Two days might not seem that long for your latest Amazon order's arrival. But for the crew of the International Space Station, waiting 48 hours for fresh supplies must be an eternity. That's why NASA and Rosaviakosmos have melded new technology and an old technique to deliver supplies eight times faster than ever before.

Since the Space Shuttle program's recent retirement, NASA has depended on Russian-built Soyuz vehicles to deliver essential items—everything from scientific equipment to fresh air and propellant. And while the International Space Station floats just 220 miles above the Earth, getting the manned Soyuz capsule and the ISS to meet requires 34 Earth orbits—it takes roughly two days. This method is inefficient, given that during the trip out to LEO, the Soyuz crew must consume air, food, and water that could otherwise be utilized aboard the ISS.

So the Russian Federal Space Agency has renovated the Progress unmanned spacecraft, which was originally developed in the 1980s. Based on the earlier Progress 7K-TG spacecraft, the new design has a modern service module (the section containing the craft's flight control systems), new rendezvous and docking systems, and a digital telemetry system. Designated the Progress-M, this 35-foot long, 16,420-pound unmanned capsule can haul nearly three tons of supplies at a time atop a standard Soyuz rocket. Last Wednesday, for example, the Progress 48 capsule delivered 1,962 pounds of propellant, 110 pounds of oxygen and air, 925 pounds of water, and 2,817 pounds of other miscellaneous supplies to the ISS—in just under six hours.

After lifting off from the Baikonur Cosmodrome in Kazakhstan, Russia's largest spaceport, Progress 48 needs just four laps around the Earth to catch and autonomously dock with the space station high above the South Pacific. "It does impose more constraints on the geometry—the orbital mechanics—of the launch, because you have less time to catch up to the space station," said space station flight director Chris Edelen. "You've got to basically launch and be in the right spot, and the space station has to be in the right spot." Once it arrives, the Progress 48 attaches itself via ISS's Pris docking compartment, a spot previously occupied by the Progress 47 capsule. Since the Progress fleet are designed to be disposable, whenever a new supply shipment is launched, the previous capsule is filled with refuse from the ISS and set adrift, eventually burning up with its cargo as the craft reenters Earth's atmosphere. The Progress 48 will remain tethered to the ISS until December, when it will meet the same fate.

This is not the first time that either NASA or the RFSA has attempted such a maneuver. "This is actually old technology," Edelen continued. "Our first ground-up rendezvous on the Gemini program was a Flight Day 1 rendezvous, and the Russians have done this before, so it's sort of a back to the future."

The space agencies plan to perform another unmanned test flight later this year, and, if that too is successful, they hope to adapt it to manned Soyuz capsules. "They're looking to eventually take this into the Soyuz phase," Dan Harman, NASA's space station manager of operations and integration, said in a press release. "If you can get the crew to orbit in six hours and onboard the International Space Station, that could be a tremendous benefit over the two-plus days it takes today." What's more, this new methodology could finally provide a way to hussle emergency supplies and crews into LEO in the event of a catastrophic system failure aboard the ISS.

[PopSci - SpaceRef - Wikipedia - Astronautix - Space 1, 2]