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Contact Me

Thank you for visiting my website. You can contact me by using the form below or by emailing me at ashirazi@homasim.com. I welcome e-mails, and I'm keen to hear everyone's opinion.

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Message Archive

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Vithawon (Georgia) - 2017/05/16 - 13:20

Hello i like your website please reply back

Hi Vithawon,
I am glad you are interested. Thanks for your message. The Email address you provided is not valid. Send an Email to me directly so we can stay in touch.

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Tony Bye (United States) - 2017/03/12 - 23:06

Thanks for the awesome website. I"ve been looking for something like this to learn about orbital mechanics. For the movies under "Special Samples" it would be nice if you could view them in the browser. You could host them on YouTube, or simply use a "video" tag on your website. One other thing that would be awesome is if you could simulate "burns" or thrust at a specific power for a specific amount of time. Anyway, thanks again for the awesome website.

Hi Tony,
I am glad you like my website. Thank you so much for your suggestions.
Videos have already been uploaded on YouTube:
More videos are about to be added. As a matter of fact, lots of changes on this site are to be made in the near future, including the orbital maneuvers regarding impulsive or finite thrust transfers with nonzero burn time as you said.

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RicK Carroll (Australia) - 2016/09/30 - 08:58

Hi. Just found your excellent site.

Very well done.

I am an elderly person who just loves science explained well.

Best wishes from the land down under.

Dear RicK,
I am so grateful to you. Glad to hear about your interest in space orbits and my simulator.
Hope you the best.

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Nashran Ali (Bangladesh) - 2016/09/29 - 12:27

Hey there,

I see that your inclination degree go from 0-90 with the difference of 30. Is there a way you can make the different much smaller so that when I use the stimulation for my IA, I do not have a huge uncertainty when it comes to analysing the data.

Thank You

Dear Nashran,
I am glad you are interested.
Such limitations in the current state of simulator will be removed in the near future. The improvement of HOMA will include simulation of space orbits with unlimited values for each orbital parameters.
I appreciate your patience in this matter.

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Phillip Soltan (United States) - 2016/08/16 - 06:09

Hi Abolfazl,
I found your website through Google. I was watching the SpaceX launch of JCSAT-16 and saw that they show altitude and speed until the end of the last rocket burn. Is there any chance you can add a simulator that just takes altitude and speed to give approximate orbital parameters?


Hi Phillip,
Thanks for your comment. In order to derive the six orbital parameters, at least six independence parameters related to the space orbit are required. So, calculating the orbital elements by using just two values of altitude and velocity is impossible.
However, it is possible to derive the orbital elements from the position and velocity vectors. In this case two vectors would have six state variables in overall (three state variables each). rx ry rz for position vector and vx vy vz for velocity vector. There is a step-by-step procedure in order to derive orbital elements from the given position (r) and velocity (v) vectors of a spacecraft.
This simulation is about to be added to this web site soon. In fact, lots of changes are about to be made in space simulation on HOMA in the near future, including derivation of orbital parameters from state vectors, derivation of orbital parameters from three position vectors (GIBS method), derivation of orbital parameters from two vectors and time (Lambert’s problem), and simulation of libration points.
Wish you the best

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Sherwood Botsford (Canada) - 2016/01/12 - 23:00

Recently I started a discussion on World Building stack exchange. So far, while lots of interest, no real answers.

The question: Sci-fi illustrators love alien planets with multiple moons in the sky. Is it possible for a central body to have multiple orbiting objects with significant angular diameter? E.g. Could Earth have two moons with angular diameter of 1/2 and 1 degree. (Our present moon is 1/2 degree)

My suspicion is that there is an lower bound on the planet/moon mass ratio. Two heavy moons will crash, with possible exception of trojan positions.

Dear Sherwood
Thanks for visiting my site.
According to motion dynamics of particles in space based on Newton law, one planet can have several moons (Jupiter has at least 67 moons in solar system). About the size of the moons, as the size and mass of the moons increases, they have more effect on the relative motion of the main planet. A good example is Pluto. Pluto has five known moons. Charon is the largest moon of Pluto with a diameter just over half that of Pluto and they are stable with no collision. When one moon has significant mass in comparison to the main planet, two objects are gravitationally locked to one another with significant effects on the motion of each other.
Such cases are usually referred as "barycenter". When the two bodies are of similar masses, the barycenter will generally be located between them and both bodies will follow an orbit around it. This is the case for Pluto and Charon, as well as for many binary asteroids and binary stars. It is also the case for Jupiter and the Sun, despite the 1,000-fold difference in mass, due to the relatively large distance between them.
In overall, the answer is yes. It is possible for a planet to have multiple giant moons which have significant size in comparison to the main planet and the motion of moons along with the main planet can be stable with no collision.

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P.Soma (India) - 2014/11/19 - 10:28

Dear Shirazi:
Congratulations. This is a good effort and so nice of you to share it with others who are interested in orbital mechanics. I am sure this will be very useful to teachers and students of Space Mechanics.
I teach space mechanics and will use your simulator in the class.
Best wishes,

Dear Soma
Thank you for your message. I am so glad that you found this simulator as a helpful tool for teaching orbital mechanics. It is so encouraging for me when I see that my simulator has helpful usage in researches and activities of other people.
Wish you the best
Blue Skies

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Subu (India) - 2014/11/16 - 12:05

Good effort dear Shirazi and I hope the beginners (flight Dynamics) will be well benefited by your product. Please add semimajor axis size 42164 km (geostationary satellites orbits) also to your simulation database. Also if you can add 2 or more satellites simultaneous simulation it will be useful for understanding relative motion of pairs or clusters of satellites.

All the best for your future endeavors and your PhD program

with warm regards

Dear Subu
Thanks a lot for your feedback. Special orbits such as GEO and Molniya are considered as top priorities for future improvements since they are more practical in real space missions.
Wishing you the very best of luck with your career as well.
Cheers :)

Homa is optimized for learning orbital mechanics and analyzing space orbits. Results are constantly reviewed to avoid errors, but I cannot warrant full correctness of all content.
Copyright © 2014-2017 by Abolfazl Shirazi. All Rights Reserved.
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