Big Bertha SSTO

[dc4bs]

So I've been working on this SSTO for quite a while and I've finally settled on this design...

There were some issues with B9, etc with v.23 but those mostly seem to be ironed out now. This is now the 1.1 v.23 compatible craft.

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Download link: http://kerbalspaceprogram.com/big-bertha-ssto/

NOTE: You can either surface mount a MechJeb box or just add the MechJeb module to the B9 S2_cockpit part.cfg file.

Bertha 1.1_v23: Requires all the "MUST HAVE" mods listed below.

Also included is the Autonomous Fuel Tank subassembly with flashing yellow beacon lights.

The only clipping on this craft is the wings. Not really any better way I know of to get the lift I needed without it.

I have placed full Autonomous Fuel Tank cargos in Munar orbit and returned to kerbin for a safe landing at KSC using one of these SSTOs. The specific craft I used was a slightly modified version of the standard Bertha. I replaced the S2 crew tank with an S2(x2) cargo bay that housed a very small Munar lander inside. After delivering the tank I successfully piloted the lander down to the Munar surface and planted a flag. Then I realized that I had failed to include solar panels on the lander so even though it had plenty of fuel, it ran out of electric power and crashed when I attempted to ascend back to the mother ship...

Mods used:

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MUST HAVE:

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B9 Aerospace - the bulk of the craft is made out of B9 parts...

NOTE: You MUST update ExsurgentEngineering.dll to the current v.23 compatible version after installing B9 or the Sabers will NOT work!

F.A.R. - Ferram Aerospace Research - This craft will NOT even get off the runway without it!

KSPX - Fuel tank used from this mod for the Cargo module.

Aviation Lights - just because it's seriously cool looking to have them on during flight operations.

Quantum Struts - Required to bring empty tanks, etc. back down from orbit safely but optional if you just end the flights of empty fuel tanks from the tracking station or use a tug to deorbit them to burn up/crash. NOTE: You will need to manually add regular struts to each cargo you load without them.

Optional:

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MechJeb - You can fly this craft without it but it is not trivial! Hand flying those LONG orbital burns on the nukes gets boring fast.

TAC Fuel Balancer - Flying this SSTO without it is a SERIOUS headache though you could mostly remedy that by adding a number of fuel lines. But I wanted this ship to look as clean as possible and tried to keep the part count as low as I could.

Known to be compatible with:

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K.J.R. - Kerbal Joint Reinforcement - Shifts the weak spots around but it flies about the same with or without so having or not having K.J.R. really doesn't seem to matter much for this craft.

Docking Port Alignment - Makes loading/docking empty tanks for return to kerbin so much simpler!

Edited December 27, 2013 by dc4bs
New version updated for v23 uploaded to spaceport

[dc4bs]

Just my luck I uploaded this the very day .23 was released and broke it.

My problem is that .23 no longer gives you any clue as to what parts are missing or bad. Only that the craft has one or more locked or invalid parts... Well, in Sandbox mode, there should be no locked parts so I have to track down what the invalid parts are and deal with them.

I may just have to rebuild the ship from scratch as I have it "mostly" memorized from rebuilding/tweaking it so much to get to the version I did release above...

[Hodo]

B9 is broke currently, SABREs don't work at all.

[dc4bs]

Yep.

I just finished some test flights running this ship with 28 Rapiers instead of the 6 nukes, 4 large sabers and 4 small sabers...

PROS:

1: It frees up 3 hot key slots due to the Rapiers auto switching ability.

CONS:

1: While it does work, it is a bit heavier (about 10 tons) and has a bit less total thrust. It reaches the end of the runway at about 180 M/s instead of the 220-230 M/s I get with the Sabers.

2: It seems to use a bit more fuel getting into orbit.

3: It's harder to tell exactly what's going on with thrust, etc as MechJeb does not yet know how to read the Rapiers yet.

The Rapiers use more intake air so you have to build up speed at a lower altitude. They auto-switch at 22 Km with the air intake setup currently on this craft. Then you have to climb further on 100% rocket power. The saber/nuke combo can make 26-27 Km before having to switch 3/5ths over to rocket. The last 2/5ths can make 40+ Km before having to switch saving some fuel and a bunch of oxidizer going up.

Overall, I think the Saber/nuke combo is more fuel efficient. Maybe with a bit more practice I can get the numbers better but so far I have not been able to make a 100 Km orbit with more than 49-50% non-cargo fuel on the Rapiers. I can make 100 Km with 60% non-cargo fuel left with the Saber Nuke combo pretty easily.

PS: I had some variants I was experimenting with in the Earth size Kerbal mod so I won't be rebuilding from scratch after all.

On Kerth, I got an SSTO to the point of needing less than 2 Km more Delta-V to make orbit. Needed less than 1 minute more burn time at full thrust when it ran out of fuel. Kerth is a bear to get into orbit around.

Edited December 19, 2013 by dc4bs

[Hodo]

The RAPIER will work on air breathing if you keep it fast. I found bringing the pitch angle down to 10deg at around 12km and just going for brute speed at that point will get you to about 27km before it will switch over.

[dc4bs]

That is also dependent on the number of intakes you have... Sure I could add more intakes but I already went from 14 to 28 engines (+ adapters, etc.). I'm trying to keep part counts as low as possible.

Also, if I added more intakes, it would not be a direct comparison between Rapiers and the Saber/nuke combination drive system.

It would be nice to have 2 Rapier sizes to work with like the Sabers.

[Hodo]

I run 3:1 intake to jet ratio on intakes and before this .23 patch I could run up to 27-30km altitude easy. Now with the newer lower flame out levels I can run them higher, not much higher but higher.

One of my most successful designs actually uses SABRE-Ms to provide bulk of its jet powered thrust, but only uses the rocket mode for the final 10-20s burn to achieve an AP of 100km. Otherwise it uses the nuke to do most of the bulk work in space.

[dc4bs]

That sounds VERY similar to what mine does. Get up to 1700+ M/s at around 26-27 Km and then a short, full power burn up to 100 Km. Circularize and all other orbital maneuvers done with 6x nukes. Anything less than 4 nukes on this craft just takes WAY too long and using 6 cut that by another 50% so the circle burn takes only 4 minutes or so instead of the 6 or more with 4 or less nukes.

[Hodo]

That sounds VERY similar to what mine does. Get up to 1700+ M/s at around 26-27 Km and then a short, full power burn up to 100 Km. Circularize and all other orbital maneuvers done with 6x nukes. Anything less than 4 nukes on this craft just takes WAY too long and using 6 cut that by another 50% so the circle burn takes only 4 minutes or so instead of the 6 or more with 4 or less nukes.

My biggest SSTO, SP-416VB uses 4 nukes to do orbital maneuvering and I don't think I have ever had a 4 minute burn to circularize orbit, 20seconds maybe 40. Sounds like you have way more vertical speed then horizontal speed. You can cut down on your burn times by gaining more speed in atmosphere before you switch over to rockets.

My average altitude is 28km before the switch, speed is around 1750-1800m/s, I maintain a 10deg climb after the switch to rockets and accelerate to 2200-2400m/s. And I make sure that my rate of climb or vertical speed doesn't go above 250m/s.

[Stone Blue]

Nice...So what kind of payload capacity?...

[dc4bs]

Nice...So what kind of payload capacity?...

Payload capacity is whatever fits in the bay.

The sample cargo (subassembly) is included. It's a 49.5 ton autonomous fuel tank. The tank only has RCS for maneuvering. It requires a tug or something if you want to move it beyond station keeping or docking.

If you can stuff something heavier in the cargo bay, I'm sure it could handle it with ease. Just might not have quite so much fuel once it reaches orbit. With the 49.5 ton cargo, it's possible to reach 100 km orbit with about 60% of non-cargo fuel left for whatever. As I said above, I've put one of these fuel taker cargoes (full) into orbit around Mun and returned to the KSC runway non-stop (no refueling).

At this point, I'm kind of on hold till B9 is updated for .23 and then we'll see if there's any change in performance on the Sabers once they are working properly again...

EDIT: Oh, and by the way, that entire station I put into orbit using this ship can be disassembled and returned to KSC safely... Well, all but the giant dish antenna as that cannot be closed again once deployed. That would have to be deorbited to burn up on it's own.

Edited December 23, 2013 by dc4bs

[dc4bs]

My biggest SSTO, SP-416VB uses 4 nukes to do orbital maneuvering and I don't think I have ever had a 4 minute burn to circularize orbit, 20seconds maybe 40. Sounds like you have way more vertical speed then horizontal speed. You can cut down on your burn times by gaining more speed in atmosphere before you switch over to rockets.

My average altitude is 28km before the switch, speed is around 1750-1800m/s, I maintain a 10deg climb after the switch to rockets and accelerate to 2200-2400m/s. And I make sure that my rate of climb or vertical speed doesn't go above 250m/s.

My top (easily achieved) speed seems to be about 1700 M/s ground speed for Bertha. I can wait and get a little more out of it like maybe 1750 or so but I'm too impatient by then as it accelerates SO slowly after 1700.

I figure 1700 is quite reasonable so I just nose up when I reach it at whatever altitude I'm at. Then the early part of my final climb to orbit is still 100% air breathing accelerating up at about 40-45 degrees. When the first flameout happens at about 28 Km I switch modes on 3/5th of the Sabers and start the 6 nukes. 2nd flameout is usually somewhere near 37 Km and the remaining 2 Saber Ms under the wings are switched over to rocket power. MECO is around 50 Km. Then I coast and setup for circularizing on the nukes only.

By climbing steeply, I'm trying to reduce the time running all the big, less efficient engines in rocket mode at full throttle. Everything after that is done on the 6 nukes only. That's how I've been getting to 100 Km orbit consistently with 59-60% Fuel left.

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EDIT: OK. Just sent Bertha up with the 50 ton payload to see what happens and verify my numbers (using the temporary Saber .part code fix that Hodo posted in the B9 thread).

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As you can see, I just got to a 100 Km orbit (pre final tweaking) with well over 60% Oxidizer. Iignore the % of Liquid Fuel. I take off with 1,800 extra Liquid Fuel for the ascent and landing back at KSC so even if I burned up ALL of the Oxidizer, there would still be a couple hundred fuel left over.

With the ship set to only use the Nukes, MechJeb is showing over 900 M Delta-V with only the remaining onboard stores and and over 4,400 Delta-V if I used the contents of the cargo tank fuel as well. Could get that even higher if I transferred the fuel from the cargo to internal tanks and tossed the empty cargo tank overboard. But that sort of defeats the purpose...

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1: I added 4 more small scoop intakes...

2: Here's my updated launch profile notes based on this latest test run:

(Full throttle all the way from start until MECO)

@ 70 (runway altitude) take off and nose up to 40 degrees

@ 5000, 35 degrees

@ 10000, 30 degrees

@ 15000, 25 degrees

@ 17500, 20 degrees

@ 19000, 15 degrees

@ 20000, 10 degrees

@ 24000-25000 (When you get to 1700 M/s nose back up to 40-45 degrees.

First flameout about 28 Km - change 3/5ths of Sabers to Rocket mode and start the 6 nukes

Second flameout around 39-40 Km - change remaining Sabers to rocket and close intakes

MECO around 50-51 Km (when apoapsis gets to 100 Km)

Setup circle burn (~4 minutes - started ~2 minutes before apoapsis with about 69+% oxidizer - ended ~2 minutes after with 63.5%)

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So getting up to speed a bit lower giving myself more time to build vertical speed before changing over to rocket power made this trip up my most efficient yet...

Your advice has been helpful.

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After work tomorrow night, I'll try using your profile with the lower angle climb method and see what I can get for fuel remaining when I reach 100 Km orbit. Maybe you're right and it will be even better.

Anyway. I gotta go get some sleep now.

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EDIT 2: So now I'm back on the B9.40c Saber part configs using the updated ExsurgentEngineering.dll

I tried the low angle climb method. At 20 Km, 10 degrees. Let it climb till 1st flameout at 1750 M/s. 1st group rocket switched and started nukes. Nosed up to 25 degrees. Switched 2nd group at 2nd flameout. Killed thrust at apoapsis 100 Km. This gave me a 1.4 minute circle burn. Ended up with 59.4% fuel left and a Delta-V of 876 M/s.

Because I changed the engine parameters, it's not 100% apples to apples comparison so I'll have to try one more flight with the new .dll and try the steep climb approach again... Ugh.

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I tried my method and went even a tiny bit more extream...

Same ascent profile altitudes & angles as above.

At 24 Km & 1700 M/s, bump up to 15 degrees and wait a few sends to let it stabilise.

Bump up to 20 and wait, etc.... Repeat up to 45 degrees.

About then I was reaching 27-28 KM and first flameout.

Switch group1 to rocket mode and start the nukes.

Reach 2nd flameout and switch 2nd group over.

As soon as predicted apoapsis hit 90 Km, I cut all the Sabers, nosed down to 25 degrees and let it ride the nukes to a predicted apoapsis of 100 Km.

Set up the circle burn node and burned another 4 minutes and 45 seconds to a nice 100 Km cirular orbit.

All this fiddling got me there with 65% fuel left over! Delta-V 950 M/s. So I'm now convinced the steeper ascent with shorter main engine burn times is the more fuel efficient route. PROVIDED you begin to nose up from low enough to get a good chunk of your vertical acceleration done while still in air-breathing mode.

The lower angle, longer main burn with the MUCH shorter circle burn is great for simplicity plus saving time and aggravation on local orbit missions where every unit of fuel is not so mission critical. Unless you are planning to leave Kerbin orbit for some reason (Mun mission, etc), the trickier, steep ascent method is probably not needed. But still good to know!

Edited December 24, 2013 by dc4bs
Verified some numbers / adding pics

[likke_A_boss]

This doesn't work for me, I have every mod on your list, and still has locked parts…..

[dc4bs]

Yes. I can't figure out what's up with that either. It worked in .22. It worked when .22 was overwritten by Steam with .23.

When I reinstalled a clean .23 from scratch and added the mods back in, it wouldn't load anymore. In .21, when you tried to load a ship with bad parts it would list them. In .23 it just says the equivalent of, "I know there are bad parts but I'm NOT going to let YOU know what they are.... Nya, nya... Ttttbbbbbbbtttt!!"

I did find a modified version I was experimenting on with the Earth sized Kerbin mod that would still load and have reworked it back as close to the original version I had posted as I could.

I'll re-post the fixed version with updated checklists and notes when I get home tonight (after 11 PM EST) with the stats as tested/noted above. Partly I was waiting to see if B9 was going to update in case any further changes break something else but I guess I will just post the current clean save of it in .23 and just give the link to the updated ExsurgentEngineering.dll required to make the B9.40c Sabers work properly with .23

Note: It will look slightly different as I added more rigidity to the craft with some retro looking external strutting. Can't really describe it. You'll just have to see it. I think it's cooler looking now. And yes, the cargo doors DO clear the struts when opening/closing.

Edited December 26, 2013 by dc4bs

[likke_A_boss]

Cool! Can't wait to see it!

[dc4bs]

I am reposting the craft files now.

NOTE: I'm only re-posting the "A" model 1.1_v23 and I'm updating the main post to reflect the new changes.

Edited December 27, 2013 by dc4bs