Standardization in Small - Micro satellites (Cubesats, ESPA, ESPA Heavy etc.)

[Rik ISS-fan]

I've searched NSF for a topic about ESPA and other small/micro satellite standards, but I couldn't find one.
In my opinion, there has to be a topic about: standardization in small, micro, and nano satellites. Thus I start this topic.
The satellites that are included in the Small, mini and micro satellite category range in mass from 10 to 500kg. (~20 to 1200 lbs)
The satellites below 10kg are discussed in the CubeSat & NanoSat Technology topic.
In this topic, satellite buses, standards coupling interfaces and rideshare structures can be discussed. 

The reason I searched for a ESPA topic, was a spacenews article from last week. I posted a reply in the CubeSat and NanoSat topic. (I've removed it there because it was off topic) This part is relevant here.

....
This was also a bit stupid in my oppinion: SpaceNews, Arianegroup .. smallsat standardisation....
  The larger segment is already standardized:
Cubesats 0.25-16U    (pocket cubes 1-4 P) [a loaded 12U/16U cubesat deployer ~32.5kg]
Here they have a point: ~30kg (or a 12/16U box); 50kg (or 100lb/45kg); 75kg ; 100kg (or 90kg/200lbf)
ESPA 15" ring; 180kg (400lbf)
ESPA Grande, 24" ring; 300kg (660lb)

OneWeb sat's as well as SpaceX sat's will indeed become standard busses.
...

Today I scrolled through the Small Satellite Conference proceedings. I found the presentation:  ESPA Class Redefined.
This presentation shows that the APL (ESPA auxiliary payload) capability for the standard 15" ring with 1/4" bolts, has been increased from 181kg (400lb) to 220kg (485lb) with a CG at 0.508m (20").
Besides this, also a ESPA Heavy class has been specified, this is a 15" ring with 5/16" bolts. It's 322kg (710lb) at 0.508m (20").

After reading this presentation, the SpaceNews article does make a valid point. ESPA has moved from 181kg to 220kg. Now a new standard has to be made for ~50kg, (100kg or 90kg/200lb), and 150-180kg (300-400lb) payloads.

ESPA specifies 15" and 24" clamp-band satellite adapters. There are also 8", 11,732", 13" clamp-bands, and there are satellite interfaces that use pyrobolts or another spring mechanism. I think that standards have to be specified for these smaller payload deployment interfaces. This makes it easier to arrange a launch for smaller payloads.

I'm thinking about 6 - 7 payload standards, for example:
- Nanosatellites or CubeSats (0.125 - 16U), mostly containerized into 12U (/16U) dispensers.
- Instead of a Cube-/ NanoSatellite container also a ~32kg (70lb) satellite can be mounted, to the ~250mm (10") rectangle bolt interface.
- 50kg (or 100lb/ 45.36kg) 8" ring or pyrobolt interface.
? 100kg (or 200-250lb (90.7-113.4kg) a 8"or 10-12" ring or pyrobolt interface ? (like Nanoracks Kaber)
- 150kg (or 300-400lb / 136-181kg) 13" or 15" ring.
- (new) ESPA 220kg 15" ring with 1/4" bolts (fasteners).
- ESPA Heavy 322kg; ring 15" with 5/16" bolts. or ESPA Grande 300kg (660lb), 24" ring.
? Small sat. <500kg 24" 5/16" bolts.??

If my estimations are correct, a plate with 4x 12U dispensers have a mass of ~150kg (new standard).
And a plate with 7x 12U have a mass of 250-322kg (ESPA Heavy). By clustering multiple cubesats with the deployment controller onto a plate, a bunch of cubesat's can take the place of a larger payload.

With these satellite standards and the cubesat-plates, the rest capacity of launchers can easier be filled, when appropriate carrying structures are developed. Lose Cubesat dispensers or Waferplate / CubeStack can be used when there is a small additional capacity on a launch. When there is a larger rest capacity a ESPA ring or mount-interface for multiple standard satellites can be used. (SSMS (6x50kg), ESPA-ring (4x/6x 220kg), SHERPA, etc.)