SpaceX took a big step toward a fully reusable launch system earlier this year by re-flying a used Falcon 9 booster, and it is making progress toward eventually recovering the rocket's upper stage and payload fairing. Now, the company is set to try to recover another key component of its space hardware—a Dragon cargo spacecraft. The launch window for the supply mission opens on Thursday, June 1, at 5:55pm ET (10:55pm BST).

This particular Dragon spacecraft was sent to the International Space Station in September 2014, and it delivered nearly 2.5 tons of cargo to the orbiting laboratory. The Dragon returned to Earth about a month later, splashing down into the ocean. It is not clear how much processing SpaceX has had to undertake to ready the spacecraft for its second flight to the station, nor has the company released a cost estimate. It also had to manufacture a new "trunk," the unpressurized rear section of the vehicle, and solar panels.

Although the company has never placed a hard dollar value on the Dragon, the savings could be considerable. SpaceX received a contract worth $1.6 billion from NASA for 12 cargo supply missions to the station in 2008—about $130 million per flight. That would have included the cost of the booster, of course, so therefore an individual Dragon spacecraft is likely valued at between $20 million to $60 million.

Rare company

In the nearly six decades of spaceflight, only a handful of spacecraft have flown multiple times into orbit around Earth. The most famous of these, of course, were the large and versatile space shuttle orbiters Columbia, Challenger, Discovery, Atlantis, and Endeavour, most of which flew dozens of missions. But the shuttle required hundreds of millions of dollars' worth of maintenance between flights, decreasing the value of its reusability.

As far as Ars can determine, only two other kinds of spacecraft, besides the space shuttle, have flown more than one time into orbit:

X-37B: The US Air Force has two of these autonomous, orbital test vehicles built by Boeing. Each of these spacecraft has made two flights, the second of which recently returned to Earth after a record 718 days in space. This mini space shuttle launches on an expendable Atlas V rocket and lands on a runway.

Soviet VA spacecraft: First developed to fly cosmonauts around the Moon, the VA capsule flew an uncrewed test flight in Earth orbit for 30 days in 1977. Less than a year later it was launched again, but this test flight made just one orbit around the Earth, according to CollectSPACE.

It is worth noting that a single Gemini spacecraft—which was an orbital class vehicle—did make two suborbital flights. The Gemini 2 capsule flew in January 1965 on an 18-minute suborbital flight to test the vehicle's heat shield. Later, the same capsule was reflown as the test vehicle for the Air Force’s Manned Orbiting Laboratory program.

No private company has ever reflown an orbital spacecraft, of course, and so SpaceX can make history on Thursday with its launch from Kennedy Space Center. If successful, it should help SpaceX transition its Dragon production line to the crew variant of the vehicle, Dragon 2. This upgraded spacecraft could begin carrying astronauts to the station as early as next year, but likely won't begin service until 2019.