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Message Archive




Kevin Bongiovanni (United States)  2020/11/12  20:23How do you translate parameters in TLE format to your simulator?
Reply: Hi Kevin,
TLE data include variety of information about the satellite and its orbit. All six orbital elements can be retrieved from TLE data. Eccentricity, inclination, argument of perigee, and right ascension of the ascending node are directly provided in TLE data. Also, the orbital mean motion and mean anomaly are directly given in TLE data, which can be converted to semimajor axis and true anomaly respectively. I suggest you to refer to the Wikipedia Page for TLEs:
https://en.wikipedia.org/wiki/Twoline_element_set
Also, for the mentioned conversion you can refer to Chapter 2 of Curtis, H. (2014). Orbital mechanics for engineering students. 2st ed. Oxford: Elsevier ButterworthHeinemann.
Best regards









Suravi (India)  2020/07/25  12:05this is a great website i love it....
great work
i would like to thank you to do this simulator it helped me a lot during my college days all thanks to the creator..
Reply: Hi Suravi,
Glad to hear that. Thanks for leaving the message.
Regards









Ricard (Spain)  2020/05/28  08:26Hi,
I believe I"m seeing some inaccuracies:
When the inclination is < 90 deg, the satellite should be flying eastward when it crosses the equatorial plane.
When the inclination is > 90 deg, the satellite should be flying westward when it crosses the equatorial plane.
Here I think I"m seeing the opposite. Am I correct?
Thanks.
Reply: Hi Ricard,
It depends on the orbital period. If the orbital period is more than 24h (semimajor axis more than 42164km) then the satellite goes westward, no matter what the inclination is. You can test it by trying a=50000, e=0, i=30 and 120. Although, the precise direction of the satellite depends on other orbital elements as well, if they are set.
For the typical Earth orbiting satellite when the orbital period is less than 24h, yes, it generally flies eastward if i<90 and westward if i>90. I checked the results and did not find any inaccuracies. If you think there is an inaccuracy within the simulation results, I appreciate if you can give me more details.
UPDATE: In the current version, the square on the plot indicates the initial point.
Thank you for your message.
Best regards,









Brandon Fletcher (United States)  2020/05/24  23:49Hey it appears your velocity vector, after calculation, shows the i and j vector reversed. They numbers are correct, the i and j components are swapped. With the given conditions eccentricity 0.001473, semimajor axis 6788, and true anomoly 30 degrees, the i component of the velocity vector should be higher than the j vector but it is not.
Reply: Dear Brandon,
Thank you so much for leaving a message. I checked the simulation results and it seems they are fine.
The coordinate system is ECI (Earth Centered Inertia). For the given condition you said, (lets assume the orbit is almost circular), the velocity of the "i" component is zero at perigee ( heta=0) and maximum at heta=90, while the velocity of the "j" component is the reverse, maximum at heta=0 and zero at heta=90deg. As the satellite moves away from perigee, the "i" velocity increases while the "j" velocity decreases. Since at heta=30, the satellite is closer to perigee, the magnitude of "i" component should be lower than the "j" component [To be exact it is (3.831) i + (6.648) j + (0) k km/s]. Remember that X axis is toward perigee and Y Axis is perpendicular to X.
Hope this helps. If you still think there still is a problem, I appreciate it if you can clarify.
Thanks again for your attention to the details.
Best Regards,









SEID (Ethiopia)  2019/10/10  22:51Its good deeds. How can I download the simulation software?
Reply: Hi Seid,
Glad you are interested. This platform is a free online simulator and can be used online.
Best regards









Joe Grutzik (United States)  2019/04/26  19:14Hi Abolfazl –
I found your HOMA Online Space Orbit Simulator from Google. I was wondering if you could help me solve a mystery. I am curious about the US robotic space plane the X37B, OTV5. I was wondering if you could help me figure out where it was at 6:30 a.m. PST on November 8th, 2018. There is a blog post describing its last know position and direction here –
https://sattrackcam.blogspot.com/2018/08/thex37botv5ismanoeuveringto.html
Is there enough information in this blog post to describe the spacecraft’s orbit? Is there a way we could use your HOMA to draw a ground track projection for the 8th of November 2018? I want to find what part of the globe the spacecraft was over at around 6:30 a.m. Pacific Standard Time.
Let me know if you can help.
Regards,
Joe
Reply: Hi Joe,
Thanks for using the simulator. In order to know the position of a space vehicle in the past, backstep propagation is needed. Same as the typical simulation, the orbital elements are needed for that. It can not be done unless the orbital parameters or the state vectors of the trajectory is known. The case you referred has some information, but it is not enough for backstep propagation.
Regards









Saqib Mehdi (Pakistan)  2019/03/08  18:22Asalam o Alikum !
How are you Sir! MY name is Saqib Mehdi, I am student of MS Global Navigation Satellite System in Institute of space & Technology Islamabad, Pakistan. I was searching a simulator and google bring me here on your website. Its very good work. MashaAllah.
Reply: Hi,
I am glad you like it.
Regards









Syed Ateeb (Pakistan)  2018/09/03  14:08i want to simulate 700 satellites in between 700900 km above the earth surface. i want them to be simulated at once so that it can be created at one go.
Reply: Hi Syed,
You have several options. If you are working in MATLAB, you need to solve the equation of motion regarding twobody or Nbody problem. You can also use System Tool Kit by AGI. The free version is available online to download. Although the free version has some limitations, you can simulate as many satellite as you want at the same time regarding twobody or SGP4 propagation models.
Best Regards









Charlie Yau (Hong Kong)  2018/06/21  05:35Hi,
I am an IB student who takes Physics and I am currently working on my IA. Would it be OK for you to provide error analysis on the simulations for further investigation? Thanks a lot!
Reply: Hi Charlie,
It would be better that you clarify on what you exactly mean by error analysis. Currently the results are based on analytical derivations of orbital elements. No approximation is used.
Regards









Pabitra Sil (India)  2018/04/04  05:05How can I find the orbital elements (like semimajor axis,eccentricity etc ) from RA and DEC of an observed asteroid. Is there any software to calculate this.
Please help me.
Reply: Hi Pabitra,
As stated before, The orbital elements are independent from each other. You cannot derive one from another, unless having additional information about the orbit.
By the way, to determine an orbit solely from observations therefore requires six independent measurements. In the absence of range and range rate measuring capability, as with a telescope, we must rely on measurements of just the two angles, azimuth, and elevation to determine the orbit. A minimum of three observations of azimuth and elevation is therefore required to accumulate the six quantities we need to predict the orbit.
I refer you to the section 5.9 "Anglesonly preliminary orbit determination" of Orbital Mechanics for Engineering Students by H. Curtis.
Best Regards









Dhruv (India)  2018/03/23  09:24Sir,
I am a student of Electronics and Telecommunication Engineering and am trying to design a software similar to yours using Python and Blender.
Could you please guide me as to how we can use the orbital parameters to plot the Satellite"s orbit?
Reply: Hi Dhruv,
I refer you to "Chapter 4: Orbits in three dimensions" of "Orbital Mechanics for Engineering Students" by H. Curtis. To be more specific, all you need to know is in Section 4.6: "Transformation between geocentric equatorial and perifocal frames".
Good Luck









Jeremy Daigle (United States)  2018/03/07  21:23How would i go about calculating RAAN, mean anamoly and argument of perigee, given that i have perigee, apogee, angle of inclination and eccentricity. Thanks. JD
a = 26023.99
Ra =42,157.195 Km (apogee including earths radius)
Rp = 9890.8 Km (perigee including earths radius)
E = 0.619796
Reply: Dear Jeremy,
You can"t do that. The six orbital elements are independent from each other. You can"t calculate some of them from the rest. Unless you have additional information about the orbit, like state vectors.
Also, it doesn"t make sense when you say I have perigee, apogee and eccentricity. Because you can calculate eccentricity (and ofcourse semimajor axis) from apogee and perigee.
Best Wishes









Ophelia (United States)  2017/12/20  18:27Hello.
I am fascinated that you have created an online space orbit simulator. I am in no way an orbital mechanic, but I think it would be neat if you would create a mechanism by whence to add multiple objects to an orbit simulator, to see if a set of multiple orbits could plausibly run without collisions or other complication, and it would also be awesome if you could add something beyond just Earthorbit, like maybe Solarorbit.
Reply: Dear Ophelia,
Thank you so much for your message. Your suggestions are exactly the ideas that I already have in my mind for future improvements. They also include the simulation of space orbit around different planets of the solar system, analyzing orbital perturbations, visualizing multiple spacecraft motion in an orbit (or several orbits) and a platform for generating transfer trajectories from one orbit to another.
Best Regards









Douglas Nuttall (Canada)  2017/09/22  05:04This is a good site, but I"m curious about a problem that I don"t see how to model. Can you suggest either a calculator or the formulae required to solve?
I think that the long travel time between earth and mars would require "gravity" (somewhere between 1/2 and 1/3 g) and shielding from particles and radiation. Which suggests to me a heavy spinning object, Which would take a great deal of effort, so I think once it"s up there, it should stay in orbit, acting as a travelling space station. Martian Buslines...
If one used a solar sail on a long boom, one could introduce a great deal of torque over a hundredsofdays trip, allowing a balanced payload to be extended by cable that would end up with very high velocity, meaning that at the connection with Mars and the Earth, the delta Vs of the payload could be very close to 0.
This spinning device could ship cargo and people in relative safety with a fairly constant artificial gravity, constant light, and slowly extending a lander (together with a counter weight in the opposite direction) on 2 km of cable. When in the right place to have the dVs on the right vector, the lander would disconnect.
So I"m looking for a way of modelling a 2 km skyhook, plus a large solar sail, on a boom to create torque. Any suggestions?
Reply: Hi Douglas,
Thanks for leaving a message. The practicality of the concept you are discussing is itself under question in my opinion regarding the current trends and efforts for interplanetary transfers. Perhaps, more details are needed about this to say whether it is possible to implement the idea or not.
Anyway, regarding the simulation of such systems, you need to mathematically model the attitude dynamics alongside the point mass dynamics since you are taking into account both the orientation and the motion of the particles.
Regards









Jeff (United States)  2017/08/01  01:57Hi!
Your orbit simulator is brilliant, but I have a couple of questions that I can"t figure out about the orbit of the ISS. Any chance you could drop me an email and relieve a bit of my ignorance?
This is for a writing project I"m working on, and your help would be greatly appreciated.
Reply: Hi Jeff,
I am glad that you are interested in my web site. I will be happy to help you with this if I can.
Regards









Vithawon (Georgia)  2017/05/16  13:20Hello i like your website please reply back
Reply: 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.
Regards









Tony Bye (United States)  2017/03/12  23:06Thanks 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.
Reply:Hi Tony,
I am glad you like my website. Thank you so much for your suggestions.
Videos have already been uploaded on YouTube:
https://www.youtube.com/channel/UC_yMCZ38IKXHu7Kg8XdD8eQ
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.
Regards









RicK Carroll (Australia)  2016/09/30  08:58Hi. 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.
Reply: Dear RicK,
I am so grateful to you. Glad to hear about your interest in space orbits and my simulator.
Hope you the best.
Cheers









Nashran Ali (Bangladesh)  2016/09/29  12:27Hey there,
I see that your inclination degree go from 090 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
Reply: 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.
Regards









Phillip Soltan (United States)  2016/08/16  06:09Hi Abolfazl,
I found your website through Google. I was watching the SpaceX launch of JCSAT16 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?
Thanks,
Phillip
Reply: 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 stepbystep 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









Sherwood Botsford (Canada)  2016/01/12  23:00Recently I started a discussion on World Building stack exchange. So far, while lots of interest, no real answers.
The question: Scifi 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.
Reply: 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 1,000fold 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.
Regards









P.Soma (India)  2014/11/19  10:28Dear 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,
soma
Reply: 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









Subu (India)  2014/11/16  12:05Good 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
SubuBangaloreIndia
Reply: 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 full correctness of all contents cannot be warranted.
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