Eve SSTO?

[Starhawk]

Oh yeah you wont be landing, just getting into orbit, I guess I misunderstood the question, that would seem like a tall order with SSTO

I think the part you're missing is 'Eve SSTO'. An SSTO that can land on, and then achieve orbit from, the surface of Eve.

[EtherDragon]

As says over the last three pages, no - not in stock.

But, theoretically, if the ship had an engine that was similar to a jet engine, but instead of using oxidizer from the atmosphere, it used oxidizer from a fuel tank... then yes, SSTO is very possible from Eve.

That's because jet engines generate a lot of thrust by propelling air through at a very high speed. Eve has lots of air, just no oxygen. That's the problem with normal jet engines on Eve, they need oxygen to turn the jet turbines inside. On Kerbin, (and on Laythe) the turbine takes oxygen from the atmosphere. Conceivably, a jet engine could be made that takes air from a fuel tank instead, but otherwise functions like an air-breathing jet engine.

Since Eve has an atmosphere the thrust would be generated the same way as on Kerbin, by forcing air through the turbine and accelerating it out the back.

[Basilo1146]

I have in the past posited a completely reusable Eve return vehicle, but a single stage one is not possible. If I ever get the motivation, I may actually try to make my idea. Simply put, instead of dropping stages as you go up, you use a single stage vehicle that puts you on a suborbital, exoatmospheric trajectory, and then use a vehicle with huge amounts of dV to rendezvous and dock with it on the suborbital trajectory, and then use that vehicles fuel and engines to finish the orbital insertion.

[EdFred]

I have in the past posited a completely reusable Eve return vehicle, but a single stage one is not possible. If I ever get the motivation, I may actually try to make my idea. Simply put, instead of dropping stages as you go up, you use a single stage vehicle that puts you on a suborbital, exoatmospheric trajectory, and then use a vehicle with huge amounts of dV to rendezvous and dock with it on the suborbital trajectory, and then use that vehicles fuel and engines to finish the orbital insertion.

Except docking will be um...a challenge considering the relative velocities of the two craft.

[tseitsei]

I have in the past posited a completely reusable Eve return vehicle, but a single stage one is not possible. If I ever get the motivation, I may actually try to make my idea. Simply put, instead of dropping stages as you go up, you use a single stage vehicle that puts you on a suborbital, exoatmospheric trajectory, and then use a vehicle with huge amounts of dV to rendezvous and dock with it on the suborbital trajectory, and then use that vehicles fuel and engines to finish the orbital insertion.

Is this really possible? Video would be awesome. This whole thing would be best thing I have ever seen done in KSP

[Technical Ben]

Except docking will be um...a challenge considering the relative velocities of the two craft.

But possible... (though my sub orbital docking was to catch and redirect a rover to the right landing zone).

It would be awesome too. I really should try setting up some "cycler" of some sort...

Edited March 20, 2015 by Technical Ben

[Deutherius]

As says over the last three pages, no - not in stock.

But, theoretically, if the ship had an engine that was similar to a jet engine, but instead of using oxidizer from the atmosphere, it used oxidizer from a fuel tank... then yes, SSTO is very possible from Eve.

That's because jet engines generate a lot of thrust by propelling air through at a very high speed. Eve has lots of air, just no oxygen. That's the problem with normal jet engines on Eve, they need oxygen to turn the jet turbines inside. On Kerbin, (and on Laythe) the turbine takes oxygen from the atmosphere. Conceivably, a jet engine could be made that takes air from a fuel tank instead, but otherwise functions like an air-breathing jet engine.

Since Eve has an atmosphere the thrust would be generated the same way as on Kerbin, by forcing air through the turbine and accelerating it out the back.

I don't think so. The thing is, jets (and specifically high bypass turbofans, which I believe you were referencing) usually have pretty low fuel/air ratios (they burn a lot of air per unit fuel). That makes them efficient on Kerbin/Earth, because they get the majority of the fuel essentially for free. On Eve, you would have to supply the combustible air yourself, and you'd need a lot of it, which would be bothersome. If you use pure oxidizer, which would burn much better than air (giving higher fuel/oxidizer ratio), you'd need much less of it per unit fuel - but hey, that sounds exactly like what a normal LFO rocket does.

So it basically boils down to exhaust utilization: nozzles vs. fans.

And if my physics knowledge isn't wrong, nozzles win. They utilize their energy straightforwardly (and pretty efficiently if we use aerospikes... also independent on air pressure). The turbofan engines would have to use most of the chemical energy to turn the fans, who would then push the air. I haven't done any math, but intuitively there is an extra step that would be wasting energy. And you cannot gain more energy from a system than you put in, so unless the Evian air is giving you energy like Kerbin's air does, the design is going to be less efficient. Also, because the thrust of a turbofan engine is a function of intake air mass flow, as the air pressure decreases, so does the thrust.

But I could be wrong

Edited March 20, 2015 by Deutherius
typo

[Basilo1146]

Except docking will be um...a challenge considering the relative velocities of the two craft.

Hence the ridiculous amounts of dV. You have to slow the orbital vehicle to the same relative speed as the launch vehicle, dock, and then perform an insertion burn. It should be doable, but I'm too lazy to try.

[Empiro]

I don't think so. The thing is, jets (and specifically high bypass turbofans, which I believe you were referencing) usually have pretty low fuel/air ratios (they burn a lot of air per unit fuel). That makes them efficient on Kerbin/Earth, because they get the majority of the fuel essentially for free. On Eve, you would have to supply the combustible air yourself, and you'd need a lot of it, which would be bothersome. If you use pure oxidizer, which would burn much better than air (giving higher fuel/oxidizer ratio), you'd need much less of it per unit fuel - but hey, that sounds exactly like what a normal LFO rocket does.

So it basically boils down to exhaust utilization: nozzles vs. fans.

And if my physics knowledge isn't wrong, nozzles win. They utilize their energy straightforwardly (and pretty efficiently if we use aerospikes... also independent on air pressure). The turbofan engines would have to use most of the chemical energy to turn the fans, who would then push the air. I haven't done any math, but intuitively there is an extra step that would be wasting energy. And you cannot gain more energy from a system than you put in, so unless the Evian air is giving you energy like Kerbin's air does, the design is going to be less efficient. Also, because the thrust of a turbofan engine is a function of intake air mass flow, as the air pressure decreases, so does the thrust.

But I could be wrong

I think fans can still win out in certain situations. With rockets, most of the chemical energy is dumped into the exhaust (especially when you're moving slowly i.e. the Oberth effect). If you're in an atmosphere, you can draw in more reaction mass. Because kinetic energy changes with the square of the velocity, if you push out twice as much mass at half the speed, your change in momentum is the same, but it only takes half as much energy. Normally in rockets you're limited in reaction mass, which is why you still want to push out the exhaust as quickly as possible, even if it costs way more energy to do so.

As for how this might influence an Eve SSTO -- I think that since most of the time during your ascent, you're moving quite slowly (~100-200 m/s), with rocket engines, you're wasting all the energy of your fuel accelerating the exhaust to 3+km/s. Using propellers / fans could definitely make sense.

Edited March 20, 2015 by Empiro

[Deutherius]

I think fans can still win out in certain situations. With rockets, most of the chemical energy is dumped into the exhaust (especially when you're moving slowly i.e. the Oberth effect). If you're in an atmosphere, you can draw in more reaction mass. Because kinetic energy changes with the square of the velocity, if you push out twice as much mass at half the speed, your change in momentum is the same, but it only takes half as much energy. Normally in rockets you're limited in reaction mass, which is why you still want to push out the exhaust as quickly as possible, even if it costs way more energy to do so.

As for how this might influence an Eve SSTO -- I think that since most of the time during your ascent, you're moving quite slowly (~100-200 m/s), with rocket engines, you're wasting all the energy of your fuel accelerating the exhaust to 3+km/s. Using propellers / fans could definitely make sense.

You definitely have a point there. I'll need to think about this concept some more.

Also, since we are in the realm of theory and not existing game parts, we might as well throw away fuel dependencies and go back to an electrically powered engine (duct fan/propeller). Electricity is cheap and looking at reaction wheels, kerbals seem to have no problems creating unrealistically high powered rotating things

[FlyingPete]

When/if nuclear engines have their own distinct fuel source, nuclear thermal jets could be a possibility. The whole point of combustion in a jet engine is to increase the energy of the reaction mass by heating it. All you need is a source of heat. One real-world example I can think of is the P-51 Mustang, which derived a slight ramjet effect from its radiator duct to offset cooling drag.

It would be an interesting thermodynamics problem to figure out the efficiency of a fuel+oxidiser jet engine running in an inert atmosphere, and how this compares to a pure rocket. High-bypass turbofans (which essentially use the jet core as a power source) could win I think.

I'd still like to see a reversed-cycle jet engine that draws in a propellium-rich atmosphere and runs on oxidiser from an onboard tank. This could be viable for Eve or Jool.

[Richmountain112]

Well, you could, but it isn't really practical. Because Eve's atmosphere is extremely thick, you'd have trouble getting out of the lower atmosphere, let alone reaching orbit. Now if you're doing a One-Way SSTO from Kerbin, that would make a fine base.

[Scarecrow71]

@Richmountain112

Please pay attention to how old a thread is before you reply.  This thread was nearly 8 years old when you necro'ed it.