Tuesday, June 09, 2015


One of the failings of silver ball was that I never got an accurate hardware in the loop simulator running.
On this project I'm not going to make the same error. 

After evaluating a number of possible solutions I've decided to use JSBSim  and I've secured the assistance of the 
Jon Berndt,  Development coordinator and chief architect for the JSBSIM, in getting that done. (I've made an arrangement where he will help me get started for a consulting fee, his time permitting)

One of my questions to him was:

>A details question.... I realize that JSBSim was built to be a flight simulator.
>I'm trying to repurpose it as a rocket simulator....

>Internally you seem to use ECEF coordinates.... I have not dug deep enough to figure out 
>if you model the inertial effects of a rotating earth...
>will one see a performance difference between an equatorial launch and aa polar launch?

>If I have a vehicle attached to the surface of the earth will it show the rotation rates of 0, or will it show the 
>the rotations rates one would see in an Earth centered inertial frame?

His answer greatly increased my confidence that I made the correct selection...
And, yes, JSBSim had a full overhaul of its EOM many years ago for full and complete EOM. It was the only non-NASA sim used in a large check case development effort that is published here: http://nescacademy.nasa.gov/flightsim/

The EOM integration takes place in ECI, full rotation effects are factored in and – yes – you would see the benefit from an equatorial launch compared to a higher-latitude launch. It is a full, vehicle simulator that can model anything from a rocket to a ball to a blimp to a sub/supersonic aircraft.

The vehicle sitting on the launch pad should show no Earth relative motion, but should show a translation and rotation relative to inertial. This was one aspect that was compared across NASA sims and JSBSim in the check case effort, and the comparison effort investigated tiny differences to make sure we were all on the same page and using the same Earth rotation rate. At this stage, I am very confident in JSBSim. That’s one nice thing about open source and broad use: the more people use it in different ways, the better the development effort goes, and the more robust the code becomes.

The simulator in general is designed to be data driven via external XML files. So one can model things like autopilot loops etc...I really want this to be a hardware in loop simulator so one of the modifications I'm asking Jon to help me put my c/c++ code into  the control loop. Eventually this will entail me taking the current state, simulating the IMU and GPS outputs feeding it into flight avionics and then taking the response from the flight avionics and giving it back to the sim to have it operate on the commanded changes.


Anonymous said...

Does JSBSim model Earth as a sphere or as an ellipsoid? The latter could, e.g., allow to see the turning of the orbital plane and better models distances from Earth center.

jccooper said...

I've seen JSBSim mentioned enough on aRocket that this post finally got me to look it up. I read through their (unfinished but) excellent manual and poked at some of the code, and it looks like a good choice. They seem already to have put some thought into rockets, and they mention on the website HITL been done before.

Their architecture is simple enough that once the vehicle itself is set up in their XML, I think it ought not be too hard to integrate your own controller, and/or create a software workalike (which is probably the first step.) Just a matter of creating your own input/output wrappers around the main simulation loop, as they suggest on p80. (It seems you could also communicate via a socket, but that seems unnecessary.)

Do you have a vehicle description already? I'm kind of inclined to try it out. If not, maybe I'll try out the Space Shuttle model they have. (The manual mentions Little Joe, which would be better, but I don't see it included.)

Paul Breed said...

One of the deliverable from Jon is a set of XML files for my conceptual otrag.
When that is done I'll make it available here.

Jon Berndt said...

In answer to anonymous, there are two gravity models. One is a simple inverse square law model, and the other is a simple spherical harmonic model (it's the one described in Stevens and Lewis aircraft simulation and control book). Geodetic position is determined as well as geocentric and ECEF. To jccooper, the manual is a bit outdated, and some of the models in the JSBSim distribution are works in progress (and have been for ten or fifteen years!). The most complete models are probably ones distributed with FlightGear. JSBSim is one of the flight models incorporated into FlightGear (and is the flight model for OpenEaagles and Outerra,as well). For a lot of the models in the JSBSim distribution there was not enough good information to complete those models. I seem to recall that the full shuttle aero model, for instance, is in a couple of books that are each 6 inches thick. The C172 model and the 737 model are pretty well developed. The J246 model is as well, but only for first stage flight and part of second stage. Some of these models were only meant to prove certain concepts in the sim as they were developed, but some are used for academic purposes. Also, some of the most complete models are held by industry and are not releasable - that's one reason we separated code from model. To get some feeling for how JSBSim is being used you could also go to the AIAA web site and search their papers for JSBSim. At last count there were about 40 papers. It is finding a lot of use in the UAV field in recent years.

I also wanted to mention that while I did write a lot of the initial code and set up the initial architecture, there have been a handful of very solid engineers that have made major contributions to JSBSim as members of the development team, and the open source paradigm that JSBSim was developed in also was instrumental in getting bug reports and feature requests. I feel that it's a pretty solid piece of work, now, thanks to the collaborative development environment.

cheapest essay writing service said...

You made some good points here. I did a search on the topic and found most people agree with your blog. Thanks

shubham sapkal said...

Happy Friendship Day 2015 messages
Raksha Bandhan 2015 wishes messages
happy raksha bandhan 2015 date calendar
friendship day essay information history for students kids

Ssc Results said...

Happy Independence day 2015 speeches
Happy Independence school speeches
Happy Independence Movies List
Happy Independence movies Free Download
Happy Independence Day Images
Happy Friendship day whatsapp status
Funny Whatsapp status for friendship day
Friendship Day 2015 images for whatsapp
Friendship Day 2cover pic for whatsapp

dip said...

Here you can Watch UEFA Chapions League 2016 Live Streaming
Champions League live stream

Amit Kumar said...

Happy Navratri 2015 Images For Whatsapp Dp
Happy Navratri Songs Free Download
Navratri dj garba songs mp3 download
Navratri images pictures free download
Navratri hd wallpapers for desktop
Happy Navratri SMS Quotes wishes messages in hindi
Navratri 2015 dress colour code
Navratri 9 days colours
Bollywood Navratri garba songs
Navratri 2015 whatsapp status
Navratri gujrati songs
Free Navratri images download
Happy Navratri hd video songs

Halloween HD Images 2015
Halloween HD Images with quotes
Halloween HD scary Images 2015
Halloween HD wallpapers
2015 Halloween images with quotes
Halloween HD Images free download
Halloween 2015 free download pictures
Halloween images for kids
Halloween desktop pictures
Halloween hd wallpapers for adults
Halloween HD Images for whatsapp, facebook
Halloween HD Images with sayings
Halloween HD Images for desktop & Cove pics

chilka babuji said...

Diwali 2015

Fancy Candles For Diwali

Diwali Wishes

Decorative Diyas For Diwali 2015

Pooja Thali For Diwali 2015

Diwali 2015

Diwali Gifts 2015

Diwali Wishes

Diwali Gift Ideas

Diwali Gift Ideas 2015

Karwa chauth Gift Ideas

8 ball pool said...

I enjoyed over read your blog post. Your blog have nice information, I got good ideas from this amazing blog. I am always searching like this type blog post. I hope I will see again..
halloween| animal jam online| happy wheels| cool math| 8ballpool| sudoku az| yoob games| happy wheels| unblocked games | hanger| tetris| friv4school| color sudoku| kumba karate
happy wheels hacked| shopping cart hero 2| whack a craft| sports heads football| raze 2

Naveen Chaudhary said...

valentine wish
valentine quotes for girlfriend
valentine day wishes for girlfriend
valentine day poems for girlfriend

killer king said...

valentine day wishes
Valentine Day Quotes For Girlfriend
Valentine day Poems
Valentine day Messages

Amit Yadav said...

valentine day wishes
valentines message for wife
valentines poems for boyfriend
valenines poems for girlfriend
valentines message for girlfriend

http://happymothersdayquotes.co.in/ said...

Mothers Day Poems
Mothers Day Poems
Fathers Day Poems
T20 World Cup Live
HSC 2016 Results

Ella Candy said...

I want you to thank for your time of this wonderful read!!! I definately enjoy every little bit of it and I have you bookmarked to check out new stuff of your blog a must read blog!
slither io | wings io | science kombat | tank trouble 4

Friv4 Games Online said...

Thanks for sharing such a nice article. It is really useful to me and all people. One think in my mind came while reading that it is not wasting of time.
happy wheels | friv | girlsgogames | games2girls | happy wheels | fireboy and watergirl

Geometry Dash said...

You’ve written nice post, I am gonna bookmark this page, thanks for info. I actually appreciate your own position and I will be sure to come back here.

Alice Denny said...

The blog or and best that is extremely useful to keep I can share the ideas. Age Of War 2
Big Farm | Slitherio | Tank Trouble
Of the future as this is really what I was looking for, I am very comfortable and pleased to come here. Thank you very much.
Happy Wheels | Goodgeme Empire | Slither.io

Friv games said...

Thank you so much for commenting, it is lovely and really makes my day!
Friv 10 |
friv games | friv 100 games

Loan Thu said...

I liked it so much and very interesting, too! Thanks for sharing the experience.
Wonderful post, really great tips and advice.
friv 3
friv 4 school
kizi 2

Deba Sheesh said...

Thanks, You wrote awesome, I have learn lots of things from your article. It's really helpful for any readers.
Battery Operated Flow Meter

عبده العمراوى said...

شركة قمة الدقة للخدمات المنزلية
شركة تنظيف منازل بالاحساء
شركة عزل خزانات بالقطيف
شركة عزل اسطح بالقطيف

Drag Racer V3 said...

I read through their (unfinished but) excellent manual and poked at some of the code, and it looks like a good choice. scorehero.net

Potty Racers 2 said...

Thanks for sharing dragracerv3game.com

Ngọc Bảo said...

I like your post. It really useful with me. Thanks for sharing these useful information!

Alice Taylor said...

This is extremely helpful info!! Very good work. Everything is very interesting to learn and easy to understood. Thank you for giving information.


Thu Lê said...

I was very impressed by this post, this site has always been pleasant news. Thank you very much for such an interesting post. Keep working, great job! In my free time, I like play game: facebooklite.com.br. What about you?

Friv4 Games Online said...

Thanks for the information you shared. Please share useful information with your friends regularly

Love Kpop said...

I realize that nothing is fair but I'm still trying. I just want to do my best and what is possible

Love Kpop said...

There are things I can not understand but I will learn it. I think nothing is too late. Then I realized that I had improved a lot.

Alice Taylor said...

thanks for your post


Friv games for Kids said...

Your article is very interesting. I think this article has a lot of information needed, looking forward to your new posts. Get permission to share:
Kizi games for kids

Games 2 Girls said...

Great post,Thanks for providing us this great knowledge,Keep it up.


ngocanhng said...

Alot of blogs I see these days don't really provide anything that I'm interested in, but I'm most definately interested in this one. Just thought that I would post and let you know. Nice! thank you so much! Thank you for sharing.

Games 2 Girls said...

Thank you for that information you article great article, I was very impressed about it, wish you would have stayed next share
instagram viewer images

Madison Smith said...

I have read your article, the information you give is very interesting.

phuctrankhang said...

Great ideas. First time I am visiting this blog. I found many entertaining stuffs in this blog. I like your writing style and language. Your presentation is also good. Thank you so much for sharing these ideas.
Dress Up Games
Minecraft Games
Girl Games

superwings said...

This is the best application on the drop today. There access to enjoy great moments of relaxation . Great! Thanks for sharing the information.
Friv 2

healthy5419 said...

Awesome blog. I enjoyed reading your articles. This is truly a great read for me. I have bookmarked it and I am looking forward to reading new articles.
Friv 2019
Didi Games
Friv 1