You may not be interested in the signals captured by radio telescopes but there are sources of radio signals closer to home.
Take for example How to Make a $19 Police Scanner.
That page is pitched to Windows users but equivalent software for Linux is available.
There are traditional police scanners but to make it a big data project, why not synchronize time with another enthusiast and capture the same signals?
Reminds me of cell towers and signal strength to locate cell phones.
And depending on how sophisticated you want to make your signal capture setup, you may harvest enough radio traffic to discover patterns in your data.
Google has sex offender maps.
Maybe you can sponsor a police location map. In real time.
And match up patrol cars with police officers, their arrest stats, etc.
Just to make it interesting.