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Cygnus Recoverable SSTO Rockets (15 to 600 tons)

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Cygnus Recoverable SSTO Rockets family

I'm happy to present you the Cygnus recoverable SSTO rocket family. Those rockets are designed to be a cost efficient way to orbit payload (from 15 tons to 300 tons) to LKO. Their mass efficiency ranges from 15% to 19%. Then you can deorbit them, reenter Kerbin atmosphere and make a slightly powered landing as near as KSC as possible to maximize cost return. You can easily get around 95% of the dry cost of the launcher.


(all picture are clickable)

Cygnus Package

Download package : Test crafts and sub-assemblies (160kB)

This file contains:

  • 11 launch stage sub-assemblies
  • 11 test rockets craft

General flying (1.0.4)

Ascent profile

  • Don't activate SAS at take-off.
  • Start gravity turn when speed is 40m/s. You should get to 45° at 8km.
  • You may experience sliding during ascent : try to compensate or activate SAS.
  • Orbit insertion burn should be from 300 to 600m/s.
  • Wobbling payloads can wreck ascent. I suggest you use the "Kerbal Joints Reinforcement" mod created by Ferram4.

In space

  • You should have 100 to 200m/s left before detaching the payload
  • When on stable orbit, detach payload and stay on the SSTO stage.
  • You should have a comfortable 200 to 500m/s of dV left for reentry.
  • As the stage doesn't have any power generation, it will run out of power in few orbits.


  • I suggest a 60m/s deorbit on the west border of the crater (90° west of KSC). This means you would slighly overshoot KSC (70km)
  • Follow retrograge if you want.
  • Deploy airbrakes as soon as possible. If you forget, you'll destroy your chutes later and crash.
  • Drogue chutes and regular chutes are configured to autodeploy at safe altitude (if you deploy airbrakes). Stage them as soon as possible (even in space)
  • If you overshoot a lot, you can burn fuel, but keep at least 100m/s for powered landing. If you're too short, you can close airbrakes, but that's dangerous : you may not slow down enough to open you chutes safely.
  • Drogues should deploy at 8km/5km (500m/s) and regular should open at 3km/800m (250m/s)
  • At 100m, enable SAS to reduce rocket flip in water.
  • Landing are powered : under 75m, tap "shift" once or twice to slow down around 5m/s.
  • On touchdown or splashdown, keep SAS on and recover the stage as soon as possible. Don't let the rocket flip in water or fall on ground, that will break some expensive parts.


  • Cygnus RR-015 can be landed without firing the engine. Beware of flipping though
  • Cygnus RR-032 and RR-100 don't have double symmetry. If you want to use them on a non eastward ascent, rotate the rocket.
  • Cygnus RR-015, RR-032 and RR-100 will probably flip when landed, Don't delay the vessel recovery.
  • Cygnus RR-075 has an additional skipper which is used only during the first ascent. It shuts down quickly by design.
  • Cygnus RR-125 don't use fuel conduits. The lateral engines will shutdown quicker than the central one. Beware of loosing power at landing

3f085756-93e7-4916-adda-532e5935fa0a.jpg bb0726a5-5e13-4d6b-9bb0-fc4ea55a0f30.jpg d0883fc2-be46-402f-bc21-8e4a8e16cd54.jpg

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Design usage

  • All Cygnus SSTO stages come with a test craft and sub-assembly. The test crafts have a dead payload of the max weight of each stage.
  • Rocket designation : Cygnus RR rocket identification is it's maximum payload
  • Techlevel is quite high, especially because of large probe core and battery.
  • Don't hesitate to remove the adapter and decoupler to use a bigger one. Also, add the fairing to the SSTO stage if needed.
  • Heat shield is designed for LKO reentry, it's half full on purpose.
  • If you have a lighter weight, I suggest reducing the engine thrust to match rocket TWR. To reduce cost, you can remove some fuel tanks. As a rule of thumb 3400m/s is sufficient to ascent properly with some comfortable margin to deorbit and partially powered landing with a TWR from 1.35 to 1.5 (tested).
  • If payload makes your rocket flip, change bottom wings to bigger ones. Also, try reducing speed between 5km and 20km.
  • No part clipping.
  • 4 winglets can be added somewhere under parachutes, but I've noticed they aren't that useful. They will probably blow during reentry.

625a194f-d191-444a-a93f-c131e6bfcf9d.jpg 66b79898-79a2-439f-a3cb-4e017e506954.jpg 27fcbd8b-bef2-4dae-aff7-3d207d0d6c32.jpg



586f4718-5b30-49f6-8e30-d89a7e17e887.jpg fa433945-da86-496c-b06a-d2f7989941d3.jpg 44fff91a-fb0b-45c8-b1ed-7beec6167593.jpg
RR-015, RR-032 and RR-050

16d337e1-9bae-4e00-ba05-67e7d4ad7975.jpg 78c96672-5a30-4ecf-a5b9-9b0d5b21b49d.jpg f34e5a10-04e0-4a4d-bce0-5098524c23cc.jpg
RR-075, RR-100 and RR-125

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RR-150, RR-200 and RR-300

e34dbb4a-9aaa-46c6-aeec-9bb738db21ef.jpg b1caa6cd-d7fb-4919-9624-66a4b55e2759.jpg
RR-400, RR-600

Feedback appreciated.:wink:

Edited by Warzouz
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You know? I think I have the light counterpart for this family figured out already. 2.5, 5, and 10mT to orbit:




And they are useful too, with the 10mT one, I launch a 3.5km/s general purpose cismunar Science-er (it can basically strip-mine Minmus of Science, or check two Munar biomes, on each flight). The 5mT one launches small orbiters for recovering kerbals and stuff in orbit, and the 2.5 lightest one can launch satellites very cheaply for mucho profit. Note they were built in a career save with minimal tech (basically, just after unlocking the Skipper, Boar, and orange tank), and part count is ridiculously low (like, around 30 parts).

Oh, and I also forgot: a good way to make rocket stable, even long thin ones, is to mess with fuel flow so the lower tanks empty first: empty, they act like a nice stabilizer in the back, instead of making you unstable when emptying from the top down.

Rune. A chemical SSTO is the perfect way to learn gravity turns.

Edited by Rune
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Yes, I find rocket SSTO easy to fly because they have the same configuration all the way up.

The only issue with my design is the techlevel. Those big probe cores are end-game (I don't know why). I had another lower tech version with 2 heat shields and a service bay with smaller battery and probe core. It worked but looked draft.

As for the light version, I worked on a 1.25m core but that wasn't too stable. Payload was very low and recover value not worth the time. I didn't thought of using the Skipper though.

I also tried to work on 5 and 7 engines version but design wasn't very easy. The rocket wasn't efficient and the funds/tons was less appealing.

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Hmmm, I was wondering if airbrakes are in the wrong way. Do you think airbrakes orientation have some effect on generated drag ?

Probably not since this is KSP, but you know, they look much better when they open the right way. And yeah, as long as you land withing about 500km of KSC (which is a sizeable fraction of the planet) you get above 90% of the cost. Plus, water is much more forgiving now to tipping over!

A few other things I found you might like for v2.0:

-To use cheap, low tech probes, put them on the other side of the fairing, or inside a service bay. EE's "activate surface attachment" helps, but you can also place them on a cubic strut to put them next to the decoupler (or inside it) without them messing with the structural integrity of your rocket on account of their weak tiny nodes. On the way down, the engines will shield them from reentry effects anyway.

-The new small fins burn up real quick. That is a plus on a design that has to be aerodynamically stable on two opposite directions at different times, you lose them high and regain stability when flying tail-first. Just in case fuel routing is not enough to keep it stable on ascent, like with my small one up there that only has one tank.

-The really awesome engine for (very) light chemical SSTOs would be the aerospike. High tech, but it has both high sea level and vacuum isp, while having a respectable TWR. But I have a feeling doing clusters of them the old way is a good way to generate a lot of drag (all those unconnected nodes and such). I want an eight-coupler!

I have been working on my end a bit, BTW. My current RLV family is 5,10,15,20,and 30mT to LKO. I think for the VAB section in R-SUV, they will be half of the new booster line, picking up with expendables at 50mT and 75, 100, and beyond. Just because you have the really heavy RLV's covered, and the part count jumps a lot when you have to go so big (currently the light ones are around 30-50 parts each).

Rune. The really nice part about airbrakes is how they cushion the impact when your booster tips over because you landed on mountains. That, and the chutes not cutting! I love that.

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About the lower tech probe core : older version had a service bay with a small battery and a small probcore in it. It was fixed at the bottom, just under the heatshield (with another heatshield on it). But that seems badly designed, I removed it as soon as I could. I even tried to add a rockamax adapter to make the rocket bottom look better, but that adapter exploded during renetry...

Adding a bigger bay on top of the stage looked better, but it usually crumbled and wobble under the payload weight.

About fins : small fins are too weak to help the rocket ascent straight. My first rocket had event bigger wings. Further more, all rockets are stable during reentry (bottom first). Only the smaller one goes sideways went chutes are mid-open, but end straight when fully-open.

About airbrakes : I didn't notices they helped when the rocket is falling down. Mayby I could try inverting them.

As for water, laying down is still dangerous. but usually you don't loose really much. You only have to recover mutiple parts.

I was also thinking about removing the reaction wheels and adding 4 vernor at the bottom of the rocket (can be hard depending on the design). As the rocket has quite some fuel left, it could be efficient. I could even reduce the battery size. But again, fixing a smaller battery to those stages is quite delicate if I want to do something clean.

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  • 2 weeks later...

As now, the two launcher family overlaps on some designs while lacking some various payload values.

I'm redisigning some of the launchers. to fit the new palyload mass

- M1-12 : 12T

- M2-26 : 25T (maybe reducing fuel load)

- M3-39 : 40T (should work without modification)

- XA : 60T (new design based on M4 with additionnal boosters)

- H2-78 : 80T (an additional central tank but TWR is already low)

- XB : 100T (new design based on M6 + 1 central engine)

- H3-120 : 120T

- H4-155 : 160T (a bit more fuel)

- H6-236 : 240T (should work without modification)

H1 will be remove (duplicate with M3 and unstable at landing)

M6 will ba remove (duplicate with H2 and less cost efficient)

XA and XB will be some new designs.

- For XB, an additional central engine and more fuel will do. The central engine will burn only for a short time (because central tank is drained by all engines. But higher TWR is only useful on takeoff. This design will probably be less mass and cost efficient.

- XA is a bit trickier. If I add another engine, I'll be more around 70T and I need a 60T range rocket. I'll try adding some central or lateral boosters (non disposable). I'll probably use 4 Reliant or 4 Aerospikes. Again, temporary usage.

Until now, I was focusing on remaining dV and TWR. I'll focus on paylaod mass to have a more coherent SSTO rocket family.

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I modified all the rockets. the 100T goes perfectly. I've improved the fuel left. Heaviest rockets have 580m/s left... That mean the dV to LKO is around 3350m/s (VAC)

I only have to figure how I'll do the 60T. (EDIT : done. Added a central skipper and some fuel to the M4 original design)

I'll upload new files tomorrow

Edited by Warzouz
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New designs are available. Here are the specifications

General modifications

- Unique set of rockets. No more double ladder...

- Easier range of payload.

- Air-brakes are in the correct angle

- more precise test payload

- Average recovery set to 97% because it's easy to get... (never got the 90%)

- Added the total net cost to the specifications.



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RR-012, RR-025 and RR-040

16d337e1-9bae-4e00-ba05-67e7d4ad7975.jpg 78c96672-5a30-4ecf-a5b9-9b0d5b21b49d.jpg f34e5a10-04e0-4a4d-bce0-5098524c23cc.jpg

RR-060, RR-080 and RR-100

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RR-120, RR-160 and RR-240


Test crafts and sub-assemblies (160kB)

Edited by Warzouz
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These are great. You have no idea how much money I've saved in my career game by using these. It's so much more cost effective to send up a rocket where you get back most of the money you spent on it. I've tried SSTO spaceplanes, but they just take so damn long to get to orbit and don't have near the fuel left that these do, plus they also take so damn long to get back to the surface. Not so with these rockets, as it takes only a fraction of the time to get them down and recovered than any spaceplane I tried ever did.

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Very true. Further more, rocket SSTO have a big advantage over plane SSTO : they are scalable.

Just take one of thos designs, double the engines, double the tanks : you double the payload to orbit. My 240 tons was even easier to create than my 12 tons.

I can't imagine how hard a plane SSTO capable to lift off 240T.

An other advatage of rocket SSTO over regular staged rockets : they grossly keep the same aero profile. They don't loose wings or have high TWR variations. I find them easier to fly.

I must admit I played beta 0.9 in science gamemode. In that mode, funds don't matter, so I prefered to create neat staging rockets.

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  • 2 weeks later...


I've to redisign the rockets. As I get more fuel in space (I've 780m/s left for deorbit and maneuver now), I come too hot and crash into the ground.

1- Airbrakes aren't as effective as the use to be.

2- Chutes can't be open before 260m/s and the rocket is too heavy to slowdown efficiently

I'll try to add drogue chutes. At what speed can drogue chutes can be open ?

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Drogue chutes did well. I can set them to auto open at safe speed. I still have to tweak them though. The issue i that I've to add as much drogue I have regular chutes. Part count rises...

I'll test more airbrakes only.

Further more, Drogue chutes makes KSC mountains very dnagerous as you may cash on them.

Further more, I find myselft with more fuel than before. I've usually 750m/s left after releasing payload (that's around 300 to 400m/s). I could remove half of it, and looking at the size of some rockets, it's not a negligeable fuel tank... (one biggest fuel tank)

As the objective of those launchers is to send payload to LKO (75km) for a very cheap price, they don't need so much fuel. 200m/s is enough to deorbit and for powered landing.

My usual dV is 3650m/S. I could target 3500m/s at optimal payload. Of course, in real usage, you're usually below the optimal payload and then, your dV is higher.

Further more, removing fuel means that TWR will rise : and when TWR rises, I add payload. In other words. I'll transfert unused fuel from the SSTO to the payload. The heaviest payload could rise to near 300T.

My clean scale of paload could be messed up...

Much testing to do

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Cygnus SSTO rockets are updated to 1.0.4

25% more payload for the same launcher. I added drogue chutes for reentry. Stage everything when you enter atmo, drogues and chutes will auto deploy safely. Beware, I've set chutes for landing below 2500m. I've also refined the reentry profile (check first post).

Cost per ton is lowered again. The 300T payload is now at a 360funds/ton !


Download URL on the first post. Please remove the old assemblies and rockets, they are obsolete.

Further more, I did a quick and dirty 600ton payload test. I works (even without KJR). This monstrosity isn't in the ZIP.


Edited by Warzouz
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  • 3 weeks later...

Cool pack of rockets. unfortunately I am having no success. I have been testing the RR-125 as it was the size i needed. no matter what I try, I blow up. I have followed the deorbit guide, staged all my chutes. but inevitably around 19K the engines rapidly overheat suddenly and the whole thing explodes.

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Hmmm. strange. I did a LOT of tries, I had never blown up. At a time I used winglet which used to blow during descent. But I never lost the whole stage (except due to a final landing poorly executed). I always aim for 75km orbit and do a 60m/s deorbit.

I play in normal carreer mode with 100% heat. No significant mod.

Did you open airbrakes ?

Did you come down bottom first ? (I don't think it's possible otherwise)

Did you use the sub-assembly or the test rocket ? (that should be the same)

What was your orbit befor deorbiting ?

Your deorbit burn was around 60m/s ?

Try to double the airbrakes.

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Hmmm. strange. I did a LOT of tries, I had never blown up. At a time I used winglet which used to blow during descent. But I never lost the whole stage (except due to a final landing poorly executed). I always aim for 75km orbit and do a 60m/s deorbit.

I play in normal carreer mode with 100% heat. No significant mod.

Did you open airbrakes ?

Did you come down bottom first ? (I don't think it's possible otherwise)

Did you use the sub-assembly or the test rocket ? (that should be the same)

What was your orbit befor deorbiting ?

Your deorbit burn was around 60m/s ?

Try to double the airbrakes.

I have tried opening airbrakes at different points in the descent. They overheat quickly so I tended to close them back up before they exploded

Yes came down engine first

Most using the test rocket.

My initial orbit was ~80km

Yes my deorbit burn was ~60m/s over the crater, giving me a shallow descent and slightly overshooting the KSC.

When should airbrakes be opened? I don't believe that was specified in the OP.

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I open airbrakes in space, when I do my deorbit burn. I even stage all the chutes in space. Then warp to atmos and physic *4 to speed things up. I only come to *1 before chutes opens (around 8km).

Dumb question : did you jettisson the test payload ? (BTW, one time I nearly crash into the test payload which scratch the pain and rip off one of the airbrakes. That was close...)

I don't remember having lost an airbrake on any of the RR models. Even when I landed a RR100 with only 2 airbrakes because I misplaced the other 2. Sure they overheat, but never to the red zone.

Except for airbrakes, is there a specific part that seems to overheat ? On the first design I used a rocakmax adapter at the bottom. It used to overheat even with a heatshield. Only that part blew up (but the control probe was on the other side, so I lost the rocket. I removed this adapter and used a double heatshield. That went well until I used the bigger probe core so I didn't need the 1.25m stuff anymore. In the current configuration, I'm not even sure I need a heatshield.

BTW, The rocket you try to land don't have heathshield, but 7 engines.

So :

- Try adding more airbrakes

- Do a lighter deorbit

Edited by Warzouz
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