ISRU powered SSTO!

[Pacca]

After much trial and error, I've finally managed to make my second ever functional SSTO, and the first SSTO I've ever created with a useful payload other then it's pilot! It's built to enter orbit, land on Minmus, spend about 2 and half months processing ore, then lift off to interplanetary space with 6,000 delta V to spare!

Kerbal X Download Page

 

Notes/Trivia:

The crafts' front-most two fuel tanks are intentionally under-fueled! This was done to help achieve liftoff on the run way; when full, the craft was too unstable for me to fly properly X3 You might want to take this into account if you decide to refuel and take off on Kerbin. Alternatively, you can try to fly it fully fueled if you think your up to the task; I doubt I'm the best at flying :Y

There's only one pilot seat and no probe control (making flying with an engineer not very ideal), and the ISRU module and drills are the smaller variants. Refueling takes awhile, even with stock speed up set to max! It does hit 4,000 delta V around halfway through refueling, so you can lift off partially empty if you know where you want to go, or need more TWR.

Lift off from Minmus can be kind of tricky, as the craft doesn't have the reaction wheel strength to pitch up at full fuel, and the craft likes to curve after a while and slam one of it's wings into the ice! Simply retracting and rextending the landing gear quickly can help you ascend if you don't have a convenient ramp to use.

 

Feel free to add your thoughts and/or suggest improvements, this is my first serious SSTO, and I'd love to keep building upon what I've learned while constructing it!

Edited October 8, 2019 by Pacca

[Guest]

Nice work, especially if it's your first serious SSTO. Long-range SSTOs are really hard. It looks pretty well optimised too, with all that capability only on 2 x Nerv and 2 x Rapier. Clever use of Big S tailfins as main lifting surfaces also.

Some thoughts which may or may not work:

• If your target is Minmus, you should be able to get away using just one Nerv. That'll significantly cut down on your dry mass, improving your efficiency, which might let you add a second command seat for the engineer. You will probably need to get your Kerbin take-off exactly right though, to be able to make orbit with the lower TWR. If you're almost there, consider adding a small Lf/Ox tank: this will let your Rapiers give a final kick of acceleration where it's needed. This will also help you launch off the airless body: the thrust vectoring from the Rapier will also help pitch your craft up.
• Your ore tank is unnecessarily big, since you can process the ore as soon as you get it. If you used a single radial tank instead, that would further cut down dry mass.
• If you dropped one of the drills and put the remaining one inside a Mk 1 utility bay, that would further cut down your dry mass and improve aerodynamics, making for a more efficient Kerbin launch. (This might require a bit of clipping though, so if you consider that cheaty, then don't do it.)
• To help launch in a vacuum, consider adding a secondary landing gear: a medium gear just in front of the centre of mass. When you lower it, it will raise the craft to an angle. Combine this with the Lf+Ox tank that lets you kick out of there with the Rapier, and I think you'll find vacuum take-off much easier.

 

 

 

[Pacca]

Thanks! I really appreciate it ^w^

• A lot of my early designs actually tried to get away with one nerv! Unfortunately, these ones always ended up stalling at about 50,000 meters, then falling back down, usually burning up if I tried to keep pushing them... Adding some oxidizer to get a short little push to space might be just what that scenario was missing though, I'll try to keep that in mind for future modifications/craft :3
• Some earlier designs did try the smaller ore tank, but I had trouble fitting it into the design without introducing drag or getting in the way. Speaking of which X3
• Your so right, I should be using a utility bay, can't believe I forgot how useful they are when designing it! Even besides it's obvious features, it's ability to function as an airbrake and a crumplezone is nice for any craft, let alone a multipurpose one. Thank you so much for the suggestion!
• That's an awesome idea! I never would have thought of it, but I love it! Again, thanks for taking the time to tell me ^w^

[Guest]

What speed did your craft hit on the Rapiers? It should be well past 1500 m/s, if you're lucky pushing 1600 m/s. If it's much less than that, your problem is aerodynamics, you definitely have the TWR for that in this design.

[Pacca]

It usually hits around those speeds, definitely. I've been wondering if it has to do with my ascent; I don't have much experience in that regard X3 I've been trying to keep it relatively flat whilst climbing, but adjusting the craft at those speeds feels quite risky (I've had quite a few attempts simply flip perpendicular during adjustments and overheat/kill all my speed), and SAS tends to slowly pitch up if left to it's own devices. 

[Guest]

Flat is good, the main thing is that you hit those speeds. However don't be afraid of pitching up to +15 degrees prograde for the circularisation if you have low TWR.

[Guest]

Hey, thought of one more optimisation, if you don't actually need the docking capability of that port in the nose. You only need one intake to feed those two Rapiers, so you could swap out the port for the shock cone intake and just put regular nose cones on the nacelles. Better aerodynamics.

(BTW I tried and it is possible to fit a drill inside a Mk1 utility bay without what I would consider cheaty clipping.)

[Pacca]

I had initially swapped the nose piece out for the docking port to keep it from overheating and provide a front facing control from point; I'm not sure either of those are necessary with the current design, so that's a great idea :3 I also have no idea how intakes work in general, so I'm glad to know I only need the one!

[Guest]

One shock cone is enough to feed four Rapiers. You do need a front facing control point but that’s your command chair, if you only have one then just make it face forward.

[Dafni]

35 minutes ago, Brikoleur said:

One shock cone is enough to feed four Rapiers.

Oh, I never knew. Cheers. Is this info available in-game somehow?

Thanks in advance, and thanks for the constructive posts. All of them. Seeing a lot of you lately. Keep it up!

[Guest]

34 minutes ago, Dafni said:

Oh, I never knew. Cheers. Is this info available in-game somehow?

Maybe? The intake air requirements and capacity are listed with the parts. I just found out by trial and error though.