Orbit for the Un-Orbitable?

[Not Colgate]

I have tried oh so many times to launch into space with the intention of orbit, but have failed horribly. I tried video tutorials, word tutorials, etc. and still no orbit. I seem to be running into the problem that I cannot become totally parallel no matter what I do, I always either keep ascending or descend horribly. Some help would be very appreciated

[rdfox]

Cut off thrust at around 2300 meters/second, then wait until you reach apokee. Pause there, use the KSP Orbital calculator to get the speed for a circular orbit at that altitude, and then unpause and burn again to circularize your orbit. It's almost impossible to inject directly into a stable orbit, much less a circular one.

[Moach]

it really depends highly on your launch vehicle and its ability to 'steer' properly...

with an unstable ride, orbit is very unlikely to be achieved... no matter how well you know what you're doing

use SAS modules - but prefer the kind that holds whatever attitude you have instead of those that keep you pointed to a fixed direction - then add a yawmaster RCS pack... you'll need the extra maneuvering power if you're trying to turn a heavy beast of a stack

if all is built well, it IS possible to launch more or less directly into a circular orbit.... it does take a lot of guesswork and trial-and-error, tho... since the needed instruments for a precision ascent have yet to be programmed into the game :

[DoctorEvo]

Cut off thrust at around 2300 meters/second, then wait until you reach apokee. Pause there, use the KSP Orbital calculator to get the speed for a circular orbit at that altitude, and then unpause and burn again to circularize your orbit.

That works fine if you have the delta-V.

It's almost impossible to inject directly into a stable orbit, much less a circular one.

Well, then I must be a sharper pilot than I thought...

What I did the first few times I achieved orbit in KSP was the usual 'climb straight up to 10 km, then start arcing over' routine, and then once I crossed about 30 km, I just completely leveled my ship off and accelerated horizontally. When my velocity vector (the little yellow dohickey) finally reached zero, I lifted the nose to keep myself from falling down again. Eventually, as I neared orbital speeds, I found that I needed less effort to keep my velocity from dropping downwards again, so I gradually reduced attitude to maintain a level flight direction. When my attitude hit zero (signifying I didn't need to 'hold' myself up anymore), I throttled back and coasted through a full (elliptical) orbit.

Then I went and looked up actual orbital speeds for Kearth, and now my orbits are much rounder. My present casual technique for achieving low orbits is largely the same, but now I have a target speed that I shoot for during the final phase (generally 2350something). But I never stop steering the ship to where I want it (i.e. flying level, at target-speed).

Also, it makes it easier if you know how to handle a ship in a vacuum (i.e. start AND stop a rotation), and also the CommandPod's SAS (damping-only) is useful for learning this precision-steering. I actually DO NOT recommend putting SAS modules anywhere but in your first stage, as they tend to lock your heading in and you have to continuously toggle them on and off to turn (thus losing their damping effect). And lastly (and importantly), try not to overcontrol. Slooooow corrections is all you should need.

[rdfox]

Yeah, I'm pretty sure you're a better pilot than I am. I have problems with overcontrol, invariably when I'm trying to damp out that last little bit of rotation. (In my defense, my keyboard's old and some of the switches don't work quite right any more, so sometimes, a key doesn't work when I want it to, or it sticks when I don't want it to...)

Still, if direct insertion into a circular orbit were easy, I'd expect NASA to use it more instead of using a circularization burn at apogee... though that may be more an efficiency thing, I'm not sure.

[DoctorEvo]

Yeah, I'm pretty sure you're a better pilot than I am. I have problems with overcontrol, invariably when I'm trying to damp out that last little bit of rotation. (In my defense, my keyboard's old and some of the switches don't work quite right any more, so sometimes, a key doesn't work when I want it to, or it sticks when I don't want it to...)

Ah.

Do you use the caps lock key? I try to turn it on as soon as I perform my final staging (and sometimes before). It's really helpful for when you're a bit heavy-handed.

Still, if direct insertion into a circular orbit were easy, I'd expect NASA to use it more instead of using a circularization burn at apogee... though that may be more an efficiency thing, I'm not sure.

The shuttle used it... In fact, NASA uses it a lot for LEO. The only launches I've observed that DIDN'T use it were Orbital Sciences Minotaur launches (and Pegasus and Taurus use similar profiles). Did the Saturn rockets hold off on S-IVB ignition? None of the launch footage ever shows past S-II separation.

And yes, it's partially an efficiency thing. My technique obviously diverges from the ideal gravity turn trajectory, and thus wastes a bit of propellant in steering the ship. Thus I've developed techniques to make a simple gravity turn work instead, but these are more difficult and require a lot of finesse on the throttle. The Space Shuttle, with it's low-thrust OMS providing the final orbit insertion, is well-suited for direct insertion into LEO, as the lower acceleration and throttleable thrust allow you to fine-tune the altitude and speed you will come out of the gravity turn at. I've found that for larger, harder-to-handle rockets, this gravity-turn/throttle manipulation is often an easier way to reach orbit than manually steering; if I find myself higher than my desired trajectory, I throttle back and allow gravity to pull the nose down; if I'm low, I throttle up and try to push higher before the nose drops. To do this, you need a stable rocket, and a good idea of what you want your ascent to look like, though.

Higher orbits tend to require a two-burn ascent, though, as it's impractical to keep an engine running at such low-thrust levels through such a long ascent.

[rdfox]

Ah.

Do you use the caps lock key? I try to turn it on as soon as I perform my final staging (and sometimes before). It's really helpful for when you're a bit heavy-handed.

Yeah. I just need more practice, and a keyboard that doesn't suck. I actually tend to use 'precise' mode all the way up from the pad--most of my boosters are pretty flexible, so I need to be gentle while trying to guide them with the Yawmaster.

The shuttle used it... In fact, NASA uses it a lot for LEO. The only launches I've observed that DIDN'T use it were Orbital Sciences Minotaur launches (and Pegasus and Taurus use similar profiles). Did the Saturn rockets hold off on S-IVB ignition? None of the launch footage ever shows past S-II separation.

And yes, it's partially an efficiency thing. My technique obviously diverges from the ideal gravity turn trajectory, and thus wastes a bit of propellant in steering the ship. Thus I've developed techniques to make a simple gravity turn work instead, but these are more difficult and require a lot of finesse on the throttle. The Space Shuttle, with it's low-thrust OMS providing the final orbit insertion, is well-suited for direct insertion into LEO, as the lower acceleration and throttleable thrust allow you to fine-tune the altitude and speed you will come out of the gravity turn at. I've found that for larger, harder-to-handle rockets, this gravity-turn/throttle manipulation is often an easier way to reach orbit than manually steering; if I find myself higher than my desired trajectory, I throttle back and allow gravity to pull the nose down; if I'm low, I throttle up and try to push higher before the nose drops. To do this, you need a stable rocket, and a good idea of what you want your ascent to look like, though.

Higher orbits tend to require a two-burn ascent, though, as it's impractical to keep an engine running at such low-thrust levels through such a long ascent.

The shuttle directly inserted into LEO after about 1984 (originally, they would cut off the mains just shy of orbit to make sure the ET would reenter without a retro-rocket, and used an OMS-1 burn about two minutes after MECO to acheive orbit), but an elliptical LEO of about 60x200 miles, typically. (Apogee varied depending on mission profile, but perigee was generally around 60 miles.) The OMS-2 burn at apogee was required to circularize even on the direct-insertion profile. (Interestingly, the OMS engines themselves are *not* throttleable; the only way to control the OMS thrust is deciding whether to make the burn on one engine, or both.)

S-IVB ignition came promptly after S-II staging, about two or three seconds after separation. There's a film from a camera inside the S-II/S-IVB adapter on Apollo 4 or Apollo 6 that shows the two being separated on the S-IVB's ullage motors, then the J-2 firing. While not as famous as the S-I/S-II staging footage, I'm sure it's up on YouTube. Lemme check... hmm. All I found in a cursory search is this footage from a Saturn IB launch, though the staging sequence was identical between the two.

(Whoever put together the footage did a horrible job of editing it, because they play the initial separation at several times normal speed, then the ignition at normal speed, then the rest of the footage at about twice normal speed...)

Ironically, despite not having throttleable engines, the Saturn V *was* programmed for direct injection into a circular orbit, with the initial parking orbit for the lunar missions being a circular 100-mile orbit. (They could stay that low because they were only staying for about four or five orbits, and they DID stay that low because it increased the payload they could carry at TLI.)

Don't most satellites headed into a GTO go into an elliptical Hohmann transfer, then use either a small second upper stage or their RCS to circularize it? After all, once you're in a GTO, the delta-vee to raise perigee is relatively low...

Anyhow, what I meant to say was that it's not that hard to directly insert into an elliptical orbit; it's just getting into a circular orbit without a separate circularization burn that I've always thought was the hard part, particularly with the instrumentation available in KSP.

(Someone once claimed to be able to do a gravity turn all the way from the pad to orbit in KSP... whoever they are, they're a far better man than I, if they can. I have enough trouble doing a gravity turn when I'm outside the atmosphere!)

[DoctorEvo]

Ironically, despite not having throttleable engines, the Saturn V *was* programmed for direct injection into a circular orbit, with the initial parking orbit for the lunar missions being a circular 100-mile orbit. (They could stay that low because they were only staying for about four or five orbits, and they DID stay that low because it increased the payload they could carry at TLI.)

Also, I imagine a fully-fuelled CSM with a mostly-fuelled S-IVB in tow had a pretty high ballistic coefficient. Not having solar panels helps a lot with that sort of thing.

Don't most satellites headed into a GTO go into an elliptical Hohmann transfer, then use either a small second upper stage or their RCS to circularize it? After all, once you're in a GTO, the delta-vee to raise perigee is relatively low...

Yep. The shuttle put quite a few up there using a spin-stabilized Star-48 solid kick motor which fired to place the satellite in GTO, and then an apogee kick motor fixed to the satellite itself performed circularization.

Anyhow, what I meant to say was that it's not that hard to directly insert into an elliptical orbit; it's just getting into a circular orbit without a separate circularization burn that I've always thought was the hard part, particularly with the instrumentation available in KSP.

Yeah... you kinda gotta sneak up on it to get it to be remotely circular. Most of my direct-inserted orbits end up with about three to five km between perikee and apokee.

(Someone once claimed to be able to do a gravity turn all the way from the pad to orbit in KSP... whoever they are, they're a far better man than I, if they can. I have enough trouble doing a gravity turn when I'm outside the atmosphere!)

Heh...

http://kerbalspaceprogram.com/forum/index.php?topic=1695.msg17425#new

8)

[Moach]

don't let anyone tell you different - it IS possible to launch straight into a circular orbit if you can manage to fly steadily through a decent gravity turn...

the general idea is this:

- liftoff -

* launch vertically, keep pointed as straight up as possible

* keep your speed under control - you don't wanna go too fast or drag will waste all your fuel

* watch the ADI (the ball thingy) and keep it under control as well as you possibly can

- roll maneuver -

* if using solid boosters, wait until separation before this, lest things get too unstable

* roll 90 degrees so east is aligned to the 'roof' of your ship (could be the other way, but upside down feelsmore 'professional')

* keep the ship steady and try to reach 10k altitude with around 170~200m/s vertical speed

- pitch over -

* make sure you have stability and able control of the vehicle at this point, if not, eject - for you probably won't make it then...

* try and keep your acceleration (Gs) in the green area, more than that puts a lot of stress on the vehicle and throws you off course

* do NOT turn of SAS - pull the nose 10 degrees or so towards east and hold it a bit

* watch while the yellow mark (your velocity vector) turns towards east - watch your speed

* as soon as you have downrange (lateral) velocity, you'll be doing a 'gravity turn'

- gravity turn followthrough -

* ensure the yellow ball keeps going down towards the horizon - if it doesn't you need a larger pitch-over angle

* if it goes down too fast, you're also in trouble... this is often caused by pitching over too low/slow - eject

* now, the most important part is to keep your nose pointed directly at your velocity vector (yellow ball) through the turn

* this will ensure you're not wasting delta-vee in cancelling momentum you've built - gravity is making your flight path curved, not thrust

* the goal is to reach 45 degrees of pitch at about 25k altitude.... adjust throttle to achieve this, try not to steer too far from the ball as you go along, since that wastes fuel

- second pitch maneuver -

* at 35k altitude there will be no more atmosphere, and you should be getting close to level with the horizon

* use whatever vertical speed you have left to keep you moving upwards up as you accel towards your orbital velocity

* if all was done right, you should be converging around a 45k apokee (don't worry, it's trick to get it right without proper instruments)

* at this time, you can more-or-less figure out a 'probable' apokee... that's your orbit altitude - use one of the calculators to figure out your target speed

* use pitch and throttle to get yourself to reach that velocity just at the same time as your vertical speed hits zero

* the above is almost impossible - so you'll more than likely have to do some burns away or towards the ground to zero out your VS

when you manage to reach the corresponding orbital speed for your altitude and be at zero vertical speed - you're in a circular orbit :cheers:

[DoctorEvo]

* ensure the yellow ball keeps going down towards the horizon - if it doesn't you need a larger pitch-over angle

Careful, now... you can always (well, sometimes) throttle back and let the nose fall if you're too high, but catching up from below is much harder. NOTHING should feel forced.

* now, the most important part is to keep your nose pointed directly at your velocity vector (yellow ball) through the turn

. . .

* the goal is to reach 45 degrees of pitch at about 25k altitude.... adjust throttle to achieve this, try not to steer too far from the ball as you go along, since that wastes fuel

Important steps. IMO, half of your other steps can be pretty much ignored.

* at this time, you can more-or-less figure out a 'probable' apokee... that's your orbit altitude - use one of the calculators to figure out your target speed

Don't be afraid to use pause.

* use pitch and throttle to get yourself to reach that velocity just at the same time as your vertical speed hits zero

You shouldn't need to use pitch (aside from staying inside the ball) as long as your timing and throttle management are reasonable.

[Moach]

yes, well... you get the point - pull your vector out from 'vertical' and let gravity lead you down as you go along....

it's hard to explain in words... pehaps someone could make a video of this :cheers:

[DoctorEvo]

yes, well... you get the point - pull your vector out from 'vertical' and let gravity lead you down as you go along....

it's hard to explain in words... pehaps someone could make a video of this :cheers:

Yeah, a lot of it is by feel, and if you don't have a good picture of what the trajectory will look like, you're going to have trouble finding it.

For instance, your '45 degrees at 25km' rule-of-thumb is nowhere near universal; it will vary from rocket to rocket and from orbit to orbit. Owing (presumably) to its lower vertical speed, my automatic orbiter preferred 45 degrees at about 30 km, and that was for a much LOWER orbit as well.

[Millitron]

I keep reading about the yawmaster, but I never really use it. I find I always lose control whenever I try it. The only times I've ever had any success with it was with exceptionally huge rockets, and even then I made sure to have it jettison along with the giant first stage.

I like to use the normal controls, and then if I think I overcorrected, I try to manually counter the turn. If that isn't enough, I'll activate the SAS until I've almost stopped the bank or roll I had problems with. I then use manual controls to fine tune it and be absolutely sure I'm pointed the right way. After this, it depends on what I'm doing. If I'm in orbital flight, I leave the SAS off, so I can easily continue to fine-tune my trajectory. If I'm still burning a main phase, especially above atmosphere, I'll re-activate the SAS to ensure I maintain my current attitude.

[DoctorEvo]

I keep reading about the yawmaster, but I never really use it. I find I always lose control whenever I try it. The only times I've ever had any success with it was with exceptionally huge rockets, and even then I made sure to have it jettison along with the giant first stage.

I like to use the normal controls, and then if I think I overcorrected, I try to manually counter the turn. If that isn't enough, I'll activate the SAS until I've almost stopped the bank or roll I had problems with. I then use manual controls to fine tune it and be absolutely sure I'm pointed the right way. After this, it depends on what I'm doing. If I'm in orbital flight, I leave the SAS off, so I can easily continue to fine-tune my trajectory. If I'm still burning a main phase, especially above atmosphere, I'll re-activate the SAS to ensure I maintain my current attitude.

What is the yawmaster, anyways?

And what I like to do is use SASs on the lower stages if manual control isn't strong enough to hold a vertical line, and then usually for my top two or three stages I'll use the command pod's RCS alone (and I'll usually hit caps lock on the last stage to make things a little more precise). And I usually won't deactivate the SAS at all, simply because a vertical line is all I need for lower stages and the damping is nice to have for upper stages (though I can fly most of my rockets just fine without it - it just requires a bit more focus).

[foamyesque]

The Yawmaster is a mod part from Sunday Punch. It's basically a turbocharged RCS system and is very, very capable of tearing your rocket apart if applied badly.

Evo: You want a challenge to your flight skills? Try this ship (uses Nova's moon mod). I can't seem to get the orbit turn to work. =(

[rdfox]

The Yawmaster is a mod part from Sunday Punch. It's basically a turbocharged RCS system and is very, very capable of tearing your rocket apart if applied badly.

It's also a visual clone for the Apollo Service Module (to the point where he has approved use of the model and texture with a new .cfg file that converts it into a fuel tank for his SPS-10 engine, making the combination look *just* like an Apollo CSM), and can sometimes be the only way to get a decent pitchover rate on particularly tail-heavy or high-thrust vehicles. (I recently tried my Nova Mark Two that emulates the biggest contemplated Nova configuration of the 60s without it, and with full input immediately after ignition, I didn't reach 45 degrees until about 35,000 meters...)

While it does require care in use (I've gotten *very* good at 'pulsing' my RCS to avoid banana-ing my rockets!), until we get thrust-vectoring, it's crucial to heavy-lifters for control, particularly below 34km.

[DoctorEvo]

It's also a visual clone for the Apollo Service Module (to the point where he has approved use of the model and texture with a new .cfg file that converts it into a fuel tank for his SPS-10 engine, making the combination look *just* like an Apollo CSM), and can sometimes be the only way to get a decent pitchover rate on particularly tail-heavy or high-thrust vehicles. (I recently tried my Nova Mark Two that emulates the biggest contemplated Nova configuration of the 60s without it, and with full input immediately after ignition, I didn't reach 45 degrees until about 35,000 meters...)

Wait, so does it use the CommandPod module?

[rdfox]

You strap the Yawmaster onto the rear of the CommandPod, like the Apollo SM was. I usually put Moach's heatshield and a micro-decoupler between the two, so that I can jettison it for re-entry and landing, but that's not required (it has insane crash tolerance because it's modeled as a crew module, so it can have an RCS, and with realistic crash tolerance, jettisoning it meant it would kill the crew on impact no matter what), and on one-way missions, it'd be a waste of upmass to include them.

So it doesn't replace the existing command pod, it's a separate module you attach to it.

[DoctorEvo]

You strap the Yawmaster onto the rear of the CommandPod, like the Apollo SM was. I usually put Moach's heatshield and a micro-decoupler between the two, so that I can jettison it for re-entry and landing, but that's not required (it has insane crash tolerance because it's modeled as a crew module, so it can have an RCS, and with realistic crash tolerance, jettisoning it meant it would kill the crew on impact no matter what), and on one-way missions, it'd be a waste of upmass to include them.

So it doesn't replace the existing command pod, it's a separate module you attach to it.

But what I mean is, in the .cfg, does it use the CommandPod module? Something like this at the top?

// --- general parameters ---
name = Yawmaster
module = CommandPod

There's only a select few modules to choose from (CommandPod being the only one I know of that has any sort of manual RCS), and if there's a way to make other parts (i.e. fuel tanks or winglets) have manual control inputs, I wanna know.

[foamyesque]

It does, but you can't mix subtypes; the part becomes unplaceable. At least, as of .8.5. I had the same idea.