best way to add dv?

[toric5]

the tile saya it all. what is the most size efficent way to add dv to your rocket?

[Psycho0124]

Add more fuel and use as few high-efficiency engines as you can.

I've gotten into the habit of using one of those orange "Jumbo 64" tanks with a single Atomic Rocket at the back. Burn times are long but it'll push massive payloads to wherever you want. You just gotta get it into orbit first.

[Wait- Was That Important?]

Essentially, the answer is always "MOAR FUEL".

You could shave off weight by removing non-fuel mass (command pods, hitchiker modules, solar panels, batteries, etc.) to save dV, but really the only way to drastically change it is with extra fuel mass.

[Alistone]

Alternately, if you have a very low T/W ratio sometimes adding an engine can help.

Specifically, if you can't reach 200m/s before you reach 12,000 feet then you are losing a lot of energy due to gravity losses during launch. Getting a better balance of thrust to weight will make reduce your gravity losses and can greatly improve your delta V

Usually though people start by adding another fuel tank. Unless you have other "opportunities" where you can improve your efficiency of maneuvering or launching then it becomes simple math.

1. Reduce non-fuel weight (fewer engines; fewer everything; possibly jettison empty parts);

2. Add more fuel weight;

3. Use engines with a higher ISP.

4. (Possibly practice "sling-shot" maneuvers to steal dV from other objects?)

[Psycho0124]

Ahh yeah. For atmospheric stuff where you need lots of delta-v quickly (LOTS of thrust), Mainsails bolted to big orange tanks set to jettison in an asparagus configuration (feeding fuel inward) will solve all your problems. If you don't make it to orbit; add more tanks+Mainsails!

Asparagus setups will let you jettison tanks as they empty out; minimizing dead weight. They make lots of debris so I usually avoid them unless there's a big rock underneath me to drop them onto (in an atmosphere or on a landing trajectory). You could just as easily turn off debris saving and asparagus-drop tanks all the way to wherever you're headed.

[hoojiwana]

For ascent from KSC, asparagus staging, keeping just below terminal velocity and executing a gravity turn all help to lower the dV requirement to get into orbit.

For maneuvers in space, using lower thrust, higher ISP engines will greatly increase dV.

And for everything, design your rocket to have as low a mass as it possibly can whilst still being able to achieve its mission.

[nyrath]

Well, delta-V depends upon two things, and two things only: the engine(s)'s Isp, and what percentage of the spacecraft's mass is fuel. You increase the Isp by using a better engine, and you increase the fuel percentage by adding more fuel tanks. You also can increase the fuel percentage by staging.

There is a complicating factor, though. Gravity. In space all your acceleration turns into delta-V. But during lift-off, each second while you are climbing into orbit imposes a "gravity tax" of 9.81 meters per second. This means your acceleration has the gravity tax subtracted from it before it is added to your delta-V. Obviously if your acceleration is less than 9.81, your ship is just going to vibrate on the launch pad while burning a hole in the ground.

To have lots of acceleration you need a large T/W ratio, which means a high thrust.

The dirty little secret of spacecraft propulsion is that systems with high thrust have low Isp, and vice versa. (Except for Zubrin's nuclear salt water rocket, and most rocket scientists are very skeptical that it will actually work. Remember the the Project Orion ship that uses a series of nuclear detonations? Imagine a drive that is a continuously detonating Orion. Ouch)

What does this mean? It means that the best propulsion for lifting into orbit is NOT going to be the best propulsion for traveling orbitally from planet to planet. You will want the Kerbal ion engine for orbit to orbit, and the others for lift-off. Especially the atomic rocket engine.

[ThatBum]

You could use ion engines and loads of xenon, and get insane amounts of Dv, but the ion engines have so little thrust that it takes forever to do a maneuver, and will require multiple passes to do large orbit modifications.

Try building your upper stage like this:

It has 5623m/s of Dv in there!

[UmbralRaptor]

the tile saya[sic] it all. what is the most size efficent[sic] way to add dv to your rocket?

It depends on the rocket, really. Switching to more efficient engines (increased Isp) can work, but may have other undesired effects. Adding fuel will improve the mass ratio, but there's an asymptotic limit in KSP, and the extra mass may cause other issues (long burn times, reduced TWR). If the design supports it, increasing the number of stages, or changing stages to use fuel crossfeed can also significantly increase the mass ratio. Even adding boosters may help, though the benefits are usually very minor.

[Francesco]

what mod does that fairing belong to? it's very cool!

but why 2 ASAS??

[hoojiwana]

Looks to me like the KW Rocketry fairings, and the extra ASAS is actually 2.5m SAS and a 2.5m probe body from KSPX.

[Francesco]

ah yes, by looking close, it's actually possible to read SAS unit.

[ThatBum]

Yep, KSPX is an amazing part pack. Now that the creator is part of the dev team, I'm hoping that at least some of it makes it into vanilla.

[Sovek]

what mod does that fairing belong to? it's very cool!

but why 2 ASAS??

1 is an SAS module and the other is an ASAS. the fairings are from the KW Rocketry pack, I prefer their fuel tanks as well. Most of my rockets use their parts.

And ÃŽâ€V is tricky to add sometimes. On light rockets, reducing uneeded/not as useful weight can go a long way to improving your ÃŽâ€V, more than adding fuel. Larger rockets, ect, require more fuel as taking off weight will not help very much (depending on how much weight is reduced). For instance I have 2 rockets, one is 54t, the other 400t (yeah... 400t), the 54t is the Intrepid series Rovers, and has a payload of 1t or similar. it has 7.4km/s of ÃŽâ€V between two stages, with the payload carrying an additional 567m/s ÃŽâ€V. Its designed to land on Mun, Minmus, and possibly other planets. The other is Pegasus 3, coming in at 397t, with about 5.7km/s ÃŽâ€V between two stages, it carries 32t into Munar orbit, a Command Module (with 3km/s ÃŽâ€V by itself) and another 2.3km/s ÃŽâ€V in the MEM. adding the 8t from the MEM drops the CSM ÃŽâ€V by about half, but the whole thing weighs 32t.

Other times, engines help, Intrepid rockets use multiple 1.25m engines because of their light weight, high efficiency vs the 2.5m engines I have. The 2.5m being heavier, less efficient, and will loose me quite a bit of ÃŽâ€V. If I used 1.25m parts for the Stage 2 booster in the Pegasus 3, I actually loose ÃŽâ€V because in order to get the results I need, the weight is above the 3.75m option, along with less Isp.

Other times, staging could help, This however is iffy, the most efficient I've found is two stages on long rockets, unless you have alot of radial tanks, then multiple tank drops can help.

[M5000]

You could use ion engines and loads of xenon, and get insane amounts of Dv, but the ion engines have so little thrust that it takes forever to do a maneuver, and will require multiple passes to do large orbit modifications.

Try building your upper stage like this:

/snip/

It has 5623m/s of Dv in there!

Dat beautiful payload/rocket combo.

Dat window style.

[toric5]

yah, jus according to the rocket equation, each new fuel tank gives diminishing return. AKA if you can get 1km/s the first stage after accent with 10 fuel tanks of a certian size, it will take more than 10 more fuel tanks to get another km/s.

[nyrath]

You could use ion engines and loads of xenon, and get insane amounts of Dv, but the ion engines have so little thrust that it takes forever to do a maneuver, and will require multiple passes to do large orbit modifications.

Try building your upper stage like this:

It has 5623m/s of Dv in there!

Dang! That's a sweet rocket!

[EndlessWaves]

Essentially, the answer is always "MOAR FUEL".

No, it's a higher percentage of fuel - at all times, not just launch.

Adding more units of fuel can even decrease the DeltaV depending on how you add them.

The key is making the ratio of fuel weight to other weight as high as possible, and more fuel only helps indirectly by shrinking your payload weight in comparison.

[Payload]

Stop using terrible engines for lifting is one thing. I cringe every time I see a main sail. Use aerospike clusters for lifting. Your initial TWR should start near 1.0 and end near 2.0 just before the stage is burned out. I see too many people building OP mods and such just throwing away dV because their ascent profile is garbage.

[Francesco]

Stop using terrible engines for lifting is one thing. I cringe every time I see a main sail. Use aerospike clusters for lifting. Your initial TWR should start near 1.0 and end near 2.0 just before the stage is burned out. I see too many people building OP mods and such just throwing away dV because their ascent profile is garbage.

aerospikes are not necessarily the best engines. a LV-T30's higher TWR can make up for its lower ISP: it depends on the specific rocket you're building.

and a takeoff TWR of around 1 is terrible advice.

[UmbralRaptor]

Stop using terrible engines for lifting is one thing. I cringe every time I see a main sail. Use aerospike clusters for lifting. Your initial TWR should start near 1.0 and end near 2.0 just before the stage is burned out. I see too many people building OP mods and such just throwing away dV because their ascent profile is garbage.

Last time I ran the numbers, a mainsail-based SSTO had a higher payload fraction (~8%) than an aerospike-based one (~7%), because the aerospike's fuel savings get eaten up by needing more engine. And at larger sizes, the mainsail is less hassle because of the built in TVC. Of course, the LV-T30's mix of Isp and TWR tends to beat both (eg: up to ~10% payload for SSTOs)...

[Sovek]

Stop using terrible engines for lifting is one thing. I cringe every time I see a main sail. Use aerospike clusters for lifting. Your initial TWR should start near 1.0 and end near 2.0 just before the stage is burned out. I see too many people building OP mods and such just throwing away dV because their ascent profile is garbage.

Umm... wow. Go back to rocket school please.

First off, a 1.0 T:W is not enough to get OFF the pad, at this point you're wasting fuel. 1.25 is IMO the minimum for a rocket, otherwise you're wasting ÃŽâ€V from gravity losses, 1.5-1.7 is ideal. Past that and its probably overkill.

Second, lets take my Pegasus 3 rocket, an apollo style rocket with a large 3.5m tank, and two radial mounted 2.5m fuel stacks with engines. The Mainsails on the 2.5m tanks, paired with the KW Griffon XX, give me a T:W of 1.7 (excellent for quick takeoffs and past 10km) and about 2.7km/s ÃŽâ€V in the first stage. a cluster of 5 Aerospikes offers only 70 m/s of extra ÃŽâ€V, at the cost of .3 from my T:W.... I can make that up easy just in the rapid acceleration from the mainsails during my initial gravity turn. Spikes only help if you're spending alot of time in the atmosphere, and possibly light rockets. Otherwise... I never touch em.

[toric5]

i never showed my rocket?

[Payload]

aerospikes are not necessarily the best engines. a LV-T30's higher TWR can make up for its lower ISP: it depends on the specific rocket you're building.

and a takeoff TWR of around 1 is terrible advice.

WOW people getting all upset. Been playing this game for a while now. Near 1 does not mean exactly one. And no, 2.0 off the pad burning liquid is a massive waste of dV.

As long as you are using efficient engines it's fine. Also, no one is going to be replacing a main sail with one ltv30. I don't mean exactly 1.0 TWR either. More like 1.5 is appropriate. Too much speed in lower atmo is just chewing up dV. Start slow and end fast is the key. Turn somewhere around 10k be full over by 60k. Best possible profile for type of vehicle I describe. Minimize lower atmo time and never burn south of 0deg while in atmo. Even though I noticed MJ does and that is horrible. I only use one LTv45 in my clusters to maintain gimbal control.

I have tried with every other combo out there. If you insist on burning liquid in lower atmo, then you should def be using aero spikes and not not the horribly inefficient main sail engine. Most people use a solid booster stage to get them to thin air before ever lighting up a liquid rocket. In this game, that is passable because everything is free. Adding more fuel is seldom the answer unless your rocket is already way OP already and it has engines on it that are too heavy and costing you payload.

I am constantly putting 30 tons worth of mining equipment in orbit on around 4500ms of fuel and still have fuel left to go to Duna and perform orbital ops when I get there. One orange tank and six boosters can put 20+ tons into orbit if you know what you are doing. No need for all this 4+ orange tank business.

Not that I am accusing anyone here of that. Just that I am constantly seeing people launching fuel for fuel's sake which is not the way to do it.

And yes my first reply perhaps wasn't worded clearly enough. Next time read what is there and not what you want to be there. I understand the youth are indoctrinated to ignore words such as Nearly, Virtually, Almost...Etc.

Edited May 3, 2013 by Payload

[ThatBum]

Dat beautiful payload/rocket combo.

Dang! That's a sweet rocket!

Jeez. All the compliments on my orbital stage. I built it in like 5 minutes, calm down. I do use it for pretty much any interplanetary mission and stick different payloads on it with subassembly loader. I also liked to use KSPX's 2.5m nuclear engine, but I find this configuration of the 4 smaller ones gives more thrust with the same fuel efficiency.

I'll put an image of the rest of the rocket up later when I get back home to my gaming machine.

Also yes, if you have a TWR of 1 on the launchpad, you won't get anywhere. That literally means that your thrust is just breaking even with gravity and you'll hover in place. If it's close to 1, you'll lift off very slowly and will probably not make it to orbit, as rockets perform poorly at low speeds (Oberth effect, it still takes effect at suborbital speed). For example, the Saturn V had a TWR of around 1.5 at liftoff.

There's also a fundamental problem with rockets: they need to lift their own fuel. Say you want to lift a payload of a certain weight. You need propellant to lift the payload. But, the fuel weighs something, so you then need more fuel to lift that fuel, and more still to lift that, ad infinitum. Fortunately you're saved from an infinite loop because the rocket gets lighter as you burn the fuel and discard stages, and other effects like the atmosphere getting lighter and the gravity turn making gravity affect you less. It still goes to show how even a little extra mass can have exponential consequences on how much fuel you need to bring with you, so try to be minimalistic in your rocket designs.

There's also the concept of max Q. It's like terminal velocity, but in reverse. There is a speed at a given altitude where the force of thrust from your engines pushing you up reaches equilibrium with the force of drag pushing you down. If you go faster than that, the drag force wins out and you're wasting Dv. See this table for terminal velocity numbers at various altitudes on Kerbin.

That's about all I have to say on the matter, good luck!