SAN FRANCISCO — It’s a tricky time for entrepreneurs whose businesses rely on the International Space Station.

Uncertainty over the timing of the orbiting outpost’s retirement and the eventual transition to one or more new platforms is making it challenging for companies to attract investors and plan for the future.

Part of the confusion stems from President’s Trump’s budget proposal to halt direct U.S. government funding of ISS after 2024. Speakers at the ISS Research & Development conference here July 23 to 26 emphasized the need for ongoing human activity in low Earth orbit and said the fate of ISS will be determined by its international partners: the United States, Canada, Japan, the Russian Federation and the European Space Agency’s 11 member states.

Even the United States has not completed a roadmap for its future in low Earth orbit.

“I can say today that the government, on the NASA side, has not decided what happens with the ISS platform itself, what happens with the program and what happens with this international partnership that we have we built over many years now, said Sam Scimemi, NASA’s ISS director.

Nevertheless, NASA, Japanese and European space station leaders at the conference said they are looking for ways to trim the outpost’s operating costs and encourage commercial investment in microgravity research and technology development with an eye toward the eventual transition from a government owned and operated platform to other space stations.

“The critical thing is we should not make a gap in low Earth orbit, said Koichi Wakata, JAXA vice president and director general for human spaceflight technology and a JAXA astronaut who helped assemble ISS and served as its commander.

Jared Stout, National Space Council deputy executive secretary and chief of staff, shares Wakata’s goal of extending access to microgravity. “NASA will always need a presence in low Earth orbit and industry will always need to operate in low Earth orbit,” Stout said.

Those comments helped to reassure entrepreneurs who are wooing investors and signing up customers for microgravity research and technology development. What the entrepreneurs really want, though, is a clear plan for the future.

“If you don’t create opportunities for companies to continue to work on ISS and have a clear path off ISS to a commercial platform, you create a market interruption,” said Christian Maender, Axiom Space in-space manufacturing and research director. Axiom is one of the companies preparing to build a private space station. “If there is not a smooth transition, companies with hardware on ISS risk losing it,” Maender said. “Most of these businesses are not going to survive that kind of transition.”

NASA should hold a competition to select a private company to use an ISS port to begin testing its platform as soon as possible, Maender said. NASA signaled plans in 2016 to award a port to a private module but has not yet done so.

“It is essential that you create a port opportunity for a private platform to help transition those customers when they are ready to move over to the commercial side,” Maender said. “Anybody who is this business knows that to build a reliable, sustainable and safe human-rated spacecraft, especially one that goes to the space station, will take three to four years.” After that, it will take time for a company to equip the new facility with the type of specialized equipment microgravity research and manufacturing firms need, he added.

Kris Kimel, co-founder and chairman of Space Tango, a business based in Lexington, Kentucky, that conducts research and manufacturing in microgravity, said his firm’s investors want to know what will happen to the business when ISS goes away, whether that is in 2025 or later. “It’s a good sign because it shows investors are taking this emerging industry seriously,” Kimel said.

Kenneth Shields, operations director for the Center for the Advancement of Science in Space, the nonprofit that manages the U.S. national laboratory on ISS, said CASIS employees inviting new companies to consider microgravity research and testing hear the same questions about predictability and confidence.

One entrepreneur suggested that instead of selecting a date to end ISS funding, U.S. government officials plan a capability-based transition, which means funding would end when certain conditions were met for a smooth transition to another platform.

If, instead, the U.S. government is going to select a “hard-line date to end ISS funding, it needs to prime the pump, pour money into things that exist and tell companies how much revenue they stand to earn from government contracts if they can scale up what they are already doing,” said an entrepreneur.