Increasing Delta-V? Stuck around 8,000

[Jimd0586]

Morning! (from west coast USA anyway!)

 

I have played KSP on and off since about 2017 and just got back into it when I dusted off my desktop. I got a Duna lander onto the planet and then back into orbit but not enough fuel home. So I am sending a rescue mission with engineer to give them more fuel and repack parachutes. Money isnt an issue, and I know I don't need 8,000 delta v but damn if I cant get more fuel efficient rockets. I dont have a picture of my current rocket but does anyone have suggestions on a good 9,000 delta v design? I assume lots of stages?

[VoidSquid]

Have you tried nuclear engines? Very fuel efficient, ISP 800m/s, in contrast to LfOx which go to max 340 m/s.

Another option would be to build a rocket with an integrated ISRU unit: you could harvest and process ore into fuel, this way you need only enough fuel for the flight to Duna, refill there, return to Kerbin.

Edited September 25, 2020 by VoidSquid

[Entropian]

Ions are also an efficient method of getting way more dV, but you have to deal with the low TWR.

[peteletroll]

Are you familiar with the rocket equation? m0/mf is limited by fullmass/emptymass ratio of tanks, which is 9 for most KSP tanks. This means that with a Poodle (350 m/s Isp) you can't get more than 350 * 9.8 * ln(9) = 7500 m/s. You can increase Isp by going nuclear, but you get much lower thrust.

Of course you can add stages, but every stage must be bigger than the next one to be useful.

Edited September 25, 2020 by peteletroll
Math error

[Grogs]

This is the photo gallery from my Dunpollo mission which landed kerbals on both Duna and Ike using an Apollo-style orbiter/lander combo. I put a lot of info on how I planned out dV on the stages that might be useful.

https://imgur.com/a/l181y1r

 

11 minutes ago, peteletroll said:

Are you familiar with the rocket equation? m0/mf is limited by fullmass/emptymass ratio of tanks, which is 9 for most KSP tanks. This means that with a Poodle (350 m/s Isp) you can't get more than 350 * 9.8 * ln(9) = 3400 m/s. You can increase Isp by going nuclear, but you get much lower thrust.

Of course you can add stages, but every stage must be bigger than the next one to be useful.

Your equation is right, but your math appears to be off. 350*9.8*LN(9) = ~7,500 m/s.

[peteletroll]

Yeah @Grogs, you're right... I'm editing my comment to hide my stupid :-)

[jimmymcgoochie]

To get more range you can try:

• Removing excess weight. Landing legs, parachutes (unless you’re going to return to Kerbin’s surface with the same craft) and anything else you can get rid of will reduce the deadweight and improve your fuel ratio which increases delta-V.
• Using a more efficient engine. The Poodle is the most efficient pure stock LF/Ox engine, but if you have Making History the Woldhound offers an ISP of 380 (but a very high mass with it) and might be better for particularly bulky craft where the excess weight is less of an issue. The NERV offers drastically better ISP than any chemical rocket (800s) but is quite heavy and has low thrust, and ion thrusters have exceptional ISP (over 4000) but are incredibly feeble and require a lot of electric charge to operate. There are a variety of mods that add different engines, from methane and hydrogen fuels to nuclear to plasma thrusters to fusion and antimatter drives, with much better thrust and efficiency than stock parts, but if you’re playing with just stock parts the Poodle and NERV are as good as you can get.
• Moar fuel! Although the extra fuel makes less and less difference due to that pesky rocket equation and will hurt your TWR too. You can get around it to some extent by using drop tanks to shed the empty tank mass as you go but in the end the fuel efficiency of the engine sets a maximum limit.

[Streetwind]

I always like to link this old post of mine in topics like this. It's a bit of a wall of text, but it does lead to a pretty nice rule of the thumb when it comes to rocket construction. Because the get the most dV possible, it helps to not only consider individual stages, but the rocket as a whole, too

[linuxgurugamer]

25 minutes ago, Streetwind said:

I always like to link this old post of mine in topics like this. It's a bit of a wall of text, but it does lead to a pretty nice rule of the thumb when it comes to rocket construction. Because the get the most dV possible, it helps to not only consider individual stages, but the rocket as a whole, too

Very nice and easy-to-understand writeup

[s_gamer101]

Every engine has a maximal possible dV, adding more fuel doesn‘t help any more once this limit is reached. 9km/s should be possible with the LV-N.

Reduce the payload mass

Edited October 13, 2020 by s_gamer101