https://www.google.com/search?q=spectrolab+gaas&ie=utf-8&oe=...
https://en.wikipedia.org/wiki/Multi-junction_solar_cell
Spectrolab is owned by Boeing.
Even at a cost of $10k per kg it makes very little sense to use 50% less efficient solar panels to save a few thousand, especially when the superior technology is also far better tested in space. It makes sense to use an Android instead of a $100k RAD hardened processor if your entire CubeSAT barely costs that much. Since most satellites cost a minimum of a million each, very few can afford the risk to save money on parts (and if you're mass producing thousands of them you can get really cheap germanium panels).
You want the greatest possible power capability in the smallest and lightest package, and right now the way to do that is a triple or quadruple junction GaAs type PV cell with a concentrator lens in front of it. Efficiencies range from 32 to 40%, vs 22.5% efficiency for the very best monocrystalline Si PV cells.
These aren't geostationary - they're low earth orbit. This means several things:
- cheap to launch - and to deorbit.
- lots of erosion compared to GEO - LEO is like being in a mild sandblaster while occasionally being shot at by rifles and howitzers.
Taking those two alone into account, you either end up building for durability or for disposability.
When you're dealing with a fleet of 4000 and your speciality/the thing you want to practice is heavy lift to LEO/MEO, you are absolutely talking about a disposable fleet where you expect daily failures and replacements. Having mass production facilities at your fingertips can't hurt.
Which is why they'd likely go for the cheaper tech that they have very low cost access to, even if it costs about the same after launch costs. Also, it would be more profitable for the collective enterprises than outsourcing such a component to a third party. Think about it - spend the money with a competitor, or at the gas station. I know which I'd do.
So - despite obvious truths re GaAs, my money is on them using their own Si cells.
At 1100 km the debris population is relatively sparse. https://en.wikipedia.org/wiki/File:Spacedebris_upd_2011.jpg
Do you see how small the difference is in absolute terms? That means that only a few hours of labor per solar cell or 100g of launched payload mean the difference between a 50x and 1x difference. Two GaAs panels ($100) will requires tens of grams less support structure than the three Si panels producing the same power ($3) so already the extra launch cost (at $5k per kg, assuming free payload support structure) for the Si panels is eating away at their benefit. Each solar cell will need hours of inspection and testing by people paid $25+/hr so even if each extra Si cell and support structure costs nothing to launch, the final cost once fully assembled, installed, and tested will be in the range of $1k-10k per solar cell.
Especially at the scale of disposable satellites, GaAs is likely to be cheaper, more efficient, and free more volume and mass in the satellite design. 4000 satellites worth of Si solar cells would be the equivalent of a few dozen decent sized residential installs so it would be a drop in the bucket for SolarCity. I don't think keeping such small scale business in-house is much of an advantage, especially when there are many other suppliers with lots of experience in using solar cells in space.
They have a satellite division which has a bunch of people designing things, but they have not launched their own yet. They have also made known their intention of fielding a global internet service via a large constellation of satellites. This application would be a step toward that goal.
http://spacenews.com/oneweb-satellites-to-settle-in-explorat...
https://en.wikipedia.org/wiki/OneWeb_satellite_constellation
This means that existing companies that build telecom satellites need to do it a new way for these constellations of lots of small satellites.
Also, I think the Falcon 9 uses VxWorks for at least some of its realtime control: http://blogs.windriver.com/vxworks/2010/12/vxworks-helping-c...
> One of the areas they focus on is scheduler performance. They do not have hard realtime requirements, but do care about wakeup latencies, he said.
It sounds like their hard real time controls are on non-Linux OSs.
http://www.spacex.com/sites/spacex/files/pdf/DragonLabFactSh...
Can anyone who works at SpaceX chime in?
That'd be a really bad idea. Linux is too complex to trust, and lacks WCET making it unsuitable for hard realtime.
There's open source options, but Linux isn't among them. I'd look at seL4 for this purpose.
Telecom satellites already require tons of specialised integrated circuits because general purpose CPUs are too complex and power hungry for the amount of bandwidth the satellites process. This SpaceX constellation will certainly have custom designed electronics, even if they don't use any rad hardened ICs.
How this will affect their choice of PV cells I don't know.
With 4000 satellites it's likely that their approach to each satellite will be smaller and much less redundancy:
If a traditional 5000 kg geostationary telecom satellite can be compared in analogy to a big, expensive, 4U, quad socket xeon server that has multiply redundant everything.
These small satellites might be much more like a facebook open compute blade server, 1+0 and redundant nothing, but much, much cheaper to build and with a software architecture tolerant of entire nodes failing and disappearing from the network.
They are very clearly Sunpower C60 or similar, a high end mono-Si cell.
I am a bit skeptical about the economics too, but apparently it works for SpaceX.
Given SpaceX deadlines it's possible that they just ran out of time for this optimization.
[1] https://sc03.alicdn.com/kf/HTB1XRXrHVXXXXXeaXXXq6xXFXXXM/3-5...
Musk might not care if Tesla and SpaceX disappear if electric vehicle mobility and affordable transport to Mars is achieved. They are a means to an end.
He has said multiple times that he thought the likelihood of success for each of Tesla and SpaceX was less than 10 percent, but that was ok, because even in failure, they would 'move the ball forward' on sustainable energy and making humanity a multi-planetary species.
The other: vast networks of companies all dependent on each other. When any one of them gets in trouble, it all comes falling down like a house of cards. And the chance of none of them getting into trouble? (1 - 0.<failure rate>)^<# of businesses>. That gets very small, very fast.
Lesson: never ever make a decision for business <b> because you also own business <a>. Too many people going from millionaire status to personal bancrupcy, at just about the moment where they're too old to start fresh, yet too young to coast.
Shouldn't the lesson be, "don't allow any singular company to become a single point of failure?"
Yes, but that requires more detailed analysis.
This seems like a pretty foolish way to do that. Mobile data over ground-based cellular systems is rapidly becoming a commodity, and at least in the areas of the world where Teslas will be sold, it's essentially ubiquitous. Why in the world would it be worth setting up and maintaining a massive satellite network just to cover the .001% of driver miles spent far enough away from a tower?
It will be a very disruptive business if he can pull it off