1. The book that knew everything

Douglas Adams’s The Hitchhiker’s Guide to the Galaxy is a small electronic book that somehow contains the useful parts of an entire galaxy. The desktop’s storage cell is less ambitious. It just needs to hold enough data to keep the compute attachment fed and the customers happy.

Entry 224 decided storage should live in dedicated cells. This entry sizes the first one.

2. What the storage cell must hold

A first-generation storage cell has four kinds of cargo:

  • Raw sensor data. Imagery from Earth observation payloads before processing.
  • Processed products. Outputs from the compute attachment: mosaics, change maps, feature masks.
  • Downlink buffer. Data waiting for a ground station pass.
  • Customer archive. Datasets customers want kept on orbit for latency or data-sovereignty reasons.

The archive is the least predictable. The other three can be estimated from the sensor and the duty cycle.

3. Capacity estimate

A moderate-resolution optical or small SAR payload might produce tens of gigabytes per day of raw data. Processed products are smaller if they are derived layers rather than full scenes. A downlink buffer needs to hold at least one full orbit of data, perhaps a few hundred gigabytes.

Add margin for the customer archive and for the fact that storage media cannot be filled to 100 %. A reasonable first cell capacity is in the 8–16 TB range. This is large enough to hold weeks of raw data and processed products, plus a modest archive, without dominating the cell’s mass or power budget.

4. How many cells

One cell is not enough. If it fails, the desktop loses all durable storage. Two cells allow mirroring. Three cells allow the storage layer to survive a single failure while remaining available during maintenance.

For the first desktop, two storage cells is the minimum credible configuration. Three is safer if the mass and power budgets allow.

5. Power and mass

Each cell draws roughly 30–60 W when active and under 10 W idle. Two cells add 60–120 W to the desktop budget, comparable to one compute attachment.

Mass depends on the drives and the cell structure. A few kilograms per cell is plausible for a first generation built around commercial SSDs.

6. Growth path

Storage demand tends to grow faster than compute demand. Customers always want more archive and longer retention. The desktop should allow additional storage cells to be added without reconfiguring the network or the software stack.

What this changes

  • A first-generation storage cell should hold 8–16 TB.
  • The first desktop needs at least two storage cells for redundancy, preferably three.
  • Storage power is comparable to a single compute attachment, not a dominant load.
  • The next entry can decide how the compute attachment talks to the storage cells: filesystem, object store, or block device.