Thrust per ton?

[Beerkeg]

How much thrust per ton do I need to get in orbit of Kerbin (100km) and then transfer to the mun, without using any of my planned landing fuel?

[lammatt]

you need ~4.6km/s dV to get into orbit (the orbital speed is about ~2250m/s...meaning there's around 2300m/s loss to drag and gravitation)

and you need a >1.0TWR in order to lift your ship

if u take g=10m/s^2 that means... you need around 10kN of thrust at least for every ton for a flyable ship

but if you want a reasonably efficient ascend... you probably want a TWR or >1.5 but nothing higher than 3-4 so that the ship dont get torn apart.

[blizzy78]

Same answer as in the "Lifting Capacities" thread: How to calculate what you need

[Tyren]

Rule of thumb: about 20 kn per ton (thats 2 tons of thrust per metric ton lifted mass)...i am running fine with it.

[Beerkeg]

k, cause my lander + fuel for landing (not a return ship) is about 80-90 tons. I kinda made it to orbit, ran out of fuel trying to get to the Mun (using the landing fuel aswell) I have no idea what kind of launcher I'd need to get it to orbit with enough fuel to get to Mun and deorbit before using my landing fuel.

I have been thinking of just launching and landing my lander in 2-3 parts cause whatever design I use, it fails. Also I forgot to use a ASAS module on my 2nd try and almost landed on the Mun, but again, ran out of fuel cause MechJeb didn't understand that I don't want it to do staging.

[capi3101]

Temstar covers this in the thread that blizzy78 provided; a TWR of 1.6 to 1.7 at liftoff is optimal. Given a Kerbin surface gravity of 9.81 meters/per second, that means you want somewhere between 15.70 to 16.68 kN per tonne for an optimal ascent.

Incidentally, those figures apply whether you're using asparagus, onion or serial staging.

[Tyren]

So ist not a matter of thrust. You run dry way before you are there, right? Well i use 3 stage rockets, first stage in lower atmosphere, second stage before orbital burn (to Keep the space clean ) and the last stage is sufficient to circularize/land on Mun. Trial and error forced me to that design, ist steady, fast (approx 4-5 mins to a 100/100 Orbit) and packs a Punch...and as mentioned before, it has about 2.0 TWR do have an emergency burn spare if needed. runs on about 75% thrust.

Another tip to save fuel according to my last line:

look up in the wiki about terminal Speed http://wiki.kerbalspaceprogram.com/wiki/Kerbin#Atmosphere to not waste fuel trying to push up the atmosphere

[lammatt]

you need another ~950m/s dV to get to Mun and another few hundred m/s dV to land

so you should keep that in mind when building your ship.

[Beerkeg]

Okay, well I just got back from work and opened up the game. The lander is 41 t, has 240kN of thrust and a TWR (no idea what that is) of 0.59.

With the launcher attached its 275t , 4500 kN thrust and TWR of 1.66

What kind of stats would I need to get this to the Mun? ( The lander part isn't a problem )

[blizzy78]

What kind of stats would I need to get this to the Mun?

What lammatt said. Keep in mind that the transfer stage will add to your liftoff payload.

[Beerkeg]

Well I tried a bunch of different launchers and I can't even get to orbit anymore... 36km was the highest I got. I even split the lander into 2 parts, so now its 14t

I see people making much heavier landers than mine, but their launcher part is much much smaller than the colossal monster I have to make to even get it going up.

Edited August 14, 2013 by Beerkeg

[blizzy78]

Just take a look at the Zenith rocket family I posted about earlier: The lifters look (relatively) small and compact, yet they can lift quite some large amounts of payload. Bigger is not always better. It's what you make of the fuel available to you. (Plus, he used a bit of trickery like part clipping to get more engines under the tanks given the available surface area.)

[TheDarkStar]

As long as it's above a bit above 1, TWR doesn't matter. What DOES matter is the delta-v, which is the the total (not net) change in velocity you can do (usually in m/s). Use the most efficient engines you can (that will still lift your rocket and don't take too long to do things) with enough fuel. Also, make sure you use asparagus staging, or at least some staging. Post some pictures of your rockets so we can help you more.

[Beerkeg]

Pictures soon.

My conclusion right now is that anything above 5t (lander + landing fuel((not return fuel))) is not possible to get into orbit without cheating.

I tried multiple designs I've seen other people use, I tried launching them myself, I tried letting MechJeb have a go (Watching rockets turn towards kerbin at 1000m) I can't get it into orbit.

Also blizzy78, I tried some of the rockets you posted, they can barely lift themselves, there's no way they could lift anything along with em.

Edited August 14, 2013 by Beerkeg

[blizzy78]

Um. Not sure if trolling I must admit. The Zenith rockets most definitely are capable as advertised.

Perhaps you could post your .craft file, that would help with this thread.

[Beerkeg]

Well I got a pic of a really scrapped down version of what I wanted to land, but no way of getting it to orbit. Even this majorly scrapped version can't reach orbit. The fuel and thrusters on it are for landing

[Johnno]

Well I got a pic of a really scrapped down version of what I wanted to land, but no way of getting it to orbit. Even this majorly scrapped version can't reach orbit. The fuel and thrusters on it are for landing

What exactly have you tried in the ways of launchers? There's plenty of threads for heavier lifting, but even with a transfer stage your payload doesn't go far beyond what an orange tank weighs.

By the way, those I-beams will (at least did for me when I tested) negate the thrust from the nuclear engines. So I'd say remove them and put on landing legs instead.

Here's a quick and dirty launcher I threw together. orange tank - skipper - decoupler - orange tank - mainsail, alt+leftclick top orange tank and add to the sides with 3x symmetry. As fast and as simple as it gets. Click the thumbnails for large pix.

Oh and I dropped the transfer stage before going in for landing so your lander has plenty of fuel.

[capi3101]

...30 tonnes? A Zenith-IV booster oughta be able to handle that no problem. I'm led to question how you usually pilot a ship into orbit.

Could you go ahead and post a picture of your ship with its normal booster attached? Just covering all the bases here.

Now, it doesn't look like you're using Subassembly Manager; I would recommend it. It's one of only two mods I utilize (the other being KER).

[Beerkeg]

Are we playing the same game? or am I just that bad at the game? I can get any probe or small 1-man lander anywhere. Getting one of those orange tanks (full of fuel) is not possible, I've never ever been able to do it. Re-fueling ships mostly have around 200 units of fuel in em. When I watch someones KSP video, it feels like they have alot more fuel in their tanks.

I see people make giant replica ships and getting them to orbit and it wouldn't even take off for me.

That launcher does not get me above 60k, trying different gravity turns, letting MechJeb try again (useless as always), no luck.

I think my best option would be to just not try doing stuff I want to (Mun Base) and just do what I can do (Space Trash)....

Edited August 14, 2013 by Beerkeg

[Johnno]

That launcher does not get me above 60k, trying different gravity turns, letting MechJeb try again (useless as always), no luck.

You're going to have to do a bit better at explaining why you're unable to do things, rather than just repeating "impossible", "I can't", "tried different things". Just go straight up until you get to 10km, then tilt to 45° and hold there until your apoapsis hits 75km. Turn off your engines, coast to AP, burn prograde (on the 'horizon' of the navball), you should even have plenty of time to make a manouver node before reaching AP.

[Beerkeg]

If I start the gravity turn at 10km I'll pass the AP at 18km. To have any chance of getting into orbit I have to start the gravity turn at 25km.

A few patches ago it was fine, I could do whatever I wanted, but at some point I had to start making smaller ships, cause they just wouldn't get to orbit. Now I'm pretty much just launching probes.

[blizzy78]

If I start the gravity turn at 10km I'll pass the AP at 18km. To have any chance of getting into orbit I have to start the gravity turn at 25km.

A few patches ago it was fine, I could do whatever I wanted, but at some point I had to start making smaller ships, cause they just wouldn't get to orbit. Now I'm pretty much just launching probes.

Please explain how your gravity turn looks like. It is not supposed to mean "at 10 km, turn hard east and point to the horizon." It's rather a gradual tilt towards the horizon while still going upwards.

[Beerkeg]

I know what a gravity turn is and what it looks like, I'm just telling you how I have to do it. More to the point, how do I get enough fuel and thrust to get my crappy stripped down Mun tower base thing, that I didn't really want, but rather wanted my other design, which is even heavier, into orbit ?

[blizzy78]

I know what a gravity turn is and what it looks like, I'm just telling you how I have to do it. More to the point, how do I get enough fuel and thrust to get my crappy stripped down Mun tower base thing, that I didn't really want, but rather wanted my other design, which is even heavier, into orbit ?

That I can't answer because you're not really helping us help you. Obviously others don't have any problem lifting large masses into orbit, only you do. So I guess you should provide more information so that we can help you.

[Johnno]

I know what a gravity turn is and what it looks like, I'm just telling you how I have to do it. More to the point, how do I get enough fuel and thrust to get my crappy stripped down Mun tower base thing, that I didn't really want, but rather wanted my other design, which is even heavier, into orbit ?

You're doing something wrong. That's all there is to it. Show us a picture of your launch vehicle with the payload on top. Show us the staging. Show it to us on the pad. Show us a picture of when you've just dropped your first stage. Show us your gravity turn.

It's all down to you, if you really want help start giving us the information we need to help you. Don't just stomp your feet and say you can't and nothing works, tell us how things don't work.

It's either your staging, not having your throttle up, not doing a proper gravity turn, or something silly like clipping stuff into your engines so that some of them don't give full thrust. But at this point it could be anything really, since you're not explaining yourself.