Circular orbit at launch

[Termonikov]

Hello dear KSP community,

I have recently started kerbal and made it up to Ike round trip without any casualties and a bunch of minmus, mun missions. But there is one thing that i haven't quite figured out yet; how do i achieve an orbit with a min PE of 50km at launch? I can burn it up to 70 km afterwards, its fine. But most of my missions goes with spending 2 of my 3 stages just for getting into a circular/eliptical orbit around kerbin.

My latest mission was ike landing and returning. But i have done it pretty luckily i suppose, because on my way back, when i manuevered for kerbin and made my PE around 20km, i had only 6 litres of fuel left. Even tho i have used 10000x time acceleration for 1.5 years to have lowest deltaV during kerbin escape(using mechjeb). So i wouldn't call it an efficient run.

My most efficient rocket contains 3 main stages with the following build up;

-Stage 3: 3x LFB KR twin boar.

-Stage 2: 4x LV-45. 720lt tank for middle engine, 3x360lt for symmetry engines with pipes going from side tanks to middle tank.

-Stage 1: Rockomax 720lt tank with terrier engine.

This is what my rocket looks like.

The following things happen according to my launch types,

1. If i tilt my rocket too much to get circular orbit earlier, it mostly ends up not being able to lift the vehicle.

2. If i tilt it medium, i will have an AP of 100km when the 3rd stage runs out of fuel, then i burn around %90 of my second stage tanks to make my orbit circular. Then i will have a little boost with 3 side Lv-45's for my escape, then after dumping side engines, i will have 1 middle Lv-45 with a full tank thanks to fuel pipes.

3. If i dont bother tilting it and let it accelerate, i will have an AP of 140-150km, but will have to spend all my second stage fuel to make it circular.

So option 2 was the best choice for me. But it still doesn't feel so efficient. Because one single Lv-45 burns for atleast 3 minutes for a proper escape. Which is pretty much the capacity of the tank.

I'm sorry if i wrote it complicated. Will make it much more clear when i upload pictures. I would appreciate any help i can get. I don't know how Scott Manley can manage things with such small rockets. Maybe it is a matter of practice. Time will show

Good day.

Edited July 21, 2015 by Termonikov

[sjwt]

Never mind, totally missed parts of your post

Edited July 21, 2015 by sjwt

[mhoram]

Welcome to the forums!

Here are a few things I noticed:

- reduce the thrust of the twin boars so that in your stages 9 and 8 the TWR is around 1.5: This will help you to not exceed terminal velocity and reduce the drag you experience.

- add nosecones on top of the twin boars: For better aerodynamics

- I count in your ship 5 engine stages and not 3 (

1. start 4 twin boars

2. drop 3 twin boars

3. drop 1 twin boar and start 4 LV-T45

4. drop 3 LV-T45

5. drop 1 LV-T45 and start the LV-909

)

- your stages #2 & #3 could be merged into a single one

- your stages #5-#7 could be merged into a single one

- you could try, if a poodle instead of the LV-T45 in the centerstack behaves better.

- for maximal effect of the wings, put them as far down as possible

Regarding your ascent, method 2 is usually the best.

It costs in the neighbourhood of 3200-3500 m/s of DV to reach orbit.

According to the MJ-readout, you shold reach orbit shortly before dumping the three LV-T45 side boosters, which also fits with the description in your second option, so your ascent looks fine.

One thing you could try is:

1. Do your usual launch until your apoapsis is near 75-80km

2. Then stop the engines and coast out of the atmosphere

3. Do a circularization burn at your apoapsis

[Termonikov]

Welcome to the forums!

Here are a few things I noticed:

- reduce the thrust of the twin boars so that in your stages 9 and 8 the TWR is around 1.5: This will help you to not exceed terminal velocity and reduce the drag you experience.

- add nosecones on top of the twin boars: For better aerodynamics

- I count in your ship 5 engine stages and not 3 (

1. start 4 twin boars

2. drop 3 twin boars

3. drop 1 twin boar and start 4 LV-T45

4. drop 3 LV-T45

5. drop 1 LV-T45 and start the LV-909

)

- your stages #2 & #3 could be merged into a single one

- your stages #5-#7 could be merged into a single one

- you could try, if a poodle instead of the LV-T45 in the centerstack behaves better.

- for maximal effect of the wings, put them as far down as possible

Regarding your ascent, method 2 is usually the best.

It costs in the neighbourhood of 3200-3500 m/s of DV to reach orbit.

According to the MJ-readout, you shold reach orbit shortly before dumping the three LV-T45 side boosters, which also fits with the description in your second option, so your ascent looks fine.

One thing you could try is:

1. Do your usual launch until your apoapsis is near 75-80km

2. Then stop the engines and coast out of the atmosphere

3. Do a circularization burn at your apoapsis

Thanks for your effort and answer. I said 3 stages just to simplify it and considered as the rocket has 3 different engine types.

1. Adding nose cones slightly REDUCE the DV. Is it still better using them? I mean IRL it certainly is but in most of the guide videos, people say that more DV is always good.

2. If i stop my engines at 75-80 AP, i won't be over 50km and will still be under the effect of gravitational pull, so the AP drops few kms. Probably lower than 70km band. I tried that and i think due to low strength of my LV-45 engines(related to huge mass), burnout at AP ends up my rocket trying to node when its descending.

3. "you could try, if a poodle instead of the LV-T45 in the centerstack behaves better." other than this, is my build and selection of engines good?

[mhoram]

1. Adding nose cones slightly REDUCE the DV. Is it still better using them? I mean IRL it certainly is but in most of the guide videos, people say that more DV is always good.

When you watch videos, make sure to know which KSP Version they rely on. In pre v1.0 versions it was better to not use nose cones. The V1.0 update greatly changed the aerodynamics so that bosters now perform better with nosecones (in most cases).

2. If i stop my engines at 75-80 AP, i won't be over 50km and will still be under the effect of gravitational pull, so the AP drops few kms. Probably lower than 70km band. I tried that and i think due to low strength of my LV-45 engines(related to huge mass), burnout at AP ends up my rocket trying to node when its descending.

Gravitational pull is the reason why your orbit is an ellipse around the planet - without any outer influences, you stay on that orbit. Drag is the reason why your apoapsis gets lower. You would have to test which altitude suits you best.

3. "you could try, if a poodle instead of the LV-T45 in the centerstack behaves better." other than this, is my build and selection of engines good?

You went to Ike and back ... can't be too bad ;-)

I have the impression that the twin boars are too overpowered for the launch: a TWR > 2 is more than needed.

Also have a look at the LV-N for the upper stages. It has the best vacuum fuel efficiency (but low thrust and high heat generation).

For making statements about the engine selection, I highly recommend to have a look at the Optimal Engine Charts thread.

[Termonikov]

Thanks alot my friend

Edited July 22, 2015 by Termonikov