How does the impulse-to-weight ratio of a propulsion system indicate an effective design?
Clash Royale CLAN TAG#URR8PPP
While going through Sutton's propulsion elements text, I came across an example where he compares the values of impulse-to-weight ratio to that of specific impulse and deems it a "fair design".
The value of the impulse/weight ratio was 187s and the specific impulse was 240s.
I'm having trouble wrapping my head around how comparing the two value lets you determine this.
launch
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While going through Sutton's propulsion elements text, I came across an example where he compares the values of impulse-to-weight ratio to that of specific impulse and deems it a "fair design".
The value of the impulse/weight ratio was 187s and the specific impulse was 240s.
I'm having trouble wrapping my head around how comparing the two value lets you determine this.
launch
add a comment |
While going through Sutton's propulsion elements text, I came across an example where he compares the values of impulse-to-weight ratio to that of specific impulse and deems it a "fair design".
The value of the impulse/weight ratio was 187s and the specific impulse was 240s.
I'm having trouble wrapping my head around how comparing the two value lets you determine this.
launch
While going through Sutton's propulsion elements text, I came across an example where he compares the values of impulse-to-weight ratio to that of specific impulse and deems it a "fair design".
The value of the impulse/weight ratio was 187s and the specific impulse was 240s.
I'm having trouble wrapping my head around how comparing the two value lets you determine this.
launch
launch
asked Dec 31 '18 at 0:38
Lil_TEELil_TEE
283
283
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The specific impulse of a propulsion system measures how much impulse you get per unit mass of propellant consumed.
The impulse/weight ratio (actually impulse/mass, and sometimes called system specific impulse) measures how much impulse you get per total mass of a launcher or stage.
A theoretical "perfect" rocket, with zero mass for structure, engine, tankage, avionics, and so on, would have the same impulse/weight ratio as the propulsion system specific impulse, but this is obviously impossible; the non-propellant components have mass. So the specific impulse is an unreachable upper limit to the impulse/weight ratio. If you have very little dry mass in your design -- very thin tanks, minimal structural weight, engine whittled by elves from an Unobtainium billet, etc., then the impulse/weight ratio is closer to the specific impulse.
The example design reaches 78% of the limiting specific impulse.
Delta IV Heavy has a system specific impulse of about 352 seconds; some rough calculations tell me its propellant-mass-specific impulse averages around 389 seconds, so it gets to about 90% of the limit.
Falcon 9 FT system specific impulse is about 259 seconds and its propellant-mass-specific impulse averages around 307, so it's about 84%.
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
add a comment |
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1 Answer
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1 Answer
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active
oldest
votes
active
oldest
votes
active
oldest
votes
The specific impulse of a propulsion system measures how much impulse you get per unit mass of propellant consumed.
The impulse/weight ratio (actually impulse/mass, and sometimes called system specific impulse) measures how much impulse you get per total mass of a launcher or stage.
A theoretical "perfect" rocket, with zero mass for structure, engine, tankage, avionics, and so on, would have the same impulse/weight ratio as the propulsion system specific impulse, but this is obviously impossible; the non-propellant components have mass. So the specific impulse is an unreachable upper limit to the impulse/weight ratio. If you have very little dry mass in your design -- very thin tanks, minimal structural weight, engine whittled by elves from an Unobtainium billet, etc., then the impulse/weight ratio is closer to the specific impulse.
The example design reaches 78% of the limiting specific impulse.
Delta IV Heavy has a system specific impulse of about 352 seconds; some rough calculations tell me its propellant-mass-specific impulse averages around 389 seconds, so it gets to about 90% of the limit.
Falcon 9 FT system specific impulse is about 259 seconds and its propellant-mass-specific impulse averages around 307, so it's about 84%.
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
add a comment |
The specific impulse of a propulsion system measures how much impulse you get per unit mass of propellant consumed.
The impulse/weight ratio (actually impulse/mass, and sometimes called system specific impulse) measures how much impulse you get per total mass of a launcher or stage.
A theoretical "perfect" rocket, with zero mass for structure, engine, tankage, avionics, and so on, would have the same impulse/weight ratio as the propulsion system specific impulse, but this is obviously impossible; the non-propellant components have mass. So the specific impulse is an unreachable upper limit to the impulse/weight ratio. If you have very little dry mass in your design -- very thin tanks, minimal structural weight, engine whittled by elves from an Unobtainium billet, etc., then the impulse/weight ratio is closer to the specific impulse.
The example design reaches 78% of the limiting specific impulse.
Delta IV Heavy has a system specific impulse of about 352 seconds; some rough calculations tell me its propellant-mass-specific impulse averages around 389 seconds, so it gets to about 90% of the limit.
Falcon 9 FT system specific impulse is about 259 seconds and its propellant-mass-specific impulse averages around 307, so it's about 84%.
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
add a comment |
The specific impulse of a propulsion system measures how much impulse you get per unit mass of propellant consumed.
The impulse/weight ratio (actually impulse/mass, and sometimes called system specific impulse) measures how much impulse you get per total mass of a launcher or stage.
A theoretical "perfect" rocket, with zero mass for structure, engine, tankage, avionics, and so on, would have the same impulse/weight ratio as the propulsion system specific impulse, but this is obviously impossible; the non-propellant components have mass. So the specific impulse is an unreachable upper limit to the impulse/weight ratio. If you have very little dry mass in your design -- very thin tanks, minimal structural weight, engine whittled by elves from an Unobtainium billet, etc., then the impulse/weight ratio is closer to the specific impulse.
The example design reaches 78% of the limiting specific impulse.
Delta IV Heavy has a system specific impulse of about 352 seconds; some rough calculations tell me its propellant-mass-specific impulse averages around 389 seconds, so it gets to about 90% of the limit.
Falcon 9 FT system specific impulse is about 259 seconds and its propellant-mass-specific impulse averages around 307, so it's about 84%.
The specific impulse of a propulsion system measures how much impulse you get per unit mass of propellant consumed.
The impulse/weight ratio (actually impulse/mass, and sometimes called system specific impulse) measures how much impulse you get per total mass of a launcher or stage.
A theoretical "perfect" rocket, with zero mass for structure, engine, tankage, avionics, and so on, would have the same impulse/weight ratio as the propulsion system specific impulse, but this is obviously impossible; the non-propellant components have mass. So the specific impulse is an unreachable upper limit to the impulse/weight ratio. If you have very little dry mass in your design -- very thin tanks, minimal structural weight, engine whittled by elves from an Unobtainium billet, etc., then the impulse/weight ratio is closer to the specific impulse.
The example design reaches 78% of the limiting specific impulse.
Delta IV Heavy has a system specific impulse of about 352 seconds; some rough calculations tell me its propellant-mass-specific impulse averages around 389 seconds, so it gets to about 90% of the limit.
Falcon 9 FT system specific impulse is about 259 seconds and its propellant-mass-specific impulse averages around 307, so it's about 84%.
edited Dec 31 '18 at 1:38
answered Dec 31 '18 at 1:26
Russell BorogoveRussell Borogove
83.6k2281361
83.6k2281361
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
add a comment |
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
Apologies for the late response but this helped a lot! Thank you so much.
– Lil_TEE
2 days ago
add a comment |
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