Can this get in orbit and get out ?

[MadMate]

So I made this rocket and realized it is almost identical with orbit training rocket, it just has better boosters and 2 extra fuel tanks but no terrier engine , my thinking is it is missing the terrier engine with 1 small fuel tank but it has 2 extra fuel tanks basically instead 5 I got 7 fuel tanks for the t-45 engine so it should make it up for terrier engine right ? for some reason I can't get in orbit, I get really close like 50k periapsis but no, maybe I am doing the gravity turn wrong ? can someone tell me if this rocket is capable of getting in orbit and getting out of it ? please  by the way there is a science storage unit in the service bay

 

Edited July 29, 2019 by MadMate

[HebaruSan]

Don't leave delta V on the table. When you swap out the Terrier for a T-45, your second stage thrust more than triples. That means you can triple the mass of that stage, which represents a big increase in fuel. Try right clicking the stages in the lower right of the screen. You'll see a display that shows you, among other things, the TWR of each stage. Anything above 2 is wasted on a vacuum stage.

This is the kind of load you can lift with a T-45 (and it gets to orbit with 1700 m/s left over):

 

[MadMate]

1 hour ago, HebaruSan said:

Don't leave delta V on the table. When you swap out the Terrier for a T-45, your second stage thrust more than triples. That means you can triple the mass of that stage, which represents a big increase in fuel. Try right clicking the stages in the lower right of the screen. You'll see a display that shows you, among other things, the TWR of each stage. Anything above 2 is wasted on a vacuum stage.

This is the kind of load you can lift with a T-45 (and it gets to orbit with 1700 m/s left over):

 

I actually made a mistake it wasn't 5 + 2 it was 5+4 fuel tanks on the training so I haven't tried but I probably could make it with like 5+6 tanks or something like that but I just got enough science to get the terrier engine and it was super easy to orbit. I even reached 1.000.000 km apoapsis then return to surface with almost half fuel left on terrier lol.

[Snark]

4 hours ago, MadMate said:

for some reason I can't get in orbit

Right, because you don't have enough dV on that rocket.

Your first stage has 1362 m/s, your second stage has 1663 m/s.  That's only 3025 m/s altogether, which simply isn't enough to get orbit-- you want 3400 m/s minimum, and that's assuming an optimal ascent path and no other problems.  If you're fairly new to KSP and still learning the ropes, I'd recommend a few hundred m/s of dV above 3400.

In addition to which, there are some other issues with that rocket:

• Poor streamlining-- the big flat front ends on the top of those boosters is going to kill your aerodynamics, so you'll waste a lot of dV to drag.  Put nosecones on them.
• Your TWR is probably too high.  I'm guessing you haven't used the thrust limiters on those SRBs?  If you haven't, and they're firing at 100% strength... two of those on a small rocket like that is way overkill.  (Try expanding the initial stage in the editor view-- it'll tell you what your launchpad TWR is).  In general you don't want your TWR on the pad to be any higher than 2 at most.  When your TWR goes way higher than 2, you end up going too fast when you're still too low in the atmosphere, and you end up wasting a lot of dV to aerodynamic drag.  (Which is made even worse by the lack of nosecones on your boosters).

As to why your changed design has so much less dV than the original... that comes back to the rocket equation, which I can go into if you like but the short answer is that "it's considerably easier to get to orbit with three stages than two", and also "you want your orbital stage to have a small, lightweight engine on it with high Isp".

[MadMate]

5 hours ago, Snark said:

Right, because you don't have enough dV on that rocket.

Your first stage has 1362 m/s, your second stage has 1663 m/s.  That's only 3025 m/s altogether, which simply isn't enough to get orbit-- you want 3400 m/s minimum, and that's assuming an optimal ascent path and no other problems.  If you're fairly new to KSP and still learning the ropes, I'd recommend a few hundred m/s of dV above 3400.

In addition to which, there are some other issues with that rocket:

• Poor streamlining-- the big flat front ends on the top of those boosters is going to kill your aerodynamics, so you'll waste a lot of dV to drag.  Put nosecones on them.
• Your TWR is probably too high.  I'm guessing you haven't used the thrust limiters on those SRBs?  If you haven't, and they're firing at 100% strength... two of those on a small rocket like that is way overkill.  (Try expanding the initial stage in the editor view-- it'll tell you what your launchpad TWR is).  In general you don't want your TWR on the pad to be any higher than 2 at most.  When your TWR goes way higher than 2, you end up going too fast when you're still too low in the atmosphere, and you end up wasting a lot of dV to aerodynamic drag.  (Which is made even worse by the lack of nosecones on your boosters).

As to why your changed design has so much less dV than the original... that comes back to the rocket equation, which I can go into if you like but the short answer is that "it's considerably easier to get to orbit with three stages than two", and also "you want your orbital stage to have a small, lightweight engine on it with high Isp".

 

Yes I am new, every time I ask simple questions, people answer me with so many new terms that training didn't even tell me about like TWR that dV and such.

 

Thank you for the detailed answer it was very helpful. 

Edited July 30, 2019 by MadMate

[Pecan]

3 hours ago, MadMate said:

 

Yes I am new, every time I ask simple questions, people answer me with so many new terms that training didn't even tell me about like TWR that dV and such.

 

Thank you for the detailed answer it was very helpful. 

Squad was originally quite against having TWR/dV figures in the game because it might make it too much about chasing the numbers instead of experimenting and having fun.  Quite a lot of us had enough failures without hiding the maths, so we used mods like MechJeb to show us the figures we were missing.  Eventually, Squad relented and that's why you have the dV and TWR displays now - if you know what they're for :-)

TWR:  Thrust to Weight Ratio, how much your engines can push compared to how much the whole rocket weighs.  If your launchpad TWR is below 1 the engines don't have enough power to lift the rocket at all and you aren't going to space today.  Bigger, more powerful engines increase your TWR but everything else decreases it by making the rocket heavier.  As others have said, a launch TWR of 2+ will be mostly wasted on Kerbin because you'll get so fast so quickly that your drag in the thick lower atmosphere will be like hitting a brick wall.  A low initial TWR, building as the rocket gets higher and the atmosphere gets thinner works well.  Conveniently, that's what happens as the engines burn fuel and so reduces total mass.  Try launch TWRs in the 1.4 - 1.6 range and, ideally, end TWRs for the first stage of 2 - 2.5.  Note that TWR is only important for launch and landing, orbital adjustments in space don't need much thrust but a TWR below 0.5 can lead to very long burn-times.  There's a lot more to tuning your TWR in each stage but it's not the sort of thing you need to think about at the beginning (or at all unless you want to).

dV: Delta-V (from maths, 'delta'=change) Change of velocity vector, how much you can change your speed and direction (since turning's just acceleration pointing a different way).  May I interest you in Tsiolkovsky's rocket equation?  Perhaps not, unless you like maths.  Anyway, you don't have to work it out, since the figures are already in KSP for you.  What it says, in plain English, is that the amount you can accelerate (change your velocity) is determined by how efficient your engines are and how much fuel they have.  In other words, better engines and more fuel allow you to accelerate more, who would have thought!  Now most spaceflight is about accelerating to adjust your speed to make a certain orbit - just around Kerbin or out to Mun, as examples - so if you know your initial speed and the target speed you know the difference is the amount you have to accelerate (backwards, possibly, if you're reducing your speed).  When launching from Kerbin that's all made a little bit - actually a huge amount - more complicated because the atmosphere wants to trap you in the gravity well and drag keeps slowing you down.  which is why we generally accept a minimum requirement of 3,400m/s but try to build-in more than that.  In space it's all much more predictable and accurate - if you can fly right!  Even more than TWR, dV is the reason to keep the rest of your rocket light.  All mass reduces your dV so even extra engines make the performance worse, as long as they already meet TWR requirements.  More fuel is good but, because it also adds mass, double the fuel doesn't mean double the dV (you might hear this called 'the tyranny of the rocket equation').  Everything else on your rocket is the enemy of dV, so try not to put on anything you don't really need.