Other people's ships?

[Imaginer1]

I'm getting really, really upset because whenever I download ships made by other people they don't work. They just completely run out of fuel on stages they're not supposed to, such as Munbug, which I can't get into a stable Kerbin orbit without using the translunar injection stage, and more. I'm just in disbelief because it always happens and it is making me feel like I'm doing something desperately wrong and I don't know what or why.

[UmbralRaptor]

Well, how do you normally fly various rockets? Describe your typical approach to orbiting, using pictures and/or video if necessary.

[Imaginer1]

Typical approach to orbiting:

1) During initial ascent, avoid the speed of sound (Actually, limit yourself to about 200m/s.)

2) Rise up to about 10km before turning to a 45º angle of thrust. At this point, don't worry about speed of sound or 200m/s and open up.

3) Once you reach about 30km fire horizontally until your apoapse is at the desired point (I usually have orbits at 100km)

4) Once near or at apoapse, fire prograde or use a navigation node.

Is there something I could be doing differently?

[UmbralRaptor]

1) The ideal speed varies quite a bit with altitude. My rule of thumb is 100 m/s at sea level, doubling every 7 km (eg: 200 m/s at 7 km, 400 m/s at 14 km, 800 m/s at 21 km). Are there any areas where you go well above/below this?

2) Do a smoother turn -- start with ~80°, and lead or chase the prograde marker down to the horizon.

3) Go for a 70-80 km orbit (it doesn't save *much*, but it's something)

[Imaginer1]

Thanks, I'll try that real fast and get you my results.

[UmbralRaptor]

Oh, something I forgot -- you can use MJ2's ÃŽâ€V recorder to see how much you spend on ascents, and if you need to refine your flying.

[Imaginer1]

I just don't understand. All of a sudden I can't orbit anything and it's annoying me.

[lobsterbark]

It should only take about 4000 delta-v to get into orbit. Unless your flying them wrong.

[UmbralRaptor]

Well, 4 km/s (or less) with FAR. Stock, you're looking at ~4.3-4.7 km/s. I aim for 4.5 km/s in typical designs.

[Imaginer1]

*Shakes head*

I don't understand why it isn't working, then... Blarg.

[Vanamonde]

If I may self-promote a bit, I've made walkthrough instructions that come with a ship, so the instructions apply specifically to that ship. It's here: http://forum.kerbalspaceprogram.com/showthread.php/25008-How-to-reach-orbit-and-a-rocket-that-can-do-it-a-walkthrough-for-newbies

[AlexanderB]

70 instead of 100 saves a load of fuel..

[Colonel_Panic]

Keep in mind that a lot of people's ships are purpose built for a mission, and contain no more fuel than is necessary, to save on mass and parts. It may have taken them some tweaking to get it right, and in those cases you can't just expect to put it in orbit on the first try.

Here's a few things I would do differently to save more fuel:

start your gravity turn earlier, as low as 5km, and follow through with it gently until around 45-50km. If your nose is pointing far above/below the prograde indicator on your navball at any time, you're wasting fuel, so try and keep the turn smooth.

Most rockets should be designed to run at full throttle and have the correct acceleration curve to minimize drag loss. If this isn't the case, it may be necessary to ease off the throttle a bit at low altitude to keep your speed down, but keep in mind that you lose efficiency whenever your engine is throttled down, too. It can sometimes be bettwe to just power through it and go a little too fast, than to fuss with the throttle and wind up losing speed after staging.

If you notice your speed is low at the end of your gravity turn (a periapsis of -200km or lower, to where it takes more than a couple seconds of burn to circularize) you started your gravity turn too late, or not shallow enough. Work on getting up your orbital velocity more before pushing your apoapsis up, by leading your prograde indicator, or starting your turn earlier.

finally you can use mechjeb to plan and analyze your ascent for you, if you're so inclined.

[Haemogoblin]

You're not alone, I've tried a bunch of my old designs and had zero success since the latest update. Planes are no exception either, from ssto no ssno.

[ZedNova]

I just floor it till 10Km and make my gravity turn.

[Colonel_Panic]

You're not alone, I've tried a bunch of my old designs and had zero success since the latest update. Planes are no exception either, from ssto no ssno.

aw crap, I really hope my spaceplanes still work... I was in the middle of a multiple-launch mission with those.

[Haemogoblin]

Thought i'd come back after a few more tries, I can almost get my old design plane into orbit again. It's as if the weights have increased, i'm a sliver of fuel away from getting back into an 80km orbit whereas before the patch I could get to 150 every time

[Colonel_Panic]

could also be a change in drag. might want to double-check your intake management.

[Mulbin]

Ahhh.... now this thread explains your problems much better! So with Munbug fuel is running out on second stage before orbit...

Let me run a test of Munbug VI tonight and I'll see if the .20 patch has made it less fuel efficient. Might not be the end of the world though as the real Apollo used the third stage to complete Earth orbit insertion... depends on how much fuel is left for transfer. Still need more info on your Dunebug problems though as I'm not clear on your throttle problem.

Some notes for Munbug...

REmember to hit hotkey "1" twice to disable gimbals before launch (it's in the Munbug main post)

Full throttle all the way up!

Begin gravity turn (tilting towards 90 degrees) at 10,000 Gradualy at first dropping to 45 degrees for second stage and continue to drop nose to horizon, if you need to use third stage tilt the nose back up to compensate for the low power.

Orbit no higher than 72,000

[Mulbin]

OK... just did a flight with Munbug VI and it is short on fuel... runs out just short of completing Munar insertion. worked fine in .20.1 with a little fuel to spare but it seems something may have changed in .20.2 Munbug VI always did need to use 3rd stage to complete orbit (it was Munbug V that had loads of spare DV) but it wasn't this tight before.

In the process of finishing Munbug VII which should have a lot more DV in the third stage so hopefully will be easier to fly.

Edited June 4, 2013 by Mulbin