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Comment by billfor | Hacker News Reader

What was interesting is how short the single engine burn was to bring it from suborbital to orbital. It was just a few seconds. I'm not even sure I saw the altitude change.

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Orbital insertion burns do not have to change the current altitude, their only required role is purely about adding speed to the orbit bringing up the altitude of the orbit's periapsis (lowest point of the current orbit) from inside the atmosphere to roughly the current altitude (or above).

Yup, Kerbal teaches you that very quickly. At the right spot in an orbit, the difference between touching water and infinite falling is very small.

Yeah it's a great way to learn a small bit of the unintuitive aspects of spaceflight. Though real launches follow a much more refined trajectory than most KSP but yeah the basic steps are still the same, though often blended together IRL due to limits on deep throttling and available relights for real rocket engines (though with mods you too can experience the need to do that in KSP, along with fun problems like ullage burns to settle fuel).

Altitude doesn't change (much) at the point where an orbit raising maneuver is performed. It increases the altitude of the rest of the orbit, with the greatest change ~180 degrees later.

If you'll excuse some poor ASCII art:

                                       _______
                  ______              /       \
                 /      \            /         \
    burn here -> *    O |    result: |    O    |
  in elliptical  \______/            \         /
    orbit                             \_______/

You should try out Kerbal Space Program you'll learn all about it. The rocket is perpendicular to the ground so the burn adds speed, and altitude on the other side of the orbit.

I haven't watched the footage yet, but if they were already at apopasis (highest point in orbit), orbital insertion would primarily raise the periapsis (lowest point) on the other side of the planet, so very little altitude change would be seen. It would be mostly an increase in velocity.

I think the mission was deliberately designed to get to just-below-orbit, have a decision point, and then proceed to orbit. So thats why it was a short burn. Because just-below-orbit is safer if anything goes wrong, they had a little pause.

edit: Also, Orbit is mostly a sideways speed thing rather than a height thing. The aim is to be "going sideways so fast that even though you are falling, you keep missing"

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