The baseline mechanism is intentionally ordinary: put a hub at the centre of a square, telescope one structural member toward each corner, and let a perimeter cord carry the membrane edges. It deploys a large, flat surface without curing chemistry, retained inflation pressure, or a chain of hinged edge members.

The interactive model shows the mechanism rather than a qualified flight design. Move the deployment control to watch the nested boom stages separate, the corner nodes pull the boundary outward, and the folded membrane flatten into its working geometry. The Structure only control reveals the complete load path beneath the fabric.

Geometry

For a square with side length s, each centre-to-corner member is half a diagonal:

hub-to-corner reach = s / √2

At the three-metre target size, the resulting geometry is:

Property Concept value
Deployed side length 3.00 m
Deployed membrane area 9.00 m²
Hub-to-corner reach 2.12 m
Structural arms four telescoping half-diagonals
Angle between arms 90°
Perimeter tension member 12.00 m closed cord
Hard boundary nodes one hub and four corners

The hub fixes the direction of all four arms. Equal deployed reach places the corner nodes on a square; the perimeter cord then establishes the membrane boundary and applies inward preload to the booms.

Deployment sequence

  1. Release the launch restraint. The membrane remains folded around the hub while the four corner nodes become free to travel.
  2. Extend the telescoping stages. Opposite arms can move as matched pairs, or all four can be driven from one synchronized hub mechanism.
  3. Pay out the perimeter cord. Each moving corner pulls two adjacent sides of the boundary into position.
  4. Open the membrane. Edge lacing transfers the expanding square boundary into the folded fabric.
  5. Latch full extension. Positive locks remove load from the deployment drive.
  6. Apply final tension. A short take-up stroke in the hub or corner nodes removes perimeter slack and flattens the membrane.

The model compresses these operations into one continuous motion so that the relationship between the parts remains visible.

Structural load path

The architecture separates the soft surface from the hard mechanism:

membrane
   ↓ distributed edge load
lacing loops
   ↓
perimeter cord
   ↓ four corner resultants
corner nodes
   ↓ compression and bending
telescoping half-diagonals
   ↓
central hub

The perimeter cord wants to pull every corner toward the centre. That resultant is carried primarily as compression in each telescoping arm. Out-of-plane pressure, thermal distortion, and deployment transients add bending, so the nested sections still require adequate overlap and anti-rotation guidance.

What belongs in the generic

The reusable mechanism should standardize:

  • the central drive and four fixed 90° boom axes;
  • nested structural sections and their deployed latches;
  • identical corner nodes;
  • perimeter-cord payout and take-up;
  • membrane lacing points;
  • deployment sensing and end-of-travel confirmation.

The membrane remains application-specific. The same chassis could carry a transparent sacrificial shield, an atomic-oxygen skin, a thermal-control surface, an antenna mesh, or a photovoltaic blanket. Those surfaces can change without redesigning the deployment kinematics.

Why this remains the baseline

Every critical transition is mechanical, visible, and resettable. The actual hardware can be deployed repeatedly during development. A bad latch, binding stage, or uneven cord is inspectable before flight. The square is established directly by the hub rather than by a cure state or residual inflation pressure.

The trade is moderate packaged volume. A nested boom cannot retract below the length of its longest stage, and each sliding interface adds clearance, thermal-expansion, and cold-welding considerations. The hub and four arms also cross the optical aperture, although they can sit behind the functional membrane and align with panel seams where shadow matters.

For this three-metre class, those are bounded engineering problems. Inflatable-rigidizable textiles become compelling when the span or launch-envelope constraint is large enough to justify one-shot material processing. They are not required to prove the membrane-frame generic.

Model boundary

The viewer represents telescoping stages, latches, cord routing, and fabric pleating schematically. It does not yet select section diameters, wall thicknesses, bearings, lubricants, tension level, drive torque, or launch restraints. Those values follow from membrane preload, disturbance acceleration, thermal gradients, allowable tip deflection, and the buckling margin of the longest unsupported stage.