# What is a good SNR value for a chipsat in LEO using bpsk?

My team and I are working on a chipsat and we are planning on launching it to LEO, we've also planned using bpsk.

However our use case is a bit different, all we need once it is in LEO is a confirmation that that the radio is still working.

In this case, what is the fair value of SNR that we should require?

Edit: I should have phrased some parts a little bit better.

By working I mean that we need to know if it survived, what we actually plan to do is have the chipsat renter the earth, and "land" in the sea for instance, however as it is reentering it'll be traveling at extremely high speeds and exposed to extremely high temperatures ( we will have a heat shield and other precautions to account for these ).

So once it lands we want to know if all the components survived this harsh exposure, so one way we figured would just be if it is possible for us to send a signal to a ground station (we'll be using a SDR receiver so we'll probably use something like GNU Radio to analyse what we receive). But this also means that, the data we need to send need not be too complicated. That is we just need to send a couple bytes for confirmation.

• Am I using Shannon-Hartley Theorem and thermal noise correctly here? The SNR tells you the possible data rate for a given bandwidth. It can be 10 or 0.1 and you can still communicate, it's just that it's a lot slower with lower SNR. So right now there is no "correct" answer to your question. Please add some details! Primarily, what is the lowest data rate you can accept? Do you just need a couple dozen bytes during a pass for confirmation? How will you track, receive, and record the signal for analysis?
– uhoh
Commented Dec 8, 2021 at 9:03
• @NgPh there are plenty of radio hardware and signal questions here, this one's certainly on-topic.
– uhoh
Commented Dec 8, 2021 at 14:52
• If' you're planning to use BPSK anyway, pick a primitive polynomial in x^20 or so, broadcast it at 1 Mbps, and you'll have a lovely timing signal to send up and back down through a simple transponder to get range and velocity measurements you can use to determine the orbit. Commented Dec 8, 2021 at 19:00
• @NgPh When/where did the cosmonauts fight wolves? hint: it wasn't in space :-)
– uhoh
Commented Dec 8, 2021 at 22:43
• @uhoh, I must (reluctantly) concede ! Commented Dec 8, 2021 at 22:54