launcher, less the savings from not modifying the current launcher to accommodate the SLS Block 1B.

Hill didn’t say if NASA has formally requested a new mobile launcher in its next budget request. “I think that was a rumor,” he said when asked by the committee about it. However, he suggested that a decision on whether or not to build a new launcher would come in the near future.

Hill said a more detailed discussion about the tradeoffs of modifying the existing launcher versus building a new one could take place at the committee’s next meeting, which would be around March 2018 based on the schedules of previous meetings. “By then,” he said, “we should know whether we’re going with modifying this mobile launcher or having the authority to go get a new one.”