CAPE CANAVERAL, Fla. If all goes as planned, three weeks after Space Exploration Technologies’ Dragon capsule lifts off for a trial cargo run to the international space station, it will parachute back to Earth with science samples and other items from the outpost, restoring a key U.S. capability lost with the retirement of the space shuttles.

The successful return of Dragon will clear the California-based firm, also known as SpaceX, to collect the last of $396 million set aside by NASA under a program to speed development of commercial space transportation services in the United States. SpaceX would move on to begin work under an even more lucrative $1.6 billion contract to deliver cargo to the station for NASA, which has been dependent on partner countries for access to the outpost since the shuttle program ended this summer.

Dragon sits on a stand in a hangar at the company’s Cape Canaveral launch site, a refurbished Titan complex located just south of mothballed space shuttle launch pads at the Kennedy Space Center. Its ride into space, a 55-meter-tall SpaceX Falcon 9 rocket, lies nearby, its stages integrated and poised for a scheduled “wet dress rehearsal” fueling test Nov. 21, a key milestone before the company’s third Falcon 9 will be cleared for liftoff.

SpaceX is planning to be ready to launch as early as Dec. 19, but NASA, which is sponsoring the mission under its Commercial Orbital Transportation Services (COTS) program, doubts it will happen before the end of the year. “We don’t have a real target launch date yet. That will probably be set mid-November,” Alan Lindenmoyer, the NASA manager for the Commercial Crew and Cargo Program office, said in an interview.

With two successful Falcon 9 launches under its belt, the last of which put a Dragon capsule into orbit, SpaceX wants to combine objectives of the final two flights in its COTS contract into a single mission, a proposal that NASA approves of in theory, though final clearance to berth Dragon at the station will be based on how the capsule performs in orbit.

“NASA is not describing this as a combination mission,” SpaceX spokesman Bobby Block told a small group of reporters gathered at the company’s Florida launch site to see Dragon, which arrived Oct. 23. “It’s more like ‘The Amazing Race.’ You have to pass each stage before you can go on to the next one. We’ll be prepared to go all the way to the station. We’re taking cargo on the assumption that we’ll be able to meet all those milestones.”

NASA is still deciding what it wants SpaceX to carry aboard Dragon, but the items include food, water, clothing and other cargo considered nonessential to station operations in case the capsule falls short of the full mission goals.

“The cargo will be beneficial if the mission is successful, but not time-critical to the on-orbit crew,” Kathy Lueders, manager of the space station’s Transportation Integration Office at the Johnson Space Center in Houston, said via email.

For the return flight, the cargo includes science samples that would expire if they were not flown back and items that need to be cleared off the station for stowage reasons. “As always, the final cargo complement may change slightly as the mission approaches,” she added.

Dragon’s flight plan and mission duration also is under review, as is SpaceX’s plan to include a commercial communications satellite as a secondary payload. An analysis to ensure Falcon 9’s second stage will not collide with Dragon when it fires to deploy the satellite is under way, Lindenmoyer said. Also pending is an analysis of SpaceX’s flight software.

The preliminary plan is for Dragon to start off 325 kilometers away from the space station for an abort test, a demonstration of free drift flight and establishment of GPS communications links. If those are successful, Dragon would use its steering jets to move in closer, stopping at 200 kilometers, then 60 kilometers and finally at 40 kilometers, where it will attempt to establish direct communications with the station. “All these things are just proving out that you can operate in any contingency,” Lindenmoyer said.

The space station portion of the mission starts with a 10-kilometer flyby beneath the orbital outpost, progressing to a 2.5-kilometer fly-under, Lueders said. Key system functionality, including GPS and the use of the crew control panel, is checked out during the 2.5-kilometer pass. Several other maneuvers, including the ability of the vehicle to abort, are checked out during this phase. “These checkouts provide additional confidence that all key systems are working prior to final approach” to the space station, Lueders said.

Dragon would then execute a race-track maneuver around the station, during which time NASA and SpaceX will review and process mission data. If all goes well, Dragon would be grappled by the station’s robotic crane between 100 and 107 hours after liftoff for berthing at the Harmony node’s nadir port.

The capsule could sit for a week or two before station crew members unload the cargo, reload it with items to be brought back and release Dragon for the return trip to Earth. The latest flight plan had splashdown occurring just over 21 days following launch.

“This has all never been done before by a private company. Each individual stage is important to get to the next stage and is an advance of what was done before,” Block said. “This stuff is tricky. We’re aiming to get it perfect. Each launch is a learning experience.”

SpaceX, which has 35 Falcon 9 missions under contract, also holds a $75 million NASA contract to develop a launch escape system, the key component to upgrade the Dragon freighter to double as a passenger spaceship.

Orbital Sciences Corp., which shares NASA’s COTS work with SpaceX, plans to debut its Taurus 2 rocket and Cygnus cargo capsule next year.