1. The mass budget is the mission

Tom Godwin’s “The Cold Equations” is the most ruthless short story about mass budgets ever written. A girl stows away on a small emergency craft; the craft has exactly enough fuel for its payload; the equation does not care about her reasons. Any demonstration mission for the keeper will be governed by the same arithmetic. The difference is that we get to design the payload, so we can make the equation kinder.

A spent-stage demo mission is the right place to start because the target is known. We know where it is, how big it is, what it is made of, and roughly how it is tumbling. The mission becomes a controlled exercise in rendezvous, contact, and minimal manipulation rather than a speculative encounter with an unknown rock.

2. Picking the target

The ideal first target is a spent upper stage in a low-inclination LEO orbit, between 400 and 800 kilometers altitude, with a slow and stable tumble. It should be large enough to be radar-tracked and small enough that a lightweight servicer can meaningfully interact with it. A Falcon 9 second stage, a Centaur, or a Briz-M fits this description. The mission is not trying to deorbit the stage; it is trying to prove we can touch it without making things worse.

The target should also be unowned in practice. Most launch providers do not actively control dead stages, and the legal path for a demonstration approach is simpler than for an active satellite.

3. The servicer sketch

For a first mission, the servicer should be deliberately small. Something on the order of 50 to 100 kilograms, launched as a rideshare, with the following minimum stack:

  • A camera and a lidar for relative navigation.
  • A small chemical or cold-gas propulsion system for proximity operations.
  • A lightweight capture interface: a gripper, a harpoon, or a magnetic pad.
  • A short-range radio for telemetry.
  • A small printed-polymer sample to leave behind or attach.

The goal is not to take the stage anywhere. The goal is to match its motion, make contact, and demonstrate that the keeper’s smallest operational unit can operate in the real orbital environment.

4. The sequence

Launch and checkout. Wait for a favorable phasing. Approach from below and behind, using the stage’s known TLE set. At a few hundred meters, switch to onboard relative navigation. Close to contact under manual or supervised autonomous control. Touch the stage. Record the contact forces, the thermal response, and any unexpected motion.

After contact, either release or attach a passive marker. The marker is important: it proves the encounter happened and gives ground observers a way to confirm the servicer reached the target. Then back away and downlink the data.

5. What it proves

This mission proves very little about asteroid capture directly. What it proves is the operational competence that asteroid capture requires: navigation, proximity operations, contact mechanics, and communication under tight constraints. It also proves that the keeper can be small. A 100-kilogram servicer that touches a dead stage is more credible than a whitepaper about a ten-ton asteroid tug.

What this changes

  • The first keeper mission is reframed as a small, rideshare-class servicer touching a dead upper stage, not as a full capture.
  • Success criteria become operational: rendezvous, contact, and safe separation rather than orbital modification.
  • The mission serves as a qualification flight for the keeper’s core contact and navigation stack.
  • The next leisure entry can estimate mass, cost, and launch opportunities for this mission profile.