Usefulness of SSTOs and spaceplanes
There's a lot of chat about SSTOs for KSP. I recently managed to design, launch into orbit, and recover an SSTO.
However I have to say that having achieved this, I don't really see what the appeal is. The remaining d/v is fairly bad, managing the different engines and fuels is cumbersome, and it's trickier to launch and land than a regular rocket. Furthermore, since you would be keeping the wings and structure for landing, you can't even toss them off once you're in space to lose mass.
Furthermore, it seems to me like there's always an awkward gap between actually being in orbit and when the airbreathing engines run out, when you still need a moderately high TWR to finish getting into orbit. I've looked at things like the Rapier but it seems to me like their vac performance is pretty bad TWR and mediocre ISP at best.
So in short, what actually is the point of making and using SSTOs or even just spaceplanes in general?
Best Answer
The point of a single-stage-to-orbit vehicle is that it can return back to the space center in one piece, where you can recover it for 100% of the initial cost (Maybe a better acronym would be SSTOAB - single-stage-to-orbit-and-back). That means getting the payload into orbit costs you nothing except fuel.
A common use-case for SSTOs is as delivery vehicle for satellites. When you have a "satellite in Kerbin orbit" contract, add a cargo bay to your spaceplane and place a satellite in it which has a small fuel tank and thruster so it can maneuver itself into place. Use your spaceplane to get it into orbit, release the satellite, maneuver the satellite into the desired orbit and deorbit the spaceplane so it returns to the space center. Fulfilling the mission then costs you nothing except the price of the satellite itself and a bit of spare-change for fuel.
When you unlocked the Mk3 spaceplane parts, you can even transport rockomax-scale parts into orbit in cargo bays, so manned missions which get into low-kerbin orbit through SSTO become an option. A more ambitioned mission might require to dock several sections in orbit, which you can all launch per SSTO.
Regarding the rapier: While it looks quite mediocre on paper in both of its roles as a jet engine or a rocket engine, the ability to fulfill both roles in one part can make more than up for it. Dedicated engines for one flight phase are just dead weight in the other. That means when you compare the TWR of rapiers with that of a combination of jet- and rocket engines, you need to add the mass of the rocket engines to that of the jet engines and vice versa. Also, having more engines means you will have to design a craft with a larger aerodynamic cross-section.
Pictures about "Usefulness of SSTOs and spaceplanes"
Is an SSTO possible?
To date, no Earth-launched SSTO launch vehicles have ever been flown; orbital launches from Earth have been performed by either fully or partially expendable multi-stage rockets.What is the principle of single state rocket?
A single stage rocket uses a single rocket motor or a cluster of motors to lift its payload to the desired altitude, and most low altitude sounding rockets are of the single stage type.Is a spaceplane possible?
Three types of spaceplanes have successfully launched to orbit, reentered Earth's atmosphere, and landed: the Space Shuttle, Buran, and the X-37. Another, Dream Chaser, is under development. As of 2019 all past, current, and planned orbital vehicles launch vertically on a separate rocket.What is SSTO KSP?
From Kerbal Space Program Wiki. This tutorial explains how to build a single-stage-to-orbit (SSTO) spaceplane that is able to launch into space and return without jettisoning any parts.Spaceplanes
More answers regarding usefulness of SSTOs and spaceplanes
Answer 2
The answers above are great: SF is correct that SSTOs are largely for fun and challenge, and Philipp points out that it can deliver small payloads to orbit. I'd like to a points.
First, SSTOs can also deliver 'non-structural' payloads (resource in tanks, science, and Kerbals) to and from orbit. I've used SSTOs to get Kerbals and supplies (TAC-LS) up to an LKO station, and bring Kerbals and science back down.
Second, while the term "SSTO" is typically applied to hybrid open-/closed-cycle spaceplanes that can can make the surface-orbit round trip at Kerbin, you can apply it to any lander that can make a in one-stage round trip (down and back). So, SSTOs on other bodies (Minmus, Mun, Laythe, etc) can be useful for moving all kinds of stuff from surface outposts to orbital stations repeatedly if you make the SSTO reusable, and if it's not reusable, what's the point?
The third point is really a sub-point of the second. If you can build an SSTO spaceplane that works on Kerbin, it should work on Laythe, too. Again, this is a very useful method for going to and from Laythe's surface for a minuscule amount of fuel, which is ALWAYS useful far from home.
Hope that helps.
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