Hybridized Ion Interplanetary Transfer

[Duxwing]

Hybridized Ion Interplanetary Transfer is escaping planetary orbit on a non-ionic motor, finishing the orbital maneuver with ion engines, slowing near the target with ion engines, and completing the maneuver with the non-ionic motor. This transfer could replace conventional all-nuclear systems on extremely light or heavy payloads, or during extremely long voyages, because the ion engines generate so much delta-V from so little fuel and engine mass that the hybrid transfer is much more efficient, solar orbit provides solar panels unblocked and reliably-oriented charging, and the non-ionic boost makes burn times tolerable. Recent advancements in ion-thruster technology have quadrupled thrust, further improving this option. If I can make KER display ion drive dV, then I will post some screenshots of possible configurations. Until then, discuss the transfer's utility and possible applications.

-Duxwing

[cantab]

You have to balance out the extra delta-V per unit mass obtained with ion engines against the delta-V lost from not taking full advantage of the Oberth effect.

And then throw in player time issue from potential long burns and part count issues from the lack of a big ion engine.

More efficient, I believe, would be to do things the other way round. Use an ion engine for a series of periapsis kicks, getting the most out of the Oberth effect and raising the apoapsis each time. When departing LKO, this means getting around 950 m/s of dV out of the ions. Then use a chemical or nuclear engine for the final ejection and transfer burn, since that needs to be completed in one pass and the ions don't have the thrust. On arrival, reverse the procedure, using the chemical or nuke engine to just barely capture then the ion to change your orbit to what you want.

I'd want an autopilot for that kind of stuff mind you.

[Geschosskopf]

My main use of ion engines is to stick them on 1 end of an I-beam, put a docking port on the other end, tape on a few lawn chairs in the middle, and use this to shuttle crew around between stations and moons. Even with MJ, even with more powerful ion engines, I don't have the patience to sit through their burns if the ship has any real mass or is going any great distance.

[Duxwing]

You have to balance out the extra delta-V per unit mass obtained with ion engines against the delta-V lost from not taking full advantage of the Oberth effect.

Adding more ion dV is trivial: this transfer maximizes payload fraction.

And then throw in player time issue from potential long burns and part count issues from the lack of a big ion engine.

Four times time acceleration plus good VAB tweaking should minimize both.

More efficient, I believe, would be to do things the other way round. Use an ion engine for a series of periapsis kicks, getting the most out of the Oberth effect and raising the apoapsis each time. When departing LKO, this means getting around 950 m/s of dV out of the ions. Then use a chemical or nuclear engine for the final ejection and transfer burn, since that needs to be completed in one pass and the ions don't have the thrust. On arrival, reverse the procedure, using the chemical or nuke engine to just barely capture then the ion to change your orbit to what you want.

I'd want an autopilot for that kind of stuff mind you.

Using ions first requires even more time because the periapsis kicks spread across many periods of waiting and may occur in darkness, requiring back-up batteries or wasted orbits; whereas using ions second performs all burns in "one pass". I like your idea of using the alternative engine to capture. Mind if I add it to the OP as Cantabian Hybridized Ion Interplanetary Transfer?

-Duxwing

[Duxwing]

My main use of ion engines is to stick them on 1 end of an I-beam, put a docking port on the other end, tape on a few lawn chairs in the middle, and use this to shuttle crew around between stations and moons. Even with MJ, even with more powerful ion engines, I don't have the patience to sit through their burns if the ship has any real mass or is going any great distance.

The burns should be much shorter because the ship will burn ions only after leaving the planetary SOI and will carry much less LFO. For example consider a twenty-ton craft going from Kerbin to Jool powered by four ion engines. The rated necessary dV is 2,000m/s, and I will add 500m/s for missed Oberth Effect. First subtract 1,000m/s dV for both alternative burns, leaving 1,500m/s. Divide by 8 kilonewtons and 20 tons, yielding 15,000s or 1.04 hours. Accelerate time by four to get .26 hours or ~15 minutes of real burn time.

Some quick Kerbal Engineer testing with Stretchy Parts yielded a payload of about 13 tons on that 20 ton craft, yielding an enormous mass fraction of 0.65, which enables you to build smaller and therefore faster-to-make lifters, ultimately saving time.

-Duxwing

Edited April 13, 2014 by Duxwing

[vger]

I've had a plan to do just this kind of thing for a while.

The only thing I REALLY wish we had access to though, is radial ion engines.

[Aghanim]

You have to balance out the extra delta-V per unit mass obtained with ion engines against the delta-V lost from not taking full advantage of the Oberth effect.

And then throw in player time issue from potential long burns and part count issues from the lack of a big ion engine.

More efficient, I believe, would be to do things the other way round. Use an ion engine for a series of periapsis kicks, getting the most out of the Oberth effect and raising the apoapsis each time. When departing LKO, this means getting around 950 m/s of dV out of the ions. Then use a chemical or nuclear engine for the final ejection and transfer burn, since that needs to be completed in one pass and the ions don't have the thrust. On arrival, reverse the procedure, using the chemical or nuke engine to just barely capture then the ion to change your orbit to what you want.

I'd want an autopilot for that kind of stuff mind you.

Unfortunately MJ doesn't have that stuff yet... you could try to program that in kOS though

[magnemoe]

The burns should be much shorter because the ship will burn ions only after leaving the planetary SOI and will carry much less LFO. For example consider a twenty-ton craft going from Kerbin to Jool powered by four ion engines. The rated necessary dV is 2,000m/s, and I will add 500m/s for missed Oberth Effect. First subtract 1,000m/s dV for both alternative burns, leaving 1,500m/s. Divide by 8 kilonewtons and 20 tons, yielding 15,000s or 1.04 hours. Accelerate time by four to get .26 hours or ~15 minutes of real burn time.

Some quick Kerbal Engineer testing with Stretchy Parts yielded a payload of about 13 tons on that 20 ton craft, yielding an enormous mass fraction of 0.65, which enables you to build smaller and therefore faster-to-make lifters, ultimately saving time.

-Duxwing

This might mix well with orbital tugs, basically an overpowered probe pushing or dragging your ship to the edge of SOI before returning to LKO to be refueled and docked with the next ship.

Aerobrake then circulate and return on ion and perhaps some 48-7S to use the remaining fuel.

[Duxwing]

I've had a plan to do just this kind of thing for a while.

The only thing I REALLY wish we had access to though, is radial ion engines.

You can create radial ion mounts with Cubic Octagonal struts.

-Duxwing

[Vanamonde]

This proposed method of how to make a transfer moved to the how-to sub-forum.

[Duxwing]

This proposed method of how to make a transfer moved to the how-to sub-forum.

Thanks!

-Duxwing