NASA and SpaceX are closing in on the first launch of humans into orbit from US soil since 2011, when the space shuttle made its final flight.

Although the space agency has not yet said so publicly, NASA is working toward a May 7 launch of a Crew Dragon spacecraft carrying astronauts Doug Hurley and Bob Behnken to the International Space Station.

Asked Monday about the early May launch date, the director of Johnson Space Center, Mark Geyer, said it is tentative and that no final decisions have been made. The International Space Station and Commercial Crew programs are continuing to consult with NASA Administrator Jim Bridenstine and the agency's chief of human spaceflight, Doug Loverro. "That's the target the two programs have agreed is reasonable, but we're still confirming with Jim and Doug really when we think we're going to launch," he said.

It's therefore possible that the Crew Dragon mission could launch any time from the second half of April through June.

Crew Dragon

The Dragon spacecraft for the crew mission will arrive at Kennedy Space Center this month and is essentially ready to go aside from a few minor issues. Loverro said as much on Monday during a visit to Johnson Space Center.

"We have some subsystems that are in the vehicle that we think might need to be re-engineered with different kinds of metal, we have a tungsten incompatibility in one of the areas that we want to replace with different kinds of tubing," he said. "It's not major, but it's something that has to be done along the way."

NASA and SpaceX are also in final discussions about additional parachute tests to certify that system for flight. It's likely that SpaceX will conduct two additional tests of brand-new parachutes in the coming weeks to satisfy NASA's needs.

Mostly, however, Loverro said NASA needs to complete its analysis of data from Dragon's successful In-Flight Abort test in January and then complete paperwork for the mission.

"Even though it sounds mundane, there is a load of paper that has to be verified, and signed off, and checked to make sure we've got everything closed out," he said. "It is probably one of the longest things in the tent to go ahead and do. It's underappreciated but critically important. You've got to make sure you've done everything you need to do along the way."

Crew readiness

NASA is also trying to determine how long Dragon's first crewed mission will take. Initially, the space agency had planned to dock the capsule to the space station for about a week before Hurley and Behnken returned to Earth. Now it wants to extend that mission so the pair of astronauts can do more work on orbit.

Later this spring, after NASA astronauts Jessica Meir and Drew Morgan return to Earth, only Chris Cassidy will remain on board the station. NASA would like to minimize the time Cassidy remains the lone US astronaut on board the orbiting laboratory, so there is discussion of extending Hurley and Behnken's mission to six weeks, or even three months. If that happens, then the two astronauts would need some more space-station related training. Specifically, NASA would like Behnken to be capable of conducting a spacewalk if the need arises. Behnken has conducted six spacewalks over two shuttle missions, but the last was in February, 2010. He will need some spacewalk proficiency training if the Dragon mission is extended. (Hurley, a pilot on the shuttle, never performed a spacewalk.)

"We're also having a conversation because the station is about to go down to one person, and so it would make sense for this mission to stay a little longer," Geyer said Monday. "And given that, there's ISS training that we would want to give these guys, including Bob so he could help Chris if we had a contingency EVA. So that's all part of the mix, and all of that is coming together, and we'll be making decisions soon about when we think it's going to launch."