36

I understand the reasons behind each of this manouveurs, however I'm wondering if this is how real rockets get into orbit. Cutting off the engine and letting the rocket loose vertical speed looks counter-intuitive to me (you basically spend a lot of fuel to accelerate and then you let the rocket slow down). In most real launches to low Earth orbit, the ...


33

Physics In regards to the physics, KSP is fairly realistic, other than it not modeling n-body physics (which isn't really relevant in scope of orbiting Earth/Kerbin). In regards to the engineering, KSP makes its parts much stronger than the real life components. The tradeoff here is that when something finally breaks in KSP, it explodes and disappears. ...


18

It's real, although many rockets heading to low orbit are engineered such that when the apoapsis reaches the desired altitude it's time to begin the final burn. Remember that orbit is not truly zero gravity no matter how many times Hollywood calls it that. Rather, it's free fall--craft in low orbit fall towards Earth just about as fast as they would here ...


7

Yes, in very broad terms this is how real spacecraft enter orbit. The maneouver is called a gravity turn, albeit KSP encourages (very) inefficient versions of it, just because it's faster (in terms of ground-to-orbit-time) and more fun (in terms of waiting-for-something-to-happen-time) to add more boosters and raise your apoapsis faster. An efficient ...


7

The short answer to your question is GNC (Guidance, Navigation & Control). Mission planning is done based on nominal (normal) performance of all systems launched through a mean atmosphere for the time of year when launch will take place. Depending on how many prior flights have taken place and how much data is available to model a specific vehicle launch ...


6

“Sailing a rhumb line” means holding a constant compass bearing. For short distances, this stays close to a great circle path.But at longer distances and/or higher inclinations, the rhumb-line path “tends north” of a great circle as shown in the Questions globular image. For a fast, short launch, a rhumb-line trajectory has the advantage of simplicity. As ...


5

The Antares will have a long coast phase due to engineering related trade offs rather than orbital-mechanical advantages. However from an an orbital-mechanical view alone, there would always be a long coast phase. Ignoring the atmosphere and engineering limitations, you would apply all your "first stage" impulse as close to instantaneously as possible to ...


5

The 'coast' is a very natural part of getting to orbit. Burning close to the planet's surface saves the total amount you have to change your velocity by. The mechanics are a tad complex but the short version is you get more energy by changing your velocity when you are going faster. As you lose speed while you ascend, its best to do all of the burning you ...


5

You can think about it (approximately) by dividing the rocket trajectory into "up" and "downrange" parts. The "downrange" part is the largest one: To get to orbit, the rocket has to generate a lot of speed in that direction. The "up" part is quite different. To end up in a low, circular orbit, the rocket has to go "up" few hundred kilometers and stop. ...


2

That is how real rockets go into orbit, and for orbit you need to lose vertical speed or it would be a spiral. Orbit is about horizontal speed though not vertical.


2

In fact it could be arbitrarily low. But wait before you rejoice. The Moon has an elliptic trajectory. This elliptic motion perturbs any orbit of a satellite in LEO. If you first assume your satellite is in the same plane as the Moon and describe the system as a time dependent Hamiltonian system with two degrees of freedom, a process called Arnold diffusion ...


2

In theory, a rocket could "follow a rhumb line" starting with any kind of directional information. But there seem to be two use cases: The very-early Pegasus rockets used a directional gyro derived from an aircraft gyrocompass, perhaps due to their aircraft parentage. This was later updated to a full IMU, eventually augmented to GPS. Another approach is ...


2

Bob's answer seems correct and covers the legal aspect, but it might be useful to note from an engineering point of view the conclusion is also correct. In particular that even when things go well: booster stages fall out of the sky, is only part of the issue. If it was all of it, we could have solved the problem already anyway. For example, its not super ...


2

The FAA, by rule, requires an exclusion for any air space over which a rocket is flying with its Flight Termination System armed. I guess they consider that the FTS might actually be used, in which case rocket pieces may be traveling in an uncontrolled way. Since Falcon 9’s 2nd stage FTS isn’t safed until well after stage separation, I think that’s enough to ...


1

Welcome to the site! I am afraid the answer you are looking for is not the one you want. Long story short, the optimal gravity turn must be calculated numerically, because the atmospheric density profile and velocity field is inherently numerically defined based on local conditions at the time of launch. (There's the standard atmosphere, and then accounting ...


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