NASA hopes to resume commercial shipments this week to the International Space Station, following months of frustrating delay.
The last successful U.S. supply run was in April. Russia and Japan have managed to fill the gap. Nonetheless, the 250-mile-high pantry isn't as full as it should be.
An unmanned Atlas V rocket arrived at its launch pad Wednesday. It's due to lift off early Thursday evening with 7,400 pounds of space station supplies.
Shipper Orbital ATK Inc. is launching from Cape Canaveral this time. Its Antares rocket is still grounded following a 2014 launch explosion that damaged the Virginia launch pad. Both the rocket and the company's cargo ship were destroyed.
The Virginia-based Orbital purchased two United Launch Alliance rockets to fulfill its shipment obligations to NASA.
NASA's other contracted shipper, SpaceX, has been grounded since a failed launch in June. The California company expects to resume deliveries in January. It had the last U.S. resupply success, back in April.
Orbital plans another shipment via an Atlas in March, followed by the return of Antares in May with a new type of Russian-built engine. A fire and explosion in the old Russian rocket engines doomed the October 2014 flight, the company's fourth resupply mission.
Orbital's latest cargo ship, named Cygnus for the swan constellation, contains food, clothes, equipment, science experiments and even storybooks, part of an astronaut-reading project for children. Some of the experiments represent redo's by schoolchildren who lost their original tests on the failed launches.
It was too late to squeeze in a spare part to restore the space station to full power. A short circuit knocked out one of eight power channels in mid-November. The replacement part will fly on a SpaceX Dragon capsule early next year.
Tom Wilson, a vice president at Orbital, said the objective is to deliver a fresh load of goods to the six station residents in plenty of time for Christmas.
Orbital's rocket men acknowledge being a little nervous about the upcoming launch, even though the Atlas has been around for decades and is a tried and true workhorse. It typically hoists satellites for the Air Force and other customers; this will be its first crack at a space station run.
"You're always a little nervous, but highly confident," Mike Pinkston, general manager for the Antares, said on the eve of the launch.
Forecasters put the odds of good weather at 60 percent for Thursday's 5:55 p.m. EST launch attempt. The outlook worsens Friday.
The Cygnus capsule is named after Mercury astronaut Deke Slayton, a commercial space pioneer. So was the one that was lost; this one is S.S. Deke Slayton II.