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How do you get into orbit around Kerbin and the Mun?


High Priest Tenebrae
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Hello, and welcome to the forums!  :)

6 hours ago, High Priest Tenebrae said:

I have not been playing very long and I was wondering how to get into a reliable Mun orbit from Kerbin. I figured you guys would know.

P.S. I don't even know how to get into Kerbin orbit.

Well, KSP skills tend to come in "layers"-- i.e. doing the harder things requires mastering the easier things first.  It's a crawl-before-you-walk thing.  :wink:

And "get to Kerbin orbit" tends to be a first step to just about anything-- you really need to master that step before you go on to subsequent challenges, such as going to the Mun.  So, my suggestion would be to focus on getting to Kerbin orbit first, before you start worrying about going Munwards.  Pretty much anybody's Mun advice is going to assume that you get to orbit first.

Broadly speaking, the challenge of doing anything in KSP boils down to:

  1. Know how to build a ship that is physically capable of doing the job, and
  2. Know how to fly the ship in order to do the job.

So, in the case of "get to Kerbin orbit", that means you need to, first, know how to build a rocket that has enough dV (i.e. "can go fast enough") to get to orbit without running out of fuel; and, second, know the right way to fly it so that you end up in orbit without wasting too much fuel.

General advice for getting to orbit is:  build a reasonably streamlined rocket with small, lightweight, low-thrust stages on top and big, heavy high-thrust stages on the bottom.  To get to orbit, launch off the pad and tip the rocket just very slightly (just a few degrees) eastwards, then just follow the :prograde: marker on your navball until you're going fast enough that your apoapsis ("Ap" marker in map view; shows how high you'll go) climbs out of atmosphere, i.e. above 70 km.  Coast up to Ap, then thrust horizontally :prograde: until you're in orbit.

That's a very vague summary, of course, but it kinda has to be because so far we don't have a lot of info from you to go on.  :wink:  If you can give us something more specific, we can offer more specific suggestions.  A few questions to get the ball rolling:

  • Are you playing career, or sandbox?
  • Can you give us a screenshot of your rocket, i.e. your best attempt so far?  A screenshot in the VAB is fine.
  • Can you describe your path as you try to get to orbit?  How fast are you going when you reach 10 km altitude, and what angle (how many degrees from vertical) are you?
  • What's the actual problem you have when you try to get to orbit?  Run out of fuel?  Rocket starts flipping around?  Have no idea what to build or fly?

 

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8 minutes ago, High Priest Tenebrae said:

The main engine is a mastodon, with 4 "swivel" engines on the side.

Okay.  So, adding up their thrusts (1303 kN for the Mastodon, 168 kN for each Swivel), that comes to a total of 1975 kN.  Depending on ship design and intended mission profile, launchpad TWR should generally be somewhere in the range from 1.2 to 2.0, which for this amount of thrust would put the ship mass in the range 100 to 160 tons, roughly.  Personally, I tend to prefer higher TWRs myself, but YMMV and it's okay to be lower-- but you certainly don't want to be lower than 1.2, so if your rocket's over 160 tons or thereabouts, you're in trouble.

Okay, so how much does your ship mass, sitting on the pad?  You haven't given the number (would be nice to know), but just eyeballing it and approximately toting up what I can see, I'm guessing it's in the ballpark of... oh... around 140 tons, maybe?

140 tons would put your TWR at 1.4, which is reasonable (though it could stand to be a bit higher to reduce gravity loss).  So... you don't have a pathologically bad TWR, but you do have pathologically bad performance if you're running out of fuel at 10 km altitude.  So there must be some issues elsewhere.

One thing I note is that you're really not making much use of staging. I see only two stages there, which means your 1st stage is somewhat wasteful because it keeps lugging along way more dead weight than it needs (e.g. fuel tanks after they're empty, engines after your TWR has climbed to the point that you don't need them anymore.

Also, be aware that that huge fairing on the front is going to generate quite a bit of drag, which will also hurt your performance.  Actually, in 1.4.2, fairing aero is broken and it'll really be awful because that payload inside will generate drag as if the fairing weren't even there.  But even when they fix that bug... the fairing's just so wide that you're gonna take a hit there.

So, some suggestions:

  • Replace the Mastodon with a Mainsail.  There's basically no reason to use a Mastodon here; the Mainsail is unambiguously better in this case.  More thrust, better Isp, much cheaper.
  • Replace the Swivels with Reliants.  They're lighter, they have a higher atmospheric Isp, they have more thrust, and you don't need the Swivels' gimbal because you've already got plenty of gimbal on your central engine.
  • Asparagus the radial boosters.  No point in lugging them along when you don't need them-- after you've burned off a fair amount of fuel and are traveling more horizontally than vertically, the Mainsail will have plenty of oomph on its own.  So, ditch them when they're no longer needed.  To do this:  Instead of attaching them directly to the central stack, mount them on radial decouplers.  Set the radial decouplers to "Enable Crossfeed".  This will cause your Mainsail to drain the radial tanks first, before it starts using its own fuel.  So, once those radial tanks are empty, then as soon as you no longer need the Reliants' extra thrust, stage them away.
  • Add some SRBs.  In this case, they would probably be a good idea.  Looks like you have room for a foursome of radial SRBs.  So, attach four Thumpers with radial decouplers, and stage those away as soon as they've burned out.  For extra bonus points:  set their decouplers to "Enable Crossfeed", then set some fuel tanks (say, 2-ton or 4-ton) on top of the radial boosters.  That way, your Mainsail and Reliants will drain those tanks (the ones atop the SRBs) first, so you get a nice little fuel bonus.
  • Consider revising your payload.  I see you've got a 100G relay antenna plus a 15G relay antenna on there.  Perhaps you like it that way just because it looks cool... but bear in mind that you're taking a huge performance hit for not much gain in signal strength, so you should consider whether you think it's worth it.  (Only you can make that call, since you're the only one who knows what your priorities are.)  :wink:  For example:  If you were so inclined, you could get rid of that 15G antenna, and mount just the 100G one, sitting right on top of the rocket pointing straight up.  If you did that, not only would your signal strength still be nearly as good (the extra 15G doesn't add much), but also it would allow you to make the fairing far smaller and more compact.
  • Resculpt the fairing.  If you change the payload, you'll be redoing this from scratch, of course.  But even if you don't... the current fairing design is bigger and draggier than it needs to be.  From looking at it, it appears that the reason it needs to have such a huge radius is to clear that projecting antenna from the 100G relay, yes?  In that case... don't have so much of a cylinder.  Make the fairing sculpted as a cone, stretching up from the fairing base to right where the projecting antenna is.  Then, once you've reached that point, slope it inwards towards closing the fairing-- i.e. don't have it project a long way up from there as a cylinder before you start to taper, as you're doing it now.  Doing that will give it a pointier, more tapered shape and (I believe) will make it more aerodynamic.  Doing all this will also reduce the total surface area and therefore the mass of your fairing, which is also good.

 

 

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17 hours ago, Snark said:

Well, KSP skills tend to come in "layers"-- i.e. doing the harder things requires mastering the easier things first.  It's a crawl-before-you-walk thing.  :wink:

Aside from agreeing with what Snark said above, I would also like to point out that many people have said that KSP doesn't have a learning curve so much as it has a learning wall.  This is the first time I've heard of KSP's learning onion, but I think that we ought to go with this premise:  it takes a long time to peel back all of the layers and you may end up in tears during the process.

More seriously, you absolutely should learn to orbit Kerbin before you go to the Mun.  We can certainly help you through that process, so don't be afraid to ask.

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Heres the thing: you first need to master BUILDING things like rockets and airplanes, then you need to master or at least understand how to achieve orbits around kerbin, THEN you can shoot for the mun. In my opinion, Im somewhere between orbits and building, as I am well educated on aerodynamics and such. Keep that in mind. Now I gotta stop my dumb plane from rolling forward on it's own.

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5 hours ago, High Priest Tenebrae said:

Thanks, I hadn't thought of that.

Yeah, if you're struggling to get to 10 km and run out of fuel then, you're probably way underpowered, as @Gogi pointed out.  It may be that you have other design issues, as well, if you're new to KSP.

Would strongly suggest posting a screenshot of your ship-- lots of folks could give specific suggestions then.  "Strap SRBs to it" is certainly one useful (and fun!) suggestion :) ... but there may be other issues as well, and an experienced KSP player could spot an awful lot of potential problems with one glance at a screenshot.

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28 minutes ago, High Priest Tenebrae said:

How? I have it saved on my PC but I can't paste it in.

Correct, because that's not how the forum works.  It won't let you paste any content directly here.  You get a screenshot into your post by linking to it, not pasting it.  Here's what you do:

  1. Upload your image to some third-party image sharing site, such as imgur.com.
  2. Once it's uploaded there, right-click on the image on its web page and choose "Copy Image Location"
  3. Paste that URL into your forum post here.
  4. Presto, it gets automagically converted into an in-line image.

:wink:

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6 hours ago, High Priest Tenebrae said:

It weighs 184.564 tonnes now

Ah, there you go.  :)

So.  Your new thrust is 1000 kN from the Thumpers, plus 1379 kN from the Mainsail, plus 800 kN from the Reliants, for a total of 3179 kN, giving you a launchpad TWR of 1.75.  That's reasonably muscular-- high enough to avoid undue gravity losses, not so high that it's overpowered-- so I expect it ought to work reasonably well.

Plus it has the added bonus that all those LFO engines won't start actually using their own fuel until they've drained 16 tons out of the SRB stacks, which gives you a nice head start on the way to orbit.

Have you tried it out?  How did it go?

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18 minutes ago, Snark said:

Plus it has the added bonus that all those LFO engines won't start actually using their own fuel until they've drained 16 tons out of the SRB stacks, which gives you a nice head start on the way to orbit

@High Priest Tenebrae make sure your booster's decouplers have crossfeed enabled, or this won't work.  It's not always enabled by default.

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Though the problem seems to have been solved, I have my 2 cents to add, so no one go anywhere =P

If @High Priest Tenebrae isn't opposed to modding, I would highly suggest they invest some time in installing Kerbal Engineer Redux, as it gives handy default readouts such as Dv and TWR for each stage of your vessel.  Would suggest even if they don't like mods, as it's practically stock at this point. 

Anyhow, you need about 3500 Dv to make LKO as a rule of thumb. [Community Dv Map]

And your TWR needs to be above 1 to actually lift off kerbin. You probably know that but figured just in case. 

 

Kerbal Engineer Redux Github Repo

Forum Page

^The mod's og dev ,@cybutek, has mysteriously disappeared and has been presumed MIA, possibly due to a kraken attack, but @jrbudda has been nice enough to pick up the mod for the time being. In any case, the current version is unofficial, but does work. 

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20 minutes ago, Geonovast said:

make sure your booster's decouplers have crossfeed enabled, or this won't work.  It's not always enabled by default.

He was following this suggestion,

7 hours ago, Snark said:

For extra bonus points:  set their decouplers to "Enable Crossfeed", then set some fuel tanks (say, 2-ton or 4-ton) on top of the radial boosters.  That way, your Mainsail and Reliants will drain those tanks (the ones atop the SRBs) first, so you get a nice little fuel bonus.

...so I suspect he gets the idea.  :wink:

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4 hours ago, High Priest Tenebrae said:

It went rubbish because as soon as I detached the thumpers, they blew up the engine.

You've got them attached way high up on the rocket, which means it "loses the race", i.e. the rocket has to travel a long distance forwards to clear the ejected boosters before they move inwards and thump it.  Also, the decouplers are attached significantly below the CoM of the boosters, which means it kicks the bottom end outwards, causing aero forces to move them inwards.

To fix this:

  • Mount the radial decouplers for the boosters as low down on the rocket as you possibly can.  (This shortens the distance it has to travel to get out in front of the boosters, giving it an advantage in "winning the race".)
  • Mount the boosters as low down on the decouplers as you possibly can.  (This means they won't rotate so much nose-inwards, so that they won't be so inclined to move inwards and hit the central stack.)

Another possibility that you could do, would be to attach those radial fuel tanks to the decouplers and put the SRBs attached below them, instead of putting the SRBs on the decouplers and attaching the fuel tanks on top.  Why this helps:  It means that the decouplers will be mounted well above the CoM of the radial boosters.  Therefore the ejector force of the decoupler will tend to kick the nose of the ejected booster away from the ship.  This will tilt the booster away, which will then cause aero forces to move it farther away from the ship.

4 hours ago, High Priest Tenebrae said:

P.S. how high is "Overpowered"? (TWR) Is it around 2?

2 is fine, for a properly designed (i.e. highly streamlined) ship, with an appropriately adjusted ascent profile.  It's what I tend to launch my own ships at, for example, and it works well for me.  Other people design their rockets differently and aim for a lower TWR, and that works well for them, too.

You probably don't want to go any higher than 2.

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15 minutes ago, Lego_Prodigy said:

Now I gotta stop my dumb plane from rolling forward on it's own.

 

Quote

If a wheeled vehicle is parked but its brakes are not engaged, it may be observed to very slowly roll east or west towards the halfway mark. It has been theorized that this occurs because the Runway is perfectly flat but the surface of Kerbin is spherical; this causes its ends to be slightly elevated, resulting in a slope where the force of gravity deviates from perfectly perpendicular to the tarmac.

 

https://wiki.kerbalspaceprogram.com/wiki/Runway

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On ‎28‎/‎03‎/‎2018 at 7:50 PM, Snark said:

 

  • Are you playing career, or sandbox?
  • Can you give us a screenshot of your rocket, i.e. your best attempt so far?  A screenshot in the VAB is fine.
  • Can you describe your path as you try to get to orbit?  How fast are you going when you reach 10 km altitude, and what angle (how many degrees from vertical) are you?
  • What's the actual problem you have when you try to get to orbit?  Run out of fuel?  Rocket starts flipping around?  Have no idea what to build or fly?

 

I play sandbox, go 80 degrees up until I get to 10,000 then go a little groundwards of horizontal to get going around Kerbin and stop going up. I usually run out of fuel just after 10,000 as they do not go up very fast. I will send a pic in a short while.

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25 minutes ago, Snark said:

 

  • Replace the Mastodon with a Mainsail.  There's basically no reason to use a Mastodon here; the Mainsail is unambiguously better in this case.  More thrust, better Isp, much cheaper.
  • Replace the Swivels with Reliants.  They're lighter, they have a higher atmospheric Isp, they have more thrust, and you don't need the Swivels' gimbal because you've already got plenty of gimbal on your central engine.
  • Asparagus the radial boosters.  No point in lugging them along when you don't need them-- after you've burned off a fair amount of fuel and are traveling more horizontally than vertically, the Mainsail will have plenty of oomph on its own.  So, ditch them when they're no longer needed.  To do this:  Instead of attaching them directly to the central stack, mount them on radial decouplers.  Set the radial decouplers to "Enable Crossfeed".  This will cause your Mainsail to drain the radial tanks first, before it starts using its own fuel.  So, once those radial tanks are empty, then as soon as you no longer need the Reliants' extra thrust, stage them away.
  • Add some SRBs.  In this case, they would probably be a good idea.  Looks like you have room for a foursome of radial SRBs.  So, attach four Thumpers with radial decouplers, and stage those away as soon as they've burned out.  For extra bonus points:  set their decouplers to "Enable Crossfeed", then set some fuel tanks (say, 2-ton or 4-ton) on top of the radial boosters.  That way, your Mainsail and Reliants will drain those tanks (the ones atop the SRBs) first, so you get a nice little fuel bonus.
  • Consider revising your payload.  I see you've got a 100G relay antenna plus a 15G relay antenna on there.  Perhaps you like it that way just because it looks cool... but bear in mind that you're taking a huge performance hit for not much gain in signal strength, so you should consider whether you think it's worth it.  (Only you can make that call, since you're the only one who knows what your priorities are.)  :wink:  For example:  If you were so inclined, you could get rid of that 15G antenna, and mount just the 100G one, sitting right on top of the rocket pointing straight up.  If you did that, not only would your signal strength still be nearly as good (the extra 15G doesn't add much), but also it would allow you to make the fairing far smaller and more compact.
  • Resculpt the fairing.  If you change the payload, you'll be redoing this from scratch, of course.  But even if you don't... the current fairing design is bigger and draggier than it needs to be.  From looking at it, it appears that the reason it needs to have such a huge radius is to clear that projecting antenna from the 100G relay, yes?  In that case... don't have so much of a cylinder.  Make the fairing sculpted as a cone, stretching up from the fairing base to right where the projecting antenna is.  Then, once you've reached that point, slope it inwards towards closing the fairing-- i.e. don't have it project a long way up from there as a cylinder before you start to taper, as you're doing it now.  Doing that will give it a pointier, more tapered shape and (I believe) will make it more aerodynamic.  Doing all this will also reduce the total surface area and therefore the mass of your fairing, which is also good.

 

 

Here is the new rocket, with all the above modifications:

NLY5You.pngIt weighs 184.564 tonnes now

Edited by High Priest Tenebrae
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