That was an excellent tutorial LoS. Can you explain how to do it more efficently? I know it is better to go at less than 100% thrust at some points, but I don't know when.
I need to update my game and play again.
well, first thing, you need a target: without a target to reach, you won't know how to reach it!
say, your flight pat has three objective: one orbit at 100k, one orbit at 500k, reentry.
now that we have an objective, we can plan how to do it with the least fuel usage. note that this will not be '
the best method evar' because, for that, you'll need a proper navigation computer, while we're doing stuff by hand
now, the easiest way to change your orbital parameters in a manually controllable, low cost manner is that hohmann transfer: to change periapsis you burn at apoapsis and vice versa. you may already have spotted the problem with this: you can raise and lower them, but not move them around. as it's not relevant to our current mission profile, I'll just ignore the problem.
having a tested and true method for orbital changes, we need only to resolve the problem of leaving atmosphere.
the problem here is that drag will cost you fuel, and balancing that drag is difficult because it increases exponentially with speed, decrease linearly with altitude and, overall, increase the more you are in the atmosphere.
the only problem is that while light rocket may benefit from partial trust larger rocket will need all the thrust available because of their higher mass: you still need to get out fast from the atmosphere but large rocket acceleration is low. also, if you're using booster in the first stage thrust management option is just not there.
so, go for 100%, it's not the best way but is good enough for all intended purposes.
now, what about direction?
in a theoretical world where you have an engine with infinite power you want to act independently on vertical and horizontal speed
1 - shoot the rocket at start with the speed (think of it as controlling the craft inertia) so that your perfectly vertical trajectory goes up to 100km and then falls back.
2 - at 100km, the moment your vertical speed gets to 0, turn on your engine and get to the exact horizontal speed you need to be orbiting.
now, the only real problem with this is step 2: using a real engine, changing your speed from 0 to orbital speed 3000km/s takes a lot of time
so, this is why we want to start gaining horizontal speed early on: first, we will reach AP already with a good horizontal speed, so instead of having to accelerate from 0 to 3000 we will have to accelerate from, say, 1500 to 3000; second, we will be around the AP altitude for longer than if we were just going up vertically.
this second point may not seem intuitive at first, but you have to keep in mind that gravity at that scale is no longer vertical, but centripetal and altitude is no longer constant if you fly absolutely straight
now, it gets tricky to do it mathematically: the more you burn horizontally, the faster you get there and the longer you have to do your burn, but you will use a lot of fuel inefficiently. you want to get there with the least speed that leaves you a comfortable but tight margin.
this depends from a lot of factor, because each rocket has it's own acceleration profile. also, we can't exactly measure our horizontal and vertical speed separately at this point, so we need to approach the problem holistically.
just start with a basic, standard profile, and then tune it up for the rocket: if you get at 100k and have not enough time to do your burn, you'll need more horizontal speed. otherwise, you may climb next time at a steeper angle.
this is what I use to start tuning the rockets: climb up vertically in the first atmosphere, climb up at 70° in the second atmosphere, climb up at 30° in the third atmosphere, fly at 0° after that. keep checking the map to see when the AP reach your insertion point (100k) and remember that X turn off the engine giving you precise control over your burns.
at any time you see the AP at 100km, shut off engine and prepare for your circularization burn. when you are a bit before the AP, get horizontal, turn on engines, go to the map view and cut off engines when PE gets at 100km
how can we do this with the best precision available to our instruments? the vertical speed indicator, near the altimeter, helps you greatly. when it's 0, you're perfectly at AP/PE. note however that it has a logarithmic scale so if you're warping around, you may overshoot it badly. you'll get used to it
now do your orbit. when you're at AP again (note: when the orbit is circular, AP/PE are almost arbitrary, so don't get too worried about doing an exact orbit for now)
now, it's time to climb at 500k. the most efficient way is to burn from PE to raise AP first, then from AP to raise PE, but it will also work the other way around (but using more fuel) as the orbit is nearly circular, it doesn't really matter this time.
do your orbit. to reenter, we need to do the same hohmann stuff, but in reverse. burning toward the planet will do you no good, as altitude is circular, you're just gaining speed. if you don't believe me, do your downward burn but from the map view and see what happens to your orbit.
what we need here is to wait for AP, then, instead of accellerating toward the orbit direction, burn against it. open the map, and you'll see your PE lowering dramatically.
to use less fuel, you don't need to get it exactly to 0. you can just get it somewhat within the atmosphere and let the atmosphere stop you. the lower you aim, the less time it will take. get the PE at around 60km and shut off the engines. stay on the map view: you'll see that the atmosphere slowed you down, but you won't probably be falling down yet: this is the concept of gradually breaking using the top atmosphere layer: uses less fuel and heats up less your capsule (not that it matters right now, still..)
land, and pat yourself on the back! you've learned almost everything you need to do the same, but around the Mun
some more note that weren't fit for the mission profile:
rotating the apoapsis where you want (say, rotating it of 45deg) is hard without a navigation computer, but you may: circolarize your orbit, then slow where you want your AP/accellerate where you want your PE
it may be useful, while on the launchpad, to go on the map and see where on kearth the launchpad is. the location is pretty easy to spot from the map view once you know where it is, and its useful to know where in the orbit you are. the purple thing on the navpall indicates the space center, but I just find it difficult to use it reliably.
to all actual rocket engineers out there: yes, I know, it wasn't the more exact of the space mechanics. it will do, nevertheless.
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