Jet engines on rockets; viable?

[HoY]

No I mean efficient. Efficient as in mass the RTG adds compared to the amount of power it puts out.

Also efficient referring to the amount if extra fuel you save by using lighter power supply's.

on a large craft it's not such a big deal but a satellite that is tight on fuel to start with you can gain or lose 100m/s worth of deltaV just by switching from an RTG to a single panel setup. Even more potentially if its small enough.

Also, I think the RTG might work a little better now that the Kethane scanners work differently but I haven't tested that yet.

And, like I said, there is no night when orbiting the planet along the terminator. Only dark during an eclipse, and its not hard to get an orbit here at all!

[Climberfx]

Well, lets see. 90% of my orbits are 90 degrees. On the direction of rotation. The amount of fuel i would expend to put that orbit you said, for me have no reason doing that. Is not efficient at all.

5 or the most 10 degree up or down the round orbit is what i need to scan, anything else, is waste of energy, plus time, because the scan will be tremendous more time consuming. So, you not convince me. RTS is the best choice. Even in a probe. And when i mean efficiency, i mean, for the purpose. What good would be for me to not have the scanner work in night? Because i will not expend a lot of energy to put it in a polar orbit, because as i said, i will not go there. Not until i deplete the resources on normal orbit.

I don't know who Kethane works before, i'm using it in the couple last versions...

P.s.: I know you can start all orbits in polar, easily in Kerbin, that you can take off that way. But normally to achieve that, you use a lot off fuel. This is not efficient.

I choose put less fuel and go for normal orbit with my RTG's. And other thing is, even with the gaps you talk about i never see it happens in scan here, with 2 rtgs in timewarp. Maybe because i do not use old versions you talk about. The new ones do not loose that, and they too not scan again a hex that already been scanner, so, in a close to 0º orbit, or some thing less then 15º, the fill area will occur in a fraction of the time that a polar one do.

Use the new Kethane, the map got gorgeous...

[HoY]

Ok your only scanning around the equator that's a completely different thing all together. Most people scan the entire planet.

As for fuel used to get into a near polar orbit, it costs an extra 30-50m/s to adjust your target inclination when you first arrive in the SOI of the planet or moon, then after that you may need to spend a couple hundred more once your circular if you didn't line yourself up to be in full sunlight.

Enough discussing orbits tho, we both use different styles and you use multi purpose crafts for scanning, not dedicated scanning satellites. That's much different.

Yes, the scanners have been changed to not waste power on already scanned hexes, and up till 2 weeks ago the map was Much much different.

[Climberfx]

I do have dedicated probes for only scan.

"As for fuel used to get into a near polar orbit, it costs an extra 30-50m/s to adjust your target inclination when you first arrive in the SOI of the planet or moon, then after that you may need to spend a couple hundred more once your circular if you didn't line yourself up to be in full sunlight."

Man my game may be a lot different then yours, because for me, changing phase of orbit, got a lot more d/v, A LOT!

And if polar orbit was the way, i think all the planets and moons and bodies rotations would me there too. Exist a reason why they are all almost in the same plane. All come from parts from the master body spin direction. Kerbol. And is like that in nature real life. You see it in Solar system. All the space station, and all things are in that plane.

But if you are making maps from the earth for other purposes, yes, i do agree with polar. But man, i have missions in all bodies (95 missions, because i'm ending the old ones) and even with all that, i do not need to explore more resources in polar yet.

And for the most people scan polar, i'm not sure about that.

The Tron Legacy have a good examples how Kethane could do the maps, but for know, it is grate to have it in map view over map.

[HoY]

Well, if you want to do a full scan of Any body you need to be in a near polar orbit. ISA mapsat and Kethane, and any other scanning satellite mods require this because unless you are in an orbit like that you literally will

Not pass over most of the surface.

You know inclination changes are extremely cheap from farther away right? You can even change from a pro-grade to retrograde orbit for just a meter per second or less if you do it from far enough away. All it takes is a little planning tho planning from that far away isn't as easy it is definitely worth the effort if you want anything other than an equatorial prograde orbit.

[numerobis]

The basic jet is more fuel (and airflow) efficient below 400 m/s and 3 km or so, I'd have to run the numbers again to find the exact boundary between turbojet and jet efficiency.

What do you mean about flaming out because you go too fast? That's not how it works: more speed means more airflow.

If you mean you're climbing too fast and the jets can't spin down fast enough, the solution is just to level out at a lower altitude so you climb slower when you've exceeded your ceiling. I typically use the MechJeb launch computer, turn off compensation, and set the top of the gravity turn at 30 km for 3 intakes per jet. I'd bump it to maybe 35km for 6 intakes per jet. With that kind of climb slope, I fly at 1% safety margin without issue.

I have on occasion noticed a bug at high altitude, above 36km, where it seems to use orbit speed instead of surface speed; click the navball back to "surface" to fix it. I don't understand the bug: it's not consistent, and I'm explicitly asking for the surface speed, not orbit speed.

MechJeb can also manage your intakes, closing some if you have more airflow than you need.

If you feel like working out how to calculate how fast jets spin up and down, we could add that to MechJeb, and you could then run with a much lesser safety margin.

[Climberfx]

Well, if you want to do a full scan of Any body you need to be in a near polar orbit. ISA mapsat and Kethane, and any other scanning satellite mods require this because unless you are in an orbit like that you literally will

Not pass over most of the surface.

You know inclination changes are extremely cheap from farther away right? You can even change from a pro-grade to retrograde orbit for just a meter per second or less if you do it from far enough away. All it takes is a little planning tho planning from that far away isn't as easy it is definitely worth the effort if you want anything other than an equatorial prograde orbit.

I know that, i already did it some times to check, but is not so cheap as people think. You expend a lot to get to that orbit, for just turn the course...

So in practice, is break even.

And yes, to do a full body, polar needed. For now, i still doing only 7 degrees orbit. Cover the part i wanna.

Edited July 7, 2013 by Climberfx

[John FX]

Climber an RTG won't power a small Kethane scanner properly. Both because the scanner uses more power than it puts out, And because the RTG doesn't work properly at time warp.

John, you can ditch ALL of those batteries and use ONE z100 radially mounted battery and one RTG mounted on opposite sides from each other, and then 2 1x6 extending solar panels.

This will save you SOO much mass you'll be able to drop a huge pile of fuel.

The secret to running your scanner on the dark side of a planet or moon is this

you don't!!

Simply orbit the body near or on the day/night terminator. Now you have solar power full time. The RTG is just onboard in case you get eclipsed or have your panels closed when your batterie dies.

You also have a command pod on the nose of this thing, would be more efficient as unmanned, and more humane lol.

Spoilers don`t seem to work anymore

The probe has to be manned, otherwise it wouldn`t be a manned probe

I really was trying to avoid RTGs as they are a bit ugly although I will go for them to drop weight and parts. I know about orbiting on the terminator but wanted to be able to orbit on the equator and still get a full kethane map. When I did I dropped some weight but not enough to drop a whole tank so I`ll have extra Dv.

This is the new sleeker, lighter version with less parts and all the same functionality. 24T in orbit and 30 parts. 38.38T and 141 parts on the pad (Includes 2 supports).

EDIT : it turned out to be harder to orbit this version so I removed two turbojets and that seems to have helped.

Edited July 7, 2013 by John FX

[Skorpychan]

Generally, with <1 intake per jet (8 intakes, 10 jets), it flamed out suddenly and hard, because the air ran out too quickly. Making it slower and ditching eight of the engines when their air thins out seems to work better, with an ratio of 4:1.

Still semi-tempted to tri-couple the intakes, though.

Also, launching a bit earlier so it doesn't just shoot up like a rocket.

A heavier, slower ascent means no flameouts happen. Evidently, the increased airflow was putting the engines out, as turbojets are prone to. I still want ramjets.

[HoY]

Climber, I'm not sure what you consider a lot of dV, but I don't consider a couple meters per second that much

You must be referring to altering your orbital inclination after you've already circularized, in which case I agree with you on that. However, to use the word again, that is not a very efficient way to set an inclination at all. The best time to set an inclination in the game right now is as far away as possible. Using mechjeb that can be up to two soi changes away from your current location, at a cost of a mere meter per second of deltaV, however even if you wait until you enter it's SOI it is still magnitudes more efficient to change your inclination from here than while your actually in orbit.

John, yes that is So much more streamlined! The one and only thing I can think of taking off by looking at the picture is this; (well its more than one thing) remove jets (all of them)

Remove the mk2 adapter fuel can you have installed in the center and mount the engine back in the center directly to the stack decoupler.

Next mount 2 engines under each of the 1.25m fuel tanks but with the cubic struts using the engine clustering technique. Bringing your total engine count to 5 instead of 7.

Run a fuel line from each of the two 1.25m jet fuel tanks to the center engine.

You'll need to just relocate those pylons with the intakes to attach to the outer jet tanks, not a big deal.

Skorpychan: your description of the problem leads me to believe your doing a regular rocket only type ascent. With jet engines that's far from ideal.

[Skorpychan]

I'm trying to tip over to 45 degrees early, but the problem is that there's no lift to assist the thing in continuing to ascend. If I go over too far, my designs lose height.

[HoY]

Yeah you are treating it more like a rocket than a hybrid. Need some screenshots of your creation plus if you have any read-out mods that show your mass and twr like mechjeb or kerbal engineer a screenshot of your staging window would help. With that info I can give you a fairly detailed ascent path you will need to follow if you want to get the most out of the hybrid design.

But first things first, you need a minimum of 4 intakes per engine. More is better but with less than 4 you may as well just use rockets instead of jets.

[Skorpychan]

It seems that the main problem is that I have no idea what the hell I'm doing... I've only been playing this game for a couple of weeks.

[HoY]

Haha, we'll you picked a somewhat tricky aspect of the game to learn right off the bat. It's not impossible to get it right this early but personally I would recommend sticking with conventional rocket designs for the immediate time being, and then once your comfortable with those start looking at making it into a hybrid or even a single stage to orbit type craft.

A lot of people don't ever use jet engines just because they make the crafts more complex and all they really care about is just getting to orbit, not really concerned with how much fuel they burn to get there. The only reason to use jets is to burn less rocket fuel and save some kerbal currency in the VAB.

[Skorpychan]

I had an idea, and ran with it. It's worked fairly well so far; with more intake spam and less engines, I think I could get it working at least as good as my standard heavy lifter.

That, however, is still fairly terribly for KSP. And I still need to work on dockings.

Stil, it made for 9 pages of discussion, and gave me more ideas to work on.

[HoY]

Never be afraid to ask the questions

[Skorpychan]

Of course. That's how things get advanced, especially with games like this.

You never know, hybrid rockets may be the new asparagus!

[Climberfx]

For me the problem is to find a good soul that answer me in my doubts.

[HoY]

Lol, what are you having trouble with climber?

[Climberfx]

Lol, what are you having trouble with climber?

No one here and at this moment.

[MBobrik]

Just managed to build my first spaceplane... 2 turbojets and 18 (!) ram intakes and 1 LV-T45. Jets took me all the way to 1600 m/s (surface) then I ignited LV-T45 w/o stopping the jets and suddenly I was at 250 KM apoapsis, and all I needed to do was just to circularize. It was over-engineered a lot, but I think I got the basics. Just intake-spam enough and the rest will take care of itself. With sufficient ram intake/jet ratio you will have air supply at say 0.09 even when you are leaving the atmosphere altogether, so you can run the jets at near half-throttle alongside with the rocket all he way until you got out of the atmosphere and then add the last 300m/s with the rocket only to circularize.

Edited July 8, 2013 by MBobrik

[HoY]

Spaceplanes are slightly easier than hybrid rockets since you can have much lower thrust, tho getting one to orbit is still an achievement