Need help with a Duna rocket

[RexProcer]

Hey guys. So I'm still pretty new to building the rockets. I've been to Minmus and the Mun many times, and am pretty far along on my tech tree, and have ~1.5m in funds. Been trying to put together a manned rocket to Duna but can't really figure it out. Any advice would be really helpful. I've seen some tutorials, but none that really describe the rocket and none that are particularly recent. Thanks!

[Randazzo]

Well, I'm going to respond to your question with more questions, but they'll potentially lead to helpful insights so bear with me.

1. Are you playing in career or sandbox? Derp

2. If you're playing career, What tech nodes do you have available?

3. Are you using Kerbal Engineer Redux/Mechjeb or playing stock?

Edit: Oh you beat my edit.

Edited May 7, 2015 by Randazzo

[RexProcer]

Career. I have all the necessary 160, and most of the important 300 science nodes available. Stock, don't wanna use add ons until I know more about the game to make it easier. Thanks man.

[NASAHireMe]

Congratulations on your progress thus far! Going interplanetary is your next big step, and once you master it, you're well on your way to conquering KSP (well, as much as one can 'conquer' this game).

If you don't already understand delta-V, I'd start there. Designing interplanetary rockets pretty much starts and ends with knowledge of your delta-v budgets and thrust-to-weight ratios.

Next, good piloting and maneuver preparation (e.g. using maneuver nodes, timing your interplanetary burn using an interplanetary window calculator-- Google it) can drastically reduce the delta-v (and thus, the complexity, size, cost, and weight) requirements of your rocket.

Old tutorials should still mostly apply. Take your Minmus rocket and scale it up a bit. Assuming you get the interplanetary window correct, a flight from LKO to Duna will take around 400 dV more than a flight from LKO to Minmus, assuming you aerocapture/aerobrake to get into a Duna orbit. Then another 400 dV to return from Duna orbit to Kerbin, again assuming you aerocapture/aerobrake to Kerbin.

Going interplanetary is the point in which I would strongly recommend installing either MechJeb or Kerbal Engineer Redux so that you can know your delta-V during construction. Not absolutely necessary (of course, you can do anything in Kerbal without mods), but very, very helpful.

[LordFerret]

Getting there isn't as big a problem as getting back. I would suggest a probe first.

[Gaarst]

Had something in 0.90:

1st stage powered by 1 mainsail with 2xJumbo64 + 2 boosters with Skippers with 1xJumbo64

2nd stage: 1 Skipper with 1xJumbo64

3rd stage (lander + return vehicle): Pod + FL-T800 + LV909

That was enough to get there and back and I usually had enough delta-v with 2nd stage so that it followed me until it crashed on Duna.

Not sure about it though, this is an old design.

It may not be enough for 1.0 but it is a good start.

(I can upload the .craft file if you'd like)

[NASAHireMe]

These two sites are an absolute must. Every player that goes interplanetary plans their journeys with either Alex Moon's Planner or Olex's planner.

[RexProcer]

Thanks for all the advice so far! I started messing around with Olex's planner a couple days back, so I think I get it.

Had something in 0.90:

1st stage powered by 1 mainsail with 2xJumbo64 + 2 boosters with Skippers with 1xJumbo64

2nd stage: 1 Skipper with 1xJumbo64

3rd stage (lander + return vehicle): Pod + FL-T800 + LV909

That was enough to get there and back and I usually had enough delta-v with 2nd stage so that it followed me until it crashed on Duna.

Not sure about it though, this is an old design.

It may not be enough for 1.0 but it is a good start.

(I can upload the .craft file if you'd like)

That would be amazing if you could do that. If nothing else, I can see where a good starting point is.

[Randazzo]

Alright, a few generic tips to start with:

Duna takes little enough to get to that you won't necessarily need nuclear rockets to get there. Without a Delta V readout though, you're taking a bit of a risk. There is supposed to be an in-game Delta V readout available from an Engineer, but it occurs to me now I've never bothered to find it. Hopefully someone else can shed some light on that.

Are you familiar with how to perform the transfer itself? Here are some resources which should help if not:

Interactive illustrated interplanetary guide and calculator for KSP - Very helpful for executing the transfers.

Launch Window Planner - Shows when the next transfer window will be. (You will need to input your in-game date for this to work properly.)

Cheat Sheet - Wiki page with Delta V map - ignore ascent values for now, they will be different.

Getting into orbit and returning is going to be less of an engineering challenge than getting there and landing. Although Delta V values have likely changed since the update, landing on Duna can be significantly more costly to perform a powered landing on and return to space than the Mun. You can reduce or eliminate the fuel required to land by using parachutes, but remember that you need an engineer to repack them, and they won't activate via staging when repacking (you'll have to right click on it to deploy afterwards - assuming it still works the same as 0.90). Ike, Duna's moon, is pretty similar to the Mun itself though.

Best I can do at the moment, when I can get in game I can put together a rocket for you to look at if nobody else has jumped in.

edit- holy ninjas!

Edited May 7, 2015 by Randazzo

[Gaarst]

That would be amazing if you could do that. If nothing else, I can see where a good starting point is.

EDIT: First link was wrong !!!

Here it is.

Edited May 7, 2015 by Gaarst

[Violent Jeb]

If you'd rather not use the launch planners, you can get set your own manoeuvre node fairly successful.

For duna, zoom out on the map screen until you can see duna and kerbin. Fast forward until duna is ~45' ahead of kerbin. If kerbin and duna were in a race, duna would be 1/4 of a lap ahead.

Now, for getting interplanetary encounters closer to the sun, you want to launch on the side of kerbin that is facing the sun.

For interplanetary encounters farther from the sun, you want to launch from the dark side of kerbin.

So, zoom in.

set a node on the dark side of kerbin (in the middle of the dark side), and add prograde until you have a kerbin escape.

Zoom back out, and you will see that your projected orbit (from the man node) will move in towards eve, then as you make a pass around kerbin, you will almost align with duna. If you fine tune the start of your burn from here, adding small amounts of prograde/retrograde, you can usually get a manual encounter. This will take ~1200dv fuel (haven't done it in 1.0.2 yet).

In .90, the entire journey took me around 12500 Dv

Remember that duna has half the gravity of kerbin, and just slightly more than the mun. You will need around 3000dv to get back off duna and get back to kerbin. For interplanetary I usually recommend extra fuel in the transfer stages, so that if you make a mistake or run low on fuel you can re-dock with an orbiting fuel tank before you leave.

[RexProcer]

So I must be doing something wrong. When I'm in game, and have everything set up per the calculator, it tells me my burn out there is about 2500 DV (about a 2m 15s burn_, and even when I got an encounter via the node, I didn't actually get an encounter. I'm doing it in sandbox right now to test it before going into career, but yea. The difference in DV from the node and calculator is gigantic, so I must be wrong somewhere.

Edited May 7, 2015 by RexProcer

[Gaarst]

So I must be doing something wrong. When I'm in game, and have everything set up per the calculator, it tells me my burn out there is about 2500 DV (about a 2m 15s burn_, and even when I got an encounter via the node, I didn't actually get an encounter. I'm doing it in sandbox right now to test it before going into career, but yea. The difference in DV from the node and calculator is gigantic, so I must be wrong somewhere.

It is impossible to execute the manoeuvre exactly as theoretically predicted.

You have to first make a general node in the direction with the approximate delta-v needed, then refine it by a few m/s using prograde/retrograde, radial/antiradial and normal/antinormal.

Usually, using different directions has following consequences:

Prograde/retrograde: moves encounter periapsis left or right when facing target prograde or retrograde (in front or behind planet)

Radial/anti-radial: encounter sooner or later (use this if you see that your position will be in front / behind the one of your target at closest approach)

Normal/antinormal: moves encounter periapsis up or down

And then you will have an encounter but it still may disappear because of the game recalculating trajectories.

So after your first "big" burn at Kerbin, you'll have to do a second one, about halfway to the encounter (or closest approach) to refine and to ensure you will actually encounter the target and get the periapsis you desire.

[MajorThomas]

What a great thread...such helpful people!

Rex, the trip planner not only gives you DV required to reach your target planet, it also tells you when your DV requirements are minimized, i.e., that's a good time to depart. You might have to wait 100-200 days (use time warp) for the relative positions of Kerbin and Duna to allow a good transfer. Kind of analogous to an orbital rendezvous, but with planets. If you wait until the right time, then you can get an encounter with your target when you setup your burn.

Also, remember this (rephrasing advice from Violent Jeb): To get to Duna, which is in a higher orbit around the sun than Kerbin, you need to leave Kerbin in the same direction that Kerbin is going around the sun. That will give you a higher orbit, which should intersect Duna. Conversely, to get to a place in a lower orbit (Eve, Moho) you need to depart Kerbin in the direction opposite Kerbin's movement around the sun.

[RexProcer]

Ok, I think I understand. So I'll have one burn up to 3309 as per the calculator, then get about halfway to target, and do another burn of whatever is needed? Gonna give it a try. Thanks a bunch for helping out a newbie everyone!

[MajorThomas]

Typically a correction burn is quite small, maybe even just 20 m/s if you were fairly close in your initial burn.

Yes, halfway is a good place to do a burn. I'm sure that the mathematics of orbital mechanics could tell you the "optimum" point to do the burn, but it may only save you a tiny bit of fuel compared to just doing the burn midway through your transfer orbit.

TBH, I've not yet been to Duna on v1.0. The trips I've made to Mun and Minmus were pretty much the same as before except for the re-entry, which is much more interesting, eventful and dangerous than ever before. The new aerodynamics and heating might make Duna landings more difficult--I dunno.

In the past I've used drogue chutes, which slow you down part way, from a point higher up in the atmosphere. They worked well for Duna re-entry, which was typically a combo of engine burning and parachuting. But now in 1.0 I see that regular parachutes behave like drogue chutes, slowing you down A LOT more when you initially deploy them, before they fully inflate. Hmm, an idea for a Duna ship is forming...

[Randazzo]

Ok, I think I understand. So I'll have one burn up to 3309 as per the calculator, then get about halfway to target, and do another burn of whatever is needed? Gonna give it a try. Thanks a bunch for helping out a newbie everyone!

Are you referring to your ships velocity?

If you're expending that much dV to get there, something is not right. Including insertion burns, that's as much as an entire round-trip should cost your dV budget (not including anything else). If you've missed your window, you're much better off timewarping to the next one than trying to force a bad transfer - and I don't mean that in a critical "Your transfer sucks!" way, I mean the transfer window is too far away, and the options you have are bad.

Edited May 7, 2015 by Randazzo

[RexProcer]

Yea, I'm not sure what the issue is. The planets seemed to be lined up in the way they should. Not really sure, still troubleshooting.

[RexProcer]

A little update. After many trials and tribulations, I was able to finally land on Duna, albeit not terribly efficiently, i had to use ~15% of my landing stage fuel supply on making sure I didn't go boom. Getting back is something totally different. Any tips on getting back? I guess, how much different is it to leave from Duna than Mun/Minmus? Thanks guys.

[Randazzo]

In theory it will take a similar dV budget to get back as it took you to get there. It should take less for your ejection burn but the insertion burn over Kerbin will be more costly. Usually around 1800 dV but it can be done for less if it's perfect, or more if it's not. Plus you need a tiny bit of juice to deorbit as well, unless you go straight for aerocapture, which may or may not be lethal.

[RexProcer]

EDIT: First link was wrong !!!

Here it is.

So after enough tries to make my fingers bleed, I THINK that unfortunately in 1.0 this ship doesn't have the juice to get back. I may be wrong, but I'm aligning the planets as I should, with Kerbin at a ~-70 degree angle to Duna. Did you use any tugboats or dock with anything in orbit?

[Gaarst]

So after enough tries to make my fingers bleed, I THINK that unfortunately in 1.0 this ship doesn't have the juice to get back. I may be wrong, but I'm aligning the planets as I should, with Kerbin at a ~-70 degree angle to Duna. Did you use any tugboats or dock with anything in orbit?

Your phase angle is not right and so your are wasting a lot of delta-v to do your manoeuvre. Did you calculate it with Olex or AlexMoon's calculators ? Because they give a phase angle of ~45° and not -70°

And it is very possible that this rocket, due to the physics change in 1.0, can no longer do the trip by itself and back; whereas in 0.90 it could do it by itself without refueling in orbit

EDIT: I just saw you should have 45° phase angle to go to Duna from Kerbin, but -70° to go back from Duna. My bad

[RexProcer]

Your phase angle is not right and so your are wasting a lot of delta-v to do your manoeuvre. Did you calculate it with Olex or AlexMoon's calculators ? Because they give a phase angle of ~45° and not -70°

And it is very possible that this rocket, due to the physics change in 1.0, can no longer do the trip by itself and back; whereas in 0.90 it could do it by itself without refueling in orbit

According to Olex, Duna>Kerbin phase angle should be -75. I was able to land on Duna, just not make it back. Sorry for not being clear.

[Beowolf]

Not having enough fuel to make it back is as common as pimples on a teenager. I've been playing two years and my first Kerbal to Duna's surface in my 1.0.2 career game ended up not able to come home. Valentina had enough to get into a polar orbit, though, so it wasn't a big deal as these things go. She spend a couple of years doing EVAs and measuring temperatures over all the biomes.

It wasn't long till I had docking ports and the grabber available for in-space refueling, and then I always send fuel depots to Duna and Eve, and later to Jool. Normally paid for by "build an orbital station" contracts. BTW, when you start getting those contracts, you don't have to put crew in them. "Room for 5 Kerbals" just means room, not warm green bodies. Comes in handy!

edit: It's also handy to send those planets a tow truck. Just a lightweight one-man craft (can be a chair instead of a pod), with a grabber and lots of delta-v. That's how I retrieve ships like Val's, with empty tanks. You can transfer fuel or monopropellant through the grabber, or just tow the ship back to your fuel depot.

Edited May 11, 2015 by Beowolf

[Anglave]

I've done a Duna land-and-return in my 1.02 Career game, let me see if I can help.

Steps for a successful Duna mission:

• Make sure your craft has enough delta-v and an appropriate TWR for each phase of the mission. I recommend referencing a simple Delta-V System Map (values for going ground-to-orbit for bodies with atmospheres are outdated on that map as of 1.x, but the new values are generally lower), and using the Kerbal Engineer Redux plugin to determine the delta-v and TWR of each stage of your craft. No need to use any non-stock parts, just install the plugin and extra information appears in the VAB
  
• Find your departure phase angle and ejection angle using the wonderful Interactive illustrated interplanetary guide and calculator
  
• Put your craft on the launch pad, go to map mode, and time warp to your departure window. Alt-F5 to make a named save here.
  
• Launch to a standard 80km Eastward equatorial Low Kerbin Orbit. The launch stage(s) of your rocket should have between 1.2 and 1.8 TWR on Kerbin, and need ~4k (atmospheric) delta-v.
  
• Go to map mode, zoom out, and set Duna as your target. Check your ascending/descending nodes, you want your orbit to be very close to coplanar with Duna's orbit. (Less than 0.5 degrees off, and better if it's 0.1 or 0.0 degrees off). Correct if necessary with a burn at your upcoming ascending or descending node (use a maneuver node to plan your burn, the pink handles are the ones you want for plane change. Perform plane change at the ascending/descending node only).
  
• Put a maneuver node ahead of your craft, at the appropriate ejection angle.
  
• Pull the prograde handle until your projected maneuver exits Kerbin's SoI. Zoom out, and gently push in on the retrograde handle until your plotted maneuver intersects Duna's orbit. You may see a projected encounter.
  
  • If your maneuver doesn't immediately show an encounter, likely it will show a closest approach. Note the "target position at closest approach". If Duna is further along in its orbit by the time you get there, and you're missing it because you're late, zoom back in and advance your maneuver node along your orbit slightly (grab the gray circle, and drag it farther ahead along your orbit). Zoom back out, apply a bit of prograde or retrograde to your maneuver as necessary, and check where Duna is at closest approach. (obviously you go the other direction if you're arriving at Duna's orbit early, drag the maneuver node back a bit around your orbit).
    
  • Repeat the above to tweak your maneuver until you find an encounter. If you're way off, you might try pushing the apoapsis of your maneuver (Sun apoapsis) out farther past Duna's orbit slightly, this will give you more intersection area to search with.
    
  • Your maneuver shouldn't require any use of the blue or pink handles.

  [*]Once you get an encounter, quicksave.

  • As a check, this maneuver should cost around 1100 delta-v. Allowing 1200 to 1300 in your craft's budget is a reasonable safety margin for human pilot error.
  
  
• If everything looks good, perform the plotted maneuver. (don't forget to quicksave).
  
• Time Warp until about the halfway point of your interplanetary journey. Toss a maneuver node out in front of your craft somewhere (hours or days ahead is fine). Use this maneuver node to "tweak" your approach to Duna. Toy gently with each axis, see if you can get your projected encounter down under 100km. It should take very little delta-v this far away.
  
  • Don't be afraid to just delete the maneuver node and make a new one, this is trial and error.

  [*]If you've got a good "cleanup" maneuver plotted, warp to and perform it.

  [*]Warp the rest of the way until you're about to enter Duna's SoI. Cross the Sphere of Influence boundary at time warp 50x or below.

  [*]As soon as you enter Duna's SoI, turn off time warp, toss a maneuver node out in front of your craft, and do final cleanup of your approach. If you want to aerocapture, plot an intercept around 15km or lower. It helps if it's near equatorial (land near the equator, at least, or your return journey will require expensive plane-change maneuvers). Once you've plotted an acceptable approach, Alt-F5 and make a named quicksave. You may want to come back and adjust for a higher or lower entry into the atmosphere (if you burn up, for example).

  [*]Warp ahead until you're almost in Duna's atmosphere (50km). Let the atmo do its work, this is the exciting part! Take some screenshots.

  [*]As you slow down and the heating effects diminish, deploy your parachutes and/or start your landing burn. Parachutes can help, but you're probably going to have to do a powered landing (I did).

  [*]It should require somewhat less than 1380 (atmospheric) delta-v to do a powered landing on Duna, with a TWR of 2 or more (on Duna). You could land with a lower TWR (anything over 1), but the closer to 1 you get the more dicey your landing will be. I hate having to do a full burn from way up just to avoid lithobraking. The atmosphere will help you slow down significantly, and parachutes can help. Budgeting between 1k and 1200 delta-v for your landing phase should be plenty of margin.

  [*]Piloting a powered landing on Duna is probably easier than landing on Mun, the atmosphere will help reduce lateral drift relative to the surface, and parachutes can help stabilize your craft.

  [*]Touchdown! Take some screenshots, do some science, while away the time until your return window.

  [*]Launch to an equatorial orbit of Duna. The atmosphere stops at 50km.

  • Launching to orbit on Duna is much easier than on Kerbin, more like Mun. It has a lower gravity so requires less thrust, and the atmosphere is pretty thin, treat it more or less like Mun.
    
  • Your Duna orbit stage requires a TWR of 1.2 or greater (on Duna), and about 1500 (atmospheric) delat-v to be safe.

  [*]Check that your orbit is coplanar with Kerbin. (you can set Kerbin as your target).

  [*]Warp to the appropriate return phase angle (you can warp much faster from the tracking station).

  [*]Plot your return to Kerbin the same way you plotted the intercept with Duna. Put a maneuver node at the appropriate ejection angle, and fiddle it around until you find an intercept. Your return should require the same 1100 or so delta-v.

  [*]Perform the maneuver, do a mid-course cleanup maneuver if necessary.

  [*]Just after you enter Kerbin's SoI, plot a maneuver that lets you aerocapture (20km or so altitude should be a capture).

  [*]Perform your final burn and/or landing site selection if you want to be fancy.

  [*]Don't burn up, then pop parachutes and marvel at the blue and green beauty of Kerbin as you float gently down to the surface.

  [*]

Here's the craft I did the journey with. Feel free to fly it, modify it, or just use it as a reference. It's not perfect, but it made the round trip on my first try.

I'm working on collecting a general KSP knowledge base, a collection guides and tips. If you're interested in checking it out, feel free!

Edited May 16, 2015 by Anglave