Hitting early career mode contract targets.

[qoonpooka]

So I've got an example contract, test the -45 liquid engine between 7km and 11km altitude, activating it through staging while at a speed between 300 and 400m/sec. I've built an orbiter that'll complete another contract (get into orbit) and figured I could mod that to also do this engine test since the -45 is perfectly fine for final lift into orbit. I've got 4,700m/sec of Delta-v which is enough for a basic orbit and then some...

For the life of me, I cannot get a combination of engines that will get me that altitude and speed combination. The closest I've come is three RT-10s, which get me almost there, but the speed and altitude is wrong and popping those things off under burn is bad for mission health, so throttling them down is no good.

Are there tools out there for helping someone figure out delta-v requirements to put a rocket into the conditions required to do these early in-atmo contracts or are they just a waste of resources?

[capi3101]

For future reference, this is the subforum for tutorials (i.e. if you're trying to help out other folks). General questions like these should go in the parent "Gameplay Questions and Tutorials" section.

Now, that said, since you've got a rocket that will make orbit, you've got a couple of options here.

1. Launch your orbital rocket. When it reaches 7k ASL, fly it along the horizon - you're not trying to make space, you're trying to build up the speed you need. Hit the staging controls to activate the T45 when they all light up (note that you don't actually have to fly with the engine - you just have to activate it via staging controls, so if need be you can simply add one to your stack somewhere and turn its thrust limiter down to zero.

2. If the problem is getting too much speed before you reach 7k, lower the throttle settings and don't let them get too high. You should still have sufficient TWR to continue climbing with less than full thrust.

3. If you really can't get going fast enough on the trip up, try testing the engine on the way back down. You might still miss the target altitude/speed range, but it may be worth a go. Maybe try a combination chute/braking engine.

4. Mount the part to be tested on an airplane, if you've got all the tech required. Even a Basic Jet powered aircraft would be capable of hitting the target altitude and speed easily enough.

[qoonpooka]

Bah. Thanks for the mis-filing tip. I think I got lost in my searching to see if my question had come up before and didn't remember where I was.

My problem, ironically, isn't that the rocket can't make speed. It's actually making speed round 5-6km, and then going too fast through the entire bracket. I might not have described this correctly before, but essentially I hit the speed green-check and then the altitude green-check flicks on just as the speed one flicks off. Normally I'd tweak down the boosters, but kicking out solid boosters while they're under burn destroys everything but the command module in the best of times. I've tried a number of ways to keep the solids away from the main body and coasting to the target (collision/explosion), as well as reducing the solid stage and going with a lower-powered liquid stage (not enough power) to get there.

The aircraft suggestion is probably the way I'll have to go. I've never done aircraft design, but then I guess I can grab those visual survey contracts too.

[Northstar1989]

You problem boils down to this- you TWR is too high. That's why you're having problems with making speed too early.

Simply pile a few more fuel tanks on the rocket. You'll increase your Delta-V budget AND reduce your TWR. Or, just use less powerful engines- but that's the less Kerbal solution.

The cheapest way to complete this contract and still make orbit would be to just use the T-45 as the launch engine (activate and deactivate it with Action Groups so you can still activate it via staging), and add or subtract fuel tanks until you hit the correct TWR to hit speed *just* before you leave the altitude bracket. If you haven't unlocked action groups yet, then radial engines and/or a single Rt-10 SRB with an appropriate-sized (read: comparatively LARGE to the SRB) rocket placed on top of it will work... You will have to appropriately (read VERY small/light) size your payload to make orbit with nothing but a single RT-10 as your launch stage though (with a T-45 kicking in as a sustainer in the contract window).

Regards,

Northstar

[qoonpooka]

Awesome, thanks for the tip. The remaining part of my question, then, is if there are tools for, or a tutorial for the maths involved in, predicting a rocket's speed and altitude at any given point during an atmospheric ascent so that I'd know where/how to tweak the thrust before I launch the thing.

[Northstar1989]

Awesome, thanks for the tip. The remaining part of my question, then, is if there are tools for, or a tutorial for the maths involved in, predicting a rocket's speed and altitude at any given point during an atmospheric ascent so that I'd know where/how to tweak the thrust before I launch the thing.

Unfortunately, not really. Your speed at a given altitude varies, among other things, based on your ascent profile (i.e. how early and sharply do you start pitching over; when do you stage, etc.) You're best off trying to fulfill as many contracts as possible with planes since it's easier to predict speed at a given altitude with a plane once you become sufficiently experienced with them, and very easy to throttle down or go into a dive to increase/decrease speed at a given altitude.

Regards,

Northstar

[qoonpooka]

Ah well. Thanks for the tips, guys. Super helpful.

I've got a plane in the air as an engine test bed now, got these contracts done, and I'm being pickier about how I choose them, now.