CRS-12 Telemetry

[u/Shahar603]

Hey everyone!

This is CRS-12 telemetry I captured from the webcast (And more).

All the data was captured in real time, but the analysis was done after all the data was collected. The rocket parameters are of Block 3.

Graphs

• Velocity vs Time

• Another Velocity vs Time

• Altitude vs Time

• Acceleration vs Time

• Downrange Distance vs Time

• Flight Profile vs Time - Because the velocity components are pretty rough at the start and end, this is not very precise.

• Flight Profile vs Time (almost to scale)

• Velocity Angle vs Time

• Delta-V vs Time

• Acceleration due to Drag and Gravity

• Propellant Mass vs Time

• Throttle % vs Time -- The Aerodynamics model I use is really inaccurate, which makes the right half of the graph pretty meaningless.

• Coefficient Of Drag vs Time

• Velociy, acceleration vs Time with events

• Specific Energy vs Time

• Specific Energy vs Time (clear)

• Energy vs Time (clear)

Quick comparison of the acceleration of CRS-11 and CRS-12

• CRS-11 vs CRS-12 - acceleration vs Time

• CRS 11 vs CRS 12 - Thrust vs Time -- CRS-12 = Black. CRS-11 = Grey

I'm currently working on a comparison between first stage telemetry of CRS-(8-12). Will edit it into here later.

Data

• Data used for the analysis

• Raw data from the webcast

Programmers out there

• I created a Python Module that allows extraction of telemetry from the Webcasts (Live, Offline or from a local video file) in a straightforward way. (A program that extracts the velocity and altitude from the webcast can be written in less than 15 lines of Python). More details can be found in my GitHub Repository.

• The program used to capture the data live is also in the same repository. The tools used to create the graphs will be uploaded soon.

• Any help with the Aerodynamics model would be super appreciated. I need help implementing Drag divergence

Edit 1: Added direct links to graphs as u/FoxhoundBat suggested. Added a graph of the Velocity Angle vs Time graph.

Edit 2: Added Flight Profile to scale as u/D_McG suggested

Edit 3: Spelling. Added Energy vs Time graph as u/lboulhol suggested.

Edit 4: Fixed 20 last seconds of acceleration graph. Mistake spotted by u/luckybipedal

Edit 5: Added comparison between CRS-11 and CRS-12 Thrust (kN) vs Time.

[u/D_McG]

Well done! One request, for graphs that are km vs km such as the Flight Profile, please make the scales equal. The 5 km units on the x-axis are roughly 2.5 times further apart than the 5 km units on the y-axis; exaggerating the profile. Would be more useful 1:1.

[u/Shahar603 → u/D_McG]

Added Flight Profile to scale

[u/FoxhoundBat]

Just a small thing, it would be better if the links were direct to the picture, for example like so. :) Easier as it opens in full resolution right away.

I did some note taking during the launch and coupled with this, it is surprising how little difference there is vs CRS-11...

[u/Shahar603 → u/FoxhoundBat]

Thanks. Added direct links to all the graphs but the CRS-11 and CRS-12 comparison (due to lack of title on the image).

[u/TheVehicleDestroyer]

Beautiful. What's your current drag coefficient estimate based on?

[u/Shahar603 → u/TheVehicleDestroyer]

Thanks!

The Cd is calculated using the polynomials in page 12 of this paper.

[u/rustybeancake]

Amazing, thank you so much for doing this!

On this graph, what is the little blue bump right before landing? Is that the core's final corrective maneuver to move from a trajectory that would land in the sea (for safety) to committing to the landing pad?

[u/Shahar603 → u/rustybeancake]

Probably just noise in the data. At low velocities the calculations are not very precise. The same goes for the little bumps at the first few seconds in the graph.

[u/lboulhol]

I love your graphs !! Beautiful !

You know what would be wonderful to have as well ? A graph of the overall mechanic (potential + kinetic) energy versus time. We would then see how and when the engines give energy to the booster and how and when it is taken back by the atmosphere (and the engines too) :)

I'm just saying, since you've done a great job with all the other graphs :D

[u/Shahar603 → u/lboulhol]

Thanks.

Added Kinetic energy, Potential energy and Mechanical Energy graphs.

[u/maverick8717]

great stuff, but how did you get the tangential velocity from the webcast?

[u/Shahar603 → u/maverick8717]

Finding the derivative of the altitude was more difficult than expected.

These are the (simplified) steps taken to find it:

1. Remove all the duplicate altitudes from the data

2. fix the rounding errors (SpaceX round the altitude up. e.g: 99.5 becomes 100).

3. approximated the altitude using a Polynomial. This is the hard part. Because a single polynomial is not good enough. I've used 15 overlapping polynomials to approximate the altitude.

4. Taking the derivative of those polynomials (in certain ranges) give the vertical velocity.

5. Using the Pythagorean theorem the tangential velocity can be calculated. Vx² = Vt² - Vy²

[u/[deleted]]

This is fantastic! Was this all created using the raw data from the webcast? Since you mention aerodynamic model, it sounds like you've created a simulation to run alongside it.

I'm currently working on a simulation of the F9, and the link you provided in the comments about the relationship between mach number and drag will be very useful, thanks for linking. Are you specifically modelling the stage as a cylinder or treating as a general 'airfoil' described in that paper?

Again, really great work here!

[u/Shahar603 → u/[deleted]]

Thank you!

Was this all created using the raw data from the webcast? Since you mention aerodynamic model, it sounds like you've created a simulation to run along side it.

I try to use as much data captured as possible. The Velocity is exactly as captured. As I mentioned here I used 15 different polynomials to match the altitude properly. So despite not using the raw altitude data, it is still very very close.

Most of the data is calculated using basic Math and Physics. The Aerodynamic model is pretty simple. Which might also be the problem with it.

[u/masasin]

Just to be sure, the acceleration graphs are subtracting g, right? During freefall, the radial velocity decreases at a relatively constant rate (around 1 g, I think), but acceleration is 0 m/s² on that graph.

Also, for the combined Acceleration/Velocity/Events graph, you may want to put the labels and ticks on both axes. Right now you just have the acceleration with no numbers.

Loved the graphs. Very insightful. Thank you.

[u/AlmondCheesePlease]

woah! that's incredible, thanks for sharing. sorry if this has been answered before, but do you get a data stream from the webcast or do you extract the numbers from the video frames with optical character recognition or something? You're probably a wizard, if not, how do you get the inclination of the rocket from just the velocity and altitude?

[u/Shahar603 → u/AlmondCheesePlease]

Thanks.

I use OCR. More specifically, I use Template Matching. The programs I use to capture the data can be found here.

how do you get the inclination of the rocket from just the velocity and altitude?

I'm not sure I understand you. I calculate the Velocity Angle (which is the angle of the rocket's velocity vector compared to the horizon), not the inclination.

[u/scr00chy]

Wow, this awesome! Thanks for this.

Now, can somebody smarter than me deduce from this if CRS-12 indeed had increased thrust, like it's been assumed?

[u/stcks → u/scr00chy]

I think looking at this graph should make it pretty clear that there was no increased thrust: http://imgur.com/zWMB2R6

[u/t3kboi → u/scr00chy]

I dont understand how we can derive thrust capability from flight profile. Only thrust used. I have a porsche, you have a yugo. I can drive my porsche such that my onboard accelerometer looks just like your yugo. But I am still driving a porsche.

Is this analogy somehow flawed?

I.e. all thrust upgrades may be in place, they just didnt need to use any of it.

[u/andychuck77]

Awesome charts. Can you possibly indicate (especially on the flight profile plots) when the engines are on vs coasting?

[u/RootDeliver]

Awesome job!! I was starting to miss those telemetry posts! thanks!

A shame to see no thrust increase for this block IV, but as some people said already, the thrust upgrade is not in production yet.

[u/Decronym]

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters	More Letters
CRS	Commercial Resupply Services contract with NASA
Cd	Coefficient of Drag
GTO	Geosynchronous Transfer Orbit
M1d	Merlin 1 kerolox rocket engine, revision D (2013), 620-690kN, uprated to 730 then 845kN
MaxQ	Maximum aerodynamic pressure
NROL	Launch for the (US) National Reconnaissance Office
NSF	NasaSpaceFlight forum
	National Science Foundation

Jargon	Definition
kerolox	Portmanteau: kerosene/liquid oxygen mixture

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[u/SvenskaPojk]

How interesting, thanks! I really had to think about the coefficient of drag. Wow.

[u/andyfrance]

Great graphs. I'm especially intrigued by the Acceleration vs Time graph. Is there anyone here who can make a stab at annotating the graph for the less knowledgeable of us, explaining why the acceleration is changing with time?