What TWR do you aim for...

[ComradeGoat]

I aim for 2 meters per second per second in space at minimum with nuclear engiNes, as otherwise those thousand meter per second burns drag on forever.

When I use the upper stage on my rockets instead of a Nerva though, I can get up to 50 m/s squared. It has a good kick to it!

Doesn't using those big atmospheric engines in space feel kinda ... dirty ... though?

(I have been known to use Mainsails from my orbital insertion stage to start my LKO->interplanetary insertion burns)

[Krizzen]

The reality is the amount of TWR you use is totally up to you. There is no "right" answer (except you'll never lift off if your TWR doesn't rise above 1.0; you can still have <1.0 TWR on the pad and get above 1.0 by burning fuel, thus reducing your mass and increasing TWR). There are tradeoffs for using high/low TWRs.

When building rockets, I keep these two rules in mind:

Rockets with a low TWR are typically more fuel efficient and less time efficient. Because of this they are mostly lighter weight.

Rockets with a high TWR are typically less fuel efficient and more time efficient. Because of this they are mostly heavier weight.

So, on the launchpad I prefer a TWR that will propel my rocket near max Q (i.e. reaches nearly exactly speeds to not exceed a fuel-optimal ascent based on atmospheric drag), which is usually around 1.7. As you ascend, you burn propellant and your TWR goes up, giving you more speed to hit max Q.

In orbit, I like about 0.5 or greater. I don't enjoy really long burns, so sometimes I slap a few more engines on my rockets to bring my TWR up and lose some delta-V in exchange. Right now, there are no dollar limits on rockets. You can build them as large as you like (or as large as your PC can handle!), so maximizing efficiency isn't a priority. When career mode is released, TWR will become much more important since it will directly impact both cost and efficiency of our rockets.

Edited May 29, 2013 by Krizzen

[Tw1]

I tend to aim for 0.5 for orbital stages. Otherwise it takes a huge amount of passes to get anywhere.

[AmpsterMan]

I aim for a TWR of at least 1.2. Of course this means that it costs me a bit more delta-v to get to orbit but it is good enough for me.

My more general rule is as long as my first stage can last until 30km (when I am pitched down to like 20° ) I'm good

[UmbralRaptor]

That's understandable because as of yet in KSP there is no cost to fuel. Though you might end up with rockets that are way over-build. In real life rocketry however the amount of fuel is a major consideration, and we will have to take it into account when career mode is implemented in the game.

Not exactly:real life fuel costs are ~1-10% of the cost of a launch. However, the *other* aspects of a rocket (tankage, engines, etc) are so expensive that shaving off a few m/s in the design process may help. (or may not, if you end up with costlier parts)

[OrbitusII]

For some reason the Skipper on my launch stages doesn't work too well alone when I'm going up with a TWR of less than 1.2-ish, so I try to get above 1.2 with most rockets.

[Reblet]

I typically go for a first stage TWR of about 1.5. In my very unscientific experiments I've found you can squeeze out a bit more dV even after gravity drag than with the 'optimal' TWR of 2 as you need to bring along less weight in engines.

[steamypete]

Altitude (m) Velocity (m/s)

0_______________97.3

1000____________110

3000____________130

5000____________160

8000____________215

10000___________260

15000___________425

32000___________2250

Going up through the atmosphere you should have sufficient thrust to weight to get as close to these values as possible. I usually aim for a thrust to weight of 2. In space It doesn't matter how much you have and it is more of a trade off between efficiency and your time/patience.

The original table can be found here.

Why are these fixed values? Is not terminal velocity different for objects with other shapes, orientations, etc?

[Wait- Was That Important?]

Doesn't using those big atmospheric engines in space feel kinda ... dirty ... though?

(I have been known to use Mainsails from my orbital insertion stage to start my LKO->interplanetary insertion burns)

Well, yeah, but I'm going for quasi-realism in my program. Using the second or third stage engine to boost a payload to Duna or somewhere is probably cheaper than launching a throwaway NERVA, or even using a tug.

[dimovski]

I have just copied over the TWR from BobCats Proton, so 1st stage 1.5,2nd 1.3 and 3rd 1

[AndreyATGB]

Why are these fixed values? Is not terminal velocity different for objects with other shapes, orientations, etc?

It is in real life but not KSP. AFAIK without mods, all ships have a drag coefficient of 0.2. Basically everything has the same drag, regardless of shape.

[numerobis]

Shape doesn't matter in KSP, and orientation only matters with wings. Terminal velocity will be lower if your ship is mostly made of SRBs, drag 0.3, and higher if you use aerospikes, drag 0.1; a handful of other parts also have drag values other than 0.2.

[TheDarkStar]

However, the aerodynamics system will be changed to be more realistic in a future version.

[numerobis]

Lately I've been aiming for a TWR of 5-10 in attempts to improve my score on zarakon's 10-minute challenge.

[SargeRho]

I don't. I just slap more engines onto it until it flies.

[Thefallenhun]

I'm sort of at a refining stage in my space program. I can't claim I pay attention to TWR per se throughout my launch, but obviously at least 1 to begin getting off the ground. I have a design now that is just massive rings of concentric boosters, and its been able to get me anywhere, but I'm running into a few problems.

So by the time I have a stable kerbin orbit, I've got about 1500 m/s left on a ring of six red boosters around my central craft, which is enough to begin but not finish long distance transfer burns. At that point the plan is to switch to 10 nuclear engines, but even with 10 since the ship is so heavy, I find that the burns are so slow that I miss my window and end up having to do expensive mid course corrections. I'm leaning away from using nuclear stuff to inject large objects on far trajectories, because quite simply it goes too slowly. Of course, in not doing so I miss out on a lot of delta V. You don't really NEED it, but now I shoot for at least .80 TWR for injection.

Though of course my upper stage with six nuclear engines injects pretty fast, but each engine only has an FLT-200 to draw from.

[SoldierHair]

Above 2 twr is just a waste.

[AmpsterMan]

I've gotten into the habbit of doing Kerbin Orbit Rendesvouz of Command module and lander module with the service module and injection stage. These are usually powered by LV-30 engines and only reach Duna and Eve.

For Jool missions I am planning a Mothership approach powered by LV-N. This however is still in the planning phase

[CalculusWarrior]

For me, it's generally anything greater than 1... If my ship is having trouble getting off the pad, I'll just add MOAR BOOSTERS and hope that the problem is fixed.

[SkyRender]

I once had a TWR of 0.08 in space. No joke. I was getting about an inch a second of delta-V.

[nerdboy64]

"Enough." I don't do any math, I just slap some tanks and engines onto my payload until it gets into space. That's not to say I don't pay attention to efficiency, just that I don't spend my time adding up part weights and engine outputs.

[Sir Nahme]

minimum: 1.2

Maximum normally: 2.4

maximum: as much as possible for lulz

[Spatzimaus]

Aim for 2.0-2.2 for your boost stages, with 1.5ish as an absolute minimum. ("Boost" meaning anything that'll fire before you hit max-Q.) Upper stages designed for operation outside the atmosphere can be much, much lower, although I try to keep them above 0.1 just to keep burn times manageable. Atmospheric stages for use above max-Q (i.e., insertion engines), if you have any, can be as high as you want.

It's also going to depend on your design. A multi-stage stack/asparagus design loses thrust at the same rate it loses mass (more or less), so the TWR you build should be the average you'll need along the way. But an SSTO booster will maintain full thrust while losing fuel, meaning you'll throttle it down as you go; in this case, your initial TWR can be a bit lower, to make up for the fact that your TWR will quickly rise as you burn off fuel. My big 400-ton SSTO booster starts off with a TWR of only ~1.7, but it would have a TWR of ~15 once it approaches the end of its flight, if I didn't constantly throttle down along the way to keep the g-forces manageable.

[Rage097]

Preferable one greater than 0/1