How to build an interplanetary SSTO?

[amateur astronaut]

I'm planning building one with mk4 parts to hold 16 kerbals in it, but all I know is you need rapier engines that can get you to LKO, and then just nuclear engines to the rest of your flight... though should i calculate the delta-V with that little community map? or just test if the rapiers work, and then just off we go? I really would like to know if I would need to make any calculations with the nuclear engines...

[bewing]

Designing a long-range SSTO is super hard. Harder than just about anything else in the game. Designing even an SSTO to LKO is really hard. Even flying an SSTO to orbit is hard.

So, my first point is that your question sounds oh so blase about a task that you will be tearing out your hair over, for a month or two.

The farthest that a mortal human can get an SSTO with only a mere month or two of effort is the surface of Duna. A better choice would be Minmus. Then you refuel with ISRU. IF you can get that far, then you can go anywhere.

So, forget about deltaV. Minimize drag. Minimize mass. Maximize lift. Optimize fuel capacity. Keep in mind that every Kerbal you add increases the mass and difficulty hugely. If you increase the difficulty too much, then you will fail because you will have made it impossible to succeed -- and nobody will be able to fix it. You will need to start with a minimal SSTO craft. Then reduce your ambitions as you improve your engineering. They will meet at some point where you can just barely get your SSTO to Minmus.

 

 

[Guest]

Here's a quick step-by-step run-down with five steps. And I'm not being facetious, you really do need to figure all this stuff out. I only managed to build my first interplanetary SSTOs pretty recently and I've been doing this for a quite a while.

For each step, start with a single-seater and no other payload, and work your way up from there.

1. Figure out how to build a plane. Understand CoM, CoL, and (the really iffy bit), centre of pressure/centre of drag, landing gear, aerodynamic stability, and aerodynamic efficiency. Consider yourself done when you're able to slap together a plane in the SPH and predict reasonably how it's going to handle before even flying it, meaning, you'll be able to make a plane that takes off, flies, and lands well with one or two test flights to work out the bugs.
2. Figure out how to fly the plane to orbit. If you did step 1 well, this means mostly just slapping on a Rapier or several depending on how big it is, and then learning the optimal ascent profile. (Hint: you will be wanting to go at > 1500 m/s surface velocity on airbreathers only, and you will be in a very shallow climb well over 20 km when this happens.)
3. Figure out how to fly the plane down from orbit. Re-entry and a controlled descent is a whole another furball.
4. Grats, if you made it this far, you're able to design and fly SSTOs. Take a break and celebrate.
5. Figure out how to make your SSTO interplanetary. The way I thought about this is basically to design a medium-size SSTO, then replace most of the payload fraction with a NERV or two and more Lf, removing most of the Ox as the NERVs will be able to do the final cruise to orbit. (Keeping some Ox on board may be useful because that way the RAPIERs can give you an extra kick of acceleration when you need it, e.g. take-off or landing.) Because of geometry I found the easiest design was 2 RAPIER + 1 NERV, with the same ratio for scaled-up designs.

You can also always look at how others have dealt with them. Here's an interplanetary SSTO I've built for example, with a crew capacity of 10 and a small cargo payload too -- the description refers to the Mun but it does reach orbit with over 2000 m/s dV so it'll make Duna (surface) or Eve (elliptical orbit) no problem, although for Jool (Laythe) I'd want to give it just a bit more fuel; I think it could do it as it is but it would be down to the wire.

https://kerbalx.com/Brikoleur/BAK-Kassius

Edited September 9, 2019 by Guest

[amateur astronaut]

Can i use the deltav map to see how much Dv I need by the nuke engines? Also glad we have that deltav tool that shows your total Dv in VAB, I mean, If MaTt LoWnE dId It ThEn EvEn I cOuLd Do It DoN't YoU tHiNk?! 

[bewing]

3 hours ago, amateur astronaut said:

Can i use the deltav map to see how much Dv I need by the nuke engines? Also glad we have that deltav tool that shows your total Dv in VAB, I mean, If MaTt LoWnE dId It ThEn EvEn I cOuLd Do It DoN't YoU tHiNk?! 

You need enough deltaV in your rocket engines to get you from a 25km altitude at 1200m/s to LKO (so, about 3000m/s -- from the map, including an allowance for drag and gravity losses), plus another 950m/s to get you to a Minmus encounter (from the map), plus another 250 m/s to enter LMO (from the map), plus another 250 m/s to land (from the map). So yes, you can use the deltaV map. But what you will find is that your craft will design itself (with some input from you), and then you will fill it up with fuel, and it will get as far as it can get, and then you will have to go back to the drawing board. And then iterate your design a hundred times. Knowing that it has enough dV to make it to Minmus is not going to be nearly as important as knowing that it flies at all.

 

[dire]

In general, the delta-V readout for an SSTO is a dirty, dirty liar. Your craft might read 17,000 dV and it turns out based on drag, TWR and other factors that you can only just barely get to LKO.

Once you actually get to LKO, you can use the dV map to guestimate how much fuel you'll need for your nuclear engines (but add 20%), but since your nukes use the same fuel as your dirty lying airbreather engines you don't actually know how much you're going to reach space with except through trial and error, and three different trials are likely to give you three different numbers.

So, good luck! I tend not to bother with SSTO's these days, preferring JATO planes, but here's something to get you started that is not an SSTO. https://kerbalx.com/direstorm/Victor-Terra-Lumen

[Pecan]

"Interplanetary"?  "SSTO"?
"Single Stage TO ORBIT"?   "Interplanetary"?

Oh yeah - that's easy.  Stick a small probe core, battery, etc. on a xenon tank and dawn engine for your interplanetary vehicle, add a decoupler and build your SSTO launch vehicle underneath it.  A few FL-T800s and a swivel should do for that, with fins and fairing.

Launch, SSTO, decouple, interplanetary.  Easy 5km/s ready to go.

Edited September 8, 2019 by Pecan

[Vakarian]

2 hours ago, Pecan said:

"Interplanetary"?  "SSTO"?
"Single Stage TO ORBIT"?   "Interplanetary"?

Oh yeah - that's easy.  Stick a small probe core, battery, etc. on a xenon tank and dawn engine for your interplanetary vehicle, add a decoupler and build your SSTO launch vehicle underneath it.  A few FL-T800s and a swivel should do for that, with fins and fairing.

Launch, SSTO, decouple, interplanetary.  Easy 5km/s ready to go.

 

I was thinking this too. All my first missions were single flight (manned and unmanned) runs cause I was too stubborn to go into orbit first haha. Now that I do though life is so much easier. But for real, Ive landed on, and returned from The Mun, Minmus, Duna and Eve in a single flight. But with Eve I got stuck in high kerbal orbit on return and had to refuel. So, I dunno.

[Aegolius13]

On 9/7/2019 at 10:07 AM, amateur astronaut said:

I'm planning building one with mk4 parts to hold 16 kerbals in it, but all I know is you need rapier engines that can get you to LKO, and then just nuclear engines to the rest of your flight... though should i calculate the delta-V with that little community map? or just test if the rapiers work, and then just off we go? I really would like to know if I would need to make any calculations with the nuclear engines...

First step is making sure your SSTO can make it to orbit at all.  Once you've accomplished that, make sure you've disabled your Rapiers.  If the nuclear engines are the only ones active, the delta-v readouts from either stock or KER should take into account the ISP of the nukes in calculating your available delta-v. 

 

If you want the maximum range possible, it will likely mean a plane that just barely has enough thrust on nuclear propulsion to make orbit, so as @bewing says it can be a very fussy process. When I was building a single-stage-to-laythe and back, I did this kind of iterative test over and over and over.  Make a tweak to plane (fuel, engines, aerodynamics, etc.).  See if it can make it to orbit.  If it can't, tweak again to address the problem.  If it can, note available delta-v in orbit.  Then make more tweaks for possible range improvements (more LF, less oxidizer, fewer engines, etc.), and lather, rinse, repeat. 

Note, however, that if you want to land somewhere and return, you may need to use additional engines to get the necessary thrust.  Rapiers in jet mode work great on Laythe; but anywhere else of course you'd have to rely on some form of rocket power.  So that may add add a complication to getting a simple available delta-v number.  I used some cheaty hyperedit testing to figure out approximately what my plane would consume landing on Laythe and getting back to orbit. 

[amateur astronaut]

an ssto that small? hmm that birdie looks noice... also its incredible how it can fly so far away...

Edited September 13, 2019 by amateur astronaut

[fulgur]

In essence, for an interplanetary SSTO you want to have RAPIERs and NERVAs. You only need a little bit of oxidant for the RAPIERs to push your apoapsis above the atmosphere, and then you can circularise with the NERVAs. It's possible to make one with Mk1 tanks, but I prefer Mk2 or Mk3. You should fill the rest of the ship with liquid fuel, and an ISRU unit. Then you fly to Minmus and refuel. From Minmus orbit dV requirements are reduced, so you can go anywhere in the system from there. I'd aim at Duna to start with because of the handy atmosphere, and you can also use Ike encounters to decrease or even capture.

Here is a very minimal SSTO which can reach Minmus:

It's one of my older SSTOs. There is one medium sized oxidant tank in the middle, and now I'm a better pilot I could reduce it further. There's some drills and science in the bays. The other thing I would now improve with Starchaser is that the wings are huge. And where we're going, we won't need wings. Because they just decrease your dV.

 

[amateur astronaut]

first i built like a huge ssto, my pc couldn't even load it in, then rebuilt by your ideas in small... it still needs flights but what i learnt from that is that bigger is not allways better

[Signo]

With a LF-only 30t craft powered by a rapier and 2 nukes you can have a pretty easy interplanetary ferry. 

You need at least a 0.50 TWR to correctly predict how far you can actually go. You can easily scale up, 4 rapiers can lift a significant amount of weight exceeding the 120t.

This one below is "oldish", but as far as I can see it is still working with the same performance as before. You were left in LKO with more or less 5k m/s with a 0.50 TWR: more than enough for a good trip and for landings on lesser bodies.

[ffx]

i did make a ssto but is a roket ssto.

[Pecan]

On 9/16/2019 at 12:11 PM, ffx said:

i did make a ssto but is a roket ssto.

Hoorah, congratulations and well done.  (Some forum bug or something, I can't "like" your post).

Just remember, all those people claiming to have made a SSTO that isn't a rocket are lying, otherwise they wouldn't be able to maneuver in space.

[ffx]

a ROKET SSTO!!!

NOT A Spaceplane

[Pecan]

10 hours ago, ffx said:

a ROKET SSTO!!!

NOT A Spaceplane

I know, that's why I said well done!!!