At the moment there is no option other than purchase each constellation key from the store 1 at a time, with the purchase button greying out after each purchase (on xbox). Which means having to swap between tabs between every single purchase.
I've got most of the chart unlocked with around 230 ish keys left to get... Having to go through the whole -purchase, swap tab, swap back, scroll down, purchase again, repeat- is highly infuriating and needlessly time consuming.
A possible way to mitigate this is to offer key bundles of 1 , 5, 10 keys so that players, while still having to deal with the greying out of the price, can purchase the very high quantity of keys needed to progress the star chart without rage quitting over the equally high quantity of time needed to navigate the menus just to do so.