To fully utilise all the resources of a planetary system it is almost always necessary to transport material goods from one location to another; in most systems different widely separated locations hold very different resources which gain value when shipped elsewhere. The hot inner planets of a planetary system often have metals, rare earths, and radioactives; the outer colder worlds have vast reserves of hydrogen, water ice, and other volatiles. For this reason two principal methods of cargo transport have developed; mass driver streams (often accompanied by Herders) and cargo ships, also known as freighters.
Some commodities which have been carried by freight ships at one time or another in history: Algae; aluminium; Bigelowes (inflatable habitats); calcium; chemical compounds; clarketech; components; computers (non-sentient); construction materials; consumer durables; cryptographic keys; cultivated soil (including Garden Paste); cybernetic enhancements; diamondoid materials; dense memory storage blocks; drone robots; drugs - medical; drugs - narcotics (often illegal trade); fertilised zygotes; fuel cells; foodstuffs (processed, preserved, ready-to eat and/or raw); gen-engineered organisms; gold; goo (blue, khaki, grey...) handheld weapons; He3; high tech equipment; ices (hydrogen, water, nitrogen, ammonia, others); iron; regolith (unprocessed); luxury goods; machine parts; macro-refined nano feedstock; metal alloys; microbots; microchips; micro-refined nano feedstock; mining bots; missiles (often illegal trade); nanomedichines (medical nano); nanonarcotics; nano-refined nano feedstock; neumanns; neural enhancements; ore (unprocessed); organic material; oxygen; platinum; probes (exploration); rarities (unusual high-value goods); recipes for nanofacture (encrypted); robots (assembled); robotic components and spares; rockets (used to launch probes, satellites,common warheads, nuclear warheads, etc.); sapphiroid materials; silicon; small ships and ship components; ship weapons; slag (dead mass for ballast and momentum exchange); smart materials; space equipment; surveillance devices; titanium; vecs; volatiles in gaseous form.
An Almucantar freight ship loaded with containerised commodities
Commodities can be carried in tanks, bulk powder carriers, containers (a typical container vessel is shown here, the Almucantar class, both loaded and unloaded); large items can be attached by straps or clamps, or may be propelled by multiple drive units (the famous Bork drive unit is versatile and powerful). For ice transport in cold outer regions most ices have structural strength which may be reinforced by fractal buckyfibre reinforcement, so tankage is often not necessary; if transported to warm inner regions an insulating outer skin will be required.