How to get this craft into orbit?

[birrhan]

it is something of an odd request. Here is the craft:

Technically it has enough dv to get into orbit. But the COM and COT are on top of each other, so when it comes times to gravity turn, this happens (note we are going east but pointed west, Kerbal style):

So I slapped some rockets on the thing (you can see that above), and it just accelerated the failure.

Then I thought to add a gas tank, up top, to shift COM above COT, like so:

The thing never ever ever ever flies true, not even to start. It seems to want to follow the prograde indicator, as if ASAS isn't engaged (it is); I actually have much better luck flying it manually.

The traditional "stick the thing on top of a bunch of orange tanks" launcher clocks in at 1800 parts and, further, blows up upon physics initiation at the launch pad, prior to ignition:

Before:

After:

So, a simple request: how do I get this craft into a stable 100 x 100 km orbit? Empty fuel tanks are OK; staging is not--craft must be SSTO, but anything can be added to get it there.

[JonhyBee]

I am no pro but I think you have about enough big orange tank on that last pic.

[Eleven]

Go back to the first screenshot vessel and put empty lander cans on top of the tanks. They add torque to prevent a tip-over on your gravity turn.

[Kosmo-not]

Start off with small rockets. You're just going to get frustrated trying to build big things at first.

[Fractal_UK]

I would say, take the engines off the bottom of the lander and find a way of mounting them radially. If you do that for the central 5 grey tanks you could attach rockomax brand decouplers underneath them and have a central launch stage of 5 orange tanks with staging around that. I'm pretty sure the reason that your rocket is blowing up in the bottom picture is because you are putting too much weight on the central stack, hence having a fatter core stage will help you.

To give an example, this is my supertanker:

Note how I've mounted the nuclear rockets there radially to keep engines out of the way of the staging. It has 7 stacks, 3 high of orange tanks in the centre with two sets of 6 radial boosters. I use crossfeed on this one rather than asparagus staging because asparagus staging is hard to set up on these kind of fat core stages (and it gets to orbit anyway, so why bother).

I believe that launcher is capable of lifting about 350t to orbit, which looks to be similar to your lander.

What is it for, by the way? Tylo?

[birrhan]

I would say, take the engines off the bottom of the lander and find a way of mounting them radially. If you do that for the central 5 grey tanks you could attach rockomax brand decouplers underneath them and have a central launch stage of 5 orange tanks with staging around that. I'm pretty sure the reason that your rocket is blowing up in the bottom picture is because you are putting too much weight on the central stack, hence having a fatter core stage will help you.

To give an example, this is my supertanker:

Note how I've mounted the nuclear rockets there radially to keep engines out of the way of the staging. It has 7 stacks, 3 high of orange tanks in the centre with two sets of 6 radial boosters. I use crossfeed on this one rather than asparagus staging because asparagus staging is hard to set up on these kind of fat core stages (and it gets to orbit anyway, so why bother).

I believe that launcher is capable of lifting about 350t to orbit, which looks to be similar to your lander.

What is it for, by the way? Tylo?

I have had poor luck building a launcher with multi-point attachments to the lander. If you have a central core and 4 peripheral tanks (attached however you like), then build up to a lander, the peripherals on the lander won't attach to the center--the game can't handle attachments at multiple points in parallel. it looks like you've integrated your launcher and lander/payload, so that's a non issue. I would LOVE to do this. Aerospikes don't stage, btw.

Mounting the aerospikes radially will only distribute weight away from vertical, which will worsen the problem I'd think. Also, there's precious little room there.

Start off with small rockets. You're just going to get frustrated trying to build big things at first.

Please don't be condescending. I asked for a "how to" not a "why not". For the record, I've logged 430 hours (about 3/4 of which I've spent in the VAB building things that don't fly), and landed a 3 man pod on every body in the Kerbol system--and returned them to Kerbin--EXCEPT for Eve. That's what this is for. From that perspective, you might understand why you appeared to be condescending. With that in mind, can you add materially to the discussion?

Go back to the first screenshot vessel and put empty lander cans on top of the tanks. They add torque to prevent a tip-over on your gravity turn.

Thank you. I'll try that. just tried. Didn't work. Got it into a gravity turn OK, but then around 20k it started bobbing around like a cork:

[Eleven]

I use Mechjeb for ascents. I have my gravity turns for large ships set to start at 8K, end at 70K and have a 50% curve, this avoided tip overs I had.

[GoDores]

It's hard to tell from the pictures but it looks like you're using only aerospike engines on the stage you want to orbit. On something with that mass, no reasonable amount of pod torque is going to keep control; you need gimbaling engines.

I have a design that uses Rockomax tanks with three aerospikes underneath each just like you have, but I mounted them farther out from the center, which leaves room to mount an LV-T45 at the center attach point for control. My design is intended as a booster stage to get my lander down to and off from heavier bodies (everything except Eve) but has enough dV to get into Kerbin orbit as an SSTO without my lander attached.

Try this, or work out another way to get one gimbaling engine per two or three aerospikes, and see if that doesn't let you fly controllably to orbit.

[Fractal_UK]

Some more ideas:

Attach winglets to your lander - you could make them detachable if you don't want them later, that might help keep it steady during the ascent. You could also try attaching monoprop tanks and RCS ports. Turn SAS and RCS on during the rough parts of the ascent, provided you can dock in orbit and refuel, burning through a load of monoprop shouldn't do any harm.

Check your fuel lines for uneven flow too, if you end up with some kind of asymmetry there, you are bound to have real problems.

[Fractal_UK]

Nevermind, GoDores is definitely right, it's the lack of gimbaling. I've just built a sort of replica craft, it's not identical but it's fairly close and I reckon that if you replace one cluster of 4x3 aerospikes with LV-909s, you should have enough gimbaling capacity to get you into orbit. I think the TWR should still be good enough too.

My replica is not quite orbit capable but I knocked it together in 5 minutes.

Keeping it on target isn't too difficult:

[Fractal_UK]

I had to manually drain the fuel out of the top stage but I got it into orbit. I think my craft is a little bit heavier than yours though, takeoff mass is 376.78t so you might have a slightly easier time of it.

I had SAS turned on but most of the time I had my finger on the F key to give me back manual control. SAS did not like my piloting one bit. You might be best served just keeping it turned off.

I like the craft, by the way. I might try and use it for something.

[birrhan]

I had to manually drain the fuel out of the top stage but I got it into orbit. I think my craft is a little bit heavier than yours though, takeoff mass is 376.78t so you might have a slightly easier time of it.

I had SAS turned on but most of the time I had my finger on the F key to give me back manual control. SAS did not like my piloting one bit. You might be best served just keeping it turned

I like the craft, by the way. I might try and use it for something.

Thanks. What kind of dv are you getting? Should be around 10500. I'll post the craft file in a bit. I've built several versions in the 350 ton range. I feel like the .LV45s are basically interchangeable, i just need the clearance for the landing gears. The pitching always gets bad when the outer stages are spent,so I'd put them on the inner ring. Build it right and the core stage should get you 6500 dv in 60 tons.

[Fractal_UK]

Thanks. What kind of dv are you getting? Should be around 10500. I'll post the craft file in a bit. I've built several versions in the 350 ton range. I feel like the .LV45s are basically interchangeable, i just need the clearance for the landing gears. The pitching always gets bad when the outer stages are spent,so I'd put them on the inner ring. Build it right and the core stage should get you 6500 dv in 60 tons.

I've had to work it out by hand but I'm pretty sure I'm not getting a delta v anything like 10,500 - if I was, orbit would be trivial. On my latest version, modified Isp seems to be about 370, mass ratio of rocket is 373.66/100.66 = 3.71. So delta-v = 4,760. This might be a slight underestimate because lv-909 Isp increases once out of atmosphere.

I don't see how that 10,500 delta v figure is possible with one stage though. Assuming solely aerospikes with Isp of 390, you're looking at a mass ratio of exp(10500/(9.81*390)) = 15.56! That only leaves you with 22.5 dry mass on a 350 ton rocket, or 15 aerospikes worth. Since we have more than 15 aerospikes on there, that figure makes no sense unless I'm completely missing something about the design.

[birrhan]

I've had to work it out by hand but I'm pretty sure I'm not getting a delta v anything like 10,500 - if I was, orbit would be trivial. On my latest version, modified Isp seems to be about 370, mass ratio of rocket is 373.66/100.66 = 3.71. So delta-v = 4,760. This might be a slight underestimate because lv-909 Isp increases once out of atmosphere.

I don't see how that 10,500 delta v figure is possible with one stage though. Assuming solely aerospikes with Isp of 390, you're looking at a mass ratio of exp(10500/(9.81*390)) = 15.56! That only leaves you with 22.5 dry mass on a 350 ton rocket, or 15 aerospikes worth. Since we have more than 15 aerospikes on there, that figure makes no sense unless I'm completely missing something about the design.

Oh, it's not possible in one stage. That's the catch, it needs to be wired to stage and yield 10500, but as an SSTO it'll get around 5000. The trick is to keep the TWR above one in that configuration. Remember, it's supposed to be an Eve lander and return vehicle. That said, the core stage, as an SSTO, will get around 4500.

[Fractal_UK]

Oh, it's not possible in one stage. That's the catch, it needs to be wired to stage and yield 10500, but as an SSTO it'll get around 5000. The trick is to keep the TWR above one in that configuration. Remember, it's supposed to be an Eve lander and return vehicle. That said, the core stage, as an SSTO, will get around 4500.

Ah, I understand. I missed the section in your previous post where you said that it was an Eve return vehicle. What is the separable contraption at the top for then, out of interest?

Given that is the case, the way I've done it is probably not the most efficient. Probably the thing to do is to have 2 aerospikes and 1 LV-909 on each engine cluster. That should keep the thrust fairly uniform across stages during the Eve ascent.

Edited May 25, 2013 by Fractal_UK

[birrhan]

Ah, I understand. I missed the section in your previous post where you said that it was an Eve return vehicle. What is the separable contraption at the top for then, out of interest?

Given that is the case, the way I've done it is probably not the most efficient. Probably the thing to do is to have 2 aerospikes and 1 LV-909 on each engine cluster. That should keep the thrust fairly uniform across stages during the Eve ascent.

Alright, gimbals aren't helping me. In fact, it's pitching over worse than before. here's the craft:

https://www.dropbox.com/s/wvntq08v79sqxwo/KSS%20Sisyphus%20Lander.craft

[Fractal_UK]

Alright, gimbals aren't helping me. In fact, it's pitching over worse than before. here's the craft:

https://www.dropbox.com/s/wvntq08v79sqxwo/KSS%20Sisyphus%20Lander.craft

Try messing about with this because it looks like you have one or two modded parts, so I don't think I'll be able to load your file: http://www./download/jnjntt23l3k2w6k/Kratos_Lander.craft

I can get this thing into orbit without using the staging. I've also added fuel tanks with docking ports to the top of the outer stages, the purpose being that you have them connected with appropriate fuel lines to create a circular fuel loop when launching in SSTO mode but when you get to Eve, you decouple them and you have switched the craft over to a crossfeed system.

It's not quite the same as yours but it should be close enough to help you figure it out.

[birrhan]

It's got KSPX; I need a 4x1.25 connector. It also has Engineer for the statistics. That's it. Your craft doesn't have the dv necessary for eve (6404 by my measurement--absolute minimum is 9000, 10,000 for some cushion, 11,500 for sea level). The craft are actually fairly divergent--your weight and thrust distribution are off of mine.

One of the reasons I made that overslung asparagus up top was to maximize dv; like I mentioned, it gets 3 kerbals over 6600 dv (currently) on 60 tons, and each stage would be TWR 1.4 or greater on Eve, could I get there. I remade it with a lower COG on the top half, still pitches. I've got 8 LV45s on the bottom now. It's a weight, and COG/COL issue, not a gimballing issue. For whatever reason the COL is WAY below the COG, but I don't know how to fix that and maintain the high TWR to lift off Eve. I think it needs a launcher. You know, capable of lifting 350 tons.

This whole thing is a cluster****. Like I said at the beginning--it won't fly itself into space (too unwieldy), it won't tolerate a lander (too heavy), so for now it's a great theoretical vehicle and that's about it.

Currently, this is the list of things I've tried:

-Lv45s (gimballing): pitches between 6000 and 25000 meters

-lander cans up top: pitches

-massive RCS spamming: not enough force to stop the pitch

-and of course, large launchers (unstable as holy hell)

So I am fresh out of ideas. This is my most recent iteration (KSPX and Engineer only mods required):

https://www.dropbox.com/s/nse4ljdrlk8mnf8/Sisyphus%20Core.craft

[Fractal_UK]

It's got KSPX; I need a 4x1.25 connector. It also has Engineer for the statistics. That's it. Your craft doesn't have the dv necessary for eve (6404 by my measurement--absolute minimum is 9000, 10,000 for some cushion, 11,500 for sea level). The craft are actually fairly divergent--your weight and thrust distribution are off of mine.

One of the reasons I made that overslung asparagus up top was to maximize dv; like I mentioned, it gets 3 kerbals over 6600 dv (currently) on 60 tons, and each stage would be TWR 1.4 or greater on Eve, could I get there. I remade it with a lower COG on the top half, still pitches. I've got 8 LV45s on the bottom now. It's a weight, and COG/COL issue, not a gimballing issue. For whatever reason the COL is WAY below the COG, but I don't know how to fix that and maintain the high TWR to lift off Eve. I think it needs a launcher. You know, capable of lifting 350 tons.

This whole thing is a cluster****. Like I said at the beginning--it won't fly itself into space (too unwieldy), it won't tolerate a lander (too heavy), so for now it's a great theoretical vehicle and that's about it.

Currently, this is the list of things I've tried:

-Lv45s (gimballing): pitches between 6000 and 25000 meters

-lander cans up top: pitches

-massive RCS spamming: not enough force to stop the pitch

-and of course, large launchers (unstable as holy hell)

So I am fresh out of ideas. This is my most recent iteration (KSPX and Engineer only mods required):

https://www.dropbox.com/s/nse4ljdrlk8mnf8/Sisyphus%20Core.craft

Not surprising really that my craft ended up being only superficially similar, it's hard to copy the function of something from a picture.

If COL is an issue though, just take off any and all lifting surfaces and start again with them. A rocket shouldn't really be having problems with this though because any lift being generated should be being cancelled out by symmetrical fins - if your CoL is off to one side though, that's a major issue.

I've had the problem that you've described while doing this testing a couple of times though and it seems to have resulted mainly from lack of gimbaling but also from assymetrical fuel use - you should really check for this, it might not be apparent because if you've set it up in the SSTO stage such that each engine has access to all of the fuel then the game might subtly be drawing fuel from one side of your rocket more than the other.

[birrhan]

Not surprising really that my craft ended up being only superficially similar, it's hard to copy the function of something from a picture.

If COL is an issue though, just take off any and all lifting surfaces and start again with them. A rocket shouldn't really be having problems with this though because any lift being generated should be being cancelled out by symmetrical fins - if your CoL is off to one side though, that's a major issue.

I've had the problem that you've described while doing this testing a couple of times though and it seems to have resulted mainly from lack of gimbaling but also from assymetrical fuel use - you should really check for this, it might not be apparent because if you've set it up in the SSTO stage such that each engine has access to all of the fuel then the game might subtly be drawing fuel from one side of your rocket more than the other.

Well, it's definitely symmetric. And I misspoke, I meant COT. I'm impressed with how much you were able to reverse engineer.

Well, I'm putting this on the back burner for a while. You were right, the core stage makes a beautiful light weight lander.

[birrhan]

I've had the problem that you've described while doing this testing a couple of times though and it seems to have resulted mainly from lack of gimbaling but also from assymetrical fuel use - you should really check for this, it might not be apparent because if you've set it up in the SSTO stage such that each engine has access to all of the fuel then the game might subtly be drawing fuel from one side of your rocket more than the other.

UPDATE: Great success!! It required (a) using 16 LV45's, ( using 9 orange tanks with associated 2.5 m engines from KSPX, and © generous RCS usage. Result was this (2000 liters fuel remaining of 29,500 initially):

thanks to everyone, in particular Fractal_UK, for their help.

[Fractal_UK]

UPDATE: Great success!! It required (a) using 16 LV45's, ( using 9 orange tanks with associated 2.5 m engines from KSPX, and © generous RCS usage. Result was this (2000 liters fuel remaining of 29,500 initially):

Good job! Have you had chance to test it for Eve ascent yet?

I spent a bit of time working on this thing:

It is a sort of rebuild of my version of the rocket using 6 asparagus stages. I got it into orbit in SSTO mode around Kerbin and thought that would be the hard part done since the Eve ascent would have access to all that asparagus staging. Unfortunately, I only got about 32km off the surface of Eve in my test. I get the impression figuring out the optimal Eve ascent profile is going to take some time but still the only hope for me might be a launch from that huge Eve mountain.

[Joe_Bender]

And the purpose of this vehicle is???????

[birrhan]

Good job! Have you had chance to test it for Eve ascent yet?

I spent a bit of time working on this thing:

It is a sort of rebuild of my version of the rocket using 6 asparagus stages. I got it into orbit in SSTO mode around Kerbin and thought that would be the hard part done since the Eve ascent would have access to all that asparagus staging. Unfortunately, I only got about 32km off the surface of Eve in my test. I get the impression figuring out the optimal Eve ascent profile is going to take some time but still the only hope for me might be a launch from that huge Eve mountain.

Not yet--I need a transfer vehicle rendezvous.

The advice I've gathered so far about Eve is this: 11500 dv to get to orbit from sea level or 9000 dv to get to orbit from the high plateaus around 6000 m high. In both cases your TWR should be about 1.5 for all stages. I have been using Kerbal Engineer religiously to hammer down those numbers. The current version has 11,200 dv and all stages have TWR of 1.4 (except the third to last stage, a very brief one at 1.1). I think she weighs 410 tons now. I think that's reasonable.