Russian engineers are finishing the design of a brand new space freighter that would replace the veteran Progress cargo ships supplying the International Space Station (ISS) with propellant, food, water and other goods, industry sources tell Popular Mechanics.

The new vehicle will be about a ton heavier than its predecessor and will feature a radical new design. If it's actually built, the next-generation cargo ship will allow Russia to reduce the number of annual cargo shipments to the ISS from four to three while still delivering all necessary provisions for three people to live more or less permanently aboard the ISS.

Not coincidently, all of these ISS problems have acquired added political significance this year. Faced with latest economic problems, and the need to reduce the number of Progress cargo launches, Russia's space agency Roskosmos made plans to cut the permanent crew of ISS cosmonauts from three to two people. However the full international crew on the ISS is supposed to include six people with half of it reserved for Russia.

To resolve this supply problem, Roskosmos ordered RKK Energia, its key contractor responsible for human spaceflight, to prepare a preliminary design of a bigger cargo ship by the end of this month. Engineers quickly put together this proposal that would combine off-the-shelf hardware with new technology.

NASA

Since 1978, seven-ton Progress cargo ships have been flying one-way supply missions to the Soviet and Russian space stations. They were instrumental in setting many long-duration records in space by Russian cosmonauts in the 1980s and 1990s. From the turn of this century, Progress have continuously supplied international crews on the ISS, including the recent "Year-in-Space" mission. After delivering their cargo, Progress ships are filled with trash and sent on a destructive reentry into the Earth atmosphere.

Over the years, Progress went through several rounds of modest upgrades, while several more radical versions were also proposed, including those that would not only deliver but also return cargo back to Earth. (The cargo return capability is now provided on ISS by the SpaceX Dragon spacecraft.) The most important new feature of the proposed cargo ship will be the six-tank cluster to carry more than 1.8 tons of propellant to the station. It will simultaneously serve as a tanker for the space station while also feeding the ship's own propulsion system. As a result, the new design provides significant mass savings in comparison to the current Progress ships, which need two separate sets of tanks for refueling and maneuvering.

The main engine for the new cargo ship will be borrowed from an existing satellite. Meanwhile, 28 small thrusters for orbit correction and maneuvering will be copied practically unchanged from the Progress.

A pressurized cargo section with an internal volume of around 18 cubic meters will accommodate around 2.4 tons of food, clothes, and other supplies for cosmonauts, including 400 kilograms of water and more than 50 kg of air. It will be connected by a lattice structure to the tanker section, which will operate in the vacuum of space. Various electronics will be spread between both compartments.

The new ship will be able to remain at the ISS up to a year and fly solo missions lasting up to a month. For its ascent to orbit, the new ship will take advantage of the most powerful version of the Russian Soyuz rocket known as Soyuz-2-1b. The three-stage booster is capable of delivering nearly 8.2-ton vehicles into orbit.

Even with all the shortcuts and the streamlined design, the new ship is not expected not reach the launchpad until at least 2020. In the meantime, the Russian crew aboard the ISS is expected to go down to two people beginning next March. In 2018, the Russian crew might go back to three people temporarily, when cosmonauts are expected to conduct extensive work outside the station to integrate the new multi-purpose module slated for launch at the end of next year.

In addition to the latest design, Russian engineers were also considering a concept of an even larger cargo vehicle, which would need Russia's new-generation Angara rocket for launch.

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