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Japan Launches "Super-Speed" Internet Satellite
A number of readers wrote in about the launch this morning of a Japanese H-2A rocket carrying a Kizuna ("Winds") satellite into orbit. Kizuna is intended to provide "super high-speed data transmission" for Japan and Southeast Asia. The news stories on the launch, such as the AP's linked here, are short on technical detail. For example they say the satellite successfully achieved orbit 175 miles above the earth — hardly suitable for Internet communications to a specific area on the surface (remember Teledesic?). Reader nebulus4 provided a link to the Japan Aerospace Exploration Agency site with an illustration and a little more detail. Such as the fact that Kizuna is destined for geosync orbit, and that a 45-cm antenna will equip eventual users for 155 Mbps down / 6 Mbps up, whereas a 5-m antenna will allow enterprises and ISPs to tap into 1.2 Gbps down. Given the latency to geosync orbit, you probably wouldn't want to use Kizuna to play an online shooter.
...the RIAA and MPAA today announced a plan to knock the satellite out of orbit with a missile to "protect the public".
22,233 miles to the satellite
round trip = times 4 = 88,932 miles
speed of light (wave propagation) = 186,282 mi/sec
latency = 88,932 / 186,282 = 0.477 seconds (on top of regular network latency)
Curse you speed of light. You win again!
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You have to multiply times four to get a useful figure. Latency is normally measured round trip. Hop up, hop down, return hop up, return hop down. Latency to geostationary orbit is half a second.
However, 175 miles up is NOT geostationary. Geostationary is 35,786 km up, give or take. The orbit is geosynchronous. That just means the orbital period is the same as the earth's rotation, so it returns to the same spot at the same time every day. It will NOT stay in the same place, however. They'll have to have several of these things in a similar orbit flying over periodically like we do for GPS satellites. It also means the round trip latency is about 3.76 msec (just less than a millisecond per hop), a heck of a lot shorter than half a second.
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175 miles is the separation altitude for the rocket. Satellites usually boost themselves to geostationary orbit. The Delta IV heavy can blast all the way to geostationary orbit but no-one can afford it.
Geosynchronous and geostationary orbits are obtained at the same radius from the Earth, about, as you say, 35,786 km above sea level. The defining factor that differentiates between geosynchronous and geostationary is the plane of the Earth the orbit is positioned over. A geosynchronous orbit that is directly aligned with the Equator is "geostationary" since it will always stay above the same position on the Earth. Plain "geosynchronous" orbits are simply aligned differently.
From the JAXA site about Kizuna:
"Scheduled orbit: Geostationary orbit at 143 degrees East longitude and at an altitude of about 36,000 km"
It is, even though the summarizer slipped up a bit (technically the term is correct, but somewhat misleading), destined for geostationary orbit.
With radio waves traveling at the speed of light what difference is 175 miles going to make?
175 miles? Try more like 22,230 miles. That's pretty much the only place you can put it unless you want your internet connection to only work 3 minutes out of every 90 minutes...
The reasons are simple physics. Gravity causes everything to want to fall towards the center of the Earth. Satellites manage to stay in orbit because they are constantly "falling" ahead of the Earth. That's why things in "low earth orbit" are referred to as being "in freefall" and not REALLY in zero gravity. Gravity is still there, only the velocity of the satellite is so high that all gravity manages to do is curve the trajectory of the satellite, not cause it to lose height. This means your satellite is going to be moving VERY fast with respect to the ground.
It's only at 22,230 miles out where the circle is so big that your satellite now appears fixed with respect to the ground. It's still moving. It's still "free-falling". But it appears to be hovering over a fixed spot over the equator - very useful for communication satellites since now you know where to aim your antenna and you don't have to bother moving it.
Seven puppies were harmed during the making of this post.
The name of the satellite has been mistranslated: 'kizuna' () means bonds (as in 'family bonds') and not 'winds', which makes a lot more sense given the satellite's function.