Single-Turbojet SSTO Spaceplane

[Bill Zarr]

I built a couple of quick SSTOs, X5 is my first post 1.0 SSTO, X6 does not fly that well due to it's offset engine layout, wing layout on it is bad. It is not so much flown into orbit as wrestled into orbit.

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[Tarmenius]

Congrats Bill Zarr! I really like the offset engine on the X6, though I wouldn't want to be the one flying it. Is the SAS enough to keep it from tumbling when the Terriers are on?

[Ferdoni]

Most of my existing non-Rapier designs go the opposite route, two turbojets and a single LV-T45. Here's my first attempt at doing it with one jet (stock aero):

http://i.imgur.com/wb3oaoT.jpg?1

Pretty ugly, but made it into a 121x80km orbit and return first time up. (It's not in the rules, but personally I don't count an SSTO as successful unless it can also land safely.) Not optimal, has a surplus of oxidizer. About 200 m/sec left on orbit. Still haven't figured out if the intake pre-cooler actually does anything or not. Will make a better one later. Hopefully prettier as well.

Craft file.

PS. Just noticed I didn't give it a name. Let's call it the Duckling Mark 1.

Very nice design! Been searching for such a thing for a while now, looks like i've found it!

[Bill Zarr]

Congrats Bill Zarr! I really like the offset engine on the X6, though I wouldn't want to be the one flying it. Is the SAS enough to keep it from tumbling when the Terriers are on?

Both the Terriers are angled upwards slightly and the turbojet is angled down slightly. Once it's in vacuum I think the Terriers could only run at about 80% throttle before it started to overwhelm the reaction wheels and nose up. If I spent more time tweaking it I'm sure I could get it to perform better, but I doubt it would ever work as well as something that was inherently balanced from the start.

[Wanderfound]

Both the Terriers are angled upwards slightly and the turbojet is angled down slightly. Once it's in vacuum I think the Terriers could only run at about 80% throttle before it started to overwhelm the reaction wheels and nose up. If I spent more time tweaking it I'm sure I could get it to perform better, but I doubt it would ever work as well as something that was inherently balanced from the start.

If you've got RCS Build Aid or Kerbal Engineer, they provide engine torque figures. Angle/reposition your engines to zero out the torque (done individually for engines that might be run in isolation, so do the Terriers and Turbo separately) and you're all cool.

It adds a lot of design flexibility:

The lateral tanks on that are raised slightly to bring the RAPIERs in line with CoM. This also raises the CoM a bit, reducing the angle required on the turbojet.

Edited May 28, 2015 by Wanderfound

[Bill Zarr]

Wanderfound, thanks for the tip. I was going by eye in the SPH, & I knew they weren't angled enough to be right through the CoM. My concern was also that the thing should be able to thrust straight for manoeuvre nodes so didn't want to angle the Terriers more than the gimbals could correct for. Might be better to add a couple of Spiders for orbital manoeuvres.

[Starhawk]

Out of curiosity, what kind of ascent profile do you use? And does it launch fully fueled?

Take off and climb at 60 degrees until you hit about 8 km. Swich SAS to follow prograde. This will allow the nose to drop while building speed. Pitch as needed to control ascent rate between 18 and 22 km. This is the fiddly part. Aim to hit about 1150 m/s (or more) at around 21-22 km.

Hit the rockets and steepen your climb to get out of the remaining atmo fairly quickly.

She launches with the radial tanks empty and the liquid fuel tank holding only 90 units.

Happy landings!

Edited May 28, 2015 by Starhawk

[Tarmenius]

... I doubt it would ever work as well as something that was inherently balanced from the start.

Maybe not, but it's still pretty cool.

Take off and climb at 60 degrees until you hit about 8 km.

It looks as though I had been starting my turns a little too late. I've been finding more success on flights that end up at 20 degrees or so by 9km than I had previously.

---

I'm curious to find out what the smallest craft of this configuration will be. Before 1.0 there were some truly diminutive SSTO spaceplanes.

Edited May 29, 2015 by Tarmenius

[RuBisCO]

23 part SSTO single-turbojet.

[georgTF]

Far from comfortable to fly or land, this variant of my previous entry sacrifices everything in order to achieve 75x75 orbit + return with a minimal part count and mass. Only 8t and less than a full 440 tank. I begrudgingly added a solar panel to prevent re-entry disasters, though it will only work in the afternoon. Yes, that and several other reasons make this approach ridiculous as the fiddly way to fly makes it not really worth bothering with. An extra winglet instead of a tail and actual batteries to provide enough electricity would be much better. But this is minimalistic i guess.

Never judge an engine by it's Isp alone! The "Twitch" engines (6 in total) turned out to outperform 2 909s though they generate enough heat to melt the tail winglets...

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Flight:

1. Cut throttle, engage RCS, press space to stage turbojet, deactivate RCS, engage SAS

2. set throttle to 2/3 and wait until the rear wheels lift off the ground. Pull up and climb to about 7-8km

3. Begin the orbital ascent at 8km, full throttle, angle of attack no less than 15 degrees (because overheating)

4. Monitor airspeed. At peak, engage RCS to activate rocket engines

5. Heat should climb to critical but without damage. If something explodes, your angle of attack or starting alt was too low

6. Check the map for your Ap. Once it reaches 75km, cut the engines, coast up and circularise

7. For re-entry set your Pe at 35km, over land on the sunny side of Kerbin. Preferably late afternoon to give the solar panel a chance.

8. Maintain a very high AoA during descent. ~70-80 degrees

9. Landing is miserable as the nose is very unresponsive. For the final approach use a tiny bit of thrust to help.

To land you'll need plenty of flat terrain to cope with around ~90-120 m/s airspeed. I got it down to 20 m/s before the plane tumbled into a fireball. Cockpit and pilot survived.

Link: TurboJet Cheapskate

Thanks in part to RuBisCO for going the "Twitch" route. My plane sucks though, and only exists to push the limits of low mass/drag SSTO.

Edited June 2, 2015 by georgTF
corrected instructions

[zarakon]

I'm curious to find out what the smallest craft of this configuration will be. Before 1.0 there were some truly diminutive SSTO spaceplanes.

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5.283t at launch (includes the Kerbal)

Command seat, reaction wheel, and batteries inside service bay

LV-909 clipped inside the Whiplash

Edited May 29, 2015 by zarakon

[Tarmenius]

RuBisCO: Let me know if you want your own name for the craft to be on the list. And what kind of flight profile do you use with it? Does it start fully-fueled?

My plane sucks though, and only exists to push the limits of low mass/drag SSTO.

Well that's one of the things we're here for anyway, so good work!

zarakon: Well done, indeed! It looks like there's even enough fuel left to de-orbit. How narrow is the margin for error on the ascent?

[zarakon]

zarakon: Well done, indeed! It looks like there's even enough fuel left to de-orbit. How narrow is the margin for error on the ascent?

I only flew it twice. First time I forgot to take out some oxidizer, so I was just barely short of reaching orbit and had about 50 unused oxidizer. So on the next flight I started with 44 less, and made it fairly easily.

I do a steep ascent at about half throttle, then around 8km I punch it and slowly nose down toward 20, then hope I don't explode. This thing is light enough that I reached 1300 surface speed before I needed to turn on the Terrier, and somehow I only got a little bit of heating on the intake.

[GoSlash27]

I decided to see how heavy I could go. I think I still have a little room, but here's where I'm at:

A little rebalancing needed. I'm hoping to squeeze just a little more out of it so I can put in a docking port.

Weighs 19.6 tonnes at launch.

A side by side comparo of the single turbojet vs. RAPIER. Not only is the RAPIER smaller and cheaper for the same performance, but it has better payload fraction besides.

Best,

-Slashy

[georgTF]

If career mode is considered, then the single rapier has a disadvantage in being placed very far up the tree and requiring several millions to unlock. Engine vs. engine it's superior for planes that fly up to LKO and no further. Going further out makes things more complicated... is it worse to lug around a useless turbojet or to use a rapier in rocket mode, which is not the most efficient engine? It's probably better to use a rapier. But in career on hard, it's going to take forever to unlock the tubojet alone, and then several forevers to get the rapier.

I also suggest that the tables in the OP either ignore total mass, or favor heavier craft. Mass is the limiting factor with single TurboJet designs because there will be a point at which it's almost impossible to go supersonic or get any use out of the engine. I'd like to see a plane that gets the absolute best out of a TurboJet and still acomplishes something.

Perhaps split tables into single seaters that would favor low mass, part count, fuel use and such and achieve LKO with the barest minimum. And a separate table for the heaviest plane that can get to LKO on a single TJ, because i think that would be more impressive, esp. since it could carry more crew/cargo.

It's a very interesting challenge overall, because it leads to builds that carry the least amount of athmospheric deadweight while allowing for very efficient rocket engines. Trouble is, the central rear node is probably an ideal place for a single rocket engine, but it's probably going to have to accomodate the jet instead. So where to place the rocket engines, which ones to choose and how far can the thing go are really interesting considerations.

[Rune]

I'm on a roll! Another design that just incidentally complies with the rules of a challenge: this is how I accomplish satellite contracts for mucho profit now:

Clocking in at 18.2mT on the runway, and a mere 23,928√ (26k with payload), of which only 1k is expendable fuel, the thing is a √ mine. I usually put payloads of about 1.5mT (no need to use more to complete two contracts at a time, those satellites have upwards of 2.5km/s), but it gets to orbit with so much margin, you can probably push it to 2mT. Sorry about the lack of engineer output, this is after all a career save.

Edit: oh, I should give it a name if it's going to be an entry. Let's call this the arrowhead, I think it fits.

Rune. It flies great, too, even though it's a bit sluggish to accelerate past Mach 1.

Edited May 30, 2015 by Rune

[GoSlash27]

Rune,

That is a seriously smexy spaceplane!

Best,

-Slashy

[match]

Simple, affordable and easy to drive:

The SSTURD

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Craft

Edited May 30, 2015 by match

[Rune]

Rune,

That is a seriously smexy spaceplane!

Best,

-Slashy

Thanks! It's really simple to put together, too. The key is to use the forward tank for fuel only to get the weight balance right. Oh, and it has couple hidden small ailerons on the front to give awesome control authority (can reenter at 45º AoA, which guarantees no flames on the way down).

Rune. I had a really inspired quarter of an hour

[Batz_10K]

I find in general I'm favouring twinjet designs now as they seem to be a bit easier to fly, but this is one that I'm using in my career game to transport Kerbals to and from my LKO station

Edit: Name - this is the K110 Backlash

Edited May 30, 2015 by Batz_10K

[RuBisCO]

RuBisCO: Let me know if you want your own name for the craft to be on the list. And what kind of flight profile do you use with it? Does it start fully-fueled?

Yeah no thanks, it was just a proof of concept I made awhile back, and no: one tank has oxidizers half empty.

I moved on to much MUCH bigger spaceplanes.

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[Tarmenius]

I decided to see how heavy I could go. ... Not only is the RAPIER smaller and cheaper for the same performance, but it has better payload fraction besides.

No question, the RAPIER seems to out-class the Turbojet everywhere it counts. Hopefully by the end of this challenge, we'll have a pretty clear picture of just how wide the gap is between the two.

I also suggest that the tables in the OP either ignore total mass, or favor heavier craft. Mass is the limiting factor with single TurboJet designs because there will be a point at which it's almost impossible to go supersonic or get any use out of the engine. I'd like to see a plane that gets the absolute best out of a TurboJet and still acomplishes something.

Genuinely, thank you for the input; it's always welcome. If the challenge favored "most massive" craft, then toward the end it would become essentially a piloting competition as the winner would be whoever could pilot the most efficient ascent. Don't get me wrong, that's a perfectly valid challenge to have, but more limited in scope than I wanted this one to be.

I'm on a roll! Another design that just incidentally complies with the rules of a challenge: this is how I accomplish satellite contracts for mucho profit now ... Sorry about the lack of engineer output, this is after all a career save.

On a roll, indeed. How long did it take you to adjust to the new aero? You've been designing (awesome) spaceplanes for quite some time; I imagine some of that skill had to be re-learned. Either way, that Arrowhead is rather impressive.

match: Well done and congrats! It reminds me of a pusher aircraft.

Batz_10K: I love the look of your K110 Backlash! It's like a mix of the ME 262 and the Corsair II. How long did it take you to balance it?

[GoSlash27]

Tarmenius,

Thanks for hosting this challenge. It really got me thinking about turbojet SSTOs and what it takes to make them work efficiently.

First thing that I noticed is that they shouldn't be balanced to just barely get supersonic in level flight like you would do with RAPIERs. By the time you hit that wall, you've already wrecked your top speed and altitude, and this is far more important for the TJ.

Probably a good idea for efficiency to keep the mass around 13-15 tonnes per engine.

I also built a twin engine testbed to compare it to my twin RAPIER design. The RAPIER got 22% payload fraction while the turbojet managed 14%, which really ain't too shabby.

There are disposables that can exceed 14% payload fraction, but I could easily see saving money by doing small jobs with the turbojet SSTO.

Thanks again,

-Slashy

[Tarmenius]

It wouldn't be much of a challenge without the participants, so thank you for joining in!

I'm really impressed by everyone's entries so far; these Forums never disappoint

[Batz_10K]

Batz_10K: I love the look of your K110 Backlash! It's like a mix of the ME 262 and the Corsair II. How long did it take you to balance it?

Thanks!

Actually not all that long - although the turbojet is offset, the CoM is pretty low and the control surfaces take care of the rest, and by the time you are out of air for your control surfaces, the turbojet has flamed out anyway. The main issue was figuring out the proper amount of fuel/number of twitch engines and ascent profile. The margins are pretty tight as that's a fairly draggy design. (there's a small docking port on the bottom which isn't visible)

This is a twinjet variant that I also use, which is much easier to get into orbit and has a lot more delta-v on orbit... it's a little more ME262

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