Help With Cargo Ship?

[Andrw]

Hi, I am trying to build a cargo plane that will be able to transport rovers, bases, and more equipment from Kerbin to Minmus. But the only problem I have is with fuel! I have some engines that fit Mk3 parts, but every time I get my plane into orbit, I don't have enough fuel to get me to Minmus and back. Could you recommend me which engines will be perfect for such a mission? 

[Vanamonde]

Does this vehicle drop stages? If not, then fuel is always going to be a big problem no matter which engines you use. In fact, building a plane which can reach space is one of the game's harder feats, and I've only barely been able to reach orbit that way myself. 

Meanwhile, welcome to the forum.

[Andrw]

Thanks

[miklkit]

Yes fuel is always the problem.  It is possible to build MK3 based spaceplanes that can make the round trip, but I found it best to set up a base to refuel them there.  This is a gas truck moving in to refuel a spaceplane.

As for engines, I use NERV and Rapier engines.  If you do not have Rapiers, then Whiplash and a rocket tuned for vacuum use will work.

[jimmymcgoochie]

Single stage to orbit spaceplanes are hard. Single stage to orbit spaceplanes that can go elsewhere afterwards are hard² because wings etc. are dead weight in space, adding fuel for space usually means adding fuel tanks externally which adds drag in the atmosphere, atmospheric engines are useless in space and vice versa (the RAPIER is the only exception but it’s a mediocre vacuum engine)… It’s possible, but you need to put a lot of time and effort into optimising the design.

If you’re set on the idea of an SSTO to take payloads to orbit, why not just build a conventional rocket stage to do the trip to Minmus and then put that inside the spaceplane’s cargo hold? The plane can do the orbit-and-back bit that it’s best at and the upper stage can do the rest without lugging a whole plane along for the ride.

[darthgently]

10 minutes ago, jimmymcgoochie said:

Single stage to orbit spaceplanes are hard. Single stage to orbit spaceplanes that can go elsewhere afterwards are hard² because wings etc. are dead weight in space, adding fuel for space usually means adding fuel tanks externally which adds drag in the atmosphere, atmospheric engines are useless in space and vice versa (the RAPIER is the only exception but it’s a mediocre vacuum engine)… It’s possible, but you need to put a lot of time and effort into optimising the design.

If you’re set on the idea of an SSTO to take payloads to orbit, why not just build a conventional rocket stage to do the trip to Minmus and then put that inside the spaceplane’s cargo hold? The plane can do the orbit-and-back bit that it’s best at and the upper stage can do the rest without lugging a whole plane along for the ride.

I'm not a fan of SSTO for all the reasons you list, now you've traded hauling wings around in space for hauling an upper stage around.  And you are still hauling the wings around.  Am I missing something?  I very well could be but am not seeing it

[jimmymcgoochie]

2 hours ago, darthgently said:

I'm not a fan of SSTO for all the reasons you list, now you've traded hauling wings around in space for hauling an upper stage around.  And you are still hauling the wings around.  Am I missing something?  I very well could be but am not seeing it

Not sure I understand? Payload to Minmus plus rocketry gubbins to get it to Minmus, launched inside the payload bay of an SSTO spaceplane, fly up, yeet the payload out to do the Minmus bit, return spaceplane to runway and recover. Which is exactly what the Space Shuttle did when launching satellites and even interplanetary probes, with the only exception bring that the Shuttle wasn’t an SSTO. I didn’t say that was the best way of doing things (as the Space Shuttle proved in various ways) but since the OP was talking about SSTO spaceplanes I kept with that idea.

[darthgently]

1 hour ago, jimmymcgoochie said:

Not sure I understand? Payload to Minmus plus rocketry gubbins to get it to Minmus, launched inside the payload bay of an SSTO spaceplane, fly up, yeet the payload out to do the Minmus bit, return spaceplane to runway and recover. Which is exactly what the Space Shuttle did when launching satellites and even interplanetary probes, with the only exception bring that the Shuttle wasn’t an SSTO. I didn’t say that was the best way of doing things (as the Space Shuttle proved in various ways) but since the OP was talking about SSTO spaceplanes I kept with that idea.

Ok, I was missing something, lol.  I was picturing hauling the upper stage in the payload bay while the SSTO did a Jool 5 or something.  Sloppy reading between the lines on my part

[miklkit]

Getting up there is the easy part.  Getting back down in one piece is the hard part.  The spaceplane has to be designed so that the CoM stays about the same when both full and empty.  This thing did it a long time ago.  It has 2 Panthers and 3 reliant (?). 

Once the Minmus base is built the whole system opens up as most fuel is burned just getting into orbit.  The big S wings and strakes carry fuel too and the strakes are the most efficient fuel tanks there are with the 1.25m fuel tanks being 2nd.  So using them doesn't hurt anything.  This one has 6 big S wings and a bunch of strakes and just delivered a rover to Bop.  It refueled at Minmus base and then went straight to Bop.