3 ms·

The rocket equation is unforgiving.

by 0xf00ff00f 4y ago

bryanlarsen 4y ago
The rocket equation is far more forgiving to big rockets than small ones, and this is the biggest one yet.
- PointyFluff 4y ago
  Honestly, I think it's just silly that we are still trying to make these things on the ground.
  - Vecr 4y ago
    In my opinion the ground is the best place to make them. It's much harder to do independent inspections of the work when you have to fly the expert who wants to look at the assembly into space and train them how to do EVAs.
  - giantrobot 4y ago
    Yeah why don't we just place an order at the first available orbital facto...oh no such thing exists. Well we can order some aluminum from an asteroid mining smelt...oh that doesn't exist. Well I'm sure the useful payload entirely built in orbit is...oh. There's no infrastructure in space to do anything. Even if you built a rocket in orbit that doesn't do you any good if the payload in sitting on a pad on the ground.
  - dekhn 4y ago
    The two things I think would be interesting to demonstrate in space is aluminum extrusion production (standardized framing) and fuel production. To do either of those sustainably in space would be an impressive accomplishment.
LeifCarrotson 4y ago
In fact, it's less wasteful in terms of absolute mass to trash the rocket. Carrying fuel, parachutes, etc. to booster separation that you don't use to boost the rocket, or worse, carrying fuel, heat shields, aerodynamic surfaces, etc. to LEO for re-entry in addition to your payload, are wasteful. Non-critical mass to lunar orbit is even more extravagant. When your rocket engine is constructed by the the best TIG welders you can find carefully fitting Inconel parts together, or your tanks made by composite experts hand-laying carbon fiber in cleanrooms, yeah, it feels a waste to see that work crash and burn (or, I suppose, the other way around - first the burn, then the crash). If your booster is as disposable as a paper cup, with new ones flying off the assembly line faster than you could hope to rework anything, perhaps either the materials or the fuel are wasted but not so much work is wasted.
- chriswarbo 4y ago
  > When your rocket engine is constructed by the the best TIG welders you can find carefully fitting Inconel parts together... it feels a waste to see that work crash and burn Note that the rocket engines used by SLS (RS-25, and to a lesser extent the solid rocket boosters) were explicitly designed for reuse, as part of the Space Shuttle program; all the way back in the 1970s. The four RS-25 engines that Artemis 1 dumped in the ocean had previously flown on Space Shuttles. IIRC they first flew in 1999 (although Shuttles only used 3 engines). > If your booster is as disposable as a paper cup, with new ones flying off the assembly line faster than you could hope to rework anything, perhaps either the materials or the fuel are wasted but not so much work is wasted. Also note that the marginal cost of an SLS launch is 4.5 billion dollars. That doesn't include all the one-off costs, like R&D; certification; restarting production lines; etc. Famously, it cost over a billion dollars to restart the RS-25 production line (so they can replace those engines being dumped in the ocean); despite claiming that the use of existing tech would save money! In fact, refurbishing & upgrading those existing Shuttle engines cost more than producing brand-new RS-25s. Again, it was claimed that reusing the existing Shuttle engines would save money... Despite the cost of these assembly lines, SLS rockets aren't "flying off" them. The (few) scheduled Artemis launches are separated by years.
  - LeifCarrotson 4y ago
    When what you're really selling is a jobs program for your constituents, perhaps consuming these rocket engines for each launch is not wasteful but good business!
  - giantrobot 4y ago
    > Also note that the marginal cost of an SLS launch is 4.5 billion dollars. Citation desperately needed.
    - dotnet00 4y ago
      Here's a good article on it: https://arstechnica.com/science/2022/03/nasa-inspector-general-says-sls-costs-are-unsustainable/ https://arstechnica.com/science/2022/03/nasa-inspector-gener...

The rocket equation is unforgiving.

bryanlarsen 4y ago

The rocket equation is far more forgiving to big rockets than small ones, and this is the biggest one yet.

PointyFluff 4y ago
Honestly, I think it's just silly that we are still trying to make these things on the ground.
- Vecr 4y ago
  In my opinion the ground is the best place to make them. It's much harder to do independent inspections of the work when you have to fly the expert who wants to look at the assembly into space and train them how to do EVAs.
- giantrobot 4y ago
  Yeah why don't we just place an order at the first available orbital facto...oh no such thing exists. Well we can order some aluminum from an asteroid mining smelt...oh that doesn't exist. Well I'm sure the useful payload entirely built in orbit is...oh. There's no infrastructure in space to do anything. Even if you built a rocket in orbit that doesn't do you any good if the payload in sitting on a pad on the ground.
- dekhn 4y ago
  The two things I think would be interesting to demonstrate in space is aluminum extrusion production (standardized framing) and fuel production. To do either of those sustainably in space would be an impressive accomplishment.

LeifCarrotson 4y ago

In fact, it's less wasteful in terms of absolute mass to trash the rocket. Carrying fuel, parachutes, etc. to booster separation that you don't use to boost the rocket, or worse, carrying fuel, heat shields, aerodynamic surfaces, etc. to LEO for re-entry in addition to your payload, are wasteful. Non-critical mass to lunar orbit is even more extravagant. When your rocket engine is constructed by the the best TIG welders you can find carefully fitting Inconel parts together, or your tanks made by composite experts hand-laying carbon fiber in cleanrooms, yeah, it feels a waste to see that work crash and burn (or, I suppose, the other way around - first the burn, then the crash). If your booster is as disposable as a paper cup, with new ones flying off the assembly line faster than you could hope to rework anything, perhaps either the materials or the fuel are wasted but not so much work is wasted.

chriswarbo 4y ago
> When your rocket engine is constructed by the the best TIG welders you can find carefully fitting Inconel parts together... it feels a waste to see that work crash and burn Note that the rocket engines used by SLS (RS-25, and to a lesser extent the solid rocket boosters) were explicitly designed for reuse, as part of the Space Shuttle program; all the way back in the 1970s. The four RS-25 engines that Artemis 1 dumped in the ocean had previously flown on Space Shuttles. IIRC they first flew in 1999 (although Shuttles only used 3 engines). > If your booster is as disposable as a paper cup, with new ones flying off the assembly line faster than you could hope to rework anything, perhaps either the materials or the fuel are wasted but not so much work is wasted. Also note that the marginal cost of an SLS launch is 4.5 billion dollars. That doesn't include all the one-off costs, like R&D; certification; restarting production lines; etc. Famously, it cost over a billion dollars to restart the RS-25 production line (so they can replace those engines being dumped in the ocean); despite claiming that the use of existing tech would save money! In fact, refurbishing & upgrading those existing Shuttle engines cost more than producing brand-new RS-25s. Again, it was claimed that reusing the existing Shuttle engines would save money... Despite the cost of these assembly lines, SLS rockets aren't "flying off" them. The (few) scheduled Artemis launches are separated by years.
- LeifCarrotson 4y ago
  When what you're really selling is a jobs program for your constituents, perhaps consuming these rocket engines for each launch is not wasteful but good business!
- giantrobot 4y ago
  > Also note that the marginal cost of an SLS launch is 4.5 billion dollars. Citation desperately needed.
  - dotnet00 4y ago
    Here's a good article on it: https://arstechnica.com/science/2022/03/nasa-inspector-general-says-sls-costs-are-unsustainable/ https://arstechnica.com/science/2022/03/nasa-inspector-gener...