3 ms·
> Traditional satellite internet uses satellites in geostationary orbits, or 35,786km high above the equator. This is great because satellites in that orbit are
by Filligree 8y ago
> Traditional satellite internet uses satellites in geostationary orbits, or 35,786km high above the equator. This is great because satellites in that orbit are stationary relative to the ground, so you just need a parabolic antenna pointed at a specific point in the sky to get great reception. But it's also terrible for latency because the signal takes 120ms just to get up, and another 120ms to get down. Assuming you live on the equator, directly underneath the satellite. For someone living in the temperate regions, typical real rtts are in the 700ms area.
This doesn't check out.
The radius of Earth is 6,300km. Assuming a receiver on the north pole, the total distance should only be sqrt((35786 + 6300)^2 + 6300^2) = 42555km, which isn't notably larger than the 36000km at the equator.
I'm sure you're still right about the latency, but it can't be just distance doing it.
- walrus01 8y agoin practical real world use the absolute minimum ping time you'll see from a 1:1 dedicated capaacity (SCPC) link via geostationary, from end terminal to larger earth station, is 489 to 491 ms. This will vary up to 495ms depending on modem modulation/framing and FEC type, and actual line of sight distance to satellite (low inclination aim angle for the antenna, if you're not directly under the satellite, vs two sites that are directly under it as viewed from geostationary). Ignoring TDMA oversubscribed VSAT networks for the moment, there are a number of different possible modulation schemes and FEC types, and FEC code rate (payload vs FEC percentages), and things that are unique to different SCPC modems, which will vary the modulation by a few ms beyond pure speed of light.
- dr_orpheus 8y agoThe latency from the distance light travels does not vary that much. The rest of the ~600 ms latency is caused by the same thing as latency on ground systems (routers, etc.). And the processors on spacecraft are not particularly fast.
- ryanmarsh 8y agoWho builds routers that go in space? Cisco? That's got to be some crazy hardware.
- dzhiurgis 8y agoApparently Elon is gonna try use consumer hardware or build their own, thats kinda part of it's cost advantage.
- dr_orpheus 8y agoCisco has built routers for space multiple times before. The first time was way back in 2003: https://en.wikipedia.org/wiki/CLEO_(router) https://en.wikipedia.org/wiki/CLEO_(router)
- ehead 8y agoI believe companies like Boeing or Space Systems Lorale do that kind of work in their satellite design groups. Same with Orbital ATK.