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I've pored over the pictures and still I can't figure it out.

I know the second stage separates from the first stage using positive force from pneumatic pushers.

I also know that the payload fairing (the wider bullet shape used to deliver satellites to space) has a mounting plate which allows for any type of payload adapter chosen by the customer.

But the space station cargo resupply missions don't use the payload fairing---they use the cargo Dragon. And the cargo Dragon attaches to the Falcon stage through the trunk. So what is that connection like, and more importantly, what type of separation system do they use?

I assumed pneumatic pushers would be it, but this doesn't seem right. For one, there are no protrusions for pusher cylinders as seen on the interstage. If they could do without those protrusions between the second stage and the trunk, they would have done without them on the interstage too, it seems.

I do see a few things on the trunk that suggest mounting points. There are six of them arranged hexagonally. Picture below. These could be collets for locking, but there is no trace of a pneumatic cylinder here or on the second stage.

enter image description here

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    $\begingroup$ are you sure there are six, looks like four to me. $\endgroup$ – user20636 Jun 10 '20 at 9:40
  • $\begingroup$ @JCRM It was six in the earlier version of the Dragon trunk, where you could clearly see a six-point hexagonal symmetry, though in the newer version there seems to be quad symmetry---so maybe four or eight holes? I'm leaning toward eight because there are holes directly under the fins, and not just between them... $\endgroup$ – user36480 Jun 10 '20 at 20:36
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Some text from this NASA paper:

Of the shock events, (1) and (2) are negligible for the payload relative to (3) and (4) due to the large distance and number of joints over which shocks (1) and (2) will travel and dissipate. Maximum shock loading (3) and (4) is measured and scaled for various preloads required for the payload fairing and payload separation systems.
The resulting maximum shock environment predicted at payload interface for payload fairing separation and payload separation (for a 937‐mm clampband separation system) is shown in Figure 5‐3. Actual shock from the payload‐specific separation system requires selection of a separation system and the associated payload mass properties.

and

SpaceX has experience integrating numerous commercially‐available and internally‐developed payload separation systems. A Marmon clamp system was flown on the first Falcon 1 demonstration flight 1 and a LightBand system from Planetary Systems Corporation was employed on the second Falcon 1 demonstration flight. Additionally, SpaceX is currently developing a low‐shock tension band separation system for the Falcon 9, which uses a non‐ pyrotechnic release mechanism.

EDIT

With thanks to commenter "Alex,"

From the 2020 Falcon 9 manual: The Falcon second-stage and Falcon Heavy side-boosters restraint, release, and separation systems use pneumatic devices that provide low shock release and positive force separation over a comparatively long stroke.

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  • $\begingroup$ How does the non‐pyrotechnic release mechanism work? Hydraulic, pneumatic, electro-motoric? $\endgroup$ – Uwe Jun 10 '20 at 11:50
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    $\begingroup$ @Uwe Right now they use hydraulic system to separation mechanism but they have a plan to move to purely electro-mechanical actuators for the Starship. You can see Elon talking about it in this video at 13:18 mark. They do this because explosive bolts cannot be tested beforehand while non-pyrotechnic mechanisms can be tested with Hardware-In-The-Loop simulation. $\endgroup$ – OrangeDurito Jun 10 '20 at 12:13
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    $\begingroup$ I very strongly suggest that is talking about the payload attachment shown on page 30 - dragon and its trunk aren't using that. $\endgroup$ – user20636 Jun 10 '20 at 12:30
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    $\begingroup$ So are you saying Crew Dragon uses a "band separation system"? A delayed correct answer >> a quick wrong answer. $\endgroup$ – Organic Marble Jun 10 '20 at 13:31
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    $\begingroup$ The interstage separation mechanism is not hydraulic. It's pneumatic. From the 2020 Falcon 9 manual: The Falcon second-stage and Falcon Heavy side-boosters restraint, release, and separation systems use pneumatic devices that provide low shock release and positive force separation over a comparatively long stroke." @Uwe $\endgroup$ – user36480 Jun 10 '20 at 18:47

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