Guadalajara, Mexico

After arriving in Mexico for an international conference on space and unveiling the schematics for a low-cost transit system to Mars, SpaceX’s Elon Musk faced a tough question from the audience.

“You’re going interplanetary, but you’re not going international,” said a woman named Anastasia, who identified herself as Russian. “When are you going to hire people from other countries than the US?” The question was met with applause from the crowded hall.

Musk, a South African who came to the United States by way of Canada and is a backer of increased immigration to the US, doesn’t have a vendetta against the global workforce. But the US government, which already makes it difficult for foreign workers to arrive, considers space technology a national security issue and generally prohibits foreigners from working on it, under rules known as International Traffic in Arms Regulations (ITAR).

The ITAR regulations are something of a sore point in the global space community, which tries to emphasize its distance, literal and figurative, from political concerns. How over-broad are the US government’s prohibitions? Even a company that designs space clothing in a Brooklyn studio must obey them and carefully track the nationality of any visitors.

So SpaceX, which aims to do business launching satellites for clients like the US Air Force, must obey these rules as well. And that means it can only have permanent residents in its workforce.

“This is not out of some desire of SpaceX to just hire people with green cards,” Musk said. “It’s because we’re not allowed to do anything else. This is not a wise policy for the US, because there are so many talented people all around the world that we would love to have work at our company. But unless they can somehow get a green card, we’re legally prevented from hiring” them.

He noted that at Tesla, his electric car company, about a third of the engineering team was born outside the US.

As with Tesla, SpaceX’s pioneering work has made it a company that many young engineers around the world aspire to work for. A recent Reddit AMA with SpaceX’s head of human resources drew multiple questions about whether and when SpaceX could hire non-US employees.

“Over time, as we make progress towards becoming a multi-planetary species, we expect that people from many nations will have the chance to participate in space exploration,” the HR executive, Brian Bjelde, wrote in response.

“I really wish we could do more,” Musk said at his Mars presentation. “It’s just, our hands are tied.”