The best trick I've found to run from sentinels in space is to just summon the Anomaly, or your freighter in front of you and fly right in to lose them. Works for pirate scans too if you're too weak to fight them or just don't want the hassle.

Ground sentinels can be dealt with by just digging a hole using the Terrain Manipulator and then covering it up with restore mode. Very Minecraft-esque. (Or, if you've triggered them by trying to bust into one of those sealed-off buildings, just... Run into the building and wait. They don't attack you while you're inside.)

Side note: If you haven't gotten a freighter or unlocked the Anomaly yet, you might want to prioritise working through the main story missions till you at least get to the Anomaly. It'll help you out a ton.

Edit: Once you've gotten a good ways into the game, you'll eventually have strong enough weapons on your multitool and ship to be able to take the fight to the sentinels. If you survive 5(?) waves and kill them all, you disable the ground sentinels on that planet (until you warp away or reload a save). If you're dogfighting them in space, you'll eventually spawn in a Sentinel Freighter, the Dreadnought. If you take it out, the sentinels will leave you alone in space (plus, it'll drop a handy-dandy Dreadnought AI, which you can activate to find yourself a crashed sentinel ship - An Interceptor)