Maneuver nodes don't seem to be very useful for extremely long burn times (using a nuclear engine)

[Kerba Fett]

I don't use nukes that much, but I have been experimenting with mixing them with higher output engines. 4 radial mount nukes and a skipper.

With all of them in use you get good TWR. As you turn down the thrust limiter on the skipper the TWR goes down while the dV remaining goes up. This lets you choose fuel efficiency or power on the fly.

(you leave the nukes at full power all the time)

[EtherDragon]

Let's see if I can't find some old footage... Yea, there it is!

So I had a great interplanetary design that I really liked. It packed a 4x engine cluster on the back and lots of extra asparagus staged fuel cells that would decouple as the mission went on. But, the main thing was the engine cluster was 2x LV-Ns and 2x LV-T30s. I would only switch on the LV-T30s when I had a big ejection burn to do, so I didn't have to orbit a bunch of times. This thing clocked in with plenty of Delta-V to reach Jool, enter and leave orbit of several of Jool's moons (launching some probes at each one...) and return to Kerbin with all of the Science! discoveries - even though I threw away two perfectly good (and full) fuel tanks!

I fired up the LV-T30s only twice, IIRC, when leaving Kerbin, and again when leaving Jool. The rest was done on longer burns with the pair of LV-Ns. Turns out I would have had more if I didn't accidentally throw away a full set of tanks.

@Kerba Fett, I really like the idea of using the thrust limiter on the big engine to tune for gas mileage.

[Xannari Ferrows]

What vessel are you using, exactly? Apparently it's really huge. Why not try sending everything to Duna in parts? [unless they absolutely have to be together]

You could also try optimizing your mass. Ask yourself the question: "What's necessary, and what's not really required?" Is everything as small and light as it can be?

If you still have extremely long burn times, you will have to make the burn in multiple passes, or in a much higher orbit. Multiple passes in low orbit are more efficient, but are a low more time consuming.

[Badsector]

I always calculate 2/3 of the burn time to manouver, example if i need 3 minutest of burn i start engines at 2 minutes to manuver, if i need 12 minutes of burn i start acelerating at 8 minutes to manouver, if you need 60 minutes of burn start at 40 minutes to manouver

[LethalDose]

Those of you who use nuclear engines - how do you plot your course to other planets when you must have a very long engine burn time?

I plot my course to other planets with nukes the same as everything else. I just don't build rockets that require 60 minute burns to Duna. Seriously, that's just absurd.

A few options are better engineering, periapsis kicks, and Minmus-Kerbin assists.

IMO the best option is just building a rocket with better TWR. Any gains your getting from the nukes is offset by the horrid accuracy caused by the low TWR. Reduce the size of your payload (my recommendation) or use bigger engines.

If you insist on using a rocket with such abysmal TWR, you can try using a series of periapsis kicks. Thrust as long as you can near your PE to raise your AP near where you want to exit. When you get too far from your PE, stop burning, and then go back around until you're back at PE. I think Manley did this for his Eve Explorer, but I couldn't find it.

The final option is to get into orbit around Minmus, then exit Minmus retrograde with a very low Kerbin PE where your ejection burn should be, and then your burn can be as low as 100 m/s or less to eject to Duna (I've done this). This can be tricky, to time, though.

[Sirrobert]

60 Minutes for a DUNA trajectory? What kind of a monster are you trying to push with that poor little engine?

[OhioBob]

60 Minutes for a DUNA trajectory? What kind of a monster are you trying to push with that poor little engine?

If we assume a normal Duna transfer having a ÃŽâ€V of about 1100 m/s, then he's trying to push about 210 tonnes for every one LV-N engine (a TWR of 0.03).

[Sirrobert]

If we assume a normal Duna transfer having a ÃŽâ€V of about 1100 m/s, then he's trying to push about 210 tonnes for every one LV-N engine (a TWR of 0.03).

That poor engine.

I just realized: I'm not familiar enough with interplanetery transfers to have the numbers, but would you even be in Duna SOI long enough to circulize with that kinda TWR?

Even if you are, at the very least you'll lose extreme amounts of efficiency from having to burn stupidly early in order to manage a capture

[maltesh]

Yeah, it's plenty of time on the typical Dunar arrival. As I recall, it's typically more than a day from the edge of the SOI to a low Dunar Periapse. Duna's not Moho, after all.

[Kryxal]

Besides, you can always do a minimal aerocapture and a second pass to get the apoapsis down.

[Superfluous J]

What kind of a monster are you, trying to push with that poor little engine?

There, I fixed that for you.

[subtle?]

[MoridinUK]

I've been ahving a problem with my tug, it is just to ferry fuel about the Kerbin system, so I simply dumped on one LV-N. It went wrong, I had a 7 min burn time to get captured by Mun and ended up in totally the wrong orbit. First attempt the engine blew up (overheated) so I have it thrust limited it just under 70% where it doesn't overheat. I think that any subsequent maneuver nodes should work themselves out properly on that thrust? (My first had assumed I could thrust at 100% it did seem to have figured out I'd be dropping my skipper part way through though. Or this thing needs a redesign too! How do you guys get Duna down to 1100 Dv? My window says 1600ish at best?

[Xannari Ferrows]

I've been ahving a problem with my tug, it is just to ferry fuel about the Kerbin system, so I simply dumped on one LV-N. It went wrong, I had a 7 min burn time to get captured by Mun and ended up in totally the wrong orbit.

How much fuel are you trying to move? If several hundred tons, it wouldn't hurt to fit more engines on.

First attempt the engine blew up (overheated) so I have it thrust limited it just under 70% where it doesn't overheat. I think that any subsequent maneuver nodes should work themselves out properly on that thrust?

The maneuver node system displays your estimated burn time based on the level of thrust you used last. Firing it at 70%, even if just for a second, will overwrite the previous maneuver node estimations.

My first had assumed I could thrust at 100% it did seem to have figured out I'd be dropping my skipper part way through though. Or this thing needs a redesign too! How do you guys get Duna down to 1100 Dv? My window says 1600ish at best?

I've actually had a little less then 900m/s burns to Duna before. The phase angles have to be extremely precise, and you make your burn in multiple passes, at periapsis, to take advantage of Kerbins' gravity (The good ol' Oberth Effect)

[Sirrobert]

There, I fixed that for you.

[subtle?]

I guess that works to

I've been ahving a problem with my tug, it is just to ferry fuel about the Kerbin system, so I simply dumped on one LV-N. It went wrong, I had a 7 min burn time to get captured by Mun and ended up in totally the wrong orbit. First attempt the engine blew up (overheated) so I have it thrust limited it just under 70% where it doesn't overheat. I think that any subsequent maneuver nodes should work themselves out properly on that thrust? (My first had assumed I could thrust at 100% it did seem to have figured out I'd be dropping my skipper part way through though. Or this thing needs a redesign too! How do you guys get Duna down to 1100 Dv? My window says 1600ish at best?

Yes, it needs more engines

[OhioBob]

How do you guys get Duna down to 1100 Dv? My window says 1600ish at best?

1050-1100 m/s is pretty normal for a Duna transfer from a low Kerbin orbit of about 70-75 km. If you haven't used it before you might consider planning your transfers using the following:

Launch Window Planner for Kerbal Space Program

[MoridinUK]

Yeah, that is what told me it would be 1600 dv from LKO (100km)

Oh so my ickle lv-N is stuggling attached to a full robomax-64 fueltank, lol! Yeah it needs more Thrust... but it is only supposed to glide about efficently with my better designed stuff docking to refuel and refuel it.. lol..

[OhioBob]

Yeah, that is what told me it would be 1600 dv from LKO (100km)

Are you sure you're looking a ejection ÃŽâ€V and not total ÃŽâ€V? Ejection ÃŽâ€V is that needed to depart Kerbin orbit on a trajectory to Duna. Insertion ÃŽâ€V is that needed to enter orbit around Duna. Total ÃŽâ€V is the sum of ejection ÃŽâ€V and insertion ÃŽâ€V. It is the ejection ÃŽâ€V that is typically about 1050-1100 m/s. Total ÃŽâ€V is usually about 1600-1700 m/s.

If 1600 m/s is the ejection ÃŽâ€V, then it's possible you may have selected a less than ideal date for launch. The application will give you the lowest ÃŽâ€V launch that lies between the earliest and latest departure dates. I generally search for the most ideal launch window in about a 2- or 3-year range, which is long enough to search a complete synodic period. If you limit the departure dates to a smaller range, you may miss out on the most ideal launch windows.

[Laie]

First attempt the engine blew up (overheated) so I have it thrust limited it just under 70% where it doesn't overheat.

Let me guess: one orange tank, one LV-N? For some reason or other, small engines tend to overheat quickly when attacked to tall tanks. If you put a smaller part between engine and tank, like a probe core, a battery, a reaction wheel, you can run the engine at full throttle without problems.

I only listed tiny pieces, but don't let that lead you astray: it's the height/length that matters. The only parts (I'm aware of) that lead to this problem are the largest Kerbodyne and Rockomax tanks.

[Kryxal]

I'd probably use a pair of LV-Ns, attached to FT-200s which are attached radially to the orange tank and linked by fuel lines from it. That would pretty well solve overheat problems AND double the thrust besides.

[MoridinUK]

Ah yes my 1600Dv is the total not just the ejection Dv. Why would I want to just fly by? lol...

Ah the tips on the LV-N! I'd like to use that extra 30% thrust! Thanks for the info! Now Can I remove the engine put a part on in space, and connect it up again? lol... (ah dang it that would throw off my RCS wouldn't it?)

I think Tug v2.0 will be out soon.

For a quick look at Tug v1.0 check out my fledgling blog thread...

[Superfluous J]

Ah yes my 1600Dv is the total not just the ejection Dv. Why would I want to just fly by? lol...

You don't want to just fly by.

You want to use Duna's atmosphere to slow down, so you get about 500ish m/s of dV for FREE. Why would you burn into Duna orbit when you can use aerobraking?

[MoridinUK]

You don't want to just fly by.

You want to use Duna's atmosphere to slow down, so you get about 500ish m/s of dV for FREE. Why would you burn into Duna orbit when you can use aerobraking?

Because I had no idea it had an atmosphere! lol...

[Sirrobert]

Ah yes my 1600Dv is the total not just the ejection Dv. Why would I want to just fly by? lol...

Ah the tips on the LV-N! I'd like to use that extra 30% thrust! Thanks for the info! Now Can I remove the engine put a part on in space, and connect it up again? lol... (ah dang it that would throw off my RCS wouldn't it?)

I think Tug v2.0 will be out soon.

For a quick look at Tug v1.0 check out my fledgling blog thread...

You can't mount something sideways in space. Only way to reconfigure is with docking ports.

But you can put the tanks on sideways and launch as usual, with docking ports on top and bellow the orange tank (so you can make it even bigger in space).

Remember, you'll probably still need a few more engines than just 2 per orange tank

[Superfluous J]

Because I had no idea it had an atmosphere! lol...

Totally fair Though I would suggest in that case sending a few probes first on flyby and impact trajectories may be in order. Knowledge is power in this game, and can frequently save you hundreds if not thousands of m/s in dV.

[MoridinUK]

Totally fair Though I would suggest in that case sending a few probes first on flyby and impact trajectories may be in order. Knowledge is power in this game, and can frequently save you hundreds if not thousands of m/s in dV.

I haven't even tried to set up an interplanetary maneuver node yet! I was trying to find a video in your first bases series that showed me, but I've not had time to look very hard! I think I may well fling a couple of probes first.. If atmosphere is there, then chutes work, if chutes work, unmaned crazy beagle like missions are go!

Can I put a flag on the back of my probe and hope it sticks up out of the ground after impact? (Place flag on Duna contract! lol)

Will you return to bases when version 1.0 is out?