SpaceX CEO Elon Musk is no stranger to Twitter feuds.

He's not afraid to call others out or say controversial statements like when he called the British diver involved in the rescue of the Thai soccer team trapped in a flooded cave last year a "pedo guy."

But this time, it was someone else who blasted Musk on social media. On Friday evening, NASA administrator Jim Bridenstine released a statement on Twitter expressing his frustrations with SpaceX and the company's delay to deliver a capsule capable of sending humans to space, despite the $2.6 billion NASA has given the company.

"I am looking forward to the SpaceX announcement tomorrow," Bridenstine said on Twitter, referencing Musk's announcement Saturday night of SpaceX's Starship prototype rocket — the eventual vehicle designed to carry crew and cargo to the moon and Mars. "In the meantime, Commercial Crew is years behind schedule. NASA expects to see the same level of enthusiasm focused on the investments of the American taxpayer. It's time to deliver."

During Musk's announcement on Saturday, he responded to Bridenstine's statement and said, "From a SpaceX resource standpoint, our resources are overwhelmingly on Falcon and Dragon. It was really quite a small percentage of SpaceX that did Starship. Less than 5% of the company, basically."

However, John Logsdon, a space policy expert and professor at George Washington University, told FLORIDA TODAY he believes that 5% of staff only being devoted to Starship development is "probably the best 5%."

"I think Bridenstine had every justification to be annoyed," Logsdon said. Though he's unsure if another NASA administrator has ever called out one of its contractors so publicly before, this is not the first time an administrator criticizes one of its contractors.

This also isn't the first time Bridenstine criticized SpaceX or Musk. Last November, The Washington Post reported NASA would order a safety review of Boeing and SpaceX after Musk took a hit of marijuana and drank some whiskey on the podcast, "The Joe Rogan Experience" back in September 2018.

"I will tell you that was not helpful and that did not inspire confidence, and the leaders of these organizations need to take that as an example of what to do when you lead an organization that's going to launch American astronauts," Bridenstine told reporters last November. Now, it seems Bridenstine's frustrations lie more with SpaceX's other ambitions as opposed to its CEO smoking pot on the internet.

Back in 2014, NASA awarded $2.6 billion to SpaceX and $4.2 billion to Boeing to develop a spacecraft that would send astronauts to the International Space Station from American soil for the first time since the space shuttle program retired back in 2011. Right now, NASA is forced to purchase rides, at $85 million per seat, aboard Russian-Soyuz spacecraft, the only vehicle currently capable of launching humans to space.

At the time, NASA had anticipated this feat could be accomplished by 2017. Almost three years later, both SpaceX and Boeing have been unable to still meet this goal, although SpaceX has gotten pretty close.

This past March, SpaceX had a successful uncrewed flight test of its Crew Dragon capsule, safely sending it to the space station and returning it back to Earth in one piece. But then in April, that same capsule exploded during testing, resulting in a series of delays for the company that was scheduled to launch astronauts as soon as July.

"Bridenstine wants both SpaceX and Boeing to deliver on their Commercial Crew programs and it's taken longer than NASA wanted and a lot of the reasons for that are because of the very stringent reviews that NASA is putting the companies through to make sure in NASA's mind, they are as safe as possible," commercial space policy consultant Jim Muncy told FLORIDA TODAY. "I think we want them to be safe so things sometimes take longer than they should."

Musk told CNN the plan is to fly astronauts in a Crew Dragon capsule within three to four months, but Bridenstine isn't that optimistic.

"The space agency will likely have to purchase more seats aboard Russian-made spacecraft in 2020, (Bridenstine) said, to ensure U.S. astronauts have continued access to the space station because of ongoing delays with its Commercial Crew Program," according to CNN's article.

SpaceX isn't the only one failing to deliver, though.

Boeing hasn't even had its orbital flight test but said it's "really close" to completing its uncrewed flight and pad abort test, Boeing's commercial crew program manager John Mullholland said in September at a monthly space luncheon in Cape Canaveral.

Those aren't the only ongoing setbacks with NASA's contractors, however. The space agency has been tasked with returning American astronauts to the moon by 2024, but Boeing is also far behind in the development of its Space Launch System, or SLS rocket that would launch humans to the moon, and Lockheed Martin still has to finish the environmental controls and life controls for a crewed flight of the Orion capsule — the spacecraft that would be mounted on top of SLS, according to Muncy.

In an interview with CNN Business on Saturday, Musk joked and said, "Did (Bridenstine) say Commercial Crew or SLS," about Bridenstine's original tweet,poking fun at how far behind schedule the space agency's heavy-lift rocket is.

Furthermore, the agency still does not have the appropriate spacesuit astronauts would need to venture onto the lunar surface, and the lunar-orbiting Gateway — a mini-space station around the moon where the astronauts would stay when they're not walking on the surface — is nowhere close to completion, either.

According to CNN's article, "Bridenstine told CNN Business that he recognized 'a lot of NASA contractors are behind schedule' and he wants to hold all of them accountable for delays."

But falling behind schedule isn't something new for NASA. Since the dawn of the space race, NASA has experienced setbacks, starting when the space agency lagged behind the Soviet Union for many space-related accomplishments.

In fact, all these delays and pressure from the White House to meet these deadlines has probably added to Bridenstine's frustrations, Muncy, who is the founder and and president of PoliSpace — an independent space policy consultancy — believes.

"(Starship) is cool and it's attracting attention and publicity. It will probably fly to orbit before SLS flies," Muncy said. "So it's obviously an irritation to (Bridenstine). I mean, obviously as an American, as a patriot, he's glad companies like SpaceX, Blue Origin and others are investing into space transportation capabilities, above and beyond what the government has asked for or contracted for but it's not a NASA project so he doesn't have anything really to do with it. And the things he's waiting for, Commercial Crew, he's still waiting for and until then, he's dependent upon the Russians."

Yet Muncy argues, though blame is to be shared on both sides, most of the frustration Bridenstine and the American taxpayers should feel is with NASA.

"The way NASA often takes on these big programs, and here I'm talking about SLS and the Gateway and other things that they're talking about doing, is they don't choose the fastest way to get them done. They don't use commercial partnerships most of the time." he said. "Most of the time they use cost plus development contract standard, you know, the old way of doing things and that tends to cost more and take a lot longer because you're paying the contractor for effort as opposed to paying the contractor for results."

For an agency that's trying to head back to the moon within the next five years and then deeper into the cosmos, "the old way of doing things" might not work anymore, but NASA might not have much of a choice.

"There are definitely members of Congress who like the old way and are skeptical of commercial and don't like Elon and therefore put a lot of pressure on Bridenstine saying, 'Well, where's Commercial Crew?"' Muncy said.

Contact Jaramillo at 321-242-3668 or antoniaj@floridatoday.com. Follow her on Twitter at @AntoniaJ_11.