Essential Loads Bus
28 V DC Essential Loads Distribution Bus
The 28 V DC essential loads distribution bus is a 30 kg electrical subsystem comprising tinned copper bus bars and MIL-DTL-38999 connectors that supplies power to safety-critical systems, including communications, navigation, and command and data handling. Stepping down power from the main 400 V bus through redundant DC-DC converters, the unit isolates essential subsystems from upstream electrical faults. Because uninterrupted availability is non-negotiable for critical telemetry and safety monitors on the lunar surface, the 100 A bus incorporates a direct battery bypass feed designed to maintain 48 hours of autonomous operation if the primary power grid fails.
28 V DC essential bus for low-power critical loads (CDH, comm, sensors) — survives main-bus faults via dedicated battery feed.
Purpose
28 V DC essential bus for low-power critical loads (CDH, comm, sensors) — survives main-bus faults via dedicated battery feed.
Context
Child of L2-PDM-BUS within the Lunar Ark system
Principles
- ▸28 V is the spacecraft heritage standard for low-power electronics
- ▸Isolated from main 400 V bus via redundant DC-DC converters
- ▸Direct battery feed bypass during main-bus fault
- ▸Critical loads only — CDH, COM, NAV, safety monitors
- ▸MIL-STD-704 compatible voltage envelope
Typical implementations
- ▸ISS 28 V essential loads bus heritage
- ▸Apollo / Shuttle 28 V architecture
- ▸Commercial spacecraft 28 V backbone (Boeing 702, Lockheed A2100)
Lunar considerations
- ▸Continuous availability is non-negotiable for safety-critical loads
- ▸Hardware-enforced isolation from main bus
- ▸Battery feed sized for 24+ hour autonomy if main fails
Specifications
Functional
| primary function | 28 V DC essential bus for low-power critical loads (CDH, comm, sensors) — survives main-bus faults via dedicated battery feed. |
| bus voltage v | 28 |
| rated current a | 100 |
| autonomy hours battery | 48 |
Physical
| mass kg | 30 |
| materials | Tinned Cu bus bars, MIL-DTL-38999 connectors |
| vacuum compatibility | True |
Operational
| power consumption w | 0 |
| thermal range c | -40, 70 |
| lifetime years | 50 |
| mtbf hours | 500000 |
Interfaces
Provides
- Always-on 28 V to CDH
- Always-on 28 V to communications
Requires
- Battery backup feed
- Primary 400 V via DC-DC
Cite this entry
Lunar Ark Codex. "Essential Loads Bus" (L3-PDM-BUS-ESS). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-PDM-BUS-ESS
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.