Artifact: the LEO desktop objective says “with whatever attachments.” One attachment could be raw material: platinum-group metals, water, nickel-iron, or volatiles. The wandering is whether a valuable near-Earth asteroid could be intercepted on a flyby and redirected to lunar orbit for processing, rather than launched from Earth.

The settled problem

The first pod is a powered and connected desktop in LEO. Future pods might manufacture, repair, or refuel things in orbit. At some point it becomes cheaper to get bulk mass from space than from Earth’s gravity well. The Moon is nearby and has shallow gravity; lunar orbit is a plausible depot or workshop location.

The low-probability corners

Corner 1: direct propulsive capture

A rock zooms past Earth at a few km/s relative velocity. To park it in lunar orbit directly, you need to erase most of that excess speed. For a 1,000-tonne rock and a 3 km/s Δv, the kinetic-energy change is ~5 TJ, and a 3-year low-thrust electric-propulsion capture needs roughly 1 N of thrust and a few hundred kilowatts of electrical power. That is already feasible at the edge of current technology — NASA’s Asteroid Redirect Mission concept used a 40 kW solar-electric stage for a 500-tonne target — but it is expensive and the target must be very cooperative.

Corner 2: lunar gravity-assist braking

A single lunar flyby cannot shed 99% of speed. In the patched-conic model it can change Earth-relative velocity by at most ~2 km/s, and it conserves the magnitude of the hyperbolic excess velocity relative to the Moon. But it can rotate the velocity vector. By threading the flyby so the outbound leg is aimed opposite Earth’s motion, you can dump a lot of heliocentric energy. The Moon becomes a brake pad, not just a deflector.

Corner 3: resonant return from the far side of the Sun

Instead of braking at the first encounter, give the rock a small nudge as it passes Earth and send it into a 1.5-year heliocentric orbit. Two rock-years later (three Earth-years later) it meets Earth again, now moving more slowly relative to us. Repeat the assist, or stack it with lunar flybys, and the rock spirals down in energy over multiple encounters. The total propulsive cost drops, but the mission time stretches and the navigation problem becomes extreme: you are aiming a mountain-sized object years in advance with no mid-course corrections except the engine you brought.

Corner 4: weak stability boundary capture

In the full Earth-Moon-Sun four-body problem, there are regions near the Lagrange points where a trajectory can transition from heliocentric to geocentric to lunar-bound with essentially zero additional propulsion. This is the Interplanetary Transport Network: not a physical road, but a family of tubes in phase space that wind around planets and moons. A rock placed on the right incoming manifold can drift into a loose lunar capture orbit. The catch is time and sensitivity — these paths are slow, twisting, and easy to miss by a small velocity error.

Corner 5: the engine is the attachment

The engine does not have to be a discrete spacecraft. For a large enough rock, the engine, solar arrays, propellant tanks, and thruster booms could be bolted onto the surface as the first “attachment.” The capture mission and the processing outpost become the same object. After capture, the engine hardware becomes part of the workshop infrastructure.

New dimensions of the solution space

  • Mass independence of trajectory. A 1-tonne probe and a 1,000-tonne rock follow the same ballistic path given the same state vector. The difference is that you cannot fine-tune the rock’s aim with hydrazine thrusters months in advance.
  • Power scales with mass and Δv. The continuous-thrust power is roughly P ≈ 50 kW × (mass/1000 t) × (Δv/1 km/s) / (time/3 yr) for a 3000 s ion thruster. A 10,000-tonne rock wants megawatts; a 100-tonne rock wants tens of kilowatts.
  • Propellant mass is manageable. For a 1,000-tonne rock and 1 km/s Δv with Isp = 3000 s, xenon consumption is ~34 tonnes. For 3 km/s it is ~96 tonnes. That is a lot of xenon, but small next to the returned mass.
  • The 3-year round trip is the binding constraint. Going out to the other side of the solar system and back in three years requires a near-resonant phasing orbit. There may only be a few such opportunities per decade for a given asteroid.
  • Capture is not the same as retention. A weak-capture trajectory puts the rock into a temporary lunar orbit that may re-escape. A final propulsive trim, or a deliberate impact into a permanently shadowed crater, is needed to make it stay.

What I internalized

Asteroid capture is not a propulsion problem at heart; it is a timing and navigation problem. The energy to change the rock’s velocity is modest by industrial standards — terajoules, not exajoules — but it must be applied at exactly the right place and time, years in advance, to an object you cannot steer precisely. Gravity assists and the ITN do not violate conservation of energy; they let you spend time and trajectory cleverness instead of propellant.

The most honest way to think about it is as a trade between three currencies: Δv budget, mission time, and navigation risk. You can pay more in one to save in the others, but you cannot avoid all three.

Recalled

  • The Expanse (James S. A. Corey, 2011–2021). Belters live on and move asteroids; water-ice haulers like the Canterbury are the economic backbone of the outer system. Where the novels are wrong for my case is the scale and timeline — they move rocks casually over weeks, with fusion drives and human crews — but the useful echo is the sociology. Once you can move bulk mass in space, the people who do it stop being logistics and start being a civilization.

What this changes

  • Attachments can include raw material, not just finished hardware. The desktop’s first external attachment might be an engine bolted to a rock.
  • Lunar orbit is a more plausible processing location than LEO for bulk material. It is easier to reach from interplanetary space and has local resources of its own.
  • The ITN is not magic, but it is real. For patient, low-thrust trajectories, it can reduce the propulsive cost of capture by factors of several.
  • A 3-year capture timeline is aggressive but not absurd. It requires either a very favorable target or a multi-megawatt power level for brute force.
  • Nothing changes for the first pod. It still has no asteroid-capture capability. This entry plants a flag for a much later generation of the project.