1. The minimum credible thing
Robert A. Heinlein’s The Moon Is a Harsh Mistress is about a colony that wins its independence by doing what is possible with the tools at hand, not by waiting for perfect ones. The keeper demo should follow the same rule. The goal is not to build the ideal servicer. The goal is to do the smallest thing that proves the keeper idea is worth taking seriously.
Entries 168 and 169 narrowed the options. Entry 168 said risk retirement costs roughly one-third of the mission budget. Entry 169 said a non-contact demo is credible but insufficient, and a hybrid with a passive marker might be the sweet spot. This entry defines that hybrid minimum demo in detail.
2. Mission scope
Objective. Approach a spent upper stage in LEO to within ten meters, hold relative position, and deploy a small passive marker that remains attached to or in the vicinity of the target.
What is not included. No grapple. No deorbit. No sample return. No orbital modification. The servicer does not push, pull, or retrieve the stage. It only proves it can get close and leave something behind.
Why this is enough. The hard part of the keeper’s future work is relative navigation and proximity operations. Attaching a passive marker is a low-risk way to add physical interaction without requiring complex contact dynamics. A funder can verify success from the ground by tracking the marker.
3. Spacecraft
- Dry mass: ~60 kg.
- Wet mass: ~75 kg.
- Bus: commercial cubesat/microsatellite bus with flight-proven power, comms, and attitude control.
- Navigation: camera plus lidar for relative navigation.
- Propulsion: cold-gas or small chemical thrusters for proximity operations.
- Payload: a spring-deployed or adhesive marker, no heavier than 1 kg.
4. Cost estimate
| Item | Cost |
|---|---|
| Launch as rideshare | $1–2 M |
| Satellite bus and components | $1.5–3 M |
| Relative navigation payload | $0.5–1 M |
| Marker and deployment mechanism | $0.2–0.5 M |
| Risk-retirement testing | $1–2 M |
| Integration, test, and operations | $1–2 M |
| Contingency | $0.5 M |
| Total | $6–11 M |
This is roughly $4–6M cheaper than the full contact demo from entry 163 and about one year shorter in schedule. It is not free, but it is in the range of a single NASA Tipping Point award or a small defense technology demonstration.
5. Schedule
- Months 0–4: requirements, target selection, and bus procurement.
- Months 4–10: payload development and navigation software.
- Months 10–16: integration, environmental test, and risk retirement.
- Months 16–20: launch, checkout, and approach campaign.
Twenty months from contract to contact is aggressive but achievable for a mission this constrained.
What this changes
- The keeper’s first credible demo is redefined as a close approach with a passive marker, not a grapple.
- The budget drops to $6–11M and the schedule to roughly twenty months.
- This version is small enough to fit into existing small-satellite technology demonstration programs.
- The next leisure entry can ask what success looks like for this specific mission and how to communicate it.