Electrically Propelled Spacecraft

[Potato Science]

I'm wondering if its possible to make a spacecraft that is propelled ONLY by electricity (Other Than Launching.) I want to make a spacecraft that is reusable, and I want to use electricity to do so. It will have Tons of solar panels but I'm wondering what engine or propulsion system I should use

[Snark]

Moving to Gameplay Questions.

What you are asking for isn't physically possible:  thrust requires reaction mass.  Therefore, there's nothing in the game that will allow you to do this.  The closest you can get with the stock game is the ion drive, which has an Isp much, much higher than anything else in the game... but even that consumes xenon.

That said, I wouldn't be surprised if there's some very science-fictiony mod out there that could have some magical reactionless drive to use. 

(Yes, I know of the theoretical possibility IRL of solar sails, photon drives, etc. But they don't exist in stock KSP, and even in a mod, they'd be impractical for gameplay unless performance were exaggerated to levels that make the ion drive look like stark realism.)

[Superfluous J]

None. You use none engines.

You can't propel a space ship with just electricity. You must throw something backwards to move your ship forward.

[ottothesilent]

Alcubecurrie drive. Requires propellants, technically, but they don't really "propel" the craft in a meaningful fashion. Plus, you can make physicists spin in their graves. Hermann Oberth will hate you.

[bewing]

The Sun and most planets have a magnetic field, and you can push against a magnetic field with electricity to get thrust. So the claim that it's strictly impossible is not exactly true.

Also a ramscoop that uses power to harvest interplanetary hydrogen and then fuse it to generate thrust can be said to be working only on electricity.

But none of these things are in stock KSP.

[Windspren]

I mean, you could use a Kraken Drive, but that's not really a legit form of propulsion. Basically, what you're asking for is impossible.

[Sharpy]

Oh, impossible by what science says, but the EM drive does seem to produce thrust.

https://kerbal.curseforge.com/projects/em-drive

Have fun!

[Chakat Firepaw]

On 23/10/2016 at 4:44 PM, bewing said:

The Sun and most planets have a magnetic field, and you can push against a magnetic field with electricity to get thrust. So the claim that it's strictly impossible is not exactly true.

While magsails are a thing, they also give over an order of magnitude less thrust than a solar sail except in very limited areas.  The only advantage they have is that a magsail can thrust towards the sun.

On 23/10/2016 at 4:44 PM, bewing said:

Also a ramscoop that uses power to harvest interplanetary hydrogen and then fuse it to generate thrust can be said to be working only on electricity.

For a value of "working" that was shown to be "not at all" thirty years ago.  It turns out that the Bussard ramjet is actually more of a parachute.

[FullMetalMachinist]

2 hours ago, Chakat Firepaw said:

It turns out that the Bussard ramjet is actually more of a parachute.

Wait, are you saying that the Bussard Collectors from Star Trek are actually based on a real thing!? 

[Snark]

2 hours ago, FullMetalMachinist said:

Wait, are you saying that the Bussard Collectors from Star Trek are actually based on a real thing!? 

For certain definitions of "real", yes. 

https://en.wikipedia.org/wiki/Bussard_ramjet

Larry Niven was fond of using them a lot in several of his stories.

[Blaarkies]

On 10/23/2016 at 10:44 PM, bewing said:

Also a ramscoop that uses power to harvest interplanetary hydrogen and then fuse it to generate thrust can be said to be working only on electricity.

If harvesting fuel is considered using only electricity to produce thrust, then we are already using electric rockets...they harvest fuel from that pipe on the launch pad

[Aegolius13]

Aren't photon rockets an actual thing, or least considered technically feasible (albeit with much less thrust than the EM drive is even alleged to have)? 

[Streetwind]

Photon rockets are absolutely a real thing... though it's not being taken serious by anyone.

Like all electric engines, we have troubles finding ways to power it. But unlike other electric engines, this isn't a case of "well, as long as we don't go further than Mars, I guess we can use solar". It is a case of "well, maybe if we had an antimatter reactor, we could build a spacecraft that actually has a measurable TWR... maybe". The energy requirements per unit of thrust are so insane, the specific power stat required by the power generation solution needs to be orders of magnitude higher than anything mankind has ever built. Else all you're going to get is the equivalent of a single LV-N trying to push a fuel tank the size of Gilly. Sure it'll run practically forever without refueling, but you're not going anywhere, either!

[Chakat Firepaw]

8 hours ago, Aegolius13 said:

Aren't photon rockets an actual thing, or least considered technically feasible (albeit with much less thrust than the EM drive is even alleged to have)? 

Yes, but they are reaction drives.  Their reaction mass is the very slight loss of mass that occurs in the release of energy.

[Aegolius13]

18 minutes ago, Chakat Firepaw said:

Yes, but they are reaction drives.  Their reaction mass is the very slight loss of mass that occurs in the release of energy.

Right, but since you can replenish electricity from solar panels or whatnot, I think they would still meet OP's inquiry re an engine that does not need fuel other than electricity.  

Of course, they're not in KSP and would be extremely weak, so not really an option.  Unless sticking an Illuminator on the back of a rocket works better than we think...

[Chabadarl]

24 minutes ago, Aegolius13 said:

Right, but since you can replenish electricity from solar panels or whatnot, I think they would still meet OP's inquiry re an engine that does not need fuel other than electricity.  

Of course, they're not in KSP and would be extremely weak, so not really an option.  Unless sticking an Illuminator on the back of a rocket works better than we think...

Solar panels has a reaction effect too... If you replenish electricity fast enough to be used in a photon reactor, that's mean you cannot ignore this effect...

Basicaly you have a photon sail but heavier (by a lot) and with more energy loss... So you will mch slower (but you can go in any direction, when photon sail allows you to go outwards the sun)

 

 

[Nicias]

3 hours ago, Chabadarl said:

Solar panels has a reaction effect too... If you replenish electricity fast enough to be used in a photon reactor, that's mean you cannot ignore this effect...

Basicaly you have a photon sail but heavier (by a lot) and with more energy loss... So you will mch slower (but you can go in any direction, when photon sail allows you to go outwards the sun)

 

 

Solar sails can be used to travel anywhere in system. If you treat them as a mirror, the thrust will always be normal to the sail. So if you point the normal somewhere between radial and prograde, you will slow down and fall towards the sun. Likewise between radial and retrograde will move you away. It is basically normal celestial navigation with the restriction that the thrust is proportional to the cosine of the angle of your engine and the sun, and you engine is always on. 

[Aegolius13]

3 hours ago, Chabadarl said:

Solar panels has a reaction effect too... If you replenish electricity fast enough to be used in a photon reactor, that's mean you cannot ignore this effect...

Basicaly you have a photon sail but heavier (by a lot) and with more energy loss... So you will mch slower (but you can go in any direction, when photon sail allows you to go outwards the sun)

 

 

Yeah I suppose that's true.  Though assuming there was a KSP photon rocket, and KSP modeled solar wind and all that, I guess you could exploit the infinite energy from an RTG to build something without the surface area that solar panels would require. But that's all quite speculative...

 

[Chabadarl]

12 hours ago, Nicias said:

Solar sails can be used to travel anywhere in system. If you treat them as a mirror, the thrust will always be normal to the sail. So if you point the normal somewhere between radial and prograde, you will slow down and fall towards the sun. Likewise between radial and retrograde will move you away. It is basically normal celestial navigation with the restriction that the thrust is proportional to the cosine of the angle of your engine and the sun, and you engine is always on. 

Sorry, you are right of course.  What I meant, is that the reaction force will be always outwards the sun. But indeed you still can go anywhere...

[natsirt721]

The Bussard ramjet would be sweet, except that 1) It has a minimum velocity of anywhere between 2 or 10 percent the speed of light to even take in enough hydrogen to sustain a reaction, 2) It is only really useful in interstellar space, and 3) Bremsstrahlung and synchrotron radiation limits the max velocity to about 12 percent speed of light, so what's the point.  Also requires proton-proton fusion, and we can't even figure out D-T fusion!

There is only one purely electrically propelled spacecraft AFAIK, and that would be a laser lightsail.  Put a battery of solar-powered gigawatt lasers around the sun and shine them at your mirrored spacecraft.  Like the solar sail, but with reasonable thrust.  

The problem with low-thrust propulsion is that IRL, you use a brachistochrone trajectory which is impractical given the way KSP handles physics and warping.  This means no (realistic) ion drives, no solar/mag sails, no VASIMR.  Current hall thrusters have thrusts in the 0.5 newton range, 4 orders of magnitude weaker than the Dawn.  Radiation pressure at earth is somewhere in the micronewton per square meter, which means your sail is going to be a few kilometers on a side for a handful of newtons of thrust - again, impractical. 

At the core of it, friends don't let friends use reactionless drives.  You gotta leave something behind.  Laser lightsail / laser launch is the closest you're going to get, and the only one that doesn't strain the bounds of modern physics.

[Chakat Firepaw]

On 25/10/2016 at 11:16 AM, Aegolius13 said:

Right, but since you can replenish electricity from solar panels or whatnot, I think they would still meet OP's inquiry re an engine that does not need fuel other than electricity. 

Solar panels aren't really an option for running a photon drive, the power requirements are too extreme, (300 MW/N).  You would need 200,000 m² of 100% efficient solar panels per Newton at 1AU from the sun.

If you are thinking of using beamed power, you are probably better off using a laser sail.

[Sharpy]

On 25.10.2016 at 9:15 PM, Nicias said:

Solar sails can be used to travel anywhere in system.

Anywhere where void is good enough.

Below 1000km Earth orbit solar sails act as parachutes.

[GoSlash27]

What LaytheDweller said. Your best bet in KSP would be a kraken drive. *IF* you can figure out a way to make one in 1.2, you can go pretty much anywhere without expending any fuel.
The devs have worked hard to eliminate phantom forces, so making one would be no easy task.

Best,
-Slashy

[septemberWaves]

Your only realistic option is a solar sail, but it doesn't exist in stock KSP.