MELBOURNE, Fla. — In scale models, the pieces fit together like Lego pieces.
Rockets snapped onto custom adapters that could be swapped in and out of a mobile launcher. An umbilical tower's lines and access platforms adjusted to fit each system.
Roll them out to a Kennedy Space Center launch complex, and virtually any commercial rocket could now blast off from a pad that for decades served only the space shuttle.
"We had a plan where essentially you could do any number of vehicles," said Dan Brandenstein, retired chief operating officer of United Space Alliance, which sketched out the concept before the shuttle's retirement. "They could just 'plug and play' the adapters they need and use the launch pad as often as they need it, and not have the overhead of owning it full time."
The company's pitch never gained traction, but the idea has won new prominence with a proposal by Blue Origin to manage KSC's launch pad 39A as a shared commercial pad, instead of NASA awarding an exclusive lease to SpaceX.
The competing proposals have billionaire CEOs (Elon Musk founded SpaceX; Amazon.com's Jeff Bezos is behind Blue Origin), industry rivals and members of Congress debating the best and most practical use for the mothballed former Apollo and shuttle pad. That has delayed at least for a few months a critical next step in Kennedy Space Center's transformation into a multi-user spaceport for government and commercial launches.
But beyond the corporate and political jockeying is a basic question: Could competitors share the pad? Would that work?
Supporters believe that would be the most fair and economical use of a special facility in which taxpayers have invested hundreds of millions of dollars. Commercial launchers would benefit by splitting the expense of operating a major piece of infrastructure, lowering launch costs.
Skeptics point out that such an arrangement has never been tried before by the larger, liquid-fueled rockets most likely to launch from pad 39A.
"This is a concept that has been proposed for decades and yet has never been implemented successfully by the government, much less the more cost-conscious and deeply competitive private sector," Frank DiBello, CEO of Space Florida, wrote this summer to NASA and federal lawmakers. Space Florida is a state agency that promotes the aerospace industry in Florida.
DiBello says he doesn't prefer one approach over another, but the best outcome and return on taxpayer investment would bring launches here sooner rather than later.
The pad's fate is in limbo as NASA awaits the outcome later this year of a bid protest Blue Origin filed with the U.S. Government Accountability Office.
NASA says it would cost more than $1 million annually to maintain the mothballed pad, an expense it can't afford moving forward. If a satisfactory lease — which NASA had hoped to award by Oct. 1 — isn't secured, 39A could sit idle or rust away.
Backed by Amazon.com's Bezos, Blue Origin says it is willing to invest heavily in pad 39A so that anyone interested, including SpaceX, could start launching from there by 2015.
Blue Origin won't have its own orbital rocket until at least 2018 but would manage and maintain the pad as a commercial spaceport, helping to ensure "the fullest use of this unique national asset."
"Multiple launch companies believe a commercial multi-user facility is feasible and desirable," said company President Rob Meyerson. "It brings more launches, and with them more jobs."
United Launch Alliance, which dominates launches of government satellites and is competing with SpaceX to launch NASA astronauts, has backed Blue Origin's idea. The Boeing-Lockheed Martin joint venture has not committed to using pad 39A but says access to it could be helpful down the road.
A new launch pad in Virginia is also promoting itself as a multi-user facility, though it has only tenant now.
To implement the concept here, Blue Origin, which operates a private suborbital launch site in Texas, would need to tackle complex technical hurdles that United Space Alliance's "plug and play" models only began to address.
Each rocket has a different height, diameter and weight and may use different propellants. Access points vary for technicians and fuel, power, electrical and communications lines. Each liftoff exerts different forces on a pad, from the way engines spew flame to the rumble they produce.
Assuming those engineering challenges can be met, potentially more daunting operational questions quickly arise. To start with, who goes first?
If launches were frequent, conflicts could arise over which are given priority and for how long. Companies might balk at a competitor calling the shots.
Worse, what if a competitor's rocket blew up on the pad, grounding launches indefinitely?
In United Space Alliance's concept, a second mobile launcher could replace a damaged one. Brandenstein said the technical challenges were manageable and companies would evaluate the risk of an accident against potential cost-savings.
"The bottom line is in anything there's challenges and nothing in that line of work is totally risk-free," he said.
But it's a risk companies have not yet been willing to take.
"People in the launch business, the biggest thing they want to do is control their own destiny," said Adrian Laffitte, a former Atlas launch director for Lockheed Martin.
"As an engineer, everything is doable," Laffitte said of the multi-user concept. "But is it going to be economical, and is it going to be something that people will want to use?"
That appears to be the key question right now.
When NASA requested proposals to lease pad 39A earlier this year, only SpaceX and Blue Origin responded. Of the two, only SpaceX has an operational rocket with an immediate manifest of payloads to launch.
As a result, SpaceX CEO Musk recently dismissed Blue Origin's multi-user approach, and United Launch Alliance's backing of it, as a "phony blocking tactic" by companies worried about SpaceX's growth.
Musk said he would welcome Blue Origin to pad 39A after a minimum five-year lease is up if the company can develop an orbital rocket that quickly.
"Frankly, I think we are more likely to discover unicorns dancing in the flame duct," he told Space News.
If more demand to launch from Kennedy Space Center soon does develop, NASA has invited companies to use neighboring pad 39B, which the agency only expects to use for its exploration rocket every other year or so.
But Blue Origin has been cool to the idea of sharing a pad with the government.
Musk says SpaceX would use pad 39A to launch civil government missions like International Space Station cargo and crews or NASA science satellites, while concentrating military launches at its existing Cape Canaveral pad, should the company win all that business. He continues to pursue a commercial launch complex outside federal jurisdiction, and calls Texas the leading candidate.
Space Florida hopes to develop one or two pads at the north end of Kennedy Space Center.
Before DiBello's tenure began in 2009, the state agency was promoting shared use of a pad it owns at Cape Canaveral Air Force Station, suitable for smaller rockets than would use 39A, but no launches materialized.
"There was clear interest on the part of a couple of people," DiBello said. "But when it came down to actually discussing the details, they were really interested for their program. They weren't as interested in a multi-user concept."