Single-Turbojet SSTO Spaceplane

georgTF · June 1, 2015

GoSlash27 mentions nuclear LF only SSTO, i swear i'm not interested, later i find myself frustrated by the very thing. I got Nerd sniped!

I did get a plane out of it though, at a small-ish cost in sanity. As i fooled around with the nuclear option, i found that the CoM likes to drift backwards as fuel is spent partly due to the nuke's mass. The solution was to place it as far forward as possible. This then makes it a little bit difficult to place wings in a way that makes the craft controlable. Several frustrating issues with takeoff and bad manners in general followed. Eventually the plane morphed into a neat design that handles heat well, has decent Dv, and flies ok but nor great. I think the tail is too large and the craft doesn't really do anything except carry two kerbals into orbit, but it's a decent baseline. That's what i'll keep telling myself at least.

I did forget fuel lines and didn't carry batteries or solar panels (which shows how much faith i had in it at the time). I added those to the craft after the flight.

Flight: (Nuclear engines are bound to the RCS action group)

1. Full throttle on the runway, don't pull up until it hits about 170 m/s. It's very lazy at takeoff.

2. Fly up to about 8-11km. It may be neccesary to dive a bit to punch through the sound barrier.

3. Aim for a very shallow climb of <5 degrees AoA at ~10km, get supersonic and let the turbojet work. It should build up speed and the craft will rise automatically.

4. Once you hit peak airspeed, activate rockets. The craft is a bit sluggish so athmospheric heat isn't a huge deal. NERVA heat is.

5. Monitor heat and Ap. Once you raise Ap to >70km cut the engine, coast up and circularise.

6. Cool off, and re-enter.

My personal re-entry point is above the eastern edge of the large Kerbin crater. Burn retro until the trajectory drops down to the large island further east of KSC. This usually drops the craft about where it needs to be to reach KSC, though i often overshoot it.

Here is the craft file, and thanks yet again to this wonderfull thread and all contributors.

Mister Dilsby · June 1, 2015

Very impressive! I have been just punching up at 30-35 degrees and this has limited my tonnage per TRJ. I will have to try a profile like this...though given somewhat limited play time, I will probably not have the patience for a long, shallow climb

georgTF · June 1, 2015

This is what others have suggested i try, including KerikBalm and is similar to Rune's explanation of how to get the most out of turbojets. They pack a huge punch but in a relatively confined area of the athmosphere and it's neccesary to somehow break through the silly drag buildup. Normally you could just use another jet, but this thread is about single designes, and a turbojet in space is a waste, so why carry more than you need.

BTW, it does not require patience at all. The jet does all the work, and you don't have to touch the controls at all. Also no losses due to pulling up at high speed. The buildup in airspeed automatically takes you from level-ish flight to a sub orbital trajectory. [edit] And more often then not melts something, but in those cases it's better to pick a slightly higher angle of attack. Assuming no other issues, either high temps due to friction, or turbojets getting out of their comfort zone too soon will be the limiting factor. If i'm limited by one extreme, i try the other until i find a sweet spot.

Edited June 1, 2015 by georgTF

Foxster · June 1, 2015

Here's a little one (4.957t) from me:

Could reduce it a bit more as the cones on top of the three Sparks don't do much and there's 20 units or so fuel to spare.

=======

Update: Might as well skinny it down to 4.412t...

Edited June 1, 2015 by Foxster

SirJodelstein · June 1, 2015

Here is my variant - the Rhacophorus (because all my crafts have frog names). 15.8t. 250m/s worth of fuel left in LKO, currently used to ferry two additional Kerbals to or from LKO. Payload fraction is not very good (unless you count the radial cockpit), but it has been a long time since I built a spaceplane. One of the my very few plane experiments that I can fly and land on the runway without problems Great sub- and supersonic maneuverability. A bit wobbly when the rocket engines kick in and the rise to orbit begins, but otherwise no problems.

I have one question though: I have hardly seen any airbrakes in the other designs. How do you all manage to not burn up on reentry without them? This plane overheats everywhere (starting at the jet engine+rear tank, but eventually the rest explodes as well). I have tried so many descent profiles, but could not find a solution for that problem other than deploying two airbrakes high up to shorten the heating phase. Using standard difficulty settings without DRE.

Edited June 1, 2015 by SirJodelstein
name of the craft

Mister Dilsby · June 1, 2015

I have added airbrakes to mine, but yes I can re-enter from LKO without them. I try to come in nose-up at 40 degrees or so, very shallow: re-entry burn is over the desert mountains ~80 degrees west of KSC, and I only burn until periapsis on the other side of Kerbin reaches 0. Intakes are open to increase drag. I think I can get away with this because (1) I don't have a lot of wing area and (2) the front of the ship is very clean, so it's just Mk2 spaceplane parts taking the brunt of the heat. The ladder and the OX-STAT panels get pretty hot, but that's about it.

ETA: And don't forget, you can use elevons a bit like airbrakes. I often tie their 'Deploy' action to the Brake group.

Edited June 1, 2015 by Kuzzter

georgTF · June 1, 2015

Planes that are mostly tanks and have a greater wing area tend to be relatively large and light when coming back down. Another factor is the distance between CoM and CoL and wheter or not the plane can keep a high angle of attack without stalling.

I try to re-enter at something like 70-80 degrees at 70km to get maximum drag and keep the nose up as long as possible. Lift/drag can sometimes completely negate re-entry effects (which is a bit unrealistic but KSP isn't perfect) to the point where a plane must dive down to avoid a high altitude stall. Such a design would have no need for airbrakes.

OTOH some of my planes had great difficulty keeping the nose high enough and could not "bleed off" airspeed before descening into the thicker part of the athmosphere. At that point it's virtually impossible to avoid high friction heat so either the wing profile needs to change (which i'm sure we'd all hate to alter) or airbrakes should be added. Airbrakes placed on the top of the airframe also tend to pivot the plane nose up for extra drag.

But yeah, long story short, depending on wing design, drag and CoM/CoL you might not need an additional airbrake. And by chance a lot of designs featured were exactly like that.

Tarmenius · June 1, 2015

So much awesome while I was away on RealLife obligations! I had no idea that the Turbojet could be pushed so far; I'm super impressed. I also couldn't be happier about the discussions taking place. Later in the evening, when I have more free time, I'll be taking what I've learned here and applying it to a new design.

---

Most of my actually-operational SSTOs do feature airbrakes to help manage heat and prevent grossly overshooting KSC on re-entry. The few that I've brought down without them have lost parts, though that was before 1.0.2. I imagine that modelling a descent after the real-life Shuttle's (high AoA + S-turns) will help mitigate some of that heat, though I have yet to try it.

Wanderfound · June 2, 2015

A new one:

Craft file at https://www.dropbox.com/s/5qzix822rswwlqo/Kerbobee.craft?dl=0

Rune · June 2, 2015

The key is that the design isn't too stable on reentry (CoL very far behind CoM). If that happens, the plane will behave a bit like a lawn dart, and you won't be able to lock high angles of attack. But if you can go to 45Ã‚Âº AoA, you will arrest your descent really high (as in, level flight at 40kms), and then your probelm is not heat (you won't see flames in extreme cases), it's keeping some speed to not stall your plane over 30kms up. What bigger airbrake than the main wing?

Rune. BTW, nice entry.

Tarmenius · June 3, 2015

Wanderfound: I really like what you did with the Oscar-Bs on your Kerbobee! The whole craft has a sort of MiG vibe to it, too. Awesome.

I'd really like to see how much mass the Turbojet can push around with FAR, to see what difference there is in practical terms between the two aero systems.

NikkyD · June 3, 2015

Shark Mk1

Below 4 tons is possible because with this setup it reaches 150 km orbit and i didnt really tweak the ascent angle, lots of space there with the heat.

- reason for the 100 kg remote unit:

a 40 kg OKTO has no torque and in space you need the torque to turn at the AP and the gimbal of the engines is not really suited for it although it might be possible with lots of patience etc

40 kg okto + 50 kg reaction wheel are both not really streamlined and the remote unit has 15 elec instead of just 5 of the okto.

I use a 100 kg Remote + 5 kg solar panel, possible is 40 kg okto, 50kg reaction wheel, 5 kg solar which nets in 95 kg. 10 kg won... but less stable i guess

(Okto also has very low temp tolerance).

If you change 1 FLT200 tank for 2x FLT 100 (because of the smaller units in which you can lower the fuel) you can drop 5 units of L+O for 50 kg or even drop 10 each for 100kg total. As seen in my screeny nr 3 i have about 10 units left at a 80/90 orbit. So if you manage a 70/70 orbit...

105 kg less would be possible but the way i built it even a bloody beginner can fly it.

Full Throttle all the way, once you lift off with the use of SAS aim for 50Ã‚Â° angle and just hold.

Once the engine tops out at 22km turn SAS prograde to minimize the mini drag losses (might still cost you 2km orbit or so).

About 1 min before you hit the AP switch engines and burn at 0Ã‚Â° angle, will have to burn 2 min.

Some minor adjustments for circ-orbit will be necessary but thats it.

Tarmenius · June 3, 2015

Very clever! I never thought to subdivide the tanks to get more precise control over fuel amounts. Also, from what I understand (someone feel free to correct me) the Shock Cone generates less drag so you could probably squeeze a little more dv out of the design that way.

NikkyD · June 3, 2015

At first i had a okto directly under the air intake. It did heat up a lot. Then i switched the tanks around and sandwhiched it, suddenly the intake could take a lot more heat. Same old story as it always has been, a tank can eat up a lot of heat and thus keep the intake cooler.

With the shock cone, it weighs more and my tests didnt show any real difference. I don't know why they changed it. Ram Intake can take more heat, weighs less and has more air than a shock cone. The special drag cube of the shock cone MAY benefit you when building bigger craft but i guess the heat-issue will far outweigh that.

Another trick, to save energy. When coasting, a lot of minimalistic designs run out of energy and you have to use batteries. You can simple disable the energy on the command unit and when you have to make a maneuver, turn it back on. With long spaceflights (in career before solar) it works with mun stuff if you have no batteries.

Update, more testing

The remote control unit seems to really be wider than 1.25m, it is visually. It has lots of drag.

Drag values at mach 3, when going straight up (reached between 7k and 9k depending on overall drag)

and "A.Cd" value in [] shortly after start with 1.0 vector

- remote control ~26 [0.17]

- Ram Intake ~72 [0.47]

- Shock Cone ~48 [0.20]

- Turbo Jet ~43 [0.49]

- FLT200 ~2 [0.04]

- FLT100 ~1.2 [0.03]

- FLT400 ~2.9 [0.07]

- radial Engine ~5.25 [0.04]

If i create a "thinner" part in the rocket, an okto with stabilizer as mentioned before, that part receives less drag but the part below it receives increased drag!

A tank below an okto would receive crazy drag like the intake!!!

Shock Cone looks superior but the flight is long and drag only matters within the first few seconds. However, the lower my drag the higher my initial AP, so more time for circ and more E_pot.

Update 2

I am down to 3927 kg and i am hitting the KSP barrier big time, just look at the screenies.

I need something like a FLT50 with only liquid fuel. There is some margin that i found. If i build unaerodynamic stuff, it costs me more liquid fuel as i accelerate slower and thus the jet runs for longer. However i always make it to 80+ km AP because the turbo simple has way too much thrust for that small thing.

So aerodynamic flaws are acceptable, overall weight matters!!! But there is no tank that fits my requirements :/

Update 3

With plugin "modular tanks" i am down to 3728 kg. The FLT100 is only used to 80%, 1/3 oxi 2/3 liq. The mod isn't giving me any discount on the empty 20% so drymass remains but i can drop the other tank and thus one drymass less. < 3700 possible, better ascent, closest orbit ever etc

Edited June 3, 2015 by NikkyD
further testing and blabla

redsh · June 4, 2015

Yet another one. 13.6 tons, stock.

Falconer · June 4, 2015

Slightly related thought here... when read this... pulled out a ramjet, stuffed it on one of the lightest cockpit planes I could build in sandbox. Then pointed it straight up after seeing how fast it turned into fireworks when flown horizontally... sucker hit 150k apoapsis...granted without the horizontal velocity to orbit. Essentially everyone here is simply using the ramjet as a non-disposable booster... and trying to eke out the best performance (most speed and altitude before switching to closed cycle as limited by thrust and atmospheric heating).

That got me to thinking... this thread deals mostly with single engine optomization for light lifts... but with the extremely high 59 TWR these things can manage while in atmosphere.. it got me thinking about using them as boosters instead. Rather than SSTO single stage plane... what about using them as a SSTO booster stage (preferably recoverable).

Initial results were kinda surprising... 12 ramjets, 1 rhino. Were able to loft 58.8 tons of payload on a 178.9 launch weight to 80k LKO (32.9% payload fraction) while burning through two 7200 tanks worth of gas (plus only a little extra liquid fuel for the ramjets). The only staging was spooling up the ramjets before engaging the liquid fuel rocket for takeoff (turn the TWR positive long enough to get to roughly mach1 as quickly as possible).... then toggling the rhino off again between 4k and 15k altutide while the ramjets did the work). Mind you that fraction will go down slightly once probe core, parachutes, and stage decoupler get added... but still...

Anyone else seen similar results... I don't think I've come anywhere close to this using liquid rockets or solid boosters. (I tried strapping on 12 sidekicks with nosecones set to 70% thrust instead... price came down slightly... but I had to use half of the payload 7200 tank to finish the orbital burn).

In terms of economy only thing close was the sidekick at about 3400 each with nosecones & radial decoupler....

What kind of a payload fraction or cost per ton are people typically looking at in KSP... (haven't played in a while.. though wiith 1.0.2 pulled it out again to play in the sandbox?).

zarakon · June 4, 2015

Falconer, there's a payload fraction challenge here: http://forum.kerbalspaceprogram.com/threads/116729-Stock-Payload-Fraction-Challenge-1-0-2-Edition

The top entries are around 50% using pretty much what you're describing - a combination of turbojets, rapiers, and rockets

NikkyD · June 4, 2015

If i fly the same trajectory with max payload, i need about 40u of liquid fuel and can get about 4t up to 70+ AP with about 1300 dV remaining.

Lets consider a booster being a turbojet with ramintake and a flt100 with only 45 units of liq, thats 2.1t per booster to lift 4t of 2nd stage.

with a 909 on the 4t about 1.26t would need to be fuel, with the usual 1/9 tank weight that would be 1.42t for fuel and tank and ofc 0.5t for the 909. So total 1.92t of 4t for the 2nd stage.

Neglecting command and steering stuff we have a total of 2.1t booster + 1.92t 2nd stage + 2.08 payload. Thats 34%.

Considering i didnt really try hard lets assume 4.5t per booster is possible and the 909 was something with 24 TWR like the rhino we had somewhere 42%

With 1 "booster" it will never be much more but if you can compensate CnC losses with bigger combos the 50% is not that impossible as others have proven

Tarmenius · June 4, 2015

redsh: Very cool high-wing design! I especially like those LV-909 pods underneath.

---

This talk of turbojet boosters has given me another idea...

Falconer · June 5, 2015

New entry... clocking in at a whopping 45.6 tons wet on the runway. Orbits at at 25.1 tons. Landed safely at just under 25 (burned off 100 units of fuel to deorbit and final approach).

Pure plain vanilla KSP 1.0.2 with completely no mods.

1 Ramjet, 4 nukes and the flattest flight profile I've ever done... It can't climb without bleeding speed at more than 5degrees nose up.... and one you're high up it doesn't want to lift the nose much til you're hypersonic and even then it's constant pull back on the stick while keeping it level. So the answer is yes... you can reach orbit with a 5degree ascent slope... with some well timed flat stretches to build up speed (about 11k for the ramjet only... about 30k once the ramjet flames out for the nukes to gain enough speed to start climbing again...). You'll enter with ~2200 m/s orbital velocity too meaning you only need a little bit to circulize.

Though above 8000m I learned the nukes are getting about 750s ISP... more at 12k when I turned em on.

It more lifts itself out of the atmosphere on wings rather than powers itself out of the atmosphere on vertical thrust like the other entrants... This became heavily apparent on reentry... I pitched the nose slightly up at 50k altitude and started to climb while bleeding speed... very high AoA solved that as intentional stall plus massive wing airbraked in no time flat well before hitting the 15-25k altutide death zone. Also putting my ballistic impact in roughly the mountains outside KSP before going prograde to keep speed and regain lift to float back into the plains...

Edit: hmm how do people post the imgur album... I can only seem to link single pics... but I'll put in the album URL

Edit Imgur album posted below.... doesn't want to edit it into this post at all.

Edited June 6, 2015 by Falconer

georgTF · June 5, 2015

To embedd imgur albums do:

{imgur}album name (it will be the last part of the url, like "qqtwu" for example) then close with {/imgur}

but replace curly brackets with normal ones (i cant otherwise i embed your album and you can't see the code).

Now for the plane. Holy cow that is astonishing! Just today i was struggleing to push a 19.2 ton 1TJ / 2 nukes design and running into all sort of problems. I have been very cheap with wings and your succes proves i was horrendously cheap. Kudos on the victory, that is, frankly abnormal! But in a good way.

Edited June 5, 2015 by georgTF

Tarmenius · June 6, 2015

Astonishing is definitely the word for this! Way to go Falconer!

Falconer · June 6, 2015

Thanks... it works on a new post.. though trying to edit it into the old post doesn't work....

... that is about the 4th iteration and the first to go orbital.. (tried 2 nukes not enough thrust... added more engines underneath what was initially a high wing... sucker would pitch up uncontrollably..... added two more engines on top of the high wing (6 nukes)... with after tweaking down nuke thrust to balance the thrust vector once the low ramjet flamed out... it just ran out of gas... So switched to midwing with 4 engines balanced symmetrically around the ramjet in the center... also added two more delta wings in the far back for 1200 more gas and more lift and to push the CoL back even farther.

Problem now is the COM is very stable in pitch/roll... but on reentry on yaw it's unstable if the nose gets too far left or right when it's dry on reentry after most of the speed is bled off. ... so it's prone to a flat spin after reentry... so the tail stabilizers need to move back farther... or add another pair there and risk the drag. I put all the remaining fuel in the forward tank... and second time I did it I had a lot more fuel leftover due to better piloting (about 280 units instead of 160). In fact, I marked the frontmost two tanks as 'do not use' which helped a lot with dynamics only unlocking them one by one as the tanks drained out and it was clear I'd need some gas for the final push to orbit, meanwhile the fuel drained from the rearmost wings into middle and then forward wing... and from the forward wing into the front fuselage tank. ramjet pulled equally from all tanks just like normal except the reserved ones, but when you turn on the rockets the fuel flow helped a lot with keeping the CoM where it needed to be.

Other than that... wondering if elminating the fuselage entirely or using the Mk2's fuel fuselage would work better... (Mk2 is lifting body... so more lift, I aavoided it because all the Mk2 adapters have oxidizer and aren't great fuel tanks). But then we got the whole lift == drag problem. It doesn't matter how much wing you have all the wing does is turn forward speed into vertical lift which is felt as drag... which all needs overcome by a single ramjet still.

Attaching nukes to precooler inlet/fuel tanks... seemed to help with the heat dissipation (also they're bolted to the large wing... not the fuselage as the next heat sink in line).

Another question:... I put my ramjet inlets on the bottom two nacelles...

Yet most designs I see on here...have them on the top of the wing? Is there a reason for that? Just a matter of KSP taste... since it may not be advanced enough know the difference?

(I know real world... top wing inlets are used for stealth reasons... but for airflow underwing are superior... underwing is higher pressure due to bernoullii effect.. and when at positive AoA the fuselage or wing helps funnel more air towards the scoop). I'm guessing KSP''s aerodynamic model isn't that advanced for this? I can think of other airflow things it probably ignores as well (the wingtip vortex and how it can be used to enhance lift for example, or increase/decrease drag).

Another question... I see a lot of people using the "Ram Air" inlet.. and not the shock cone. The shock cone just doesn't work as well with ramjets? by the time it's in it's prime the ramjet is falling off so it's made for rapiers? I chose the ram air... because the sucker never really gets to shock cone speeds before the ramjet shuts off... (the ramjet flames out about 700-800 m/s IIRC).

Edited June 6, 2015 by Falconer

georgTF · June 6, 2015

I've had ramjets flame out at >1400 m/s though not on the more succesful designs. Going that fast usually means a flat, depressed trajectory which comes with a huge price in heat and possibly drag loss. Though as long as you're fighting drag with an efficient engine, you should be fine.

As for ramjet vs shock, i saw a post about it recently and i'm not convinced either is a clear cut winner. They both seem to work fine.

Wing lift vs wing drag? yeah drag is no friend of yours, but not having lift forces the plane to fly with a higher Angle of Attack. This moves the thrust vector off prograde which robs you a lot. If you need a certain amount of life to acomplish the goal, then pay the price in drag. As long as it's worth it... it's worth it. Besides, wings are about the least draggy parts in the game.

Lift is also going to come in handy when diving to puch through the sound barrier. Not having enough tends to drop the plane too steeply or it once again suffers from thrusting off prograde by a few degrees. That is a crucial period of the ascent and i'd want it to go as smoothly and as quickly as possible.

[edit]

There comes a point when pushing too much weight on a single turbojet becomes an excercise in frustration and possibly efficiency as well. Certainly when using the Mk2 fuselage where both the single and twin fuel adapters are similar so the only price is the mass of the extra jet. As well as it's uselessnes in space, but if you just want to lift stuff into orbit a twin TJ + n Nukes build is probably the optimal way to go. There will be no problems going transonic for starters, and if damn near 50t can reach orbit on a single one, then an interplanetary SSTO will work wonders with two.

Still, a tremendous achievement there. Well done on pushing the limits!

Edited June 6, 2015 by georgTF

NikkyD · June 6, 2015

As i wrote some posts up,

- Ram Intake ~72 [0.47]

- Shock Cone ~48 [0.20]

So at mach 3 the shock has 2/3 of the drag, but weighs double (matters only on really light weight planes). Shock however has less air and takes 100 less heat.

The precooler nacelle has a very high heat dissipation, so attaching "hot" parts to it helps cool them off faster or keeps them cooler for a bit longer.

Single-Turbojet SSTO Spaceplane

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