Newb Questions Regarding Putting Stuff Into Orbit

[Hovis]

Hi guys, first post, many questions. I'm a giant newb, I've got Mechjeb and I'm able to get stuff into orbit and dock ships and, well, that's about it. My current stumbling block is trying to get something bigger into play.

Some problems I've faced:

1. If I have a station set up (usually a cylinder atop the rocket) I tend to find that the rocket blows up. Usually one of the connections, typically the one connecting the rear engine of the station, gives out, and boom. I'm wondering if I am accelerating too hard, or if the weight of the station itself is the problem?

2. Is there any mileage in a piggy-back launch like the Space Shuttle, or is that a dead end? A huge number of Kerbals have died in my experiments with this method of launch. I feel bad. But is there something in it? Typically I find that either I lose control of the rocket and it tips over, or if I put a buttload of power into the first stage to offset it then it just tears itself up. Is there a solution?

3. Are there any general things I should be aware of when looking at the Centre of Mass, Centre of Thrust and Centre of Lift? Do I just want to keep them all near the bottom?

4. If I want to build an interplanetary ship in space, do I effectively have to dock all the parts together or are there other ways? Docking links have a bad habit of snapping on me when I've fired up engines.

I don't want to get ahead of myself, but I am basically fishing to build an orbital hub station (working name Gas And Gulp) and also put together some sort of huge roving colony craft. I like the idea of a ship that can essentially visit all the different planets without having to return home (though it will get getting resupply runs from Kerbal along the way).

Any help much appreciated.

Also on a completely unrelated matter, is there a way to tell Mechjeb I want to go to the moon? Sort of baffled by that. I know it's not related but it's been bugging me.

[EndlessWaves]

1. KSP parts are fairly close to the their structural limits, so they will collapse if you pile too many on top of themselves. You're looking at around 4 of the largest 1m tanks or two of the largest 2m tanks (same overall height). It's often stronger to build out sideways. Accelerating too hard can cause the problem as well, but there's more margin there.

2. Dead end. It's possible but both halves need to maintain the same thrust to weight ratio all the way up which means they both burn fuel and you have to manually transfer it over before you eject the 'booster'.

3. Centre of lift needs to be behind the center of mass as that's where the drag will naturally try to pull it (so your craft is unstable if it's in front). Center of thrust has to be lined up so it goes through the center of mass (or would if the arrow extended to infinity) or the ship won't fly straight in vacuum.

4. Dock them together, you can dock multiple ports at once for a stronger connection. Having high acceleration in space is generally just wasteful though - so throw away the weight of a few engines and you'll have less structural problems and more range.

Mechjeb's orbital operations component does mun/minmus transfers.

[capi3101]

1. More likely the design of the rocket. I have similar problems with my heavy lifters - without sufficient struts, something just pops off and usually blows the whole thing up. EAS-4 Struts are your friends.

2. Can't help you here; haven't tried a shuttle yet. My understanding is that they're impractical...in general. The shuttle really was a big waste of time in RL; probably is going to prove to be the same in KSP...

3. Make sure your center of thrust aligns with the center of lift. You can occasionally get them out of alignment when moving things around in the VAB and that means a constant lean to your rocket as it flies. It's kind of annoying, actually. The closer the center of mass is to your engines the better, but that's something that's going to be dependent on your designs.

4. There are other ways, but it really depends on the target. I've gotten ships to Duna in one piece off the ground from Kerbin. If you're heading to Tylo, you're probably going to have to put something together in space. A return-trip Eve lander almost begs to be built in one piece on the ground, and that's something that has to have 12,000 delta-V just to get back to Eve's orbit. My interplanetary craft? I'm building it in orbit piece by piece. Try using multiple docking ports. There's also a mod that has something called "Quantum Struts" that sound like an abject cheat; I'm sure someone around here will ultimately recommend them to you.

[ThatBum]

1. Put struts between the station and the booster. If the station is too large for one launch, launch a core and add modules to it, like they do in real life. This involves orbital rendezvous though, which is a whole different can of worms. Also stations shouldn't need engines, as they don't need to go anywhere.

2. It comes down to getting the center of mass to the center of the craft, and directly inline with the center of thrust. Else it's going to list to the side it's unbalanced towards. It's incredibly difficult to balance a shuttle style launch with two SRBs on either side, a main liquid engine, and a drop tank. It's easier to get a spaceplane to orbit with conventional vertical stating, less weight balance nonsense to worry about.

3. In spaceplanes the center of lift should be as close to the center of mass as possible, or else the lift will make it start pitching up or down, and trim (ctrl+WASDQE) will be required to stabilize it, reducing efficiency and range of control surface motion. Center of thrust should be under the center of mass for rockets and behind for spaceplanes, else it will be top heavy relative to where the thrust is. It usually is unless you're using radial engines, in which case you should be careful.

4. Try using Quantum Struts for added structural integrity. Or perhaps make a heavy docking port like this.

MechJeb question: Get out Maneuver Planner, select the Mun, and use Hohman transfer to get there. Assuming you're using MechJeb 2, MechJeb 1 does it some other way I can't remember. See MechJeb's thread, MechJeb 2 is much more capable.

[Alistone]

1. Rocket engine blows up: some possible causes from my experience:

a. Initial launch too jerky. Before starting the stage the engine weight hangs down a bit. The sudden jerk of starting can cause it to impact whatever is above it instead of just pushing upward. I have sometimes overcome this by activating and then throttling up the engines before releasing the launch clamps

b. Too much force/power. When using a large orange tank with a mainsail engine near my final stage I find that it tends to break apart due to sheer engine power. Other than using as many struts as possible I finally found that burning fuel from higher tanks and leaving the fuel tank directly above the engine full would keep my vehicle in one piece.

(f=ma, so less mass on top requires less force to accelerate thus reducing the force passing through the middle section to the top. When it burned the fuel directly above it then it worked in reverse; raising the center of mass for the rocket and eventually causing catastrophic failure in the connecting segments.)

I also avoid using RCS fuel tanks anywhere that will experience "mainsail" thrust. The RCS fuel tanks are just too flimsy.

c. Overheating? Not sure if this is your problem, but the solution tends to be less throttle and a close eye. Sometimes seperatron rockets placed in a bad spot will cause an engine to explode as they pass it when staging.

2. I avoid wings on my rockets... too many kerbals lost to changing force vectors of lift as a result of the velocity and atmospheric density.

3. I don't pay much attention to center of mass for rockets, but top-heavy is prone to tipping over and hard to steer. Having engines thrust as far down as possibly makes it easier to steer with thrust vectoring but you have to leave ASAS running if you have a topheavy craft because if it turns too far sideways it is like balancing a broomstick on the palm of your hand and it will just fall over.

4. There are mods that allow you to do "orbital construction" and "launch from orbit". I haven't tried them though.

[Hovis]

Thanks for the help guys!

[Hovis]

Okay sort of follow up question, but it's something that has been vexing me since I've been playing the game, looking at mods, watching videos etc.

What exactly constitutes a heavy payload?

By which I mean, here I am in game, on Kerbal (metaphorically speaking) what is the most I should be reasonably expecting to put into space?

I mention this in specific reference to fuel, because fuel weighs a hell of a lot and I tend to find that most of my refuelling tugs that I launch are typically having to get high on their own supply, in order to make it out of the atmosphere.

So where should I be aiming? What's the sort of practical maximum to get into orbit from Kerbal, and what sort of tonnage of cargo should I be expecting to lift with ease, given that I'm a bit of a newb (though to be fair I've been eating, sleeping and dreaming the game since I bought it, it's ridiculously good).

Also, sort of related, what sort of Delta V level should I be aiming for to get different tonnages into a 200km orbit? I know that about 4k usually gets me into orbit, but if that's all I have typically the tanks are empty when I arrive. I struggle to get much higher than 4-5k.

[Alistone]

What exactly constitutes a heavy payload?

By which I mean, here I am in game, on Kerbal (metaphorically speaking) what is the most I should be reasonably expecting to put into space?

I mention this in specific reference to fuel, because fuel weighs a hell of a lot and I tend to find that most of my refuelling tugs that I launch are typically having to get high on their own supply, in order to make it out of the atmosphere.

So where should I be aiming? What's the sort of practical maximum to get into orbit from Kerbal, and what sort of tonnage of cargo should I be expecting to lift with ease, given that I'm a bit of a newb (though to be fair I've been eating, sleeping and dreaming the game since I bought it, it's ridiculously good).

Also, sort of related, what sort of Delta V level should I be aiming for to get different tonnages into a 200km orbit? I know that about 4k usually gets me into orbit, but if that's all I have typically the tanks are empty when I arrive. I struggle to get much higher than 4-5k.

A full orange tank into a 100km orbit with a "tug" is generally a heavy payload. It takes a lot of work, and it may be a mostly empty tank while you're learning the optimal launch curve. But practicing with a fuel payload gives you a lot of wiggle room while you're learning since you probably won't run out of fuel.

Since your tug should have some efficient atomic engines, it is very little fuel needed to move from a 100km to a 200km orbit.

If you can launch a full orange tank; then you learn docking and make a space station. After than you can refuel in orbit if you need more fuel for a longer mission.

It takes some balance of your terminal velocity. If you have to throttle back to avoid excessive drag losses then you could be carrying more fuel or less engines. If you can't reach terminal velocity during launch you could be carrying more enginges (or less fuel).

It is common to burn half of your launch fuel before you reach 12,000 meters in elevation.

[capi3101]

Okay sort of follow up question, but it's something that has been vexing me since I've been playing the game, looking at mods, watching videos etc.

What exactly constitutes a heavy payload?

By which I mean, here I am in game, on Kerbal (metaphorically speaking) what is the most I should be reasonably expecting to put into space?

Also, sort of related, what sort of Delta V level should I be aiming for to get different tonnages into a 200km orbit? I know that about 4k usually gets me into orbit, but if that's all I have typically the tanks are empty when I arrive. I struggle to get much higher than 4-5k.

Well, the most I've launched so far has been a fueling module that weighs a little over 45 tonnes - that consists of a design with two heavy docking ports (custom piece, .28 tonnes each), a Probodobodyne OKTO core with 4 PB-NUKs, 12 RCS Thruster Blocks, 2 of the Large FL-R1 RCS tanks and two X200-32 fuel tanks (one orange tank equivalent). I got that up into a 100k orbit on a DSTO that weighed close to 600 tonnes at the get-go and used 9 Mainsails (8 in Stage 1 and 1 in Stage 2, with fuel ducts going from the Stage 1 cans to the Stage 2 can). Stage 2 used 1FL-R1 RCS tank and 4 X200-32s, and the Stage 1 engines each had 2 X200-32s and 2 X200-8s of their own (used the 8s to attach to the Hydraulic Detachment Manifolds, which I attached to Stage 1 via Modular Girder Segments and a hell of a lot of struts. My Stage 2 has more than enough gas to deorbit itself once the can's in the air, so I imagine it'd make 200 km fairly easily.

Even if it didn't, the can's got enough RCS fuel to make to 200; you'd be amazed what you can accomplish with those little RCS block thrusters. My flying gas can makes it to its target fully fueled.

If I've done the math right (this is based on the data in the Advanced Rocket Tutorial on the wiki, which I think is confusing as hell), it should take only 145.07 m/s of delta-V to boost from 100km to 200km (about ~4650 m/s from the ground). I wouldn't put any stock in that figure until we can get a guru to verify it.

[ThatBum]

About heavy payloads. It's all relative to the rocket you're using and comes down to the TWR, or thrust-to-weight ratio. If the rocket has a TWR of less than 1 at the launchpad, it won't be able to get off the ground. It the TWR is exactly 1 it will break even with gravity and hover in place. Ideally, it should have a TWR of about 2 fully assembled with the payload attached. If the TWR is low, like 1.2 or something, it will lift off very slowly and might not be able to make it to orbit.

You can calculate your TWR per stage by adding up all your thrust sources of that stage, adding up the weight of all your parts, and dividing the former by the latter. The TWR will slowly improve as the rocket gets lighter from burning fuel. When you stage, you'll get a new TWR. Some addons can do this for you in realtime, like MechJeb or Flight Engineer.

[Hovis]

Ahaa, I typically aim for a 200k orbit. If it'd be easier to stabilise at 100k then step it up then that would be a big saving.

Getting a TWR around two sounds like good sense too, thanks. I used to go for that, or even higher, but then realised I was tending to damage my aircraft with the acceleration. Since then it's been around 1.60 usually, maybe bumped up with solid fuel boosters to get the early burst of speed. Aiming for two seems like a good compromise.

[ThatBum]

There's also the concept of max Q. It's kind of like terminal velocity, but in reverse. If you keep accelerating, you'll eventually reach an equilibrium between the force of drag pushing you down and the force of thrust pushing you up. If you accelerate beyond that point, the drag force will win out and force will be wasted. There's probably a table of terminal velocity numbers for various altitudes somewhere...

[Alistone]

There's also the concept of max Q. It's kind of like terminal velocity, but in reverse. If you keep accelerating, you'll eventually reach an equilibrium between the force of drag pushing you down and the force of thrust pushing you up. If you accelerate beyond that point, the drag force will win out and force will be wasted. There's probably a table of terminal velocity numbers for various altitudes somewhere...

The point at which the forces are equal is near terminal velocity. A chart can be found on the wiki

http://wiki.kerbalspaceprogram.com/wiki/Basic_Maneuvers

Altitude (m) Aprox. Terminal Velocity (m/s)

500 105

1,000 110

2,000 120

3,000 130

5,000 160

8,000 215

10,000 260 (remember to start your gravity turn!)

13,000 350

15,000 425

16,000 470

32,000 2250

[Eric S]

1. If I have a station set up (usually a cylinder atop the rocket) I tend to find that the rocket blows up. Usually one of the connections, typically the one connecting the rear engine of the station, gives out, and boom. I'm wondering if I am accelerating too hard, or if the weight of the station itself is the problem?

Personally, I tend to aim for a 2.2 TWR, and if the ship can't handle that, figure out how to strut things so it holds together better. Sometimes I even go so far as to put 8 symmetrically mounted pylons around the top of one stage, and strut them to the bottom of the next stage. Or some other part that's breaking under acceleration.

2. Is there any mileage in a piggy-back launch like the Space Shuttle, or is that a dead end? A huge number of Kerbals have died in my experiments with this method of launch. I feel bad. But is there something in it? Typically I find that either I lose control of the rocket and it tips over, or if I put a buttload of power into the first stage to offset it then it just tears itself up. Is there a solution?

It can be made to work, though that's a lot easier with an addon that someone wrote that allows you to adjust the thrust of engines to handle things like that. While a functional solution, that means that you're lifting engines that aren't using their full thrust at any point in the launch, which is inefficient. Personally, I consider it more trouble than it's worth.

3. Are there any general things I should be aware of when looking at the Centre of Mass, Centre of Thrust and Centre of Lift? Do I just want to keep them all near the bottom?

You need to make sure that the center of thrust goes through the center of mass, otherwise you'll have steering problems in space or during vertical ascents. Center of Lift is something you only need worry about if you're building a space plane. On the other hand, if you're using control surfaces to guide a rocket, make sure that they're towards the back of the rocket, having a lot of drag towards the nose of the craft causes it to be inherently unstable.

4. If I want to build an interplanetary ship in space, do I effectively have to dock all the parts together or are there other ways? Docking links have a bad habit of snapping on me when I've fired up engines.

Five solutions, three of which are addons:

1) quantum struts: I tend to avoid these only because I like to minimize the amounts of science fiction in my game.

2) docking struts: A more realistic version of quantum struts.

3) multi-port docking: A way of using multiple docking ports per connection to strengthen said connection. Can have problems with fuel flow, can be a pain to dock.

4) Common Berthing Modules: basically, docking modules that are designed to be stronger (they're heavier than regular docking ports and more expensive, but not as much so as the multi-port docking stuff, and if you're doing complex ships, the lower part count is important).

5) Really big launch craft: I've seen stock launchers capable of lifting over 100 ton payloads, and a few that can break the 200 ton mark.

Personally, I usually go with option 4.

I like the idea of a ship that can essentially visit all the different planets without having to return home (though it will get getting resupply runs from Kerbal along the way).

Look into the Kethane mod. There's official resource mining functionality coming "soon" to KSP, but until then, the Kethane mod allows you to mine resources and manufacture your own rocket fuel during the course of the mission.

Also on a completely unrelated matter, is there a way to tell Mechjeb I want to go to the moon? Sort of baffled by that. I know it's not related but it's been bugging me.

Which version of mechjeb? 1.X and 2.X do that in completely different ways.