NinjaMoreLikeANonja OP t1_jdc9e2g wrote

Hindsight is 20/20, and engineering hindsight is hyperspectral 20/20 so…

Honestly, there are not that many ham radio modules for Arduino. We were also supply chain limited (this was in the midst of the COVID parts shortages) and the RFM96 was usually in stock.

I just spoke with SBUDNIC’s radio engineer last night and we talked a bit about this because we are in the midst of creating a more formal conference paper that details the project. His feeling is that the board is likely fine, and that we just made some shit assumptions about duty cycle and link margin and the like when we were finalizing transmission protocols. I agree with him.

So yes- I would use it again.


NinjaMoreLikeANonja OP t1_jd7cy3w wrote

A bunch of us took a class called ENGN1760: The Design of Space Systems, taught by Rick Fleeter. Rick is a true spacelord engineer through and through (among his many achievements: he invented and launched a precursor system to GPS) so he’s- as you’d imagine- pretty well connected. He came into a launch opportunity and passed it on to the class.

At the end of the semester, four of us decided to keep going and build the project into what it is today. We grew the team to ~40 folks at Brown, and then another ~25 folks elsewhere in the world who were consulting/helping out/working with our launch provider. No one got paid- everyone did this out of the love of the game. Pretty amazing.

We aren’t the first folks to put a drag sail on a satellite but we are likely the first folks to do it as cheaply and quickly as we did it. Our hope is that the satellite demonstrates that deorbiting is not expensive, from both a financial and mass perspective. The system cost maybe $150 and weighs ~$250 grams. In the space world, that’s pretty damn good. About $140 of that build cost was the Kapton film- that stuff is expensive!- so if someone were to find a more affordable space-safe material, the system could be made far more cheaply. I would love to see that.


NinjaMoreLikeANonja OP t1_jd5nrcw wrote

Yes! There’s a ham radio on SBUDNIC. We tapped into the TinyGS network. Our specific module was the RFM96. This part of the mission failed. We also built two wide angle cameras into the front end of SBUDNIC, with the intent that we would transmit a couple potato vision quality images down from space over ham band. We tested the ever-living daylights out of that subsystem and- for reasons that will forever remain unknown- it just failed to work on orbit. We never actually heard a radio ping of any kind from SBUDNIC.

That being said, we know the satellite was alive- at least in the beginning- otherwise the sails would not have deployed.

We optimized for satellite lifetime rather than broadcast frequency. It’s totally possible that we were just never in the right place at the right time to catch SBUDNIC’s radio blast. It was set up to transmit every 10 minutes, for about a minute. The TinyGS network is pretty great, however we were broadcasting at 50mW so it was a VERY quiet signal even in the best of times. It’s not impossible- it’s been done before by other satellites- but it’s certainly challenging.


NinjaMoreLikeANonja OP t1_jd5fe1c wrote

There is actually atmosphere in space! The atmosphere never really ends, it just kinda slowly gets less and less dense. Technically, there's Earth atmosphere on the Moon, but it's just suuuuuuuuuper duuuuuuper basically-not-really-there. Also, the Sun spews hot space gasses at us constantly so there's drag from that too.

At 550km where SBUDNIC was initially deployed, there's very very little but- over the course of thousands of orbits- the drag adds up! It takes a long time.


NinjaMoreLikeANonja OP t1_jd5exo7 wrote

We are not the first people to do a drag sail by any means, so companies are already using this tech. The difference is that we did it faster and WAYYYYY cheaper than it's been done before, especially at the scale of a cubesat.

Our aerospace professor Rick Fleeter had access to a launch slot so 4 of us decided to spin up the project into something big. It grew from there into a team of 65+ plus students and engineers from across the world. All the engineering and fab was done at Brown by students; the multinational part of the team was our launch partner, D-Orbit, who provided a carrier satellite for the ride up to space.


NinjaMoreLikeANonja t1_jd590gl wrote

100% correct. Think about it like this- two objects are in orbit around the Earth, each moving at 17,000+ miles per hour depending on how high the orbit is, and those two objects must touch. In the worst case velocity scenario, the two objects are counter-rotating in the same orbit so closing speed is 34,000+ mph. In the worst case positioning scenario, one object is orbiting along the Equator, and the other is orbiting over the Poles. The two satellites must hit one another- without destroying either satellite- at one particular point in space. Not. Gonna. Happen. The amount of propellant required to make that kind of shift would be greater than the mass of both satellites combined. Cool in theory, and maybe possible one day if there are a shitload of janitor satellites up in a bunch of orbits around the Earth, but extraordinarily hard to do in practice.


NinjaMoreLikeANonja t1_jd582os wrote

Changing trajectory means changing orbit and changing orbit takes energy. The presumed (and soon to be legally mandated) end of life goal of all smallsats and cubesats is to burn up in the atmosphere. You can do that by reserving a last gasp of propellant on the satellite to lower the satellite's orbit, but that assumes that there is a thruster on board somewhere. A lot of small satellites don't have thrusters. The drag sail approach is nice because it's passive, and all the energy required is collected from atmospheric impact rather than stored on the satellite as a propellant of some kind.


NinjaMoreLikeANonja t1_jd3ajvz wrote

Hey everyone! I’m Marco, the Chief Engineer from SBUDNIC. I’m legit shocked/delighted by the response here, and so I’ll be doing an AMA tonight at 6:30 EST. U/theantimosby will likely also be stopping by; he is one of SBUDNIC’s engineers. See you then!