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RiverForge

Sector coordination · ground to station

Modular spacecraft · ISAM / MOSA

One keel. Replaceable rooms.

The living hull is not a one-piece miracle. It is a berthing hatch for people, a docking ring for ferries, and small ORU latches for boxes that fail. Same lesson as ice class: the interface is the mass tax.

Kit visualization

Rooms off the spine.

Tap a class. Native lights. Adapter is copper.

  1. 01 · native · bolt

    Habitat

  2. 02 · none · ORU

    Power

  3. 03 · none · ORU

    Propulsion

  4. 04 · native · bolt

    Docking

Spine

  1. 05 · adapter · ORU

    Life support

  2. 06 · native · bolt

    Workshop

  3. 07 · none · ORU

    Science

  4. 08 · native · bolt

    Logistics

Four mating faces: square berth, circular dock, robotic latch, small plug

CBM · IDSS · SIROM · iSSI

People use hatches. Payloads use latches. Mixing them is an adapter you carry for life.

Robotic arm berthing a habitat module to the carrier

Berth · large module

The module does not fly itself in. The arm places it. That is why CBM exists.

Keel coverage

56

4 native · 1 adapter · CBM

Adapter tax

12%

Unprepared hulls pay more. Ice-belt logic, in orbit.

MOSA index

63

Watch

Coverage plus prepared interfaces.

Mating class

Common Berthing Mechanism. Square hatch, 1,300 mm. Large modules that cannot fly themselves into a port.

Berth

Passage
1,300 mm
Androgynous
No
Power
After mate
Capture
Robotic berthing · Canadarm class

Data: ISS utilities after hard mate. Flown or planned on ISS USOS, Cygnus, Dragon 1.

72

NASA ISAM: a prepared craft carries fiducials, fill ports, and standard latches from the drawing. Zero is a legacy bus you service with luck.

Coverage by class

How much of the eight-room keel each standard can hold without a custom adapter.

Keel fit

Against CBM. Native is a bolt. Adapter is a ring you carry for life. None means pick another class.

  1. native · bolted · idx 14

    Habitat

    Sleep, galley, sickbay. Separate from cargo.

  2. none · ORU · idx 6

    Power

    Solar + storage. No single-string bus.

  3. none · ORU · idx 8

    Propulsion

    Station-keeping and slow transfer. Twin.

  4. native · bolted · idx 5

    Docking

    Ferry, tug, barge. The harbour.

  5. adapter · ORU · idx 7

    Life support

    Air, water, heat. The hard constraint.

  6. native · bolted · idx 6

    Workshop

    Repair in place. Spares, not prayers.

  7. none · ORU · idx 4

    Science

    Observation and materials. Payload, not chrome.

  8. native · bolted · idx 9

    Logistics

    Stores, freeze, waste. The unglamorous half.

Design rules

  1. Prepared, not heroic

    NASA ISAM: a prepared hull carries fiducials, fill ports, and standard latches from the drawing. Unprepared craft make every service a special.

  2. Crew hatch ≠ ORU latch

    CBM and IDSS move people. SIROM and iSSI move boxes. Mixing them is an adapter tax you pay forever.

  3. Open interfaces

    MOSA: major interfaces are consensus standards you can verify. A private bolt pattern is a lock-in, not a design.

  4. Replace the box, not the ship

    Power, propulsion, ECLSS, science are orbital replacement units. Habitat and workshop stay bolted. That is the living keel.

Sources

  • CBM 1,300 mm square hatch; IDSS 800 mm circular, androgynous — docking vs berthing on ISS, Dragon 2, Starliner, Orion.
  • SIROM: mechanical + power + data + thermal; ±5 mm / ±1.5°; 150 W; SpaceWire 100 Mbit/s — Sener / STRIDE papers.
  • iSSI space-demonstrated 2022 — iBOSS. Prepared vs unprepared servicing — NASA GSFC ISAM. Open major interfaces — DoD MOSA.