How to Make a CubeSat

Yeah, it would be useful for that. In general, anything involving tracking changes on the Earth is fair game for CubeSats. I haven't heard of any organizations / companies using CubeSats for El Niño, but I think that could be a use case in the future. I think there is also a pretty good use case for gov agencies tracking hurricanes that might form due to the influence of El Niño.

I work on a CubeSat team and there are a few reasons why CubeSat teams choose aluminum.

1) CubeSat spec rules. The rules guiding CubeSats technically only allow aluminum. "3.2.15 Aluminum 7075, 6061, 5005, and/or 5052 will be used for both the main CubeSat structure and the rails." You can get a waiver, but it makes more sense to just keep to the spec for practical reasons. The CubeSat spec doesn't matter as much to private companies I think, but it does matter if you are a non profit or student team trying to get a launch with NASA.

2) Ease of use. This is the biggest reason (besides the CubeSat spec) most teams use aluminum. Aluminum is just so easy to build with compared to say carbon fiber. You can easily bend and drill aluminum to make the shapes you want for cheap. Carbon fiber is just difficult to work with.

3) Temperature resistance. Carbon fiber doesn't handle extreme temps as well. Outer space is extremely cold and in some cases it can cause carbon fiber to weaken. Meanwhile, titanium is a horrible choice because of its high temperature resistance. NASA explicitly tells people to not use it because Titanium has such a high melting point it can survive re-entry to Earth and accidentally hurt someone or destroy property.

4) Air trapping. Sometimes air can get trapped in composites like Carbon Fiber. This can result in it trying to escape into space and damaging the CubeSat. It's a major risk factor and one of the big reasons to avoid carbon fiber unless it's made in a specific way to ensure that doesn't happen. Unfortunately, it is hard to find carbon fiber that meets those standards.

5) Cost. For a 1/32 thickness 12" x 12" sheet of carbon fiber, it is 35 dollars. Same sheet size / thickness for aluminum is 16 dollars. That is over half the price. However, CubeSats are small (10 cm x 10 cm x 10cm in some cases) so material cost isn't as big of a deal as you might think. The bigger concern is the added weight might increase your launch cost. However, in practice the weight savings are negligible at the smaller CubeSat sizes. I should also note that the aluminum is mostly for the frame / chassis and that doesn't consume that much material. NASA charges nothing for their student / non profit launches so weight doesn't matter there as long are you aren't over the limit. For private launches, they usually round off the weight anyhow. Sometimes to the nearest whole KG, other times to the first decimal place. Either way, you probably aren't too concerned about weight due to the limited material used. I know for ours using Carbon Fiber wouldn't actually save on launch costs due to the rounding. If we were near the border or were doing a bigger sized CubeSat, then sure it might save us, but there are other things we can do first to save weight before switching materials. I think if we were building a very big CubeSat then yeah we might become concerned over the weight costing us extra. However, weight isn't the biggest factor for us simply because of the other reasons. Even if we wanted to, we couldn't use Carbon Fiber due to the air trapping and temperature issues.

Overall, the benefits of a lighter weight material like carbon fiber just isn't worth the difficulties that come with working with it. As a result, the standard is to use aluminum because it's cheap, works well, and is easy to use.

Edit: I said a 1U sat was around the size of a Rubik's cube before. However, I underestimated how small Rubik's cubes are. A Rubik's cube is 5.6cm on each size vs 10cm for the 1U CubeSat.

So we are actually adding imagery to our satellite so I think I can answer these pretty well.

For question 1, I do think you could use it for astrophotography. You could probably capture pictures of the stars if you have stabilization on the CubeSat. However, the photos would probably be similar to the photos taken of space from the ISS. What I mean by this is you might be able to take photos of the stars, but it wouldn't be able to see anywhere as far out as Hubble. I know a bunch of CubeSats use smartphone quality cameras so you would probably get a decent photo that might make a nice desktop wallpaper, but it wouldn't really compare to a bigger satellite. It would show an overview of the stars, but it wouldn't be significantly different from existing images imo except maybe it being from a different perspective. As far as zooming in, that would actually be kind of hard due to space constraints. CubeSats are small, like really small (10 cm x 10 cm x 10 cm in some cases). So it would be hard to fit any substantial zoom lens system in there. That might make getting ultra close ups hard. Maybe as camera tech improves in the future what you are suggesting would be possible though. Aiming it at a specific planet also might be a bit of a challenge. CubeSats mostly don't have propulsion (although we are adding an ion thruster in ours). They can use reaction wheels to rotate though. However, accurately rotating it towards a tiny planet in the sky could be hard. However, I will say you could go for a really big CubeSat design and fit a good camera system in that. Then if you solve the aiming issue you could get some really cool images that are zoomed in on planets / stars.

For question 2, we actually considered trying this. I had the idea to live stream the satellite on Twitch. We discovered that livestreaming it was hard. If you are sending data from the CubeSat to earth, the data transmission is very slow. That basically rules out livestreaming. Maybe you could transmit it to a big communications sat in orbit which then sends it to Earth. However, I suspect the data transmission speed might still be less than ideal. Plus, using a communications sat network (like Iridium) could be expensive. Let's say though communication tech gets better and you can transmit directly to Earth at a fast speed. There is still are two major issues. Regulations and getting ground stations. Every single ground station (basically an antenna on Earth that gets data from space) requires you list it on your FCC application. If it involves ground stations in other countries (especially countries the USA isn't friendly with) it can get very messy from a regulations perspective. Also, getting those partnerships to begin with can be messy as well. There are some networks like SatNogs that do allow for receiving data from volunteer ground stations in other countries. Although, I don't know if they would really be practical for livestreaming due to coverage. I know Amazon has some offerings where they let you access their ground station network that might allow for livestreaming one day. However, I haven't really explored too much into it. I also haven't heard of any teams using AWS Ground Station personally though. Honestly, you'd be forced into using Iridium regardless due to coverage being shoddy for ground stations. Overall though, I think the data speeds just aren't there yet to livestream, at least not with LoRa (which is the protocol a lot of teams use for transmission).

Who is offering a 1U for $20k? Is that to sun-sync, or one of the last-minute ISS specials?

I forgot to note that the Carbon fiber comparison isn't entirely comprehensive. Carbon fiber is stronger so you could get away with a thinner sheet which saves money. However, I will say it still somewhat illustrates the significant cost difference there. If you do have a big enough cubesat then I do think it could make a difference to launch costs. However, the advantages of aluminum and significant drawbacks to carbon fiber mean that using it isn't practical regardless.