Efficient into Kerbin Orbit

[amoksepp]

Hi folks,

at first i have to say english isnt my native language, so if anything isnt clear, just ask me and i will try to write it with other (maybe correct^^) words.

Before some days i decided to start a new game in KSP after a longer break and tried to optimize some of the basics.

I found a image: 
and asked myself how much will i need and how much i can get better with it.

My testings are highly orientated at this thread:

Every test had the follow rules: 100 km AP/PE Orbit / Turn Start 0.5 km / Turn start velocity 20 m/s / 65 % Turn Shape / No manual control, only MJ2. And all  Delta V datas base on the vacuum (the data you will see when you are in the VAB or in Orbit, not on the launching pad)

 

Test 1 "acceleration" (End turn altitude = 70 km)

acceleration max = 17 m/s    -> didnt got into orbit (146 m/s missing)

acceleration max = 25 m/s    -> didnt got into orbit (146 m/s missing)

acceleration max = no max    -> didnt got into orbit (160 m/s missing)

The acceleration has only a little impact on the delta V

 

 

Test 2 "Turn End Altitude": (acceleration max = 25 m/s)

End turn altitude 70 km -> didnt got into orbit (146 m/s missing)

End turn altitude 35 km -> Orbit with 35 m/s left

End turn altitude 20 km -> didnt got into orbit (ship exploded because air resistance)

A good turn altitude (35km) saved 181 m/s Delta V

 

 

Test 3 "TWR"  (acceleration max = 25 m/s and End turn altitude 35 km)

I build a new rocket for this test (picture 1-4) and reduce the max throttle in the first try to 50% (1,6 TWR at the launching pad)  and in the second i didnt reduced the throttle. (3,2 TWR).The rocket had 4462 m/s Delta V

Try 1 50 % = 934 m/s left = 3582

Try 2 100 % = 1006 m/s left  = 3456

 

https://picload.org/image/rogwdwwg/test3try1vab.jpg

https://picload.org/image/rogwdwwd/test3try1start.jpg

https://picload.org/image/rogwdwwo/test3try2vab.jpg

https://picload.org/image/rogwdwwc/test3try2start.jpg

(couldnt post the picture into the thread, i used the "insert into post" button, but nothing happens.

I tried it with 4. completly different rockets (one with 3 stages and booster, one with only 1 stage, one with a single rocket and 2 stage, one with 3 rockets and 2 stages). I needed everytime about ~3450. 

I got a better result with the S3 KS-25x4 "Mammoth" Liquid Fuel Engine. But the reason for this result is the follow:  this engine has the smallest cap between "Engine lsp: 295(ASL) - 315 (VAC)" So it wasnt really better, our infos from the delta V in the VAB arent 100 % correct if we compare two different engines without depending it on the engine lsp. i could to the math for this but i'm to lazy : ).

 

 

First Result:

The amount of needed Delta V depends highly on the "Turn altitude end" and just a little bit on the "Acceleration". The TWR has also a big role, if you have far to less your rocket wouldnt start and a higher TWR (3,2) is still better than a lower (1,6)

Like i already said, if i get some suggestions from other user and other results i will do more tests with a better documentation.

 

Greetings from a germany hobby space engineer ^^

 

Edited January 13, 2017 by amoksepp

[Mikki]

Hallo da, sorry i`m in a hurry but i just have seen your dV map is slightly outdated, Duna for example is actually 1200 dV finally....
welcome to the forums!

[amoksepp]

The map depends on the version 1.2.1 it should be the only up to date information ^^

 

Where did you got this info?

 

And thx  : )

Edited January 13, 2017 by amoksepp

[diomedea]

@amoksepp: that thread you are using as a reference is outdated, tests were done with KSP 1.0 and lots of changes have been made to the game since then. In particular drag calculations.

The value reported in that map for getting in a 80 km circular orbit from Kerbin (3400 m/s) is a good average of what required with KSP 1.2.x, as such a good indication for planning space missions. I'd say your tests actually confirm what that map shows.

Still, actual DV required to get to orbit depends a lot from TWR and drag of the vessel used. If no drag existed (no atmosphere on Kerbin), getting to a 80 Km circular orbit would take ~ 2559 m/s DV (this value comes from comparing the total energy of a spacecraft while in orbit against its total energy while landed at sea level). Clearly, if we could build rockets so slim to present a minimal drag during the whole ascent, the total DV expenditure could approach that limit. You've also found the "turn altitude end" being a crucial factor to a lower DV expenditure, that confirms a pure gravity turn to be the best possible ascent profile (all thrust always goes to accelerate the vessel, instead of being spent to change its direction of travel).

[Ruedii]

I find that starting at a 5-15 degree angle all the way back at the base helps a lot on reducing delta-v consumption.  I can usually get up to 72-80km with between 2800 and 3000 DeltaV

(As a note, I use a pure gravity turn and an angled launch with this method.  I only accelerate to between 40-100m/s while maintaining angle.  This creates 2-10 delta-v of losses.)

Edited January 13, 2017 by Ruedii
(Moar info)

[amoksepp]

Thx for your informations.

I m aware that the thread i used as reference is outdated, but the ideas how to do the tests will remain everytime the same : )

I did about 30 starts with different rockets and only the rockets with a better lsp (or better said a smaller gap between ASL VAC)  got a lower delta V usage into orbit... so i would say my actual results arent perfect, but still good.

[septemberWaves]

One of the best tricks for lowering delta-v to orbit is to angle the entire rocket towards prograde at launch using the launch clamps to stabilize it. You need a high-thrust first stage to pull this off, but it starts you off mid-way through your gravity turn and so reduces gravity losses.

Another thing that I've found reduces delta-v somewhat is to have a booster configuration like the single-booster Atlas V rocket*. The asymmetrical design will end up with an angled thrust vector even when your rocket is pointing directly up, and so until the booster is jettisoned the rocket behaves as though it's further angled on its gravity turn than it actually is. These sort of things are a pain to fly though.

*This is also how my space shuttles tend to fly, and it usually works quite well for them.

Edited January 13, 2017 by eloquentJane