TDD Examples
And a Few Small Hacks
October 9, 2025
1 Voyager II
In July 2023, operators sent a command to Voyager II - a space probe travelling more than 2 billion miles away from the Earth 1.
That command caused the antenna on the probe to assume a different angle.
While the antenna was previously pointed straight to the Earth, now it was pointing somewhere else. This meant it could neither receive signals from the Earth, nor send them back.
One chance of restoring communications with the probe was a periodic reset scheduled for October. That would mean three months without contact.
A month later, the operators tried sending the strongest signal they could emit, into as wide a range as possible.
Thankfully, one of their attempts worked, and that restored the communications channel.
It turns out the way NASA keeps in touch with its spacecraft resembles a command-line interface (CLI).
If you are familiar with any Linux shell (Bash, Zsh, etc.), you are already a step closer to understanding, and even operating, space probes!
Devices with Linux on board run on Mars 2.
Over such a long distance, the round-trip time (RTT) is around 20 minutes.
Luckily, as someone commented 3:
Huge delays between keypresses is what Vi (and Vim, of course) was designed for.