Questions for the FAR pros.

[ATSinged]

Not your normal FAR post really, because I can get payloads to space consistently without a lot of problems, but it could be much better I'm sure.

My first week with FAR and I'm thrilled with it. I'd already been moving towards simple designs and away from asparagus staging, it's efficient but unrealistic I guess, I never cared for it. My current booster family worked OK for the most part with relatively minor tweaking to things like TRW, adding fins or nose cones and the odd mid stage set of reaction wheels. There were a few spontaneous unplanned disassembles and the odd case of lawn darting but I'd say it went well. I do have some questions for the FAR pros though.

Questions:

I can launch all of my designs, kick over 5-10 degrees at 65-75 m/s and they will pretty much follow the prograde, I can turn SAS off after the initial kick over and they still fly true, needing only an occasional tap on the D key in some cases.

My heavier boosters all seem to become bottom heavy and want to nose up later in the ascent (say 35K - 55K) as the upper tanks drain, I've taken to turning off the top tank, perhaps the top 2 for most of the launch to get around this, which works like a charm (I don't have orange tanks / mainsails in this career yet). Is this common? Any suggestions for avoiding having to do this?

How do you guys get those perfect ascent profiles and not fall so far behind apoapsis? On my best launches I usually wind up 5-7 minutes or more behind it and the problem seems to be in the upper part of my profile. It seems most of my launches would naturally circularize at around 60-65K, which is obviously a bit low, this is true for both my light designs and heavier ones.

Moar boosters is obviously not the solution here

Moar skill and better design likely is

The needed tweaks are likely very minor, but I don't see them. A bit more thrust in the later phases? TRW at launch is usually about 1.35 or so, main stack engines are tweaked so max throttle gives me about 1.5 when I decouple the SRBs, maybe 7.5K meters, 40 degrees from vertical, obviously this goes up as fuel drains, what is a good TRW at say 65K, maybe that would help me set the throttle for a better late profile.

Finally, maybe a mod question: Telemetry, I'd like to be able to record a few launch profiles, just the simplest data, time, distance downrange, altitude, angle, speed in an effort to improve my consistency and design, but all I can find are some highly complex, mission control type mods, nothing simple and easy. Any suggestions?

Edited March 6, 2015 by ATSinged
Got some good advice!

[ratchet freak]

moar stages!!

then decrease thrust in the later part of the launch so the apo stay to within a minute

[capi3101]

Been learning FAR myself; I had no trouble making the switch as far as rockets were concerned. Planes - there's another matter.

Most of the same tricks for rockets still work in FAR - the key things are that you need less delta-V to make orbit, in general less thrust, a gentler turn and aerodynamic bits like nosecones. A 1.25 TWR on the pad will get you to orbit just fine if you've got the delta-V you need. Most of the ascent profile I used to use in stock still applied once I'd finished the turn to 45 degrees - just stay there until you're 35 seconds to Ap, then tilt down gradually to 20 degrees and hold that until you're 45 seconds to Ap, then 10 degrees until you're 55 seconds to Ap. After that you can go to 5 degrees or lower and just hold that until your Ap is where you want it for orbit.

How fast are you going when your heavy boosters start to nose up?

Incidentally, I've discovered that you don't have to abandon asparagus - but rockets that are longer rather than wider do fare better in FAR as a rule.

[ATSinged]

Moar stages? I've been in a minimalistic phase lately, SRBs around a central stack of fuel tanks with enough dv to get the payload in to orbit, shooting for around 3800dv with FAR. The only staging has been ditching the SRBs, then ditching the main stack just barely suborbital (I don't like space debris). Dropping some weight from the bottom of the stack that is getting bottom heavy does make a lot of sense, so I'll play with that.

This is career with FAR, Procedural Fairings, Karbonite and Stage Recovery BTW.

I'm not sure what my speed is when they go bottom heavy, above mach 2, maybe mach 2.5ish, but I'll pay attention to it tonight and update the thread.

I had pretty much already abandoned asparagus when I installed FAR, asparagus is just unbeatable for getting stuff to orbit efficiently, I've use it a lot, but I didn't like doing it for a pretty silly reason which basically goes "it doesn't look like a rocket to me". I was also working to reduce cost to orbit, part count and complexity, so it all kind of fell together in to working on more conventional (NASA like) boosters.

[Streetwind]

If you want your rocket to tilt over more, go slower. It helps both in the sense that you're taking longer to exit the atmosphere, allowing more time for the gravity turn; and that there will be less airflow that will try to keep the orientation fixed forward.

In other words, LESS BOOSTERS!

[ATSinged]

Are you allowed to say "LESS BOOSTERS" on this forum? I find the idea to be nearly sacrilegious.

Advice noted and appreciated however!

[Van Disaster]

If you keep falling short, kick over slightly later/faster, you'll fly a slightly steeper ascent then. You can shape the profile by throttling up & down a little, but if you're going too flat and you're at full throttle already there's not much you can do other than pull the nose up yourself. Rocket engines do gimbal - mostly quite a lot more than ours do - so it's not like you can't steer most real rockets ( Vega excepted, I think... that's pretty much all SRB ).

I'd recommend Telemachus for telemetry, except I'm not sure it works for 0.90.

[capi3101]

Here's a question - what kinds of payloads are you putting up (what kind of fairings are you using, what's the rough payload mass you're shooting for, etc.)? Could you show us a screenshot of one of your rockets?

[ATSinged]

I'll see if I can get a couple of screenshots posted tonight. Promise not to laugh, I read forums but I play in a little bit of a vacuum as well.

It is early career and I've only got 2 boosters I use at this point. I just monkey with the fuel load to get about the right delta v for the cargo. I'm mostly satellite launch contracts and scan-sat launches which are coming in around 1500-2500kg depending on what has to go up and where I need to send it. Using procedural fairings and I'm careful to allow sufficient space inside the fairing, nothing clips , usually the conic fairing, but I don't think conic vs egg shaped matters?

I've got a 3 man capsule rig up that lands on Minimus, much heavier (25t?) which is 3 cans riding a skipper with a 6 dialed back SRBs giving it an early boost. No fairings at all, but I guess it's more aerodynamic to begin with, oddly it flies almost exactly the same, same flight path, same questions, maybe a few more presses on the A and D keys but it basically goes like the lighter one.

Absolute truth is, I'm finding it a lot easier to get to orbit with FAR for more reasons than just the reduced delta v needed. If something is set up decently, it flies better than stock IMO. It's just harder for me to get to orbit efficiently, without a long coast period or having to nose up a lot at the end of the trajectory and I'm a bit of a perfectionist. Ideally, I'd love to click launch, tip a little, stage once and see 80x80 but I know I'll never get one set up quite THAT good, besides some taps on the A and D keys make me feel useful

[Van Disaster]

You won't get that in a real rocket either, it's not like their payload usually ends up in circular orbits unassisted

[NathanKell]

That's magnified in KSP. It's nearly impossible (though not 100% impossible, of course!) to get an efficient single-burn-to-orbit in KSP because the ascent is so short comparatively. Much easier on realer scales. You might consider trying 64K for example.

For normal sizes, your best bet is an efficient turn that ends up at, like, 75km x 20km. That should lead to anywhere between 20 (if you nail it) and 200m/s (if it's more like 75 x -20) to circularize at apoapsis, which is fine.

[ATSinged]

Thanks folks, I think I've got things sorted out well enough, FAR is a different animal and I really like it. Cussed at it a few times when something got ripped off the side of my rocket on reentry, but still glad I installed it.

Basically, I wound up with sort of a mishmash of the advice in this thread, adding a lower stage, more aggressive TRW in the second stage for a bit higher apoapsis, some minor redesign and deciding a couple things just wouldn't make it to orbit with the engines I had available at that tech level etc. Pretty much, within aerodynamic reason, if I want it in orbit, I'll get it to orbit at this point. I'm generally hitting 80ish x20ish pretty consistently and just doing a minor circularization burn.

[eddiew]

If things being ripped off annoys you, remember that you can turn off structural failures in the FAR options (button on the KSC screen)

Personally I tend to build my rockets on an incline (with launch clamps holding them in place), go up 30km with SAS on and set to prograde, then manually control the nose from there. Particularly over 50km there's very little drag from the air and you can start flipping the rocket as if you were in vacuum without risk of URD.

That said, if you like an ultra-flat ascent profile - spaceplanes may be your thing! It takes a while to get the knack, but I have a few that will have a 30km PE by the time they have a 100km AP, with the final orbital burn being about 50m/s. Very satisfying when they work smoothly

[ATSinged]

I'll probably have a go at building a space plane in the future, that is something I never tried in last go around with KSP (long time ago).

[eddiew]

FAR is pretty much designed for spaceplane fans - rockets do change behaviour, but they spend much less time in atmosphere and on the whole it's much easier to make a FAR stable rocket.

The time required in the SPH to get your first bird flying can seem intimidating, but it's ever so satisfying when you do

[Van Disaster]

You can put pretty large wings on your rockets, even - https://imgur.com/a/ussfe - just on that thing which would be pretty slick as a standard sort of rocket, it saved ~300dV to orbit, and that was 0.25 FAR which had no skin drag.