Need help with a cargo spaceplane SSTO to duna

[Interstellar Yeet]

Hello kerbonauts. I've landed on Duna before with a spaceplane I built myself, but right now I'm trying to build one and it has a few requirements. It's gotta be able to drag some weight with it and have a Mark 3 CRG 100 cargo bay and it should have a ramp. I want to bring a rover or a small base to Duna. I have come up with a freakin huge design but I can't manage to get it into orbit, it's just too heavy. I'm gonna upload some pictures and the craft file. Should I just give up on this design and start from scratch or has anyone built something similar that works?

https://imgur.com/a/EYMYdUG This is what my design looks like.

https://www.dropbox.com/s/xj5ocm5xp3piabx/Sputnik LXIX.craft?dl=0 this is the craft file. I would appreciate any tips or help.

[bewing]

Yeah, when you are building a rocket and you need to haul more mass, you make the rocket bigger. But that technique doesn't work for spaceplanes. To go further and get more done with a spaceplane, the point is all about cutting. Cutting mass, cutting parts, cutting drag. So from my point of view you went in the wrong direction with this monster.

I suppose that theoretically you might get it to work. You might be able to mount kickbacks behind all those rapiers and launch it vertically -- that might be enough to get it to orbit.

But I've got a lot of issues with this design anyway. Too many intakes. Too many engines. 2.5m parts make better nacelles than MK3 parts. I'd switch the rapiers for whiplashes and go for a pure LF design. Those twin-tails probably aren't doing you any good because they are too far forward. No fuel capacity in the wings. Your landing speed on Duna is probably going to be about a billion m/s, since you aren't trying for a vertical landing. I'm amazed you can even get it off the ground on Kerbin.

[Rocket In My Pocket]

How dead set are you on the SSTO concept?

Converting this to a shuttle and launching it on a booster assembly would simplify your design problems a lot.

Draining all the fuel out of it and sending it up empty, then filling it in orbit would be even easier, besides the obvious refeuling rendezvous you'd have to do with a separate tanker.

[AeroGav]

4 hours ago, Interstellar Yeet said:

Hello kerbonauts. I've landed on Duna before with a spaceplane I built myself, but right now I'm trying to build one and it has a few requirements. It's gotta be able to drag some weight with it and have a Mark 3 CRG 100 cargo bay and it should have a ramp. I want to bring a rover or a small base to Duna. I have come up with a freakin huge design but I can't manage to get it into orbit, it's just too heavy. I'm gonna upload some pictures and the craft file. Should I just give up on this design and start from scratch or has anyone built something similar that works?

https://imgur.com/a/EYMYdUG This is what my design looks like.

https://www.dropbox.com/s/xj5ocm5xp3piabx/Sputnik LXIX.craft?dl=0 this is the craft file. I would appreciate any tips or help.

Can you clarify your objective a little?

 

Do you mean it has to go to Duna orbit, or the surface of Duna

Judging by the parachutes, it seems you plan the latter.   I also presume you want to do that unrefuelled.   A round trip to Duna's surface means a small payload fraction,  so even with an efficient design a craft that can put CRG 100 worth of cargo down there is going to be huge.   What in god's name do you need that much cargo for ?!

 

[AeroGav]

OK,  I quickly put together a version of your craft that at least can reach orbit,  with a light payload of science bays and habitat modules filling the cargo space.

https://www.dropbox.com/s/fnznun8t0f077oj/Sputnik LXIX.craft?dl=0

4 nervs. 4 panthers and 4 rapiers.   Because of the drag reduction i've done, it's actually overpowered for this weight,  and has too much ox and not enough liquid fuel.  

5 hours ago, bewing said:

Yeah, when you are building a rocket and you need to haul more mass, you make the rocket bigger. But that technique doesn't work for spaceplanes.

It would not work for a rocket SSTO either.  The key is SSTO.    If you are not staging,  going bigger and bigger doesn't help much.

A space vessel's mass largely comprises the following 3 items

• fuel
• engine
• payload

if you're wanting  a large amount of cargo and a large amount of fuel, the only thing that can give is engine mass.   Engines are heavy, especially jets.   Try substituting half your rapiers for panthers (lighter, once you get past mach 2 the rapier thrust goes up 3 or 4 times normal so you  don't need loads of them)  and reduce drag so you need less engines in the first place.

I KSP, fuselages produce most drag by far.  I try to avoid using cylindrical tanks where possible,  trying to  keep all my fuel in Big S wings and Strakes.  That also means largely nerv powered ascent to space.     As a bonus,  all that lift means your craft has nice low takeoff and landing speeds.

5 hours ago, Rocket In My Pocket said:

Converting this to a shuttle and launching it on a booster assembly would simplify your design problems a lot.

Depends on where your talents lie,  i'm very basic on the rocket front and find launching shuttles with off-axis thrust etc.  very very hard.

If i'm struggling to get the performance out of a single stage space plane i prefer to go the route of jettisoning engines and fuel tanks from underwing mounts close to CG.

https://kerbalx.com/AeroGav/Kranker

This mid tech airplane punches off the panthers (and their fuel tanks) when they flame out,  then completes the ascent on 3 nervs.  Reaches orbit with 4000dv remaining.   Obviously in sandbox i'd use better jet engines and big S wing parts instead of mk1 tanks for fuel.

The panther pods are over the CG,  so jettisoning them does not affect handling (it does get very quiet though,  especially if you do it by mistake right after liftoff)

On a grander scale, there is this beast https://kerbalx.com/AeroGav/Steven-Tylo

Spoiler

 

 

 

 

... and also this dinky little example, same tech level as the Kranker (panther/nerv, dry wings)https://kerbalx.com/AeroGav/Foxbat-with-drop-tanks

Spoiler

 

 

unfortunately due to smallest size landing gears, you can't really fit big drop tanks under the wings (without it looking silly), but it's got enough to do tourist flybys of Mun easily.

Edited November 27, 2018 by AeroGav

[Interstellar Yeet]

Alright guys. I'm really new at the game and I haven't been to any other planets than Minmus, the Mun and Duna. And I've only sent a spaceplane SSTO to duna, never a rocket. But I've seen people send like big bases to Duna with a plane and like someone sends rovers or bases on wheels and drives them out of the cargo bay, and that's what I wanna do. I guess I don't necessary need a CRG 100 cargo bay but it has to have a ramp and that part I'm really struggling with. I normally use a fuel adapter in the back which makes it easy get a lot of delta V and TWR but with the cargo ramp i just dont know how to build a good plane that can get all the way to duna. And all the tutorials and stuff I've seen is really outdated

[bewing]

1 hour ago, Interstellar Yeet said:

i just dont know how to build a good plane that can get all the way to duna.

So, the first question is: does it need to go all the way to duna and land on one tank of gas? Or can you choose refuel it in orbit? Because getting stuff to duna on one tank of gas is unbelievably difficult. Do you need to make it back to Kerbin again? That makes it even harder.

Second difficult point is landing on duna. Are you married to the idea of landing horizontally on the wheels? Or is it OK to land on the tail and then drop gracefully onto the wheels?

Third difficult point is the mass of the cargo. Every tonne that you add makes the problem exponentially more difficult. So you have to design the cargo first and specify the exact mass of it. None of this, "Oh, I'd like to have this and this and this ... oh yeah, I forgot, I'd like to have that too!" kinda stuff.

Fourth, as I basically asked before: are you married to the idea of a SSTO that takes off horizontally? Are you OK with taking your spaceplane and adding some SRBs and launching it vertically?

Once you answer these four questions, then we can show you some stuff.

 

 

Edited November 28, 2018 by bewing

[Interstellar Yeet]

5 minutes ago, bewing said:

So, the first question is: does it need to go all the way to duna and land on one tank of gas? Or can you choose refuel it in orbit? Because getting stuff to duna on one tank of gas is unbelievably difficult. Do you need to make it back to Kerbin again? That makes it even harder.

Second difficult point is landing on duna. Are you married to the idea of landing horizontally on the wheels? Or is it OK to land on the tail and then drop gracefully onto the wheels?

Third difficult point is the mass of the cargo. Every tonne that you add makes the problem exponentially more difficult. So you have to design the cargo first and specify the exact mass of it. None of this, "Oh, I'd like to have this and this and this ... oh yeah, I forgot, I'd like to have that too!" kinda stuff.

Fourth, as I basically asked before: are you married to the idea of a SSTO that takes off horizontally? Are you OK with taking your spaceplane and adding some SRBs and launching it vertically?

Once you answer these four questions, then we can show you some stuff.

 

 

Okay so first question; I want to get to Duna on one tank of gas yes. I could refuel it in LKO that would be pretty fun I guess! I like docking even though I've only done it a few times. And i would prefer to get back to kerbin again. For the landing, yeah I would like to land on the wheels. I did that the first and only time I landed on Duna. I'm not sure what the mass of the cargo is yet because I haven't made it. I'm working on that right now but to be honest I dont really care. I'm just playing sandbox and having fun. All I want is to bring more than the science junior and the other small gadgets... As long as I can actually move it out of the cargo bay and to the surface of Duna then I'm pleased. Could be a tiny rover or a small rocket with a science lab or just a rocket with some kerbals on it. And I've never tried to launch a spaceplane vertically, nor tried to land one vertically. I've only built 1 functioning spaceplane SSTO that I landed on Duna and crashlanded in the ocean on Kerbin and that took me 5 days. I launched and landed on my wheels and I had a cargo bay with only the basic science gadgets in it.

[bewing]

OK, so let's assume a refueling stop in LKO, because that makes things a lot easier.

To land a big spaceplane on Duna on the wheels, you need a lot of wing and some rockets on the belly to take some of the weight. It's actually a lot easier to land it on its tail, if you decide to change your mind.

Transporting and handling a small rover is much much easier than transporting some kind of rocket hopper. So I'd recommend doing the rover. For rovers, keep in mind the width of the flat grille on the floor of the MK3 cargo bay and ramp. You want the wheels of your rover to fit that width. If you start going over that width, then you will have a very hard time getting your rover out.

To transport a rover in a cargo bay, you either need to use a decoupler or a docking port. The rover has to be physically attached to either one or the other of those during transport. Then you decouple or undock the rover when you want to roll it out of the cargo bay. A decoupler is a one-time deal -- once you send the rover out, you can never get it back into the cargo bay again. A docking port will allow you to get the rover back into the bay and lock it in place again.

But still, the same basic answer from above applies. You want to make this spaceplane as small as you can get away with. And there are a lot of tricks for that. Keep the thing as simple as possible.

Even something as simple as this craft would probably do everything you want:

https://pastebin.com/raw/77D24Ffs

 

[Interstellar Yeet]

On 11/28/2018 at 4:42 AM, bewing said:

OK, so let's assume a refueling stop in LKO, because that makes things a lot easier.

To land a big spaceplane on Duna on the wheels, you need a lot of wing and some rockets on the belly to take some of the weight. It's actually a lot easier to land it on its tail, if you decide to change your mind.

Transporting and handling a small rover is much much easier than transporting some kind of rocket hopper. So I'd recommend doing the rover. For rovers, keep in mind the width of the flat grille on the floor of the MK3 cargo bay and ramp. You want the wheels of your rover to fit that width. If you start going over that width, then you will have a very hard time getting your rover out.

To transport a rover in a cargo bay, you either need to use a decoupler or a docking port. The rover has to be physically attached to either one or the other of those during transport. Then you decouple or undock the rover when you want to roll it out of the cargo bay. A decoupler is a one-time deal -- once you send the rover out, you can never get it back into the cargo bay again. A docking port will allow you to get the rover back into the bay and lock it in place again.

But still, the same basic answer from above applies. You want to make this spaceplane as small as you can get away with. And there are a lot of tricks for that. Keep the thing as simple as possible.

Even something as simple as this craft would probably do everything you want:

https://pastebin.com/raw/77D24Ffs

 

Oh thanks! I didn't see ur post until now. So what's this link you posted? Is it a craft file?

[bewing]

1 hour ago, Interstellar Yeet said:

Oh thanks! I didn't see ur post until now. So what's this link you posted? Is it a craft file?

Yes, that's a craft file.