The Interstellar Ramjet concept is 60 years old

(Robert Bussard in 1959 with his Astronutica Acta issue)

Here is a wonderful history of our theoretical investigations into interstellar travel using the interstellar medium itself (Hydrogen) for fuel.  About twenty years ago, I personally was discussing the limits of such travel with my oldest son. As you know, some regions of interstellar space contain too little hydrogen to fuel a Bussard ramjet. My son suggested sending several "tanker ships" ahead of the main passenger liner to gather hydrogen from adjacent regions and leave the h2 in the path of the passenger liner.  I don't think this concept was ever published in the modern resurgence of academic study and I am too lazy to write up the math.

Interestingly, Bussard himself mentioned the use of an extremely-large magnet field for the ram scoop but is usually not credited.