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SpaceX has the Dragon 1 (Cargo) and Dragon 2 (Crew). It unveiled Dragon 2 about 1 year ago (30 May 2014). Dragon 2 is a radical change over Dragon 1 with many parts that are untested.

I would think that the best way to test Dragon 2 for human flight would be to start using it for the cargo missions. There are a lot of aspects about Dragon 2 that could be tested in cargo missions that would be useful to ensure that the design is optimal. Some things I would think could be tested include:

  1. Aerodynamics and heat shield for re-entry
  2. Parachute landings
  3. Electronics, software and other sub-systems
  4. Docking mechanism to ISS
  5. SuperDraco engines in space conditions
  6. Life support systems
  7. General reliability of all the components used

SpaceX seem to prefer testing more and using existing missions to test. Since they are already doing the resupply missions, why not test the Dragon 2 on those missions?

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I suspect the CRS contract specifies the use of Dragon 1, that alone would rule out use of Dragon 2.

There is one physical difference that would impact CRS: Dragon 2 has a smaller hatch than Dragon 1, so some cargo won't fit on Dragon 2.

SpaceX would have to do at least one flight outside the CRS program to qualify Dragon 2. The docking mechanism is new, and Dragon 2 is capable of automatic docking (Dragon 1 is berthed instead, i.e. it flies to a point near the station, and a robotic arm moves the Dragon to its docking port).

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    $\begingroup$ I would think that NASA would be somewhat flexible on this point in the contract as it means that the craft they will send their astronauts in, will be better tested. $\endgroup$
    – neelsg
    Commented May 29, 2015 at 7:54
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    $\begingroup$ @neelsg These are government contracts we're talking about here. Flexibility is not something they're known form. $\endgroup$
    – T.J.L.
    Commented Oct 7, 2019 at 14:16
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The ISS has 3 different types of docking ports. You can see most of them in this image from the question: Will the ISS need more docking ports?

enter image description here

The port the Shuttle is using in that image is the PMA, (Pressurized Mating Adapter) and it is getting an upgrade in June 2015 when the SpaceX Dragon CRS-7 mission delivers the LIDS adapter for the PMA. This is where the Commercial Crew vehicles will dock. (Third port type is on the Russian segment where Progress, Soyuz, and ATV dock).

The Commercial Cargo vehicles use the CBM (Common Berthing Method) ports, that require capture by the CanadArm and manual intervention. Crew will use PMA since it can dock on its own and leave on its own, quickly. A CBM berth will take too long to depart in the case of an emergency.

CBM's are wider than PMA ports, so larger cargo can be moved in one piece, which is why this was preferred for cargo.

Thus the crew and cargo vehicles have a fairly large physical difference.

In order to test Crew features on a cargo flight a third configuration would be required, most of the crew features, but a different docking port.

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  • $\begingroup$ So, if I understand correctly, after the docking post is upgraded in June 2015, they are more likely to use Dragon 2? $\endgroup$
    – neelsg
    Commented May 29, 2015 at 7:55
  • $\begingroup$ @neelsg It depends. They have to finish the Crew Vehicle, compete for CRS-2, work on BRF/MCT. I am thinking that a third Dragon config just for testing is probably not something they want to take on. $\endgroup$
    – geoffc
    Commented Jun 2, 2015 at 1:04

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