ATV & Dragon
Wouldn't SpaceX be better licencing the automatic docking technology that's in the ATV for the Dragon capsule instead of the manual procedure the IIS crew need to do?
History is just days away from being made as SpaceX' Dragon cargoship finally blasted off successfully on its Falcon 9 rocket this morning on its way to a rendezvous with the International Space Station. Falcon 9 at lift-off (source: SpaceX webcast) Elon Musk's private space firm has had a number of setbacks with the latest …
Probably because it's not just a bolt-on module and would require significant time and money to get right. I'm sure they are working on auto-docking, but when they have the arm on the station, it's best to get the 'basic' bit of just flying up to the station right. This launch is actually putting things ahead of schedule. SpaceX was planning to perform a test flight of a Dragon up to the ISS, but not dock with it, but that flight was cancelled. If they can match orbit and be docked, even manually, it will be a significant achievement.
The whole point of Dragon is to maintain the best weight to thrust ratio. By keeping the spangly stuff off they keep the weight down and can lift more cargo. They are a for profit business, not NASA and need to keep an eye on the bottom line much more critically than the spendocrats in the US Gov with their $2200 hammers.
Hatch size is an issue. The access to an ATV, Soyuz or Progress is around 80cm (Russian design so metric!) diameter so anything carried up in one of them has to fit. The CBM used by the HTV and now (hopefully) Dragon is 51" (NASA design, not metric) square so much bigger items can be transferred.
The shuttle docking had the small sized tunnel as well which is why a lot of the resupply was carried in the MPLMs which were lifted out of the shutttle cargo bay and berthed to a CBM for unloading.