1. The signal and the listener

Carl Sagan’s Contact is about a message from far away and the effort to hear it clearly. The desktop’s communications attachment has the opposite problem: it must send its own signals clearly, to ground stations and to other spacecraft, while listening for commands from Earth.

Entry 228 closed the storage arc. This entry turns to the attachment that makes the desktop connected.

2. What the communications attachment does

A first-generation communications attachment handles four traffic types:

  • Telemetry and command. Low-rate, reliable links to the ground for health data and operator commands.
  • Payload data downlink. High-rate links that move processed Earth observation products from storage to customers.
  • Inter-satellite links. Connections to other spacecraft, including relay constellations or other desktop nodes.
  • Customer access. Direct network access for customer payloads that need to reach their own ground systems.

Not all of these are required on day one, but the attachment should be designed to grow into them.

3. Minimum viable definition

A first communications attachment could be:

  • One or more software-defined radios, allowing bands and waveforms to be updated after launch.
  • An S-band link for telemetry and command, using heritage ground station networks.
  • An X- or Ka-band link for payload data downlink, where spectrum and licenses allow.
  • A set of antennas with modest steering, either body-fixed or on simple gimbals.
  • A network interface that routes traffic between radios, compute, storage, and customer payloads.

The key idea is flexibility. A software-defined radio can be reprogrammed as customers and regulations change.

4. Power estimate

Communications power depends heavily on data rate and distance. A telemetry link might use 10–20 W. A high-rate payload downlink can use 50–100 W or more during a ground station pass. The attachment is not always transmitting, so average power is lower than peak power.

For budgeting, assume 50–100 W peak and 20–30 W average. This is comparable to a compute attachment.

5. Interface to compute and storage

The communications attachment should look like another network device to the compute and storage cells. Data to downlink is read from the object store, formatted by the compute attachment or a dedicated communications processor, and passed to the radio. Commands from the ground arrive at the radio and are forwarded to the platform’s command system.

This separation lets the communications hardware evolve without changing the compute or storage software.

6. Laser communication as a future upgrade

Optical or laser communications offer much higher data rates than RF for the same power. The technology is maturing but not yet as available as RF ground station networks. The first desktop can use RF and reserve physical volume and power for a future laser communications upgrade.

What this changes

  • The communications attachment is a flexible, software-defined radio system with S-band for control and X/Ka-band for payload data.
  • It connects compute and storage to the ground and to other spacecraft through standard network interfaces.
  • Peak power is significant but intermittent; average power is moderate.
  • The next entry can decide whether the first desktop also needs its own sensor attachment or relies on customer payloads for Earth observation data.