Is it possible to make a useful SSTO without rapiers?

[Shyrka]

I'm in the middle of a hard-mode career game and I've unlocked turbojets, ram intakes, etc. so I've started investigating plane-based SSTOs, mostly in order to cut costs so I can unlock the next tier of KSC builds sooner. Unfortunately, all the old tricks I knew about building heavy-lift and long-distance SSTOs no longer work. Multiple intakes per engine, turbojet/nuke combos, etc are all off the table. Reading around, the vast majority of SSTOs people are showing off lifting payloads to orbit or visiting minmus, etc. feature RAPIER engines. Since RAPIERs are now at the far end of the tech tree I can't utilise them. Is it possible to build a non-RAPIER SSTO that can do useful work any more? I've managed to get one into orbit running with quad turbojets and dual reliants but with no cargo and barely enough Delta-V to de-orbit, let alone travel elsewhere.

Edited May 30, 2015 by Shyrka

[capi3101]

It's definitely doable. Try a combination Turbojet with eight Twitch engines (what used to be called 24-77s) for every 25-30 tonnes of plane you've got at takeoff. And make sure that roughly half your plane's mass is dedicated rocket fuel. When you takeoff, head to 10k as fast as your plane will manage, then level out to about 10 degrees above the horizon and start picking up speed. If you start seeing heat indicators, increase your pitch angle. At 25k light the Twitches and pull up as hard as you dare.

Start with that and see where it gets you.

Edited May 29, 2015 by capi3101

[GoSlash27]

Shyrka,

SSTO spaceplanes really aren't cost effective unless you're just going to LKO and back. If you're going farther than that, it pays to use a vehicle designed for the purpose.

I have seen one turbojet hybrid so far that looks to have (potentially) decent payload fraction.

^design ctsy. Juzeris

Unfortunately, it's a bit cheaty, so I'm not sure how much it's performance would suffer without resorting to the cargo bay to mask drag.

Best,

-Slashy

- - - Updated - - -

It's definitely doable. Try a combination Turbojet with eight Twitch engines (what used to be called 24-77s) for every 25-30 tonnes of plane you've got at takeoff. And make sure that roughly half your plane's mass is dedicated rocket fuel. When you takeoff, head to 10k as fast as your plane will manage, then level out to about 10 degrees above the horizon and start picking up speed. If you start seeing heat indicators, increase your pitch angle. At 25k light the Twitches and pull up as hard as you dare.

Start with that and see where it gets you.

capi,

Would that 25-30 tonnes require 2 turbojets or just one? Also, what kind of payload fractions are you seeing?

Thanks,

-Slashy

Edited May 29, 2015 by GoSlash27

[capi3101]

capi,

Would that 25-30 tonnes require 2 turbojets or just one? Also, what kind of payload fractions are you seeing?

Thanks,

-Slashy

One turbojet and about 15% payload fraction (i.e. not much better than asparagus staging used to be, but at least with a spaceplane you're getting most of the cash for all your parts back). I am using FAR these days, but I played in the new stock aero while ferram was still building Euler and I can definitely say that there's not as wide of a gulf between stock aero and FAR these days as there used to be. A Turbojet engine in FAR still produces 166.77 kN of thrust on the Runway, so at 25 tonnes you've got a TWR of 0.71 and with thirty tonnes you're at 0.57. The wiki puts the figure for a single Turbojet at a nice, even 180 kN, and that would be for the stock game, so the TWRs there would be even higher. Half your mass in rocket fuel gives you somewhere in the neighborhood of 1800 m/s of delta-V (with the Twitch engine's 290 Isp), which is what I've seen folks recommending lately.

EDIT: Told you guys wrong in that first post - it's not eight Twitches; it's sixteen. You can get the same amount of thrust from a pair of Thud (Mk55 Radial) engines if part count is an issue - they have higher Isp but the increased mass will offset that.

Edited May 29, 2015 by capi3101

[Starhawk]

A turbojet based spaceplane is definitely doable.

Check out the Single Turbojet Challenge thread.

As Slashy pointed out, you're not going to get much more than LKO and stay cost effective.

If you are going just to LKO and back, there's no reason they can't be a viable solution. I've used one for early career rescue missions. Very cost-effective for that sort of thing since I can recover all the cost of the equipment by landing at KSC.

Happy landings!

[moronwrocket]

A better plan would be to install Stage Recovery and throw chutes on your lifters.

Or spending a dozen hours to come up with a plane. This one uses 4 turbos and 2 reliants, and has about ~650 dV left at 75 km. Cargo is 6 kerbals + 1 pilot. I suck at SSTOs, so I assume experts can do much better.

Javascript is disabled. View full album

[georgTF]

I think it depends on the definition of "useful".

Lifting cargo to LKO by rocket is easier though more costly, but more often than not, a portion of the cost (or it's entirety) can be offset by picking up a contract. I wouldn't bother with a spaceplane, certainly not a Mk2 as they seem to be the most difficult to build. I'd try to build one for fun and frustration, but wouldn't see it as a need.

Lifting kerbals to LKO or rescuing them from the Kerbin system is a perfect job for a spaceplane and they can do that very well even on a single TurboJet though for greater carry capacity i prefer 2 TurboJets + 1 T-30/45/Aerospike (the spike is far up the tree, behind a 550 science node and a 3.5 mil R&D upgrade)

It's possible to place a satellite anywhere in Kerbin system for slightly more than 10.000 which is easily offset by the contract. Using a spaceplane would offer marginal savings and i'd not want to bother saving a few thousand with one.

The perennial disadvantage of a spaceplane is allways that it has to carry all wings, tanks, athmospheric engines and other doodads with it wherever it goes. With LKO refuelling and an Aerospike or Poodle it's possible to go places and i do like the idea of an all-in-one craft. However there will be a price to pay in efficiency. Spaceplanes that only reach LKO suffer less from efficiency penalties, but they seem to be limited to taxi service or light/medium cargo. Once you need to burn absurd amounts of fuel, you're no longer saving as much. It's also neccesary to land on the runway to get 100% cost back, minus fuel, and re-entry can be very annoying or difficult.

I think there are roles that can be better served with a spaceplane but going that route just to save money can lead to madness as they are frustratingly difficult to build. Better to make money with rockets than save with planes i say.

@moronwrocket

That is a very nice looking plane. Though the winglets up front fill me with dread. Does that re-enter safely?

Edited May 29, 2015 by georgTF

[Xannari Ferrows]

This sounds like a challenge...

[Shyrka]

Thanks for the replies so far. In general, the consensus appears to be that, whilst it's possible to make SSTOs without rapiers, they're not much use for anything other than rescuing the odd kerbal from LKO. This is more or less what I expected so thanks for confirming my suspicions.

[capi3101]

I'd also say they're good for delivering satellites to LKO for cheap. A 25-30 tonne plane can easily lift a probe with enough juice of its own to make orbit around Mun or Minmus, possibly further. Hell, Wanderfound built a sci probe that was slightly over half a tonne and delivered it to orbit in a Service Bay (OKTO 2, 4 OX-STAT panels, a Reaction Wheel, a small antenna and Thermometers; it was something like 685 kg IIRC); that's definitely good enough for "Science around Kerbin" contracts.

[Slam_Jones]

I made one in 0.90 with a single TurboJet and a 48-7S "Spark". Since then, however, both have been changed, and the 48-7S just doesn't provide enough power :\

[GoSlash27]

Thanks for the replies so far. In general, the consensus appears to be that, whilst it's possible to make SSTOs without rapiers, they're not much use for anything other than rescuing the odd kerbal from LKO. This is more or less what I expected so thanks for confirming my suspicions.

Shyrka,

They're far from "useless". They're ideal for placing kerbals/fuel/oxidizer/monoprop into stations or vehicles under construction in LKO. It's just that turbojet SSTO spaceplanes are going to end up more expensive, larger, and less efficient than RAPIER ssto spaceplanes.

Best,

-Slashy

[Pecan]

Yes. SSTO rockets are quite simple to build and can lift substantial payloads to orbit.

[moronwrocket]

@moronwrocket

That is a very nice looking plane. Though the winglets up front fill me with dread. Does that re-enter safely?

Still looks like a plucked chicken in Chase view to me.

I haven't had any issues with re-entry. Running stock atmo in 1.0.2. Hell, it lights up more on the way up than the way down. I suspect it might be possible to remove the winglets and put on more elevons at the rear if you're worried they'll rip off.

Feel free to give it a try and give me any tips. http://kerbalx.com/moronwrocket/Y-3

[Maukse]

I have a turboramjet/lv-909 design able to put 4,5 tons in lko, on a dual bay (small+long). Craft weight is 24 tons.

Based on the same design, mkII crew shuttle, 6 kerbals. Can take screenshots if you want.

[cybersol]

In my career save, I was using a Mk2 SSTO plane with turbojets and a poodle as both a rescue and small (3-6t) satellite launcher. It could do 2 LKO rescues and launch a satellite that could fulfill 2-3 sat contracts all in one launch with full recovery.

Edit: Here's a picture:

Edited May 30, 2015 by cybersol
Added picture

[Shyrka]

Shyrka,

They're far from "useless". They're ideal for placing kerbals/fuel/oxidizer/monoprop into stations or vehicles under construction in LKO.

-Slashy

That's pretty much what I meant: they seem to be pretty much restricted to working in LKO. If that's the case, that's fine, I can still do satellite launches, etc. I had been hoping to launch orange tanks into orbit or use them as mun/minmus crew shuttles but it sounds as if that's not possible these days. I can live with that although it's a bit of a come-down from the heady days of 0.90.

For now I'm converting my existing launch rockets to be partially recoverable which is helping to reduce launch costs. I'll probably look into SSTO rockets too for lifting heavy payloads onto LKO. I'm building an orbital fueling station so eventually my LKO-restricted SSTOs can refuel and head on to my mun and minmus research stations.

[problemecium]

This may be beating a dead horse, but whatever - check "Applied Sciences Division" in my signature.

[HansonKerman]

Try a "Dart" Areospike Engine.

[Not Sure]

It really can be done quite easily with some knowledge. I simply use a combo of Whiplashes and thuds, for SSTO’s going to LKO you should be looking at engine TWR more than engine ISP.

[Kerbal101]

Check the thread date, guys.  
A lot of things have changed since then, please find a newer thread instead?   Thank you!

Locking.