Ascent questions

[Renaissance0321]

1. What is terminal velocity as applied to ascending in a rocket and what do I do with it? Throttling down throttling up etc.

2. Everybody says turn 45 degrees at about 10km because gravity helps in some way. So should my prograde be at 45 degrees or my rocket? Cuz my prograde is usually at a much lower angle when I have low TWR.

3. If you have a higher TWR but not as much dV could you still reach the same altitude as a lower TWR but more dV? How much TWR is too much? Too little?

4. Recently I've started debris management such as equipping parachutes to empty fuel tanks i decouple during ascent. However the parachutes don't seem to slow them down enough to stop them from exploding after hitting the ground. Does anybody have any suggestions for how to handle that and also stuff I drop in space (realistic solutions plz)

Sorry lots of questions but I've been playing for a while and this stuff has been nagging me. Thanks

[xcorps]

1. The most fuel efficient speed. Stay as close to TV as possible.

2. Ship.

3. TWR is only a measure of how easy it is to escape the gravity of the body that is acting on you. Having a low TWR and lots of Dv means you can't get away. Having a high TWR and low Dv means you can't get away. It takes about 4900 DV to get to orbit no matter what your TWR is (as long as it's above 1). If your TWR is 10,000 and you have 500 DV, you aren't going to space. If you have 99999999 DV and your TWR is .9, you aren't going to space. If your twr is 2.0 and you have 4900 Dv, you will get to space faster than if you had a twr of 1.4 and 4900 DV.

As someone else so eloquently explained a few months ago that finally turned on the lights for me, Dv is the currency you spend to get from point A to point B. TWR is how fast you spend it.

If you aim at prograde with positive acceleration, you will still move up even if prograde marker is showing down. That's why you do the gravity turn, so you "fall off" the planet. It saves you a lot of fuel to make a good turn when you burn for circular orbit because you don't have to fight your upward movement. The best turn ends at like 70k, when you chop engines and drift to the apogee you want and begin your burn. You should already have a good bit of surface velocity, so that you ease into the burn. The prograde marker is usually right at or below the horizon, which is what you want because you have to kill some of that vertical speed.

Edited April 7, 2014 by xcorps

[Rus-Evo]

So will terminal velocity be the same in all cases? Ive been sticking to a speed limit of 117ms below 10km.

[xcorps]

TV changes as you gain altitude, decreasing. There is no TV in a vacuum, because it's there's no drag from atmosphere. The blue lines under the altitude display show you the "breakpoints" of TV. The darker the blue, the higher the TV. At the upper edges of the atmosphere, TV is like 2.6k. There's a chart on the wiki.

But yes, it's the same for every ship.

[capi3101]

1. Terminal Velocity is the speed at which an object's acceleration due to the force of gravity will be exactly countered by the object's deceleration due to the force of atmospheric drag, i.e. the maximum speed at which it can fall barring any additional outside forces. During a launch, it's the speed at which your delta-V losses to the combined force of each (gravity and drag) is minimized, and so you want to try to keep your ascent velocity close to terminal velocity as you can in order to get the most out of your booster's delta-V. In KER, this is also represented by a stat under the Surface tab called "Atmospheric Efficiency" - you want to try to keep that value as close to 100% as you can manage during the ascent; below 100% and you're losing delta-V to gravity, above that and you're losing delta-V to drag.

2. The gravity turn, yes. Your rocket gets a little bit of a boost in its velocity due to the rotational speed of the planet when you go to launch, velocity you get to keep if you launch in the direction of the planet's spin (eastward for all bodies in KSP). Your ship's heading needs to be at the 45 degree elevation mark and you need to hold it there until the prograde vector comes around to match, then follow the vector provided you're at least 35 seconds to apoapsis; if not, stay at 45 until you're 35 seconds to apopasis. Again this is a way of maximizing your booster's available delta-V.

3. As a rule, you don't want your TWR on your launch stage to be any less than 1.2; below that you'll have horrific gravity losses. 1.6-1.7 is considered optimal. Above 2.2 you'll be hitting delta-V losses due to drag (provided you're launching from a body with atmosphere such as Kerbin); you'll also be putting stress on the parts and risking unplanned disassembly. The other part of your question there is mostly irrelevant, particularly once you get into space - deltaV only measures how often and how much you can make changes to your velocity, TWR measures how fast you can make those changes. You can go to any "altitude" with any combination of the two, provided you have the fuel to get there in the first place. That said, as a rule delta-V is more important in most situations. TWR's main importance is during launch. 1.6 TWR and 4500 m/s of delta-V will get you to orbit. Hell....1.2 TWR and 4500 m/s of delta-V will get you to orbit, just not as fast.

4. You're going to have to equip enough chutes to handle a soft landing of the equipment, just like you would with a capsule or any other part of a ship you want to retreive intact. I'll humbly point you to http://ksp.freeiz.com/ , and suggest you don't sweat it too much if the added chutes make your designs more complex than they would be otherwise. If you're really keen on launching and landing with every bit still attached to your ship, you should try SSTO spaceplanes (for which there are several great guides available on these forums; ask and I can point you out to 'em).

[Superfluous J]

The "easy" (not efficient, but not particularly INefficient) guidelines are to turn to 45 degrees at 10km and then stop burning when your apoapsis is where you want it (I like 80km, but many prefer 100).

While lifting off, until you get to 5km keep it below 150m/s. Don't go over 200m/s until you're over 7km, and don't go over 260 until you've passed 10km. Assuming you didn't have to throttle down for any of those, just keep going full throttle until you get your apoapsis up to the top. If you had to throttle down, keep your throttle where it was when you were at 10km for another 5km or so and then throttle up all the way. After 15km or so, it's very hard to get a ship on a decent ascent path (what I described above) over terminal velocity.

Once you've got good at all that, a better trajectory is to burn straight up for 5-10km, and then slowly tilt East, kind of dragging your prograde marker down to the horizon as you lift from about 10km to about 40km. It takes a lot of practice to get the timings right but once you've got it, you'll almost be in orbit before you've even left the atmosphere, and will use a bit less fuel to do so. Plus, you'll feel like a baws

Edited April 7, 2014 by 5thHorseman

[EtherDragon]

Maybe one of my Labs will help explain it:

1. Terminal Velocity is the speed at which a gravity pulling down (acceleration) a falling object and air resistance (deceleration) are exactly equal. This same velocity can be used to determine how fast you should go during ascent. Check This Wiki Chart to see estimated terminal velocities at various altitudes. Notice, keeping your speed under 100m/s is good up to 1000m, but then you can get as high as 250m/s by the time you reach 10,000m.

2. This refers to your rocket, but I should point out that everyone says this is an ok guide to start with - the actual ascent profile will differ based on the capabilities of each individual rocket.

3. To an extent, yes - more TWR means that you spend less time overcoming gravity, (which saves fuel). But too much TWR means you are either A. going too fast, wasting fuel pushing against atmospheric drag, or B. carrying extra useless weight (in the form of big heavy engines) wasting fuel hauling useless weight. The closer to terminal velocity, the better, as this is the most efficient speed to go (best balance between drag and gravity).

4. For any recoverable debris stuff, you have to "fly" them each down. Otherwise the "on-rails" simulation might not handle them right, in the atmosphere. Your fuel tanks and boosters need to come down at less than 8m/s to be retrieved without damage. If you have some de-orbiting tugs with grabby arms, you can have them retrieve the debris.

[Renaissance0321]

Thanks for the replies guys, helps a lot

[Aedile]

I assume you are playing un-modded?

Full throttle to 100-120m/s, throttle down so your speed almost stops increasing and don't fiddle anymore. The turning does not only help, it is required part of going to orbit. The completely unrealistic, and not very efficient way, is to boost vertically up to 10 km. 300m/s at 10 km is good speed. If you are going for equatorial orbit, turn 45 degrees, full throttle until you reach desired apoaps. Wait until around apoaps, boost to raise your periaps. If they change the KSP aerodynamic model however, this won't be the best way to do it.

The key for going to equatorial orbit, is your orbital prograde. It starts at horizon at heading 90 as launchpad is on equator ( you can switch navball and see it at any time).

Basically going to orbit consist of increasing your altitude +gravity turn. After the first several km (10 is good) where you are mostly occupied with drag and staging, you begin your turn. at 7-8 km switch your naval to orbit ad see where is your pro-grade - you want is somewhere around 45degree pitch on 90 heading. By throttling up if it's too low, turn slightly right if it's too high. Try to get it around therer. At 250-300 m/s at 10km should not be far. Start turning towards it. From now on boost orbital pro-grade. Now here depends on your TWR. (move to map, if you don't have a mod which shows you your orbital stats). If you have enough TWR, throttle up/down so your apoapsis keeps around 60-30 seconds from you. If you don't have enough twr you might need to pitch up a little. Pro grade will naturally move towards the horizon. Once your apoaps is high enough, stop engines wait for it and burn to fix the periapsis.

Other orbits are similar as well, but you'll need to overcome the planet rotation, so the gravity turn is a bit different, as you'll need to overcome the planet rotation, rather than utilize it. But again the idea is to gain most speed after you fix your orbital prograade and boost in its direction.