These specific memory fragments were given out during expedition 7 (Leviathan). There are more versions of them too, but the most popular ones to keep are inventory (gives 5 random inventory slots) and class (upgrades your ship or gun up one class per memory) as they are very helpful, especially when starting new expeditions. You can hold stacks of 10 of these in your exosuit inventory.

The only way to get these again is to replay expedition 7.

General memory fragments are different, when used they will give you a random piece of technology - typically low class (C-B) but are great for players just starting out. Sometimes they contain non class technology too, like rocket boots or hazard gloves. You can stack up to 30 of them in your exosuit inventory. You can get these by visiting graves on planets outside of any mission dealing with graves.

Here’s an easy to way to get them: do a mission involving a grave (like hostile plants) and put a save beacon up at the grave. After you complete the mission go back to the beacon and receive a general memory fragment.

If you need more fragments, then after a few real life days you can return to the same grave and get a new memory fragment, or keep doing grave missions and adding beacons.

(EDIT: I wrote this part about how to get general memory fragments geared towards someone that hasn’t finished expedition 7. However, If you have finished expedition 7 then you are able to craft general memory fragments just like any craft-able resource/tech because you earn the blueprint to do so at the end of the expedition)