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100055

Increase Delta-V of rocket

Question

I'm playing a Career mode game with no mods (except MechJeb), and this is the largest rocket I've been able to build. It works well for traveling within the Kerbin system so far, but I want to start going to other planets, but it clearly lacks enough Delta-V to do so (only 7500 m/s). I only have all the 90-Science nodes of the tech tree researched, plus Heavier Rocketry and Command Modules. I would like to increase its Delta-V to (hopefully) 10000 m/s, but am unable to do so. Adding more boosters renders its TWR too small to lift itself. Any ideas?

Picture here

Edited by 100055

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I'm no expert, but do you really need 3 kerbals? Because you can always convert the rockomax pieces to the smaller ones, and use the much lighter one man pod. This should let you add more rockets.  

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1 hour ago, 100055 said:

Adding more boosters renders its TWR too small to lift itself.

Maybe that's because your boosters are too big. The TWR of the booster itself should be higher then the TWR of the core stage so it actually applies net thrust. If they are equal, the booster is basically just carrying itSelf. If it's lower, the core carries the booster.

equal or lower is fine in some designs, when the booster feeds the core with fuel. In this case it's like a better droptank.

Edited by Physics Student

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Why you got a antenna? It is a crewed ship right? They don't need antenna's for control. Toss it!
Generally you only need 3 landing legs to land, maybe increase spring and dampener strength by right clicking on them if it tends to fall on touchdown, this saves some weight.

I can't see any solar panels? Go any not shown on the pic? If you don't have them you'd better put one on and remove all batteries for all I care. As long as you make sure your getting sunlight 10-20EC is all you need.
Try to do a re-entry test by launching into a highelliptical kerbin orbit. Did you waste all the ablator on your heatshield?
If not, try to empty as much ablator as you can, this also saves weight. 
Any monopropellant in the command module? You don't need it, empty it and this will also save weight.

Do you seriously need all those tailfins at the bottom? You got a skipper or mainsail (can't make up) that has swivel right?
Most of the weight is at the bottom. Maybe only 2 or 4 of the smalles tailfins at the bottom would be enough for stability if you get center of drag issues in case you remove them. The smaller ones save drag and weight and you'll have more delta-v on the 1st stage.

By the looks of it I think you could do with only the center engine for attitude control. Are all the other outer engines on the asparagus 1st stage reliant T30 engines or are there also T45 swivel engines. T30 is lighter and better and maybe you can properly control it with only reliant engines.

Some general info.

To go to other places you shouldn't think in total Delta-V from the Launchpad. Rather you need to setup your interplanetary mission profile by creating the necessary modules first.
To practice yourself, limit yourself to 1 kerbal landing per interplanetary world. This makes things easier for you. If you get the hang of it you can scale things up and get more kerbals there. Don't make things unnecessary difficult for youself if your still in the learning curve.

What I would do is first set a target. Let's say this is Duna. 
First you want to test a vehicle that can land from Duna orbit on Duna, take off again, fly and land back to Kerbin.
You can test this by using the correct thrust on the stages and making sure you got plenty of delta v and a capsule with heatshield and parachutes.
You will also need parachutes to land on Duna, so make sure you repack them using a engineer on the ground or have sufficient parachutes on the return stage.

After you build this module (can weight like 10 tons) then you should start to create a rocket in the VAB to get that weight and shape into Duna orbit.
This is better then building the rocket from scratch and then start fiddling how your gonna get it done on Duna.

Try to watch some interplanetary stock tutorials like by guys such as "Scott manley" on his youtube account.
He explains it by narrating his own playthrough with some very basic and sometimes more advanced tips for people new to the game.  

Edited by Helmetman

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You could do it like this (note the first set of liquid boosters stage before the SRBs) but I'd prioritise researching specialized construction first to get the standard clamp-o-trons then assemble something in orbit. Also comms are going to be an issue beyond KSOI until you research better antennae.

 

Edit: Oh and I completely agree with @Helmetman about mission planning and smaller payloads rather than just throwing raw delta-V at the problem. For example a mission to (loose elliptical) Eve orbit takes less delta-V than a Mun landing if you use an optimal transfer window.

Edited by Aelfhe1m

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Try going for a classic "Dealty IV Heavy"/"Falcon Heavy" build. Toss the 1.25m side boosters. Copy your core stage and strap a pair to the outside. Do not use fuel crossfeed. Instead, add extra tanks to the central stack. Your goal is a configuration where the side boosters run empty and are decoupled, leaving a half-empty center stage that has enough TWR to continue by itself even though it would not have enough TWR if it was completely full.

You could get a similar effect by crossfeeding into the center stage and having said center stage be small enough to have enough TWR even when full, but while the effect is similar, the dV yield isn't. At the end of the day, the only thing that gets you dV is your mass fraction. Crossfeed has its uses, but it doesn't always help you go further. More raw fuel, on the other hand, does. You will grow as a rocket builder if you stop relying on fuel lines as crutches, and start to work with mass fractions. :wink: 

In accordance to advice in that link, I would also try to beef up your upper stages. You have high-Isp Poodles on them, but pull only 2000 m/s out of each of them. That's less than six times their Isp, so you're not really getting good bang for your buck. Try bumping them both up to around 3000-3500 m/s. Or the middle one to 3000 and the upper one to 3500. Or whatever happens to fit with the tank sizes you have available to you. Don't sweat the details, just let the Poodles do more work so you can benefit from their Isp more.

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Just add a clamp-o-tron docking port jr and refuel in LKO with a refueling ship you send up on a second launch. That way you could even add some more tanks to the two upper stages and send them up empty at first to avoid adding weight to your current design.

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On a side note, since I'm not seeing any, I recommend you get a few solar panels on that thing if you're going interplanetary.  The poodle (which I'm assuming you're using) has an alternator, but personally I'd hate to fire the engine to charge up the batteries.

Second tossing the antenna.  Looks like all your science is going to be recovered, so you won't need to transmit anything.

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@100055:

Drop the 1.25m boosters and add either Kickbacks or 2.5m boosters.  Generally (with the sometimes exception of solid rocket boosters such as the Kickback), you want your stages to go for about two minutes before you need to start the next one:  you have this for your core but not for the side boosters.  Thirty seconds of burn is nigh-useless for a liquid-fuelled booster stage.  Also, your TWR for each of your booster stages increases by .01; the boosters are carrying themselves and not really doing much else.  That's not to say that they don't help at all:  if they're asparagus-staged then you do get the benefit of essentially starting with a fully-fuelled core stage that already has some speed and altitude, which is probably why you see less delta-V if you take those boosters away.  But that's all the help you're getting from them; they're worthless otherwise.  For boosters, you always want to add net thrust--this means that you need the boosters to have higher thrust-to-weight than the core.  Usually, the 1.25m engines are weaker than the 2.5m types (the exceptions are the Vector and Dart, which you don't have yet), so for a comparable fuel load, you end up losing delta-V if you use them against a 2.5m core.  You're only managing because you have three FL-T800 fuel tanks stacked on each one, so it's a more-than-comparable fuel load.

However, that larger fuel load is also at the limit of what the basic 1.25m engines can lift:  less fuel gives more TWR but an even more pathetic burn time, and more fuel leaves you on the pad, unable to lift at all.


To put it in other words, your design has reached the point of diminishing returns; this rocket is as good as this rocket will ever be.  If you want a better rocket, then you need a new rocket.  Add a few of the tall 2.5m tanks with Skippers--I doubt you're at a point where you need Mainsails yet, except maybe on the bottom of your core stage.  Perhaps I'm wrong:  play with the design a bit and see what works.  You unlocked Heavier Rocketry; you may as well use some of the things you find there.  In any case, you ought to have no trouble getting 10km/s by improving this design.

Edited by Zhetaan

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2 hours ago, Palaceviking said:

Moar boosters (well nobody else was going to say it)

Actually my advice is less boosters. The major issue with his design is it is a big, heavy but not particularly powerful rocket . Streetwind's idea of DeltaIV alike design is a interesting one , another is SRBs (with crossfeed enabled and LFO tanks on top). Depending on the destination a Terrier instead of the uppermost Poodle is a considerable mass saving (since that is the last stage it will make a big difference for the whole rocket)

A bit problematic to give more specific advice since the OP didn't defined a particular objective. A craft tailored for a given celestial body/mission can be made much more efficient.

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29 minutes ago, Spricigo said:

A bit problematic to give more specific advice since the OP didn't defined a particular objective. A craft tailored for a given celestial body/mission can be made much more efficient.

OP stated "beyond Kerbol's SOI".  Which would presumably start with Duna.  The catch is that while this is fine for landing on Ike (or Gilly) and orbiting Duna (or Eve), it really can't return from a Duna landing (assuming those landing legs are meant for landing).

Rockets (especially KSP rockets, I have no real experience in others) need to built top down.  Everything from the landing legs up needs to be able to get back out of the gravity well its designed for and then proceed to back to Kerbol (or whatever is next).  The  Mk1-2 capsule is a pretty bad, I'd much rather have a mk1 capsule/mk1 crew cabin together for half (actually 1/2.2) of the mass.

I'd recommend an Apollo-style lander/mothership* for anything beyond Kerbol: while coming back from Duna orbit doesn't take *that* much fuel, it is still quite a bit more than the Mun.  Don't take the fuel needed for that to the surface.  Once you have the lander and return system set up, then you can build the capture and transfer stages (these are using poodles, right?  Also expect to burn home on a poodle and ditch the Duna ascent rocket the only better than poodles are Nervs, and they are beyond your tech level).  Only once they are all built should you worry about how to get the thing into orbit (expect to break the thing up into separate launches depending on where you are in career mode).

For getting into orbit:
Most of the advice is good, but I'd still make my "Falcon Heavy style" design [if  you tried  that] with crossfeeds.  Spacex wanted to do it because it is more efficient, and you want to increase the delta-v so keep the crossfeeds.
Moar boosters, especially kickers (the biggest SRB).  These show up in all the "cheap and cheerful" (lost cost without recovery) contests for a reason.  Don't be afraid to strap multiple boosters each other to save on decouplers (although this is less important with kickers.  They cost enough more than decouplers to be worth it).

* If you aren't confident on your docking skills, start with rescuing kerbanauts and progressing to real docking.  You really want to use a mothership/lander for interplanetary flights.  Also, rescue missions are a cheap source of kerbals.

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2 minutes ago, wumpus said:

OP stated "beyond Kerbol's SOI".  Which would presumably start with Duna. 

Yes, but the way OP define it give me the impression he may want a "one size fits all" design. That is the reason of my remark.

Having some sub-assembles for particular tasks  (e.g. a series of Launch Vehicles 1t, 5t, 10t ...) may help to speed-up the design and allow more time to explore. But usually is the customization of the craft for the task at hand that gives the more relevant advantage.

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It's actually not very clear what your objective is.  You have parachutes and landing gear on your final stage, which means you are looking to land somewhere. That upper stage is only 2100 deltav, which is not enough to land on many places, let alone returning back to Kerbin. Your rocket should be designed around your objective.

 

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6 minutes ago, Gilph said:

That upper stage is only 2100 deltav, which is not enough to land on many places, let alone returning back to Kerbin. Your rocket should be designed around your objective.

Gily and Ike are possible. That said, one does not land on Gily, rather you dock onto it. Ike is bigger but not that large to make the poodle necessary anyway.  So the craft is either not good enough or overkill. :/

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Lots of good suggestions here, but I'll add something different: if you have Heavier Rocketry, you have the TwinBoar.  It's preposterously good at lifting heavy payloads for cheap (especially in conjunction with Kickbacks for even moar dumb thrust).  As mentioned above, if you need more payload than one can lift, you can add a couple more to the sides, Falcon Heavy style.  

Depending on your mission profile, you could potentially go with something like a Terrier top stage, then a Poodle, then a Skipper, then however many TwinBoars/Kickbacks you need.  That should be able to break 10,000 m/s without too much trouble. 

But yeah, it's advisable to figure out what mission you want to perform, figure out what your needs are for that mission (delta-v, TWR, landing, etc), and design your rocket backwards from the top.  

Finally, I'm going to respectfully disagree with those who suggest doing things on a modular basis, or refueling in orbit.  It is not really more efficient to launch a lot of smaller payloads to orbit, versus doing it in one.  If you really economize your rockets it might be slightly cheaper, but I don't see how it's easier.  And in some ways it's less efficient - you need docking hardware, duplication of some parts (e.g. probe cores), and you'll end up spending some of your fuel on rendezvous maneuvers.

 

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I'm a spaceplane person but what do you think of this rocket for a  lightweight, 90 tech Duna mission ?

https://www.dropbox.com/s/9bpq0uqy8tz8biy/DUNA.craft?dl=0

J5Y0BIE.jpg

1DyXf8E.jpg

I guess it helps a lot that the pod is the lightest possible.  The transfer fuel tank is on a docking port, the idea is to leave that in orbit of Duna and hook up to it again after ascending from the surface.   It's got a heatshield on the top and there's elevons on the bottom of the lander can to keep that end pointing forward on re-entry to Kerbin.    Either side of the can, on decouplers, is our landing / science hardware - pair of Oscar Bs,  landing legs, mystery goo containers, and the landing parachutes (will need a burst from the engine though to cushion the touchdown , no doubt).

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Thanks for all the suggestions. One more question: How do I add more Delta-V to a lander? Using taller tanks makes it tip over easily, and making it wider by adding tanks and engines around the main tank will increase air resistance during the initial launch. 

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Increasing the dV is simple:

Increase the Amount of fuel and/or reduce weight.

Assuming you are refering to the pic in the first post:

Strip all unnessesary, like monopropellant. Use the lightest antenna that can make the planned distance. Reduce batteries and Solarpaneels to a minimum. Reduce the amount of ablator - they are designed to allow reentries on Eve and Laythe too, the full amount isnt needed for a Kerbin reentry.

(The MK1-2 Capsule is very heavy btw, a MK2 Lander Can + adapter + MK1 Pod reduces the weight by 1to./25%)

Where do you want to land? Mun? then remove the Poodle, use a Terrier instead. (-1.25to.)

 

To increase the amount of fuel you can radial attach some 1,25m tanks, place nosecones on top of them. For max performance add decouplers between tank and nosecone (upside down so the decoupler will be jettisoned too).

To add just a bit of fuel consider to place a 1,25m tank on top of the MK1-2

 

Consider a lander with 2 stages. Add a small tank and engine between the maintank/poodle which has only enough dV (+ reseve) to bring you back in orbit and then to Kerbin.

 

In worst case: build a lander which is just able to return to orbit. Rendevouz and transfer crew/science then, ditch the lander and return. In this case the Lander itself doesnt need any Ablator nor parachutes.

(If you have problems rendevouzing - ask :wink: )

Edited by Draalo

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15 hours ago, AeroGav said:

I'm a spaceplane person but what do you think of this rocket for a  lightweight, 90 tech Duna mission ?

The launch TWR of more than 2.5 means you could easily carry more fuel in the first stage.  And you messed up the staging because your first stage uses the fuel of the second, which makes the Poodle and the decoupler dead weight.

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On 23/09/2017 at 12:54 AM, Aegolius13 said:

Finally, I'm going to respectfully disagree with those who suggest doing things on a modular basis, or refueling in orbit.  It is not really more efficient to launch a lot of smaller payloads to orbit, versus doing it in one.  If you really economize your rockets it might be slightly cheaper, but I don't see how it's easier.  And in some ways it's less efficient - you need docking hardware, duplication of some parts (e.g. probe cores), and you'll end up spending some of your fuel on rendezvous maneuvers.

While not necessarily more efficient possibly it is.  Unfortunately, the mooar [stuff] approach seems,  IME, much more common than well thought optimization as motivation to use orbital construction.  :/

 

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11 hours ago, Harry Rhodan said:

The launch TWR of more than 2.5 means you could easily carry more fuel in the first stage.  And you messed up the staging because your first stage uses the fuel of the second, which makes the Poodle and the decoupler dead weight.

The high initial TWR only lasts till the Hammer SRBs burn out,  after that it's more sedate.    I left crossfeed enabled on the decoupler between the Poodle and first stage engine so I have some flexibility as to when to switch to Poodle.  Basically as soon as I feel happy that we've got enough upward velocity I can ditch the heavy first stage engine and get on the lighter, more efficient poodle. 

I may have messed up with the final Kerbin re-entry part,  I don't think that heat shield protects the lander can very well , maybe because there's a decoupler between them. 

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22 minutes ago, AeroGav said:

  I left crossfeed enabled on the decoupler between the Poodle and first stage engine so I have some flexibility as to when to switch to Poodle. 

That flexibility is not much of an advantage if it only allow you to stage at a bad moment anyway. It only really make sense if you plan to top those tanks somewhere along the way.

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6 hours ago, AeroGav said:

The high initial TWR only lasts till the Hammer SRBs burn out,  after that it's more sedate.   

You can adjust the thrust of SRBs in the VAB. Initial TWR should be 1.5

Note that the SRBs now burn longer.

1500m/s dV from the main engine + booster are enough to lift you high enough for the Poodle to be efficient.

If your TWR allows you to add fuel, allways add it to the upper stage untill that TWR reaches critical minimum.

If you still can add fuel add it to the 2nd stage.

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