Nuclear engine interplanetary transfer sloooooowwwwwwwww

[Claytsuk]

Is it usual to have to do 3 or 4 orbits around kerbin before actually building up enough momentum to escape kerbin on a course for duna? Got 2 nuclear engines burning like a mofo for 20+ minutes....

Is there a better way?

[Shiftyeyesshady]

In space, you can be fast or you can be efficient.

Efficient is generally better in every way except patience. Two nuclear engines is one of the more efficient builds there is. If you want to go a bit faster, replace your two nukes with a poodle. I don't have the math in front of me, but one poodle is supposed to be more efficient than 3 nukes.

[Scialytic]

That depends on your definition of "better." Adding more LV-Ns, (or replacing them with higher TWR engines) will improve your acceleration at the cost of needing more fuel for the same delta-v. Duna isn't hard to get to; you don't need to maximize efficiency if you don't want to.

I don't have the math in front of me, but one poodle is supposed to be more efficient than 3 nukes.

For munar missions perhaps, but not for interplanetary. Credit to MarcRan17 for this graph:

Edited May 23, 2013 by Scialytic

[Uberick]

I usually start prepping for a transfer by burning to almost escape velocity whn I have nukes, then make a final push in a series of burns. If you dont like waiting try more nukes on decouplers, so you can do one burn to escape, and then dump the extra engines when youre done so your return stage is lighter. Usually one nuke is plenty to push a reasonably sized return vessel.

[Claytsuk]

Thanks for the tips guys!

When is it okay to start a burn before the marker point' some times if a burn is going to be 20 mins is it okay to start 10 mins early and burn 10 mins longer and still be accurate in the end?

[EndlessWaves]

The poodle is appalling, it should be avoided at all costs (well, at least until cost matters). If you want more oomph then multiple LV-Ns is often the best way. The next best option is something like an LV-T30 or aerospike but with less than half the fuel consumption in vacuum you can often add a lot of LV-Ns before you reach the same additional weight as doubling your fuel.

[Specialist290]

Thanks for the tips guys!

When is it okay to start a burn before the marker point' some times if a burn is going to be 20 mins is it okay to start 10 mins early and burn 10 mins longer and still be accurate in the end?

That's pretty much right on the money. For myself, if my burn is anywhere longer than 10 seconds, I'll split the total burn time in half and start that much before the time to the node. (Any less than that, and I'm not hugely concerned about the precision losses in most cases.)

A trick that might help reduce the wait on long burns from "excruciating" to merely "almost intolerable" is to turn on Physical Timewarp with Alt + [.]. Of course, if your ship has any wobble, physical timewarp will magnify it that much more, since you're basically telling your computer to skip steps in the physics calculations.

[karolus10]

It is a good idea to make transfer burn (or even few) to higher orbit earlier and then made final burn, this way you splitting the burn into few shorter ones.

After you get on escaping trajectory (or close), you don't had to worry about low thrust .

Having ASAS or auto-pilot on larger interplanetary stages is priceless if you want go AFK during long burn (but physical time warp is not recommended without supervising).

[georgTF]

I would argue against the Poodle being appaling. Only the mainsail is bad for interplanetary travel, the Poodle is actually quite good. The nukes are the quite sucky really. You do need many to reduce maneuvre time but even with 5 of them an interplanetary injection will take forever. And 5 nukes is getting very heavy. Their weight and low thrust offset the low fuel use. Maneuvres that stretch over 20 minutes are also to require corrections so sometimes it's better to have a punchier engine. They are not my ideal choice for heavy stuff though sattelites and probes are a little better. Also, if you wish to send fuel tanks across IP distances, then nukes are almost mandatory because you want most of the fuel to actually get to destination, rather than be used for travel.

[jwenting]

another disadvantage of nukes is their size. They're bloody long, which can make a rocket unstable in flight.

[Psycho0124]

I love NERVAs! My standard interplanetary stage consists of one Jumbo-64 with a single NERVA on the back. Set up a burn, light the engine and go grab a coffee.

My general rule of thumb is to use NERVAs any time my ship isn't within an atmosphere or fighting a strong gravity well. That 800 isp is just too sweet a deal to pass up for me, especially since I fly seat-of-the-pains and need to make corrections here and there. Once you're in orbit, you have all the time in the world to make your burns.

[Klajan]

NERVAs are so good for Orbital operations. If you can tolerate hours of burningtime, Ionengines are better but... I dont´want to burn for 3 Hours till I finaly get my transfer. This is the reason, why my interplanetary Mothership uses 16 NERVAs to propell around 400t of mass. Still takes forever to do anything.

[magnemoe]

In space, you can be fast or you can be efficient.

Efficient is generally better in every way except patience. Two nuclear engines is one of the more efficient builds there is. If you want to go a bit faster, replace your two nukes with a poodle. I don't have the math in front of me, but one poodle is supposed to be more efficient than 3 nukes.

This depend on how much dV you need and the weight of the craft. For small probes the small orange radial engines are very efficient as they are light.

However if you want 3000 m/s dV on something heavier than an probe the LV-N is your answerer.

If you want more trust, use multiple engines or use some moded nuclear engines who are heavier but give more trust.