/johnny
For the CRS variant of Dragon, the ISS’s Canadarm2 will grapple its Flight-Releasable Grapple Fixture and berth Dragon to the station’s US Orbital Segment using a Common Berthing Mechanism.[39] The capsule does not have an independent means of maintaining a breathable atmosphere for astronauts and instead circulates in fresh air from the ISS.[40] For typical missions, Dragon is planned to remain berthed to the ISS for about 30 days, similar to the Japanese HTV uncrewed vehicle.[41] The CRS Dragon’s capsule can transport 3,310 kilograms (7,300 lb) of pressurized cargo to the ISS in a volume of 6.8 cubic metres (240 cu ft) and return 2,500 kilograms (5,500 lb) of cargo in that same volume.[42] The CRS Dragon’s trunk can transport 3,310 kilograms (7,300 lb) of unpressurized cargo in a volume of 14 cubic metres (490 cu ft), and can dispose of 2,600 kilograms (5,700 lb) of waste in that same volume by destructive re-entry.[42]
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http://en.wikipedia.org/wiki/Dragon_(spacecraft)