Mechanical Pump Assemblies
Centrifugal/Positive-Displacement Fluid Loop Pump Assemblies
Mechanical pump assemblies are electrically driven centrifugal or positive-displacement units that circulate working fluid through closed piping networks connecting heat acquisition cold plates, heat exchangers, and radiators. On the lunar surface, external thermal cycling between -173°C and +127°C stresses seals and housing joints, while the surrounding vacuum requires hermetic motor enclosures and solid lubricants like molybdenum disulfide or PTFE composites to prevent outgassing. Because mechanical wear limits pump service life to 5–10 years, thermal transport systems employ redundant pump pairs and isolation valves to allow robotic cartridge replacement without draining the loop.
Electrically-driven mechanical pumps that provide forced circulation of working fluid through the thermal transport loops, maintaining design flow rates against system pressure drops.
Purpose
Generate the motive force to circulate thermal working fluid through closed-loop piping networks connecting heat acquisition cold plates, heat exchangers, radiators, and heat pump interfaces. Must deliver stable, controllable flow rates across the full range of thermal operating modes while supporting hot-swap robotic replacement.
Context
The pump assemblies are the mechanical heart of each fluid loop in L2-TCS-FLOP. Each independent loop requires at least two pumps (primary + redundant) to maintain single-fault tolerance. Pumps are the primary wear item in the fluid loop system with bearing and seal degradation limiting service life to 5-10 years, requiring periodic robotic replacement. Pump speed modulation is the primary means of adjusting loop heat transport capacity in response to changing thermal loads.
Principles
- ▸Centrifugal pumps convert rotational kinetic energy to fluid pressure via an impeller; suitable for high-flow, moderate-pressure applications
- ▸Positive-displacement pumps (gear, vane, diaphragm) trap and move fixed fluid volumes per revolution; better for precise flow control and high-viscosity fluids
- ▸Pump affinity laws: flow proportional to speed, head proportional to speed squared, power proportional to speed cubed
- ▸Net Positive Suction Head (NPSH) must exceed fluid vapor pressure to prevent cavitation, especially critical for two-phase loop operation
- ▸Brushless DC motor drives eliminate brush wear and enable hermetic sealing for vacuum-compatible operation
Typical implementations
- ▸ISS ETCS ammonia pump: centrifugal, 3600 RPM, 544 kg/hr flow rate, hermetically sealed motor
- ▸ISS ITCS water pump: centrifugal, variable-speed BLDC motor, 20-year design life with redundancy
- ▸Orion MPCV coolant pump: positive-displacement gear pump for propylene glycol/water
- ▸JWST Mid-Infrared Instrument cryocooler helium compressor/circulator
Lunar considerations
- ▸Vacuum environment requires hermetically sealed motor/pump housings with zero external leakage
- ▸Bearing lubrication in vacuum: solid lubricants (MoS2, PTFE composites) or magnetic bearings to eliminate liquid lubricant outgassing
- ▸Modular cartridge design enables robotic hot-swap without draining the loop: isolation valves upstream/downstream of pump module
- ▸Thermal environment cycling (-173C to +127C on exterior) stresses seals and housing joints; pumps should be in thermally controlled enclosures
- ▸Lunar dust must be excluded from pump maintenance interfaces via sealed quick-disconnect fittings with dust covers
Specifications
Functional
| primary function | Provide forced circulation of thermal working fluid through closed-loop piping at controlled flow rates and pressures |
| inputs | Electrical power from L1-PWR via motor drive electronics, Speed/flow commands from L2-TCS-CTRL, Working fluid from loop return manifold |
| outputs | Pressurized working fluid to loop supply manifold, Telemetry: pump speed (RPM), differential pressure, motor current, bearing temperature, vibration signature |
| flow rate range lpm | TBD (estimated 5-50 LPM per pump depending on loop) |
| differential pressure kpa | TBD (estimated 50-200 kPa) |
| speed control accuracy pct | +/- 2% |
| single fault tolerance | Redundant pump per loop (automatic switchover on failure) |
Physical
| materials | Aluminum 6061-T6 (pump housing, impeller), Stainless steel 316L (shaft, wear rings), PTFE composite (shaft seals, bearing cages), Neodymium magnets (BLDC motor rotor), Copper windings (BLDC motor stator) |
| operational temp range c | -40, 70 |
| storage temp range c | -173, 127 |
| vacuum compatible | True |
| vibration output | Must be characterized and isolated from sensitive instruments |
Operational
| thermal range c | -40, 70 |
| lifetime years | 10 |
| mtbf hours | 60000 |
| notes | 5-10 year replacement interval. Modular LRU design for robotic hot-swap. Pump housing remains installed; cartridge insert (motor+impeller+bearings) is the replaceable element. |
Interfaces
Provides
- Fluid motive force: pressurized working fluid at design flow rate to loop supply manifold
Requires
- Regulated DC power for BLDC pump motor (estimated 50-500W per pump depending on loop size)
- Speed setpoint commands, start/stop commands, fault response directives
- Isolation valves upstream/downstream enabling pump cartridge replacement without loop drain
- Robotic manipulation for pump cartridge extraction and installation
Cite this entry
Lunar Ark Codex. "Mechanical Pump Assemblies" (L3-TCS-FLOP-PUMP). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-TCS-FLOP-PUMP
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.