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The Falcon 9 can not be launched for less than $1M. Falcon 9 does not reuse the second stage. Elon has said that the second stage is approximately 20% of the co

by SEJeff 5y ago

The Falcon 9 can not be launched for less than $1M. Falcon 9 does not reuse the second stage. Elon has said that the second stage is approximately 20% of the cost of a Falcon 9 launch. A Falcon 9 needs to have some work done between each launch. Some of the Falcon 9 parts are not actually reusable (crush cores for the landing legs as an example). This is why they can not ever simply fill up a landed Falcon 9 booster, put a new second stage on it, and launch it again. The Starship / Superheavy combo is designed to be able to literally just refuel and go. The Falcon 9 booster is mostly made of aluminum, which is up to 60% more expensive than stainless steel. The Starship / Superheavy are stainless steel. Methane (Starship fuel) is massively cheaper than Kerosene (Falcon 9 fuel). Methane also has a much higher specific impulse, which means you can use less of it to get the same increase in velocity. Methane can be stored in liquid form in same temperature as oxygen, which means less insulation the two propellant tanks. Inversely, Kerosene will freeze at the temperatures required to get oxygen into liquid form. Basically, nothing you said is accurate.

oses 5y ago
The combination of Methane and the full flow staged combustion cycle also means significantly reduced coking in the engine, so it drastically prolongs the time between engine refurbishments.
- ordu 5y ago
  Do you know how a reduced coking works? I've read about the raptor engine[1] and it explains how fuel rich hot mixture leads to coking, it explains how USA solved this problem before (by using hydrogen as a fuel), but how Musk managed to solve it? Partially burned methane should produce free carbon atoms, shouldn't it? Doesn't it raise a coking problem? [1] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
  - jjk166 5y ago
    In a conventional hydrocarbon fueled engine, you're using a fuel with hydrocarbon chains at approximately room temperature to cool the engine. With only a little heat addition, you get up to a temperature where these chains can shed hydrogens and convert their C-C-H bonds to C=C double bonds. These bonds in turn allow hydrocarbon chains to join together into larger molecules that can coagulate and stick to the walls. Methane on the other hand is starting out at a much lower temperature, and it's very difficult to get methane molecules to react with each other to form large molecules as you're not starting with any single C-C bonds. Isolated free carbon atoms (soot) aren't much of a problem.
  - mr_toad 5y ago
    > Partially burned methane The raptors don’t run fuel rich, which should reduce that problem.
    - nautilius 5y ago
      Oh that’s interesting, do you have some more information or a link?
    - ordu 5y ago
      According to the link above they do. Full-flow means to have two pre-burners one going fuel rich while other going oxygen rich. Though I'm not a rocket scientist and I'd be grateful if proven wrong.
Tuna-Fish 5y ago
> Elon has said that the second stage is approximately 20% of the cost of a Falcon 9 launch. 20% of the cost of the whole rocket. With no reuse. Now that reuse has cut the cost of launch way down, the second stage is much more than that of the cost.
- SEJeff 5y ago
  Oh very good point. The GP’s $1 million number per falcon 9 launch was ludicrous.
  - barbegal 5y ago
    Indeed, I'm using the fact that it's ludicrous to make the case that a $2M starship launch is equally ludicrous.
    - btilly 5y ago
      No, it is not ludicrous. As Elon likes to point out, imagine how expensive it would be to fly if, after every flight, they threw away the plane. That's exactly what people traditionally did with rockets. The result is that the cost to fly a jet is mostly the cost of the fuel, while the cost to fly a rocket is the cost of the rocket. Consider a Falcon 9 launch. Thanks to reuse, the cost to relaunch is in the neighborhood of $30 million. The cost of the fuel is about $200,000. Over 99% the launch cost is depreciation, maintenance, or having to replace what you didn't reuse. The aim with Starship is to make the cost of a launch as close to the cost of the fuel as they can get.
    - simonh 5y ago
      I’m not sure you understand the arguments being made here. $1m per launch for F9 is ludicrous because 20% of the rocket, by manufacturing cost, is expended on every launch. For Starship none of the rocket is expended per launch, the only costs are site operations, fuel and depreciation on the rocket over a hundred or more flights. They are aiming for daily launches of starship, so the site operations costs would be divided by potentially hundreds of launches per year instead of the one or two dozen a year nowadays. The cost model per flight of Starship is more like that of a jumbo jet than that of a Falcon 9.
barbegal 5y ago
You raise a few good points. Falcon 9 launches could be 30% cheaper if fully reusable but that only reduces a launch cost down to $25M. I am skeptical of the claim that they will just be able to refuel and go. Every reusable space vehicle has had that goal and always cost more than expected to refurbish for the next launch. Yes, we may get there eventually but not in the next few decades, the risks of a catastrophic component failure are too high to do no refurbishment. The starship and super heavy are certainly cheaper to construct but that has more to do with fabrication techniques than the material cost. Methane is less dense than kerosene so needs larger tanks but it does have more energy per unit mass. The overheads of using cryogenic fuel are reduced on a larger rocket but the performance gain is probably only 10% or so. I am not aware of any significant insulation between tanks on the Falcon 9 and it certainly isn't a major cost factor.
- Robotbeat 5y ago
  > Every reusable space vehicle has had that goal and always cost more than expected to refurbish for the next launch. There have only been 2 reusable launch vehicles ever, and both were only partially reusable. Shuttle and Falcon 9. Falcon 9 has already made massive strides in reducing any refurb costs between missions. there is no reason that you couldn’t build one that requires no maintenance in between flights for the same reason that there’s no reason you can’t make an upper stage that can do multiple firings per flight without any maintenance in between. Upper stage reuse will be trickier, but ultimately there’s no fundamental reason why refurb has to be done in between every flight.
  - rbanffy 5y ago
    Upper stage reuse doesn’t require a landing. If you could refuel an upper stage in space, you could use it for deep space exploration. Do they deliberately deorbit the Falcon second stage? Would be interesting if we could keep a couple parked in LEO and refuel them for different missions.
    - bryanlarsen 5y ago
      But then you need a different vehicle to refuel the original one. If you're doing that, why not just use that second vehicle for the mission and forget about reuse? Reusing second stages in space only really makes sense once you are making your fuel in space.

by SEJeff 5y ago

oses 5y ago

The combination of Methane and the full flow staged combustion cycle also means significantly reduced coking in the engine, so it drastically prolongs the time between engine refurbishments.

ordu 5y ago
Do you know how a reduced coking works? I've read about the raptor engine[1] and it explains how fuel rich hot mixture leads to coking, it explains how USA solved this problem before (by using hydrogen as a fuel), but how Musk managed to solve it? Partially burned methane should produce free carbon atoms, shouldn't it? Doesn't it raise a coking problem? [1] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
- jjk166 5y ago
  In a conventional hydrocarbon fueled engine, you're using a fuel with hydrocarbon chains at approximately room temperature to cool the engine. With only a little heat addition, you get up to a temperature where these chains can shed hydrogens and convert their C-C-H bonds to C=C double bonds. These bonds in turn allow hydrocarbon chains to join together into larger molecules that can coagulate and stick to the walls. Methane on the other hand is starting out at a much lower temperature, and it's very difficult to get methane molecules to react with each other to form large molecules as you're not starting with any single C-C bonds. Isolated free carbon atoms (soot) aren't much of a problem.
- mr_toad 5y ago
  > Partially burned methane The raptors don’t run fuel rich, which should reduce that problem.
  - nautilius 5y ago
    Oh that’s interesting, do you have some more information or a link?
  - ordu 5y ago
    According to the link above they do. Full-flow means to have two pre-burners one going fuel rich while other going oxygen rich. Though I'm not a rocket scientist and I'd be grateful if proven wrong.

Tuna-Fish 5y ago

> Elon has said that the second stage is approximately 20% of the cost of a Falcon 9 launch. 20% of the cost of the whole rocket. With no reuse. Now that reuse has cut the cost of launch way down, the second stage is much more than that of the cost.

SEJeff 5y ago
Oh very good point. The GP’s $1 million number per falcon 9 launch was ludicrous.
- barbegal 5y ago
  Indeed, I'm using the fact that it's ludicrous to make the case that a $2M starship launch is equally ludicrous.
  - btilly 5y ago
    No, it is not ludicrous. As Elon likes to point out, imagine how expensive it would be to fly if, after every flight, they threw away the plane. That's exactly what people traditionally did with rockets. The result is that the cost to fly a jet is mostly the cost of the fuel, while the cost to fly a rocket is the cost of the rocket. Consider a Falcon 9 launch. Thanks to reuse, the cost to relaunch is in the neighborhood of $30 million. The cost of the fuel is about $200,000. Over 99% the launch cost is depreciation, maintenance, or having to replace what you didn't reuse. The aim with Starship is to make the cost of a launch as close to the cost of the fuel as they can get.
  - simonh 5y ago
    I’m not sure you understand the arguments being made here. $1m per launch for F9 is ludicrous because 20% of the rocket, by manufacturing cost, is expended on every launch. For Starship none of the rocket is expended per launch, the only costs are site operations, fuel and depreciation on the rocket over a hundred or more flights. They are aiming for daily launches of starship, so the site operations costs would be divided by potentially hundreds of launches per year instead of the one or two dozen a year nowadays. The cost model per flight of Starship is more like that of a jumbo jet than that of a Falcon 9.

barbegal 5y ago

You raise a few good points. Falcon 9 launches could be 30% cheaper if fully reusable but that only reduces a launch cost down to $25M. I am skeptical of the claim that they will just be able to refuel and go. Every reusable space vehicle has had that goal and always cost more than expected to refurbish for the next launch. Yes, we may get there eventually but not in the next few decades, the risks of a catastrophic component failure are too high to do no refurbishment. The starship and super heavy are certainly cheaper to construct but that has more to do with fabrication techniques than the material cost. Methane is less dense than kerosene so needs larger tanks but it does have more energy per unit mass. The overheads of using cryogenic fuel are reduced on a larger rocket but the performance gain is probably only 10% or so. I am not aware of any significant insulation between tanks on the Falcon 9 and it certainly isn't a major cost factor.

Robotbeat 5y ago
> Every reusable space vehicle has had that goal and always cost more than expected to refurbish for the next launch. There have only been 2 reusable launch vehicles ever, and both were only partially reusable. Shuttle and Falcon 9. Falcon 9 has already made massive strides in reducing any refurb costs between missions. there is no reason that you couldn’t build one that requires no maintenance in between flights for the same reason that there’s no reason you can’t make an upper stage that can do multiple firings per flight without any maintenance in between. Upper stage reuse will be trickier, but ultimately there’s no fundamental reason why refurb has to be done in between every flight.
- rbanffy 5y ago
  Upper stage reuse doesn’t require a landing. If you could refuel an upper stage in space, you could use it for deep space exploration. Do they deliberately deorbit the Falcon second stage? Would be interesting if we could keep a couple parked in LEO and refuel them for different missions.
  - bryanlarsen 5y ago
    But then you need a different vehicle to refuel the original one. If you're doing that, why not just use that second vehicle for the mission and forget about reuse? Reusing second stages in space only really makes sense once you are making your fuel in space.