By the way, currently it’s only possible to return up to 50kg of cargo from the ISS. After the Space Shuttle was retired, Soyuz became the only spacecraft that can actually return anything to Earth from the ISS and there is pretty much only space for three people and nothing else in that thing.
Dragon is supposed to bring back 600kg in its first test flight to the ISS, but it can bring back up to 3.000kg. That’s still not much compared to what the Space Shuttle could do (14.000kg), but it’s a lot more than what is currently possible.
So even if it takes another three years until the first manned flight, Dragon can be very useful as a cargo ship for the ISS (despite the fact that the ISS already has three cargo ships: the Russian Progress, the Japanese HTV and the European ATV – those three ships can deliver tons of cargo but they all can return nothing).
The ability to do about 4 Dragon flights to the ISS for the incremental cost of a single 2011 Shuttle launch does mean the raw down-mass capability is actually pretty comparable, though.
One thing, though, Dragon won’t deliver is volume. There was lots of space in the Space Shuttle. (But I just wanted to add that for completeness sake, not to claim that the Shuttle was super awesome.)
Yes, but that volume would not have been used for station maintenance missions. If you look at the manifests for the shuttle, they hardly ever used all that volume even for station construction.
Dragon is supposed to bring back 600kg in its first test flight to the ISS, but it can bring back up to 3.000kg. That’s still not much compared to what the Space Shuttle could do (14.000kg), but it’s a lot more than what is currently possible.
So even if it takes another three years until the first manned flight, Dragon can be very useful as a cargo ship for the ISS (despite the fact that the ISS already has three cargo ships: the Russian Progress, the Japanese HTV and the European ATV – those three ships can deliver tons of cargo but they all can return nothing).