Fuel Cells - Each of the three fuel cell power-plants consists of a hydrogen compartment, an oxygen compartment, and two electrodes (conductors), one hydrogen and one oxygen. The electrolyte (substance through which ions are conducted) is a mixture of potassium hydroxide and water and provides a constant conduction path between electrodes. The hydrogen electrode is nickel and the oxygen electrode is nickel and nickel oxide. Each fuel cell can produce between 1430 watts and 563 watts with a maximum of 53 amps. In this model each fuel cell must have both reactant valves. Example: for Fuel Cell 1 to operate - both valves V1A and V1B must be on, and each valve must be supplied with a minimum amount of reactant to produce power. If reactant valves are on and each has the minimum amount required, then the fuel cell can supply power to one or both of the DC main busses (main buss A or B). If fuel cell is supplying power to only one buss, then the output is the full 52 amps (1420 watts). However, if one fuel cell is supplying both busses then each buss receives half the current and power. 

Reactants  - The reactants (hydrogen and oxygen) are supplied to the cell under regulated pressure (referenced to a nitrogen gas supply which also is used to pressurize the power-plants). Chemical reaction produces electricity, water, and heat, with the reactants being consumed in proportion to the electrical load. The byproducts (water and heat) are used to maintain the drinking water supply and to keep the electrolyte at the proper operating temperature. Excess heat is rejected through the space radiators. Currently this model allows both oxygen and helium flows to be either 100% or 0% based on tank valves either open or closed. Example: if valve O2V1 is open (set to 1), then O2 Valve manifold will see a value of the gas weight at that point in the simulation. As long as the value is above the minimum required then the regulator will supply the fuel cells with 100% gas required. 

Batteries - Three batteries provide power for sequence controllers, and supplement the fuel cells during periods of peak power demand. Two additional silver oxide-zinc batteries (not in this version of the model) are independent of and completely isolated from the rest of the dc power system, and are used to supply power for explosive devices. These batteries are not recharged. The main batteries (A, B, C) are rated at 40 A-hr and can provide 37 volts. Battery A can supply current to DC Buss A when switch SBA-A in closed. Battery B can supply current to DC Buss B when switch SBB-B in closed. Battery C can provide either buss current when either switch B1C-A or B1C-B is closed. 

O2 and H2 Storage - The cryogenic (ultra low temperature) gas storage system supplies the hydrogen and oxygen used in the fuel cell power-plants, as well as the oxygen used in the environmental control subsystem. The system consists of storage tanks and associated valves, switches, lines, and other plumbing. The hydrogen and oxygen are stored in a semi-gas, semi-liquid state; by the time they reach the fuel cells, however, they have warmed considerably and are in a gaseous state. Each Oxygen tank holds 330 pounds, and the Helium tanks hold 30 pounds. 

Inverters - Solid-state inverters supply the ac power for the spacecraft. These inverters are devices which convert dc electrical power from the dc busses into ac. Both the fuel cell power-plants and batteries, the two electrical power sources in the spacecraft, produce dc power. The inverters operate from the two 28-volt dc main buses (connecting circuits) to supply 115 120-volt, 400-cycle, 3-phase ac power to two ac buses. Normally two inverters are used; however, one inverter can supply all primary ac electrical power needed by the spacecraft. The inverters will disconnect if operating voltage input drops to between 16 and 19 volts dc. This model drops ac voltage at 19 volts dc. 

Normal Operating Configuration: 

Fuel Cells - Each of the three fuel cell power-plants consists of a hydrogen compartment, an oxygen compartment, and two electrodes (conductors), one hydrogen and one oxygen. The electrolyte (substance through which ions are conducted) is a mixture of potassium hydroxide and water and provides a constant conduction path between electrodes. The hydrogen electrode is nickel and the oxygen electrode is nickel and nickel oxide. Each fuel cell can produce between 1430 watts and 563 watts with a maximum of 53 amps. In this model each fuel cell must have both reactant valves. Example: for Fuel Cell 1 to operate - both valves V1A and V1B must be on, and each valve must be supplied with a minimum amount of reactant to produce power. If reactant valves are on and each has the minimum amount required, then the fuel cell can supply power to one or both of the DC main busses (main buss A or B). If fuel cell is supplying power to only one buss, then the output is the full 52 amps (1420 watts). However, if one fuel cell is supplying both busses then each buss receives half the current and power. 

Reactants  - The reactants (hydrogen and oxygen) are supplied to the cell under regulated pressure (referenced to a nitrogen gas supply which also is used to pressurize the power-plants). Chemical reaction produces electricity, water, and heat, with the reactants being consumed in proportion to the electrical load. The byproducts (water and heat) are used to maintain the drinking water supply and to keep the electrolyte at the proper operating temperature. Excess heat is rejected through the space radiators. Currently this model allows both oxygen and helium flows to be either 100% or 0% based on tank valves either open or closed. Example: if valve O2V1 is open (set to 1), then O2 Valve manifold will see a value of the gas weight at that point in the simulation. As long as the value is above the minimum required then the regulator will supply the fuel cells with 100% gas required. 

Batteries - Three batteries provide power for sequence controllers, and supplement the fuel cells during periods of peak power demand. Two additional silver oxide-zinc batteries (not in this version of the model) are independent of and completely isolated from the rest of the dc power system, and are used to supply power for explosive devices. These batteries are not recharged. The main batteries (A, B, C) are rated at 40 A-hr and can provide 37 volts. Battery A can supply current to DC Buss A when switch SBA-A in closed. Battery B can supply current to DC Buss B when switch SBB-B in closed. Battery C can provide either buss current when either switch B1C-A or B1C-B is closed. 

O2 and H2 Storage - The cryogenic (ultra low temperature) gas storage system supplies the hydrogen and oxygen used in the fuel cell power-plants, as well as the oxygen used in the environmental control subsystem. The system consists of storage tanks and associated valves, switches, lines, and other plumbing. The hydrogen and oxygen are stored in a semi-gas, semi-liquid state; by the time they reach the fuel cells, however, they have warmed considerably and are in a gaseous state. Each Oxygen tank holds 330 pounds, and the Helium tanks hold 30 pounds. 

Inverters - Solid-state inverters supply the ac power for the spacecraft. These inverters are devices which convert dc electrical power from the dc busses into ac. Both the fuel cell power-plants and batteries, the two electrical power sources in the spacecraft, produce dc power. The inverters operate from the two 28-volt dc main buses (connecting circuits) to supply 115 120-volt, 400-cycle, 3-phase ac power to two ac buses. Normally two inverters are used; however, one inverter can supply all primary ac electrical power needed by the spacecraft. The inverters will disconnect if operating voltage input drops to between 16 and 19 volts dc. This model drops ac voltage at 19 volts dc. 

Normal Operating Configuration: