Ещё советую обратить внимание вот на это
"SpaceX plans to launch its Dragon 2 spacecraft aboard its Falcon 9 launch vehicle to deliver up to 3,307 kg
of upmass. The Dragon 2 was initially designed for crew missions, but with modifications, the spacecraft
can also be used to transport cargo. The vehicle has a pressurized capsule that can carry up to 2,507 kg
of upmass and returned downmass along with an external trunk below the capsule that can carry up to
800 kg of additional unpressurized upmass and downmass. For the CRS-2 contract, SpaceX also proposed
using the Dragon 1 spacecraft used for its CRS-1 missions, but NASA selected the Dragon 2 due to lower
integration costs and per-mission pricing. However, the docking configuration for Dragon 2 has
limitations regarding the size of the hatch such that larger items including spacesuits and large cargo
bags cannot fit." Т.е. ни о каких 6 тоннах (заявленных на сайте SpaceX) речи не идёт
