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To Spaceplane, Or To Not Spaceplane


Scarecrow71
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I am in the plannng phase for my Jool-5 run as part of the Kerpollo Challenge, and I know what I want to build as the mothership.  What I intend on doing is having 6 completely expendable landers, one for each moon and then one to put in Jool's upper atmosphere to collect science with.  I am sure I could save some weight by using a single lander, but I gotta have all that fuel anyhow...and I want the Level Three nod here (a different Kerbal landing on every moon).

So, the question here is what type of lander should I use?  Should I go traditional, with a can or one of the Munar modules?  Or do I use spaceplanes to land and return?  Are there advantages or disadvantages to using either?

I've seen a lot of people use a Spaceplane as the mothership with landers in the cargo bay, but I really want to do something different than that.

Any thoughts or ideas?

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Unless there’s an atmosphere there’s no point using a space plane- especially for Tylo.

A simple design of Mk1 lander can - FL-T400 fuel tank - Terrier is enough to land on Pol, Bop and Vall, plus you can stick an expendable stage underneath it and use it for Tylo too, so that one lander can do 4/5 moons. A Laythe SSTO plane can be done with relative ease compared to Kerbin, the lower gravity and thinner air makes it easier to accelerate and you’ll get closer to orbital velocity on air-breathers alone.

 

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One problem you’ll run into is that a Tylo lander is fairly massive.  Spaceplanes can become enormous when you start adding a lot of weight.  This can be overcome, but it is a problem.

Next, if you are planning on using your large space plane launch vehicle to land on Laythe, leaving a small orbiter above.  It is not easy finding a really long flat spot on Laythe, and landing an enormous plane is difficult.  It can be done, of course, but I prefer taking smaller planes to the surface of Laythe.  With a plane big enough to launch a Jool-5 mission- I personally would not want to land something that big on Laythe.

9 hours ago, jimmymcgoochie said:

Unless there’s an atmosphere there’s no point using a space plane- especially for Tylo.

I don’t think I can say that any better.  I’m not 100% convinced that a space plane is even the best choice for Laythe- I just like using them.  But the rest of Jool’s moons have no atmosphere, so there would be no benefit for using planes.  Tylo is hard enough already, using useless airplane parts would unnecessarily complicate your Tylo mission.

9 hours ago, jimmymcgoochie said:

A Laythe SSTO plane can be done with relative ease compared to Kerbin, the lower gravity and thinner air makes it easier to accelerate and you’ll get closer to orbital velocity on air-breathers alone.

Also this.  My philosophy is any plane you can get to Kerbin orbit will easily get to orbit at Laythe.  I think the biggest advantage to using a plane at Laythe is the ability to adjust your landing site if needed.  The islands on Laythe can be difficult to hit with a ballistic entry and parachutes.  

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38 minutes ago, 18Watt said:

Tylo is hard enough already, using useless airplane parts would unnecessarily complicate your Tylo mission

Can you explain this please?  With no gravity or atmosphere, what is it that makes Tylo difficult?

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12 minutes ago, Scarecrow71 said:

With no gravity or atmosphere, what is it that makes Tylo difficult?

Oh, Tylo has plenty of gravity.  I believe it is similar to Kerbin in both size and mass (therefore gravity..).  So to get from the surface of Tylo to orbit, you'll need roughly the same dV as it would take to get to orbit of Kerbin.

What makes it worse is that during landing there is no atmosphere to slow you down.  Landing on Kerbin doesn't require and dV at all- let the atmosphere slow you down, and then use parachutes or wings to gently hit the surface.

But on Tylo, you will also need an incredible amount of dV to land there.  And then the same amount of dV to get back to orbit.

You may be confusing Tylo with Bop or Pol.  Bop and Pol are tiny, and require very little dV to land on.  Tylo is big, and requires a lot of dV both for landing and getting back to orbit.

I don't recall what the dV maps say about Tylo, but I suspect they will suggest ~2400 dV.  That means you need 2400 to land, then another 2400 to get back to orbit.

I usually aim for well over 3000 dV for landing at Tylo, because unless your TWR is high your landing burn will not be very efficient.   For the ascent from Tylo I like to have at least 2600 dV, which will just get me to orbit.  I like to have a little fuel left to maneuver to rendezvous and dock too.

Edit:  I think you use Mech Jeb?  Mods like that can help you perform a more efficient burn to the surface.  But it's still going to take over 2400 dV to get from a 15 km Tylo orbit to the surface.

Edited by 18Watt
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3 hours ago, Scarecrow71 said:

Well, that certainly changes the approach i was gonna use.  Or, rather, forces me to adjust the lander I was going to use specific to Tylo.  But that is some good info.  Thanks!

Having done a couple of Grand Tours (landing on every solid body in the system) I can safely say that Tylo is second only to Eve in terms of delta-V requirements, and is the highest in terms of landing delta-V because it's nearly the size of Kerbin, has a bit less gravity and no atmosphere to aerobrake in like Eve, Kerbin and even Laythe. First focus on getting back into orbit from the surface, then build your descent stage to get that ascent stage down to the surface intact and without using its own fuel.

Laythe is the only place other than Kerbin where air-breathing engines work. Air-breathers are an order of magnitude more efficient than rockets plus planes can fly to a nearby island in a way rockets cannot so of course you're going to use a plane on Laythe. Designed right, you might not even need oxidiser at all- a good jet engine plus a NERV can get you to orbit.

A simple lander can - FL-T400 - Terrier lander can land and return from Vall, so will be enough for Bop and Pol too. With a bit of tweaking, that same design could also serve as your Tylo ascent stage which means you only need to take one lander, one Laythe plane and one Tylo descent stage with you instead of five different landers, cutting weight, cost and part count in one fell swoop.

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4 minutes ago, jimmymcgoochie said:

instead of five different landers, cutting weight, cost and part count in one fell swoop.

I have a tendency to overthink, and therefore over-engineer.  I am looking at using multiple landers because:

  1. It helps me keep easy track of dV for each surface; and
  2. I plan on transferring leftover fuel back to the main ship, which helps with overall fuel needs; and
  3. I'd rather have it and not need it instead of need it and not have it.

With this being my first Jool-5, I want to overthink and make mistakes so I can identify and correct them next time.  However, lot of good info from both you and 18Watt.  And for that I say thank you!

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I would use one lander for Val, Pol and Bop. The benefit here is that the lander who can land and take off from Val should be able to get to Pol and Bob from Val or Tylo orbit. 
This saves fuel over using the mothership. Spaceplanes works well on Laythe, they have the benefit of being very fuel efficient. 

Tylo is hard to land on, require lots of dV and things happens vast. Will almost advice against using the default lander as an accent stage for an Tylo lander as TWR and landing leg requirements will be much higher than you need for other places, You will also have to take the legs with you while you can drop all extra weight on takeoff. 

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1 hour ago, magnemoe said:

This saves fuel over using the mothership. Spaceplanes works well on Laythe, they have the benefit of being very fuel efficient. 

Per the rules of the Kerpollo Challenge, I must have a ship in orbit with a Kerbal in it over every body I land on.  So the mothership has to be in orbit around Val when I land on Val, and in orbit over Laythe when I land there, and so on.

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6 minutes ago, Scarecrow71 said:

Per the rules of the Kerpollo Challenge, I must have a ship in orbit with a Kerbal in it over every body I land on.  So the mothership has to be in orbit around Val when I land on Val, and in orbit over Laythe when I land there, and so on.

Got it, and yes it make some realism sense unless your lander is pretty large. 

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23 hours ago, Scarecrow71 said:

Per the rules of the Kerpollo Challenge, I must have a ship in orbit with a Kerbal in it over every body I land on.  So the mothership has to be in orbit around Val when I land on Val, and in orbit over Laythe when I land there, and so on.

nothing says you have to stop at mothership and lander. indeed, having done a lot of grand tours, i find the best architecture is three-fold: mothership, lander, and taxi.

the taxi is a smaller mothership that can ferry your lander from the mothership to low orbit, and back.

consider it: the mothership is big, and expensive to move. if you have to orbit every moon, it uses up lots of fuel. you want to park it somewhere, and use its engines as little as possible.

the lander needs a high thrust to fight gravity. it must have big engines, to get the high thrust. all the weight from the engines is going to kill its deltaV, and adding fuel will force you to add even bigger engines. you don't want your lander to be too heavy with fuel.

so, how to get your lander from the mothership without increasing fuel consumption too much? The taxi is the answer to that. the taxi is small enough, only slightly bigger than the lander. but it has low power, high efficiency engines, so it's much more fuel-effective. tipically i use nervs for the taxi, while the lander needs chemical engines, in your case tipically terriers.

the taxi can ferry the lander from wherever the mothership is parked to low orbit. it allows for a much smaller lander, because the lander can now hold only the bare minimum of fuel to land and orbit, and it's much cheaper than using the mothership for the same purpose.

and of course, in your case it will also let you keep an astronaut in orbit while you land.

Edited by king of nowhere
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@king of nowhere

You need enough fuel for the motheship to get to Jool and back, and you need enough fuel to land on every moon.  You also need enough fuel for the taxi to get to every moon.  I dont see how that is any different than not using a taxi at all?

I'm also currently struggling with ship design to just get to Jool and back; fuel is becoming an issue as I need enough for all 5 moons...and Tylo has serious fuel requirements.  Isn't adding a taxi just increasing complexity unnecessarily?

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I don't remember how much of your tech tree is unlocked, but if you have ISRU available that is helpful.  Pol and Bop are good candidates for ISRU refueling.

Otherwise, your approach of designing a mission backwards seems good to me.  In other words, figure out how to do the landings, then figure out how to get the equipment out there, then figure out how to get the whole thing into orbit of Kerbin.

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31 minutes ago, 18Watt said:

I don't remember how much of your tech tree is unlocked, but if you have ISRU available that is helpful.  Pol and Bop are good candidates for ISRU refueling.

Otherwise, your approach of designing a mission backwards seems good to me.  In other words, figure out how to do the landings, then figure out how to get the equipment out there, then figure out how to get the whole thing into orbit of Kerbin.

I have never done ISRU before.  Not that this is a deterrent; I had never done interplanetary, or docking, or EVA maneuvers before either.  I've also never had this much of the tech tree unlocked before, so I have the parts to play with.

I have all but the final tier unlocked, so I do have mining capabilities available.  But adding this to any launch adds a whole new host of problems and concerns, as well as parts needed to deal with this.  Ore containers, and drills, and survey scanners, just to name a few.  And I have to read up on how to do it, which again isn't a deterrent...but it will slow me down.

My issue in design right now is height.  As in, the rocket is too tall for the VAB, which means I am out of vertical space to build.  I have scrapped my original idea of multiple landers, as well as landing different Kerbals on every moon.  I built a Tylo lander that has ~6000 total m/s of dV, so that should work.  The issue beyond that, and apart from height, then simply becomes fuel.  I need probably twice that to do all 5 landings, and then at least 12000 to get to Jool and back and get into orbit of every moon.  And then 3400 minimum to get into LKO.  That is ~28000 m/s of total dV.  That is a lot of fuel.

I am going to go read up on ISRU now.  I really want to do this without having to be marked as ISRU in the attempt...but I may have no choice.

Edited by Scarecrow71
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2 hours ago, Scarecrow71 said:

I have all but the final tier unlocked, so I do have mining capabilities available.  But adding this to any launch adds a whole new host of problems and concerns, as well as parts needed to deal with this.

Yes, ISRU is definitely something you want to test and practice with before going off to Jool.  

  • The equipment is large, and weighs a lot.  The refiner is over 4 t.
  • They require a lot of electricity.  Out at Jool solar power is greatly reduced, so that is another problem.  
  • They also require cooling, which is another mechanic to figure out.
  • Getting all that to work as intended requires a lot of testing.

However, it does greatly expand your range.  Once you figure out ISRU you essentially have an unlimited fuel supply.  Although doing a Jool-5 without ISRU is absolutely possible, the ability to refuel makes it much easier (my opinion).

But yes, adding ISRU is a complication you would need to figure out before arriving at Jool, and realizing it doesn't work as planned.  My opinion is it is worth learning.  However, it is not absolutely necessary.  I use ISRU for every trip to Jool, because the way I do things (bigger is better...) the added weight of the ISRU equipment isn't that significant.  

2 hours ago, Scarecrow71 said:

I have scrapped my original idea of multiple landers

Re-using landers saves an incredible amount of weight.  For every ton of useful payload I launch into orbit of Kerbin, I figure I need 10 tons of booster, or more.  So every extra lander you bring along requires a large addition of boosters, at some point that becomes unmanageable.  Tylo is really the only Jool moon that requires it's own lander.  It's possible to make a reasonable-sized lander that will work on the other four: Laythe, Vall, Bop, an Pol.  Since Laythe has an oxygen atmosphere, I usually go with a spaceplane for Laythe, but a traditional lander with parachutes (similar to what worked on Duna..) will also work on Laythe.  The hard part is actually hitting land on Laythe.

Actually, I have also built Laythe landers which float upright, and are able to lift off from the water.  A wide, flat lander like you'd use on Duna might be a possiblility if you don't want to mess with spaceplanes.

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38 minutes ago, 18Watt said:

Tylo is really the only Jool moon that requires it's own lander.  It's possible to make a reasonable-sized lander that will work on the other four: Laythe, Vall, Bop, an Pol.  

I am going to have a lander that is capable of working on Tylo, and then use that for the other 4 as well.  I figure that, if it can get off Tylo, it will get off the others.  And it won't need as much fuel for the others, so if I refuel it once...maybe twice...that should be good.

I do need to learn mining and such, and I dont want to do that on the fly.  I am going to try completing Jool without it at level 1, and then probably do a level 3 with ISRU.

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2 minutes ago, Scarecrow71 said:

I figure that, if it can get off Tylo, it will get off the others.

Absolutely.  Just like Duna, a parachute or three will help at Laythe.

3 minutes ago, Scarecrow71 said:

I do need to learn mining and such, and I dont want to do that on the fly.

Yeah, there is a learning curve with ISRU.  For me it's easier with ISRU, but I wouldn't count on ISRU fuel at Jool until I had a good understanding how it works..

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15 hours ago, Scarecrow71 said:

@king of nowhere

You need enough fuel for the motheship to get to Jool and back, and you need enough fuel to land on every moon.  You also need enough fuel for the taxi to get to every moon.  I dont see how that is any different than not using a taxi at all?

I'm also currently struggling with ship design to just get to Jool and back; fuel is becoming an issue as I need enough for all 5 moons...and Tylo has serious fuel requirements.  Isn't adding a taxi just increasing complexity unnecessarily?

the taxi is very lightweight. the mothership is heavy. moving around the taxi is much cheaper than moving around the mothership. It saves deltaV on the mothership.

Once in low kerbin orbit, your mothership needs 2000 m/s to reach Jool. Then, if you want to actually go to low orbit on all the planets, you need

- 200 m/s to get captured by laythe, then you can circularize by aerobraking

- 600 m/s to leave laythe

- 300 m/s to circularize around Vall, and just as much to leave

- 800 m/s to circularize around Tylo, and just as much to leave

- roughly 1000 m/s for the Bop/Pol part of the mission

- 1000 m/s to return to Kerbin

total 7000 m/s.

with a taxi you park your mothership in high jool orbit, so you only need 3500 m/s for the mothership, plus a little extra for the taxi. the point of the taxi is that it is much more light than the mothership, so that moving it around is almost free.

say your lander has a dry weight of 2 tons, including a terrier engine (Mk1 lander can, terrier, and a few amenities). to this, you add 3 tons of fuel - and 375 tons of fuel tanks. Your lander has a bit over 2800 m/s deltaV, with TWR 1.11. It can orbit tylo comfortably, and it can go down and up on all the other moons.

Your taxi now has to carry that around. you want a crew pod on it, so let's say your taxi has a dry weight of 5 tons: 4,1 for nerv+Mk1 crew pod, and the rest on amenities like batteries, reaction wheels, and the likes. Add in the lander, which is dry weight as far as the taxi is concerned, you can add only 8 tons of fuel (and 1 ton of fuel tank) and you get 4300 m/s of deltaV. at a very low thrust, but the taxi will only move in orbit, you don't need high thrust. Actually, your taxi has a better deltaV than that, because on the return trip the lander will be empty. 4300 m/s is more than enough to carry the lander anywhere in the jool system and then return to the mothership to refuel.

So you have this 19-ton package, that consumes no more than 8 tons of liquid fuel and 3 tons of rocket fuel for every landing, and it lets you reach all your target. your mothership must only carry 50 tons of fuel to the jool system, and then the taxi will move around. All your mothership has to do is carry 60 tons of lander+taxi+fuel with 3500 m/s.

if you do not use a taxi, then your mothership must do all those transfers itself. it means that, when it brakes around vall, it will carry with itself all the fuel needed to land on tylo, all the fuel needed to reach bop and pol, all the fuel needed to return to kerbin. and then it will carry them back out of vall. and so on for all the moons. it's ridiculously more expensive.

this is a simplified model, because it does not account for a special tylo lander nor a laythe lander, but those make the use of a taxi even more poignant. if you have a taxi, you park the laythe lander in high jool orbit and only move it when you land on laythe. if you use the mothership, then you will be carrying your heavy laythe lander up and down tylo's gravity well. or, if you land first on laythe, you carry the tylo lander up and down needlessly.

isru will definitely simplify the mission (so much so, that i stopped using it because it wasn't fun). even then, a taxi would be useful, if nothing else because you won't need to carry around the mining equipment. but with isru, you can be as wasteful as you like, fuel is infinite. so it doesn't really matter (that's why i'm not having fun with stock isru; it does not reward good design).

On 11/25/2021 at 12:15 PM, magnemoe said:

Tylo is hard to land on, require lots of dV and things happens vast. Will almost advice against using the default lander as an accent stage for an Tylo lander as TWR and landing leg requirements will be much higher than you need for other places, You will also have to take the legs with you while you can drop all extra weight on takeoff. 

I solved the problem by putting the landing legs on the expendable descent stage. additional benefit that, as you land with the descent stage almost empty, you have really high twr near the end, when you need it most.

additional complication, this design requires a lander with wheels to get away from the spent descent stage. but i want to move around the surface anyway... still, just adding a small command probe on the descent stage so you can use its last fuel to fly it away should suffice.

AIBvWBB.png

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And I'm stuck.  I am having problems designing anything beyond a lander here.  I keep hearing I need 3 landers AND a taxi AND a mothership.  And yet I still haven't seen anything about how to actually design this, which is where I struggle.  The mothership still needs to carry all 4 of these items, as well as having enough fuel to get from surface to LKO to Jool and back to LKO.  And the landers need enough fuel to get to 5 different surfaces, and the taxi needs enough fuel to shuttle everything around Jool's system.

How are people accomplishing this?  Am I just really that bad at rocket design that I can't do it?  I know - I thought I couldn't do anything earlier, and I got around it.  Which made several other planets easier.  But this?  I'm stuck, and need some serious help with design.  The reason I asked about Spaceplanes to begin with was that I keep seeing all these posts about SSTO planes to hop all over the place easily, and yet I can't seem to find anything that shows how to actually build one.  I keep running out of height in the VAB, or I don't have enough fuel to make the full trip, or I don't have enough TWR to get off Kerbin's surface.

Where am I going wrong?  What am I missing here?  Whenever I design something, I can't seem to figure out where to put the rest of the stuff.  For example, I've got the following 2 different designs going, neither of which is very useful:

GoYt2Lp.png

kVSH4b7.png

The first shot was a design I thought would work, using a different lander for each moon in the Jool system.  The top lander is for Tylo, and the others are for, well, the other 4.  The thought was that after each lander was finished, I would transfer the remaining fuel out of its tanks and back into the main tanks for the mothership and then jettison the lander; this would save on weight traveling to the next moon, as well as conserving fuel.  Unfortunately, the height and TWR become an issue; the VAB isn't tall enough to accommodate this, and I cannot put enough engines on this thing to get off the ground.  Like, seriously, I cannot put enough engines on this thing.

The second shot is a simplified design, using only a single lander that has enough fuel capacity to get on and off Tylo.  I added the parachutes because I keep hearing that you can use chutes on Laythe much like you use them on Duna.  The thought here was that I'd have to carry enough fuel on the mothership itself to continue refueling the lander until you hit all 5 moons, but I cannot put enough tanks on the mothership to refuel the lander appropriately and move about the Kerbol system.  Or get off Kerbin, for that matter.  Weight becomes a major issue here.

The design I used to do a lot of the other landings simply won't work here; that design is predicated primarily on the nuclear engine to get around the system, and that won't work because I need oxidizer to refuel the lander tanks.  The nuclear engine only uses liquid fuel, which means if I try that design I have to have both tanks for the nuclear engines and tanks to refuel the lander.  Again, too much weight and not enough TWR to do anything effectively.

What am I missing here?  I cannot wrap my head around the taxi idea; I cannot visualize it in this challenge.  I get 1 launch; I cannot launch something into orbit and then send a second ship up to go dock with it.  This has to be a single launch.  And before anyone says "ISRU", that is simply not an option at the moment.  I don't know how to do ISRU, and having to do that then adds more complexity and weight to this that I simply don't have the capacity to add.

Help?

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4 hours ago, king of nowhere said:

isru will definitely simplify the mission (so much so, that i stopped using it because it wasn't fun). even then, a taxi would be useful, if nothing else because you won't need to carry around the mining equipment. but with isru, you can be as wasteful as you like, fuel is infinite. so it doesn't really matter (that's why i'm not having fun with stock isru; it does not reward good design).

I solved the problem by putting the landing legs on the expendable descent stage. additional benefit that, as you land with the descent stage almost empty, you have really high twr near the end, when you need it most.

additional complication, this design requires a lander with wheels to get away from the spent descent stage. but i want to move around the surface anyway... still, just adding a small command probe on the descent stage so you can use its last fuel to fly it away should suffice.

AIBvWBB.png

You are landing the entire thing in one stage? Looks like the legs are on the other engines, I would stage during decent to save dV and make an more nimble lander.
Or is this an Tylo ssto as in two ways?
Using legs to re-dock is an nice touch, robotic is probably better if you have that.
Is the rover able to operate on Val on its own? 

And ISRU helps a lot is in you can now operate infinity, you need infrastructure for it however, 
4pfkEdL.png
Like how the long MK4 tanks looks small on the Jool express resupply ship. 

It carry 3 major payloads, an tail sitter jet able to take off from water to explore all of Laythe biomes. An Tylo lander who is an SSTO with refueling from Tylo base and an fuel depot to drop on Laythe to refuel the jet, the spaceplane I build for Laythe was not able to land on biomes on the other side or the planet and return, yes I could reach orbit refuel from tanker, land and return but it also required flat areas to land and take off who an tailsitter solved with the bonus of landing on water. 
 

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2 hours ago, Scarecrow71 said:

I keep hearing I need 3 landers AND a taxi AND a mothership.

You don't need to do any of those things. I think the Kerpollo challenge stipulation for a mothership to be left in orbit could be satisfied by something like the Apollo CSM. 3 landers is honestly probably a good idea, but I've seen designs where the Tylo lander is also used for the smaller moons (usually after staging most of it away). I've also seen a couple Jool 5 runs where a single lander docks onto modules that allow it to land on Tylo and Laythe.

2 hours ago, Scarecrow71 said:

I keep seeing all these posts about SSTO planes to hop all over the place easily, and yet I can't seem to find anything that shows how to actually build one.

A lot of people bring SSTO spaceplanes to Laythe because they work there and because they usually have a plane ready to go for the mission. If you don't and aren't comfortable building one, I honestly suggest skipping it, at least for now. It's completely possible to land on and take off again from Laythe with a conventional lander. Since it sounds like you don't know yet, Laythe is pretty much just Kerbin but again. it has 80% the gravity and a slightly thinner atmosphere, but if you don't do a lot of flying in this game you probably won't notice the difference. Parachutes basically make landing on Laythe free.

I'm looking at your landers and am noticing even the small ones have aerospike engines on them. Those are very cool, but also very situational engines. You'll want to be using more efficient ones mostly, especially for your transfer stage/mothership and your landers for Bop/Pol/Vall. The Terrier, the Spark, the NERV typically. I can't really tell but it looks like you have parts from Making History? if you do I think the cheetah as also worth considering.

If your going by the TWR reported by the little dV panel in the VAB to decide what engine to use, make sure you have it set to vacuum when you're designing anything that's meant to be used in space, and for your landers set it to the moon it's supposed to be landing on to see the real TWR on that moon. I think you'll find you can get away with a lot less thrust.

3 hours ago, Scarecrow71 said:

seriously, I cannot put enough engines on this thing.

Do you know how to "asparagus" your launchers? basically you feed fuel from your outermost boosters into the next stage so that only the stage that's about to be jettisoned is losing fuel at any time. It's theoretically the most efficient way to build a launcher. I've managed to lift some seriously stupid things into orbit like this and people on here have done even more. I don't know if I'm telling you what you already know since it looks like you deleted any launch stages from your craft before posting screens.

If your problem is literally TWR on the pad, Use the 5m fuel tanks and spam Vector engines. you can put like 10-11 comfortably under each booster stack. Massive lagfest, but it'll get you to space for sure.

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1 hour ago, Zacspace said:

If your going by the TWR reported by the little dV panel in the VAB

I'm using MJ's readout for dV.

1 hour ago, Zacspace said:

Do you know how to "asparagus" your launchers?

Yep.  And again, I cannot put enough engines and tanks on this thing.  Keep in mind that, per the rules of the challenge, I need to leave a ship in orbit with at least 1 kerbal in it over every moon I land on.  So at a minimum I need 1 mothership and 1 lander.  This means I need enough fuel to:

  1. Get the whole contraption into LKO.
  2. Get the whole contraption to Jool.
  3. Move the whole thing from moon to moon.
  4. Land on every moon.
  5. Get the command module home.

And keep in mind that I have to do this in 1 launch.  I can't send stuff up into LKO and then launch a second time to collect stuff.  1 launch.

I know I'm bad at rocket design, but I am missing something basic here.  I'm out of room going vertical, and the thing will not stay together no matter how many struts I use.  Autostart doesn't keep it together either.  I have looked and looked, and I cannot find any post that helps with this.  I cannot give up, but I'm stuck right now.

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@Scarecrow71 I'll try to keep things simple and show you how to get maximum reusability, which means you need to take less stuff to Jool. Less stuff = less weight = less boosters required to get to space in the first place.

6JsB0qk.png

A pretty boring looking lander, you might think, but this thing is a Jool V powerhouse- it can fly up from the surface of Tylo into orbit as well as land and return from Vall, Bop and Pol too (with refuelling in between landings). Low part count, lightweight, low tech, but it'll do the job nicely.

Root part is the lander can mk1, then FL-T400 tank and LV-909 Terrier engine. Add some mini RCS thrusters and a junior-sized docking port so it can dock to other vessels, add a battery and (if you really want to) a reaction wheel, and a couple of solar panels to recharge it as the Terrier doesn't generate power when it's running. That's it- 16 parts, 3.5 tons and you're set for three out of five moons already. Add two more FL-T400 tanks on the main ship to refuel, job done.

Getting this thing down to Tylo in the first place takes a bit more oomph- it's possible to do with 1.875m parts from the Making History DLC, but I'll show you how to do it with plain stock 2.5m parts instead.

8dZgfZR.png

Pretty simple really- 1.25m decoupler, 1.25 to 2.5m C7 fuel tank adapter, X200-16 fuel tank, RE-L10 Poodle engine (two nozzle configuration!) and four large landing legs. Total delta-V on that stage is well over 3km/s, more than enough to land on Tylo, and the TWR at Tylo starts at 1.65 fully loaded. I looked at using a smaller X200-8 fuel tank, but the delta-V margins for that were a bit too close for comfort; an overbuilt descent stage just means you'll save some fuel on the ascent stage.

For Laythe, I still recommend a single-seater SSTO, the smaller the better. I can share a craft file of something I've used in the past that works really well, but it uses the Making History inflatable airlock so I might have to tweak it if you don't have that DLC, as well as a couple of RTGs for power which can be swapped to solar panels if necessary.

Moving between the moons of Jool is pretty easy as they're all fairly close together. Capturing into orbit of Jool can be done without any fuel at all if you get an intercept of Tylo at the right time for a gravity assist; it's technically possible to do the same in reverse on your way back, but that's a lot more difficult.

Demo flights of the Tylo descent and ascent stages: https://imgur.com/a/xEQN5CU

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4 hours ago, magnemoe said:

You are landing the entire thing in one stage? Looks like the legs are on the other engines, I would stage during decent to save dV and make an more nimble lander.
Or is this an Tylo ssto as in two ways?
Using legs to re-dock is an nice touch, robotic is probably better if you have that.
Is the rover able to operate on Val on its own?

I though the docking port between the rover and the descent stage was more evident.

the rover has 2500 m/s, with TWR 1.7 on Tylo. I made it with redundant engines because i have part failure; it can still reach orbit with 6 engines if one is broken.

The descent stage is expendable. it also has 2500 m/s once docked to the rover, so, enough for the landing. it also has redundant engines, it can work with 6. it can land on tylo with a bit of fuel left - that fuel is lost, though, no way to recover it. An ssto landing stage for that rover would weight well over 100 tons, while the heavy descent stage is only 35 tons.

So, I land with the heavy descent stage, hitting the surface with its landing legs. by the way, they cushion very well, i've crashed on the surface at 20 m/s and survived. also, landing this thing is a breeze; an extremely wide base to land even on very irregular ground, and a lot of thrust because by that time the fuel tank is mostly empty.

after landing i detach the rover, and i cannot dock it again - i tried when working on alternative systems, even if i use rockets to float gently against the docking port, it fails.

the rover returns to orbit on its own power afterwards.

with the exception of tylo (and OPM Slate), which require heavy descent stages, the rover is capable of landing from orbit and orbiting again from any other smaller body, up to Duna or OPM Wal.

it's by far the best non-isru system i ever came up with.

some pictures under the spoiler

Spoiler

fImAZ5z.png

kr2GMwV.png

i8NZCK7.png

1 hour ago, Scarecrow71 said:

And keep in mind that I have to do this in 1 launch.  I can't send stuff up into LKO and then launch a second time to collect stuff.  1 launch.

 

huh. i didn't knew that.

then you set out to perform a very difficult task. there are very few instances of a jool 5 launched all in one go; most of us launch stuff in orbit one by one, and assemble the spaceship there.

Just be aware that doing it in a single launch is very, very complex, and don't feel bad if you fail.

 

I think you may find some inspiration from my Marco Polonium mission. I sent it to orbit in multiple launches, because i had weight limitations on the launch pad. But the overall shape of the ship is something that you could use

8hnmJrw.png

The tylo-laythe lander (7) can also perform as a lander for everywhere else, though the light lander (2) is lighter and cheaper. With the tylo descent stage (9) you can assemble them in line, with the rest of your mothership behind (including the fuel needed for everything). the whole stack may be linear and stable enough to be launched from kerbin in one go.

And by the way, using nuclear and drop tanks you could get by without a taxi. though a well-made taxi does provide utility with minimal increase in complexity. Here is my first really dedicated taxi

5308mYO.png

it's got a docking port in front to put the lander, and another docking port on the back to dock with the rest of the mothership. it has 4 engines because i'm playing with part failure and i need redundancy, but 2 would have been fine - and would have saved 6 tons of dry weight. same goes for the multiple antennas and reaction wheels.

as you can see, the taxi is nothing more than a fuel tank with rockets and docking port. if made for it, you can stack it in line (and it helps if you have to launch the whole thing from kerbin in one go). it's just a convenient way of bringing the lander from high orbit to low orbit without having to move around the rest of the mothership. you can even dock it in the back of your mothership and use the taxi's engines for additional thrust; you can have the rest of the "mothership" be nothing but a bunch of fuel tanks

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2 hours ago, Scarecrow71 said:

I'm out of room going vertical, and the thing will not stay together no matter how many struts I use.

I looked at your kerpollo thread and noticed that your Dres rocket was an absolute unit. The one you used for Eeloo was more reasonable, but the transfer stage seemed a bit overkill. I have a few tips:

- You don't need high TWR in orbit. Am I wrong to assume you're using mechjeb to plot and pilot your interplanetary transfers? I know it just slams you into the atmosphere if your burn takes too long because it tries to do it all in one go. Consider either doing the transfer yourself, splitting it up into multiple burns, or starting from a higher orbit so that you'll have enough time with smaller/fewer engines. The mass of extra engines (and their fuel) adds up quick.

- I saw your Eeloo encounter was very energetic it probably took a lot more dV to capture into Eeloo orbit than you expected. Try and keep your encounter with another planet close to your solar apoapsis and you won't need to overbuild so much (saving you mass). It's hard to get a direct Eeloo encounter in the first place, so I understand, but you pay for it in the end. For Jool specifically, if you get a nice, clean encounter you can gravity capture into orbit of one of the main 3 moons using a Tylo encounter for just a few hundred m/s (or none at all if you're very patient). It saves thousands of m/s over doing a capture burn into Jool orbit and then transferring to a moon.

- the struts you used on your Dres rocket would make sense in real life, but KSP's modeling of structural stuff like that is probably where the game diverges most from reality. Struts aren't really structural elements so much as they're like a visual representation of the physics engine considering two parts to be connected. There's practically no benefit to having a strut between two parts that already have a strut or are directly connected to each other. Strut orientation doesn't matter, and it doesn't matter where on a part you connect a strut. You want, generally, to put struts and autostruts between the extremities of your rocket and parts that have more inertia, or parts that are far away from it. I autostrut to root and to heaviest part a lot. People on here seem to recommend against it, I think they just use too many. You'll also want to stay away from rigid attachment mostly, if you make your ship too rigid it won't be able to absorb vibrations and will just shake apart. You can also have this problem from too many autostruts.

- Build wide, not tall. Don't be afraid to give your boosters boosters, and put boosters on those boosters if you need to.

I don't know what parts you have unlocked, but you'll find this a lot easier if you make everything you're taking to Jool as small and light as possible. Kilograms of payload you save can be tons of rocket you don't have to build.

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