Why do chemical rockets encompass a weird shape on this thrust vs. Isp graph?











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Consider this graph of engine thrust versus specific impulse (from https://dawn.jpl.nasa.gov/mission/ion_prop.html):



enter image description here



Most propulsion technologies encompass roughly rectangular regions on the graph. Electric propulsion is the union of two rectangular regions (ion and magnetic). However, chemical propulsion has an irregular shape.



Why does chemical propulsion have this irregular shape?










share|improve this question
























  • Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
    – Uwe
    yesterday








  • 2




    Speculation: small engines have relatively higher thermal losses than large ones.
    – Hobbes
    yesterday






  • 1




    @Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
    – Dan Neely
    yesterday










  • ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
    – J...
    yesterday










  • I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
    – Mooing Duck
    yesterday















up vote
9
down vote

favorite












Consider this graph of engine thrust versus specific impulse (from https://dawn.jpl.nasa.gov/mission/ion_prop.html):



enter image description here



Most propulsion technologies encompass roughly rectangular regions on the graph. Electric propulsion is the union of two rectangular regions (ion and magnetic). However, chemical propulsion has an irregular shape.



Why does chemical propulsion have this irregular shape?










share|improve this question
























  • Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
    – Uwe
    yesterday








  • 2




    Speculation: small engines have relatively higher thermal losses than large ones.
    – Hobbes
    yesterday






  • 1




    @Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
    – Dan Neely
    yesterday










  • ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
    – J...
    yesterday










  • I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
    – Mooing Duck
    yesterday













up vote
9
down vote

favorite









up vote
9
down vote

favorite











Consider this graph of engine thrust versus specific impulse (from https://dawn.jpl.nasa.gov/mission/ion_prop.html):



enter image description here



Most propulsion technologies encompass roughly rectangular regions on the graph. Electric propulsion is the union of two rectangular regions (ion and magnetic). However, chemical propulsion has an irregular shape.



Why does chemical propulsion have this irregular shape?










share|improve this question















Consider this graph of engine thrust versus specific impulse (from https://dawn.jpl.nasa.gov/mission/ion_prop.html):



enter image description here



Most propulsion technologies encompass roughly rectangular regions on the graph. Electric propulsion is the union of two rectangular regions (ion and magnetic). However, chemical propulsion has an irregular shape.



Why does chemical propulsion have this irregular shape?







engines thrust specific-impulse






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday

























asked yesterday









Dr Sheldon

2,331833




2,331833












  • Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
    – Uwe
    yesterday








  • 2




    Speculation: small engines have relatively higher thermal losses than large ones.
    – Hobbes
    yesterday






  • 1




    @Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
    – Dan Neely
    yesterday










  • ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
    – J...
    yesterday










  • I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
    – Mooing Duck
    yesterday


















  • Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
    – Uwe
    yesterday








  • 2




    Speculation: small engines have relatively higher thermal losses than large ones.
    – Hobbes
    yesterday






  • 1




    @Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
    – Dan Neely
    yesterday










  • ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
    – J...
    yesterday










  • I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
    – Mooing Duck
    yesterday
















Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
– Uwe
yesterday






Acheivable Isp is smaller for low thrust chemical engines than for larger ones. Different fuel/oxidizer combinations are used for small, medium and large thrust engines. But I would like to see this graph extended to MN (meganewtons). The F-1 engine of Saturn V had about 7 MN, the J-2 engine of second and third stage 1 MN.
– Uwe
yesterday






2




2




Speculation: small engines have relatively higher thermal losses than large ones.
– Hobbes
yesterday




Speculation: small engines have relatively higher thermal losses than large ones.
– Hobbes
yesterday




1




1




@Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
– Dan Neely
yesterday




@Uwe it'd roughly just extend farther right. Low 300's (solid) to mid 400's (hydralox) is still the performance range for really big chemical engines.
– Dan Neely
yesterday












ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
– J...
yesterday




ISP is a measure of the average kinetic energy of the exhaust products. All this is telling you is that for low thrust chemical engines it is difficult to produce very high exhaust velocities. Only when the engines get above a certain size can they accommodate the infrastructure required to produce the highest chemical exhaust velocities. For smaller engines to achieve such high ISP would require adding too much weight to the designs, eating up any delta-V the higher ISP might add, so they are simply not made.
– J...
yesterday












I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
– Mooing Duck
yesterday




I speculate that the shape is wierd because the graph is logarithmic. On a non-logarithmic scale, it's probably just a diagonal parabola.
– Mooing Duck
yesterday










3 Answers
3






active

oldest

votes

















up vote
12
down vote



accepted










I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident.



10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than making significant maneuvers, so reliability, simplicity, and light weight are more critical than specific impulse. I'm not sure if it's not actually possible to make high-Isp small thrusters, or if it's just that no one bothers.



In particular, I note that Aerojet's catalog of bipropellant (MMH+NTO) thrusters (which get around 300 seconds Isp) extends down to 22N; below that, they offer catalyzed hydrazine monoprop thrusters (around 220 seconds) down to 1N; the engineering simplicity of requiring only a single propellant tank pays for the loss in specific impulse (and it's probably tricky to get good bipropellant mixing in such a small combustion chamber). These two categories of thruster contribute to the left two-thirds of the chemical engine envelope in the plot.



Further up and to the right, small hydrogen-oxygen engines stake out the high end of the Isp envelope: the Chinese YF-73 at 44kN and 420 seconds, then a bunch of engines in the neighborhood of the US RL10: 65-100 kN and 440-460 seconds. That's the high-water specific impulse mark for production chemical engines, the space shuttle main engine RS-25 is off the right hand side of the chart at 2200kN and 452 seconds. Again, I'm not sure whether it's possible to make high-Isp hydrogen-oxygen engines smaller than ~40kN or whether it's just not done.






share|improve this answer























  • Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
    – leftaroundabout
    yesterday


















up vote
7
down vote













The historical NASA document "SPACE HANDBOOK: ASTRONAUTICS AND ITS APPLICATIONS" has a useful table, which I will partially reproduce here:




TABLE 1.-Specific impulse of some typical chemical propellants



Low-energy monopropellants________________________ 160 to 190.



High-energy monopropellants: Nitromethane_______________________________ 190 to 230



Bipropellants (liquid): Low-energy bipropellants___________________________ 200 to 230.



Medium-energy bipropellants________________________ 230 to 260.



High-energy bipropellants___________________________ 250 to 270.



Very high-energy bipropellants_______________________ 270 to 330.



Super high-energy bipropellants_______________________ 300 to 385.



Boron metal components and oxidant____________________ 200 to 250.



Lithium metal components and oxidant___________________ 200 to 250.




It seems very likely to me that the "Chemical" category encompasses several different fuels, and probably both solid and liquid fuels, which is why it's not a uniform shape.



Someone more expert might be able to guess which specific fuels compose the various areas.






share|improve this answer

















  • 2




    That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
    – Russell Borogove
    yesterday


















up vote
3
down vote













The "Chemical" shape exists because of two clear regimes. This is a bit by chance because of the propellants involved but basically its this:




  • engines on the left are pressure fed or solid

  • engines on the right are various types of pump fed (expander cycle/gas generator/staged combustion/electric)


As an aside the diagram doesn't really clarify the whole range of posiblities for electrically augmented hydrazine monopropellant, e.g.
- power augmented catalytic hydrazine thruster (Isp = 250 - 280)
- hydrazine arcjet (Isp 550 - 600)






share|improve this answer























  • Aren’t arcjets covered by “electrothermal” in the plot?
    – Russell Borogove
    yesterday










  • They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
    – Puffin
    11 hours ago










  • I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
    – Russell Borogove
    10 hours ago











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3 Answers
3






active

oldest

votes








3 Answers
3






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
12
down vote



accepted










I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident.



10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than making significant maneuvers, so reliability, simplicity, and light weight are more critical than specific impulse. I'm not sure if it's not actually possible to make high-Isp small thrusters, or if it's just that no one bothers.



In particular, I note that Aerojet's catalog of bipropellant (MMH+NTO) thrusters (which get around 300 seconds Isp) extends down to 22N; below that, they offer catalyzed hydrazine monoprop thrusters (around 220 seconds) down to 1N; the engineering simplicity of requiring only a single propellant tank pays for the loss in specific impulse (and it's probably tricky to get good bipropellant mixing in such a small combustion chamber). These two categories of thruster contribute to the left two-thirds of the chemical engine envelope in the plot.



Further up and to the right, small hydrogen-oxygen engines stake out the high end of the Isp envelope: the Chinese YF-73 at 44kN and 420 seconds, then a bunch of engines in the neighborhood of the US RL10: 65-100 kN and 440-460 seconds. That's the high-water specific impulse mark for production chemical engines, the space shuttle main engine RS-25 is off the right hand side of the chart at 2200kN and 452 seconds. Again, I'm not sure whether it's possible to make high-Isp hydrogen-oxygen engines smaller than ~40kN or whether it's just not done.






share|improve this answer























  • Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
    – leftaroundabout
    yesterday















up vote
12
down vote



accepted










I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident.



10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than making significant maneuvers, so reliability, simplicity, and light weight are more critical than specific impulse. I'm not sure if it's not actually possible to make high-Isp small thrusters, or if it's just that no one bothers.



In particular, I note that Aerojet's catalog of bipropellant (MMH+NTO) thrusters (which get around 300 seconds Isp) extends down to 22N; below that, they offer catalyzed hydrazine monoprop thrusters (around 220 seconds) down to 1N; the engineering simplicity of requiring only a single propellant tank pays for the loss in specific impulse (and it's probably tricky to get good bipropellant mixing in such a small combustion chamber). These two categories of thruster contribute to the left two-thirds of the chemical engine envelope in the plot.



Further up and to the right, small hydrogen-oxygen engines stake out the high end of the Isp envelope: the Chinese YF-73 at 44kN and 420 seconds, then a bunch of engines in the neighborhood of the US RL10: 65-100 kN and 440-460 seconds. That's the high-water specific impulse mark for production chemical engines, the space shuttle main engine RS-25 is off the right hand side of the chart at 2200kN and 452 seconds. Again, I'm not sure whether it's possible to make high-Isp hydrogen-oxygen engines smaller than ~40kN or whether it's just not done.






share|improve this answer























  • Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
    – leftaroundabout
    yesterday













up vote
12
down vote



accepted







up vote
12
down vote



accepted






I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident.



10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than making significant maneuvers, so reliability, simplicity, and light weight are more critical than specific impulse. I'm not sure if it's not actually possible to make high-Isp small thrusters, or if it's just that no one bothers.



In particular, I note that Aerojet's catalog of bipropellant (MMH+NTO) thrusters (which get around 300 seconds Isp) extends down to 22N; below that, they offer catalyzed hydrazine monoprop thrusters (around 220 seconds) down to 1N; the engineering simplicity of requiring only a single propellant tank pays for the loss in specific impulse (and it's probably tricky to get good bipropellant mixing in such a small combustion chamber). These two categories of thruster contribute to the left two-thirds of the chemical engine envelope in the plot.



Further up and to the right, small hydrogen-oxygen engines stake out the high end of the Isp envelope: the Chinese YF-73 at 44kN and 420 seconds, then a bunch of engines in the neighborhood of the US RL10: 65-100 kN and 440-460 seconds. That's the high-water specific impulse mark for production chemical engines, the space shuttle main engine RS-25 is off the right hand side of the chart at 2200kN and 452 seconds. Again, I'm not sure whether it's possible to make high-Isp hydrogen-oxygen engines smaller than ~40kN or whether it's just not done.






share|improve this answer














I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident.



10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than making significant maneuvers, so reliability, simplicity, and light weight are more critical than specific impulse. I'm not sure if it's not actually possible to make high-Isp small thrusters, or if it's just that no one bothers.



In particular, I note that Aerojet's catalog of bipropellant (MMH+NTO) thrusters (which get around 300 seconds Isp) extends down to 22N; below that, they offer catalyzed hydrazine monoprop thrusters (around 220 seconds) down to 1N; the engineering simplicity of requiring only a single propellant tank pays for the loss in specific impulse (and it's probably tricky to get good bipropellant mixing in such a small combustion chamber). These two categories of thruster contribute to the left two-thirds of the chemical engine envelope in the plot.



Further up and to the right, small hydrogen-oxygen engines stake out the high end of the Isp envelope: the Chinese YF-73 at 44kN and 420 seconds, then a bunch of engines in the neighborhood of the US RL10: 65-100 kN and 440-460 seconds. That's the high-water specific impulse mark for production chemical engines, the space shuttle main engine RS-25 is off the right hand side of the chart at 2200kN and 452 seconds. Again, I'm not sure whether it's possible to make high-Isp hydrogen-oxygen engines smaller than ~40kN or whether it's just not done.







share|improve this answer














share|improve this answer



share|improve this answer








edited yesterday

























answered yesterday









Russell Borogove

76.1k2238326




76.1k2238326












  • Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
    – leftaroundabout
    yesterday


















  • Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
    – leftaroundabout
    yesterday
















Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
– leftaroundabout
yesterday




Would be interesting indeed whether small high-Isp engines are possible, with modern 3D-printing techniques and whatnot. I'd see considerable interest for such engines in the near future.
– leftaroundabout
yesterday










up vote
7
down vote













The historical NASA document "SPACE HANDBOOK: ASTRONAUTICS AND ITS APPLICATIONS" has a useful table, which I will partially reproduce here:




TABLE 1.-Specific impulse of some typical chemical propellants



Low-energy monopropellants________________________ 160 to 190.



High-energy monopropellants: Nitromethane_______________________________ 190 to 230



Bipropellants (liquid): Low-energy bipropellants___________________________ 200 to 230.



Medium-energy bipropellants________________________ 230 to 260.



High-energy bipropellants___________________________ 250 to 270.



Very high-energy bipropellants_______________________ 270 to 330.



Super high-energy bipropellants_______________________ 300 to 385.



Boron metal components and oxidant____________________ 200 to 250.



Lithium metal components and oxidant___________________ 200 to 250.




It seems very likely to me that the "Chemical" category encompasses several different fuels, and probably both solid and liquid fuels, which is why it's not a uniform shape.



Someone more expert might be able to guess which specific fuels compose the various areas.






share|improve this answer

















  • 2




    That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
    – Russell Borogove
    yesterday















up vote
7
down vote













The historical NASA document "SPACE HANDBOOK: ASTRONAUTICS AND ITS APPLICATIONS" has a useful table, which I will partially reproduce here:




TABLE 1.-Specific impulse of some typical chemical propellants



Low-energy monopropellants________________________ 160 to 190.



High-energy monopropellants: Nitromethane_______________________________ 190 to 230



Bipropellants (liquid): Low-energy bipropellants___________________________ 200 to 230.



Medium-energy bipropellants________________________ 230 to 260.



High-energy bipropellants___________________________ 250 to 270.



Very high-energy bipropellants_______________________ 270 to 330.



Super high-energy bipropellants_______________________ 300 to 385.



Boron metal components and oxidant____________________ 200 to 250.



Lithium metal components and oxidant___________________ 200 to 250.




It seems very likely to me that the "Chemical" category encompasses several different fuels, and probably both solid and liquid fuels, which is why it's not a uniform shape.



Someone more expert might be able to guess which specific fuels compose the various areas.






share|improve this answer

















  • 2




    That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
    – Russell Borogove
    yesterday













up vote
7
down vote










up vote
7
down vote









The historical NASA document "SPACE HANDBOOK: ASTRONAUTICS AND ITS APPLICATIONS" has a useful table, which I will partially reproduce here:




TABLE 1.-Specific impulse of some typical chemical propellants



Low-energy monopropellants________________________ 160 to 190.



High-energy monopropellants: Nitromethane_______________________________ 190 to 230



Bipropellants (liquid): Low-energy bipropellants___________________________ 200 to 230.



Medium-energy bipropellants________________________ 230 to 260.



High-energy bipropellants___________________________ 250 to 270.



Very high-energy bipropellants_______________________ 270 to 330.



Super high-energy bipropellants_______________________ 300 to 385.



Boron metal components and oxidant____________________ 200 to 250.



Lithium metal components and oxidant___________________ 200 to 250.




It seems very likely to me that the "Chemical" category encompasses several different fuels, and probably both solid and liquid fuels, which is why it's not a uniform shape.



Someone more expert might be able to guess which specific fuels compose the various areas.






share|improve this answer












The historical NASA document "SPACE HANDBOOK: ASTRONAUTICS AND ITS APPLICATIONS" has a useful table, which I will partially reproduce here:




TABLE 1.-Specific impulse of some typical chemical propellants



Low-energy monopropellants________________________ 160 to 190.



High-energy monopropellants: Nitromethane_______________________________ 190 to 230



Bipropellants (liquid): Low-energy bipropellants___________________________ 200 to 230.



Medium-energy bipropellants________________________ 230 to 260.



High-energy bipropellants___________________________ 250 to 270.



Very high-energy bipropellants_______________________ 270 to 330.



Super high-energy bipropellants_______________________ 300 to 385.



Boron metal components and oxidant____________________ 200 to 250.



Lithium metal components and oxidant___________________ 200 to 250.




It seems very likely to me that the "Chemical" category encompasses several different fuels, and probably both solid and liquid fuels, which is why it's not a uniform shape.



Someone more expert might be able to guess which specific fuels compose the various areas.







share|improve this answer












share|improve this answer



share|improve this answer










answered yesterday









Roger

82919




82919








  • 2




    That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
    – Russell Borogove
    yesterday














  • 2




    That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
    – Russell Borogove
    yesterday








2




2




That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
– Russell Borogove
yesterday




That table is extremely dated (ca 1958 maybe?) -- hydrogen/oxygen isn't even listed, but the RL10 was flying a 425+ sec specific impulse on hydrogen/oxygen by 1962.
– Russell Borogove
yesterday










up vote
3
down vote













The "Chemical" shape exists because of two clear regimes. This is a bit by chance because of the propellants involved but basically its this:




  • engines on the left are pressure fed or solid

  • engines on the right are various types of pump fed (expander cycle/gas generator/staged combustion/electric)


As an aside the diagram doesn't really clarify the whole range of posiblities for electrically augmented hydrazine monopropellant, e.g.
- power augmented catalytic hydrazine thruster (Isp = 250 - 280)
- hydrazine arcjet (Isp 550 - 600)






share|improve this answer























  • Aren’t arcjets covered by “electrothermal” in the plot?
    – Russell Borogove
    yesterday










  • They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
    – Puffin
    11 hours ago










  • I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
    – Russell Borogove
    10 hours ago















up vote
3
down vote













The "Chemical" shape exists because of two clear regimes. This is a bit by chance because of the propellants involved but basically its this:




  • engines on the left are pressure fed or solid

  • engines on the right are various types of pump fed (expander cycle/gas generator/staged combustion/electric)


As an aside the diagram doesn't really clarify the whole range of posiblities for electrically augmented hydrazine monopropellant, e.g.
- power augmented catalytic hydrazine thruster (Isp = 250 - 280)
- hydrazine arcjet (Isp 550 - 600)






share|improve this answer























  • Aren’t arcjets covered by “electrothermal” in the plot?
    – Russell Borogove
    yesterday










  • They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
    – Puffin
    11 hours ago










  • I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
    – Russell Borogove
    10 hours ago













up vote
3
down vote










up vote
3
down vote









The "Chemical" shape exists because of two clear regimes. This is a bit by chance because of the propellants involved but basically its this:




  • engines on the left are pressure fed or solid

  • engines on the right are various types of pump fed (expander cycle/gas generator/staged combustion/electric)


As an aside the diagram doesn't really clarify the whole range of posiblities for electrically augmented hydrazine monopropellant, e.g.
- power augmented catalytic hydrazine thruster (Isp = 250 - 280)
- hydrazine arcjet (Isp 550 - 600)






share|improve this answer














The "Chemical" shape exists because of two clear regimes. This is a bit by chance because of the propellants involved but basically its this:




  • engines on the left are pressure fed or solid

  • engines on the right are various types of pump fed (expander cycle/gas generator/staged combustion/electric)


As an aside the diagram doesn't really clarify the whole range of posiblities for electrically augmented hydrazine monopropellant, e.g.
- power augmented catalytic hydrazine thruster (Isp = 250 - 280)
- hydrazine arcjet (Isp 550 - 600)







share|improve this answer














share|improve this answer



share|improve this answer








edited yesterday

























answered yesterday









Puffin

4,9631733




4,9631733












  • Aren’t arcjets covered by “electrothermal” in the plot?
    – Russell Borogove
    yesterday










  • They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
    – Puffin
    11 hours ago










  • I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
    – Russell Borogove
    10 hours ago


















  • Aren’t arcjets covered by “electrothermal” in the plot?
    – Russell Borogove
    yesterday










  • They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
    – Puffin
    11 hours ago










  • I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
    – Russell Borogove
    10 hours ago
















Aren’t arcjets covered by “electrothermal” in the plot?
– Russell Borogove
yesterday




Aren’t arcjets covered by “electrothermal” in the plot?
– Russell Borogove
yesterday












They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
– Puffin
11 hours ago




They might be, I actually found that particular bubble on the plot hard to understand. N2H4 decomposes, I think, to H2, N2 and NH3, the presence of most of those in the bubble made me wonder what the labels meant.
– Puffin
11 hours ago












I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
– Russell Borogove
10 hours ago




I read that as "electrothermal thrusters using hydrogen, hydrazine, or ammonia as reaction mass".
– Russell Borogove
10 hours ago


















 

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