Duna launcher.

[nascarlaser1]

Hi guys!

It me again... srry about all my posts about duna, I keep realizing that thinking I know how to go to duna is much different then actually knowing how to go to duna .

So here is my (hopefully) last question(s) about Duna. I have my lander built and tested via hyperedit, I've got Kerbal Alarm clock installed and it says I've got 14 Kerbal days till my next transfer window, and I got all my emergency abort plans installed and ready.

The one thing I don't have, is a functioning launcher for all this . My current launcher has 9 of the biggest fuel tanks and mammoth engines (1 in middle of stack and 8 around it for asparagus staging). This can get me all the way to orbit around the sun (this is me practicing without the transfer window), but as soon as I begin my retrograde burn, I run out of fuel.

Am I overcomplicating things? Should I wait till the transfer window appears and then just launch this thing without any testing (since I already know that my current tests aren't exactly accurate without that window? Also, Are maneuver nodes absolutely required for going to duna, or can I just fly a simple mun mission where I just intercept duna and then descend?

 

Thxs!

[Pecan]

Yes, you are overcomplicating things.  No, you should only launch without any testing if you want your launch to be the test.  No, maneuver nodes are not required for going anywhere but how will you know when to burn without one?  Why would you not want one?  You can 'just' aim for Duna and go straight from launch to landing but ... good luck with that ^^.

So let's start at the beginning.  There are three basic steps to going anywhere - i) launching to orbit, ii) transferrring between (origin) orbit and (destination) orbit, iii) landing.

You say you need a 'launcher' but from your descripion I think you're intending to launch and transfer in one go.  Don't, if you can help it.  First; Duna's a lot further away than Mun so setting-up your transfer burn once you're already in a stable Kerbin orbit is a lot easier.  Second; maneuvering in space (ie; your transfer burn at each end, plus any corrections) requires completely different engines from launching through an atmosphere to get into orbit in the first place.

Your current launcher is big.  Maybe that's because your lander is but probably it's because you're asking it to do both those different jobs.  Instead, make it just launch the lander plus a (new) transfer stage.

So, let's start at the end (sometimes it works better that way).  You have your lander so that's the final step covered.  You know it's mass and you can look-up the dV needed to get from LKO to LDO.  Design and build a space-only transfer vehicle that can push your lander between the two planets and establish a stable orbit from which to prepare for landing.  NB: Go for efficient engines; TWR doesn't matter in space (much.  Give yourself at least 0.2-0.4 though or burns will take ages).

Finally, you have a complete space-vehicle (lander+transfer) that you need to launch into LKO.  You know their combined mass and the dV/TWR required to get to orbit.  Now you can design your launch vehicle.

With a set-up like this you need to do a lot more burns than launch-to-land but each is easier, you get much longer to plan them and more time to adjust them.
1.  Launch ascent/orbit insertion: do it as soon as you're ready.  No need to wait for the transfer window as you're only going to LKO.  You've practiced going to LKO.  Should be easy ^^.
(1a, b, c ... correction burns, probably not needed)
2.  Transfer 1, Kerbin escape: set up that maneuver node whenever you like.  14 days is quite a few orbits (depending on altitude) but you can set and adjust it as much as you like, several days ahead.  Alternatively, leave it to just a few hours before you're intending to go and you still have a couple of real hours to tweak it 'just so'.
(2a, b, c, ... correction burns, almost certainly needed)
3.  Transfer 2, Duna capture: It's a lot easier to land from a stable orbit, rather than just screaming in from interplanetary space.  Do yourself a favour - capture into orbit, think about where you want to land, then do it.
(3a, b, c, ... correction burns, depends where you want to land)
4.  Land deorbit/braking: well you've already practised this using hyperedit, so you know better than anyone else how it'll go.

(Parts have changed but to give you ballpark figures my old tutorial return Mun lander (1 kerbal) could do one-way Duna trips.  The lander + transfer stage was 4.72t and it's launch vehicle was 39.2t - one orange tube and one FL-T800)

Edited June 13, 2017 by Pecan

[Kryxal]

I wouldn't be surprised if you're going overboard on your TWR on the launcher ... one tank and one Mammoth is a fair bit more engine than the tank+engine combo needs.  To a great degree, an asparagus setup means the outer parts are just lifting themselves and extra fuel for the inner parts.  Consider either adding fuel or switching to Skippers, and add fuel to the center stack.  A more-efficient transfer engine's also a good idea, and you can afford to finish getting into orbit with it too.

[nascarlaser1]

Thxs @Kryxal and  @Pecan.

 

I was going to try the docking idea, but my docking skills often (read "always") result in 2 space craft becoming 20 pieces of debris ... Is there anyway to build launcher that can do both? My lander is only about 15t (give or take a few decimals) so its not huge. I don't use maneuver nodes mostly because I have no idea how they work .

btw I have no intention of coming home from Duna, so return stages aren't necessary. Jeb was caught stealing the snacks again, so he is banished to duna till I get better at flying .

[Human Person]

3 hours ago, nascarlaser1 said:

This can get me all the way to orbit around the sun (this is me practicing without the transfer window), but as soon as I begin my retrograde burn, I run out of fuel.

Wait! How exactly do you do your interplanetary transfer? Going into a solar orbit and then doing a retrograde burn? Or do you mean you run out of fuel during the insertion burn at duna?

I highly recommend taking a Delta v map and calculating your delta v per stage (or have a mod like MechJeb, Kerbal Engineer or Basic delta v do it for you) to make your rocket meet the requirements as part of the design process.

Edited June 13, 2017 by Physics Student

[nascarlaser1]

8 minutes ago, Physics Student said:

Wait! How exactly do you do your interplanetary transfer? Going into a solar orbit and then doing a retrograde burn? Or do you mean you run out of fuel during the insertion burn at duna?

I highly recommend taking a Delta v map and calculating your delta v per stage (or have a mod like MechJeb, Kerbal Engineer or Basic delta v do it for you) to make your rocket meet the requirements as part of the design process.

This would be my first ever interplanetary travel (that was done on purpose, on my way to minimus I once forget to watch the map and end up close to duna's orbit ). I couldn't figure out how to test my launcher without the transfer window, so I was doing a solar orbit. I used KER to check the delta-v and I think it has enough.

[Human Person]

11 minutes ago, nascarlaser1 said:

I couldn't figure out how to test my launcher without the transfer window, so I was doing a solar orbit. I used KER to check the delta-v and I think it has enoug

I see where the problem is. your testing method is way more inefficient than the actual transfer you'll be doing later on. The Oberth Effect will safe you lots of delta v.

Don't worry.

Edited June 13, 2017 by Physics Student

[FancyMouse]

1 hour ago, nascarlaser1 said:

This would be my first ever interplanetary travel (that was done on purpose, on my way to minimus I once forget to watch the map and end up close to duna's orbit ). I couldn't figure out how to test my launcher without the transfer window, so I was doing a solar orbit. I used KER to check the delta-v and I think it has enough.

All the delta V map assumes you directly burn from planet's low orbit to a transfer orbit. If you burn to escape first, then burn in solar orbit, it's going to be inefficient, and the number you require is going to be a lot bigger than what the delta V map shows. If you just match your fuel delta V number to the map, but you don't choose the right way to burn, then no wonder you're running out of fuel.

[nascarlaser1]

2 hours ago, FancyMouse said:

All the delta V map assumes you directly burn from planet's low orbit to a transfer orbit. If you burn to escape first, then burn in solar orbit, it's going to be inefficient, and the number you require is going to be a lot bigger than what the delta V map shows. If you just match your fuel delta V number to the map, but you don't choose the right way to burn, then no wonder you're running out of fuel.

I am not sure how to test my launcher without the actual transfer window. I don't want to wait for the transfer window to appear, and then find out that my launcher is useless and have to wait for the next window to appear for a second test.

[Aegolius13]

1 hour ago, nascarlaser1 said:

I am not sure how to test my launcher without the actual transfer window. I don't want to wait for the transfer window to appear, and then find out that my launcher is useless and have to wait for the next window to appear for a second test.

I often use a separate "test" save,  and the time warp to the desired window.   

Can you provide a screenshot and/or craft file?  Your rocket sounds immense, so it's likely overkill on thrust, delta v or both.   If you do the launch window and maneuvers right,  getting to Duna barely costs more than going to the moons.  Potentially less if you aerobrake.

[Weywot8]

 

You can test it now actually. If it works, all that means is that on the actual day, you will have some extra dV when you get to Duna. The launch "window" can be very large, depending on how much extra dV you are willing to accept outside of the minimum. See graph below - assuming you are already at a 100x100km orbit around Kerbin (~3600-3800dV to get to to orbit to begin with, dump the early ascent stages). Then a minimum of 1290dV to get to Duna in this transfer window, launching from this orbital height. 

Then 1300dV to break - but we can ignore most of this with aerobreaking

The point being that with 140dV more (~10 % extra), you can leave anytime within the black zone and still make it to Duna. Thats about 25 Kerbin days on either side of the ideal departure date.

So with some spare tankage, that's going to be 1500dV on your interplanetary transfer stage +  probably 600-700dV Duna orbital insertion stage with aerobreaking (you've experimented, so what works best for you, probably use the same engines as interplanetary transfer - dump the empty tanks from before though) + ~1500dV landing stage (your lander)

Work backwards to pick the best engines for each stage to minimse weight and overall tankage. 

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. Or just save the game under a new file name and reload when you are satisfied after experimenting.

Share some pretty pics (zoomed in by stage if possible) of your craft. If it's as big as it sounds we can probably point things out without too much hassle. Some intrepid soul might also build you a new rocket design for the lander with the craft files.

Edited June 14, 2017 by Weywot8
spelling

[Spricigo]

1 hour ago, Aegolius13 said:

I often use a separate "test" save,  and the time warp to the desired window.   

Can you provide a screenshot and/or craft file?  Your rocket sounds immense, so it's likely overkill on thrust, delta v or both.   If you do the launch window and maneuvers right,  getting to Duna barely costs more than going to the moons.  Potentially less if you aerobrake.

I have the same impression,  which was further deepened after I look at suggestions made in OP's previous  thread about Landers. 

Seems like a serious mass saving can still be made. Specially if OP decide to revise his lander, allowing further optimisation of previous stage. 

In any case images/craft file would help. 

 

[Weywot8]

Hmm, had a go at it. Am assuming the 15t lander lets you get home from Duna but a bit of it's fuel can be used for the final landing (and it has chutes). So, mock payload at about 15t.

Interplanetary (1350dv), aerobreak+retrograde burn to orbit Duna (700dV) + initial landing deorbit (700dv) - the tanks are only filled with liquid fuel

Ascent and circularization stage ~3500dv on mechjeb but in reality ~3750dV. I launch at full throttle and then pull back at Mach 2.2ish down to 2TWR so the SRBs burnout and get staged first, followed by the radial tanks. I can get to a 100X100km parking orbit with 3150dV on this setup with ~600dV spare (aggresive tilting on launch). That's alot of extra dV to muck around with. Parachute spam on the initial stages from force of habit - I use the Stage Recover mod. 

An added plus, the ~600dV from a higher TWR engine for the initial part of the interplanetary transfer before switching to LV-N's means less course correction later on.

Play around with the design to fit your launch preferences/handling ability. Everyone's advice on having a lighter lander is a really good one to follow if possible - notice how Pecan's total mass was only 45t vs 270t for this chunky contraption.

 

[Reactordrone]

8 hours ago, nascarlaser1 said:

Thxs @Kryxal and  @Pecan.

 

I was going to try the docking idea, but my docking skills often (read "always") result in 2 space craft becoming 20 pieces of debris ... Is there anyway to build launcher that can do both? My lander is only about 15t (give or take a few decimals) so its not huge. I don't use maneuver nodes mostly because I have no idea how they work .

btw I have no intention of coming home from Duna, so return stages aren't necessary. Jeb was caught stealing the snacks again, so he is banished to duna till I get better at flying .

If you have no intention of returning just launch him there on a Kerbal X. Plenty of fuel in those for a one way mission to Duna. If you want to test interplanetary flight without having to wait for another transfer window you can F5 now and fly as many simulated missions as you like and just reset the game with the F9 key.

[nascarlaser1]

Thxs everyone! either later today or tomorrow if I have time I'll post some screenshots and possibly a craft file (Kerbalx is being annoying lately and sometimes it wont load for me).

[Scarecrow]

A ship capable of getting to Mun and back is certainly capable of getting to Duna, especially if you have no intention of returning.  In fact I used a Mun ship a while back to go to Duna, the only change I made was to add some chutes to the lander.  Job done.

[Cpt Kerbalkrunch]

On 6/13/2017 at 1:45 PM, nascarlaser1 said:

Thxs @Kryxal and  @Pecan.

 

I was going to try the docking idea, but my docking skills often (read "always") result in 2 space craft becoming 20 pieces of debris ... Is there anyway to build launcher that can do both? My lander is only about 15t (give or take a few decimals) so its not huge. I don't use maneuver nodes mostly because I have no idea how they work .

btw I have no intention of coming home from Duna, so return stages aren't necessary. Jeb was caught stealing the snacks again, so he is banished to duna till I get better at flying .

My laptop was on vacation in California (for repair) and just returned home, plus we've been insanely busy at work, so I haven't been stalking the forum as much. Just read through this thread and there's plenty of good advice, but it was this entry that really jumped out at me. This is a game that's heavy on opinion and individualism. You don't need a degree (though it probably helps) and you don't need mods (though they certainly look pretty cool), but the one thing I think is absolutely essential and (almost) impossible to play without is the use of maneuver nodes. It can be done, sure, but it would make the game so incredibly tedious and difficult that almost no one would play it.

Opinions vary on the best way to learn, but for core concepts like maneuver nodes, I think playing through the training missions is your best bet. Trial and error is my favorite way to play, but that's after you have the basics down. There are also untold numbers of videos out there, but (again) for the core concepts of the game, I think the training missions are better because instead of watching someone else do something, you are actually doing it yourself. I don't think I can over-stress the importance this had for my learning curve. I know you're already playing the game, so playing the training missions at this point might feel like you're going backwards, but I think it's worth the detour. As with all things, though, it's just my opinion. Feel free to ignore.

Edited June 15, 2017 by Cpt Kerbalkrunch

[nascarlaser1]

7 minutes ago, Cpt Kerbalkrunch said:

My laptop was on vacation in California (for repair) and just returned home, plus we've been insanely busy at work, so I haven't been stalking the forum as much. Just read through this thread and there's plenty of good advice, but it was this entry that really jumped out at me. This is a game that's heavy on opinion and individualism. You don't need a degree (though it probably helps) and you don't need mods (though they certainly look pretty cool), but the one thing I think is absolutely essential and (almost) impossible to play without is the use of maneuver nodes. It can be done, sure, but it would make the game so incredibly tedious and difficult that almost no one would play it.

Opinions vary on the best way to learn, but for core concepts like maneuver nodes, I think playing through the training missions is your best bet. Trial and error is my favorite way to play, but that's after you have the basics down. There are also untold numbers of videos out there, but (again) for the core concepts of the game, I think the training missions are better because instead of watching someone else do something, you are actually doing it yourself. I don't think I can over-stress the importance this had for my learning curve. I know you're already playing the game, so playing the training missions at this point might feel like you're going backwards, but I think it's worth the detour. As with all things, though, it's just my opinion. Feel free to ignore.

Thxs! . I never ever touched the training missions in the first place lol, so going backwards doesn't concern me.

[Cpt Kerbalkrunch]

1 hour ago, nascarlaser1 said:

Thxs! . I never ever touched the training missions in the first place lol, so going backwards doesn't concern me.

Excellent. By the third training mission I was smiling like an idiot and I knew this was the greatest game ever made and that it would own my free-time from then on. Almost 2,000 hours later I've been proven right on both counts.

I think you're going to be very happy that you decided to run through them (that you've gotten as far as you have without using them at all I find pretty impressive). There are things you'll already know, but plenty you don't yet. I really think it'll make you a better player in a quicker timeframe (and with less frustration). On a personal note, I gave up on the docking mission. I kept trying but got frustrated. Did my first docking in-game like 3 months later (finally realized the key was relative velocity). It was an unforgettable moment akin to your first Mun landing. 

[nascarlaser1]

As requested by @aegolius, @Weywot8 and @Spricigo Here is a photo of my launcher with a fake payload on top. the payload weighs exactly 15.580t (which is as close to the actual lander's weight as I could get it) and the rocket weighs 1,199.4t.

the craft file was not uploading sadly, but as stated the launcher is literally 8 of the big tanks with 1 of the medium kerbodyne tanks on, all arranged around the middle stack that has just 1 of the big tanks in asparagus staging and 1 of the kerbodyne adapters on top since the payload is mk2 in size.. 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.

 

5 minutes ago, Cpt Kerbalkrunch said:

Excellent. By the third training mission I was smiling like an idiot and I knew this was the greatest game ever made and that it would own my free-time from then on. Almost 2,000 hours later I've been proven right on both counts.

I think you're going to be very happy that you decided to run through them (that you've gotten as far as you have without using them at all I find pretty impressive). There are things you'll already know, but plenty you don't yet. I really think it'll make you a better player in a quicker timeframe (and with less frustration). On a personal note, I gave up on the docking mission. I kept trying but got frustrated. Did my first docking in-game like 3 months later (finally realized the key was relative velocity). It was an unforgettable moment akin to your first Mun landing. 

Thxs!

[Cpt Kerbalkrunch]

@nascarlaser1 The guys you tagged have good knowledge and will no-doubt give some good advice, but I already know the first thing they're going to say is that your rocket is bigger than what you need (note I didn't say "too big"; I don't believe there is such a thing). I'm a fan of large rockets myself, but it's mostly because I like multi-Kerbal ships. My landers are often in the 100-200 ton range, which is why I'd have such a huge rocket. My first piece of advice would be to dump the big-S wings. As long as you don't pitch over too far on your gravity-turn, nothing is going to stop those Mammoths. If I ever really feel like I need control in an atmosphere, the Delta Deluxe winglets are my usual choice. Beyond that, I'd say start from the top down and streamline the whole thing. Try to make use of SRB's for power on your launch (Kickbacks are awesome; as any as you need). They're cheap and you don't have to carry them around for very long. I'm on my phone, so I can't see your ship well enough for more specific advice. As I said though, the other guys you mentioned will have good recommendations.

Edited June 15, 2017 by Cpt Kerbalkrunch

[nascarlaser1]

1 minute ago, Cpt Kerbalkrunch said:

@nascarlaser1 The guys you tagged have good knowledge and will no-doubt give some good advice, but I already know the first thing they're going to say is that your rocket is bigger than what you need (note I didn't say "too big"; I don't believe there is such a thing). I'm a fan of large rockets myself, but it's mostly because I like multi-Kerbal ships. My landers are often in the 100-200 ton range, which is why I'd have such a huge rocket. My first piece of advice would be to dump the big-S wings. As long as you don't pitch over too far on your gravity-turn, nothing is going to stop those Mammoths. If I ever really feel like I need control in an atmosphere, the Delta Deluxe winglets are my usual choice. Beyond that, I'd say start from the top down and streamline the whole thing.are use of SRB's for power on your launch (Kickbacks are awesome; as any as you need). They're cheap and you don't have to carry them around for very long. I'm on my phone, so I can't see your ship well enough for more specific advice. As I said though, the other guys you mentioned will have good recommendations.

Thank you! 1 question though.

For all my flights since I learned how to orbit, I have begun my gravity turn a soon as I clear any launch clamps I have. With the SRBs, I cannot turn well. Is it ok that I have to wait to do my gravity turn? All my rockets (except for starter ones in career) use LF/OX, and the ones the use SRBs go straight up and come straight down .

[Cpt Kerbalkrunch]

2 minutes ago, nascarlaser1 said:

Thank you! 1 question though.

For all my flights since I learned how to orbit, I have begun my gravity turn a soon as I clear any launch clamps I have. With the SRBs, I cannot turn well. Is it ok that I have to wait to do my gravity turn? All my rockets (except for starter ones in career) use LF/OX, and the ones the use SRBs go straight up and come straight down .

The lack of a gimbal makes them tougher to maneuver for sure. The Delta Deluxe winglets will fix that. If you have, say, 8 Kickbacks radially around a central fuselage, put a winglet on each one. They have excellent control ability, and this way you dump them with the boosters (since you'll no longer need them, dump the weight). You'll probably need sepatrons to push them away (always a safe bet). As an alternative to the winglets, you can also use Vernors. They have surprising power and can fit almost anywhere. Just turn on RCS and they'll give you good control. Other methods include the regular RCS ports, small engines like the Twitch, or just extra reaction wheels. You can experiment and see which you like best. Some may work better with a certain design, for instance. No matter what, SRB's are definitely worth the extra engineering needed to control them. They're a great, cheap way to get into orbit.

[nascarlaser1]

2 minutes ago, Cpt Kerbalkrunch said:

The lack of a gimbal makes them tougher to maneuver for sure. The Delta Deluxe winglets will fix that. If you have, say, 8 Kickbacks radially around a central fuselage, put a winglet on each one. They have excellent control ability, and this way you dump them with the boosters (since you'll no longer need them, dump the weight). You'll probably need sepatrons to push them away (always a safe bet). As an alternative to the winglets, you can also use Vernors. They have surprising power and can fit almost anywhere. Just turn on RCS and they'll give you good control. Other methods include the regular RCS ports, small engines like the Twitch, or just extra reaction wheels. You can experiment and see which you like best. Some may work better with a certain design, for instance. No matter what, SRB's are definitely worth the extra engineering needed to control them. They're a great, cheap way to get into orbit.

thanks! modifying launcher now!

[septemberWaves]

On 6/13/2017 at 7:45 PM, nascarlaser1 said:

I was going to try the docking idea, but my docking skills often (read "always") result in 2 space craft becoming 20 pieces of debris ... Is there anyway to build launcher that can do both? My lander is only about 15t (give or take a few decimals) so its not huge.

If you can get the two craft close enough to crash them into each other, you're already more than half way to being able to dock them properly. The trick, once you can get them close to each other, is to learn to slow down early enough, and to not accelerate too fast once you're very close. It helps to practice around a low-gravity body like Mun or Minmus. I'd suggest trying out docking every so often. If you try it enough times you will get the hang of it, but you'll never be able to do it if you always respond to the question of "should I use docking?" with "no, it never works out".

That being said, getting 15 tonnes to Duna doesn't really need an orbital rendezvous method. Compared to the image you showed earlier, I think it can be done with only about 1/9 the amount of fuel you're using (ish) in a single-stack two-stage rocket with no boosters and no asparagus staging. That's just a vague approximation but if you use one of the largest Kerbodyne tanks with a Mammoth, and a Rhino with a half-size Kerbodyne tank as the second stage, you should probably be able to transport 15 tonnes to Duna with fuel to spare, provided your ascent profile is efficient (it's not uncommon for players unfamiliar with a gravity turn to waste upwards of 1500m/s of delta-v on an inefficient ascent, and that's more than a Duna transfer takes). And honestly, if the setup I described doesn't work, adding 2 or 4 Kickback engines to boost the first stage will definitely do it. Getting back to Kerbin after is a different matter (though it's really not much delta-v), but I assume you've taken that into consideration with your 15 tonne lander design considering you don't like to dock things.