Would there be any advantages for a rocket with two “half stages”?











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A "half stage" is a rocket stage which separates with its engines, but not fuel tanks. Common examples include Atlas (1.5 stages), Atlas-Agena (2.5 stages), and Atlas-Centaur (2.5 stages).



On paper, one could create a "one-and-two-half-stage" rocket. It burns for a while, then drops some engines. Then it burns some more, and drops more engines. It then burns its remaining engines to orbit.



Alternately, a "two-and-two-half-stage" rocket is also theoretically possible. It burns for a while, drops some engines, burns some more, and drops its lower stage. The upper stage burns for a while, drops some engines, and then finished its burn to orbit.



I'm sure such a design would have numerous disadvantages (feel free to point them out in the comments). However, are there any advantages over other designs?



Related:




  • Why not keep the engine for multi-stage rockets?

  • Could the Atlas-B (SM-65B) have made it to orbit without jettisoning the first-stage engines?










share|improve this question






















  • I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
    – uhoh
    Nov 11 at 6:46










  • The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
    – Uwe
    Nov 11 at 19:03










  • One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
    – Uwe
    Nov 11 at 19:24










  • There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
    – Russell Borogove
    Nov 12 at 5:10















up vote
2
down vote

favorite












A "half stage" is a rocket stage which separates with its engines, but not fuel tanks. Common examples include Atlas (1.5 stages), Atlas-Agena (2.5 stages), and Atlas-Centaur (2.5 stages).



On paper, one could create a "one-and-two-half-stage" rocket. It burns for a while, then drops some engines. Then it burns some more, and drops more engines. It then burns its remaining engines to orbit.



Alternately, a "two-and-two-half-stage" rocket is also theoretically possible. It burns for a while, drops some engines, burns some more, and drops its lower stage. The upper stage burns for a while, drops some engines, and then finished its burn to orbit.



I'm sure such a design would have numerous disadvantages (feel free to point them out in the comments). However, are there any advantages over other designs?



Related:




  • Why not keep the engine for multi-stage rockets?

  • Could the Atlas-B (SM-65B) have made it to orbit without jettisoning the first-stage engines?










share|improve this question






















  • I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
    – uhoh
    Nov 11 at 6:46










  • The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
    – Uwe
    Nov 11 at 19:03










  • One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
    – Uwe
    Nov 11 at 19:24










  • There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
    – Russell Borogove
    Nov 12 at 5:10













up vote
2
down vote

favorite









up vote
2
down vote

favorite











A "half stage" is a rocket stage which separates with its engines, but not fuel tanks. Common examples include Atlas (1.5 stages), Atlas-Agena (2.5 stages), and Atlas-Centaur (2.5 stages).



On paper, one could create a "one-and-two-half-stage" rocket. It burns for a while, then drops some engines. Then it burns some more, and drops more engines. It then burns its remaining engines to orbit.



Alternately, a "two-and-two-half-stage" rocket is also theoretically possible. It burns for a while, drops some engines, burns some more, and drops its lower stage. The upper stage burns for a while, drops some engines, and then finished its burn to orbit.



I'm sure such a design would have numerous disadvantages (feel free to point them out in the comments). However, are there any advantages over other designs?



Related:




  • Why not keep the engine for multi-stage rockets?

  • Could the Atlas-B (SM-65B) have made it to orbit without jettisoning the first-stage engines?










share|improve this question













A "half stage" is a rocket stage which separates with its engines, but not fuel tanks. Common examples include Atlas (1.5 stages), Atlas-Agena (2.5 stages), and Atlas-Centaur (2.5 stages).



On paper, one could create a "one-and-two-half-stage" rocket. It burns for a while, then drops some engines. Then it burns some more, and drops more engines. It then burns its remaining engines to orbit.



Alternately, a "two-and-two-half-stage" rocket is also theoretically possible. It burns for a while, drops some engines, burns some more, and drops its lower stage. The upper stage burns for a while, drops some engines, and then finished its burn to orbit.



I'm sure such a design would have numerous disadvantages (feel free to point them out in the comments). However, are there any advantages over other designs?



Related:




  • Why not keep the engine for multi-stage rockets?

  • Could the Atlas-B (SM-65B) have made it to orbit without jettisoning the first-stage engines?







stages






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 11 at 3:29









Dr Sheldon

4,4771547




4,4771547












  • I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
    – uhoh
    Nov 11 at 6:46










  • The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
    – Uwe
    Nov 11 at 19:03










  • One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
    – Uwe
    Nov 11 at 19:24










  • There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
    – Russell Borogove
    Nov 12 at 5:10


















  • I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
    – uhoh
    Nov 11 at 6:46










  • The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
    – Uwe
    Nov 11 at 19:03










  • One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
    – Uwe
    Nov 11 at 19:24










  • There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
    – Russell Borogove
    Nov 12 at 5:10
















I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
– uhoh
Nov 11 at 6:46




I've just asked a somewhat related question: Quantitative benefits of Atlas II's engine-dropping or 1.5 staging?
– uhoh
Nov 11 at 6:46












The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
– Uwe
Nov 11 at 19:03




The ability to drop some engines increases complexity of the rocket. The pipes for fuel and oxidator to the dropable engines need extra valves to close and a separation flange. Electrical connections should be cut and hydraulics too if used.
– Uwe
Nov 11 at 19:03












One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
– Uwe
Nov 11 at 19:24




One of the 5 F-1 engines of the first stage of Saturn V was switched off after some time to limit acceleration. One F-1 engine's weight was 8,361 kg, only 0.36% of the launch mass of the first stage and 6.18 % of the dry mass of the stage.
– Uwe
Nov 11 at 19:24












There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
– Russell Borogove
Nov 12 at 5:10




There was a proposal to modify the Saturn V first stage to drop the four outboard boosters Atlas style; that would drop about 25% of the dry mass of the stage!
– Russell Borogove
Nov 12 at 5:10










2 Answers
2






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oldest

votes

















up vote
3
down vote



accepted










A 1-and-2-half stage could have gentler acceleration curves than Atlas. That launcher, derived from an ICBM design, accelerated steeply to about 7g, dropped the booster section, then accelerated from 1.3g back to nearly 8g on the sustainer.



With two separate booster sections and a smaller sustainer, it could reduce its thrust in smaller steps, keeping the g-force peaks lower and the troughs higher, maintaining similar average acceleration while putting less stress on the payload.



The big disadvantage, of course, is that a booster section that can safely detach from a rocket in flight is heavier than the same engines would be if they were permanently attached. I note that Atlas’ booster masses about twice as much as a pair of H-1 engines while producing comparable total thrust.






share|improve this answer






























    up vote
    3
    down vote













    One big advantage of the half-stage on first stage of the rocket - which is similar to the advantage of using short-burn SRBs as boosters, like with Arianne 6: high TWR early on.



    High thrust-to-weight ratio early on is very desirable, significantly reducing gravitational losses, thanks to increasing the speed a lot early on: with higher initial vertical speed everything happens sooner: gravitational turn, orbital insertion - and that means way less gravitational losses. But that also means reaching MaxQ sooner - and in denser atmosphere, meaning it's "harder". In this case reduction of thrust through disposing of extra engines may be a viable option.



    The problem with extra engines on 2nd stage is that it's usually light enough to be propelled by a single engine. In case it is not so, dropping the extra engines might be desirable to reduce TWR at the end of the burn (to protect the payload and rocket structure) - at no efficiency loss; throttled engine losses a significant fraction of specific impulse: less combustion products; lower chamber pressure; lower exhaust speed. Disposing of engines will not reduce efficiency, but will reduce thrust - and get rid of mass that is no longer needed at the reduced thrust. The practicality of that is questionable though: vacuum-optimized nozzles are big, and matter to engine efficiency - and often there's simply no room to squeeze more than one into the diameter of an upper stage. And you're still carrying the empty tank mass, no longer needed. Implementing these disposable engines as boosters with own (smaller) fuel tanks might be more practical.






    share|improve this answer





















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      2 Answers
      2






      active

      oldest

      votes








      2 Answers
      2






      active

      oldest

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      active

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      active

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      up vote
      3
      down vote



      accepted










      A 1-and-2-half stage could have gentler acceleration curves than Atlas. That launcher, derived from an ICBM design, accelerated steeply to about 7g, dropped the booster section, then accelerated from 1.3g back to nearly 8g on the sustainer.



      With two separate booster sections and a smaller sustainer, it could reduce its thrust in smaller steps, keeping the g-force peaks lower and the troughs higher, maintaining similar average acceleration while putting less stress on the payload.



      The big disadvantage, of course, is that a booster section that can safely detach from a rocket in flight is heavier than the same engines would be if they were permanently attached. I note that Atlas’ booster masses about twice as much as a pair of H-1 engines while producing comparable total thrust.






      share|improve this answer



























        up vote
        3
        down vote



        accepted










        A 1-and-2-half stage could have gentler acceleration curves than Atlas. That launcher, derived from an ICBM design, accelerated steeply to about 7g, dropped the booster section, then accelerated from 1.3g back to nearly 8g on the sustainer.



        With two separate booster sections and a smaller sustainer, it could reduce its thrust in smaller steps, keeping the g-force peaks lower and the troughs higher, maintaining similar average acceleration while putting less stress on the payload.



        The big disadvantage, of course, is that a booster section that can safely detach from a rocket in flight is heavier than the same engines would be if they were permanently attached. I note that Atlas’ booster masses about twice as much as a pair of H-1 engines while producing comparable total thrust.






        share|improve this answer

























          up vote
          3
          down vote



          accepted







          up vote
          3
          down vote



          accepted






          A 1-and-2-half stage could have gentler acceleration curves than Atlas. That launcher, derived from an ICBM design, accelerated steeply to about 7g, dropped the booster section, then accelerated from 1.3g back to nearly 8g on the sustainer.



          With two separate booster sections and a smaller sustainer, it could reduce its thrust in smaller steps, keeping the g-force peaks lower and the troughs higher, maintaining similar average acceleration while putting less stress on the payload.



          The big disadvantage, of course, is that a booster section that can safely detach from a rocket in flight is heavier than the same engines would be if they were permanently attached. I note that Atlas’ booster masses about twice as much as a pair of H-1 engines while producing comparable total thrust.






          share|improve this answer














          A 1-and-2-half stage could have gentler acceleration curves than Atlas. That launcher, derived from an ICBM design, accelerated steeply to about 7g, dropped the booster section, then accelerated from 1.3g back to nearly 8g on the sustainer.



          With two separate booster sections and a smaller sustainer, it could reduce its thrust in smaller steps, keeping the g-force peaks lower and the troughs higher, maintaining similar average acceleration while putting less stress on the payload.



          The big disadvantage, of course, is that a booster section that can safely detach from a rocket in flight is heavier than the same engines would be if they were permanently attached. I note that Atlas’ booster masses about twice as much as a pair of H-1 engines while producing comparable total thrust.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 11 at 15:53

























          answered Nov 11 at 7:32









          Russell Borogove

          78.7k2260344




          78.7k2260344






















              up vote
              3
              down vote













              One big advantage of the half-stage on first stage of the rocket - which is similar to the advantage of using short-burn SRBs as boosters, like with Arianne 6: high TWR early on.



              High thrust-to-weight ratio early on is very desirable, significantly reducing gravitational losses, thanks to increasing the speed a lot early on: with higher initial vertical speed everything happens sooner: gravitational turn, orbital insertion - and that means way less gravitational losses. But that also means reaching MaxQ sooner - and in denser atmosphere, meaning it's "harder". In this case reduction of thrust through disposing of extra engines may be a viable option.



              The problem with extra engines on 2nd stage is that it's usually light enough to be propelled by a single engine. In case it is not so, dropping the extra engines might be desirable to reduce TWR at the end of the burn (to protect the payload and rocket structure) - at no efficiency loss; throttled engine losses a significant fraction of specific impulse: less combustion products; lower chamber pressure; lower exhaust speed. Disposing of engines will not reduce efficiency, but will reduce thrust - and get rid of mass that is no longer needed at the reduced thrust. The practicality of that is questionable though: vacuum-optimized nozzles are big, and matter to engine efficiency - and often there's simply no room to squeeze more than one into the diameter of an upper stage. And you're still carrying the empty tank mass, no longer needed. Implementing these disposable engines as boosters with own (smaller) fuel tanks might be more practical.






              share|improve this answer

























                up vote
                3
                down vote













                One big advantage of the half-stage on first stage of the rocket - which is similar to the advantage of using short-burn SRBs as boosters, like with Arianne 6: high TWR early on.



                High thrust-to-weight ratio early on is very desirable, significantly reducing gravitational losses, thanks to increasing the speed a lot early on: with higher initial vertical speed everything happens sooner: gravitational turn, orbital insertion - and that means way less gravitational losses. But that also means reaching MaxQ sooner - and in denser atmosphere, meaning it's "harder". In this case reduction of thrust through disposing of extra engines may be a viable option.



                The problem with extra engines on 2nd stage is that it's usually light enough to be propelled by a single engine. In case it is not so, dropping the extra engines might be desirable to reduce TWR at the end of the burn (to protect the payload and rocket structure) - at no efficiency loss; throttled engine losses a significant fraction of specific impulse: less combustion products; lower chamber pressure; lower exhaust speed. Disposing of engines will not reduce efficiency, but will reduce thrust - and get rid of mass that is no longer needed at the reduced thrust. The practicality of that is questionable though: vacuum-optimized nozzles are big, and matter to engine efficiency - and often there's simply no room to squeeze more than one into the diameter of an upper stage. And you're still carrying the empty tank mass, no longer needed. Implementing these disposable engines as boosters with own (smaller) fuel tanks might be more practical.






                share|improve this answer























                  up vote
                  3
                  down vote










                  up vote
                  3
                  down vote









                  One big advantage of the half-stage on first stage of the rocket - which is similar to the advantage of using short-burn SRBs as boosters, like with Arianne 6: high TWR early on.



                  High thrust-to-weight ratio early on is very desirable, significantly reducing gravitational losses, thanks to increasing the speed a lot early on: with higher initial vertical speed everything happens sooner: gravitational turn, orbital insertion - and that means way less gravitational losses. But that also means reaching MaxQ sooner - and in denser atmosphere, meaning it's "harder". In this case reduction of thrust through disposing of extra engines may be a viable option.



                  The problem with extra engines on 2nd stage is that it's usually light enough to be propelled by a single engine. In case it is not so, dropping the extra engines might be desirable to reduce TWR at the end of the burn (to protect the payload and rocket structure) - at no efficiency loss; throttled engine losses a significant fraction of specific impulse: less combustion products; lower chamber pressure; lower exhaust speed. Disposing of engines will not reduce efficiency, but will reduce thrust - and get rid of mass that is no longer needed at the reduced thrust. The practicality of that is questionable though: vacuum-optimized nozzles are big, and matter to engine efficiency - and often there's simply no room to squeeze more than one into the diameter of an upper stage. And you're still carrying the empty tank mass, no longer needed. Implementing these disposable engines as boosters with own (smaller) fuel tanks might be more practical.






                  share|improve this answer












                  One big advantage of the half-stage on first stage of the rocket - which is similar to the advantage of using short-burn SRBs as boosters, like with Arianne 6: high TWR early on.



                  High thrust-to-weight ratio early on is very desirable, significantly reducing gravitational losses, thanks to increasing the speed a lot early on: with higher initial vertical speed everything happens sooner: gravitational turn, orbital insertion - and that means way less gravitational losses. But that also means reaching MaxQ sooner - and in denser atmosphere, meaning it's "harder". In this case reduction of thrust through disposing of extra engines may be a viable option.



                  The problem with extra engines on 2nd stage is that it's usually light enough to be propelled by a single engine. In case it is not so, dropping the extra engines might be desirable to reduce TWR at the end of the burn (to protect the payload and rocket structure) - at no efficiency loss; throttled engine losses a significant fraction of specific impulse: less combustion products; lower chamber pressure; lower exhaust speed. Disposing of engines will not reduce efficiency, but will reduce thrust - and get rid of mass that is no longer needed at the reduced thrust. The practicality of that is questionable though: vacuum-optimized nozzles are big, and matter to engine efficiency - and often there's simply no room to squeeze more than one into the diameter of an upper stage. And you're still carrying the empty tank mass, no longer needed. Implementing these disposable engines as boosters with own (smaller) fuel tanks might be more practical.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 11 at 5:53









                  SF.

                  30.6k8100222




                  30.6k8100222






























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