Need help with obscenely inefficient ship!

[Broax]

Hi all!

I've recently made a successful trip to Duna. I've managed to take a lander to the surface and am about to do the return trip which, hopefully, will also be a success... My problem is my ship is rather big (a total of 436 parts) and I can't help but think it's massively inefficient.

First some information: I use Deadly Reentry and TAC Life Support which creates a couple of necessities (food, water, ablative shields, etc) that need some attention. Also I wanted to make this a 4 Kerbal mission. 2 to stay in orbit and 2 to land on Duna. The ship in turn is comprised of the following modules:

• Engine module: 8 LV-N Nuclear Rocket Engines;
  
• Cargo module: Life support systems, solar panels and batteries, scientific instruments, and a cargo bay with emergency supplies (strut points, pipes, etc.);
  
• Landing module: Lander can, backup engine for descent (apparently it was useful as I didn't pack enough chutes), ascent stage, etc;
  
• Two return capsules: MK1-2 pods with 0-10 monopropellant engines with enough fuel to break orbit;
  
• A "living" module: Partially because I needed to stabilize the center of mass after adding the LM and partially because I think such a long trip on small capsules would suck. Since half of the point of adding this was to center the center of mass I added a mobile lab, a hitchhiker module and PPD-12 Cupola Module which would become the command module;
  
• Finally I added a small escape ship with small engines and enough fuel to bring the MK1-2 pods back to Kerbin in case something went wrong with the main ship. This also was put in so I could place a couple of extra struts and give some extra stability to the ship.
  

Since the ship is so big I had to build it in orbit so it took me about 7 launches to strap everything in place, refuel, and prepare for the trip.

Image one: Sending the engines to orbit.

And yes, I used Mechjeb as doing all this by hand would be horribly tedious and I couldn't be bothered to make so many launches.

Anyway, after a long while I managed to dock everything in place, reinforce the structure with a modest amount of struts and blast heading for Duna....

Image two: Full ship orbiting Duna.

Here you can see the full ship... On the back (obviously) you have the fuel and engines, in front of them lies the mentioned cargo bay, then (to the left) the lander and (to the right) the "command" module. Both up and down you have the two return pods and just in front of them you get the small return ship. You might also notice that both Bob and Bill are on the LM while Jebediah is on the Command module. I know the command traditionally goes down but Jeb felt he was having all the fun so he decided to pass the honor down to his crew. What can I say? I like to imagine their story...

Anyway... Am I horribly clumsy? Is there a simpler way to take 4 Kerbals down do Duna and back? Is the massive amount of fuel I used too much? I often see so many people with much simpler designs I can't help but wonder if what I've done is just too clunky...

TL;DR: I made a huge ship to take me to Duna. I can't help but think how much bigger I would make one to go even farther away... Can you share some tips on how to move Kerbals around?

On extra bit of information that might be useful... The total mass of the ship is 178,29 tons (that's 23,73 tons from the lander and 154,56 tons from the "main" ship).

Also any general tips or comments on my ship/mission are well appreciated. There's also a bonus poll so I can figure if 400 parts is too much or not.

Thanks for the help everyone!

EDIT: Marked this as "Answered!"... I'll make sure everyone gets +1 rep for the good help!

Edited September 29, 2014 by Broax
Added information about the mass of the ship

[BDelacroix]

Not unusual. The fact you can strut in space is a huge boon. I have never found that mod nor have I convinced myself on if I want to use it or not.

I don't bother with escape ships since if something goes wrong, I just build another ship to go get them. However, I am not using life support, so there is no reason to just go rescue a crew 5 years out. It also means I don't bring supplies.

In general, I have a thin scaffold with docking ports on it and a large one up front and at the back. I then ship up dual engine pods to put on them (I prefer pullers to pushers as it avoids the inverted pendulum problem of control). You have to imagine where the center of mass is and keep it generally in the center or you will begin to spin. I also find docking port connectors are rather rubbery and appear to only connect at a single point rather than around the ring. That means they flop. The advanced wheel is also apparently made of rubber, those flop.

You can kind of guess the center of mass as the camera apparently focuses on that center when viewing the ship. Zoom way in and if you are in between your engines, you are likely to be ok.

Some tricks I've learned in moving unwieldy ships:

1. Since you are using mechjeb. Turn on smooth throttle and I use limit throttle to 10% if I have a construct that is particularly wobbly. It means longer burns, but plan for that. I also limit to 40m/s and terminal velocity. It saves mucho fuel. You aren't likely to run into those limits with heavy craft.

2. I used to try to put RCS on things. I have moved away from that. It is only really useful for docking. So any ship you want to dock with, go ahead and put on the RCS. I'd love if mechjeb would only use RCS for the forward/backward movements and leave turning to the wheels, I haven't found a way to make it do that yet.

3. The one exception to #2 is my little tugs. They are all RCS only fueled. That is because they are made to haul around the parts once they are near each other. Which I guess is a sort of secondary docking.

4. Turning large ships takes a long time. RCS can help but I find it makes the ship wobble, badly sometimes. So I stick to just well placed wheels now. It is a lot slower, but a lot less wobbly. Not going to do quick turns.

[Broax]

Thanks for the tips!

Definitely useful regarding the maneuverability specially since I never game much thought to putting the engines on the front... But in large® ships it does make a lot of sense...

As for putting struts in space, I find it immensely useful for making larger ships (or at least to give some stability for ship that built in modules but not so much for stationary objects like space stations). If you decide to use it I use the Kerbal Attachment System (KAS). It really good 'cause it not only lets you build struts but allows you to do lots of stuff like installing pipe ends to allow resource transfers between parts that aren't connected or don't have crossfeed. It also has fully functioning towing parts like winches or magnets, it allows to add small parts to ships like small photovoltaic panels or small batteries (it's a life saver if you forget to deploy the panels until the ship runs out of power) and it has small containers to store parts.

Not only it expands what you can do in the game it also gives you something to do while on EVA. It's one of the most enjoyable mods I have and one of the ones I most highly recommend.

[Stratzenblitz75]

At a glance, I can see a few things you can do to reduce the mass of your craft and therefore, make it more efficient:

1. I see 2 Rockomax MK 55 radial engines on your lander. These engines are TERRIBLE. They only get 320 ISP in vacuum and they have mediocre TWR. Get rid of them and replace them with something more efficient like a few Rockomax 48-7S or an aerospike. With a more efficient engine, you'll need less mass in fuel.

2. I see a lot of radial mono prop tanks and a large mono prop tank on your transfer stage. This mono prop is really weighing your ship down; the mass of all the containers I see on your transfer stage is 7.9 tons! You do not need this much mono prop for docking, remove the large tank and reduce the amount of radial tanks (2 radial tanks should be plenty).

3. I see you have two Rockomax HubMaxs. These two modules have a mass of 3 tons! Replace them with something else.

4. There might be a problem with you return pods. A Duna->Kerbin transfer takes more than 100 days and I don't see enough life support on your return pods (unless you have it clipped inside the ship somewhere) to survive the journey. If you want life support for 3 kerbals to survive the return trip then you would have to add at least 3 tons of life support (which means you have to add more fuel to move that extra mass). Also, since you only have 4 Kerbals, you don't need two Mk1-2 command pods to bring them home. 1 return pod consisting of a Mk1-2 pod and a Mk1 pod would work better. Also if you want to take the return pod approach, I think it would be better to have just have 1 return pod and have 1 of your NERVA engines undocked-able so you can dock it to your return pod. As it stands, your two current pods are adding 18 tons of mass to your ship. (which is a lot!)

5. Consider removing the cupola. I know the view is pretty, but that view costs 4.5 tons.

6. Also consider removing some of the NERVA engines. I know the burn will take longer but its worth it in the mass you get to save. (if the burn is too long, use "periapsis kicks" to split it into multiple burns.)

Basically, this is what you do to make your ship more efficient. Look at every part on your ship and determine if you can use a better part or whether you even need it at all. By removing unnecessary mass you can reduce the size of your transfer stage.

I hope you find my advice somewhat useful.

[Red Iron Crown]

I'd love if mechjeb would only use RCS for the forward/backward movements and leave turning to the wheels, I haven't found a way to make it do that yet.

That is an option in either the RCS Balancer or Translatron window (can't remember which at the moment and I'm not on my KSP computer to check). One of my favorite features of MJ, only uses monoprop for translation and reaction wheels for turning.

[Taki117]

Generally speaking you need to cut down on your weight. You only need about 1300-1500 m/s to get off Duna, and it only has 1 surface biome. (plus flying at, upper atmosphere, space near, and space high over) so really you don't need the science lab, and you can skip the materials bay because it's very heavy. As others have pointed out your lander engines are very inefficient, and you have far too many engines. Those structural panels aren't doing you any favors either, nor is all that RCS. You should really only have RCS on your lander, and even then only a minimal amount. If you are having issues with docking I suggest lots of practice rendezvous and docking in LKO so that you are really efficient with it. Something else that doesn't seem to have been touched on is transfer windows. It's best if you leave during the window because you won't need as much fuel to get there, or back.

[Broax]

At a glance, I can see a few things you can do to reduce the mass of your craft and therefore, make it more efficient:

1. I see 2 Rockomax MK 55 radial engines on your lander. These engines are TERRIBLE. They only get 320 ISP in vacuum and they have mediocre TWR. Get rid of them and replace them with something more efficient like a few Rockomax 48-7S or an aerospike. With a more efficient engine, you'll need less mass in fuel.

2. I see a lot of radial mono prop tanks and a large mono prop tank on your transfer stage. This mono prop is really weighing your ship down; the mass of all the containers I see on your transfer stage is 7.9 tons! You do not need this much mono prop for docking, remove the large tank and reduce the amount of radial tanks (2 radial tanks should be plenty).

3. I see you have two Rockomax HubMaxs. These two modules have a mass of 3 tons! Replace them with something else.

4. There might be a problem with you return pods. A Duna->Kerbin transfer takes more than 100 days and I don't see enough life support on your return pods (unless you have it clipped inside the ship somewhere) to survive the journey. If you want life support for 3 kerbals to survive the return trip then you would have to add at least 3 tons of life support (which means you have to add more fuel to move that extra mass). Also, since you only have 4 Kerbals, you don't need two Mk1-2 command pods to bring them home. 1 return pod consisting of a Mk1-2 pod and a Mk1 pod would work better. Also if you want to take the return pod approach, I think it would be better to have just have 1 return pod and have 1 of your NERVA engines undocked-able so you can dock it to your return pod. As it stands, your two current pods are adding 18 tons of mass to your ship. (which is a lot!)

5. Consider removing the cupola. I know the view is pretty, but that view costs 4.5 tons.

6. Also consider removing some of the NERVA engines. I know the burn will take longer but its worth it in the mass you get to save. (if the burn is too long, use "periapsis kicks" to split it into multiple burns.)

Basically, this is what you do to make your ship more efficient. Look at every part on your ship and determine if you can use a better part or whether you even need it at all. By removing unnecessary mass you can reduce the size of your transfer stage.

I hope you find my advice somewhat useful.

Thanks for the tips!! I'll make sure to change the engines on the lander module. You gave me a good couple of tricks to reduce the weight. As for the life support the ship has more then enough, most of it is hidden under the structural panels...

I'll have to rework the whole ship... but this is a good starting point..

Generally speaking you need to cut down on your weight. You only need about 1300-1500 m/s to get off Duna, and it only has 1 surface biome. (plus flying at, upper atmosphere, space near, and space high over) so really you don't need the science lab, and you can skip the materials bay because it's very heavy. As others have pointed out your lander engines are very inefficient, and you have far too many engines. Those structural panels aren't doing you any favors either, nor is all that RCS. You should really only have RCS on your lander, and even then only a minimal amount. If you are having issues with docking I suggest lots of practice rendezvous and docking in LKO so that you are really efficient with it. Something else that doesn't seem to have been touched on is transfer windows. It's best if you leave during the window because you won't need as much fuel to get there, or back.

Thanks for the comment... Initially the science lab was there to give some counter-weight for the landing module to the center of mass could be more aligned to the center of thrust.

I'm gonna change the engines for lighter and more efficient ones and try to work on my docking skills... Sometimes I'm able to dock in a couple of seconds but sometimes it still takes for ages!

Thanks for the tips everyone!

[Taki117]

Thanks for the comment... Initially the science lab was there to give some counter-weight for the landing module to the center of mass could be more aligned to the center of thrust.

I'm gonna change the engines for lighter and more efficient ones and try to work on my docking skills... Sometimes I'm able to dock in a couple of seconds but sometimes it still takes for ages!

Thanks for the tips everyone!

A tip for docking is to use your RCS as little as possible. Get lined up and speed matched, then close the distance. A good rule of thumb is 1/100th your distance until you are about 1km away, then it should be 1/10th your distance, docking should be no more than 1 m/s. RCS is used mainly for lateral translation as you make your approach. Also, don't be afraid to move your target port to face your incoming ship, it works both ways. Also, might I suggest NavyFish's Docking Port Alignment Indicator?

[Yakky]

At a glance, I can see a few things you can do to reduce the mass of your craft and therefore, make it more efficient:

1. I see 2 Rockomax MK 55 radial engines on your lander. These engines are TERRIBLE. They only get 320 ISP in vacuum and they have mediocre TWR. Get rid of them and replace them with something more efficient like a few Rockomax 48-7S or an aerospike. With a more efficient engine, you'll need less mass in fuel.

2. I see a lot of radial mono prop tanks and a large mono prop tank on your transfer stage. This mono prop is really weighing your ship down; the mass of all the containers I see on your transfer stage is 7.9 tons! You do not need this much mono prop for docking, remove the large tank and reduce the amount of radial tanks (2 radial tanks should be plenty).

3. I see you have two Rockomax HubMaxs. These two modules have a mass of 3 tons! Replace them with something else.

4. There might be a problem with you return pods. A Duna->Kerbin transfer takes more than 100 days and I don't see enough life support on your return pods (unless you have it clipped inside the ship somewhere) to survive the journey. If you want life support for 3 kerbals to survive the return trip then you would have to add at least 3 tons of life support (which means you have to add more fuel to move that extra mass). Also, since you only have 4 Kerbals, you don't need two Mk1-2 command pods to bring them home. 1 return pod consisting of a Mk1-2 pod and a Mk1 pod would work better. Also if you want to take the return pod approach, I think it would be better to have just have 1 return pod and have 1 of your NERVA engines undocked-able so you can dock it to your return pod. As it stands, your two current pods are adding 18 tons of mass to your ship. (which is a lot!)

5. Consider removing the cupola. I know the view is pretty, but that view costs 4.5 tons.

6. Also consider removing some of the NERVA engines. I know the burn will take longer but its worth it in the mass you get to save. (if the burn is too long, use "periapsis kicks" to split it into multiple burns.)

Basically, this is what you do to make your ship more efficient. Look at every part on your ship and determine if you can use a better part or whether you even need it at all. By removing unnecessary mass you can reduce the size of your transfer stage.

I hope you find my advice somewhat useful.

I generally agree with Stratzenblitz75. But in particular, I wanted to underscore how many NERVA engines you have and how much they weigh. At 2.25 tons each, you have 18 tons of NERVA engines. For interplanetary transfer stages, you really only need one engine, not 8, since you don't need to have a high thrust to weight ratio. That will save you a huge amount of mass. See if you can design a configuration that just has a single NERVA engine with drop tanks that you can dispose as the fuel gets used up.

Granted having only one NERVA will lead to some tediously long burns. Your Kerbin escape burn will probably be too long to be feasible to complete in only one orbit, so you'll have to do it over the course of two or more orbits, boosting a little each time as you come around to the optimal point in the orbit, until finally you escape. (This is more efficient than having a single very long burn where much of the thrusting occurs too far away from the optimal point.)

Edited September 28, 2014 by Yakky

[technion]

6. Also consider removing some of the NERVA engines.

I know it's the controversial thing, but I'd drop several of them. There's 18T worth of LV-N there and that reaches a point where the efficiency gains from the engine are overtaken by all that weight. Personally, I would:

* Ditch the four on the outside altogether, and replace them with skippers

* Run fuel lines from the outside tanks to the inside

* Run the outside tanks as a "transfer booster" stage, which will make the transfer much more efficiency and fuel friendly

* Decouple those tanks when empty

* Reduce the engines on the orange tank from four to three. That central stage should still provide enough dv for capture + return home (I'm assuming most of that top part is the lander and not returning)

[Stratzenblitz75]

It's best if you leave during the window because you won't need as much fuel to get there, or back.

This. If you aren't already, you need to launch during optimal launch windows to save the most fuel. To do this, I highly recommend you use this launch window planner. Give it a time frame, an origin, and a destination and it will find the best launch window within that time-frame, tell you how much Delta-V you need and tell you what ejection angle to use.

I generally agree with Stratzenblitz75. But in particular, I wanted to underscore how many NERVA engines you have and how much they weigh. At 2.25 tons each, you have 18 tons of NERVA engines. For interplanetary transfer stages, you really only need one engine, not 8, since you don't need to have a high thrust to weight ratio. That will save you a huge amount of mass. See if you can design a configuration that just has a single NERVA engine with drop tanks that you can dispose as the fuel gets used up.

Granted having only one NERVA will lead to some tediously long burns. Your Kerbin escape burn will probably be too long to be feasible to complete in only one orbit, so you'll have to do it over the course of two or more orbits, boosting a little each time as you come around to the optimal point in the orbit, until finally you escape. (This is more efficient than having a single very long burn where much of the thrusting occurs too far away from the optimal point.)

This a certainly true in most cases; one NERVA will usually be a better option than multiple. However, I do not recommend using 1 NERVA engine for heavy ships (like yours). Seriously, at one point, your sanity is more important than saving fuel. I once did 9 periapsis kicks to perform an escape burn with my ~80 ton ship. No-one should have to be subjected to such tedium.

Also, there are cases where having a higher TWR on your transfer stage is important. For example, a burn from Kerbin to Jool requires about 1 Km/s Delta-V past Kerbin escape velocity (for about 2 Km/s in total for the transfer). In this case, you can't do periapsis kicks to break this 1 Km/s figure down into multiple burns (since you're on a escape velocity). Instead, its better to just add more engines and complete the 1 Km/s Delta-V Kerbin escape burn at Kerbin periapsis to take full advantage of the Oberth effect. (if that makes any sense at all)

[technion]

Also, there are cases where having a higher TWR on your transfer stage is important. For example, a burn from Kerbin to Jool requires about 1 Km/s Delta-V past Kerbin escape velocity (for about 2 Km/s in total for the transfer). In this case, you can't do periapsis kicks to break this 1 Km/s figure down into multiple burns (since you're on a escape velocity). Instead, its better to just add more engines and complete the 1 Km/s Delta-V Kerbin escape burn at Kerbin periapsis to take full advantage of the Oberth effect. (if that makes any sense at all)

A similar issue is the trip I just made to Moho. While setting up the transfer with precisenode, literally one dv in any direction was enough to lose the intercept, and 2dv in some directions was enough to even lose the separation markers. This means the burn needs to be exceedingly accurate. The moment you try to do it over multiple periapsis kicks, where the time you spent doing one orbit can be significant, you'll end up way from the target.

[technion]

I should have said this earlier but.. I don't see parachutes.

You are using chutes to land on Duna right?

[Frank327]

I don't know how difficult the mission is with life support and heat shielding but this was my duna + ike mission with at least the habitation module.

In my experience you can make sleek and efficient spacecraft if you keep it well organized. Keep the main ship and the lander apart so you only need one docking port and you don't get problems with the centre of mass. Your construction with the hubmax looks really odd, though I don't know if it matters much. Also you never need as much rcs as you put on the craft. On this ship I used the lv909 as a one size fits all engine, but that was because it's in career mode and I didn't unlock nukes yet.

[Broax]

Wow... I did get a lot of replies!

Thanks for the tips everyone. It seems to be the consensus I could do with a lot less weight and better planning. Also I probably should do a bit of practice so I can feel confident with (a lot) less RCS fuel. As for the amount of nuclear engines... I agree that 8 engines probably is a bit of overkill and probably does more harm that good but I wouldn't do this with only one engine as I wouldn't survive the boredom of such a long burn and that required corrections for multiple burns would be too much of a hassle...

As for having enough food/parachutes, that wasn't an issue as I did land safely on Duna's surface! The chutes are all only on the Landing Module and Return Pods. Food supplies are a bit worrying but I think it'll be just enough for the return trip.. The two side tanks are both going to be separated from the main ship (if you look closely they don't have any fuel left because they're feeding the main tank). I just kept them for the screen 'cause I wanted to show the full thing...

I've received a lot of good tips for future missions and this will be helpful designing future rockets. I seem to be too fixed on the traditional rocket design so I'm going to start building things around the ship instead of always going for the "big tube" design.

As a token of my appreciation (and for bragging rights ofc) here's a pic of my crew on the surface!

Sorry for the last image being so dark but my screen was set with high brightness at the time so I forgot to turn on the lander lights...

Once again thanks everyone for the help! I'm going to go ahead and set this to "Solved"!