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... Continued from part 3.
The Sands of Duna
Part 4: We have ignition
The author of this post (and story), collinsmark, is not affiliated with Squad nor Kerbal Space Program.
We've waited long enough. So let's get this ship out the launch pad.
Kerbals chosen for this mission are
We've been through much of this launch business before, but launches are always exciting in KSP. So here's a bit of it.
[Figure 17: Prepare for launch]
[Figure 18: We have liftoff (1/3)]
[Figure 19: We have liftoff (2/3)]
[Figure 20: We have liftoff (3/3)]
Don't forget to throttle back to keep the surface velocity somewhere around terminal velocity (as a function of elevation. See earlier post near the beginning of this thread). Keep an eye on the surface velocity and altitude; adjust throttle accordingly.
[Figure 21: First, asparagus stage separation]
[Figure 22: Shooting through the clouds (clouds are from a visual add-on pack)]
[Figure 23: SRB separation]
Recall that the SRBs are configured to separate using action groups rather than normal staging, since it's difficult to determine when the SRBs will burn out relative to asparagus stages.
[Figure 24: Started pitchover (and I remembered to disable SAS and RCS this time!)]
Here we've started the pitchover, which leads into to the gravity turn. With stabilization systems (SAS and RCS) disabled, the rocket naturally pitches over because the center of mass (thus center of gravity) is higher than the center of thrust. Gravity does most of the work bringing the rocket to a more horizontal pointing orientation.
Keep in mind that later we need to counteract this with re-enabling SAS and/or RCS, or by manual steering adjustments. Hypothetically speaking, if we were to allow the rocket to reach a horizontal orientation, the torque caused by gravity would drop to zero, but the rocket still would have a bit of angular momentum that would necessitate steering. Also, realistically speaking, we don't necessarily want to jump straight to a horizontal position. So we'll turn the SAS back on (and maybe the RCS too) once we angle around 45 degrees or so.
[Figure 25: Continuing pitchover/gravity turn. Notice SAS and RCS are still disabled.]
[Figure 26: Second, asparagus stage separation]
[Figure 27: Raising altitude and apoapsis]
[Figure 28: Third, asparagus stage separation]
It might look like something has gone horribly awry in Figure 28, but no, that's normal. The fireworks are from the sepratrons firing, together with the radial decouplers ejecting, where atmospheric drag is minimal. Those sepratrons are cool. "Never leave home without 'em!"
[Figure 29: Continuing our initial, orbital insertion]
I'll skip the rest of the initial, orbital insertion for the sake of brevity. We've been through that before.
Suffice it to say the ship got into a low, roughly circular orbit with an altitude just above 70,000 meters (somewhere between 70,000 and 80,000 m). There's a little bit of fuel left in the center stack tank (the one holding the fuel for the high-thrust engine cluster), but not much.
Full Series
Part 1: Introduction and Basics
Part 2: Efficient Launch Into Orbit
Part 3: Rocket Design Basics
https://www.physicsforums.com/threads/kerbal-space-program-rocket-design-and-orbital-mechanics.970334/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun.970335/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun-part-2.970336/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-land-on-the-mun.970337/
https://www.physicsforums.com/threads/kerbal-space-program-mun-touchdown.970338/
https://www.physicsforums.com/threads/kerbal-space-program-staying-on-the-moon.970339/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-leave-lander.970340/
https://www.physicsforums.com/threads/kerbal-space-program-walking-on-the-mun.970341/
https://www.physicsforums.com/threads/kerbal-space-program-leaving-the-mun.970342/
https://www.physicsforums.com/threads/kerbal-space-program-rendezvous-and-docking.970343/
https://www.physicsforums.com/threads/kerbal-space-program-prograde-retrograde-and-approach.970344/
https://www.physicsforums.com/threads/kerbal-space-program-prepare-for-docking.970345/
https://www.physicsforums.com/threads/kerbal-space-program-docking-and-lander-reunion.970346/
https://www.physicsforums.com/threads/kerbal-space-program-heading-home.970347/
https://www.physicsforums.com/threads/kerbal-space-program-entering-Earth's-orbit.970348/
Part 19: Landing Back on Earth
Part 20: Launch for Duna
https://www.physicsforums.com/threads/kerbal-space-program-duna-probe-launch.970351/
Part 22: Duna Rocket Launch
https://www.physicsforums.com/threads/kerbal-space-program-duna-burn-and-periapsis.970354/
https://www.physicsforums.com/threads/kerbal-space-program-duna-oberth-effect.970355/
https://www.physicsforums.com/threads/kerbal-space-program-duna-mid-course-corrections.970356/
https://www.physicsforums.com/threads/kerbal-space-program-using-gravity-to-orbit-duna.970357/
https://www.physicsforums.com/threads/kerbal-space-program-landing-on-duna.970358/
https://www.physicsforums.com/threads/kerbal-space-program-exploring-duna.970359/
https://www.physicsforums.com/threads/kerbal-space-program-launching-off-duna.970360/
https://www.physicsforums.com/threads/kerbal-space-program-fast-return-path-from-duna.970361/
Part 31: Advanced Duna Flight Math
https://www.physicsforums.com/threads/kerbal-space-program-burn-2-to-escape-duna.970363/
Part 33: Returning to Earth From Duna
The Sands of Duna
Part 4: We have ignition
The author of this post (and story), collinsmark, is not affiliated with Squad nor Kerbal Space Program.
We've waited long enough. So let's get this ship out the launch pad.
Kerbals chosen for this mission are
- Melmon Kerman
- Jontop Kerman
- Caller Kerman
We've been through much of this launch business before, but launches are always exciting in KSP. So here's a bit of it.
[Figure 17: Prepare for launch]
[Figure 18: We have liftoff (1/3)]
[Figure 19: We have liftoff (2/3)]
[Figure 20: We have liftoff (3/3)]
Don't forget to throttle back to keep the surface velocity somewhere around terminal velocity (as a function of elevation. See earlier post near the beginning of this thread). Keep an eye on the surface velocity and altitude; adjust throttle accordingly.
[Figure 21: First, asparagus stage separation]
[Figure 22: Shooting through the clouds (clouds are from a visual add-on pack)]
[Figure 23: SRB separation]
Recall that the SRBs are configured to separate using action groups rather than normal staging, since it's difficult to determine when the SRBs will burn out relative to asparagus stages.
[Figure 24: Started pitchover (and I remembered to disable SAS and RCS this time!)]
Here we've started the pitchover, which leads into to the gravity turn. With stabilization systems (SAS and RCS) disabled, the rocket naturally pitches over because the center of mass (thus center of gravity) is higher than the center of thrust. Gravity does most of the work bringing the rocket to a more horizontal pointing orientation.
Keep in mind that later we need to counteract this with re-enabling SAS and/or RCS, or by manual steering adjustments. Hypothetically speaking, if we were to allow the rocket to reach a horizontal orientation, the torque caused by gravity would drop to zero, but the rocket still would have a bit of angular momentum that would necessitate steering. Also, realistically speaking, we don't necessarily want to jump straight to a horizontal position. So we'll turn the SAS back on (and maybe the RCS too) once we angle around 45 degrees or so.
[Figure 25: Continuing pitchover/gravity turn. Notice SAS and RCS are still disabled.]
[Figure 26: Second, asparagus stage separation]
[Figure 27: Raising altitude and apoapsis]
[Figure 28: Third, asparagus stage separation]
It might look like something has gone horribly awry in Figure 28, but no, that's normal. The fireworks are from the sepratrons firing, together with the radial decouplers ejecting, where atmospheric drag is minimal. Those sepratrons are cool. "Never leave home without 'em!"
[Figure 29: Continuing our initial, orbital insertion]
I'll skip the rest of the initial, orbital insertion for the sake of brevity. We've been through that before.
Suffice it to say the ship got into a low, roughly circular orbit with an altitude just above 70,000 meters (somewhere between 70,000 and 80,000 m). There's a little bit of fuel left in the center stack tank (the one holding the fuel for the high-thrust engine cluster), but not much.
- Question: Should we raise our orbit to a higher, circular orbit as an intermediate step before heading off to Duna?
- Answer: No, absolutely not.
- Question: Why not?
- Answer: So we can leverage the Oberth effect and save fuel.
- Question: But our center-stack tank is nearly out of fuel. Once that's gone we're going to be left with a single, LV-N Atomic Rocket Motor that has about as much thrust as sick hamster. We're going to have a hard time keeping our Kerbin escape/Duna injection burn near periapsis, since we're moving so much faster in the low orbit. Oberth effect or not, we want to keep our prograde burn as close to periapsis as reasonably possible, and that will be difficult since burns will take longer with such a low thrust engine. Are you sure you want to keep such a low orbit?
- Answer: Yes. We have another trick up our sleeve.
Full Series
Part 1: Introduction and Basics
Part 2: Efficient Launch Into Orbit
Part 3: Rocket Design Basics
https://www.physicsforums.com/threads/kerbal-space-program-rocket-design-and-orbital-mechanics.970334/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun.970335/
https://www.physicsforums.com/threads/kerbal-space-program-getting-to-the-mun-part-2.970336/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-land-on-the-mun.970337/
https://www.physicsforums.com/threads/kerbal-space-program-mun-touchdown.970338/
https://www.physicsforums.com/threads/kerbal-space-program-staying-on-the-moon.970339/
https://www.physicsforums.com/threads/kerbal-space-program-preparing-to-leave-lander.970340/
https://www.physicsforums.com/threads/kerbal-space-program-walking-on-the-mun.970341/
https://www.physicsforums.com/threads/kerbal-space-program-leaving-the-mun.970342/
https://www.physicsforums.com/threads/kerbal-space-program-rendezvous-and-docking.970343/
https://www.physicsforums.com/threads/kerbal-space-program-prograde-retrograde-and-approach.970344/
https://www.physicsforums.com/threads/kerbal-space-program-prepare-for-docking.970345/
https://www.physicsforums.com/threads/kerbal-space-program-docking-and-lander-reunion.970346/
https://www.physicsforums.com/threads/kerbal-space-program-heading-home.970347/
https://www.physicsforums.com/threads/kerbal-space-program-entering-Earth's-orbit.970348/
Part 19: Landing Back on Earth
Part 20: Launch for Duna
https://www.physicsforums.com/threads/kerbal-space-program-duna-probe-launch.970351/
Part 22: Duna Rocket Launch
https://www.physicsforums.com/threads/kerbal-space-program-duna-burn-and-periapsis.970354/
https://www.physicsforums.com/threads/kerbal-space-program-duna-oberth-effect.970355/
https://www.physicsforums.com/threads/kerbal-space-program-duna-mid-course-corrections.970356/
https://www.physicsforums.com/threads/kerbal-space-program-using-gravity-to-orbit-duna.970357/
https://www.physicsforums.com/threads/kerbal-space-program-landing-on-duna.970358/
https://www.physicsforums.com/threads/kerbal-space-program-exploring-duna.970359/
https://www.physicsforums.com/threads/kerbal-space-program-launching-off-duna.970360/
https://www.physicsforums.com/threads/kerbal-space-program-fast-return-path-from-duna.970361/
Part 31: Advanced Duna Flight Math
https://www.physicsforums.com/threads/kerbal-space-program-burn-2-to-escape-duna.970363/
Part 33: Returning to Earth From Duna
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