Comment by mr_toad 3 days ago
The only real advantage is 24/7 power without having to use batteries (or some other power supply at night or when cloudy). The way solar prices are going the problem of suppling power when the sun isn’t visible is a real bottleneck.
I think a prerequisite to doing any really big stuff in space would be fully and rapidly reusable launch rockets, which could get costs down by a couple orders of magnitude.
And geostationary isn't necessary for this. You could go a bit higher or lower and still have 24/7 sunlight. Relay your communications through Starlink or something and you have full connectivity.
That said, I think orbital data centers still don't make sense, for all the reasons described in the article.
There's one obvious potential application, which is caching of common requests. If something like segments of streams or any CDN contents is cached on the satellite, it reduces communication to a single hop for a large portion of traffic (IIRC, 70% or so?). Storage is very lightweight these days and failure to read cached data is not critical, so putting lots of SSDs on a LEO constellation satellite seems like a no-brainer to me if you're trying to optimize bandwidth usage.
That seems like it would make the most sense on the "last mile". So, adding caches to the LEO satellite ISP birds would be a good idea. I wonder if Kupiter, StarLink, et. al. do that. (And if not, their reasoning against it since they've surely considered it.)
Geosynchronous orbits do not pass through the Earth's shadow as much as you might think. These orbits sit in the same plane as the equator, which is tilted 23.5 degrees when compared to a line from the sun to the earth.
They still pass through the earth's shadow in the weeks around the equinoxes though. Worst case is about 70 minutes of shadow.
That said, it seems more likely to me that there is no requirement to stay over the same spot on the earth, and a lower altitude sun-synchronous orbit would be used.
The article covers why this doesn’t work in detail.
For 24/7 solar... you are either in a sun synchronous orbit or in a very high orbit.
The sun synchronous are polar orbits ($$$) that are preferred for earth observation (so that the sun is casting the same shadows). As these are polar orbits, the satellite is not overhead all the time and getting a satellite into such an orbit takes a bit of work.
A SpaceX is at about $3k / kg to LEO. The numbers I see suggest a $20k / kg to a polar orbit.
The next option is being far enough out of the way that the earth's shadow isn't an issue. For that, instead of a 500 km sun synchronous orbit, you'd be going to 36,000 km orbit. This is a lot further from the surface, takes a lot more fuel... and it's a geostationary orbit.
However, as a geostationary orbit, these spots are valuable. Slots in this orbit are divided into slots.
https://www.astronomy.com/space-exploration/wealthy-nations-...
> There are only 1,800 geostationary orbital slots, and as of February 2022, 541 of them were occupied by active satellites. Countries and private companies have already claimed most of the unoccupied slots that offer access to major markets, and the satellites to fill them are currently being assembled or awaiting launch. If, for example, a new spacefaring nation wants to put a weather satellite over a specific spot in the Atlantic Ocean that is already claimed, they would either have to choose a less optimal location for the satellite or buy services from the country occupying the spot they wanted.
> Orbital slots are allocated by an agency of the United Nations called the International Telecommunication Union. Slots are free, but they go to countries on a first-come, first-served basis. When a satellite reaches the end of its 15- to 20-year lifespan, a country can simply replace it and renew its hold on the slot. This effectively allows countries to keep these positions indefinitely. Countries that already have the technology to utilize geostationary orbit have a major advantage over those that do not.
Furthermore, the "out of a nations control" - those slots are owned by nations. Countries would likely be very annoyed for someone to be putting satellites there without authorization. Furthermore, they only work with the countries on those areas. They also require spacing to ensure that you can properly point an antenna to that satellite.
Furthermore, geosynchronous orbits have a 0.5 second round trip lag. This could be a problem for data centers.
Misbehaving satellites in the geosynchronous orbit are also of concern ( https://en.wikipedia.org/wiki/Galaxy_15 ).
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Putting things in these orbits is pricy. For LEO, you'd need a lot of them. For geosynchronous, the idea of servicing them is pretty much a "you can't do that" (in 10 - 20 years they use their last fuel and get pushed to a higher orbit and pretty much get forgotten about).
Satellites in geosynchronous orbit are things that need to be especially well behaved because any orbital debris in that area could really ruin everyone's day.
Compute in space doesn't make sense.