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View Full Version : A fun on-line toy - orbit a satellite!



jst
2004-Aug-11, 06:25 PM
http://www.colorado.edu/physics/2000/applets/satellites.html

A nice little applet someone designed to simulate how hard it is to orbit a satellite.

No math required

The Supreme Canuck
2004-Aug-11, 07:12 PM
Try getting it into lunar orbit. I've only been able to pull off three complete lunar orbits. Hard.

jst
2004-Aug-11, 07:16 PM
Try getting it into lunar orbit. I've only been able to pull off three complete lunar orbits. Hard.

I've yet to establish a stable (only in the sense of not crashing over the course of a few hours) orbit around the moon.

Managed it various times with the earth, but the moon is really hard to do.

tofu
2004-Aug-11, 07:16 PM
that is too cool. Looks like it uses a lot of the same code as this one:
http://www.colorado.edu/physics/2000/applets/orbits.html

The Supreme Canuck
2004-Aug-11, 07:19 PM
You really want a challenge, try doing a stable transfer orbit. :o

ToSeek
2004-Aug-11, 07:47 PM
We've done this before. (http://www.badastronomy.com/phpBB/viewtopic.php?t=1906)

ToSeek
2004-Aug-11, 07:49 PM
that is too cool. Looks like it uses a lot of the same code as this one:
http://www.colorado.edu/physics/2000/applets/orbits.html

If you enable "show force" and get the orbit just right, it looks as if the electrons are taking turns stabbing the nucleus.

I'm easily amused. ;)

jst
2004-Aug-11, 08:15 PM
We've done this before. (http://www.badastronomy.com/phpBB/viewtopic.php?t=1906)

You know, I thought you might, but my -admitedey cursory- search didn't show it up.

Oh well, nothing like a blast from the past!

ToSeek
2004-Aug-11, 08:41 PM
We've done this before. (http://www.badastronomy.com/phpBB/viewtopic.php?t=1906)

You know, I thought you might, but my -admitedey cursory- search didn't show it up.

Oh well, nothing like a blast from the past!

I wasn't complaining - I had a lot of fun with it before and will have some more now.

CUStudent
2004-Aug-11, 09:07 PM
Here's a summer vacation question...would this be considered a three-body problem? Aren't those chaotic and impossible to solve analytically?

BTW, I think my thermo professor from last semester wrote this applet. Go Buffs!

[edited to add the following comment]

The Science Museum of Virginia in Richmond has an old exhibit much like this....it's a big table with the earth and the moon dangling from the ceiling above two approximately correct 'gravity' wells. The goal is to roll large ball bearings so they orbit around the earth, the moon, or an earth-moon-return trajectory. It's a great exhibit, my favorite as a kid.

sts60
2004-Aug-12, 06:36 PM
A restricted three-body problem, as the little satellites appear to have negligible mass (they don't seem to attract each other, nor affect the Earth or the Moon). So, it would still admit an analytical solution.

jst
2004-Aug-12, 08:25 PM
I wish they made the field bigger... I'd like to see everything on this scale, but with enough background to cover your screen. then you could see some of your really big orbits, too

The Supreme Canuck
2004-Aug-12, 08:28 PM
Anybody know JavaScript?

ToSeek
2004-Aug-12, 08:44 PM
Anybody know JavaScript?

It's not JavaScript; it's java. I know both, but it would help to have the source code as a starting point.

The Supreme Canuck
2004-Aug-12, 08:45 PM
Wow. Shows how much I know.

Anyway, that other thread that you linked to has someone talking about the source code. He found out the values for the masses of the Earth and Moon that way, apparently.

Edit: Looks like the poster is Timm.

jst
2004-Aug-12, 08:51 PM
And as a courtesy (and a legality), you should ask the original programmer first.

EDIT:

That said, if you view the source for the page, it looks like all you need to do is figure out a way to change the height and width values from 400 when the applet loads....

but to do that on your own site you'd need the applet first, right? you can't call it from another site?

JohnD
2004-Aug-12, 09:08 PM
What is missing?

I downloaded this in my lunchtime at work - great fun!

When I do the same at home, all I get is an empty frame, and no game.

What is missing from my home machine? Java?

John

ToSeek
2004-Aug-12, 09:46 PM
And as a courtesy (and a legality), you should ask the original programmer first.

EDIT:

That said, if you view the source for the page, it looks like all you need to do is figure out a way to change the height and width values from 400 when the applet loads....

That probably just changes the scale; it wouldn't let you see larger orbits or anything.


but to do that on your own site you'd need the applet first, right? you can't call it from another site?

If you look at the source, you should be able to figure out where the applet is and download it.

jt-3d
2004-Aug-12, 10:09 PM
What is missing?

I downloaded this in my lunchtime at work - great fun!

When I do the same at home, all I get is an empty frame, and no game.

What is missing from my home machine? Java?

John

Most likely, you need to either update Virtual Machine at microsoft or pop over to Sun and grab JRE (http://java.sun.com/j2se/desktopjava/jre/index.jsp). I gave up on VM myself since MS likes to break it from time to time.

JohnD
2004-Aug-13, 08:09 AM
Thank you jt!

I've now got a contra-rotating satellite that's been going for twenty minutes or more.
The behaviour of the satellite's orbit has given me a new insight into the 'shepherd moon' idea. The orbit is, on average, a bit less than halfway between Earth & Moon, precessing around the Earth in the same direction as the orbit. It becomes more and more elliptical with closer and closer passes to Earth, until it has an encounter with the Moon at apogee, when the orbit becomes more circular again. And so on.

This has also given me new respect for the flight engineers who get these things into a real, three dimensional orbit around the Earth, let alone around Saturn.

Anyone tried to park a satellite in the Moon's Lagrange points? In the model, I mean.
Is there a way to show our best attempts to each other?

John

Indigo
2004-Aug-13, 10:47 AM
this is superb! As has been mentioned before, a way to expand the view to fill the whole screen would be useful, as would an option to add more planets - the chance to actually send one to mars, for example, would be great!

Are there any other versions like this?

I now have 4 fast moving satellites in permanent Earth orbit, and manged to get something orbiting the moon for a full "month"! I've also got a good few things out on wildly elliptical orbits that pop back into the system every now and then :)

There goes any work done today!

Glom
2004-Aug-13, 12:57 PM
No maths. :evil: I could do it on SpaceSimulator.

Argos
2004-Aug-13, 01:24 PM
*** ALERT: THAT THING IS HIGHLY ADDICTIVE ****

Very cool. I managed to make the smallest body be in a stable orbit for about four minutes. It would correspond to a nearly a year. long lasting orbits are achieved more often when the body inserts itself counterclockwise.

Maksutov
2004-Aug-13, 02:18 PM
Multiple swings around the Moon with Earth returns. One month of lunar orbit. Many stable Earth satellites. But a stable lunar orbit seems almost impossible.

ZaphodBeeblebrox
2004-Aug-13, 03:31 PM
Multiple swings around the Moon with Earth returns. One month of lunar orbit. Many stable Earth satellites. But a stable lunar orbit seems almost impossible.

Hmmm ...

Just like reality.

Aside from the Earth being right Next Door, so to speak, The Moon also has a Very Bumpy Internal Structure; thus Any Lunar Orbit, should decay Rather Rapidly.

Amadeus
2004-Aug-13, 04:28 PM
I'am no good at this.

Can't orbit the moon

The only earth orbits I can get are eliptial.... though they seem to be able to keep going for about 30 mins.

Argos
2004-Aug-13, 07:10 PM
Many stable Earth satellites.

I got just one in hundreds of attempts. It would be nice having a body like that orbiting Earth. Its orbits would alternate from highly elliptical (with tight fly-bys) to circular, but it would never be caught by the Moon, or be thrown on Earth. It was a pity having to turn the computer off. It was like a god having to destroy its perfect creation...

ToSeek
2004-Aug-13, 07:38 PM
Many stable Earth satellites.

I got just one in hundreds of attempts.

Be sure you have your satellites orbit in the opposite direction from the moon. That seems to help for some reason.

aurora
2004-Aug-13, 07:48 PM
Many stable Earth satellites.

I got just one in hundreds of attempts.

Be sure you have your satellites orbit in the opposite direction from the moon. That seems to help for some reason.

Yes, in a reverse orbit between the Earth and Moon, the Moon seems to continually adjust the orbit to be more and then less elliptical.

Orbiting in the normal direction, I can only get an orbit to work if it is close to the Earth where the Moon has little influence.

Argos
2004-Aug-13, 07:56 PM
Many stable Earth satellites.

I got just one in hundreds of attempts.

Be sure you have your satellites orbit in the opposite direction from the moon. That seems to help for some reason.

Ok, but I want some challenge! :D

Swift
2004-Aug-16, 01:25 PM
This (http://www.engr.newpaltz.edu/~biswast/) professor's website has games called "Black Hole Orbiter" and "Quantum Duck Hunt"

JohnD
2004-Aug-17, 11:43 PM
All,
Playing with the original Colorado site game, I've discovered some useful tactics.
1/ Multiple mouse clicks get a stream of 'satellites' that track the sheaf of possible orbits from that point. For instance, do so some way from the Moon, and as they fall to Earth you clearly see the seperation that was shown by that comet that fell into Jupiter.
2/ Do this about one diameter outside the Moon, as it goes by. Some of the sheaf of orbits include many of the Moon itself, some for more than two 'months'. The orbits are odd, in that the satellite rounds the Moon close by outside its orbit, slows, then catches up inside, to almost come to a halt about 15 degrees in front of the Moon and repeat, more or less but never the same.

BUT, I'm still trying to land a satellite in a Lagrange point, and have it stay there. Lots that slowly pass the point about 60 degrees ahead or behind seem to hesitate there, but never settle. If the L-points are supposed to 'attract' space debris, why is it so difficult to get one to stay there?
John

ToSeek
2004-Aug-18, 12:58 AM
The L4 and L5 points are home to stable orbits so long as the mass ratio between the two large masses exceeds 24.96.

- http://www.physics.montana.edu/faculty/cornish/lagrange.html

Maybe the mass ratio is off for this example? That does seem to be a pretty heavy moon. In any case, you probably have to get it pretty close to the mark to get a stable orbit there.

Indigo
2004-Aug-19, 09:43 AM
Is anoyone else finding this applet no longer works?

:(

Argos
2004-Aug-19, 02:34 PM
I canīt see any problem with it in my browser. Maybe your Java permissions...

Grey
2004-Aug-19, 04:55 PM
Maybe the mass ratio is off for this example? That does seem to be a pretty heavy moon. In any case, you probably have to get it pretty close to the mark to get a stable orbit there.
Correct. Looking at the source for the web page, the mass ratio is only 6 to 1, so L4 and L5 aren't stable. I sent e-mail hoping to get the actual applet source so that I could play, but I haven't heard back. It looks like it's been a long time since most of these were updated, so it might be hard to find the person who actually worked on the various applets.

MachineElf
2004-Aug-20, 11:25 AM
Hi, first time poster long time lurker here. :D
I had fun playing with this little program so i thought i would do a google for similar stuff and found this.

http://www.geocities.com/Paris/6502/impact.html

With this one you can have multiple objects and set parameters such as mass and diameter and it also runs full screen.
One drawback is the balls bounce of the edge of the screen but the source is available so maybe someone here with java knowledge could tweak this.

Have fun :D

Argos
2004-Aug-20, 12:29 PM
You can easily translate that Java code into ActionScript to make a Flash movie. Few adaptations are required.

Welcome. :)

JohnD
2004-Aug-20, 03:41 PM
Akll,
I would be cautious with that one.
Although it claims to be sponsored by IBM, it loaded multiple copies of itself onto my screen and then went haywire - flashing screens everywhere.

Alt/Ctrl/Del got rid, but I have a line of empty application boxes alng the bottom of my screen. I'm about to run McAfee virus checker. Let you know.
John

MachineElf
2004-Aug-20, 05:00 PM
Akll,
I would be cautious with that one.
Although it claims to be sponsored by IBM, it loaded multiple copies of itself onto my screen and then went haywire - flashing screens everywhere.

Alt/Ctrl/Del got rid, but I have a line of empty application boxes alng the bottom of my screen. I'm about to run McAfee virus checker. Let you know.
John

I googled Impact and Gravity Simulator before i posted the link and and found alot of pages including universities/educational sites that link to the applet so i can be pretty sure it is legitimate.

JohnD virus is not a term that should be used lightly, it would be a shame for people to miss out on a fun program due to one persons scaremongering.

Anyway here is the homepage of the author, I guess people will have to make up there own minds.

http://www.geocities.com/Paris/6502/

JohnD
2004-Aug-20, 08:54 PM
Machine Elf,
As one of the little people who live behind my computer screen and do all the writing, I have no doubt you know the difference between a virus and any other horror that comes down the phone line. The rest of us can go on calling them viruses, worms, crabs or thingummyjigs. I speak as I find, and after logging onto that website the odd things that I described happened.

Moreover, I did run McAfee - no viruses (that's what McAfee calls them), and then AdAware. Then the PC froze - very odd! I had to switch off to make any progress. Re-boot (you see I do know some jargon!) went smoothly, and here I am again. But I'm not going back to the site you cited.

John
PS. You do it, lots of others do it. You copy the post to which you are replying into yours, even when that previous post appears immediately above on the board, and immediately below when you are composing yours. Why? This is definitely a US habit - it never happens on UK message boards!
J.

ToSeek
2004-Aug-20, 09:02 PM
You do it, lots of others do it. You copy the post to which you are replying into yours, even when that previous post appears immediately above on the board, and immediately below when you are composing yours. Why? This is definitely a US habit - it never happens on UK message boards!
J.

I like to make sure people know what I'm responding to. It's potentially ambiguous when I don't quote, so just about the only time I don't is when I'm entering the second post on the thread (and responding to the first, of course).

MachineElf
2004-Aug-20, 11:46 PM
Machine Elf,
As one of the little people who live behind my computer screen and do all the writing, I have no doubt you know the difference between a virus and any other horror that comes down the phone line. The rest of us can go on calling them viruses, worms, crabs or thingummyjigs. I speak as I find, and after logging onto that website the odd things that I described happened..

Hmm..maybe some kind of windows error?


Moreover, I did run McAfee - no viruses (that's what McAfee calls them), and then AdAware. Then the PC froze - very odd! I had to switch off to make any progress. Re-boot (you see I do know some jargon!) went smoothly, and here I am again. But I'm not going back to the site you cited.

So you admit you were wrong and jumped to conclusions, there wasn't a virus and now your trying to insinuate that the page from 1997 contains spyware. Errr...ok :roll:
Maybe it's time for an upgrade JohnD your system seems unstable.
Did adaware find anything or not?


John
PS. You do it, lots of others do it. You copy the post to which you are replying into yours, even when that previous post appears immediately above on the board, and immediately below when you are composing yours. Why? This is definitely a US habit - it never happens on UK message boards!
J.

I am at a loss to explain this...you dont like to be quoted when your wrong is my best guess.
Maybe you thought you could go back and edit your mistake.

You seem to have taken this personally JohnD, please don't.
You panicked because your computer crashed, it happens.
Just admit that the link didn't melt your pc or eat your mousemat.

Have fun and stay safe :D

MachineElf

Spacewriter
2004-Aug-21, 01:25 AM
I've had a satellite orbiting in same direction as the moon, with its apogee precessing with the moon's orbit for about 10 minutes now...

cool!

JohnD
2004-Aug-21, 07:41 AM
Machine Elf,
Maybe so. When one knows as much as you do, it is easy to feel calm. When one is a mere user, one feels very much more vulnerable.

This medium can be as personal as a quiet chat between two people - in that situation, a third person butting in, unknown to the protagonists and uninvited, is offensive especially if they hijack the conversation and start swearing. That's what it feels like, sort of.

So forgive me if I am alarmed by apparently illmannered behaviour by an unfamiliar website. How do I know if this lout (the website) is just ill mannered or dipping for my wallet while I am distracted? I get out of the conversation and stay away.

Best wishes,
John
PS you were teasing me with all that quoting, weren't you? Look, no quotes at all!

MachineElf
2004-Aug-21, 09:26 AM
JohnD,
Fair enough, I can understand that you may have been concerned by your computer acting in an unfamilar way but to be honest if this is the first time your pc has done something unexepcted then you have been very lucky.

I hope that you can understand that for me to find that my first post on this board is followed up with a virus warning was a little disconcerting.
After all you only get one chance to make a first impression. :D

Anyway enough has been written on this little episode and i wish you well.

MachineElf

BTW The reason I generally quote the message i am replying to is that on faster moving boards there can be other replies posted while you are typing yours so it makes it clear to what you are referring. This isn't just a practice of our american friends as I am in the UK.

PS Look no qoutes :wink:

Grey
2004-Aug-22, 08:17 AM
While looking for something else, I found this (http://www.ai.mit.edu/people/wessler/halo/) entertaining siumulation for those that were interested in exploring orbits at the Lagrange points.

JohnD
2004-Aug-22, 11:35 AM
All,
Despite previous experience and reassured by Grey's staus as a Fellow (No offence, Elf) I ventured to this one and very interesting too!

Bizzarely, it allows one to "delete the Sun", whereupon everything else zooms off into space, of course.

Strangely, if you start it again (reset) in 'coarse' mode, the L1 satellite orbits the Sun, instead of staying around the planet as it does in 'normal' mode. That solar orbit is eccentric, but it is not 'circularised' by an approach near the planet as happened in the Colorado applet. Is this because the Sun has so much more mass than the Planet?

Previous posts here said that the original Colorado applet did not allow Lagrange items because the masses of the Sun & Planet were too similar. Here, the Sun is said to be 'very heavy', LGs are clearly possible, so I presume the masses are very different.
JOhn

PS Why are these "Halo" orbits? I thought the Halo was the Oort cloud.

Grey
2004-Aug-22, 03:08 PM
...reassured by Grey's staus as a Fellow
Don't take that too seriously! :)


Strangely, if you start it again (reset) in 'coarse' mode, the L1 satellite orbits the Sun, instead of staying around the planet as it does in 'normal' mode.
Hmm, no, it looks like when you reset, that moves everything to the starting positions and velocities, but doesn't recreate objects that you've deleted. So, that central object is now the Planet, since there's no Sun to center on, and it makes sense for the other objects to orbit it, since there's no other massive object (if you turn off tracking on the Planet after deleting the Sun, you'll see that only L1 actually orbits, the others are too far away and moving too fast, so they fly off on nearly straight trjectories). Likewise, if you've changed the initial velocities of objects, Reset returns them to that new set value. If you wanted to completely restore the applet to the original settings, you'd have to reload the page, I think.


Here, the Sun is said to be 'very heavy', LGs are clearly possible, so I presume the masses are very different.
The Sun is set at a mass of 1000, while the Planet is 10, easily larger than the necessary mass ratio. If you change the Planet's mass to 40, very close to the limit, the object at L4 becomes unstable immediately, while L5 seems to continue to be stable (though you might be able to find a stable L4 orbit by changing some of the initial parameters here). A Planet mass of 50 makes both unstable immediately.

You'll also see the planet move in and out when changing the mass - you've changed the center of mass for the system, so it's initial velocity gives it an elliptical orbit, rather than a circular one. You could likewise play with adjusting the Sun's mass, but you'd need to change all the initial velocities if you wanted everything to remain in orbit.


PS Why are these "Halo" orbits? I thought the Halo was the Oort cloud.
Certainly "halo" is used for other things (galactic halos, for example), but I'm not absolutely certain. My guess, though, would be that the objects move in a circle, but there's no central object that they're orbiting - it's just a ring (well, more or less) in open space.

JohnD
2004-Aug-22, 07:59 PM
Thanks, Grey. Reassuring or not, your explanation and demonstration give me more to think about and play with.

It's nice being a god, isn't it!
John