1. What Mark Watney would notice

Andy Weir’s The Martian is obsessed with power budgets. Every watt has a source, a storage limit, and a consequence. The desktop is not stranded on Mars, but the same discipline applies: if the sensor, compute, communications, and robotics all turn on at once, something must give.

Entries 230 through 235 defined the sensor attachment. The result is a modest but commercially credible Earth observation imager: 3–5 m resolution, steerable bracket, onboard processing pipeline, and a price list. This entry closes that arc and decides what to define next.

2. What the sensor arc settled

The desktop’s baseline sensor is not a flagship science instrument. It is a workhorse product that gives the compute attachment something to process and gives customers a reason to buy.

The decisions are:

  • Baseline 3–5 m optical imager plus customer payload slots.
  • 25–35 km swath, four multispectral bands, 6–12 kg mass.
  • Steerable bracket for 2–4 day revisit without spacecraft body roll.
  • 5–10 W average power, 10–15 W heat rejection.
  • Onboard L0-to-L1C pipeline with cloud screening and compression.
  • Scenes, archive slices, change feeds, and raw data as product tiers.

These numbers are not final engineering specifications. They are a boundary inside which detailed design can happen. That is exactly what a ledger entry should do.

3. What remains outside the arc

Several hard questions were deliberately not answered:

  • How does the imager share the nadir face with antennas, radiators, and docking fixtures?
  • What happens when a customer payload wants the same pointing axis?
  • How is the sensor replaced or upgraded over the desktop’s lifetime?
  • What calibration infrastructure is needed on the ground?

These are integration and operations questions, not sensor questions. They will be answered when the rest of the desktop’s attachments are known.

4. Why power is next

The next attachment to define is the power attachment: solar arrays, batteries, and power distribution. There are three reasons for this order.

First, every other attachment is downstream of power. Compute, storage, communications, sensors, robotics, and thermal control all consume electricity. The power attachment is the attachment that enables the others.

Second, the desktop’s power budget from entry 187 is still an aggregate number. It needs to be decomposed into generation capacity, storage capacity, peak load capability, and distribution architecture.

Third, solar arrays are one of the largest physical attachments on the spacecraft. Their area, deployment method, and pointing strategy drive structural and thermal design in ways that cannot be deferred.

5. The power questions to answer

The next few entries should answer:

  • How much solar array area does the desktop need?
  • Does it use body-mounted panels, deployable wings, or a mix?
  • What battery chemistry and capacity are appropriate?
  • How is power distributed to attachments with different voltage and reliability needs?
  • What is the eclipse power budget, and how deep a discharge is acceptable?

These are ordinary engineering questions, but they deserve their own ledger arc because the answers constrain almost everything else.

What this changes

  • The sensor attachment arc is closed with a consistent set of specifications, products, and prices.
  • The next arc will define the power attachment: generation, storage, and distribution.
  • Integration questions about the sensor are held until the power, thermal, and structural attachments are defined.
  • The desktop’s attachment grid now has a proven pattern: define function, then specs, then mounting, then power/thermal, then processing, then products.