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TheAlmightyOS

Rocket Science: harder than anticipated

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Hi all. Posting because I am having issues between the game crashing on start (NOT asking for support here. It’s a mod thing. I will figure it out) and having issues getting my rockets into space when it does load. As I only have maybe 4-5 hours a week to play it is frustrating to see my well planned (or should that be NOT well planned?) rockets+payload imitate the trajectories of ICBM’s or run out of fuel before they can complete their primary objective.

It’s the math and the mods I am using. I am trying to use Near Future Propulsion, B9 and just about anything RoverDude makes to create a transport system. The goal is to mine karbonite on various planets, use large transport vessels to drop off supplies and pick up the karbonite at those planets, then move on and deliver the karbonite to a refinery/space station/orbital shipyard where fuels, metals and other resources are created from the karbonite and new ships launched. I try to use engines that have a low fuel consumption rate but high electric charge use. One example is the LF-9 Magnetoplasmadynamic Engine. Another choice is the insanely powerful HX-HPD. I have even tried the nuclear GNR-3750. However I can never hit that TWR sweet spot. My rocket is either too heavy to lift off due to fuel or lacks the fuel necessary.

Don’t misunderstand. I might not be a math genius but I get the general concept and know my way around excel. I can build rockets that work. I can go to Mun and (crash)land on the surface then return. But the moment I try to make an interplanetary hauler or space station or a rocket with a colony payload I run into trouble.

Any advice from those that have more free time than I do?

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Kerbal engineer and watching your deltaV and Trust to weight ratio should be all it takes (and a gravity turn, but I assume you got that covered)

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Welcome to KSP! Your plan sounds awesome. I play stock so others may have better advice on NFP but my advice mainly is to not get discouraged. Even a mun mission is quite a feat for a new player. A couple bits of advice just to get some principles down is to think a lot about staging. You're going to need a range of engines to get various payloads out out of the lower atmosphere and into orbit. It takes a lot of experimentation to find that spot for your play-style. The next bit of advice is to think about orbital construction with docking ports. Most of my big interplanetary missions require a few launches, getting components up, docking them, and then using a refueler to top them off before making the transfer burn. Its a big challenge, and a big part of the reward for those of us who are obsessed haha

Good luck!

Ps... ^Also that!

Edited by Pthigrivi

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You can get Kerbal Alarm Clock. Never was fancy to figure out how it works myself, but as far as I know you can plan transfer windows with it. Also go find some interplanetary tutorials on youtube.

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How about assemble your interplanetary transport in orbit like a station? Sounds like you are reaching the upper limit of what can be send up from kerbin at once. Still not very sure what exactly the problem is though, appears to me that you are attempting to make an interplanetary craft in one go straight from ground to orbit.

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A picture or description of your launch stages would help in diagnoses from the pros. Having only used stock engines myself, I could only guess that the fancypants engines are just too heavy to deliver the power needed on a lower stage.

Also, I am not a pro.

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When I last used Near Future, the electrical engines were coded to produce almost no thrust in atmosphere. They're strictly engines for deep space. The low TWR, when you take into account the mass of the hardware needed to power them as well as the engines themselves, also makes them a dubious choice for landing on Mun-sized or larger bodies.

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Yeah, when I first got the game, I had trouble getting to orbit at first. It surprised me, since I already knew a few things about how orbits and rockets worked, and didn't make a lot of the typical "newbie" mistakes. Rather, I had to get a feel for how the parts worked, what was structurally stable in KSP, how the stock atmosphere behaves, and so on. So don't feel bad if some designs aren't working, despite knowing a lot about what you're doing already.

I definitely agree with using Kerbal Engineer, since just having the thrust-to-weight ratio, burn time, and delta-V numbers available helps A LOT when planning a rocket.

With Engineer, I'll usually plan for my rockets to have about 5km/s of dV in the lifter stages (you technically don't need more than about 4.5km/s, but ~10% safety factor is really useful). I'll also tune the engine thrust to get somewhere between a TWR of 1.6 and 2.0 on the pad (usually more like 1.6 to 1.8), and ideally keep it under 2 until 15km or so of altitude. Working with those numbers during the design phase in the VAB, it's fairly easy to get a lifter that works on the first try, including large ones.

Generally speaking, it's OK to use high-thrust but low-efficiency engines in the lower stages. This is what they're meant for, and they'll be dropped relatively early in the flight. So make sure you're using the high efficiency engines in space, but high thrust engines at the pad.

This part may not be necessary info in this case, but could help newbie readers:

Also, I can't stress enough how important it is to have a good launch profile. In KSP's stock atmosphere (version 0.90 and earlier), you want to go straight up until about 8km-12km altitude, and then start your gravity turn, by gradually tilting to the east (a little extra free velocity from the planet's rotation). By the time you hit the upper atmosphere, you should be going almost horizontal. The lateral (horizontal) velocity is energy you get to keep in orbit. Any time you're going straight up, you're spending fuel on fighting gravity. But early in the launch, you need to get out of the thicker part of the atmosphere, so you want to go straight at first and get out of the high-drag environment.

A lot of people start out going straight up, and then at apogee they'll tilt over and burn horizontally. This works, but is less efficient.

If your TWR is too low in the middle of this atmospheric transit, you may find it hard to keep your trajectory going upward sufficiently. TWR can fall below 1 on a later stage as long as it's well after you've started the gravity turn and have built up some velocity.

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Thank you everyone. Reading though all these I realize what I am missing and it is so *ing obvious: Stages. I am trying to do this in one stage. These heavy haulers are so large the final stage is about all I can fit in the VAB. I need hanger extender but that isn't updated for 0.90 yet. There are ways around that. Building in orbit has been suggested. Might try that till HE is updated.

I do have Kerbal Engineer. It helps and is a great tool. Let's me know if I am going to break orbit but not if I am going to have any fuel after I get up there.

Someone suggested pictures. I don't have any unfortinately. I build a failing craft, deconstruct and try again. Next time I make an attempt I will post a screenshot here.

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Oh yeah man you'll be amazed at the difference. Some really crazy efficient things are possible if you plan it right. 3 stages is pretty typical, some solid boosters to get you up to 10k, a mid-TWR upper atmosphere driver for the gravity turn, and a high ISP stage to circularize at low kerbin orbit.

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A simple way to add a first stage without adding height is to put on 2, 4, 6, or 8 radially attached solid boosters. One of my rockets has 36 of them!

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A simple way to add a first stage without adding height is to put on 2, 4, 6, or 8 radially attached solid boosters. One of my rockets has 36 of them!

Heck yeah. At least in 0.90 and earlier (since things will change somewhat in 1.0), building wide doesn't incur any penalties unless you're using something like FAR/NEAR. With some creative use of fuel lines, you can use your "upper" stage engines simultaneously and not have any dead weight, and still have full tanks in the middle when you drop the radial boosters.

I have to say. Fuel lines rock. :)

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I think I am startting too big. I was going to create the heavy haulers first and use them to launch the inital stations/bases. However that is just too impractical. Instead I am going to use a smaller launch system to put a extraplanitary launchpad in orbit and then build the heavy frieght haulers in orbit.

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You might also be running into some big diminishing returns by pushing too much fuel into orbit.

Using Engineer, This: http://www.kingtiger.co.uk/kingtiger/wordpress/wp-content/uploads/2014/02/KerbinDeltaVMap.png

and this: http://ksp.olex.biz/

You should be able to get really close to tight delta-v's. Remember that wasted fuel is dead-weight payload and you pay exponentially down the line to deliver it. Also remember with a little practice you can aerobrake and aerocapture into Duna, Eve, and Jool.

Needless to say there's a lot going on. Its awesome you're thinking big, but also think about working small. Its much easier to get a better sense of what's efficient and then apply that to bigger designs.

Edited by Pthigrivi

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You might also be running into some big diminishing returns by pushing too much fuel into orbit.

Yeah... not just fuel either... Just noticed the storeage/transport tanks on my haulers were full. Thought they started off empty. So 50k+ of dead weight right there.

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Yeah totally. One of the coolest things about this game is how much you learn about practical space travel. Everything is weight and momentum. Keep weight down, and don't waste momentum. All of a sudden it becomes obvious why they left the command module in lunar orbit during Apollo 11, because there's no sense carrying your return fuel all the way down to the moon and back when you can leave it in orbit and re-rendezvous. The same principle applies everywhere.

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This affair about add-ons has been moved to Add-on Affairs.

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So I changed up and started building smaller w/stages as recommended. Now I can get my smaller station mock-ups into orbit but I am still having some issues with payload. To be more specific, choosing payload. The station design I am building right now I intend to use in orbit over all planets (and a few moons) in the solar system. As I stated before, the station is intended to be a refinery, a shipyard, a habitat and a fuel & supply depot. For power I intend to use both solar and nuclear. Also, karbonite detectors and collectors are going to be attached. By the time I add station-keeping engines and thrusters and try to launch (taking all the fuel/supplies out of the storage tanks this time) I drop below 1 TWR, even with boosters. Now I have thought about sending it up in sections but that would mean each section would need it's own control module. Or would it? Suggestions?

Once again, I am sorry for lack of screenshots. Steam on Linux seems to be eating my screenshots. When I get them I will post them

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By the time I add station-keeping engines and thrusters and try to launch (taking all the fuel/supplies out of the storage tanks this time) I drop below 1 TWR, even with boosters. Now I have thought about sending it up in sections but that would mean each section would need it's own control module. Or would it? Suggestions?

How about some small but efficient space tugs which grabs your station modules in a very low orbit and dock them together?

They don't need much deltaV and TWR. About a 1000 m/s should be more than enough (that already takes you from orbit to the moon) with a TWR of ~0.5 in space? You archieve that easily with a probe module, a medium sized tank (the 'quarter-of-the-orange tank') and a small high ISP engine (LV-Ns or LV-909). Add a bit of RCS and there you go. It should weight way less than 10 tons in total which you can launch with a simple lifter (orange tank + Skipper should do it).

I think you are over-engineering. Just try to build a bit more simple.

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I figured it out (i think)

after fiddling around with how the extraplanetary launchpad works and asking RoverDude a question I think I know how I am going to do this.

First, I designed and saved my base. When it is in orbit I will take a screenshot as it is too big to see in the VAB (figured out screenshots btw, the button was not bound correctly).

Secondly, I designed a heavy lifter with a simple payload of RocketParts and a EP Launchpad. Once in orbit I start building. As it builds I keep it stocked with rocket parts via my heavy lifter.

After the base is created I decommision the first EP launchpad.

Testing this tonight. Will let you guys know how it goes.

As for the tugs idea, I like it. Starting work on the tugs now. I left a space on the station for the tugs to remain docked while not in use. Have an idea for using RoverDude's D.E.R.P. or AES pods as overpowered tugs/transports just because I think it would be hillarious to see a tiny little cockpit straped to a 2.5m engine :sticktongue:

Edited by TheAlmightyOS

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So, yeah.... utter failure.

*Aqua*, hammer meets nail: I am over-thinking this by a mile. I think I am suffering from part overload. There are so many awesome parts I want to use I try to use too many at once and turns whatever I am working on into a heavy, unusable mess. I am particular interested in (mostly) electric powered craft. And I made quite a powerful MPV (multi-purpose vehicle, what I am calling the tugs) one using xenon pulse engines. However it could only sustain full burn with ~160kn of thrust for 38 seconds and then took an hour to recharge. Not exactly the model of efficiency. :(

As for the base itself, I can not get it built. Even with constant launches and resupplies it would take over a week of non-stop grind to keep the EP launchpad stocked. I will have to redesign the launchpad to be more efficient. possibly my heavy lifter as well.

In other words: rocket science isn't hard, I just suck at it :(

Edited by TheAlmightyOS
I suk @ speeling to

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