The plan

Axiom plans to build the core of its space station at the ISS before the international laboratory retires, which is currently scheduled for 2024 but could be delayed until 2028. When the ISS finally calls it quits, Axiom's station will detach and become a fully independent commercial complex.

The company's first module, called the "Multi-Purpose Module," or simply, Module 1, would launch in late 2020. The current plan is to heave it into space all in one shot, providing Axiom can find the right rocket; at about 9 meters long and 5 meters wide, Module 1 will be a huge payload. (An alternative concept is launching the module in pieces and assembling it in space.)

Module 1 has its own propulsion system, meaning it will fly to the ISS under its own power after being dropped off in orbit. Axiom is currently proposing NASA connect the module to the forward-most port of the ISS, where a new mating adapter was recently installed to accommodate commercial crew vehicles. That mating adapter could then be moved to Module 1 and still be used for U.S. crew vehicle access.

Axiom and NASA have conducted a feasibility study on the concept, and are currently discussing all this under a Space Act Agreement; formal commitments have yet to be made. Officials at the agency's Johnson Space Center did not immediately respond to requests for comment.

The extent to which Axiom's customer astronauts would interact with the rest of the ISS is still unclear, but Module 1 will be self-sustained from the get-go. It has its own life support systems, sleeping quarters, restroom, galley, and experimentation and storage areas. Axiom says the module can support up to seven astronauts—though there probably won't be a lot of elbow room until the company adds up to two more modules between 2020 and 2024.

I recently spoke with Amir Blachman, the company's vice president of strategic development, and asked him who would build Module 1.

"Structurally, we're going to be utilizing one of the companies that built most of ISS," he said, adding the module would have a rigid structure and be similar in appearance to existing ISS components. Axiom expects to formally announce which company will build Module 1 around May or June of this year.

Initially, the company won't employ its own astronauts. The space station will serve as an off-world co-working habitat, with Axiom training crewmembers that want to use its facilities. The training will be conducted by SGT, the aforementioned contractor that currently trains NASA astronauts.

In 2019, Axiom plans to send a customer's astronaut to the ISS for a short-duration stay before the first module arrives. Because of the time required to prepare for the mission, the astronaut will begin training this year—meaning Axiom is set to begin generating revenue. The company hasn't formally booked a ride to orbit, but but Blachman said it would likely be on either a Soyuz or Dragon flight.

Commercial market

According to Axiom, a private space station can address a market of up to $37 billion between 2020 and 2030.

The actual figure will be lower if the ISS remains operational beyond 2024, but Axiom still expects a substantial revenue stream as soon as Module 1 is in place. I told Blachman I was skeptical: If such a huge market exists, why hasn't anyone already stepped in to fulfill it?

He said the company's top funding source would be sovereign countries wanting to send their own astronauts into space.

"There are more than 20 countries that want to send astronauts into space," he said. Some of those already have human spaceflight programs, while others want to develop one for reasons that include national prestige and fostering STEM education and technology development.

There is a currently a backlog of these would-be astronauts, Blachman said, due to limited ISS capacity and a shortage of launch vehicles.

The ISS can only support about seven crew members at a time. There are always two NASA astronauts, and even after Russia's decision to reduce its crew complement to two, either ESA or JAXA has an astronaut on board at least half of the time.

The other limiting factor is Soyuz seats. The stalwart Russian spacecraft can only hold three people, which keeps the station's staff count at six, until SpaceX and Boeing begin flying crew vehicles in 2018.

But even then, NASA wants an extra astronaut of their own aboard in order to conduct agency-sponsored research. Axiom's station, then, offers a commercial alternative for sovereign astronauts.