Low Tech Space Aviation

[Guest]

Started another career and since I think rockets are kinda dull, I've been trying to solve problems with planes as soon as it's feasible. It's fun to try to come up with a space plane that's good for something with Tier 1 tech. Obviously at this point it means rocket planes as there are no airbreathers powerful enough to be useful.

So far, the best I've come up with is this -- the Jetstream, all stock. With those boosters it has enough legs to get to Minmus and back, which means it's good for tourists and search/recovery missions. This is in fact one thing tier 1 planes can do better than rockets -- it's tricky to build a re-entry module that seats three and behaves well. Only non-recoverable parts are the SRBs. 

I did manage to build a Tier 1 single-engine SSTO (uses the Swivel) but once up there, there was barely any fuel for manoeuvring so it's not really practical for anything.

[Rocket In My Pocket]

Neat idea, always fun to try something different!

I'm not entirely sure if I'd call that a "spaceplane" or just a rocket with wings though.

Having the ability to land at the KSC is something that could be valuable in the early career mode when funds are tight, certainly.

[Guest]

Oh, it's a plane all right, by most reasonable definitions of the word. Other than being rocket-powered, the only rocket-like thing about it is take-off -- near-vertically and with boosters rather than off a runway -- but that doth not a rocket make. Once off the ground, it flies aerodynamically, relies on lift rather than thrust to stay aloft, is controlled with control surfaces rather than thrust vectoring, and the launch profile is like a plane's -- climb with a constant pitch up at around 30 degrees rather than a parabolic arc with a gravity turn. Re-entry and landing is just like any ol' spaceplane's of course.

(Or, put another way -- swap the space-optimised Terrier for an atmosphere-optimised Swivel, and it'll take off the runway beautifully and do a nice little sub-orbital hop all on its own, and I don't think many people would dispute its plane-ness in that configuration. It just doesn't have the grunt to get into orbit without the extra assistance.)

Edited December 28, 2017 by Guest

[AeroGav]

3 hours ago, Brikoleur said:

Started another career and since I think rockets are kinda dull, I've been trying to solve problems with planes as soon as it's feasible. It's fun to try to come up with a space plane that's good for something with Tier 1 tech. Obviously at this point it means rocket planes as there are no airbreathers powerful enough to be useful.

So far, the best I've come up with is this -- the Jetstream, all stock. With those boosters it has enough legs to get to Minmus and back, which means it's good for tourists and search/recovery missions. This is in fact one thing tier 1 planes can do better than rockets -- it's tricky to build a re-entry module that seats three and behaves well. Only non-recoverable parts are the SRBs. 

I did manage to build a Tier 1 single-engine SSTO (uses the Swivel) but once up there, there was barely any fuel for manoeuvring so it's not really practical for anything.

Nice design.  I usually find pointy cockpits (and the mk1 in particular) very vulnerable to heating, you'll want to swap to an inline cockpit with service bay and nose cone in front as soon as possible.   Even the mk3 cockpit isn't as sturdy as a mk1 inline, thanks to it not being right at the front.       If you don't have the inline cockpit yet,  I suppose you could just put the mk1 command pod on the front instead,  it has a bit higher tolerance than the airplane cockpit and having a small nose cone/parachute on the very front does protect a small part of it from the heat

[Guest]

Heat isn't a problem; the big wing area bleeds off enough speed on re-entry before it gets there. Got to about 70% of critical but not past that.

-- I managed to make a marginally useful tier 1 SSTO without boosters: powered by a single Reliant, and has two drop tanks on the wings. Take-off is a quite a bit trickier than with this one though and it's not really any cheaper so there's not much point though.

[AeroGav]

I do have a basic Juno/Terrier on my Kerbal X page but it only just gets to orbit.    I have made a version with jettisonable jet engines that has more Delta V,  but that's only enough extra for a medium orbit - can't even get a Munar flyby.    With Panther,  you could probably get similar performance with jettisonable panther instead of thumpers and takeoff horizontally, but i suppose that's just a sideways move.

[fourfa]

4 hours ago, Brikoleur said:

SSTO ... has two drop tanks

???

[Guest]

Drop tanks don't count.

[Guest]

Made a slightly updated design for a complex mission. Swapped out nose part for an inline Mk1 + NCS adapter, tipped with a docking port Jr, and added a science collection box to the utility bay. The mission is a double rescue from low Munar orbit, plus science return from my Munar station. The docking port is needed to collect the science from the Munar station, plus I want to refuel there -- while it might be theoretically possible to do the LMO rescues and be able to return, the margins of error get too thin for my liking (and I'm not 100% sure it's even doable). 

I also noticed that liquid fuel boosters based on Reliants cost about the same as those Kickbacks, m/s per m/s, and experimented a bit with them. It's a bit of a sideways move. The Kickbacks have a better TTW ratio so take-off is easier and more efficient, but because of the insane acceleration near the end of the burn I have to fly a pretty high arc, which puts me at about 120-140 klicks which is slightly sub-optimal. The LF boosters make for a more efficient insertion because they're lighter and more controllable, but because of the poor early TTW, take-off is inefficient so what I win there I kind of lose in gravity, aerodynamic, and manoeuvring losses early on. I think I'll stick to the Kickbacks, that 7 g acceleration near the end is fun.

[Rocket In My Pocket]

8 hours ago, Brikoleur said:

Drop tanks don't count.

I hate to say this, because I love using drop tanks on spaceplanes too, but yeah; they do count.

If you stage anything at any point, it's not a "single stage to orbit." It's just a spaceplane.

"A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles."

[Guest]

Suit yourself, I don't count them.

Anyway, here are a couple more relatively low-tech spaceplanes -- they've dipped into tier 2 tech but not deep.

This one will lift about 12-14 tons to LKO. Only tier 2 parts are the medium landing gear.* It flies very nicely.

*This payload has a tier 2 aeroshell though.

And here's one from the "because why not?" file -- it works, but really isn't worth the hassle. Not an optimised design, more of a proof of concept really. The big plane only goes sub-orbital, the little one has to do a short burn to get the rest of the way. I didn't check if the big one has enough legs to fly back to the KSC; in any case it would take way too long to be fun.

Edited December 29, 2017 by Guest

[Guest]

Okay, best yet. All Tier 1 tech. SSTO with a medium-sized payload, I haven't explored the limits but I'm estimating it somewhere between 10 and 15 tons. Flies beautifully, CoM barely shifts and thrust torque is not a problem. I would like heavier landing gear, now I've had to pile on rather too many light ones. But hey, it works.

Beauty shot, preparing to land at dawn. (I did aim for the KSC but, uh, I missed.)

Clearly Skippers are the way to go for early SSTOs. 

Edit: A variant -- used the Osprey to piggyback the Sparrow into orbit. This configuration is a bit finicky as thrust torque does become a problem; basically I have to use a shallow launch profile to stay in the atmosphere as long as possible, then finesse the rest of the way, and the Sparrow will have to do a little circularisation burn at the end. Still, it works and is 100% recoverable!

(By the way, O ye masters of arguments about semantics, is this an SSTO or a two-stage to orbit? The Osprey will get itself into orbit after releasing the Sparrow, but the Sparrow does need to do a circularisation burn because of the thrust torque problem. It would be possible to finesse that by dialing down the Skippers and using the Terrier to maintain centre of thrust so the combo could reach orbit together... but that would be stupid as I'd be burning fuel on the Sparrow unnecessarily, and I haven't bought fuel lines so I can't transfer resources between the two.)

Edit edit: HA! solved the thrust torque. Bought a fuel line, so I can transfer resources between the craft. Now when it starts to go out of control, I cut the engines, dial down the Skippers to 20%, fire up the Terrier, and go. Before detaching, fuel up the Sparrow for a cool 2800 dV.

Edited December 30, 2017 by Guest

[Rocket In My Pocket]

5 hours ago, Brikoleur said:

By the way, O ye masters of arguments about semantics, is this an SSTO or a two-stage to orbit? The Osprey will get itself into orbit after releasing the Sparrow, but the Sparrow does need to do a circularisation burn because of the thrust torque problem.

If any physical thing comes off your spacecraft before it's in orbit (70k Ap/Pe) it's not a single stage to orbit. Pretty simple.

Keep in mind I'm not being a "stickler" it's just the definition. I build tons of spaceplanes, but hardly any SSTO's, as I don't see an issue with losing un-needed bits personally. It is what it is though, no reason to claim it's an SSTO if it isn't. As far as I'm concerned actual SSTO's are for elitist's who like to show off.

All nice planes btw, impressive work!

[Guest]

That Osprey design is super-versatile, a real workhorse. I've stripped it down a bit though, there are some unnecessary bits on the ones above.

I can swap things around lots of ways for lots of different missions. The highest load I've managed to fully loft to LKO has been 27 tons, and it could do a bit more -- there was a quite a bit of fuel left over. That one had a triple-Skipper configuration for power and the payload was roof mounted.

It was a bit of a special case though: a refueling launch bound for Minmus, probe core controlled, and powered by a Poodle. I could control the thrust torque nicely by having it drain first and then running the Poodle to balance out the torque.

Multi-probe launches are a doddle -- I mount them on the centre hull to the rear, pointing backward. Doesn't even need an aeroshell. 

Large-volume/relatively low-weight launches -- like a space station core + propulsion unit + lander -- are mounted at two nodes: the un-aerodynamic stuff in the front, covered with an aeroshell, and the propulsion unit at the back. No thrust torque in this configuration, and the Poodle can help once past 12 k altitude.

I've also used it to recover landers. In that configuration, I dock them at the back of the centre hull, and I built up the lower wing surface towards the back so it shields it on re-entry. 

And finally, I made a utility shuttle system that can do a Mun or Minmus roundtrip with a couple of rendez-vous manoeuvres while up there -- to pick up science, do crew rotation, or rescue operations. In that system, the Osprey is automated, while the long-distance shuttle is basically a plane without wings or control surfaces but with very good RCS, roof-mounted. I get to orbit, park the Osprey there, do my thing with the Qalam shuttle, then re-dock in the same position (pretty easy with the robust RCS), and re-enter the whole thing.

(The tanks on the Qalam are procedural, but that's an aesthetic choice; they're set up to be identical in spec to the corresponding stock ones.)

And it's all Tier 1 tech! Okay so lately I am using some Tier 2 stuff but it's refinements rather than requirements -- the 2.5 metre aeroshell for payloads that need it, medium landing gear instead of multiple light ones, better control surfaces, that sort of thing.

I've been making planes in KSP for a while now but this one is by far the most useful design I've come up with. They fly really well, they're easy to balance and easy to adapt for any number of scenarios, and both take-off and return are dead easy.

(In fact, this is by far the most fun KSP career I've had, and I haven't even left the Kerbin system yet. I'm playing with hard physics but lenient career settings for funds although not science; however I started with about 2000 science and enough funds to upgrade my runway so I could start flying planes right away without having to grind for them. On the other side, I've resolved not to use mobile processing labs to grind out science -- if I'm going to use them at all, only as a place to level up my Kerbals and a shortcut to reset experiments. Those things ruin the game for me...)

[Guest]

Finally, the successor to the Osprey. This one adds a few tons of absolute lifting power, greatly expands the available space for cargo, eliminates the thrust torque issues the Osprey has with certain loads almost completely, and retains CoM even better. 

Still doable with Tier 1 tech. This one has Tier 2 landing gear and control surfaces, but they're convenience rather than essential. 

 

[Guest]

Pushing into Tier 2, but I think this still counts as fairly low-tech -- no fancy propulsion or anything, just better fuel systems which give better aerodynamics and more structural integrity. Doing this with Tier 1 parts only would probably put a significant dent in the lifting capacity.

This is the Firewing-H, fitted with a 50-ton payload about to go into orbit. This would be above its effective lifting capacity if the payload didn't provide some propulsion of its own, but this space station core + propulsion/fuel store bound for Duna does. The liquid-fuel boosters docked to the propulsion unit will be discarded during the initial burn for Duna.

With Mainsails instead of Skippers I could certainly push the lifting capability of this design a fair bit further. They have twice the thrust so I could replace all those gray Rockomaxes with orange ones. I suspect volume is the practical limiting factor for this design also.

Edited January 6, 2018 by Guest

[Guest]

So here's the final (?) iteration of the Firewing, before moving to jet powered craft. The payload weighed in at 48,310 kg. No drastic changes, just refinements when new tech became available --

• Two of the Skippers upgraded to Mainsails for a better T/W ratio
• Wing profile changed to delta, to accommodate the bigger control surfaces
• Bigger reaction wheels (convenience only, makes rolling around in orbit nicer)

It flies really nicely now. CoM barely shifts when you take into account dropping the payload, and the entire flight profile is easy as pie. Unsticks at about 140 m/s, point it up at 45 degrees, then follow prograde when you hit 500 m/s, circularise at 75 klicks. To return, set Pe to 50k, point to radial out until it flattens out. Use the docking controls from there on out to stop it being too twitch. Landing is gentle and easy at around 40 m/s.

Edited January 8, 2018 by Guest

[Guest]

... and here is the final (?) rocket-powered Osprey. Similar refinements as with the Firewing above. She has just lofted to orbit Valentina in a plane bound for Duna. I guess the Dunaplane is an evolution of the Jetstream in the original post. 

These are no longer low-tech. We have plenty of Tier 2 tech in all of these -- fancy reaction wheels, avionics, and aerodynamics. Which means I guess this is as good a time as any to conclude this thread. Thanks for the likes and the comments everyone!