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| How much helium pressurant does a SpaceX Falcon 9 use? I would appreciate actual numbers, the following is only a wild-ass guess, and could be off by an order of magnitude. DO NOT QUOTE THIS, FIND ACTUAL SPACEX VALUES INSTEAD. I was unable to, sigh. | How much helium pressurant does a SpaceX Falcon 9 use? |
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| A Falcon 9 burns LOX and kerosene, and has a fueled pad weight of 333 metric tonnes. That puts 10 metric tonnes in low earth orbit. Those are the only solid numbers I have from SpaceX, from here on is rank speculation. | This is updated with some numbers - the helium is heated to 500F (533K) and pressurized to 60 to 100 psi (414 to 689 KPa). Assume 420 KPa. |
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| * The big unknowns are the temperature and pressure of the helium after expansion, hence its mass density in the propellant tanks. | A Falcon 9 burns LOX and kerosene, and has a fueled pad weight of 333 metric tonnes. That puts 10 metric tonnes in low earth orbit. |
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| * The heat capacity ratio of helium is 1.66, which means that adiabatic expansion makes it very cold and relatively dense * The big assumptions: Tank pressure of 3 MPa and temperature of 290K (cribbed from Sutton, example 9.2, p228 of 5th edition). . This is optimistic regards temperature. I would expect the expanded helium to be much colder and denser. If it is heated during expansion, less helium will be needed, and as a bonus it will boil some LOX, adding gas volume from that. |
* The helium is heated to 500F (533K) and pressurized to 60 to 100 psi (414 to 689 KPa). Assume 450 KPa as the tanks empty. |
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| 300 metric tonnes of propellant is 215 tonnes of LOX and 85 tonnes of RP1, or 190 m³ of LOX and 105 m³ of RP. Call it 300 m³ of tank volume to fill with helium at 30 atmospheres, including the additional volume of the high pressure tanks that supply the helium. The density of helium at STP ( 273.2K, 101.3 KPa ) is 0.1786 g/L or 0.1786 kg/m³. At 290K and 3 MPa, helium will be about 5 kg/m³. So the total mass of helium consumed will be about 1500 kilograms (!). | 300 metric tonnes of propellant is 215 tonnes of LOX and 85 tonnes of RP1, or 190 m³ of LOX and 105 m³ of RP. Call it 300 m³ of tank volume to fill with helium at 30 atmospheres, including the additional volume of the high pressure tanks that supply the helium. The density of helium at STP ( 273.2K, 101.3 KPa ) is 0.1786 g/L or 0.1786 kg/m³. At 533K and 450 Pa, helium will be about 0.4 kg/m³. So the total mass of helium consumed will be about 120 kilograms. |
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| For every kilogram to orbit, 0.15 kilograms of helium are expended. If the launch puts a 7 passenger Dragon capsule into orbit, the helium use is about 200 kilograms per passenger. | For every kilogram to orbit, 12 grams of helium are expended. If the launch puts a 7 passenger Dragon capsule into orbit, the helium use is about 17 kilograms per passenger. |
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| For comparison, a Siemens "zero loss" MRI machine contains 30 liters of recirculating liquid helium, about 3.75 kg. The helium lost by one Falcon 9 launch could be used for 400 MRI machines, each performing thousands of MRIs per year. | For comparison, a Siemens "zero loss" MRI machine contains 30 liters of recirculating liquid helium, about 3.75 kg. The helium lost by one Falcon 9 launch could be used for 30 MRI machines, each performing thousands of MRIs per year. |
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| Helium pressurant may increase performance, but when the geologically-trapped helium runs out, eventually this may could cost thousands of lives in the future per passenger launched today. Nitrogen is lower performance, with a significant impact on payload to orbit, but there is a heck of a lot more of it! | Helium pressurant may increase performance, but when the geologically-trapped helium runs out, eventually this may could cost hundreds of lives in the future per passenger launched today. Nitrogen is lower performance, with a significant impact on payload to orbit, but there is a heck of a lot more of it! |
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| Current helium prices are relatively low (about $20/kg) because the US government is selling off the helium reserve. Annual production is 23,000 tonnes per year. SpaceX consumes a tiny fraction of that, and launch rates could saturate existing launch facilities without greatly increasing that fraction. The issue is the long term - helium collects in only a small fraction of gas wells, and when those are depleted, that's it. No more helium, unless we concentrate it from the tiny percentage present in Earth's atmosphere. At 5 ppm, we would need to process 200,000 kilograms of atmosphere at 100% efficiency to produce 1 kilogram of helium. Relative to that, centrifuge isotope separation look easy. The resulting helium would be enormously expensive. This is no way to establish a long term presence in space. | Current helium prices are relatively low (about $20/kg) because the US government is selling off the helium reserve. Annual sales are 23,000 tonnes per year. SpaceX consumes a tiny fraction of that, and launch rates could saturate existing launch facilities without greatly increasing that fraction. The issue is the long term - helium collects in only a small fraction of gas wells, and when those are depleted, that's it. No more helium, unless we concentrate it from the tiny percentage present in Earth's atmosphere. At 5 ppm, we would need to process 200,000 kilograms of atmosphere at 100% efficiency to produce 1 kilogram of helium. Relative to that, centrifuge isotope separation look easy. The resulting helium would be enormously expensive. This is no way to establish a long term presence in space. |
Pressurant
How much helium pressurant does a SpaceX Falcon 9 use?
This is updated with some numbers - the helium is heated to 500F (533K) and pressurized to 60 to 100 psi (414 to 689 KPa). Assume 420 KPa.
A Falcon 9 burns LOX and kerosene, and has a fueled pad weight of 333 metric tonnes. That puts 10 metric tonnes in low earth orbit.
- Assume that 90% of the pad weight is propellant in full tanks, which will be displaced by helium.
- Assume LOX and RP1 Kerosene with an oxidizer to fuel ratio of 2.56 (mass ratio, not stochiometric)
- Assume RP1 density of 810 kg/m³ and LOX density of 1140 kg/m³
- The helium is heated to 500F (533K) and pressurized to 60 to 100 psi (414 to 689 KPa). Assume 450 KPa as the tanks empty.
300 metric tonnes of propellant is 215 tonnes of LOX and 85 tonnes of RP1, or 190 m³ of LOX and 105 m³ of RP. Call it 300 m³ of tank volume to fill with helium at 30 atmospheres, including the additional volume of the high pressure tanks that supply the helium. The density of helium at STP ( 273.2K, 101.3 KPa ) is 0.1786 g/L or 0.1786 kg/m³. At 533K and 450 Pa, helium will be about 0.4 kg/m³. So the total mass of helium consumed will be about 120 kilograms.
For every kilogram to orbit, 12 grams of helium are expended. If the launch puts a 7 passenger Dragon capsule into orbit, the helium use is about 17 kilograms per passenger.
For comparison, a Siemens "zero loss" MRI machine contains 30 liters of recirculating liquid helium, about 3.75 kg. The helium lost by one Falcon 9 launch could be used for 30 MRI machines, each performing thousands of MRIs per year.
Helium pressurant may increase performance, but when the geologically-trapped helium runs out, eventually this may could cost hundreds of lives in the future per passenger launched today. Nitrogen is lower performance, with a significant impact on payload to orbit, but there is a heck of a lot more of it!
Current helium prices are relatively low (about $20/kg) because the US government is selling off the helium reserve. Annual sales are 23,000 tonnes per year. SpaceX consumes a tiny fraction of that, and launch rates could saturate existing launch facilities without greatly increasing that fraction. The issue is the long term - helium collects in only a small fraction of gas wells, and when those are depleted, that's it. No more helium, unless we concentrate it from the tiny percentage present in Earth's atmosphere. At 5 ppm, we would need to process 200,000 kilograms of atmosphere at 100% efficiency to produce 1 kilogram of helium. Relative to that, centrifuge isotope separation look easy. The resulting helium would be enormously expensive. This is no way to establish a long term presence in space.
BTW, a 10 inch party balloon is about 9 liters, or 1.5 grams of helium. Small compared to an MRI machine, tiny compared to a SpaceX launch, but that adds up. Please do not invite me to parties with helium balloons, I will see lost lives, not festivity.