6 ms·

What amazes (and saddens) me is that we don't seem to have not even a far fetched theoretical approach to dramatically improve rockets within the next few decad

What amazes (and saddens) me is that we don't seem to have not even a far fetched theoretical approach to dramatically improve rockets within the next few decades.

cookingrobot 8y ago
There are catapults: https://techcrunch.com/2018/02/22/spinlaunch-2/ https://techcrunch.com/2018/02/22/spinlaunch-2/
- zyxwvu 8y ago
  I'm pretty sure that would lead to a near absolute zero survivability for anyone on board a system like that.
  - 2trill2spill 8y ago
    Yea, but a catapult or railgun would be fine for water, certain foods and other durable goods. Then the crew could take a smaller, cheaper rocket up.
    - zyxwvu 8y ago
      That's true. I wonder what the energy use would be in comparison to chemical rockets. And if it would be inherently safer since it wouldn't be moving via a controlled explosion.
mickronome 8y ago
It's a bit sad, I do long for the stars and planets. However, rramatically improving rockets might be like trying to improve the carriage to get a much faster personal transport, while keeping the horse. It seems to be the case, that the cost of launching commercial payloads are still "low" enough compared to the cost of the payloads since there are few big budget ventures that tries to make lifting much cheaper through alternative methods. I'm not saying that space elevators or other alternative lift devices are feasible, but we tend to get huge investments even into tech that seems absolutely implausible if there is a big market. The lack of these makes investments makes it plausible that the current launch costs are actually acceptable for all current, and expected near future commercial actors.
- philwelch 8y ago
  The nice thing about rockets is that you can start as small as you'd like and build progressively larger and larger rockets and get the engineering details right before you have to worry about getting into space. Space elevators, skyhooks, and launch loops are all big enough that it's an all-or-nothing deal. You can test individual components, but a whole end-to-end space elevator has to be exactly the distance between ground and geosync or else it just doesn't work. At best, you could build smaller versions of this stuff on the moon first and then scale up to Earth-size later, taking into account such factors as water, atmosphere, and the fact that the Earth is not tidally locked with the sun. But that requires hauling metric fucktons of parts and equipment to the moon, even if you're using lunar resources to build the space elevator itself, so there's no guarantee you end up ahead in the end. The basic physics behind rockets is simple as all hell, and it still required von Braun to spend his entire adult life building progressively bigger and bigger rockets and refining the design details. The V2 only needed to be able to land nose-first 200 miles from where it was launched, but without that knowledge and experience, the Saturn V would have been impossible. That's the kind of iteration that's fundamentally impossible with these other launch systems.
  - snovv_crash 8y ago
    With a space elevator, don't you need a mass some distance above geosync to hold the weight of the cable and the payload as it ascends?
    - yellowapple 8y ago
      I think the counterbalance is more to make sure that the center of gravity is actually the thing in geostationary orbit.
    - philwelch 8y ago
      Yeah, it's not the type of thing you can iterate on and get usable results for without the whole thing. It's not like you can build a tiny space elevator and use it to bomb London, for example.
- 8y ago
stcredzero 8y ago
Nuclear rockets are a dramatic improvement on chemical rockets. We've already built those. Ion engines are a dramatic improvement on chemical rockets. We are currently using those. Robert Forward also calculated that almost any conceivable mission in the solar system could be accomplished by an antimatter rocket with only a 3/5ths fuel fraction. Fusion rockets would be a somewhat watered-down version of that. (Though, nowhere near what's shown on The Expanse with Epstein Drives.) Beamed propulsion throws out the rocket equation altogether, as do light sails.
- vkou 8y ago
  The problem with beamed propulsion is that you still need a rocket, or some equivalent thereof to stop going, whenever you get to your destination. Not an issue for flybys, but an issue if you want to get into an orbit.
  - mLuby 8y ago
    Or just a mirror ahead of the spacecraft!
  - stcredzero 8y ago
    The problem with beamed propulsion is that you still need a rocket, or some equivalent thereof to stop going, whenever you get to your destination. False. Robert Forward has a technique for deceleration for interstellar lightsail craft, which is described in Rocheworld and one of his science books. Magsails using beamed particle propulsion can also exploit the interstellar medium to decelerate without onboard fuel. Not an issue for flybys, but an issue if you want to get into an orbit. Carrying a small rocket for a circularization burn is vastly cheaper than a 1st stage. This is covered in Jordin Kare's modular laser launch proposal, and this technique was also considered for Bull's light gas space gun. Those can produce launch economics approaching those of space elevators.
    - Alupis 8y ago
      > False. Robert Forward has a technique Sorry, but you're citing a science fiction author as proposing a credible method, yet don't even state what that method is. Yes, I know Robert Forward used to work in aerospace, but his fiction writings are... fiction. He's been out of the industry since 2002 and a hand-wavy "he has a technique" doesn't strike me as being particularly credible.
akeck 8y ago
If I understand the article, that would require either a new both radically strong and radically lightweight material for the non-propellant parts the rocket (assuming H/O propellant), or using non-chemical physics for propellant that exceeds the payment energy of H/O, and that is stable enough to be relatively safe. Or both.
mLuby 8y ago
Well, rockets sure, but we have other propulsion technologies that aren't governed by the rocket equation: solar sails, magnetic sails, and laser propulsion all come to mind. And even with momentum rockets, ion drives, fission rockets, and fusion rockets are massive improvements over the standard chemical rockets we use today.
tscs37 8y ago
We tried many approaches. Nuclear has amazing power ratios but detonating a nuclear warhead to get moving is somewhat of a problem when you're close to earth. Fission Heat Engines are quite good but not good enough for takeoff. Ion engines suffer the same fate. Almost no alternative propulsion method can replace takeoff boosters, thusly limiting the mass you can put into space. With limited mass you can only make engines that big. Or bigger if you assemble them in space which opens other cans of worms.
- archgoon 8y ago
  > Nuclear has amazing power ratios but detonating a nuclear warhead to get moving is somewhat of a problem when you're close to earth. It's not really a 'near earth' issue. Fallout concerns can probably be mitigated (and Freeman Dyson came up with a few ideas in that direction). Research in this direction, however, got killed as part of the various test ban treaties. From the perspective of trying to reduce any country's desire for having a nuclear bomb program, Project Orion, and other nuclear solutions, is a no go. So even if you were to promise "We'll only start the nuclear component when we hit the moon" the proliferation concerns would still kill NASA's interest in pursuing it. So yeah; it's not really a technical issue at it's core (though you definitely have technical issues to solve), but rather a political one (which certainly doesn't invalidate it).
- hughes 8y ago
  Nuclear rockets do not have to be about detonating nuclear warheads. Nuclear thermal rockets have no detonation, no fallout and no wide-scale meltdown risk. They've been demonstrated[1] to have efficiencies 3-4x greater than conventional engines without sacrificing thrust. [1] https://en.wikipedia.org/wiki/Project_Timberwind https://en.wikipedia.org/wiki/Project_Timberwind
mikeash 8y ago
I don’t think we need to. Look at what SpaceX’s BFR will be able to do. There isn’t anything fundamentally new there, just lots of refinement.
wizardforhire 8y ago
aerospikes There’s a lot of reason why they haven’t been used yet, but I think most the compelling argument against them is that they won’t be used until fuel costs become the competitive factor in launch prices. https://youtu.be/K4zFefh5T-8 https://youtu.be/K4zFefh5T-8 https://space.stackexchange.com/questions/3004/why-arent-linear-aerospike-engines-in-common-use https://space.stackexchange.com/questions/3004/why-arent-lin... Nuclear rockets are quite the concept but have their obvious limitations. This video is worth checking out if you haven’t seen it yet. https://youtu.be/eDNX65d-FBY https://youtu.be/eDNX65d-FBY
- ballooney 8y ago
  Aerospikes are not a dramatic improvement in anything. They just buy you a bit more nozzle efficiency, and that only really comes into its own for ssto.
2trill2spill 8y ago
Maybe not as dramatic as we would all like, but it would be nice to see some work put into trying to revive the idea of the air-augmented rocket. Apparently the Russians worked on the idea in the 1960's[1]. But the PR-90 look like its as far as they got with the idea[2]. But maybe there won't be one dramatic change that makes rocket travel cheaper. Maybe we keep iterating on rocket and rocket engine designs and eventually looking back it seems revolutionary. As composites get better and better more and more of rockets will be made from composites instead of the current material of choice, lithium aluminum alloy. Plus the increased use of oxygen rich combustion[3] with it's improved efficiency. Also it looks like Ch4/LOX might be more common in the future[4][5][6], which is good because Ch4/LOX has a higher ISP then RP-1 and also is significantly more dense then H2 propellant. There's also so called "slush" or "super chilled" propellants[7], Spacex has even been using it for awhile[8]. So maybe the future will be extremely light, reusable, oxygen rich, staged combustion, methane burning rockets with super chilled propellants? [1]: http://www.astronautix.com/g/gnom.html http://www.astronautix.com/g/gnom.html [2]: http://www.astronautix.com/p/pr-90.html http://www.astronautix.com/p/pr-90.html [3]: http://www.americaspace.com/2015/05/29/new-oxygen-preburner-firings-a-major-step-toward-rekindling-u-s-hydrocarbon-rocket-engine-leadership/ http://www.americaspace.com/2015/05/29/new-oxygen-preburner-... [4]: https://spaceflightnow.com/2017/10/20/worlds-largest-methane-fueled-rocket-engine-test-fired-by-blue-origin/ https://spaceflightnow.com/2017/10/20/worlds-largest-methane... [5]: https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) [6]: http://www.russianspaceweb.com/soyuz5-lv-ptk.html http://www.russianspaceweb.com/soyuz5-lv-ptk.html [7]: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790004067.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197900... [8]: http://www.businessinsider.com/spacex-deep-cryogenic-cryo-liquid-oxygen-lox-rocket-fuel-2017-1 http://www.businessinsider.com/spacex-deep-cryogenic-cryo-li...
- neolefty 8y ago
  revive the idea of the air-augmented rocket Does Skylon fit the bill? https://en.wikipedia.org/wiki/Skylon_(spacecraft) https://en.wikipedia.org/wiki/Skylon_(spacecraft) It pushes the limits of materials and design. But I think a reusable 2-stage rocket—as boring as it sounds—will end up working better in the near term. It can be done with safe margins.
Robotbeat 8y ago
Honestly, we do. The rocket equation is not just exhaust velocity, it's ALSO mass fraction. And material advances can make a huge difference there. Chemical rockets are also much more efficient devices than is given credit for. A good, very optimized two stage rocket like SpaceX BFR (and the ITS concept before it) can get payloads to orbit using just ~300 Megajoules per kg (250MJ/kg in the more efficient tanker configuration). The specific kinetic energy of orbit is about 25MJ/kg (40MJ/kg if we include gravity and aero losses and changes in altitude), so rockets are total 10% efficient at converting chemical energy directly into orbital energy, and with an optimized, high pressure and variable mixture ratio hydrogen rocket engine architecture with some improvements in materials science, we could improve that to 20% or more. That beats the chemical to mechanical efficiency of the typical car. That translates to between $1 and $10 per kg to orbit. That's 3 orders of magnitude less cost than today, if we can master reuse. So arguably, chemical rockets are perfectly fine for achieving orbit cheaply.

What amazes (and saddens) me is that we don't seem to have not even a far fetched theoretical approach to dramatically improve rockets within the next few decades.

cookingrobot 8y ago

There are catapults: https://techcrunch.com/2018/02/22/spinlaunch-2/ https://techcrunch.com/2018/02/22/spinlaunch-2/

zyxwvu 8y ago
I'm pretty sure that would lead to a near absolute zero survivability for anyone on board a system like that.
- 2trill2spill 8y ago
  Yea, but a catapult or railgun would be fine for water, certain foods and other durable goods. Then the crew could take a smaller, cheaper rocket up.
  - zyxwvu 8y ago
    That's true. I wonder what the energy use would be in comparison to chemical rockets. And if it would be inherently safer since it wouldn't be moving via a controlled explosion.

mickronome 8y ago

It's a bit sad, I do long for the stars and planets. However, rramatically improving rockets might be like trying to improve the carriage to get a much faster personal transport, while keeping the horse. It seems to be the case, that the cost of launching commercial payloads are still "low" enough compared to the cost of the payloads since there are few big budget ventures that tries to make lifting much cheaper through alternative methods. I'm not saying that space elevators or other alternative lift devices are feasible, but we tend to get huge investments even into tech that seems absolutely implausible if there is a big market. The lack of these makes investments makes it plausible that the current launch costs are actually acceptable for all current, and expected near future commercial actors.

philwelch 8y ago
The nice thing about rockets is that you can start as small as you'd like and build progressively larger and larger rockets and get the engineering details right before you have to worry about getting into space. Space elevators, skyhooks, and launch loops are all big enough that it's an all-or-nothing deal. You can test individual components, but a whole end-to-end space elevator has to be exactly the distance between ground and geosync or else it just doesn't work. At best, you could build smaller versions of this stuff on the moon first and then scale up to Earth-size later, taking into account such factors as water, atmosphere, and the fact that the Earth is not tidally locked with the sun. But that requires hauling metric fucktons of parts and equipment to the moon, even if you're using lunar resources to build the space elevator itself, so there's no guarantee you end up ahead in the end. The basic physics behind rockets is simple as all hell, and it still required von Braun to spend his entire adult life building progressively bigger and bigger rockets and refining the design details. The V2 only needed to be able to land nose-first 200 miles from where it was launched, but without that knowledge and experience, the Saturn V would have been impossible. That's the kind of iteration that's fundamentally impossible with these other launch systems.
- snovv_crash 8y ago
  With a space elevator, don't you need a mass some distance above geosync to hold the weight of the cable and the payload as it ascends?
  - yellowapple 8y ago
    I think the counterbalance is more to make sure that the center of gravity is actually the thing in geostationary orbit.
  - philwelch 8y ago
    Yeah, it's not the type of thing you can iterate on and get usable results for without the whole thing. It's not like you can build a tiny space elevator and use it to bomb London, for example.
8y ago

stcredzero 8y ago

Nuclear rockets are a dramatic improvement on chemical rockets. We've already built those. Ion engines are a dramatic improvement on chemical rockets. We are currently using those. Robert Forward also calculated that almost any conceivable mission in the solar system could be accomplished by an antimatter rocket with only a 3/5ths fuel fraction. Fusion rockets would be a somewhat watered-down version of that. (Though, nowhere near what's shown on The Expanse with Epstein Drives.) Beamed propulsion throws out the rocket equation altogether, as do light sails.

vkou 8y ago
The problem with beamed propulsion is that you still need a rocket, or some equivalent thereof to stop going, whenever you get to your destination. Not an issue for flybys, but an issue if you want to get into an orbit.
- mLuby 8y ago
  Or just a mirror ahead of the spacecraft!
- stcredzero 8y ago
  The problem with beamed propulsion is that you still need a rocket, or some equivalent thereof to stop going, whenever you get to your destination. False. Robert Forward has a technique for deceleration for interstellar lightsail craft, which is described in Rocheworld and one of his science books. Magsails using beamed particle propulsion can also exploit the interstellar medium to decelerate without onboard fuel. Not an issue for flybys, but an issue if you want to get into an orbit. Carrying a small rocket for a circularization burn is vastly cheaper than a 1st stage. This is covered in Jordin Kare's modular laser launch proposal, and this technique was also considered for Bull's light gas space gun. Those can produce launch economics approaching those of space elevators.
  - Alupis 8y ago
    > False. Robert Forward has a technique Sorry, but you're citing a science fiction author as proposing a credible method, yet don't even state what that method is. Yes, I know Robert Forward used to work in aerospace, but his fiction writings are... fiction. He's been out of the industry since 2002 and a hand-wavy "he has a technique" doesn't strike me as being particularly credible.

akeck 8y ago

If I understand the article, that would require either a new both radically strong and radically lightweight material for the non-propellant parts the rocket (assuming H/O propellant), or using non-chemical physics for propellant that exceeds the payment energy of H/O, and that is stable enough to be relatively safe. Or both.

mLuby 8y ago

Well, rockets sure, but we have other propulsion technologies that aren't governed by the rocket equation: solar sails, magnetic sails, and laser propulsion all come to mind. And even with momentum rockets, ion drives, fission rockets, and fusion rockets are massive improvements over the standard chemical rockets we use today.

tscs37 8y ago

We tried many approaches. Nuclear has amazing power ratios but detonating a nuclear warhead to get moving is somewhat of a problem when you're close to earth. Fission Heat Engines are quite good but not good enough for takeoff. Ion engines suffer the same fate. Almost no alternative propulsion method can replace takeoff boosters, thusly limiting the mass you can put into space. With limited mass you can only make engines that big. Or bigger if you assemble them in space which opens other cans of worms.

archgoon 8y ago
> Nuclear has amazing power ratios but detonating a nuclear warhead to get moving is somewhat of a problem when you're close to earth. It's not really a 'near earth' issue. Fallout concerns can probably be mitigated (and Freeman Dyson came up with a few ideas in that direction). Research in this direction, however, got killed as part of the various test ban treaties. From the perspective of trying to reduce any country's desire for having a nuclear bomb program, Project Orion, and other nuclear solutions, is a no go. So even if you were to promise "We'll only start the nuclear component when we hit the moon" the proliferation concerns would still kill NASA's interest in pursuing it. So yeah; it's not really a technical issue at it's core (though you definitely have technical issues to solve), but rather a political one (which certainly doesn't invalidate it).
hughes 8y ago
Nuclear rockets do not have to be about detonating nuclear warheads. Nuclear thermal rockets have no detonation, no fallout and no wide-scale meltdown risk. They've been demonstrated[1] to have efficiencies 3-4x greater than conventional engines without sacrificing thrust. [1] https://en.wikipedia.org/wiki/Project_Timberwind https://en.wikipedia.org/wiki/Project_Timberwind

mikeash 8y ago

I don’t think we need to. Look at what SpaceX’s BFR will be able to do. There isn’t anything fundamentally new there, just lots of refinement.

wizardforhire 8y ago

aerospikes There’s a lot of reason why they haven’t been used yet, but I think most the compelling argument against them is that they won’t be used until fuel costs become the competitive factor in launch prices. https://youtu.be/K4zFefh5T-8 https://youtu.be/K4zFefh5T-8 https://space.stackexchange.com/questions/3004/why-arent-linear-aerospike-engines-in-common-use https://space.stackexchange.com/questions/3004/why-arent-lin... Nuclear rockets are quite the concept but have their obvious limitations. This video is worth checking out if you haven’t seen it yet. https://youtu.be/eDNX65d-FBY https://youtu.be/eDNX65d-FBY

ballooney 8y ago
Aerospikes are not a dramatic improvement in anything. They just buy you a bit more nozzle efficiency, and that only really comes into its own for ssto.

2trill2spill 8y ago

Maybe not as dramatic as we would all like, but it would be nice to see some work put into trying to revive the idea of the air-augmented rocket. Apparently the Russians worked on the idea in the 1960's[1]. But the PR-90 look like its as far as they got with the idea[2]. But maybe there won't be one dramatic change that makes rocket travel cheaper. Maybe we keep iterating on rocket and rocket engine designs and eventually looking back it seems revolutionary. As composites get better and better more and more of rockets will be made from composites instead of the current material of choice, lithium aluminum alloy. Plus the increased use of oxygen rich combustion[3] with it's improved efficiency. Also it looks like Ch4/LOX might be more common in the future[4][5][6], which is good because Ch4/LOX has a higher ISP then RP-1 and also is significantly more dense then H2 propellant. There's also so called "slush" or "super chilled" propellants[7], Spacex has even been using it for awhile[8]. So maybe the future will be extremely light, reusable, oxygen rich, staged combustion, methane burning rockets with super chilled propellants? [1]: http://www.astronautix.com/g/gnom.html http://www.astronautix.com/g/gnom.html [2]: http://www.astronautix.com/p/pr-90.html http://www.astronautix.com/p/pr-90.html [3]: http://www.americaspace.com/2015/05/29/new-oxygen-preburner-firings-a-major-step-toward-rekindling-u-s-hydrocarbon-rocket-engine-leadership/ http://www.americaspace.com/2015/05/29/new-oxygen-preburner-... [4]: https://spaceflightnow.com/2017/10/20/worlds-largest-methane-fueled-rocket-engine-test-fired-by-blue-origin/ https://spaceflightnow.com/2017/10/20/worlds-largest-methane... [5]: https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) https://en.wikipedia.org/wiki/Raptor_(rocket_engine_family) [6]: http://www.russianspaceweb.com/soyuz5-lv-ptk.html http://www.russianspaceweb.com/soyuz5-lv-ptk.html [7]: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790004067.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/197900... [8]: http://www.businessinsider.com/spacex-deep-cryogenic-cryo-liquid-oxygen-lox-rocket-fuel-2017-1 http://www.businessinsider.com/spacex-deep-cryogenic-cryo-li...

neolefty 8y ago
revive the idea of the air-augmented rocket Does Skylon fit the bill? https://en.wikipedia.org/wiki/Skylon_(spacecraft) https://en.wikipedia.org/wiki/Skylon_(spacecraft) It pushes the limits of materials and design. But I think a reusable 2-stage rocket—as boring as it sounds—will end up working better in the near term. It can be done with safe margins.

Robotbeat 8y ago

Honestly, we do. The rocket equation is not just exhaust velocity, it's ALSO mass fraction. And material advances can make a huge difference there. Chemical rockets are also much more efficient devices than is given credit for. A good, very optimized two stage rocket like SpaceX BFR (and the ITS concept before it) can get payloads to orbit using just ~300 Megajoules per kg (250MJ/kg in the more efficient tanker configuration). The specific kinetic energy of orbit is about 25MJ/kg (40MJ/kg if we include gravity and aero losses and changes in altitude), so rockets are total 10% efficient at converting chemical energy directly into orbital energy, and with an optimized, high pressure and variable mixture ratio hydrogen rocket engine architecture with some improvements in materials science, we could improve that to 20% or more. That beats the chemical to mechanical efficiency of the typical car. That translates to between $1 and $10 per kg to orbit. That's 3 orders of magnitude less cost than today, if we can master reuse. So arguably, chemical rockets are perfectly fine for achieving orbit cheaply.