SpaceX will try to send a dummy to the International Space Station this weekend in a key test for resuming manned US space flights, perhaps this year if all goes well.
Since the shuttle Atlantis returned to earth on July 21, 2011, no American astronaut has blasted off from US soil for a tour in space.
NASA pays Russia to get its people up to the orbiting research facility at a cost of 82 million dollars a head, round trip.
In 2014, the US space agency awarded contracts to SpaceX and Boeing for them to take over this task.
But the program has suffered delays as safety requirements are much more stringent for manned flights than for unmanned missions to deploy satellites.
No one in America wants to relive the tragedies of the US space shuttles Challenger and Columbia, which disintegrated in mid-air in 1986 and 2003.
Three years behind schedule, a Falcon 9 rocket is scheduled to blast off Saturday from Cape Canaveral at 2:49 am (0749 GMT) with a Crew Dragon capsule in its nose. It will aim for a rendezvous one day later with the ISS. The capsule is scheduled to return to Earth on March 8.
If all goes well, two astronauts will be aboard the next time such a seven-seat capsule is launched. That is supposed to happen in July but delays are possible.
"These things always take longer than you think," said Lori Garver, who was the number two official at NASA when the contracts were awarded to SpaceX and Boeing under then president Barack Obama.
Back then this decision was controversial, with lawmakers complaining about changing the way America sends people into space and the loss of contracts and jobs for big, veteran aerospace companies based in their states.
"We have very few heroes left, and astronauts are our heroes. And loosening our grip at NASA and allowing companies to take the lead on transporting them was a challenge for some. It still is," said Garver.