The Square Canisters Apollo 13 Had, and What They Almost Cost the Crew

For a hot Friday evening in Cologne, the best ice cream shop is the nearby store whose current offer keeps the total low without turning dessert into a long extra trip. Compare the ice cream with the rest of tonight’s list, then weigh the price difference against the distance home and the time it will spend out of the freezer.

In April 1970, Apollo 13’s crew faced a rising carbon-dioxide problem after the mission’s oxygen-tank explosion. The lunar module had square lithium-hydroxide canisters; the command module used round openings. Engineers on the ground worked from the materials already available in the spacecraft and sent the crew instructions for an adapter. NASA’s Apollo 13 mission history documents how that practical constraint became part of getting Jim Lovell, Jack Swigert, and Fred Haise home.

Start with the whole Friday-night basket

A tub of ice cream can look cheap on its own. That tells you very little about tonight’s actual spend.

Maybe you also need fruit, drinks, snacks, or something for dinner. A supermarket with the lowest frozen-dessert offer could still leave you paying more for everything else. Add the whole list before choosing a store, then check the total for a one-store plan alongside any split plan.

That keeps the decision small and useful: pick up everything close to home, or make one additional stop because the full basket makes it worthwhile. A single discounted item should not quietly decide your entire evening.

Let distance count before the ice cream melts

Cologne is spread across the Rhine, with neighbourhood errands often looking close on a map until they become a detour at the end of a hot day. A plan that saves a little money but adds a long drive, walk, or tram ride has a cost of its own.

Best Price Alert compares nearby offers against distance, then lets you set how much convenience matters tonight. Move the balance toward convenience when you are heading home with frozen food. Move it toward savings when an extra store is genuinely nearby or already on your route.

The result should be easy to act on: one shop that covers the basket at a sensible total, or two stores when the lower combined price is large enough to justify the second stop. The point is to see the tradeoff before you leave, rather than discovering it beside an overfull freezer bag.

Current offers need a quick reality check

Weekly offers change, and an ice-cream deal only helps if it is active when you shop. Check the current catalogue details in the app, including the store location, before setting out. If the offer has ended, the cheapest-looking plan is no longer a plan.

This is also why it helps to save a reusable Friday list. Put the usual warm-evening items on it, add anything specific for tonight, and rerun the comparison when the weekly offers change. You avoid rebuilding the same list from scratch, while still checking the prices that matter this week.

For a wider look at why one attractive discount can hide a more expensive basket, read The Five Discounted Items That Can Hide a Higher Grocery Bill.

Choose the plan you will actually complete

Apollo 13’s engineers did not need the most elegant solution. They needed one that worked with the parts available inside the spacecraft. Friday shopping has the same, much smaller, logic: the best plan is the one that fits the stores, time, temperature, and energy you actually have.

If the one-store total is close, take the nearby option and get home. If a second store meaningfully lowers the full basket and sits along the way, make the split. Keep the decision grounded in the total, the distance, and the offer dates, rather than chasing the lowest price on one carton.