1. The grid that cannot fail

Isaac Asimov’s Foundation returns as the recalled work because the Galactic Empire’s planets are linked by vast energy and transport networks that function quietly until they don’t. A spacecraft’s power distribution network is smaller but similarly invisible: converters, buses, and switches that must work perfectly because there is no repair crew.

This entry reads about power electronics and distribution in spacecraft.

2. Bus architecture

Spacecraft use one or more power buses to move energy from sources to loads. Common choices include:

  • Unregulated bus: the bus voltage follows the battery and array state. It is simple but requires loads to tolerate a wide input range.
  • Regulated bus: a main converter holds the bus at a fixed voltage, simplifying load design at the cost of converter mass and losses.
  • Hybrid bus: partially regulated or multiple buses for different load classes.

Bus voltage is a system-level choice. Traditional values include 28 V and 50 V; newer high-power spacecraft use 100 V or more to reduce current and cabling mass.

3. DC-DC converters

DC-DC converters transform the primary bus voltage into the secondary voltages needed by processors, sensors, radios, and actuators. A NASA abstract on radiation-hardened DC-DC converter design notes that power converters are particularly sensitive to radiation: total dose causes gradual degradation, while single-event effects can disturb feedback control and PWM circuits.

Microchip’s space-grade DC-DC converters offer rad-hard options with decades of flight heritage. EPC Space promotes gallium-nitride-based converters for higher switching frequency, efficiency, and power density than traditional silicon.

4. Power MOSFETs and single-event burnout

Power switches are vulnerable to single-event burnout (SEB), in which a heavy ion triggers a parasitic bipolar transistor in a MOSFET and destroys the device. A review of SEB in silicon carbide MOSFETs explains that wide-bandgap devices are attractive for space power but require careful derating and protection.

Mitigation techniques include:

  • Voltage derating: operating MOSFETs well below their rated voltage.
  • Current limiting: fast current detection and shutdown before thermal runaway.
  • Redundant switches: so that one failure does not open or short the bus.
  • Rad-hard or rad-tolerant parts: for paths where failure is catastrophic.

5. Distribution and protection

Power distribution units use latching current limiters or electronic circuit breakers to isolate faults. A short in one load should not collapse the main bus. Key functions include:

  • Inrush limiting: preventing startup currents from tripping protection.
  • Sequential switch-on: powering subsystems in a controlled order after a bus recovery.
  • Telemetry: reporting voltage, current, and status for each channel.
  • Remote control: allowing ground or autonomy to switch loads on and off.

6. What this changes

  • The desktop needs a deliberate bus voltage and distribution architecture.
  • DC-DC converters are both radiation-sensitive and mission-critical; they need either rad-hard parts or robust protection.
  • Power switches need SEB protection and fault isolation.
  • The next entry will synthesize the power reading arc into requirements for the desktop.