Do I have enough delta-v for a 75km orbit?

[CitricThunder]

I've been messing around with delta-v and such, and started using this calculator. I calculated my delta-v of my small aircraft to be around 8688.54 m/s (which is probably wrong). My ship has 4 5 LV-T30 engines, 10 FL-T400 fuel tanks, small parachute, MK1 Command pod, 1 stack decoupler and 4 aerodynamic nose cones. As seen here. I can only manage to get a 75km apoapsis and once I start to form my periapsis, i run out of fuel before I can even get my orbit halfway around Kerbin. Am I doing something wrong? Btw I saw people could form an orbit with only 4.5 km/s of delta-v, so I figured i'd up that it and try it out.

EDIT-I launch straight up to ~10km and turn to 45 east until my apoapsis is around 75km, and turn horizontal to even out my orbit.

Edited February 14, 2014 by CitricThunder

[CaptainKipard]

8688.54 m/s is almost twice the amount you need for Low Kerbin Orbit. There could be any number of reasons you're not getting up there:

1. Bad/No staging. The ship in the pic has no radial decouplers at all. You need to drop empty tanks.

2. Bad launch profile. instead of going straight up, and then straight at 45 degrees, try to slowly turn so that you're at 90 degrees by the time your ApA is 75km.

3. Too much power. If you're launching at full throttle with 5 engines, then you're just wasting fuel by trying to fight atmospheric drag. Keep your thrust-to-weight ratio at about 2 in lower atmosphere.

You should grab Kerbal Engineer and design your rockets more intelligently with it.

Also nose cones don't do anything unless you have Ferram Aerospace Research installed. In fact they just add dead weight.

Edited February 13, 2014 by Cpt. Kipard

[CitricThunder]

The main reason there's no radial decouplers is because I have yet to unlock them in R&D because I don't really care as much as I should about it. As for the power, after launching i'll put my engines at around 30-40% and once my apoapsis is where I want it, i'll set it to full throttle. I'll try to slowly turn into 90 degrees.

And I actually forgot that I already had Engineer Redux installed, but I don't have the part yet. I'm going to give myself some research points and unlock the part

EDIT-I lied about the radial decouplers, looked right past them *facepalm*

[CitricThunder]

I'll remove the nose cones aswell

[Taki117]

The main reason there's no radial decouplers is because I have yet to unlock them in R&D because I don't really care as much as I should about it. As for the power, after launching i'll put my engines at around 30-40% and once my apoapsis is where I want it, i'll set it to full throttle. I'll try to slowly turn into 90 degrees.

And I actually forgot that I already had Engineer Redux installed, but I don't have the part yet. I'm going to give myself some research points and unlock the part

EDIT-I lied about the radial decouplers, looked right past them *facepalm*

You should have the part, It's available from the start but if you do have the 8688ish m/s that you claim that little ship can land on the Mun and return, with 1548m/s to spare!.

[Dave Kerbin]

I can't see them in the screenshot, do you have fuel lines installed to feed fuel from the center to the 4 outer tanks (you said you have 4 engines and it doesn't look there is a 5th engine in the center to use that fuel)?

[CitricThunder]

So, after easing in to the 90 degrees and adding some radial decouplers, I was able to form a perfect 77k orbit with about 2 km/s delta-v left

[CitricThunder]

No fuel lines, but there is a 5th engine in the middle

[Dave Kerbin]

I've taken a look at that online calculator, and it might just be my browser (Firefox) but it doesn't seem to be giving the right numbers at all. It's really obvious if you just change the ISP and ask it to solve the equation again - you get the same delta-v even though the ISP has changed.

Doing it manually by looking at your screenshot and reading your description you have an absolute maximum of 4150 m/s of delta-v. That's excluding the mass of the decoupler and nose cones and assuming a vacuum for maximum ISP. It also assumes the center tank is being used.

When I include all the parts, assume there are no fuel lines and use a more realistic average ISP for atmosphere I get 2600 m/s.

Edit: Ok, you say there is a 5th engine in there. Using a good estimate of the average atmospheric ISP you have 3450 m/s. In a vacuum (best case) you have 3760 m/s.

Edit2: Sorry, I forgot the chute. It eats up about 10-20 m/s of delta-v depending on which case.

Edited February 14, 2014 by Dave Kerbin

[ShadowDragon8685]

My advice is to use MechJeb to ride your gravity turn, and because of the very, very useful "Limit throttle to terminal velocity" setting that automatically throttles you down so you're riding the edge of terminal velocity, which is the most optimal speed. When you're riding the edge of terminal velocity, you're using as much of your thrust to get away from gravity as you can, without wasting any fighting against air pressure. You do not need to hit mach 8 to break orbit. It's flashy and showy, so you can if you want to, but you do not need to.

Even if you refuse to do that, though, at least use Kerbal Engineer Redux to calculate your dV and such in-game. (MechJeb gives you your dV readouts too.)

Anyway, 4,500 dV, puts you into basically any Kerbin orbit, high or low, if you do the gravity turn right. It does this whether you're launching a tiny ion probe of a gigantic space station.

[CaptainKipard]

So, after easing in to the 90 degrees and adding some radial decouplers, I was able to form a perfect 77k orbit with about 2 km/s delta-v left

Congrats. With practice and better ship design you'll be able to shave even more off of your dv expenditure. Google asparagus staging, and check out Scott Manley on Youtube. He's got a few KSP tutorials for beginners.

My advice is to use MechJeb to ride your gravity turn, and because of the very, very useful "Limit throttle to terminal velocity" setting that automatically throttles you down so you're riding the edge of terminal velocity, which is the most optimal speed (...)

Alternatively use Kerbal Engineer and manually keep your Atmospheric Efficiency at 100% at most.