4 ms·

The amount of preparation is much, much more than every other "accessible" installation. Typos are the worst to recover from, backspace usually doesnt exist. As

The amount of preparation is much, much more than every other "accessible" installation. Typos are the worst to recover from, backspace usually doesnt exist. As I've sent commands to our Linux-running satellites, its usually prepending your commands with ctrl-c characters and a couple newlines at the end, just to make sure it runs and nothing is left in the buffer. There is also a possibility that commands get executed multiple times, and there are usually limits in transmission speed, processing speed, and frame length. Sending a lot of characters over a terminal can cause characters to be eaten, creating typos you can't see, affecting the commanding immensely.

abnry 5y ago
Very fascinating! You haven't happened to written a blog post or something on this, have you? I am sure HN would love reading about it.
- diamondo25 5y ago
  Sorry, I did not. There are plenty of stories on the internet about cubesats, they get launched by universities even :)
bentcorner 5y ago
Isn't there some way to ensure that what you typed is what is being executed? Dropping characters from the terminal sounds terrifying. I don't know enough about ssh and terminals to know if it's possible to type "12345" and see "12345" echoed back to me but really what the remote session sees is "1245".
- diamondo25 5y ago
  Yes, terminals usually echo back the characters. In our case this would be buffered and we could request the buffer. But that would still take some operations. Best way, usually, is to send a bunch of commands in a way you ensure proper order of execution (eg write a file, check checksum of file, execute file), and make sure you can pull the logs afterwards. Nowadays, links and systems get easier to work with, and you can sometimes have a literal TTY open to the system, like Reactor Hello World has ( https://reaktorspace.com/reaktor-hello-world/ https://reaktorspace.com/reaktor-hello-world/ ). However, this is over S-band, which is a 2Mbit/s link, so overhead for a stable TTY (or ethernet connection) is a lot less than using UHF/VHF.
3pt14159 5y ago
I'm surprised theres no error correction in your uplink. Crazy.
- diamondo25 5y ago
  It depends on the API. If your API is "put this data over uart to the TTY", and the uart of the device is overloaded and drops characters... Or maybe mangles characters due to bitflips. Or what have you. Its all possible!
- nonameiguess 5y ago
  One of the more interesting projects I ever had to complete was while awaiting clearance when I first started working for the NRO years back in ground processing algorithms (no longer work there, by the way). One of the long time guys gave us an assignment to implement the BCH error-correcting code, and then iteratively optimize it until we were able to implement the algorithm for computing the code published in a company proprietary whitepaper that was more efficient than any of the publicly published algorithms. That was just everything that is fun about programming. The actual production implementation corrected up to 8 bits per block, though I can't remember the block size any more. Ground processing was a totally separate program and contract from mission control, though, so my team only ever received data from the satellites. We never sent data to them.

abnry 5y ago

Very fascinating! You haven't happened to written a blog post or something on this, have you? I am sure HN would love reading about it.

diamondo25 5y ago
Sorry, I did not. There are plenty of stories on the internet about cubesats, they get launched by universities even :)

bentcorner 5y ago

Isn't there some way to ensure that what you typed is what is being executed? Dropping characters from the terminal sounds terrifying. I don't know enough about ssh and terminals to know if it's possible to type "12345" and see "12345" echoed back to me but really what the remote session sees is "1245".

diamondo25 5y ago
Yes, terminals usually echo back the characters. In our case this would be buffered and we could request the buffer. But that would still take some operations. Best way, usually, is to send a bunch of commands in a way you ensure proper order of execution (eg write a file, check checksum of file, execute file), and make sure you can pull the logs afterwards. Nowadays, links and systems get easier to work with, and you can sometimes have a literal TTY open to the system, like Reactor Hello World has ( https://reaktorspace.com/reaktor-hello-world/ https://reaktorspace.com/reaktor-hello-world/ ). However, this is over S-band, which is a 2Mbit/s link, so overhead for a stable TTY (or ethernet connection) is a lot less than using UHF/VHF.

3pt14159 5y ago

I'm surprised theres no error correction in your uplink. Crazy.

diamondo25 5y ago
It depends on the API. If your API is "put this data over uart to the TTY", and the uart of the device is overloaded and drops characters... Or maybe mangles characters due to bitflips. Or what have you. Its all possible!
nonameiguess 5y ago
One of the more interesting projects I ever had to complete was while awaiting clearance when I first started working for the NRO years back in ground processing algorithms (no longer work there, by the way). One of the long time guys gave us an assignment to implement the BCH error-correcting code, and then iteratively optimize it until we were able to implement the algorithm for computing the code published in a company proprietary whitepaper that was more efficient than any of the publicly published algorithms. That was just everything that is fun about programming. The actual production implementation corrected up to 8 bits per block, though I can't remember the block size any more. Ground processing was a totally separate program and contract from mission control, though, so my team only ever received data from the satellites. We never sent data to them.