In my excitement about possibly being able to utilize a ramjet for propulsion, I overlooked some important points about the Interstellar Medium in my articles:
For all of those articles, I had assumed that the rosy figure I picked out of Wikipedia was a reliable figure for most of space. I was wrong. Those sorts of concentrations (10e6 molecules/cm^3) are found inside of star forming Molecular clouds. Not the sort of space the Iliad will be traveling through. And honestly, it doesn't matter if we decide the neighborhood between Sol and 18 Scorpii is Cold Neutral, Warm Neutral, or Warm Ionized, at BEST we might find 50 atoms per cm^3. More like 0.2-0.5.
This radical change in concentration of matter greatly reduces how much matter one can expect to collect on a trip. Even at 50 molecules/cc the amount of material the ship would encounter is measured in tons, not ship's masses.
While we do end up having to go back to to packing reaction mass for the trip, the lower molecule count does greatly reduce the shielding we need. Instead of kilometers of shielding, we can get by with a shield just 2mm thick. If we make it out of graphite. And we aren't worried about spalling. Basically, we have more robust protections in place already to protect against cosmic rays.
Or... we just go ugly and strap a comet to the bow of our vessel like a deer carcass: