1. The floating forest

Larry Niven’s The Integral Trees is set in a gas torus around a neutron star, where life clings to kilometre-long trees that drift in free fall. The trees are not anchored; they are structures that exist because the forces around them hold them in place. The desktop is anchored by no tree, but its structure is the same kind of equilibrium: a balance of launch loads, thermal distortion, deployment forces, and the mass budget.

Entries 247 through 251 defined the structural attachment. This entry closes that arc and decides what to define next.

2. What the structural arc settled

The desktop’s structure is now a coherent subsystem rather than a default box.

The decisions are:

  • The structural attachment carries loads, defines interfaces, and enables access.
  • The body is a roughly 1 m frame-and-panel aluminium structure.
  • Primary loads are sized for roughly 6 g launch acceleration plus deployment, thermal, and robotic operations.
  • The layout assigns faces for radiators, solar arrays, sensors, communications, and internal equipment.
  • Materials are 6061-T6 aluminium for the frame, aluminium honeycomb panels for sides, with 7075-T6 for high-stress fittings.
  • Attachment interfaces include alignment pins, rails, a motor-driven latch, blind-mate connectors, and a thermal contact surface.
  • Standard form factors let attachments be designed independently.
  • Robotic access is designed into the layout with clear arm envelopes, fiducials, lighting, stowage, and external servicing fixtures.
  • Structural attachment mass is roughly 20–30 kg.

These decisions give the propulsion and attitude control systems known hard points for thrusters, tanks, and actuators. They also give the operations attachment a known map of what can be reached and replaced.

3. What remains outside the arc

Several integration questions were deliberately deferred:

  • How are propellant tanks mounted and isolated from the rest of the structure?
  • Where exactly do thrusters fire without impinging on solar arrays, radiators, or antennas?
  • How does the attitude control system interface with the structural frame for reaction wheels and magnetorquers?
  • What is the exact bolt pattern and connector pinout for the attachment standard?

These will be answered when the propulsion, ADCS, and operations attachments are defined.

4. Why propulsion is next

The next attachment to define is the propulsion attachment: thrusters, propellant tanks, feed lines, and valves. There are three reasons for this order.

First, the desktop must maintain its orbit. LEO drag, collision avoidance, and eventual disposal all require delta-v. Without propulsion, the desktop is a passive object with a limited lifetime.

Second, propulsion is structurally intrusive. Tanks need volume and mounting. Thrusters need clear exhaust plumes. Feed lines need routing. These decisions cannot be made after the structure is frozen.

Third, propulsion couples to power and thermal. Thruster heaters keep propellant from freezing. Power is needed for valves and catalyst beds. Propellant slosh affects attitude control. The propulsion design must be developed alongside the structure, power, and ADCS.

5. The propulsion questions to answer

The next few entries should answer:

  • How much total delta-v does the desktop need over its lifetime?
  • What propellant and thruster technology are appropriate?
  • How are tanks sized and mounted within the structure?
  • Where are thrusters placed to avoid plume impingement?
  • How is propulsion integrated with attitude control and orbit manoeuvres?
  • What safety margins and failure modes must be managed?

These are ordinary engineering questions, but they deserve their own arc because the answers determine whether the desktop can stay in orbit and avoid becoming debris.

What this changes

  • The structural attachment arc is closed with consistent specifications for loads, layout, materials, interfaces, and robotic access.
  • The next arc will define the propulsion attachment: delta-v budget, thrusters, tanks, and integration.
  • Integration questions about structure are held until propulsion, ADCS, and operations attachments are defined.
  • The desktop’s attachment grid now has a fourth proven pattern, following the sensor, power, and thermal arcs.