Duna launcher.

[Cpt Kerbalkrunch]

@eloquentJane's assessment of 4 Kickbacks sounds pretty good. Eight is my standard number for everything because of the absurdly large landers I build, but for what you have in mind they would probably be overkill. In fact, you might even be able to downsize to Thumpers, depending on how much mass your final draft ends up with.

[Scarecrow]

Just as proof that if necessary you can keep things quite simple and still get to Duna, I built this after reading your thread and noting that you are intending to make it a one way trip.  Without the requirement to have a vessel capable of returning, it removes quite a lot of what you need to launch in the first place.

If you want details of the craft, I'd be happy to provide them, but I am hoping it shows that you don't need to go really big just because you are flying beyond Kerbin's system.

As a break down, the first stage is enough to get the vehicle in to a parking orbit around Kerbin, so effectively a SSTO.

The second stage gets what's left to Duna, and puts it in orbit once it gets there.

The third stage is the lander.

 

 

Edited June 15, 2017 by Scarecrow

[septemberWaves]

My estimate was about 1km/s less delta-v than was needed. So I added another full-size and one minimum-size Kerbodyne tank and this was the result (ignore the mods, the rocket itself is all stock except for the 15-tonne simulated payload and MechJeb). This should have enough delta-v to reach Duna, as well as having built-in avionics, power generation, and some monopropellant for attitude control. It has a bit of extra delta-v, but it compensates for poor piloting and/or wanting to de-orbit the upper stage (I'll probably be using derivatives of this rocket in my own gameplay). This is about the amount of fuel you need to reach Duna orbit with a 15 tonne payload.

[nascarlaser1]

Thxs guys!

41 minutes ago, Scarecrow said:

Just as proof that if necessary you can keep things quite simple and still get to Duna, I built this after reading your thread and noting that you are intending to make it a one way trip.  Without the requirement to have a vessel capable of returning, it removes quite a lot of what you need to launch in the first place.

If you want details of the craft, I'd be happy to provide them, but I am hoping it shows that you don't need to go really big just because you are flying beyond Kerbin's system.

As a break down, the first stage is enough to get the vehicle in to a parking orbit around Kerbin, so effectively a SSTO.

The second stage gets what's left to Duna, and puts it in orbit once it gets there.

The third stage is the lander.

(I snipped pics due to size of quote)

1 question, what is a parking orbit? all the things I've launched have been at orbits that normally either stop at 70-75km or that are  super irregular (PE=70km AP=215km). I was also planning on launching this thing in one go a few minutes before my KAC alarm for the transfer window (which is set to ring 1 minute before the window appears).

[septemberWaves]

3 minutes ago, nascarlaser1 said:

1 question, what is a parking orbit? all the things I've launched have been at orbits that normally either stop at 70-75km or that are  super irregular (PE=70km AP=215km).

A parking orbit is essentially the first orbit your spacecraft reaches after being launched, before transferring to a better-defined mission orbit. Generally a parking orbit has less precise parameters than an orbit that is used for major mission purposes (it can have quite a lot of deviation from an "ideal" orbit while still being acceptable) because of the potential for variations in the ascent profile. If, for example, you launch a spacecraft into what is supposed to be an 80x80km orbit but a 72x93km orbit is perfectly acceptable since you're going to transfer to a more precise orbit later, that first orbit is a parking orbit.

Note that a parking orbit might also be a phasing orbit, if you're remaining in the parking orbit while you catch up with a rendezvous target. For example, you might be attempting to rendezvous with a space station in a 250x250km orbit (with very low eccentricity) by maneuvering from the aforementioned parking orbit, which would also make that parking orbit a phasing orbit. However, in reality a phasing orbit is usually a far more precisely-defined orbit than the initial parking orbit - for example, a Soyuz spacecraft travelling to the ISS launches into a low parking orbit, then uses the on board OMS (orbital maneuvering system) to transfer to a specifically-planned phasing orbit which will allow mission control to easily calculate (based on existing calculations for the phasing orbit; the same phasing orbit is used each time) when the transfer maneuver to the ISS should take place, rather than having to recalculate for every slight change to the parking orbit of each launch.

[Scarecrow]

57 minutes ago, nascarlaser1 said:

Thxs guys!

1 question, what is a parking orbit? all the things I've launched have been at orbits that normally either stop at 70-75km or that are  super irregular (PE=70km AP=215km). I was also planning on launching this thing in one go a few minutes before my KAC alarm for the transfer window (which is set to ring 1 minute before the window appears).

A parking orbit is just a normal orbit before making a burn to go somewhere else.  NASA chose this method for their moon missions, rather than just launching and going straight to the Moon, as it allowed them to check everything was OK once the vehicle was in space and it also gave them a slightly bigger window to make the lunar injection burn.

In short, it's just a temporary orbit.

In KSP a parking orbit allows you to fine tune a manoeuvre node to optimise your injection burn, which helps to minimise any correction burns during transition to intercept your target.

Edited June 15, 2017 by Scarecrow

[Cpt Kerbalkrunch]

@Scarecrow's got a good design there. Very much what I was thinking for a good, simple launch to Duna (been running it through my mind, but I can't participate cuz I'm stuck at work ). The no-return lander pains me to see, though. I know it's your first trip, and a good opportunity to get your feet wet, but (as I'm sure the designer already knows), with a few add-ons and tweaks, it could easily be turned into an Apollo-style lander that could get you back home. You have to be confident in your docking ability though, so maybe leave that for next time. For your first trip, though, run through your checklist. Battery, solar panels, antenna and science instruments (unless you're playing sandbox), and for Duna, a couple of drogue chutes to go along with your main chute. If you've got all that, yer ready to rock. Best way to see if a rocket works is to launch it and find out. Hope all goes well. 

[Weywot8]

7 hours ago, nascarlaser1 said:

The payload is a probe core and bunch of random bits and pieces strapped together to make it the same weight. I use the big-s delta wings to maintain control.

Sort of helpful but not entirely. A picture of the actual craft would be best because we could be wasting our time with comments that might not be helpful. 

Having said that:

•  Asparagus staging has a very specific definition. Let's all use key phrases with the same meaning in mind to avoid confusion.

Based on geometry alone, you can't have strictly asparagus staged the rocket. Only 6 tubes can fit around 1 tube with the same diameter. The lack of struts was also a giveaway...

Backtracking a bit more, most people here on the forums generally think of a "stage" as detachment of weight. So it's really by number of detachments + last stage. And there are many ways to get your rocket to CPD (Controlled Planned Disassembly) instead of RUD (Rapid Unplanned Disassembly aka KABOOM)

Taking a mock 15.7 ton lander as payload (the rocket is overpowered so even 20 tonnes isn't going to change things) and actually rebuilding your very Kerbal rocket of MOAR boosters with the same components + decouplers and fuel lines + struts: ~7100dV (ignoring Stage 0, where your own actual lander can get down to Duna surface from Duna orbit)

~7100dV is more than enough unless you are really bad at putting things into Kerbin orbit. If that's the case, a bigger, more dV rocket isn't going to help much. The Mammoths also steer without needing fins.

Notice the decouplers and fuel lines in this setup. Fuel lines all feeding into the central tank and in this setup, you can see the decouplers further below. Struts to hold everything together wobble free. 

With true asparagus staging, ~7850dV. Note the fuel lines feeding into the tank beside it until the final one drains into the center. And as each tank empties, it get's detached. Symmetrical on the other side.

Hope that solves the main problem. Everyone else has given great advice on optimisation as well - stuff to keep in mind for future missions.

[Aegolius13]

I like to work backwards - think of what you need to do last in the mission, then come up with a stage for that.  Then figure out what you need to do to get that stage to its starting point, and so on.  (But keep in mind that stages do not always have to end at end at certain milestones.  You can use the same stage to finish your ascent from Kerbin, circularize, start an ejection burn, and so forth). Here is a quick-and-dirty rocket employing this method:  

 

 

For this mission, as I understand it, you just need to get your 15 ton lander to Duna.  So the final step before that is the trasfer from LKO to Duna orbit.  That's a vacuum only stage, and because we're not landing on anything, you don't need need a ton of TWR (anywhere above .4 is doable without too much hassle).  In an ideal case you need only a little over 1000 m/s of delta-v to get to Duna, but that requires getting an ideal launch window, hitting maneuvers at the right time, and aerobraking on the way into Duna.  For this example, I've gone all the way up to about 2500 m/s, which is a huge cushion.  The Poodle happens to be a great stage for medium payloads like yours (it has the highest ISP of any chemical engine), and one 3200 tank plus one 1600 tank will get you a little over 2500 m/s of delta v, with a starting TWR a little over 0.5. That takes care of our space needs.

Now we just need something that will get the payload + poodle stage to LKO.  For this part, we need around 3000-3500 m/s of delta v, need a TWR that stays at at least 1.2 for most of the way up, but can be a little lower once you're close to LKO.  As a general rule of thumb, when my first vacuum stage is a Poodle, I often like my core stage to be Skipper.  And I often pair the skipper with an orange tank.  So we can try that, but by itself it's way lacking in both TWR and delta v.  We could upgrade to a Mainsail, TwinBoar or even Mammoth, but those are all considerably more expensive options.  So instead I treat this skipper as the upper half or so of my launch rig, and then figure out later how to get THAT partway to orbit.  To up the TWR a little for this sustainer stage, I reduce from from an orange tank to another 32 + 16 combo.  

Now, to build the rest of the launchpad.  Without getting too fancy, we can increase TWR and delta v quite a bit by adding two radial LF boosters, with orange tanks, skippers, and adapter nosecones.  These are asparagus staged to feed the central stack.  This gets us pretty close to the desired stats, but thrust is still a little low for my liking.  Solution: add a couple Kickbacks.  SRB are great final addons for your launch stage since they're very cheap for the thrust they provide, and their bad ISP is less of a problem when they're the first thing to burn out.  And while they can't steer, that will not be a problem if you burn concurrently with gimballed engines like the Skippers.  While opinions vary, I almost never turn the thrust on my SRBs down since I like all the launch TWR my gear will provide me.  Finally, a few stuts or autostruts may be needed to keep the thing together.  

So that gives you a pretty small, cheap and easy-to-fly rocket that should get you to Duna with tons of room to spare.  You probably won't need any more control surfaces, but if you do, a few small winglets at the very bottom will add some more control. 

[Spricigo]

. @Cpt Kerbalkrunch gave a important warning.  Let me add emphasis : get the basic sorted out .

The trouble you have with a interplanetary mission can be traced back to difficulties with setting up a maneuver node,  following a gravity turn or choosing the right engine for a certain flight phase.  So it makes all sense to ask yourself: how can I improve my flight path? How add a component in a given direction will affect my trajectory?  What are the pros and cons of this engine? 

Notice that I didn't said to not go for 'more advanced'  objectives.  Rather that is the small details define if you reach the objective or not. OTOH there is nothing wrong with doing multiply mission in Kerbin's SoI to learn how to launch,  land,  rendezvous,  docking... 

About the current mission:

You may consider a one week before and after the ideal time to transfer as your launch window.  I highly recommend using Transfer planner  to know how much deltaV you need if you depart a bit earlier/later. In any case design a transfer vehicles capable of this maneuver (either poodle+tanks or nerv+tanks)  and then a launch vehicle capable of putting it (and the lander) in LKO.  Docking in LKO may allow for multiple smaller launchs (including refuelling)  but is relatively easy to do in a single launch. Your current design need a severe mass reduction, too much deltaV and thrust for the task at hand. 

[nascarlaser1]

Thxs everyone! in my picture I strapped the fuel lines and struts to the inside of the fuel tanks. I didn't realize they were important otherwise I would of taken a screenshot of the ship from above it to show the inside. @Weywot8 what do you mean by the actual craft? The picture I took was of the launcher I was using (I've changed it since then to mirror everyone's suggestions). I used a fake payload at the time since I thought I was going to upload it after taking he picture, but kerbalx disagreed with me on that idea . I couldn't upload the actual lander because there are some mod parts attached, so the payload would've been a substitute until kerbalx stopped working for me, by which point I'd already closed KSP and didn't want to wait the 15 minutes it takes the game to load (I use waaayy too many mods for stuff) just to take another picture. A picture of the original lander is posted in this thread:

The newest version of the pictured version includes the modifications that @Scarecrow suggested in the above thread, including changing the engines out and removing the heat shield. If you guys do need an up to date picture of my lander/launcher, I wont be able to post it until next week because I probably wont be playing KSP for the rest of the weekend starting today .

Thanks everyone!

 

p.s. don't think it matters but if it does I am still playing 1.2.2.

Edited June 16, 2017 by nascarlaser1

[Weywot8]

11 hours ago, Weywot8 said:

• Very impressed you got this far without understanding maneuver nodes but on the other hand, perhaps now is a good time to figure them out  along with some orbital mechanics.
• ~7100dV is more than enough unless you are really bad at putting things into Kerbin orbit. If that's the case, a bigger, more dV rocket isn't going to help much. 

At this point, have to agree with Spricigo & Cpt Kerbalkrunch - this is not a rocket problem, this is more a Kerbal Piloting 101 problem. It not an issue of having enough dV or even optimising rocket design. The overbuilt launcher and the lander has more than enough dV to get a careful Kerbal to Duna's surface and on a good day, orbit around Eeloo.

I suggest looking at some interplanetary flight tutorials such as below, even though it's a bit old. 

Don't forget about in-flight/deep space course adjustments, aerobreaking for Duna orbit capture and landing and all the other fun stuff.

Read the KSPedia primer on rocket maneuvers.

 

[Spricigo]

4 hours ago, Weywot8 said:

At this point, have to agree with Spricigo & Cpt Kerbalkrunch - this is not a rocket problem, this is more a Kerbal Piloting 101 problem. It not an issue of having enough dV or even optimising rocket design. 

I'd rather say it's a composite problem. There is advance to be made in his design but to take advantage he need better piloting and planning. 

Is easy to feel overwhelmed when there is many issues to deal with.  My advice is to try to simplify things and face the issues one by one.  Training scenarios are a good start, another option is trying to replicate something suggested in a YouTube tutorial.