4 ms·

My favorite thing about Rocket Lab is the rocket engine they use[1]. By replacing the turbopump with a electric motor they were able to remove one of the single

My favorite thing about Rocket Lab is the rocket engine they use[1]. By replacing the turbopump with a electric motor they were able to remove one of the single most complicated and expensive parts of a rocket engine. As battery densities keep increasing we should see electrically fed engines being used on bigger and bigger rockets. [1]: https://en.wikipedia.org/wiki/Rutherford_(rocket_engine) https://en.wikipedia.org/wiki/Rutherford_(rocket_engine)

rocqua 8y ago
As I recall, it remains the case that rocket engines get worse performance with an electric fuel pump. Electric has two issues. First of all, the energy density (after controlling for efficiency of electric motors / turbo pumps) is lower than that of rocket fuel. Second of all, an empty battery weighs as much as a full one, whereas used fuel no longer weighs down the rocket.
- wolf550e 8y ago
  They disconnect and dump the battery mid-flight on ascent to not carry the mass of the empty battery, which might be counted as half a stage in rocket terminology (like https://en.wikipedia.org/wiki/SM-65_Atlas https://en.wikipedia.org/wiki/SM-65_Atlas) See: https://www.youtube.com/watch?v=sPwMuUxSrcA&t=1625 https://www.youtube.com/watch?v=sPwMuUxSrcA&t=1625
syntaxing 8y ago
Super interesting! I wonder if there is an orbital limit to this technology. From what I remember, Rocket labs is mainly focusing on low orbital launches. As great as batteries are, they are no where near the energy density of the propellants out there. Though the advancement of electrical pumps for rockets is super exciting!
- Gibbon1 8y ago
  I saw a paper that examined pressure fed, turbo pumps, and electric. Electric beats both pressure fed and turbo pumps at the size Rocket Lab is targeting. At large sizes turbines beat electric but the plumbing is much more complex and technically challenging. I'm suspicious that electrics are viable for first stages where performance advantage is less important. For first stages the cost is linear with ISP. Where it's exponential for second and third stages. (X^2 and X^3!!) For instance the Protons's first stage specific impulse is 285, Electron rockets specific impulse is 303. That's totally comparable.
  - syntaxing 8y ago
    I would love to read that paper if you can find it! Does metal 3D printing mitigate any of these challenges? Or is the problem a packaging problem where there is a minimum size required for the mechanical parts?
    - Gibbon1 8y ago
      This is the paper I'm drawing most of my blather from. Apparently helpfully linked from the great wiki. https://www.aacademica.org/hernan.emilio.tacca/9.pdf https://www.aacademica.org/hernan.emilio.tacca/9.pdf I did some more looking, the linked study says that turbopumps scale better then electric as the burn time increases. Because burning fuel and oxidizer is more weight efficient than batteries. At short burn times that's offset by the increased weight of the turbopump. Along with my earlier comment, the Proton first stage only burns for 130 seconds. Which puts first stages in the short burn category where eletrics do well. *but never as good as turbo pumps. Which supports the idea that electric systems can compete for large first stages by being simple, cheap, and reliable. More whack is relanding first stage electric fed rockets. Ala SpaceX.
      - syntaxing 8y ago
        Super awesome! Thanks! I really wish I learned more about rockets during my graduate studies. Haven't really learned much about them besides supersonic nozzles and the math behind the staged combustion cycle during my ICE class. Any good websites or books you recommend to learn more about them?
    - Gibbon1 8y ago
      > Does metal 3D printing mitigate any of these challenges? I remember reading an interview with some NaSA engineers who were reverse engineering the F1 engines used for the Saturn V. He said notable was the amount of welded assemblies vs ones machined using 5 axis mills, and parts created via Powder Metallurgy on modern designs. http://atlaspressedmetals.com/index.php/pm-advantages/history-of-pm http://atlaspressedmetals.com/index.php/pm-advantages/histor...
neaanopri 8y ago
Electric turbopumps are an answer to the question: "how small can you make a commercially viable orbital rocket?" Atmospheric drag effects rocket performance less and less the larger a rocket gets (square-cube law), so that a rocket like the Space Shuttle can effectively ignore the atmosphere. Conversely, the smaller a rocket gets, the harder and harder launch gets. This is the problem Rocket Lab has decided to attack. A decade ago, SpaceX launched the very similar Falcon 1. Falcon 1 was designed a decade ago, and you can see a large amount of the tech advancements in the last decade in Rocket Lab's design: 1. Cheap, lightweight Lithium Polymer (LiPo) batteries. 2. Cheap and performant brushless motor controllers. 3. Additive manufacturing for cheaply making complex parts without significant labor costs. 4. Advances in composites to enable the first orbital-class composite-bodied rocket. Without any one of these advances, Rocket Lab would not be viable. It still may end up not being viable. Rocket Lab can never compete on bulk orbital cargo pricing. However, Rocket Lab's vision of applying recent tech advancements to bring down the smallest possible launcher size is extremely commendable.
- mmirate 8y ago
  > Cheap and performant brushless motor controllers. Moreso than the good old 8-bit (in both senses iirc) AVR? > Additive manufacturing for cheaply making complex parts without significant labor costs. Who, when, and how, has 3D printing ever been used for materials stronger than ABS plastic?
- Gibbon1 8y ago
  > Rocket Lab can never compete on bulk orbital cargo pricing. Rocketlab business model is to compete with SpaceX on scheduling and orbits for small satellites. Not on price per Kg to orbit. That fits in with the trend to make satellites smaller.
- trainingaccount 8y ago
  A variation of a couple of degrees during launch would rip the Shuttle's wings off, so "ignore" is not the right word here.
  - 8y ago
iamcreasy 8y ago
Yeh, they also let drop batteries from the 2nd stage to reduce weight.

rocqua 8y ago

As I recall, it remains the case that rocket engines get worse performance with an electric fuel pump. Electric has two issues. First of all, the energy density (after controlling for efficiency of electric motors / turbo pumps) is lower than that of rocket fuel. Second of all, an empty battery weighs as much as a full one, whereas used fuel no longer weighs down the rocket.

wolf550e 8y ago
They disconnect and dump the battery mid-flight on ascent to not carry the mass of the empty battery, which might be counted as half a stage in rocket terminology (like https://en.wikipedia.org/wiki/SM-65_Atlas https://en.wikipedia.org/wiki/SM-65_Atlas) See: https://www.youtube.com/watch?v=sPwMuUxSrcA&t=1625 https://www.youtube.com/watch?v=sPwMuUxSrcA&t=1625

syntaxing 8y ago

Super interesting! I wonder if there is an orbital limit to this technology. From what I remember, Rocket labs is mainly focusing on low orbital launches. As great as batteries are, they are no where near the energy density of the propellants out there. Though the advancement of electrical pumps for rockets is super exciting!

Gibbon1 8y ago
I saw a paper that examined pressure fed, turbo pumps, and electric. Electric beats both pressure fed and turbo pumps at the size Rocket Lab is targeting. At large sizes turbines beat electric but the plumbing is much more complex and technically challenging. I'm suspicious that electrics are viable for first stages where performance advantage is less important. For first stages the cost is linear with ISP. Where it's exponential for second and third stages. (X^2 and X^3!!) For instance the Protons's first stage specific impulse is 285, Electron rockets specific impulse is 303. That's totally comparable.
- syntaxing 8y ago
  I would love to read that paper if you can find it! Does metal 3D printing mitigate any of these challenges? Or is the problem a packaging problem where there is a minimum size required for the mechanical parts?
  - Gibbon1 8y ago
    This is the paper I'm drawing most of my blather from. Apparently helpfully linked from the great wiki. https://www.aacademica.org/hernan.emilio.tacca/9.pdf https://www.aacademica.org/hernan.emilio.tacca/9.pdf I did some more looking, the linked study says that turbopumps scale better then electric as the burn time increases. Because burning fuel and oxidizer is more weight efficient than batteries. At short burn times that's offset by the increased weight of the turbopump. Along with my earlier comment, the Proton first stage only burns for 130 seconds. Which puts first stages in the short burn category where eletrics do well. *but never as good as turbo pumps. Which supports the idea that electric systems can compete for large first stages by being simple, cheap, and reliable. More whack is relanding first stage electric fed rockets. Ala SpaceX.
    - syntaxing 8y ago
      Super awesome! Thanks! I really wish I learned more about rockets during my graduate studies. Haven't really learned much about them besides supersonic nozzles and the math behind the staged combustion cycle during my ICE class. Any good websites or books you recommend to learn more about them?
  - Gibbon1 8y ago
    > Does metal 3D printing mitigate any of these challenges? I remember reading an interview with some NaSA engineers who were reverse engineering the F1 engines used for the Saturn V. He said notable was the amount of welded assemblies vs ones machined using 5 axis mills, and parts created via Powder Metallurgy on modern designs. http://atlaspressedmetals.com/index.php/pm-advantages/history-of-pm http://atlaspressedmetals.com/index.php/pm-advantages/histor...

neaanopri 8y ago

Electric turbopumps are an answer to the question: "how small can you make a commercially viable orbital rocket?" Atmospheric drag effects rocket performance less and less the larger a rocket gets (square-cube law), so that a rocket like the Space Shuttle can effectively ignore the atmosphere. Conversely, the smaller a rocket gets, the harder and harder launch gets. This is the problem Rocket Lab has decided to attack. A decade ago, SpaceX launched the very similar Falcon 1. Falcon 1 was designed a decade ago, and you can see a large amount of the tech advancements in the last decade in Rocket Lab's design: 1. Cheap, lightweight Lithium Polymer (LiPo) batteries. 2. Cheap and performant brushless motor controllers. 3. Additive manufacturing for cheaply making complex parts without significant labor costs. 4. Advances in composites to enable the first orbital-class composite-bodied rocket. Without any one of these advances, Rocket Lab would not be viable. It still may end up not being viable. Rocket Lab can never compete on bulk orbital cargo pricing. However, Rocket Lab's vision of applying recent tech advancements to bring down the smallest possible launcher size is extremely commendable.

mmirate 8y ago
> Cheap and performant brushless motor controllers. Moreso than the good old 8-bit (in both senses iirc) AVR? > Additive manufacturing for cheaply making complex parts without significant labor costs. Who, when, and how, has 3D printing ever been used for materials stronger than ABS plastic?
Gibbon1 8y ago
> Rocket Lab can never compete on bulk orbital cargo pricing. Rocketlab business model is to compete with SpaceX on scheduling and orbits for small satellites. Not on price per Kg to orbit. That fits in with the trend to make satellites smaller.
trainingaccount 8y ago
A variation of a couple of degrees during launch would rip the Shuttle's wings off, so "ignore" is not the right word here.
- 8y ago

iamcreasy 8y ago

Yeh, they also let drop batteries from the 2nd stage to reduce weight.