RGClark
Mathematician
The most difficult part of getting a trajectory sim for a rocket to orbit is estimating the air drag on the rocket. The losses that arise from gravity drag and steering drag are easy to calculate.
Then it is notable that free rocket trajectory simulators such as OpenRocket and RASAero can do sims even up to high altitude and at high Mach values while including the effects of supersonic air drag.
Then can these sims be adapted to do sims of rockets to orbital space? Most rockets to orbit follow a flight to orbit making use of a "gravity turn." What this is is that the rocket makes a small angle pitch over maneuver, commonly only in the range of 3 to 5 degrees, and then we let gravity gradually turn the rocket horizontally so that the rocket is eventually thrusting horizontally, to achieve the needed tangential velocity for orbit.
The OpenRocket and RASAero sims though don't seem to have included this capability of changing the pitch angle, i.e., angle of attack, during the flight. So this would need to be a modification added to the software.
At least with OpenRocket you can somewhat emulate it by doing two separate sim runs. The first is done so that it has the first booster stage run to completion and get to some altitude. Then you run a separate sim with the remaining stages starting at that ending altitude provided by the first stage and at your desired starting pitch angle.
Problem is though while OpenRocket allows you to input starting altitude and starting pitch angle when you run a simulation it does not allow you to enter a starting velocity, so this emulation would be of the case where the upper stages start from 0 velocity. This though is not the most efficient trajectory for an orbital flight.
So still OpenRocket would need an adaptation where a stage could pitch over some time during the flight. You would also want the adaptation to also allow the complete flight without having to break it up into separate sims.
Another adaptation that would be required is to allow multiple parameters to be varied to find the optimal combination to get the most payload to orbit and/or the highest orbital altitude. For instance, in addition to finding the optimal pitch angle and altitude to perform the pitch over, you also need to know what's the best combination of coast phases. Users of the sims are aware of the fact that changing the length of the coast time between stage burns can significantly change the altitude. This is also the case for what is the maximal velocity that can be achieved, and therefore maximal payload deliverable to orbit.
This capability of varying multiple parameters would be computationally intensive though. For instance, my laptop is a ca. 2010 Windows 7 computer, and often I get a "Out of Memory" error just with fixed pitch and altitude, when I tried to do the OpenRocket emulation of an orbital flight, as broken into two sims.
Bob Clark
Then it is notable that free rocket trajectory simulators such as OpenRocket and RASAero can do sims even up to high altitude and at high Mach values while including the effects of supersonic air drag.
Then can these sims be adapted to do sims of rockets to orbital space? Most rockets to orbit follow a flight to orbit making use of a "gravity turn." What this is is that the rocket makes a small angle pitch over maneuver, commonly only in the range of 3 to 5 degrees, and then we let gravity gradually turn the rocket horizontally so that the rocket is eventually thrusting horizontally, to achieve the needed tangential velocity for orbit.
The OpenRocket and RASAero sims though don't seem to have included this capability of changing the pitch angle, i.e., angle of attack, during the flight. So this would need to be a modification added to the software.
At least with OpenRocket you can somewhat emulate it by doing two separate sim runs. The first is done so that it has the first booster stage run to completion and get to some altitude. Then you run a separate sim with the remaining stages starting at that ending altitude provided by the first stage and at your desired starting pitch angle.
Problem is though while OpenRocket allows you to input starting altitude and starting pitch angle when you run a simulation it does not allow you to enter a starting velocity, so this emulation would be of the case where the upper stages start from 0 velocity. This though is not the most efficient trajectory for an orbital flight.
So still OpenRocket would need an adaptation where a stage could pitch over some time during the flight. You would also want the adaptation to also allow the complete flight without having to break it up into separate sims.
Another adaptation that would be required is to allow multiple parameters to be varied to find the optimal combination to get the most payload to orbit and/or the highest orbital altitude. For instance, in addition to finding the optimal pitch angle and altitude to perform the pitch over, you also need to know what's the best combination of coast phases. Users of the sims are aware of the fact that changing the length of the coast time between stage burns can significantly change the altitude. This is also the case for what is the maximal velocity that can be achieved, and therefore maximal payload deliverable to orbit.
This capability of varying multiple parameters would be computationally intensive though. For instance, my laptop is a ca. 2010 Windows 7 computer, and often I get a "Out of Memory" error just with fixed pitch and altitude, when I tried to do the OpenRocket emulation of an orbital flight, as broken into two sims.
Bob Clark