WASHINGTON — SpaceX Chief Executive Elon Musk lashed out at Blue Origin and United Launch Alliance Tuesday night, accusing the two companies of trying to stymie SpaceX’s expansion plans with a “phony blocking tactic” that has stalled the lease of an old space shuttle launch pad SpaceX wants to take over.

Both SpaceX and Blue Origin want to lease Launch Complex 39A at Kennedy Space Center, Fla., from NASA. Blue Origin, a 13-year-old startup backed by Amazon.com founder Jeff Bezos, gave NASA a proposal in July for converting the pad “into a commercial spaceport available to all launch companies,” the company’s president, Rob Meyerson, told SpaceNews in an email Wednesday. SpaceX, in contrast, proposed an exclusive-use lease for its Falcon family of rockets, but said late last week it would be open to sharing the pad with other users

SpaceX’s apparent about-face came three weeks after Blue Origin filed a protest with the U.S. Government Accountability Office (GAO), preventing NASA from leasing the pad until the dispute is resolved. The GAO has until Dec. 12 to issue a ruling; NASA — eager to save the $1.2 million annual maintenance cost — had been hoping to lease the pad by Oct. 1, the start of the government’s 2014 budget year.

Blue Origin’s bid to transform Pad 39A into a commercial spaceport has received backing from several U.S. lawmakers — including Washington’s Patty Murray, the senior senator from Blue Origin’s home state — who have written NASA Administrator Charles Bolden in support of turning the idle shuttle pad into a multi-user facility. United Launch Alliance (ULA), the Denver-based Boeing and Lockheed Martin joint venture that launches the vast majority of U.S. government payloads, also weighed in, telling SpaceNews in July it planned to “continue to share our technical expertise in launch infrastructure with Blue Origin to enable their leadership to manage the asset for multi-user capability, for which ULA could be one of the users.” 

SpaceX’s bid for Pad 39A received an implicit assist from Florida’s congressional delegation this month when U.S. Sens. Bill Nelson (D) and Marco Rubio (R) and all 27 of the state’s House members wrote Bolden following Blue Origin’s Sept. 3 GAO protest to encourage the NASA boss to ignore outside pressure in selecting a caretaker. 

SpaceX currently launches its Falcon 9 rocket from nearby Cape Canaveral Air Force Station, Fla., and is preparing to conduct its first launch from Vandenberg Air Force Base, Calif., as soon as Saturday. 

On Friday, SpaceX appeared to change its position on Pad 39A exclusivity, emailing reporters to say NASA and other launch providers would be welcome to use the launch complex if SpaceX gets the five-year lease.

In an email response Tuesday night to a SpaceNews query, Musk elaborated on the reasons for the pivot while taking a swipe at Blue Origin.

“[Blue Origin] has not yet succeeded in creating a reliable suborbital spacecraft, despite spending over 10 years in development,” Musk wrote. “If they do somehow show up in the next  5 years with a vehicle qualified to NASA’s human rating standards that can dock with the Space Station, which is what Pad 39A is meant to do, we will gladly accommodate their needs. Frankly, I think we are more likely to discover unicorns dancing in the flame duct.”

In his Wednesday statement to SpaceNews, Meyerson made no mention of Blue Origin using Pad 39A to conduct its own orbital launches. 

“We have committed significant funds to enable launches by other users beginning as early as 2015 and have garnered interest and support from nearly all U.S. commercial launch providers” Meyerson wrote. “We look forward to working with NASA and the launch community to make fullest commercial use of [Launch Complex] 39A.”

Blue Origin received two rounds of funding from NASA’s Commercial Crew Program to work on a biconic capsule that would launch atop ULA’s Atlas 5 rocket. Blue Origin sat out the third round, which split $1.2 billion between SpaceX’s Falcon 9-launched Dragon capsule and Atlas 5-launched entries from Boeing and Sierra Nevada. 

SpaceX began transporting cargo to and from the space station for NASA in 2012 under a 12-flight, $1.6 billion contract awarded in 2008. In addition to its effort to transform Dragon into a U.S. alternative to Russian Soyuz vehicles for ferrying astronauts to the space station, SpaceX is developing a rocket called Falcon Heavy with an eye toward taking Pentagon business away from ULA.

In his email to SpaceNews, Musk interpreted ULA’s backing of Blue Origin’s Pad 39A proposal in the context of the increasingly fierce SpaceX-ULA rivalry.

“I can’t say for sure whether [Blue Origin’s] action stems from malice. No such doubt exists about ULA’s motivation,” he wrote.

ULA declined to comment on Musk’s barb, but reiterated the company’s stance on the launch pad.

“NASA’s LC-39 is a great national asset and should be utilized to preserve the most flexibility and accommodate multiple launch providers,” ULA spokeswoman Jessica Rye wrote Wednesday in an email. “A multi-user pad should be embraced by all the potential launch providers because it enables our country to be more competitive and better utilize key infrastructure.”

Musk’s email is reproduced below in its entirety.

From a SpaceX standpoint, we view [Blue Origin] and [United Launch Alliance’s] action as a phony blocking tactic and an obvious one at that. BO has not yet succeeded in creating a reliable suborbital spacecraft, despite spending over 10 years in development. It is therefore unlikely that they will succeed in developing an orbital vehicle that will meet NASA’s exacting standards in the next 5 years, which is the length of the lease. That said, I can’t say for sure whether [Blue Origin’s] action stems from malice. No such doubt exists about ULA’s motivation.

However, rather than fight this issue, there is an easy way to determine the truth, which is simply to call their bluff. If they do somehow show up in the next  5 years with a vehicle qualified to NASA’s human rating standards that can dock with the Space Station, which is what Pad 39A is meant to do, we will gladly accommodate their needs. Frankly, I think we are more likely to discover unicorns dancing in the flame duct.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...