The agreement under which the European Space Agency (ESA) will supply the service module for the second flight of NASA’s Orion crew capsule introduces an important international element to a program that at the moment is the only credible potential means of taking human explorers to destinations beyond low Earth orbit.

This is a good thing: International space programs can be messy and complicated — even more so than national ones — but in this day and age it is difficult to imagine any country mounting a meaningful solo mission to an asteroid or other deep-space destination. It makes sense, then, to get prospective partners involved at the ground floor.

The Orion agreement stems from the international space station partnership, whereby ESA and other agencies pay NASA, the prime integrator, in hardware and services for access to resources aboard the orbital facility. ESA’s current in-kind contribution is the Automated Transfer Vehicle for station logistics and reboost, but with that program’s end in sight, a replacement was necessary. Under the deal announced Jan. 15, ESA will supply the service module — Orion’s primary electrical power and propulsion component — for one mission and build spare parts that could be used for a second.

Given that Orion is primarily intended for deep-space exploration, its link to the space station seems a bit tenuous. But that’s beside the point: The point is that ESA is now on the critical path to a 2017 NASA mission in which an unmanned Orion capsule will pay a visit to the Moon. It seems likely, but by no means guaranteed, that an ESA module will be used on the next scheduled Orion mission, which also will fly to the Moon around 2021 but this time with astronauts aboard.

European officials have expressed hope that ESA-provided service modules will be used on subsequent Orion missions to destinations unknown, and the economics seem to support that: Future versions should be cheaper than a U.S. alternative given that the nonrecurring engineering costs in the ESA hardware will already have been sunk.

That logic might not sit well with U.S. industry and its congressional patrons. But both should consider the fact that aside from the heavy-lift Space Launch Vehicle being developed to launch Orion, NASA has no programs or plans to invest in other hardware, such as landers, that likely would be needed for deep-space excursions. Giving ESA responsibility for the service module in theory would free up NASA funds to invest in those systems, many if not most of which would be built by American contractors.

The larger point, of course, is that space exploration, beginning with the space station, has become an international endeavor. The ESA-NASA arrangement on Orion represents at least tacit recognition of that reality, and a key first step in building a future program.