SpaceX's plan to fly two private citizens around the moon would put the company ahead of NASA's planned crewed flight with its Space Launch System (SLS) megarocket.

Yesterday, SpaceX announced its intention to send passengers on a crewed Dragon spacecraft, launched with a Falcon Heavy rocket, around the moon near the end of 2018. This would follow on the heels of the company's robotic and crewed flights to the International Space Station, and an uncrewed Falcon Heavy moon trip.

NASA's own mission, which would be the first crewed flight using the SLS and its new Orion spacecraft, is scheduled for 2021. NASA recently began an investigation into whether it could put astronauts on SLS and Orion's first launch, scheduled for 2018 — but officials have said that a crewed version of that launch wouldn't fly until 2019. Assuming SpaceX is on schedule, its fly-around would come first. [How SpaceX's 2018 Moon Flight Will Work]

SpaceX going first "might change the acceptable-risk discussions NASA has with the ASAP [Aerospace Safety Advisory Panel]," Scott Hubbard, researcher in the Stanford University Department of Aeronautics and Astronautics, told Space.com. "I could imagine that if this independent entrepreneur has done it, and successfully identified the risk factors, it would be real information, not speculation."

"Others might then ask about [the] need for SLS and Orion — but two suppliers are always better from a competition/cost POV," he added via email. Hubbard worked at NASA for 20 years and ultimately led its Ames Research Center, and he currently chairs SpaceX's independent Safety Advisory Panel for Commercial Crew, which focuses specifically on the design and risks of their program to carry astronauts to the International Space Station.

During Elon Musk's teleconference yesterday, the SpaceX CEO said that NASA astronauts would "take priority" if the agency wanted to be the first to fly that type of mission. NASA released a statement saying the agency would work closely with SpaceX to ensure the company met all safety requirements and continued to fulfill its space station delivery contract.

As for SpaceX's ambitious time frame, Hubbard said it should be feasible in principle, purely considering the company's transportation capabilities, but that technical questions remain.[SpaceX Falcon Heavy to Be Reusable (Video)]

"The key technical issue will be demonstrating life support in the Dragon for two people for the duration of the mission," he said. "With reasonable margins, the length of mission will be longer than planned for commercial crew. The key programmatic issue is level of risk: Is it understood? Has it been mitigated sufficiently?"

If SpaceX can address those issues, it will be on track to launch a moon mission on the 50th anniversary of Apollo 8, NASA's first mission to orbit the moon. That could certainly serve to spur other commercial spaceflight companies, and NASA, into action. Hubbard pointed to when he held a workshop with The Planetary Society that said astronauts could orbit Mars by 2033, and not long after Lockheed Martin came out with a Mars Base Camp plan for 2028 and SpaceX came out with their Red Dragon Mars mission now scheduled for 2020.

This moon announcement "sets a bold new goal," Hubbard said. "There are people that are out there moving the goalposts with some significant technical credibility behind them, and this goal of two paying customers and an Apollo 8 loop around the moon in 2018 could well stimulate others to join in."

"The more groups you have trying this, the better off we are as a spacefaring nation or a spacefaring species," he added.

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.