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I think the most exciting application for this would be for launching spacecraft. The tyranny of the rocket equation makes launches super expensive because roc

I think the most exciting application for this would be for launching spacecraft. The tyranny of the rocket equation makes launches super expensive because rockets have to carry fuel to lift the fuel and so on. So it we can provide energy for a launch from the ground it could be amazing.

mpoteat 6y ago
I think all forms of electric propulsion have too small thrust compared to the mass of the electric engine for that to work. However, electric planes could benefit a lot from not having to carry their battery.
- soperj 6y ago
  or even carrying a much smaller battery, since a huge amount of energy is used just for take off.
  - NickNameNick 6y ago
    The 'Electric Runway' concept pops up from time to time. I'm not sure how developed it is, in the absence of large electric aircraft.
qppo 6y ago
I think the only way to do that (in principle) would be to make an electric jet engine and power it wirelessly, which becomes less efficient and powerful the further from the transmitting array and thinner the atmosphere before replacing the atmosphere with its own propellant (you can't push against nothing in a vacuum). But if you did have such an engine/transmitter maybe you could make an electric plane that gets recharged as it passes over transmitting stations on the ground.
- mrfusion 6y ago
  I guess it really depends on how much power they can transmit. If you get a lot of power, the simplest concept Would be an electric heater to increase the temperature of the propellant above what it could get through combustion. The higher the temperature the greater the expansion and the more thrust per pound of propellant is obtained.
  - qppo 6y ago
    That's essentially how a jet engine works but replacing the combustion chambers with electric heaters - and it sounds really expensive in terms of power consumption. An alternative is a kind of plasma propulsion engine called a VASIMR [0] engine. I don't want to do the napkin math but my gut is the most practical electrical mechanism to get enough delta-V to LEO is a railgun but doing the acceleration up front would have probably have undesirable effects on the payload. [0] https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magn...
sacred_numbers 6y ago
I don't think wireless electric spacecraft are really viable for getting into Earth orbit, at least not in the foreseeable future. In order to escape Earth's gravity well, a spacecraft must be accelerating at more than 9.8 m/s (1 g), and realistically at double or triple that rate to minimize fuel consumption. Imagine a spacecraft with a mass of 100 tons (including fuel and payload). Let's also assume a specific impulse of 2,956 (the highest thrust version of VASIMR according to this source: http://www.projectrho.com/public_html/rocket/enginelist.php#id--Electromagnetic_(Plasma)--VASIMR http://www.projectrho.com/public_html/rocket/enginelist.php#...). If we require an acceleration of 2 g and assume that our engine is 100% efficient we would require about 28 GW of electricity. This is approximately equivalent to the average electricity consumption of California. I don't think it would be possible (with current or projected future technology) to build a receiver that could handle 28 GW of electricity and still stay under 100 tons. If we could build such a receiver I don't think it would be able to survive accelerating through Earth's atmosphere. The silver lining, though, is that wireless power transfer is a very useful technology for use in space after getting to orbit. Lasers are probably a better technology than microwaves for transferring power over interplanetary distances, but the concept is the same. If we ever travel to another star there is a pretty good chance that the journey will be at least partially powered by an array of very large lasers.
- Emrod 6y ago
  Power density of direct heat exchange engines exceeds anything chemical rockets have to offer us at this stage. Beaming about 80MW would help get rid of the first stage of a rocket which represents about 80% of carried weight. I imagine this would cut space payloads cost significantly :)
  - vchak1 6y ago
    With this, could you not also use say balloons to get the rocket up till a particular point, and then switch to beamed power?
    - cwkoss 6y ago
6gvONxR4sf7o 6y ago
That's more a question of momentum, which this would barely provide.

mpoteat 6y ago

I think all forms of electric propulsion have too small thrust compared to the mass of the electric engine for that to work. However, electric planes could benefit a lot from not having to carry their battery.

soperj 6y ago
or even carrying a much smaller battery, since a huge amount of energy is used just for take off.
- NickNameNick 6y ago
  The 'Electric Runway' concept pops up from time to time. I'm not sure how developed it is, in the absence of large electric aircraft.

qppo 6y ago

I think the only way to do that (in principle) would be to make an electric jet engine and power it wirelessly, which becomes less efficient and powerful the further from the transmitting array and thinner the atmosphere before replacing the atmosphere with its own propellant (you can't push against nothing in a vacuum). But if you did have such an engine/transmitter maybe you could make an electric plane that gets recharged as it passes over transmitting stations on the ground.

mrfusion 6y ago
I guess it really depends on how much power they can transmit. If you get a lot of power, the simplest concept Would be an electric heater to increase the temperature of the propellant above what it could get through combustion. The higher the temperature the greater the expansion and the more thrust per pound of propellant is obtained.
- qppo 6y ago
  That's essentially how a jet engine works but replacing the combustion chambers with electric heaters - and it sounds really expensive in terms of power consumption. An alternative is a kind of plasma propulsion engine called a VASIMR [0] engine. I don't want to do the napkin math but my gut is the most practical electrical mechanism to get enough delta-V to LEO is a railgun but doing the acceleration up front would have probably have undesirable effects on the payload. [0] https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magn...

sacred_numbers 6y ago

I don't think wireless electric spacecraft are really viable for getting into Earth orbit, at least not in the foreseeable future. In order to escape Earth's gravity well, a spacecraft must be accelerating at more than 9.8 m/s (1 g), and realistically at double or triple that rate to minimize fuel consumption. Imagine a spacecraft with a mass of 100 tons (including fuel and payload). Let's also assume a specific impulse of 2,956 (the highest thrust version of VASIMR according to this source: http://www.projectrho.com/public_html/rocket/enginelist.php#id--Electromagnetic_(Plasma)--VASIMR http://www.projectrho.com/public_html/rocket/enginelist.php#...). If we require an acceleration of 2 g and assume that our engine is 100% efficient we would require about 28 GW of electricity. This is approximately equivalent to the average electricity consumption of California. I don't think it would be possible (with current or projected future technology) to build a receiver that could handle 28 GW of electricity and still stay under 100 tons. If we could build such a receiver I don't think it would be able to survive accelerating through Earth's atmosphere. The silver lining, though, is that wireless power transfer is a very useful technology for use in space after getting to orbit. Lasers are probably a better technology than microwaves for transferring power over interplanetary distances, but the concept is the same. If we ever travel to another star there is a pretty good chance that the journey will be at least partially powered by an array of very large lasers.

Emrod 6y ago
Power density of direct heat exchange engines exceeds anything chemical rockets have to offer us at this stage. Beaming about 80MW would help get rid of the first stage of a rocket which represents about 80% of carried weight. I imagine this would cut space payloads cost significantly :)
- vchak1 6y ago
  With this, could you not also use say balloons to get the rocket up till a particular point, and then switch to beamed power?
  - cwkoss 6y ago

6gvONxR4sf7o 6y ago

That's more a question of momentum, which this would barely provide.