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Introducing AESAT

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5:49 am
April 29, 2010


Luke Maurits

Adelaide, Australia

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I've pushed the first version of a new program for the CSTART Software Library to my clone of the Hg repo.  The program is called AESAT, for Atmospheric Entry Simulation and Analysis Tool.  It numerically solves the mathematical model of reentry trajectories which is presented in CTR-0001.  You can see the code here.

AESAT is in very early stages right now, still purely command line and with a few shortcomings which I'll try to improve over time.  Even at this stage, though, it does its basic job well enough: given some spacecraft specifications (mass, cross-sectional area, drag and lift coefficients) and some reentry parameters (velocity and angle of entry) it will simulate the reentry from start to finish, computing at each stage the altitude, velocity, flight path angle, acceleration, dynamic pressure and down-range distance travelled, and will also find the maximum acceleration and dynamic pressure values, and the times at which they occur.  It saves all this into a CSV file so you can make your own graphs with, e.g. gnuplot (eventually I'd like it to do its own plotting, like USOFS).

There are still some things to tidy up, but for now it is at least producing physically sensible results, e.g. increasing lift extends the duration of flights and decreases the peak acceleration, and acceleration profiles for ballistic reentries have a symmetrical peaked structure (they look a lot like low-variance Normal distributions, actually), which fits in with stuff I've read and other graphs I've seen.

There is no thermal modelling involved as of yet, but I might get around to that eventually when I've spent more time reading up on entry heating models.

I wrote this mainly thinking of CLLARE and/or the up-in-the-air pre-CLLARE orbital spacecraft project, although it occurs to me now that it would be just as useful for OHKLA, for modelling the reentry of the nosecone component with all the avionics onboard.

PS: As you may have noticed, I've created a new forum for discussing our software projects – there was nowhere else suitable to put this post, and sticking it in the Community/General forum didn't seem appropriate, since software projects are something we're always going to have to discuss.

Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.

4:52 pm
April 29, 2010


Rocket-To-The-Moon

Grand Forks, North Dakota, USA

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Post edited 4:53 pm – April 29, 2010 by Rocket-To-The-Moon


This sounds like a very useful piece of software. Is there any chance that we will be able to link this with USOFS so that we can model the entire mission profile?

 

How hard would it be to make some of these programs web based so that everyone can easily run them?

 

Also, this is the first time I've laid eyes on CTR-0001, very interesting and well done.

Main Workgroups: Propulsion & Spacecraft Engineering

2:50 pm
April 30, 2010


J. Simmons

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Very cool.  I have only had time to glance at the code and CTR, but this looks like a good place to start.  And I am very excited to see software being coded up to handle astro related material.  I was thinking I should go back and look through my various graduate textbooks and code up anything that looked useful while it was still fresh.  Hopefully this will inspire me to get off my butt and do so.

Speaking of textbooks, you might find this one interesting (Introduction to Astrodynamic Reentry).  It is the free ebook from my graduate reentry class at AFIT.  There are some very useful reentry equations (including thermal) at various levels of fidelity.  The text could probably also be used to generate some test cases for the
code as well.  If I can make some time after the quarter is over, I'd be happy to help implement the equations and/or test cases as a part of the tool if that works for you. 

3:30 pm
April 30, 2010


antinode

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Nice work Luke. Do you think it's best to keep all these trajectory calculating programs as simple and single purpose, and then make it possible to pipe their outputs between each each other? In the long run, how do you see these types of programs being used by people?

I agree with RTTM in that this a web interface would be great, and that it should accompany "CTR-001" as a learning tool. I'd really like to create a roadmap for the CTR pretty soon, by the way11. It still lacks a clear definition.

Thanks for the book Simmons. Tons of info the cite in there.

5:44 pm
April 30, 2010


Rocket-To-The-Moon

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J. Simmons said:

Speaking of textbooks, you might find this one interesting (Introduction to Astrodynamic Reentry). 


 

The math is way over my head, but that book looks like a wealth of knowledge.

Main Workgroups: Propulsion & Spacecraft Engineering

12:31 am
May 1, 2010


Luke Maurits

Adelaide, Australia

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Thanks for all the feedback, guys.

Better integration between AESAT and USOFS would indeed be a good thing.  Right now it's possible only in the most primitive way: running USOFS, writing down the conditions at the time of zenith, then copying those values as the initial conditions for AESAT (currently only possible by modifying source) and running AESAT.  Obviously there are much better ways of doing this than that.

On this topic, it's worth noting that a big current shortcoming is that AESAT and USOFS currently both use exactly the same model for atmospheric density vs height (based on this Wikipedia entry), with the same code duplicated in each program.  It would be much better practice to factor this common code out into its own library.  This would be a sensible start to the long-discussed idea of a central library with common utility functions for things like aerodynamics, astrodynamics, etc., which could be called from various independent utilities.  We could even go a step further and implement the logic of USOFS and AESAT as libraries and then have a single application which can perform the independent functions of USOFS or AESAT or combine the two for a complete flight simulation.  This actuall makes a lot of sense: it would be great to have one progarm which could chain together various libraries: an "ascent library" (which could be a straight-up suborbital library like USOFS or a new one with a pitching program which achieves orbit), a "middle flight library" (which would probably just be an accurate orbit simulator, taking into account e.g. non-spherical gravity perturbations, solar wind, etc., etc, but we might also want a more complicated one which included a few maneuvers) and then a "reentry library" (there might be a few versions of these, depending on the extent to which reentry guided).  The user could specify a choice of library for each phase and then the program would simply run them in sequence, using the output from each as the input to the next.  This would be pretty cool.

As for a web interface, this is certainly possible, and I'd be able to write one, although only Rizwan would have the access to actually upload it.  It's also worth noting that I could only produce a very basic and inefficient web app for this in a reasonable amount of time.  To make a very nice AJAX-based interface that was pleasant to use and didn't require lots of page reloads is something I could probably create in time, but there would be learning curves along the way and it might be more efficient to get somebody else to do it.

Antinode, I am starting to agree with you that the Tech Report System needs clearer definitions of intent and there may be a need for a second system for project specific things.  E.g. I think something like, for instance, a detailed power budget for CLLARE, warrants a certain kind of document, like a report, but which is clearly distinct from general educational material in a lot of ways.  I would be happy to discuss this in more detail elsewhere on the forums.

J. Simmons, thanks a lot for that reference, it looks very helpful.  At a first glance, it looks like the equations for planar flight presented there are the same as those used in CTR-0001 and AESAT, but expressed in a different coordinate system.  However, there is definitely material toward the end of that text which deals with stuff I've not seen before (My reference for this has been "Space Vehicle Design" by Griffin and French – it goes about as far as Loh's Second Order solutions), and it looks like there are lots of great examples in there which could be used to validate the output of AESAT.

Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.

4:53 pm
May 10, 2010


natronics

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Nice work!  I haven't looked into reentry mechanics yet, so this is pretty neat.

 

BTW have you thought about making a reusable integration engine? I think you'll find RK4 all over the place and it's nice not having to copy code every time.

 

Also thaks J. Simmons for the book suggestion.

7:17 pm
May 11, 2010


KellyJ

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Post edited 7:20 pm – May 11, 2010 by KellyJ


7:19 pm
May 11, 2010


KellyJ

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Hi guys,

There is an open source program called "Space Trajectory Analysis" (STA) which is available from:
Also there is NASA's General Mission Analysis Tool (GMAT). I have just downloaded it and will have a look, but it could be very useful for broad level mission planning work.
http://gmat.gsfc.nasa.gov/

 

Not sure yet how much re-entry work they can do, but worth looking at.

Regards,

5:19 am
May 12, 2010


Luke Maurits

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Hi Kelly,

Those look like really useful links!  Thanks very much for passing them on.  I'll try them out sometime soon and see to what extent they can be of use to us.

Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.

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