90t to Kerbin Orbit

[ibanix]

So I'm looking to put down an ISRU+Miner on Minmus so I can make fuel there.

My complete miner-lander runs about 30t: ISRU, tank for the fuel, 4x miners, small nuclear plant (from mods), skycrane engine, and a few radiators. Since I need to get this to Minmus and land it, my upper stage (Kerbin->Minmus) is another engine+tank which gets me about 1200m/s. This brings the weight up to around 90t.

So now I'm trying to build a first stage (Kerbin->orbit) that will lift that 90t, and I'm having a devil of a time. Mammoth engine with the largest Mk3 tank, and then 4x KS-25s under the orange tanks, set up in an asparagus system: This is only getting me about 3300m/s, which is not *quite* enough to get to an orbit I can work with.

Is there a better way to launch really big payloads from Kerbin? Anything larger than what I have seems to be seriously diminishing returns. Better to launch dry and fuel in orbit, and launch a separate fuel can?

[Tatonf]

Have you tried using the Kerbodyne fuel tanks ? 90 tons is pretty easy to put in orbit.

Even without launching my game, I could tell you that 2 big Kerbodyne tanks with mammoth plus 4x1 big kerbodyne tanks with mammoth asparagus staging would be totally overkill for this task.

[steuben]

Pics of your launcher will help.

But I've had good luck in the 500 tonne cargo range with onion/asparagus staging, launcher at about 5-6 Kt. Just wish I could break the Kt cargo barrier. Using stock parts in by designs.

[ibanix]

Alright, here we are. I actually did try with the larger Kerbodynes, and I think they *might* work. I still feel like I need more dV.

 

First, whole thing:

 

 

Second, just payload and upper stage:

 

[Superfluous J]

Regarding your last question, yes. It's far easier to fly up 500 tons of fuel than it is 400 tons of fuel attached to 100 tons of spaceship. This is because you have a large amount of control over the shape of your fuel lifter, while the ship has to fit into the confines of the mission parameters. Also, you can use the final engine of your fuel ship in the very first stage if you build correctly.

This is the "Why God, Why." It can get 660 tons into LKO, most of that fuel. Just as an example:

It's more than you need, obviously. Your fuel lifter could probably be half this size.

[Tatonf]

Well I wasn't actually planing to build it but here you go :

 

The top of the rocket is a fictional payload of 91 tons, so the rocket fuel is not used here.

I've made some changes relatively to my previous post, so the rocket is less overkill now, but can still make orbit with 300 m/s left.

The two boosters use the mammoth engine while the main one use a Rhino (because it have a better Isp). This is NOT asparagus staged.

[ibanix]

Nice, thanks for all the spot-on advice.

Follow-up question: Best method to control attitude while ascending? Vernor engines, reaction wheels, or monoprop thrusters?

[Tatonf]

The gimbal of the engines is generaly good enough for me.

[Superfluous J]

5 minutes ago, ibanix said:

Nice, thanks for all the spot-on advice.

Follow-up question: Best method to control attitude while ascending? Vernor engines, reaction wheels, or monoprop thrusters?

I prefer - in order - reaction wheels, gimbals, fins, vernors, monoprop. Mostly due to weight vs utility concerns. I love not having to bring monoprop tanks, and reaction wheels work everywhere. You can't beat the stopping power of escaping gas, though.

Except with a planet's surface, but that's outside our mission parameters.

Edited April 15, 2016 by 5thHorseman

[AeroGav]

I'm not yet brave enough to tackle stuff from the "challenges" section of the forum but this kind of thing can be fun.  Particularly as I'm a spaceplane head,  and i've never built a large rocket.

What mods are allowed btw?    I have tweakscale installed ATM but won't use it,  what about Modular fuel tanks?   This lets you swap the contents of tanks to suit a particular need.    For example, I was going to radially cluster 3 mark 1 liquid fuselages around the payload and put a NERV at the bottom of each for the upper stage, but I need 18 tonnes of fuel to get from LKO > Minmus and was thinking of fitting a 2.5M tank and swapping the contents to be 100% LF , not waste any space for oxidizer.   Is that cheating?

 

[ibanix]

4 minutes ago, AeroGav said:

 For example, I was going to radially cluster 3 mark 1 liquid fuselages around the payload and put a NERV at the bottom of each for the upper stage, 

 

I've done exactly that for secondary stages for long interplanetary missions. You need to add a bit of cooling (read: radiators).

[regex]

I think it was @Laie who told me you could get 190 tons to LKO with three Mammoths and a Rhino.  Craft basically uses the Falcon Heavy model with crossfeed (2 boosters feeding core), but don't bother throttling the core like you'd do with identical stages IRL (reference Angara 5).  Rhino is your upper.  The LV is eminently controllable on gimbal alone, although you may prefer something for roll control on the upper.

If you go without crossfeed you may need to reduce the payload and throttle the core down for launch since the boosters and core are identical.

[Warzouz]

1 hour ago, regex said:

I think it was @Laie who told me you could get 190 tons to LKO with three Mammoths and a Rhino.  Craft basically uses the Falcon Heavy model with crossfeed (2 boosters feeding core), but don't bother throttling the core like you'd do with identical stages IRL (reference Angara 5).  Rhino is your upper.  The LV is eminently controllable on gimbal alone, although you may prefer something for roll control on the upper.

If you go without crossfeed you may need to reduce the payload and throttle the core down for launch since the boosters and core are identical.

That's much possible. I've a 2 mammoth 100T lifter which is a recoverable SSTO

[AeroGav]

https://onedrive.live.com/redir?resid=7003A8806D8A6B2C!728&authkey=!AOsqIdClIzQFSOc&ithint=file%2ccraft

 

This is what I finally came up with, lot of Kerbals died to make this happen.   I'm an airplane person so this is the first heavy lift rocket I've built successfully.  

That black and white tank at the top is partially filled to make a 30t payload.  

I've taken the largest available 1.25m tank  and used Modular Fuel Tanks so that it holds only LF and no OX - brings it's capacity up to 800 LF.     I've then mounted two of these radially to the payload, with NERV engines on the bottom of each 1.25m tank.      Then I took the smallest size 2.5m tank, again swapped it over to LF only, and stuck it to the bottom of the payload with a decoupler.   There's a pair of fuel ducts to feed its contents into the 1.25m,  and it the decoupler can be used to jettison it when empty.    This comprises the Minmus injection stage (50T).   

The core stage is the second smallest 2.5m tank with 4 Dart aerospikes.  There are four orange tank boosters around the side, and asparagus is used.  

The first two boosters to get dropped don't bother with fins and have only one engine type - quad Vectors.    

The two that hang on longest, have winglets and stage off the Vectors for the more efficient, and lighter Darts once we hit 1.3 Mach.  

302 Total weight.

Launch technique -

1. Off the pad, all those vectors give an insane 5g acceleration.  Jeb likes it.   I start holding down the CTRL key at 185m/s so we don't start getting mach effects/drag down low, with the aim to stopping acceleration at about 225m/s

2. At about 8km, and with some gravity turn done (it's a bit reluctant tbh, maybe too many fins) i hit the prograde assist and Z to go max power, accelerate through the sound barrier FAST.

3. At 1.25 mach  I press space bar to swap two of our orange tanks over to Dart engines instead of Vectors.

4. Shortly after this the left/right side orange tanks are dry, SPACE to stage em' off.   This stage also starts up the NERVs.

5. next stage drops the remaining two boosters.

6. next stage drops the core stage, so the NERVs are our only power.

7. final staging is to drop the small 2.5m tank when it's empty, the NERVs then just run off the type 1 tanks they attach to.

 

I am however, an airplane person so usually use a spaceplane for the IRSU job.  Nice to have landing gear to taxy over the surface on, and the Big S wings have plenty space to stock up on LF to refuel clients with.            For minmus i would just use solar panels , Minmus is bugged and solar panels give power even at nighttime.  I was squirrelly about bringing just one drill and dropping down to the much less efficient small converter, but honestly, if you're not having to stop and start the equipment every day and night cycle, you just "fly " the vessel but go into a high rate of time acceleration and are done in no time.       It's nice to have enough capacity to refuel your client in one hit though.

This plane just did a series of planet hopping flights that ended @ Eeloo.   It's got the rubbish small converter, only one small drill and the lame solar panels (not the fabby Gigantors, they won't fit without clipping).   Even so,  it can refill it's 3300LF capacity in one Minmus day.    Install something like Kerbal Attachment System and you can put filler caps on your ships.   With my experience of that tour, i'd probably have more batteries in place of that stupid little fuel tank i'm using as a radial attach node at the front of the bay.  And I wouldn't take off with ore onboard hoping to convert in orbit - not worth it with the less efficient converter, it's just dead weight.  Fill the LF, bring the smallest possible amount of oxidiser the tweakables allow for the Vernors , and no mono or ore when taking off.

https://onedrive.live.com/redir?resid=7003A8806D8A6B2C!719&authkey=!APpaxbR8Rs0uLHQ&ithint=file%2ccraft

**this craft needs tac fuel balancer and kerbal joint reinforcement to work, most likely..

 

Edited April 16, 2016 by AeroGav

[Wanderfound]

On 15 April 2016 at 10:41 AM, ibanix said:

Alright, here we are. I actually did try with the larger Kerbodynes, and I think they *might* work. I still feel like I need more dV.

 

First, whole thing:

 

 

Second, just payload and upper stage:

 

Notice the difference between your one and everyone else's?

Nosecones, fairings. You're trying to push a barn door through the sound barrier if you fly as pictured. Make it slick and sporty:

Edited April 16, 2016 by Wanderfound

[GoSlash27]

ibanix,

 Here's a cheap design that's good for 135t to LKO:

http://s52.photobucket.com/user/GoSlash27/slideshow/KSP/CnCRocketFactory/Cheep135

Best,
-Slashy

[ibanix]

5 hours ago, Wanderfound said:

Notice the difference between your one and everyone else's?

Nosecones, fairings. You're trying to push a barn door through the sound barrier if you fly as pictured. Make it slick and sporty:

I never actually thought they were that effective until reading a recent thread in which the poster did actual experiments with cones/fairings and total distances travelled. Now I'm putting them on everything that launches from Kerbin.