Roll 1d4, on a 1 pirates have a large presence in the system.
Check for pirate encounters each time a PC vessel moves to a new orbit. Roll 1d6, on a 1 pirates have detected your vessel. If this orbit contains a pirate base an encounters occurs on a 1 to 3. The lead vessel of the crew will hail the PCs, roll on the Pirate Reaction table to determine their attitude.
Pirate Reactions (1d6)
1-2: Attack, the pirates make dire threats and engage.
3-4: Extortion, the pirates demand 1d6x1000 credits to ensure safe passage, parties unable to pay will be attacked.
5: Neutral, the pirates are kind of bored and looking to chat.
6: Friendly, the pirates are willing to impart the PCs with some system data or an item if they have the cash.
Roll 1d3 for the number of vessels in the encounter. Roll 1d5 for the Hull Class of each pirate vessel. The total value of each should be no more than (1d4 + Hull Class) x 100,000 credits. That number is entirely arbitrary and possibly terrible, I ain't got time to stat those ships for you.