The general rule is that if a prepositional phrase is really short (3-4 words or less), you don't need the comma. If it's longer, or at all confusing, you add the comma.
So, 'In 1952 the explorer landed on the island and claimed it for Spain.' is fine because the prepositional phrase is only 2 words.
But, 'On the morning before our wedding anniversary, my husband surprised me with a trip to Las Vegas.' would need the comma because it's so long.
And, 'After sweeping up my sister washed the floors.' definitely needs a comma after up, because it's confusing. It sounds like you're sweeping up your sister.