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Is there any possibility that the power consumption is greater than power supply on ISS? What happens (or potentially would happen) if we plug too many electric devices so that ISS couldn't handle it?

I believe that there is an emergency system which powers life control system when fuses are blown. Would astronauts then have to replace the fuses? If yes, how much time do they have for that?

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    $\begingroup$ Just wondering what country you are residing in -- many countries have switched over almost entirely to resettable breakers rather than fuses for commercial and residential buildings. $\endgroup$ Mar 21, 2019 at 15:49
  • $\begingroup$ @CarlWitthoft I'm from Poland, and now I'm quite convinced that this happened here too, but I was probably influenced by my experience with car fuses ;) $\endgroup$
    – Elgirhath
    Mar 21, 2019 at 18:29
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    $\begingroup$ @CarlWitthoft One of those countries is the UK - but I still refer to "fuses" and "the fusebox". $\endgroup$ Mar 21, 2019 at 18:30
  • $\begingroup$ Fuses are still somewhat common in industrial applications since a small, inexpensive fuse can break incredibly large fault currents without exploding and/or welding closed. (here "small" means "size of a section of pencil at least" and "inexpensive" means "$30 usd"). $\endgroup$
    – ikrase
    Jan 27 at 7:01

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This answer addresses only the US side of the ISS.

Like everything else on the ISS, it's complicated.

enter image description here

Fuses are not commonly used on the ISS. There are fuses within the battery subassemblies, to protect against internal battery shorts.

The common circuit protection device on the ISS is the Remote Power Controller (RPC), a commandable "smart circuit breaker". An RPC monitors the current passing through it and opens the circuit if the current exceeds a limit for a specified amount of time. The RPC can be commanded to reset once the problem has been resolved. The RPCs are grouped into RPC Modules (RPCMs). If the input voltage to an RPCM drops too low, all the RPCs in the RPCM will open.

If the power usage gets higher than the supplied power can handle (for example, if a solar array is lost), the onboard computers (MDMs) can command a 'load shed'. Using tables preloaded into the software, the MDM(s) controlling the electrical power system will command the RPCs on a set of devices open, powering them off.

If the power loss event is predicted, the flight controllers can most likely do a better job of powering down the station based on the current configuration than the load shed tables would. They would send commands to open the desired RPCs.

enter image description here

I believe that there is an emergency system which powers life control system when fuses are blown.

As stated, fuses are not commonly used, and there is no such emergency system. The ISS already runs off battery power when the solar arrays are not generating power. The load shed tables are built so that critical functions are the last to be turned off.

Acronymology:

  • ARCU - American / Russian Conversion Unit
  • BCDU - Battery Charge / Discharge Unit

  • BGA - Beta Gimbal Assembly

  • DDCU - DC / DC Converter Unit
  • ECU - Electrical Control Unit
  • IDA - Integrated Distribution Assembly
  • IEA - Integrated Electronics Assembly
  • MDM - Multiplexer / Demultiplexer (an absolutely awful name for an onboard computer)
  • PFCS - Pump / Flow Control System
  • PVA - Photovoltaic Array
  • PVR - Photovoltaic Radiator
  • RPDA - Remote Power Distribution Assembly
  • SPDA - Secondary Power Distribution Assembly
  • SSU - Sequential Shunt Unit
  • Z1 - the name of a centrally located ISS truss unit

Source - personal notes. NASA does not provide a good reference source for the ISS. There is some information in this paper, from which the images are taken.

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There's an MCC-H flight control position that allocates and monitors power usage onboard the ISS: SPARTAN (Station Power, ARticulation, Thermal, and ANalysis). NASA does love their acronyms.

During nominal operations if the power draw reaches the maximum allocation, SPARTAN is not doing their job.

Unforseen events like a LOAC (Loss of Attitude Control) can cause a drop in power generation though. Less insolation to the SAWs (Solar Array Wing) due to an unplanned shift in Station attitude can trigger load sheds of less critical systems/payloads, leaving sufficient power for critical systems like ECLSS.

This is a good resource for more details on the ISS power system: https://ntrs.nasa.gov/api/citations/20160014034/downloads/20160014034.pdf

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