Massive steady reusable heavy SSTO (rocket)

[Warzouz]

I like big rocket (don't ask me why )

In carreer mode, big rockets are costly. I have a space station in LKO, I would like to refuel it but I only have a 22T launcher partially reusable. I want to build something bigger and scalable (50 /10 / 150T)

As my 22T launcher is very stable and easy to fly rocket (both manually and with MJ), I wanted to start from there

(Sorry I can't post screenshot now, I'll try this evening)

Basic design

It's a 3 or 4 S3-720 extra large fuel tanks (I don't have the biggest yet) on to of a mamoth. It's helped by 2 or 4 biggest SRB. I've added 4 wings at the bottom and 4 winglets in the middle to help control. This stage can go to space, circularize the payload and deorbit itself.

As I only have the smallest flat probe core, I put it on top of the stage under the payload decoupler. I only need 4 struct to get it stable, even with tall payloads under fairing. It's quite ugly, but it works.

The 2 renetry I did got different results, but successful. The first one went head first until the chute was open. The second one went sideways and didn't even burn in atmosphere (nearly no flame effect). In both cas, landing (in water) let me salvaged ALL the stage (except SRB which were ditch after take-off).

The new design

I go for the heaviest first (able to lift off nearly 150T). I have a central 4 * S3-720 tanks with no engines at the bottom and 6 lateral 3 * S3-720 tanks with mamoth at the bottom. Each engin has one wing at the bottom. winglets is added at the bas of the stage nose cone). Fuel lines feed the lateral tank with the central tank. No SRB are needed. With 145T / 4 orange tanks (stacked and fuel locked), I get a dV of 3700m/s. I only use 6 struts to fix the first stage. Yes, it's a big rocket...

I succeeded in orbiting at LKO (manually and with MJ). It's quite stable except in the first few seconds seconds, but I suspect it's due to the very tall payload. I get 400m/s (without payload) to deorbit the first stage. Now the tricky part :

I need a probe core, and some batteries. I don't want to put them at the top because they are too small. So I put them in a bay at the bottom of the central tank (the one without engine). I add some adapters (the very large one and the rockamax). Then the small bay and a small heat shield.

And my problemOn reentry, the rocket always come bottom first. The rockamax adapter overheats quickly and blast. The bay is deconnected from the rocket (which don't have battery and probe controle). I'm unable to open the chutes in low atmosphere.

And an non important thing : I also loose my 6 winglets, which is strange because on the basic stage reentry I didn't loose anything.

- How can I organise the central bottom of my craft to add that stuff and survive reentry ?

NB : I'll add some screen this evening

[Xannari Ferrows]

How steeply are you entering? Technically there's no figure for how to survive reentry. If you don't have a heat shield, take it slow and steady. If you still encounter this issue, I'd need to see the craft's appearance to help.

[Warzouz]

I don't know exatly. I made a 120m/s retrograde at 75km and then, when starting heating, an additionnal 250m/s (all the fuel left) to slow down a bit.

My goal is to land as near as KSC as possible.

[magnemoe]

Good idea with an heatshield on it, test it, you probably don't need all the abalastive covering. You could also put this below the nosecone on the side rockets if I understand your design right.

Airbrakes high up is also an good idea, this let you get more control on you landing, basicaly you overshoot a bit then use airbrakes to slow down.

Same with some parachutes.

[Warzouz]

I'll test that as soon as possible.

Other question :

How to use drogue chutes ?

For now I only use regular radial chutes (I have 24 of them, probably not enough, but that's easy to fix afterwards). Can I use drogue chute to deploy in upper atmoshere to slow down (until they burn). If not, how do you use them ?

[Warzouz]

After some dirty calculations, the first stage has a 13% efficiency in mass (wet payload mass / wet total mass). This is quite low, but I hope to recover 100% of the dry mass and funds (except discount for distance to KSC). As the first stage is not only on suborbital but taken into orbit, you can land it anywhere and not only on the other side of Kerbin, where recover rate is around 20%. 80% refund on dry mass should be reasonnable.

The effective funds / payload ton should be quite low.

[TheXRuler]

I haven't played much 1.0 but I would recommend a smaller braking burn, in .90 with FAR and DRE I usually circularized at ~71km and then lowered my Pe to ~35km. Also, dump all your leftover fuel before reentering the lighter you are the faster you will slow down

The drogue chutes probably will not make much difference, they should burn up more or less instantly (at least as soon as you get enough pressure to slow down), however maybe airbrakes in the upper atmosphere could help a little.

Edited May 11, 2015 by TheXRuler

[Warzouz]

OK, I used a doble heat shield. That worked

First landing : damaged but nothing exploded. I need more chutes...

I'll try a more shallow angle.

[Laie]

I don't know exatly. I made a 120m/s retrograde at 75km

That's actually quite a lot and will make for a very steep re-entry.

Other question :

How to use drogue chutes ?

Like any other. They seem to be a little pointless right now: ordinary parachutes act as drogues when semi-deployed... I never really felt the need to add drogues.

Besides, the lowest possible semi-deployment altitude is somewhere around 4200-4500m; the highest possible drogue deployment is 5000. That leaves drogues with only a few short moments to do their work.

[TheXRuler]

I agree with laie on that the drogue chutes are pretty much useless. Semi-deployment should not act as a drogue chutes (as far as I know it doesen't do that in real life) however with chutes fully deploying instantly and ripping crafts apart I see why they do it that way, I just think they should either slightly rework semi-deployment (ie a max amount of time like 30 seconds) or do it more like the realchutes mod in wich chutes deploy gradually, then at least drogues would have a use

[Warzouz]

I did a 60m/s deorbit and hit water past KSC at 10m/s. The winglets survived (I added airbrakes and doubled the chutes - 48 now). Still, I broke something but I recovered most of it.

Stage price with fuel : 439 600

Stage price without fuel : 366 900

Stage recovery : 340 500 at 94%

Total loss in funds : 99.1k

Per payload ton : 683 funds / ton

Full rocket weight : 1138T

Stage weight (fueled) : 994T

Payload weight : 144.3T

Weight efficiency : 12.7%

TWR : 1.51 on launch pad

dV for 145T = 3675m/s

dV to deorbit (without payload) = 350m/s

I'll do more tweaking tomorrow

(click to enlarge)

[TheXRuler]

~140t to orbit for ~100k is actaully quite reasonable, the only way to exceed this that I know of is using a gigantic SSTO.

[Warzouz]

I'm still hitting the ground at 10m/s with 48 chutes (15m/s with 24 chutes)

At that speed, the engins aren't detroyed but tanks can. How can I secure the rocket without adding more chutes ?

For now, lateral engines and tanks are connected to the central tank at the topmost tank. Then I added tanks top to bottom and finally the engine. I fixed the engines with a single strut to the central tank, then added fuel line.

Do you think that would matter if I attached the engine first (not even sure that I can)? or even the bottom tank. then build bottom to top and attach a strut at the top ?

[TheXRuler]

Hmmm I don't think it'll be possible to slow down much by adding more chutes, either keep a little fuel to make one last braking burn right before touchdown, or avoid landing in the ocean, if you touchdown on land your landing legs can absorb the shock with far less damage to your spacecraft.

[Warzouz]

I usually have fuel left after dorbit which I use to slowdown (usually nearly 300m/s). I could keep it for a near touch down burn. I'm not sure that 300m/s slowdown in upper atmo does much for heat protection.

I don't have landing struts just because it's not too easy to target landing point. Let's say I've 50% to overshoot KSC.

I'll try some tweaks. But tests are quite long to perform... (take-off, circularize, release payload, set deorbit node, manage renetry, final landing)...

Also I'll try to ass some more aerobrakes. I've only added 1 per engine. Maybe I could save on heatshields.

[magnemoe]

Why don't use the engines to slow down before landing, this way you save on parachute mass too. you only need trust a few seconds.

[TheXRuler]

If you go shallow enough the high altitude braking burn shouldn't be necessary. What I reccomend is to remember how much fuel you have left in orbit after your initial deorbit burn, then go to the VAB and edit your fuel tanks so that you have the same level of fuel as after your initial deorbit burn and then find out how many engines you have to turn of to get a TWR of about 0.9. Maybe set an action group for this? If neccesarry you could play around with the thrust limiters to fine tune your TWR. Then when you want to deorbit you just activate the action group/set the thrust limiters and deorbit as usual, burn ~all your fuel leaving about 3 seconds of fuel for the final braking burn. Then, when you are only ~2 seconds from impact you hit the "z" (or "y" depending on qwertz or qwerty) key to fire your engines up to 100%, that should slow you down sufficiently.

[n0xiety]

I land this huge thing with no parachutes when im returning from duna. Mining really made it too easy tho. I land refuel go for another planet land refuel continiue.

If i were to try landing with parachutes im guessing more than 100 would be needed

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Edited May 12, 2015 by n0xiety

[Laie]

I land this huge thing with no parachutes when im returning from duna.

Thats... impressive. Though I wonder why you land it at all, rather than refuel on, say, the Mun.

That said and back to topic: personally, I prefer to have a few chutes even when going for a powered landing. Don't need to be many, but they do straighten out your ship and make sure that you don't even have to think about controls. You'll come down nose up without sideslip and can concentrate on throttling.

[n0xiety]

Thats... impressive. Though I wonder why you land it at all, rather than refuel on, say, the Mun.

Well ofc i can just keep this thing at minmus and just send shuttles back and forth for my kerbals and the science i bring back from planets yet when returning from another planet aerobreaking is a must at kerbin and it just seems easier to me to reenter and salvage the craft then send another one for a different mission. About the landing the bottom part is so heavy because of the engines and the fuel being consumed at the top levels first leaving only the bottom ones with fuel it never tries to flip and goes bottom first, tho i could always swap 4 of those nose cones with XL chutes for more stability. Btw noticed you accomplished jool-5 challenge. Bet it would be too easy with this thing now that we have mining. If it can takeoff from kerbin and reach minmus to refuel it can takeoff from anything excluding jool and eve ofc.

[Dreambish]

@Laie on Drogue chutes: Like any other. They seem to be a little pointless right now: ordinary parachutes act as drogues when semi-deployed... I never really felt the need to add drogues.

They seem nice for small, awesome planes that you just want to have a small, red braking parachute trailing behind it after landing :

Edited May 12, 2015 by Dreambish
Well, dunno how the quotes work yet

[Warzouz]

Well, I tried a powered landing. easy, finally, except those western mountains of KSC aren't a safe place to land ...

Ah, better

edit : BTW, airbrakes are VERY usefull to tweak landing site. They really create a LOT of drag. I landed at KSC just after reloading my previous descent in the mountains.

Edited May 12, 2015 by Warzouz

[kulkan1]

I land this huge thing with no parachutes when im returning from duna. Mining really made it too easy tho. I land refuel go for another planet land refuel continiue.

If i were to try landing with parachutes im guessing more than 100 would be needed

http://imgur.com/a/VorbV

Are you using any mods for this? Would you mind sharing the .craft?

[Warzouz]

Hmmm, my test launches when smoothly, so I reduced the size of the bottom wing. I thought that having a very tall (4 stacked orange tank (+ bay and nose cone) payload would be a sufficient limit test.

But using my launcher in real situation turned badly. I'm trying to orbit space stations elements. Even using struts, I can't avoid heavy wobble. I can't event add 2 orange tanks with docking ports and struts (I don't have the BIG ports)

With wobble, the rocket tend to flip. I had to return to the big wings.

Still struggling with ascent it seems.

Suggestions ?

[Bev7787]

Apparently air brakes deployed in atmo works. Try that