Author Topic: SpaceX Falcon Mission Simulations  (Read 21612 times)

Offline ChrisC

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SpaceX Falcon Mission Simulations
« on: 02/04/2017 02:00 PM »
[Moderator Note:  This was split off from the Iridium Next Flight 1 Discussion thread.  Several of the participants in this discussion mentioned creating a more general simulation thread, so here it is.  If anyone thinks I split off too much I could always stick some of it back in the Iridium thread, just let me know.  -gongora]



Here's the webcast paired with some great animations. I really like the charts showing the altitude and velocity of both stages for the duration. I didn't realize it took soooo long for the first stage to get back down to the altitude it had at MECO.  https://youtube.com/watch?v=CGL2FEMxDE0

That's really interesting, especially to see the velocity changes (e.g. how much each burn slows down S1).

Note how S1 resumes accelerating after the entry burn completes, but only for a few seconds and then starts decelerating again, WITHOUT engines burning, due to descending into thicker atmosphere.  It's slowing down during nearly the entire atmospheric descent because it's going faster than terminal velocity.

This needs to get paired with the graph (video?) that someone here produced that inferred the ACCELERATION data from the velocity data shown on the webcast screen.  Although, as I recall, only S2 data was shown.  SpaceX, are you listening?  Give us S1 data (from telemetry) on the screen as well, and the community will produce cool graphics for you ...
« Last Edit: 02/22/2017 10:28 PM by gongora »
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Offline meekGee

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Here's the webcast paired with some great animations. I really like the charts showing the altitude and velocity of both stages for the duration. I didn't realize it took soooo long for the first stage to get back down to the altitude it had at MECO.  https://youtube.com/watch?v=CGL2FEMxDE0

That's really interesting, especially to see the velocity changes (e.g. how much each burn slows down S1).

Note how S1 resumes accelerating after the entry burn completes, but only for a few seconds and then starts decelerating again, WITHOUT engines burning, due to descending into thicker atmosphere.  It's slowing down during nearly the entire atmospheric descent because it's going faster than terminal velocity.

This needs to get paired with the graph (video?) that someone here produced that inferred the ACCELERATION data from the velocity data shown on the webcast screen.  Although, as I recall, only S2 data was shown.  SpaceX, are you listening?  Give us S1 data (from telemetry) on the screen as well, and the community will produce cool graphics for you ...
I was looking at the atmospheric portion too.

My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.
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Online OneSpeed

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My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

If you watch this sim of the Iridium launch, you can see that the g forces peak at 4.6 at the 7:20 mark, purely due to aerodynamic forces. The rocket is travelling at 686 m/s, or about Mach 2, way in excess of terminal velocity. If it was in 'equilibrium' the g forces would be close to 1.

« Last Edit: 02/09/2017 10:54 AM by OneSpeed »

Offline meekGee

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My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

If you watch this sim of the Iridium launch, you can see that the g forces peak at 4.6 at the 7:20 mark, purely due to aerodynamic forces. The rocket is travelling at 686 m/s, or about Mach 2, way in excess of terminal velocity. If it was in 'equilibrium' the g forces would be close to 1.



That's the sim.

If you look at this video of the real thing, you see a smooth drop in velocity from the end of the last burn, almost along a straight line

(Skip forward to approx second 460, similar to your 7:20 mark)

https://www.youtube.com/watch?v=NT50R2dLht8?t=459


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Offline mme

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My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

If you watch this sim of the Iridium launch, you can see that the g forces peak at 4.6 at the 7:20 mark, purely due to aerodynamic forces. The rocket is travelling at 686 m/s, or about Mach 2, way in excess of terminal velocity. If it was in 'equilibrium' the g forces would be close to 1.



That's the sim.

If you look at this video of the real thing, you see a smooth drop in velocity from the end of the last burn, almost along a straight line

(Skip forward to approx second 460, similar to your 7:20 mark)

https://www.youtube.com/watch?v=NT50R2dLht8?t=459
I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.
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Offline meekGee

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My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

If you watch this sim of the Iridium launch, you can see that the g forces peak at 4.6 at the 7:20 mark, purely due to aerodynamic forces. The rocket is travelling at 686 m/s, or about Mach 2, way in excess of terminal velocity. If it was in 'equilibrium' the g forces would be close to 1.



That's the sim.

If you look at this video of the real thing, you see a smooth drop in velocity from the end of the last burn, almost along a straight line

(Skip forward to approx second 460, similar to your 7:20 mark)

https://www.youtube.com/watch?v=NT50R2dLht8?t=459
I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.

Well FC is a simulator, but he managed to get the timing of all events to within a few seconds, and then tweaked the sim parameters to match reality. I think that's pretty good.

I'm using it to estimate trends, not nail down precise numbers.
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Online OneSpeed

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I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.

Well FC is a simulator, but he managed to get the timing of all events to within a few seconds, and then tweaked the sim parameters to match reality. I think that's pretty good.

I'm using it to estimate trends, not nail down precise numbers.

Flight Club is a launch and landing trajectory visualiser, not a simulator. It is replaying the velocity and altitude data gleaned from the SpaceX broadcasts, where it is available. Where it is not, they appear to be interpolating as best they can to match the video they have.

SpaceSim is an n-body simulation of the solar system. The simulation takes account of all of the forces acting on the rocket, including mass, thrust, drag (including skin friction) and lift. The process of matching the broadcast data to the flight profile is extremely manual and time consuming. But when they do match, it is quite revealing. For example we know that for return to flight, the first stage must have been throttled to between 90 and 95% of the FT spec.

Offline meekGee

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I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.

Well FC is a simulator, but he managed to get the timing of all events to within a few seconds, and then tweaked the sim parameters to match reality. I think that's pretty good.

I'm using it to estimate trends, not nail down precise numbers.

Flight Club is a launch and landing trajectory visualiser, not a simulator. It is replaying the velocity and altitude data gleaned from the SpaceX broadcasts, where it is available. Where it is not, they appear to be interpolating as best they can to match the video they have.

SpaceSim is an n-body simulation of the solar system. The simulation takes account of all of the forces acting on the rocket, including mass, thrust, drag (including skin friction) and lift. The process of matching the broadcast data to the flight profile is extremely manual and time consuming. But when they do match, it is quite revealing. For example we know that for return to flight, the first stage must have been throttled to between 90 and 95% of the FT spec.

I thought so too initially, but he appears to be visualizing his simulation, based on some of the comments he's left in the conversation threads.

However - if he has a robust simulation, and he tweaks the underlying parameters to match reality, then that's even better than just blindly reading numbers from the SpaceX feed.

You can look at his results for different missions and see how well it works.

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Online OneSpeed

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I thought so too initially, but he appears to be visualizing his simulation, based on some of the comments he's left in the conversation threads.

However - if he has a robust simulation, and he tweaks the underlying parameters to match reality, then that's even better than just blindly reading numbers from the SpaceX feed.

You can look at his results for different missions and see how well it works.

Fair enough, so I've added a couple of lines of code to SpaceSim to output Velocity, Acceleration and Altitude of just the first stage to a .csv file. The output is attached below, and is similar in many respects to the Flight Club S1 profile. One observation I would make is that the drag should drop quite suddenly as the stage goes subsonic, but only SpaceSim appears to be taking account of this.

My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

Going back to your original point though, both profiles, however they are obtained, confirm that the g forces are only in 'equilibrium' very briefly, at around the 7:03 mark, and that the stage is well above terminal velocity at the 7:20 mark.

Edit: fixed stage numbering
« Last Edit: 02/12/2017 09:17 AM by OneSpeed »

Offline meekGee

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I'm not following.  Shouldn't the acceleration be the derivative of the velocity?  (Are you always doing dS - along the path?)

Altitude of course is unrelated, but why is the acceleration at 0 over so much of the time?

How do you define aerodynamic equilibrium?  And should that only be relevant only between the entry burn and the landing burn starts?



I thought so too initially, but he appears to be visualizing his simulation, based on some of the comments he's left in the conversation threads.

However - if he has a robust simulation, and he tweaks the underlying parameters to match reality, then that's even better than just blindly reading numbers from the SpaceX feed.

You can look at his results for different missions and see how well it works.

Fair enough, so I've added a couple of lines of code to SpaceSim to output Velocity, Acceleration and Altitude of just the second stage to a .csv file. The output is attached below, and is similar in many respects to the Flight Club S2 profile. One observation I would make is that the drag should drop quite suddenly as the stage goes subsonic, but only SpaceSim appears to be taking account of this.

My interpretation is that it is at terminal velocity very quickly, but that the terminal velocity is of course decreasing with density.

It's not the same thing as being above terminal velocity. It means they are always at equilibrium, and there's no residual of the speed they've been traveling at 2 seconds ago.

Going back to your original point though, both profiles, however they are obtained, confirm that the g forces are only in 'equilibrium' very briefly, at around the 7:03 mark, and that the stage is well above terminal velocity at the 7:20 mark.
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Online OneSpeed

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How do you define aerodynamic equilibrium?  And should that only be relevant only between the entry burn and the landing burn starts?

In this case I take aerodynamic equilibrium to mean that for a free falling object, gravitational and aerodynamic forces are equal and opposite, and so it does not accelerate. If we are discussing your interpretation of whether or not the stage is at terminal velocity, then yes, that should only be relevant between the entry burn and the landing burn.

I'm not following.  Shouldn't the acceleration be the derivative of the velocity?  (Are you always doing dS - along the path?)

Altitude of course is unrelated, but why is the acceleration at 0 over so much of the time?

Drag between the initial boost and the boostback burns is nearly zero because of the altitude, and so therefore is the acceleration. Acceleration between the boostback and entry burns is also near zero for the same reason.
However acceleration in the initial boost phase also appears to be zero in the plot I've posted. This is clearly not correct.

Sorry for the long winded explanation, but SpaceSim uses a parent / child relationship to determine the effect of thrust of a stage on any parent stages. At launch, the parent object is the payload. Its child is the second stage, and its grandchild is the first stage. The first separation event changes that relationship. The payload now has only the second stage as a child, and the first stage becomes a parent with no children. Once separated, calculations are performed separately, as you'd expect. In SpaceSim the acceleration is only known for parent objects, so when I plotted the first stage acceleration, that value was skipped while it was still a grandchild, i.e. in the boost phase, and only plotted once it became a parent object.

Anyway, I've attached a plot of velocity, acceleration and altitude for the payload, and the acceleration in the boost phase is what the first stage would also experience.

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I'm not following.  Shouldn't the acceleration be the derivative of the velocity?  (Are you always doing dS - along the path?)

Altitude of course is unrelated, but why is the acceleration at 0 over so much of the time?

Drag between the initial boost and the boostback burns is nearly zero because of the altitude, and so therefore is the acceleration. Acceleration between the boostback and entry burns is also near zero for the same reason.
However acceleration in the initial boost phase also appears to be zero in the plot I've posted. This is clearly not correct.

I think he meant that acceleration due to gravity is missing.

Offline meekGee

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I'm not following.  Shouldn't the acceleration be the derivative of the velocity?  (Are you always doing dS - along the path?)

Altitude of course is unrelated, but why is the acceleration at 0 over so much of the time?

Drag between the initial boost and the boostback burns is nearly zero because of the altitude, and so therefore is the acceleration. Acceleration between the boostback and entry burns is also near zero for the same reason.
However acceleration in the initial boost phase also appears to be zero in the plot I've posted. This is clearly not correct.

I think he meant that acceleration due to gravity is missing.
Well it's hard to separate out once you're in air, since the direction of motion is not known.
« Last Edit: 02/12/2017 03:29 PM by meekGee »
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Online OneSpeed

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I think he meant that acceleration due to gravity is missing.
Well it's hard to separate out once you're in air, since the direction of motion is not known.

Yes, the internal term in SpaceSim is RelativeAcceleration, acceleration relative to gravity, which is calculated later. Gravity is not considered a constant because it is a n-body simulation of the solar system.
« Last Edit: 02/12/2017 08:04 PM by OneSpeed »

Offline meekGee

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I think he meant that acceleration due to gravity is missing.
Well it's hard to separate out once you're in air, since the direction of motion is not known.

Yes, the internal term in SpaceSim is RelativeAcceleration, acceleration relative to gravity, which is calculated later. Gravity is not considered a constant because it is a n-body simulation of the solar system.

I understand that - but where is it coming from?

The velocity is along the path (I assume) so if you differentiate that, you get the full acceleration. (in vector form)

You can subtract 1 g in the "Z" direction, but this only makes sense when in free fall.  (Is that what you did?)

Once you hit the atmosphere, the aerodynamic forces can be in any direction.  So you can't define "equilibrium" as just "0 g".

It's trickier to tease this out than it appears at first blush.

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Offline mme

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I think he meant that acceleration due to gravity is missing.
Well it's hard to separate out once you're in air, since the direction of motion is not known.

Yes, the internal term in SpaceSim is RelativeAcceleration, acceleration relative to gravity, which is calculated later. Gravity is not considered a constant because it is a n-body simulation of the solar system.

I understand that - but where is it coming from?

The velocity is along the path (I assume) so if you differentiate that, you get the full acceleration. (in vector form)

You can subtract 1 g in the "Z" direction, but this only makes sense when in free fall.  (Is that what you did?)

Once you hit the atmosphere, the aerodynamic forces can be in any direction.  So you can't define "equilibrium" as just "0 g".

It's trickier to tease this out than it appears at first blush.
Sorry, I'm being hand wavy and should let OneSpeed explain since he really knows what he is talking about and I'm just expressing my understanding of what the graphs represent.

The acceleration that is being graphed (after the initial boost and separation [1]) is in the stage's reference frame, not Earth's.  There is no subtraction of the 1 g going on.  The "RelativeAcceleration" is relative to free-fall in the n-body space.

I'm probably not right, but in my mind it is summing all the forces on the stage (gravity, thrust, drag) and expressing the resulting "g-force" that is being experienced by the stage. It is not expressing dV/dT relative to an observer on Earth.  It is dV/dT relative to the stage in free-fall and what "free-fall" means is calculated in realtime (so it's not a fixed 9.8 m/s^2).

[1] Before first stage separation, the calculation is done for the payload because that's how the software models the problem and since everything is connected at that point it's a reasonable simplification.
« Last Edit: 02/13/2017 02:01 AM by mme »
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Offline meekGee

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I think he meant that acceleration due to gravity is missing.
Well it's hard to separate out once you're in air, since the direction of motion is not known.

Yes, the internal term in SpaceSim is RelativeAcceleration, acceleration relative to gravity, which is calculated later. Gravity is not considered a constant because it is a n-body simulation of the solar system.

I understand that - but where is it coming from?

The velocity is along the path (I assume) so if you differentiate that, you get the full acceleration. (in vector form)

You can subtract 1 g in the "Z" direction, but this only makes sense when in free fall.  (Is that what you did?)

Once you hit the atmosphere, the aerodynamic forces can be in any direction.  So you can't define "equilibrium" as just "0 g".

It's trickier to tease this out than it appears at first blush.
Sorry, I'm being hand wavy and should let OneSpeed explain since he really knows what he is talking about and I'm just expressing my understanding of what the graphs represent.

The acceleration that is being graphed (after the initial boost and separation [1]) is in the stage's reference frame, not Earth's.  There is no subtraction of the 1 g going on.  The "RelativeAcceleration" is relative to free-fall in the n-body space.

It's probably not right, but in my mind it is summing all the forces on the stage (gravity, thrust, drag) and expressing the resulting "g-force" that is being experienced by the stage. It is not expressing dV/dT relative to an observer on Earth.  It is dV/dT relative to the stage in free-fall and what "free-fall" means is calculated in realtime (so it's not a fixed 9.8 m/s^2).

[1] Before first stage separation, the calculation is done for the payload because that's how the software models the problem and since everything is connected at that point it's a reasonable simplification.
Right.

And with that in mind, the ambiguity arises.

If it is showing zero when free floating in space, then it shouldn't show zero when in aerodynamic equilibrium.

But what it SHOULD show depends on how things are defined.

Is this only in Z axis, for example?   Because the velocity seems to be in the dS direction.

(But the altitude of course isn't)

What is the source of the acceleration graph?  Is it derived from the velocity curve? Seems like it isn't, since it doesn't match.

So what are we looking at, before we draw conclusions from it?

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Online OneSpeed

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It's trickier to tease this out than it appears at first blush.

Absolutely!

The acceleration that is being graphed (after the initial boost and separation [1]) is in the stage's reference frame, not Earth's.  There is no subtraction of the 1 g going on.  The "RelativeAcceleration" is relative to free-fall in the n-body space.

I'm probably not right, but in my mind it is summing all the forces on the stage (gravity, thrust, drag) and expressing the resulting "g-force" that is being experienced by the stage. It is not expressing dV/dT relative to an observer on Earth.  It is dV/dT relative to the stage in free-fall and what "free-fall" means is calculated in realtime (so it's not a fixed 9.8 m/s^2).

[1] Before first stage separation, the calculation is done for the payload because that's how the software models the problem and since everything is connected at that point it's a reasonable simplification.

That's a great summary of what I've tried to express so far. Thanks.

SpaceSim is open source, and if you want to see the code, or just run it for yourself, it's at https://github.com/zlynn1990/SpaceSim . zlynn1990 has done a fantastic job, writing the vast majority of the program. I've added mostly aerodynamic enhancements starting July 2016. If you happened to download SpaceSim before that date, the drag calculation would have been different. If you then happened to use it to model the Iridium 1 launch, and put a couple of lines of code in the F9S1 and DemoSat classes to output the velocity and altitude, you'd end up with plots that did not take account of the step change in drag in the transonic region.

Also, those couple of lines of code would have problems correctly outputting acceleration, as meekGee has identified. The RelativeAcceleration parameter is a vector, but I am only printing its magnitude. If it has any horizontal component, aerodynamic equilibrium would not be achieved when the magnitude of the RelativeAcceleration equals the magnitude of gravity. In other words, my two lines of code are a hack.

However, SpaceSim does correctly take account of gravity. The data in the spreadsheet I attached upthread suggests that equilibrium is reached at second 426 (7:06), but the vertical (z) component of the velocity vector is smaller than its magnitude, and so equilibrium is reached in the simulation earlier, at second 423 (7:03), when drag is less.


Hey folks, I'm late to the party. I'm the guy who made Flight Club

I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.

Well FC is a simulator, but he managed to get the timing of all events to within a few seconds, and then tweaked the sim parameters to match reality. I think that's pretty good.

I'm using it to estimate trends, not nail down precise numbers.

Flight Club is a launch and landing trajectory visualiser, not a simulator. It is replaying the velocity and altitude data gleaned from the SpaceX broadcasts, where it is available. Where it is not, they appear to be interpolating as best they can to match the video they have.

SpaceSim is an n-body simulation of the solar system. The simulation takes account of all of the forces acting on the rocket, including mass, thrust, drag (including skin friction) and lift. The process of matching the broadcast data to the flight profile is extremely manual and time consuming. But when they do match, it is quite revealing. For example we know that for return to flight, the first stage must have been throttled to between 90 and 95% of the FT spec.

Flight Club is a simulator. Myself and zlynn1990 (of SpaceSim fame) collaborated a bunch on tweaking our atmospheric models and such when we were independently building our simulators. Just wanted to clear that up. Let me know if you have any questions about how Flight Club does things - happy to help in any way.

Offline mme

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Hey folks, I'm late to the party. I'm the guy who made Flight Club

I'm pretty sure those first stage numbers where generated by the FightClub.io "trajectory visualizer."  Space X did not provide them on the webcast.  I think this is a matter of competing simulations and I'm suspicious of FightClub's smooth deceleration.

Well FC is a simulator, but he managed to get the timing of all events to within a few seconds, and then tweaked the sim parameters to match reality. I think that's pretty good.

I'm using it to estimate trends, not nail down precise numbers.

Flight Club is a launch and landing trajectory visualiser, not a simulator. It is replaying the velocity and altitude data gleaned from the SpaceX broadcasts, where it is available. Where it is not, they appear to be interpolating as best they can to match the video they have.

SpaceSim is an n-body simulation of the solar system. The simulation takes account of all of the forces acting on the rocket, including mass, thrust, drag (including skin friction) and lift. The process of matching the broadcast data to the flight profile is extremely manual and time consuming. But when they do match, it is quite revealing. For example we know that for return to flight, the first stage must have been throttled to between 90 and 95% of the FT spec.

Flight Club is a simulator. Myself and zlynn1990 (of SpaceSim fame) collaborated a bunch on tweaking our atmospheric models and such when we were independently building our simulators. Just wanted to clear that up. Let me know if you have any questions about how Flight Club does things - happy to help in any way.
Thanks for clearing that up and thanks for creating FlightClub!  I wonder if the apparent differences are more to do with the model or the assumptions for various inputs.  I was also starting to feel like maybe we should create a simulation thread for these topics if people wanted to continue debating the implications of different simulations.
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... I was also starting to feel like maybe we should create a simulation thread for these topics if people wanted to continue debating the implications of different simulations.

Sounds like a good idea. I've got a plot for the CRS-10 first stage I'd like to post, but it makes no sense in this thread. There are Mars simulation threads, so perhaps a Falcon one would make sense?

Flight Club is a simulator. Myself and zlynn1990 (of SpaceSim fame) collaborated a bunch on tweaking our atmospheric models and such when we were independently building our simulators. Just wanted to clear that up. Let me know if you have any questions about how Flight Club does things - happy to help in any way.

Thanks for setting the record straight!

Thanks for clearing that up and thanks for creating FlightClub!  I wonder if the apparent differences are more to do with the model or the assumptions for various inputs.  I was also starting to feel like maybe we should create a simulation thread for these topics if people wanted to continue debating the implications of different simulations.

No problem, and my pleasure! The apparent differences probably arise from a couple of things. I've tried to make Flight Club as generic as possible for different launch vehicles, which has possibly (though I have no reason to believe this is the case) made some of the logic around landing leg and grid fin deployments a bit wonky. You know, vehicle-specific things.

Then my atmospheric model is sound, as it is based on interpolated NASA data. However, the vehicle-specific drag models may need some fine-tuning. I have created a drag coefficient vs Mach number curve for the F9, but it's all educated guessing. I'm sure zlynn1990 has created his own educated guess, independently of mine.

... I was also starting to feel like maybe we should create a simulation thread for these topics if people wanted to continue debating the implications of different simulations.

Sounds like a good idea. I've got a plot for the CRS-10 first stage I'd like to post, but it makes no sense in this thread. There are Mars simulation threads, so perhaps a Falcon one would make sense?

Yeah sounds like a plan. I've already gotten my first stage portion for CRS-10 sufficiently matching reality (not perfectly - about 97%) and I'm working on my stage 2 portion now (see link below for both). I'll happily submit some discussion to that thread if it exists!

https://www.flightclub.io/results/?id=06466dd9-3a0a-492c-8bd5-58248ff31960&code=CR10
« Last Edit: 02/21/2017 01:09 AM by TheVehicleDestroyer »

Offline TOG

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Then my atmospheric model is sound, as it is based on interpolated NASA data. However, the vehicle-specific drag models may need some fine-tuning. I have created a drag coefficient vs Mach number curve for the F9, but it's all educated guessing. I'm sure zlynn1990 has created his own educated guess, independently of mine.


First off, great respect for the work involved in developing the process.  It shows a great love of the math involved in modeling a complex process.

And a question:  When you formulate the drag coefficient vs. Mach number curve, are you also taking into account the atmospheric density based on the altitude of the reading?  When I did some similar simulators, years ago for shuttle reentry and landing, that was one area that bit me in the back-side.  That and the effect of heating on the surface drag for localized atmospheric turbulence.  I had several calculations relating to the heat loss as the spacecraft moved through the atmosphere and the effect on the local density.

Out of mathematical curiosity, of course.

Thanks!
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Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #23 on: 02/23/2017 01:19 PM »
Special thanks to gongora for setting up this thread. As promised, here is the CRS-10 first stage profile. The velocity is in m/s, but for the altitude, divide by 10 to get kms. For the acceleration, divide by 100 to get relative gs. A full simulation is coming soon.
« Last Edit: 02/23/2017 01:20 PM by OneSpeed »

Re: SpaceX Falcon Mission Simulations
« Reply #24 on: 02/24/2017 05:21 PM »
Flight Club simulation has also been finished

Data: https://www.flightclub.io/results/?code=CR10
Live: https://www.flightclub.io/world/?code=CR10&w=2
Live synced with webcast:

The timing of events in the webcast included quite a few delays. I analyzed them in my post to r/SpaceX here: https://www.reddit.com/r/spacex/comments/5vk3e8/slug/de2nqc2

I would copy and paste over but I don't know if it's possible to do tables on this forum? Sorry, NSF noob
« Last Edit: 02/24/2017 05:25 PM by TheVehicleDestroyer »

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #25 on: 02/25/2017 01:48 AM »
I would copy and paste over but I don't know if it's possible to do tables on this forum? Sorry, NSF noob

You can do tables, but it requires quite a bit of manual formatting. It's probably easier to just attach a spreadsheet.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #26 on: 03/26/2017 02:38 AM »
Here is the latest simulation I have been working on in collaboration with NSF user ZLynn1990. This mission demonstrates how the Falcon Heavy could launch a crewed Dragon V2 around the moon. Unlike the Apollo missions, this is not a free return trajectory. Elon has stated that dragon will pass by the moon and coast out to 400,000 miles (640,000km). Few details are known about this mission, so what we created is a best guess based on the current known specification of the Falcon Heavy and Dragon V2 capsule.


Offline Proponent

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Re: SpaceX Falcon Mission Simulations
« Reply #27 on: 03/26/2017 01:04 PM »
That's amazing, OneSpeed -- thank you!

I'm surprised that the lift is so large during ascent.  It sometimes exceeds the drag by an order of magnitude.  Would Falcon Heavy actually fly at angles of attack large enough to generate such lift?  I'd have thought that from pitch kick to a low dynamic pressure, FH would be flying a gravity turn.

If it were up to me, I would probably let negative perigees be shown, because it gives you a feeling for the shape of the orbit.

A couple of really minor points/questions.  Somewhere in cis-lunar space, the atmospheric density rises to 0.001 kg/m3, and drag becomes postive -- a minor bug in the atmospheric model?

Again, that was really cool!


Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #28 on: 03/26/2017 06:37 PM »
This is by far the best way to show this mission I've found. They should show your work in schools across the nation!

A couple of question: will the Dragon only get so far from the lunar surface at minimum, three or four lunar diameters? I hope for all that money the those astronauts will get to fly few km from the surface :)

Also: upon re-entry in Earth's atmosphere, I see that heating rate goes up to over one MW/m^2 but air density remains 0.000kg/m^3. Is this expected?

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #29 on: 03/27/2017 11:02 AM »
Thanks for the feedback!

I'm surprised that the lift is so large during ascent.  It sometimes exceeds the drag by an order of magnitude.  Would Falcon Heavy actually fly at angles of attack large enough to generate such lift?  I'd have thought that from pitch kick to a low dynamic pressure, FH would be flying a gravity turn.

It would certainly start out as a gravity turn. I've tried a few times now to match the velocity and altitude data provided in the SpaceX webcasts to simulations. There seems to be a trend. Once the dynamic pressure drops sufficiently, they introduce a small negative alpha, which favours horizontal acceleration over vertical. The F9 and FH have a very high fineness ratio, so lift/drag ratio is surprisingly high, the angle of attack doesn't need to be large to generate significant (negative) lift.

If it were up to me, I would probably let negative perigees be shown, because it gives you a feeling for the shape of the orbit.

I understand where you are coming from, but the predictive traces are not just showing the newtonian orbit, they include aerodynamic effects. So, if there is an atmosphere the trace may well stop completely at the planet's surface. Unfortunately, the traces can become quite erratic when approaching a planet's atmosphere from a large distance at a high update speed, but I figure that is better than just ignoring atmospherics completely.

A couple of really minor points/questions.  Somewhere in cis-lunar space, the atmospheric density rises to 0.001 kg/m3, and drag becomes postive -- a minor bug in the atmospheric model?

That definitely sounds like a bug. Thanks, I'll have a closer look.

A couple of question: will the Dragon only get so far from the lunar surface at minimum, three or four lunar diameters? I hope for all that money the those astronauts will get to fly few km from the surface :)

The closer you get to the moon, the larger the gravity assist. This profile gives about the right kick for a 400k mile apogee. For a 300k mile apogee, the closest approach would be even higher, about 17,000 kms. If you come too close, the kick is enough to reach Earth escape velocity, and the Grey Dragon would not have enough ΔV to return to Earth. Ever.

Also: upon re-entry in Earth's atmosphere, I see that heating rate goes up to over one MW/m^2 but air density remains 0.000kg/m^3. Is this expected?

Yes, it is. I'll see if I can push a code change for the display of really low values of density (this issue is even more marked on Mars).

Offline Proponent

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Re: SpaceX Falcon Mission Simulations
« Reply #30 on: 03/27/2017 01:09 PM »
A couple of question: will the Dragon only get so far from the lunar surface at minimum, three or four lunar diameters? I hope for all that money the those astronauts will get to fly few km from the surface :)

This whole thing really puzzles me.  I'd have thought that most passengers would want to approach the moon as closely as possible, and that SpaceX would want to keep the mission profile as simple as possible, especially for the first mission.  Put those two factors together, and doesn't it add up to an Apollo-style figure-of-eight free-return trajectory (an in-plane, co-rotating, circumlunar free-return trajectory, in the terminology used in the plot attached to this post)?  Then the only burns needed after TLI are small course course corrections.

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #31 on: 03/27/2017 02:54 PM »
A couple of question: will the Dragon only get so far from the lunar surface at minimum, three or four lunar diameters? I hope for all that money the those astronauts will get to fly few km from the surface :)

This whole thing really puzzles me.  I'd have thought that most passengers would want to approach the moon as closely as possible, and that SpaceX would want to keep the mission profile as simple as possible, especially for the first mission.  Put those two factors together, and doesn't it add up to an Apollo-style figure-of-eight free-return trajectory (an in-plane, co-rotating, circumlunar free-return trajectory, in the terminology used in the plot attached to this post)?  Then the only burns needed after TLI are small course course corrections.

It makes a lot more sense if Elon meant 400,000 km when he said 400,000 miles.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #32 on: 03/27/2017 08:32 PM »
This whole thing really puzzles me.  I'd have thought that most passengers would want to approach the moon as closely as possible, and that SpaceX would want to keep the mission profile as simple as possible, especially for the first mission.  Put those two factors together, and doesn't it add up to an Apollo-style figure-of-eight free-return trajectory (an in-plane, co-rotating, circumlunar free-return trajectory, in the terminology used in the plot attached to this post)?  Then the only burns needed after TLI are small course course corrections.

It makes a lot more sense if Elon meant 400,000 km when he said 400,000 miles.

Yes, I get that, but from https://phys.org/news/2017-02-spacex-people-moon-year.html

"The paying passengers would make a long loop around the moon, skimming the lunar surface then going well beyond, perhaps 300,000 or 400,000 miles distance altogether. It's about 240,000 miles distance to the moon alone, one way."

There appears to be no confusion between miles and kilometers in this statement. The inconsistency I see is in the mission times quoted so far. From the sim, it will be three days to the moon, and another week to the 400k mile apogee. It would be a further week for the return to earth, nearly 17 days altogether.

The Grey Dragon is going to be limited in available ΔV compared to Apollo, so I suspect this 'rollercoaster' mission profile is designed to do something spectacular (a new altitude record) with limited resources. This won't be the first Dragon 2 mission, so although certainly risky, it would be a logical incremental step.

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #33 on: 03/27/2017 08:42 PM »
This whole thing really puzzles me.  I'd have thought that most passengers would want to approach the moon as closely as possible, and that SpaceX would want to keep the mission profile as simple as possible, especially for the first mission.  Put those two factors together, and doesn't it add up to an Apollo-style figure-of-eight free-return trajectory (an in-plane, co-rotating, circumlunar free-return trajectory, in the terminology used in the plot attached to this post)?  Then the only burns needed after TLI are small course course corrections.

It makes a lot more sense if Elon meant 400,000 km when he said 400,000 miles.

Yes, I get that, but from https://phys.org/news/2017-02-spacex-people-moon-year.html

"The paying passengers would make a long loop around the moon, skimming the lunar surface then going well beyond, perhaps 300,000 or 400,000 miles distance altogether. It's about 240,000 miles distance to the moon alone, one way."

There appears to be no confusion between miles and kilometers in this statement. The inconsistency I see is in the mission times quoted so far. From the sim, it will be three days to the moon, and another week to the 400k mile apogee. It would be a further week for the return to earth, nearly 17 days altogether.

The Grey Dragon is going to be limited in available ΔV compared to Apollo, so I suspect this 'rollercoaster' mission profile is designed to do something spectacular (a new altitude record) with limited resources. This won't be the first Dragon 2 mission, so although certainly risky, it would be a logical incremental step.

How long does it take to get to a 300k mile apogee and back?

“This would be approximately a weeklong mission, and it would skim the surface of the moon, go quite a bit farther out into deep space and then loop back to Earth,” Musk said. “I’m guessing, probably distance wise, maybe 300,000 or 400,000 miles.”

http://www.cbsnews.com/news/spacex-moon-mission-planned-for-2018/

Offline Proponent

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Re: SpaceX Falcon Mission Simulations
« Reply #34 on: 03/27/2017 09:24 PM »
How long does it take to get to a 300k mile apogee and back?

The orbital period of a 0 x 300,000-mi orbit is about 9.9 days.

Quote
“This would be approximately a weeklong mission, and it would skim the surface of the moon, go quite a bit farther out into deep space and then loop back to Earth,” Musk said. “I’m guessing, probably distance wise, maybe 300,000 or 400,000 miles.”

http://www.cbsnews.com/news/spacex-moon-mission-planned-for-2018/

Both that CBS article and Jeff Foust's piece in SpaceNews specifically mention a free-return trajectory and a week-long trip.  Foust does not mention 300,000 miles.

My guess is that the 300,000-mile figure is just wrong (I know Musk said it, but....), and the intended profile is a low-altitude free-return.
« Last Edit: 03/27/2017 09:50 PM by Proponent »

Offline deruch

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Re: SpaceX Falcon Mission Simulations
« Reply #35 on: 03/28/2017 04:25 AM »
Could the discrepancy between miles vs. km be explained by a mix up between "altitude" and total distance traveled?
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Re: SpaceX Falcon Mission Simulations
« Reply #36 on: 03/28/2017 11:25 AM »
How long does it take to get to a 300k mile apogee and back?

I've refactored the sim for a 300k mile (480,000km) apogee. If Grey Dragon arrives at the moon in 3 days, at a pericynthion of about 16,500kms, the gravity assist then kicks it to 480,000kms right on 7 days after TLI. At that point, there needs to be a 'boostback' burn to shorten the perigee of the Earth orbit for re-entry, which would take place in another 5 days.

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Re: SpaceX Falcon Mission Simulations
« Reply #37 on: 04/01/2017 05:00 AM »
I've analysed the SES-10 launch profile as best I can from the broadcast footage. The S2 velocity and altitude is complete up to 620 seconds, but the rest has only a few data points.

Firstly, to get the simulation to match the data, I had to throttle back the first stage slightly more than the previous three missions. Assuming a nominal 7,607 kN thrust at sea level, the burn started at 88.5%, (CRS-10 91.5%), dropped slightly for max Q, then increased to 90% (c.f. 92.5%) up until the 150 second mark, where acceleration was limited to 4Gs.

For the second stage, I had the same issue that LouScheffer noted recently, i.e. that 100% thrust is not sufficient to produce the second stage performance we are seeing recently. I had to throttle to 106%, and even then had trouble matching the curve for a while. From the 330 second mark, 100% thrust seemed correct, until the 500 second mark, where acceleration was again limited to 4Gs until SECO.

The first stage landing was interesting because there was no boostback burn. From the video I had a fairly good idea of the orientation of the booster, when the entry burn started and finished, and when the landing burn started. I also knew when the booster went transonic. When I plugged what data I had into the sim, I got the profile attached below. It was interesting that Elon was talking after the launch about using the new titanium grid fins to enhance the glide of the booster (which would also give it more time to slow aerodynamically), because if the sim is correct, then to some extent that's what they've done here. The barge would have had to have been about 600kms downrange for this profile to be feasible.

Edit: after closer inspection of the broadcast videos from the 1:40 mark, SpaceX have introduced a first stage pitch up manoeuvre. If I include this manoeuvre in the simulation, the altitude and velocity match the broadcast data. However, most of the glide on descent now occurs between the entry and landing burns.
« Last Edit: 04/02/2017 11:33 AM by OneSpeed »

Re: SpaceX Falcon Mission Simulations
« Reply #38 on: 04/03/2017 03:59 PM »
Flight Club's recreation of SES-10 is up here:

All data (plots and 3D view) are here: https://www.flightclub.io/results/?code=SS10
The live replay can be watched here: https://www.flightclub.io/world/?code=SS10&w=2

The big difference between my simulation and OneSpeed's above is that I'm not using the uprated Merlin 1D thrust figures - my 1D's are still at 756kN instead of 845kN. However, with this thrust figure at close to 100% (dropped to 90% for MaxQ), my trajectory has still matched the webcast data closely.

So who knows what to think. Do we have a collection of Merlin thrust vs. Mission anywhere? Did this mission definitely use the 845kN version?

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #39 on: 04/03/2017 11:38 PM »
Flight Club's recreation of SES-10 is up here:

All data (plots and 3D view) are here: https://www.flightclub.io/results/?code=SS10
The live replay can be watched here: https://www.flightclub.io/world/?code=SS10&w=2

The big difference between my simulation and OneSpeed's above is that I'm not using the uprated Merlin 1D thrust figures - my 1D's are still at 756kN instead of 845kN. However, with this thrust figure at close to 100% (dropped to 90% for MaxQ), my trajectory has still matched the webcast data closely.

So who knows what to think. Do we have a collection of Merlin thrust vs. Mission anywhere? Did this mission definitely use the 845kN version?

I have seen no evidence at all that they are actually flying the uprated Merlin yet, and both your and OneSpeed's simulations are good evidence that they are not.

Online Flying Beaver

Re: SpaceX Falcon Mission Simulations
« Reply #40 on: 04/12/2017 09:43 PM »
Been playing around in Flight Club recently (Getting to orbit with a F9 from scratch on the first attempt was pretty surreal, thanks KSP!) and I've come up with this rather interesting profile.

10,000kg payload to 32.5deg 250km by 220km orbit with second stage burn to depletion.

MECO at t+145s, 1.5km/s.

First stage boostback to LZ-1, with only 99km apogee.

Extremely low entry force on S1 (only slightly higher than MaxQ on ascent), with extended (20s) entry burn.

Seems like a pretty nice time for the first stage. Are there any obvious issues with it though?

https://www.flightclub.io/results/?id=0d9a43bc-328a-481d-9cbc-22321c3f95d3&code=NONE
« Last Edit: 04/12/2017 09:44 PM by Flying Beaver »
Saw OG-2 Booster Land in person 21/12/2015.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #41 on: 04/13/2017 12:35 PM »
...10,000kg payload to 32.5deg 250km by 220km orbit with second stage burn to depletion.
MECO at t+145s, 1.5km/s.
First stage boostback to LZ-1, with only 99km apogee...

Seems like a pretty nice time for the first stage. Are there any obvious issues with it though?

CRS-10 was the most recent RTLS profile: MECO at T+143s, 1.675km/s. The payload was about 7,000kg, but if I re-run my CRS-10 sim with your payload, I only see a reduction of about 25m/s at MECO. Are you sure about your 1.5km/s value, two seconds later? What throttle settings are you using?

Re: SpaceX Falcon Mission Simulations
« Reply #42 on: 04/13/2017 01:35 PM »
https://www.flightclub.io/results/?id=0d9a43bc-328a-481d-9cbc-22321c3f95d3&code=NONE

If you visit the link posted, you'll see there's a graph of throttle settings over time. The MaxQ throttle looks like 70% from T+50 to T+75. Bit extreme, I reckon, but probably explains the dV deficiency.

Seems like a pretty nice time for the first stage. Are there any obvious issues with it though?

The main problem I have is that your landing burn lasts for almost 90s. The retropropulsion through the entire lower atmosphere is the reason why the aerodynamic pressure on descent is so low, but this is extremely inefficient! Also the landing burn is at about 50% throttle the entire time which is also very inefficient. Best to do as short a landing burn as possible to minimize gravity losses - so you wanna maximise aerobraking and burn at a high throttle setting when you do start the burn.

Kudos getting to orbit on the first attempt though, that's pretty impressive :)

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Re: SpaceX Falcon Mission Simulations
« Reply #43 on: 04/13/2017 09:48 PM »
https://www.flightclub.io/results/?id=0d9a43bc-328a-481d-9cbc-22321c3f95d3&code=NONE

If you visit the link posted, you'll see there's a graph of throttle settings over time. The MaxQ throttle looks like 70% from T+50 to T+75. Bit extreme, I reckon, but probably explains the dV deficiency.

Seems like a pretty nice time for the first stage. Are there any obvious issues with it though?

The main problem I have is that your landing burn lasts for almost 90s. The retropropulsion through the entire lower atmosphere is the reason why the aerodynamic pressure on descent is so low, but this is extremely inefficient! Also the landing burn is at about 50% throttle the entire time which is also very inefficient. Best to do as short a landing burn as possible to minimize gravity losses - so you wanna maximise aerobraking and burn at a high throttle setting when you do start the burn.

Kudos getting to orbit on the first attempt though, that's pretty impressive :)

But it is still 10tons to LEO, with RTLS, no matter how inefficient the landing burn.

Would the reason for SpaceX not using a profile like this be about having a buffer for second stage performance?
Saw OG-2 Booster Land in person 21/12/2015.

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Re: SpaceX Falcon Mission Simulations
« Reply #44 on: 04/13/2017 11:34 PM »
But it is still 10tons to LEO, with RTLS, no matter how inefficient the landing burn.

Would the reason for SpaceX not using a profile like this be about having a buffer for second stage performance?

That, and if you are launching Dragon to the ISS (which is probably why you can afford RTLS), your apogee should be at least 400kms, and your orbital inclination around 51.64°.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #45 on: 05/02/2017 12:15 PM »
A preliminary S1 profile for NROL-76. Thrust still appears to be 90% of rated, so perhaps not Block 4.

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Re: SpaceX Falcon Mission Simulations
« Reply #46 on: 05/02/2017 12:19 PM »
I already did analysis here and here, if you want to compare and contrast.

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Re: SpaceX Falcon Mission Simulations
« Reply #47 on: 05/02/2017 12:25 PM »
A preliminary S1 profile for NROL-76. Thrust still appears to be 90% of rated, so perhaps not Block 4.

Interesting. Did you subtract the acceleration caused by gravity? Also, what is the jump in velocity near 245s and 337s?

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Re: SpaceX Falcon Mission Simulations
« Reply #48 on: 05/02/2017 12:35 PM »
I already did analysis here and here, if you want to compare and contrast.

Thanks, I should explain what I've done, perhaps it's slightly different. Using the telemetry as a guide, I've created a simulation of the launch profile. Then I've output the velocity, altitude and acceleration from the sim to a spreadsheet. So, the acceleration is new information. Other parameters like thrust, orientation, dynamic pressure and heating are also available, but I'm still refining this particular sim, there was so much new information in the broadcast!

Interesting. Did you subtract the acceleration caused by gravity? Also, what is the jump in velocity near 245s and 337s?

Yes, relative acceleration. The two jumps are an artefact of the sim. Above 150kms in altitude it considers the velocity to be no longer including the earths rotation. Well spotted!

Offline Welsh Dragon

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Re: SpaceX Falcon Mission Simulations
« Reply #49 on: 05/02/2017 12:57 PM »
I already did analysis here and here, if you want to compare and contrast.

Thanks, I should explain what I've done, perhaps it's slightly different. <snip>

Ah yes, didn't realise that, good point. Mine are just straight plots from the telemetry.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #50 on: 05/02/2017 01:05 PM »
Mine are just straight plots from the telemetry.

You've also derived acceleration though, and very interesting to see the noise in that data. It is quite a challenge working out what information to discard.

Offline Welsh Dragon

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Re: SpaceX Falcon Mission Simulations
« Reply #51 on: 05/02/2017 01:33 PM »
Yes, the acceleration data is quite noisy, when going down to single second resolution. It might be possible to get better data out of the stream, as the velocity data updates multiple times a second (altitude data is much coarser). Conceivably, you could take multiple measurements per second and average them out, to smooth out the noise a bit. That's a lot of work though, and I don't know what it'll add. We're already working off figures that have gone through a lot of filtering and lag etc before they hit the stream, so the accuracy is going to be limited regardless.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #52 on: 05/02/2017 06:04 PM »
How do you guys extract data from the webcast? Perform an OCR frame by frame to extract the speed and altitude?

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Re: SpaceX Falcon Mission Simulations
« Reply #53 on: 05/02/2017 06:12 PM »
I literally sit there and copy the numbers off manually. Every 5 seconds for the whole flight, every second for the burns.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #54 on: 05/02/2017 09:45 PM »
I literally sit there and copy the numbers off manually. Every 5 seconds for the whole flight, every second for the burns.

Similar. I then re-run the sim many times tweaking throttle, orientation and payload until the data points line up as close as I can get. It's interesting how often this reveals constant throttle settings for extended periods. The simulator is then effectively applying a very strong filter to the noise in the source data.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #55 on: 05/02/2017 10:33 PM »
I did the automated OCR in the past for a whole different application. I will try this thing...

Offline Welsh Dragon

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Re: SpaceX Falcon Mission Simulations
« Reply #56 on: 05/03/2017 06:55 AM »
Sounds like it could be very useful.  I'd love to hear how you got on.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #57 on: 05/03/2017 08:17 AM »
If the system allows the attachment, I have created a CSV file with the data. It's completely raw and it does NOT have a timestamp, just velocity and altitude data, for each line. Timestamp can be inferred as each frame is 1/29.970 of a second (don't get me started). Please suggest a format for the timestamp I can add it.


Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #58 on: 05/03/2017 08:31 AM »
How I did it:
- download the Youtube video of the launch. It's probably illegal/against the terms of use of Youtube in some jurisdictions.
- inspect the file to find T start and T end of the flight
- cut it out with ffmpeg:
ffmpeg -ss 11:59 -i nrol.mp4 -t 9:04 -vcodec copy -acodec copy cut.mp4
- crop out the relevant data on screen and save individual images of each frame:
ffmpeg -i cut.mp4 -filter:v "crop=192:24:1040:140" img/frame%05d.png
- at this point we need to enhance the images so that the OCR program has an easier time decodign them: I figured that pushing the levels and inverting the image would help:
for i in *.png; do convert $i -threshold 40% -negate proc/$i; done
- now, gocr works better if instead of giving individual images, we group several, so it can create some sort of internal database and other second order effects; however, we have more than 16k files and if we really put them together we get a huge image and gocr will runaway. So I decided to analyze 1000 images at a time. Also, by specifying we want only digits and the decimal point, and lowering the confidence threshold, we get an acceptable result:
for i in `seq -w 0 16`; do echo $i; convert -append frame${i}*.png table.png && gocr -a 80 -C "0123456789." table.png >> list.txt; done
- at this point I had to manually correct a bunch of non-recognized characters "_" but it just took few minutes
- create the final CSV:
while read -r a b; do echo "$a,$b"; done <list.txt >NROL76.txt


All of the above done in pretty much any classic Linux environment with bash gocr ffmpeg and imagemagick
« Last Edit: 05/03/2017 08:37 AM by manoweb »

Offline Welsh Dragon

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Re: SpaceX Falcon Mission Simulations
« Reply #59 on: 05/03/2017 10:48 AM »
Cool, seems to match well with the data I got. Be interesting to look at the burns in more detail, to see whether averaging frames can help bring the noise down a bit.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #60 on: 05/03/2017 04:24 PM »
Do you think it makes sense to add a timestamp column? It could contain the seconds since T0. Also, it would be trivial to do that in the spreadsheet just by adding 0.033s (or, 0.0333667000334 as it is 1/29.97 of a second in theory) on each line, so not sure it's worth it

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Re: SpaceX Falcon Mission Simulations
« Reply #61 on: 05/11/2017 11:24 AM »
This is a simulation of the NROL-76 launch created with NSF user zlynn1990. The broadcast gave us the best view yet into the first stage recovery process with amazing footage and telemetry data. It allowed us to tweak a lot of previously unknown aerodynamic properties for the first stage during the recovery process. This simulation follows the webcast telemetry data very closely throughout the launch and landing process.

This video also shows a very speculative simulation of how the fairing was landed in the ocean. We have very little information here, so everything happening is a complete guess. A supersonic ballute is deployed around mach 6 to help stabilize the fairing while re-entering the atmosphere. Nitrogen thrusters are used to maintain and correct attitude. Once the fairing is below 100 m/s a parafoil is deployed. This helps guide the fairing to the final landing zone (a bouncy castle like setup). Once the fairing is nearly above the ocean it flares up to help reduce velocity and essentially stalls into the landing structure.

« Last Edit: 05/11/2017 11:25 AM by OneSpeed »

Offline IainMcClatchie

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Re: SpaceX Falcon Mission Simulations
« Reply #62 on: 05/12/2017 01:55 AM »
Fabulous stuff.  Thank you!

Do I understand correctly that this was NOT a "block 5" launch?

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #63 on: 05/12/2017 02:25 AM »
People are not even sure it was a Block 4, whatever that means...

Offline deruch

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Re: SpaceX Falcon Mission Simulations
« Reply #64 on: 05/12/2017 03:15 AM »
It took me multiple rewatches to figure out what was going on at ~5:47s when the video seemed to suggest that the fairing half "throttled down" during its reentry.  I was stuck trying to understand what sort of propulsion system you thought it had on it until I finally caught that the "throttle down" was connected to Stage 2.  Oops.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #65 on: 05/16/2017 08:48 AM »
OCR data, chart and spreadsheet, for SpaceX's Inmarsat-5
« Last Edit: 05/16/2017 08:50 AM by manoweb »

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #66 on: 05/16/2017 02:09 PM »
OCR data, chart and spreadsheet, for SpaceX's Inmarsat-5
Excellent!

Can you overlay SES-10 on the same graph, or attach the spreadsheet?

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #67 on: 05/16/2017 04:06 PM »
I have not done SES-10. This launch was special in the fact it was expandable so they broadcast the totality of the "second stage telemetry" from launch to SECO... Let me have a look at SES-10 video

Offline gospacex

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Re: SpaceX Falcon Mission Simulations
« Reply #68 on: 05/16/2017 04:08 PM »
OCR data, chart and spreadsheet, for SpaceX's Inmarsat-5

Great! Can you graph acceleration?

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #69 on: 05/16/2017 04:43 PM »
gospacex, I think it should be easy once you have time and velocity data. Right now I'm doing OCR of SES-10. Maybe somebody good with spreadsheets (I am "so-so", I used to be good with Lotus 1-2-3, but I haven't practiced much since then) can share the effort and add acceleration (jerk?) data? :D

envy887 I did not realize the SES-10 (and older!) webcasts have full stage2 telemetry. The only exception was NROL76, the one I started with, that had full stage1 telemetry, that was my source of confusion.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #70 on: 05/17/2017 12:14 AM »
This is SES10 data and graphic:

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #71 on: 05/17/2017 12:42 AM »
This is the comparison between SES-10 and Inmarsat-5

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #72 on: 05/17/2017 01:06 AM »
This is the comparison between SES-10 and Inmarsat-5

Fantastic, thank you!

You can clearly see the throttle-down for trans-sonic is at around 320 m/s for each. But Inmarsat hits transsonic earlier and higher, and accelerates through it faster than SES-10. The Inmarsat booster is going higher and accelerating faster all the way to staging despite pushing a larger payload.

SES-10 is known to be a v1.2 Block 1 booster, so Inmarsat definitely was upgraded. But was it upgraded from NROL-76? The first stage telemetry could show the difference. It would be awesome if you could overlay that data.

Interestingly, the Mvac doesn't appear to have been upgraded. The lower acceleration of the second stage is explained by the higher payload mass.

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #73 on: 05/17/2017 03:25 AM »
I have created a small github project; this is an application that "helps" reviewing the data from the OCR phase. It's at its initial commit, it serves a purpose, but it's far from being "usable" by the masses :D

However if anybody is interested in using it, please let me know.

https://github.com/alesanmanoweb/SpaceXocr

Offline TrueBlueWitt

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Re: SpaceX Falcon Mission Simulations
« Reply #74 on: 05/17/2017 07:12 AM »
This is the comparison between SES-10 and Inmarsat-5

Fantastic, thank you!

You can clearly see the throttle-down for trans-sonic is at around 320 m/s for each. But Inmarsat hits transsonic earlier and higher, and accelerates through it faster than SES-10. The Inmarsat booster is going higher and accelerating faster all the way to staging despite pushing a larger payload.

SES-10 is known to be a v1.2 Block 1 booster, so Inmarsat definitely was upgraded. But was it upgraded from NROL-76? The first stage telemetry could show the difference. It would be awesome if you could overlay that data.

Interestingly, the Mvac doesn't appear to have been upgraded. The lower acceleration of the second stage is explained by the higher payload mass.

Let's not all forget that SES 10 S1 had a lot more mass going uphill with Landing legs and Grid Fins, plus whatever other re-usability feature on First stage weren't there for Inmarsat..  Do those more than offset the heavier mass of the Satellite in terms of First Stage performance?

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #75 on: 05/17/2017 02:12 PM »
Let's not all forget that SES 10 S1 had a lot more mass going uphill with Landing legs and Grid Fins, plus whatever other re-usability feature on First stage weren't there for Inmarsat..  Do those more than offset the heavier mass of the Satellite in terms of First Stage performance?

The landing legs and grid fins are certainly a factor, and SES-10 may not be the best point of comparison. It launched at only 87.5% of rated thrust, which makes sense when you consider it was the first ever re-use of a first stage, and SpaceX would have been very keen to give it the best chance of success. Perhaps Echostar 23 would be a better reference? Anyway, Inmarsat-5 appears to have launched at 90% of rated thrust, and although it went to 94% after Max Q, I'm not sure we've seen a block 4 yet. Interestingly, the second stage appears to have reverted from 107% to 98% of rated thrust for the first minute or so, and none of the stages have used any high AoA manoeuvres this time. Apologies for the step in velocity at 150kms.
« Last Edit: 05/17/2017 02:13 PM by OneSpeed »

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #76 on: 05/17/2017 04:03 PM »
Let's not all forget that SES 10 S1 had a lot more mass going uphill with Landing legs and Grid Fins, plus whatever other re-usability feature on First stage weren't there for Inmarsat..  Do those more than offset the heavier mass of the Satellite in terms of First Stage performance?

The landing legs and grid fins are certainly a factor, and SES-10 may not be the best point of comparison. It launched at only 87.5% of rated thrust, which makes sense when you consider it was the first ever re-use of a first stage, and SpaceX would have been very keen to give it the best chance of success. Perhaps Echostar 23 would be a better reference? Anyway, Inmarsat-5 appears to have launched at 90% of rated thrust, and although it went to 94% after Max Q, I'm not sure we've seen a block 4 yet. Interestingly, the second stage appears to have reverted from 107% to 98% of rated thrust for the first minute or so, and none of the stages have used any high AoA manoeuvres this time. Apologies for the step in velocity at 150kms.

I pulled 10-second intervals off the webcasts for both I5F4 and Echostar 23. The difference in burn time appears to be close to the difference in acceleration, suggesting I5F4 had about 2% additional prop load but ran at the same thrust except around transonic.
« Last Edit: 05/17/2017 05:21 PM by envy887 »

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #77 on: 05/17/2017 06:13 PM »
The landing legs and grid fins are certainly a factor, and SES-10 may not be the best point of comparison. It launched at only 87.5% of rated thrust, which makes sense when you consider it was the first ever re-use of a first stage, and

Out of curiosity, how did you make this graphic?
1) Did you use your own data or you used the one I provided (I am trying to see if my work is actually useful to people :) )
2) How did you graph the acceleration (this is basic spreadsheet usage, I know, but I'm still curious)
3) How did you calculate the thrust, this one seems tricky

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #78 on: 05/17/2017 06:15 PM »
I pulled 10-second intervals off the webcasts for both I5F4 and Echostar 23. The difference in burn time appears to be close to the difference in acceleration, suggesting I5F4 had about 2% additional prop load but ran at the same thrust except around transonic.

Hello Envy887, pulling values manually from the video seems a pretty boring task... If you need just point me to which mission you like and I can extract the telemetry data easily, all ~16000 points of it. In the previous posts I always provided either a CSV file or LibreOffice spreadsheet, is the format not good enough? I'd rather spend time on the telemetry extraction tool, and see you guys do the spreadsheet analysis :D

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #79 on: 05/17/2017 06:27 PM »
I pulled 10-second intervals off the webcasts for both I5F4 and Echostar 23. The difference in burn time appears to be close to the difference in acceleration, suggesting I5F4 had about 2% additional prop load but ran at the same thrust except around transonic.

Hello Envy887, pulling values manually from the video seems a pretty boring task... If you need just point me to which mission you like and I can extract the telemetry data easily, all ~16000 points of it. In the previous posts I always provided either a CSV file or LibreOffice spreadsheet, is the format not good enough? I'd rather spend time on the telemetry extraction tool, and see you guys do the spreadsheet analysis :D

I haven't seen data for Echostar-23, a CSV of that data would be great :D

Offline manoweb

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Re: SpaceX Falcon Mission Simulations
« Reply #80 on: 05/17/2017 07:39 PM »
Yeah so far I've done NROL-76 (first stage), Inmarsat-5, SES-10. I can do Echostar-23. I think I will do all launches in 2017 now that I have built my tool. I will include also the timestamps

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #81 on: 06/05/2017 01:51 PM »
Here is a sim of the CRS-11 first stage profile.

Points of interest include:
1. The booster appears to launch at slightly less than full throttle (84% of the published block 5 figures) before throttling up to 91% of block 5 after about 5 seconds.
2. What appears to be a minimum thrust single engine ullage burn starting half way through the flip at 2:40.
3. A 1:3:1 engine entry burn at 6:10.


Offline hkultala

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Re: SpaceX Falcon Mission Simulations
« Reply #82 on: 06/05/2017 02:54 PM »
Highest throttle at boostback burn.

So they do not want to risk the payload / want to maximize reliability when stage 2 and payload are attached by using it with "full throttle", and are only using full throttle for boostback. 

(but propably they would use full throttle if they would lose one engine, to compensate for the loss of thrust)

And high T/W is very important for the boostback burn, as it's flying away from the launch & landing site and the faster the boostback burn is, the shorter distance it has to travel.

« Last Edit: 06/05/2017 02:57 PM by hkultala »

Offline deruch

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Re: SpaceX Falcon Mission Simulations
« Reply #83 on: 06/08/2017 04:28 AM »
Points of interest include:

2. What appears to be a minimum thrust single engine ullage burn starting half way through the flip at 2:40.


I think this is related to how fast they are trying to do the flips now.  With all the authority of the burning engine, they can afford to do a higher rotational speed flip and still ensure that they can maintain enough prop at the bottom of the tanks and that they can handle any off-axis impulses from any sloshing.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #84 on: 07/01/2017 08:19 AM »
Here is a sim of BulgariaSat-1. The telemetry for this mission and the next is not complete, but there are similar missions that help fill in the gaps, in this case SES-10.

This mission was of course most notable for the first coast-to-coast re-use of a booster, but the profile had a couple of points of interest as well.

1. As per SES-10, the high AoA of the entire rocket from the 1:40 mark. Does anyone know why this manoeuvre has only been used for these particular GTO satellite missions?

2. The initial S2 orbit is about 160 x 480kms, and the GTO burn occurs at about 250kms. I've seen it suggested that ideally such a burn should occur at perigee, where velocity is highest, minimising the ΔV requirement. Does anyone have any insight into why the GTO burn was done this particular way?

3. Elon Musk: 'Rocket was suddenly slammed sideways right before landing. Heavy gust or something malfunctioned onboard. Reviewing telemetry.' I've attempted to model the effect of a heavy gust at the 8:30 mark, at about 400m altitude.


Offline Rebel44

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Re: SpaceX Falcon Mission Simulations
« Reply #85 on: 07/06/2017 08:31 PM »
Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GEO (with some reserve for sending 2nd stage to graveyard orbit)
« Last Edit: 07/06/2017 08:57 PM by Rebel44 »

Online jpo234

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Re: SpaceX Falcon Mission Simulations
« Reply #86 on: 07/06/2017 08:32 PM »
Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GTO (with some reserve for sending 2nd stage to graveyard orbit)
There are no available data on Block 5 right now.

Offline Rebel44

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Re: SpaceX Falcon Mission Simulations
« Reply #87 on: 07/06/2017 08:55 PM »
Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GTO (with some reserve for sending 2nd stage to graveyard orbit)
There are no available data on Block 5 right now.

There is posted performance on SpaceX website for LEO and GTO (and few others) which based on what we know appears to be expected block 5 (expendable) performance
22 800 kg to LEO
 8 300 kg to GTO

Even estimated GEO performance based on block 3 performance would be appreciated.
« Last Edit: 07/06/2017 08:56 PM by Rebel44 »

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #88 on: 07/06/2017 08:56 PM »
...
There are no available data on Block 5 right now.

The listed performance on SpaceX website is for a Block 5 launch. Block 3/4 will be retired long before anyone buying a launch right now gets to the pad.

Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GTO (with some reserve for sending 2nd stage to graveyard orbit)

Expendable Block 3/4 mix to GTO is what you just saw yesterday: 6781 kg to GTO, slightly supersync. There's no need for a GTO graveyard orbit, the upper stages decay quickly. Expendable block 5 is supposed to ptu 8300 kg to GTO.

If you mean direct to GSO, then my my calculations Block 3/4 will put about 1200 2100kg and Block 5 about 4000 3000 kg direct to GSO. The spacecraft RCS can probably handle the move to graveyard orbit, it's a >1 second burn on a 38% throttled MVac.

Edit: poor recollection of previous calculations, corrected.
« Last Edit: 07/06/2017 09:09 PM by envy887 »

Offline Rebel44

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Re: SpaceX Falcon Mission Simulations
« Reply #89 on: 07/06/2017 08:58 PM »

Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GTO (with some reserve for sending 2nd stage to graveyard orbit)

If you mean direct to GSO, then my my calculations Block 3/4 will put about 1200 kg and Block 5 about 4000 kg direct to GSO. The spacecraft RCS can probably handle the move to graveyard orbit, it's a >1 second burn on a 38% throttled MVac.

Yeah, I mixed up GTO and GEO
Thanks for the estimate!

Offline envy887

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Re: SpaceX Falcon Mission Simulations
« Reply #90 on: 07/06/2017 09:08 PM »

Can someone here please calculate from available data what is performance of expendable F9 1.2 block 3 and expendable F9 1.2 block 5 to GTO (with some reserve for sending 2nd stage to graveyard orbit)

If you mean direct to GSO, then my my calculations Block 3/4 will put about 1200 kg and Block 5 about 4000 kg direct to GSO. The spacecraft RCS can probably handle the move to graveyard orbit, it's a >1 second burn on a 38% throttled MVac.

Yeah, I mixed up GTO and GEO
Thanks for the estimate!

Certainly, but I'm afraid I recalled wrong above - I was calculating in pounds and for FH a few days ago :D

Rechecking my math, Block 3/4 gets 6800 kg to GTO, with a stage mass of 4500 kg and Isp of 348, that is about 2100 kg to GSO.
Block 5 gets 8300 kg to GTO, with same stage and Isp that is about 3000 kg to GSO.

LOX boiloff will reduce this somewhat, but I don't have a good way to estimate that.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #91 on: 07/09/2017 04:52 AM »
Here is a 'compari-sim' between the Inmarsat-5 F4 and Intelsat-35e mission profiles. They are very similar in many ways, but:

1. The relative effect of the S1 throttle and shutdown profiles is interesting to view.
2. The sims generated the following post SECO-2 S2 masses, with and without a 200Kg allowance for plane change:
MissionNo plane changeWith plane change
Iridium-5 F45.5mT5.3mT
Intelsat-35e5.3mT5.1mT
I'd assumed both missions were burn to depletion, but perhaps some of the difference can be attributed to a variation in fuel densification between the missions?

« Last Edit: 07/09/2017 06:03 AM by OneSpeed »

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Re: SpaceX Falcon Mission Simulations
« Reply #92 on: 08/15/2017 03:06 PM »
Here is a comparison of CRS-11 and 12. Although Hans Koenigsmann suggested that the CRS-11 and 12 profiles would be very similar, there are some differences.

Edit: To summarise:
1. From launch to throttle back for Max-Q is almost identical. The small difference is accounted for by the extra 200kgs of payload.
2. CRS-12 stays throttled back for longer than CRS-11, perhaps to minimize stress on the rocket and/or the payload?
3. CRS-12 stages lower and slower, and its boostback burn results in a slightly lower S1 apogee.
4. CRS-12 compensates for the reduced uprange ballistic trajectory by using a slightly higher AoA to enhance glide after the entry burn. Although the highest AoA so far for a RTLS profile, ASDS profiles have used similar AoA in the past.
5. CRS-12 also uses a shorter and higher thrust S2 burn to compensate for the payload and ΔV differences.

« Last Edit: 08/16/2017 02:02 AM by OneSpeed »

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #93 on: 08/27/2017 04:17 AM »
The Formosat-5 mission had an unusually light payload of 475kg, and so there was a lot of excess ΔV available. A conventional mission profile would require at least two S2 burns: first to an elliptical orbit, and a second circularisation burn at apogee. But Formosat-5 was delivered to a 730km x 717km orbit with a single S2 burn. So what then was the mass penalty for this? Here is a compari-sim between Formosat-5 and a modified BulgariaSat profile, also with a 475kg payload, and polar injection to a 725km circular orbit.


Offline titusou

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Re: SpaceX Falcon Mission Simulations
« Reply #94 on: 09/10/2017 04:06 PM »
The Formosat-5 mission had an unusually light payload of 475kg, and so there was a lot of excess ΔV available. A conventional mission profile would require at least two S2 burns: first to an elliptical orbit, and a second circularisation burn at apogee. But Formosat-5 was delivered to a 730km x 717km orbit with a single S2 burn. So what then was the mass penalty for this? Here is a compari-sim between Formosat-5 and a modified BulgariaSat profile, also with a 475kg payload, and polar injection to a 725km circular orbit.

This, by far, is the best explanation (and easiest) on how SpaceX pull off circular orbit with single S2 burn.

Superb work OneSpeed!

Titus

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Re: SpaceX Falcon Mission Simulations
« Reply #95 on: 09/11/2017 01:30 PM »
The FCC STA for mission 1346 (the FH Demo mission) has the coordinates for the ASDS landing of the core booster about 340kms downrange from LC-39A. This corresponds with an extremely lofted trajectory, not unlike that used for Formosat-5. In the Formosat-5 case, a single S2 burn took the satellite to a circular orbit. What could FH achieve with a similar profile?

Here is a speculative FH simulation bounded by an ASDS landing about 340kms downrange, and a 6mT payload, the same as advertised by SpaceX to GTO. By tuning the orientation towards the end of the S2 burn, it is possible to set the perigee of the orbit achieved to a suitable re-entry altitude about 5.5 hours after lift-off. Entry velocity would be about 10km/s.


Offline karki

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Re: SpaceX Falcon Mission Simulations
« Reply #96 on: 09/11/2017 11:01 PM »
The FCC STA for mission 1346 (the FH Demo mission) has the coordinates for the ASDS landing of the core booster about 340kms downrange from LC-39A. This corresponds with an extremely lofted trajectory, not unlike that used for Formosat-5. In the Formosat-5 case, a single S2 burn took the satellite to a circular orbit. What could FH achieve with a similar profile?

Here is a speculative FH simulation bounded by an ASDS landing about 340kms downrange, and a 6mT payload, the same as advertised by SpaceX to GTO. By tuning the orientation towards the end of the S2 burn, it is possible to set the perigee of the orbit achieved to a suitable re-entry altitude about 5.5 hours after lift-off. Entry velocity would be about 10km/s.



Are you assuming SpaceX will be testing S2 survivability at GTO reentry velocity? What's the consensus around here on a non-standard S2 being considered an adequate test of Falcon Heavy in the eyes of the customer, either official (for things like DoD requirements) or unofficial (general PR. customers "feel good" about it)?

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #97 on: 09/16/2017 01:57 AM »
SpaceX have indicated that they would like to recover the Falcon Heavy Demo second stage, but the difficulty of this task cannot be underestimated. Following on from the previous sim, Earth EDL at 10km/s will generate heat over 10x greater than S1 recovery. With its mass concentrated at the tail, the Falcon S2 would not inherently be passively stable, so providing sufficient control authority would be challenging. But what if the Falcon S2 could be modified (as others have suggested) to have comparable dynamics to the BFS, and still support existing payloads? Here is a speculative 'Frankenstein' approach:

1. An overlapping clamshell nose cone that would not prevent the use of the current fairings and PAF.
2. Some ballast near the nose, (a toroid?) sufficient to make the ship passively stable.
3. Three strakes of a similar form to the BFS strakes, but containing extra nitrogen tanks and thrusters. The strakes could also have the BFS split body flaps mentioned (but not so far visualised) for additional control authority.
4. Additional TPS, and a shroud to protect the Merlin Vacuum engine during re-entry.
5. The sim shows that for an S2 dry mass of 6mT, the terminal velocity is well under 100m/s. This means that a parafoil (as is likely for the v2.0 fairings) would be a viable option for landing. There would then be no need for supersonic retropropulsion or a propulsive landing (which would have required additional sea level engines and fuel). The parafoil (and perhaps a drogue chute) could be housed in the dorsal strake, just above and behind the centre of gravity.

For a typical ISS mission profile, the Falcon S2 might re-enter after a single orbit and land at a large open space like Edwards Air Force base. Here then is a simulation of such an Earth EDL profile (note: I don't have a 3D model for the 'Frankenstage', so I've utilised a cargo BFS model where roll is required).


Offline john smith 19

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Re: SpaceX Falcon Mission Simulations
« Reply #98 on: 09/17/2017 07:51 PM »
What are you using as the simulator?
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Online OneSpeed

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Re: SpaceX Falcon Mission Simulations
« Reply #99 on: 09/18/2017 02:13 AM »
What are you using as the simulator?

The program is called SpaceSim. It is written in C# and you can download it and the source code here: https://github.com/zlynn1990/SpaceSim
« Last Edit: 09/18/2017 09:53 PM by OneSpeed »

Offline john smith 19

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Re: SpaceX Falcon Mission Simulations
« Reply #100 on: 09/18/2017 04:45 PM »
What are you using as the simulator?

The program is called SpaceSim. It is written in C# and you can download it and the source code here: https://github.com/zlynn1990/SpaceSim
Noted.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline IainMcClatchie

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Re: SpaceX Falcon Mission Simulations
« Reply #101 on: 09/18/2017 08:15 PM »
That's some nice work.

I don't mean to look a gift horse in the mouth, but I'll note that all the zooming in and out seems less than ideal.  You might have two views simultaneously, one close up showing the spacecraft attitude, and one far away showing the trajectory.

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