Earlier today, China took a huge step forward in their quest for a continual human presence in space: they launched Tianzhou-1, an unmanned resupply ship that will dock with their space station, Tiangong-2. I’d also like to add that I predicted this would happen back in 2012, when I claimed that their first space station, Tiangong-1, was actually a prototype of a resupply ship. I think I was right!
If you’ll forgive me, I just want to revel in this sadly rare moment of accuracy with this quote from my 2012 article about Tiangong-1:
So, in a nutshell, here’s what the Chinese are doing: they’ve outfitted what will become a future cargo vessel with a life support system and supplies, allowing their Shenzou crew to practice orbital docking, some limited space station living, test life support and propulsion systems for both future space stations and on their future station-supporting cargo ship all in one efficient mission. When they build Tiangong 2, they’ll already have some experience and a resupply ship. It’s pretty clever.
Holy crap, that’s pretty much exactly how things have turned out: Tianzhou-1 (the name means ‘heavenly vessel,’ like the free water bottle you’ll get when you enter the afterlife) is based directly on the original Tiangong-1 ‘space station,’ and it’s now being used to resupply Tiangong-2. I’m sure plenty of other observers figured this as well, but just let me have this tiny victory, please.
Really, though, what I think doesn’t matter a bit. What’s important here is that an automatic-docking resupply ship is absolutely crucial to long-term habitation in space. The Tianzhou series is basically filling the same role as the Soviet/Russian Progress resupply ships, which have been in continuous use since they resupplied the Salyut 6 space station in 1978, and continue to bring cargo and fuel to the ISS to this day.
Tianzhou-1 is based on China’s crewed spacecraft, Shenzhou, which is in turn effectively a modernized and enlarged Soviet/Russian Soyuz design. There’s a service module providing propulsion, fuel, and electricity via solar panels, and a cylindrical cargo module, which has a pressurized section and can have an unpressurized section as well, usually with fuel tanks to refuel the orbiting station.
This mission will mostly focus on having Tianzhou-1 dock, transfer fuel, and undock from Tiangong-2, multiple times. The main goals of the mission will be to test the automatic docking and refueling procedures.
It’s not clear if Tiangzhou-1 has any cargo in its pressurized compartment that will be used on the space station by later Taikonauts when they return to Tiangong-2. Personally, I’m skeptical it has any actual cargo, because I’m not certain there’s any way to transfer that cargo to the station.
In fact, I think that with the current setup of Tiangong-2, there is no way at all to transfer cargo, because Tiangong-2 has only one docking port. The Soviets didn’t launch any unmanned cargo ships to their space stations until they had a station with multiple docking ports, Salyut 6, which had two, one at each end.
With at least two ports, one can have a crewed ship docked, leaving the other free for a cargo craft. When the cargo craft is docked, the crew can unload the supplies and equipment from the pressurized cargo compartment. There’s no way to do that now with Tiangong-2, unless they were to leave some poor, lonely sap in the station without a Shenzou return spaceship, which I’m pretty sure they’d never do.
So, if I may undertake a new prediction here: this may be the only time we’ll see a Tianzhou cargo ship dock with Tiangong-2. The cargo ships will be used much more extensively when the Chinese launch Tiangong-3 in 2022 or so, which will be a space station module very similar to the old Soviet/Russian Mir core module, and will contain multiple docking ports.
Once that happens, we’ll have two continuously-occupied space stations in Earth orbit, and that’s when things should get really fun.