The astronauts currently aboard the International Space Station are having trouble getting new supplies.

Yesterday, SpaceX launched a rocket to ferry 4,100 pounds of food, scientific equipment, and other cargo up to the space station — but it exploded shortly after launch due to unknown technical problems:

Meanwhile, the previous resupply mission — a Russian cargo capsule launched in April — went spinning out of control in orbit due to problems with its rocket, and eventually disintegrated in the Earth's atmosphere.

The good news? The three astronauts in space won't starve, as there's plenty of extra food on board. But delivering supplies to a tiny outpost 249 miles above the Earth isn't easy — and this puts some extra pressure on Russia's upcoming mission on July 3.

The Space Station has a few extra months of food

The world's space agencies try to plan for the worst-case scenario — so the space station is typically equipped with several extra months' worth of food and other supplies.

Right now, NASA has about three months' worth of food on board, so the astronauts will be fine until the Russian supply run later this week. They'd even be fine if the next cargo mission, scheduled to be delivered by the Japanese space agency in mid-August, failed too.

However, if that somehow happened, those on board —including Scott Kelly and Mikhail Kornienko, who are spending a full year in space as part of a new experiment — might have to dip into their last few months' worth of food and start eating a bit less.

They should get an additional delivery from another Russian mission, scheduled for July 22, but that ship will primarily be carrying another team of three astronauts, so its cargo capacity is limited. Still, cutting back to a reduced diet would allow them to stretch food and other supplies until late September, before which additional SpaceX and Russian missions are scheduled to run.

Other space station inhabitants have been forced to do this before. In 2004 — in the midst of a hiatus of Space Shuttle flights due to the Columbia disaster — occupants had to start eating a stripped-down diet (consuming 2,700 calories a day, instead of 3,000) as they awaited a delayed resupply capsule. When it finally arrived, they had just a few weeks' worth of food left — if it had been delayed again, they would have been forced to evacuate.

Most of the water and oxygen are recycled on board

Because it's so expensive to carry any mass up into orbit, the space station is equipped with sophisticated systems that recycle water and oxygen. This means that if resupply missions were halted, the crew would run out of food way before they ran out of water or oxygen.

Aboard the space station, all the water vapor exhaled by astronauts — as well as the sweat and urine they excrete — is purified back into fresh water for them to use. If this water wasn't recycled, about 60,000 pounds of it per year would need to be sent up to support a six-person crew. (Additionally, if the water vapor weren't sucked out of the air, it'd gradually cause the station's components to rust.)

Some of this water is also used as a raw material for the station's oxygen production systems. Electricity (generated by solar panels) is used to split water molecules into breathable oxygen and hydrogen gas. The hydrogen used to be vented out to space, but a system installed in 2011 combines it with carbon dioxide exhaled by the astronauts to produce potable water and methane — so the loop of oxygen and water used on board is essentially closed.

Still, small amounts of water are lost in a few places in the system: the water purification process produces some unusable salty brines, and some water vapor is lost whenever the airlocks are opened. To address this, some tanks of water and backup tanks of oxygen are sent up on resupply missions as reserves.

But this failure could put more pressure on upcoming missions

Due to these redundancies, the astronauts on board the space station certainly won't starve or die of thirst anytime soon. But the failure of this SpaceX resupply mission isn't ideal — especially because of a few other recent events.

NASA contracts with two private companies — SpaceX and Orbital Sciences Corporation — to carry out its resupply missions. But Orbital's rocket exploded on the launch pad in October, and its missions have been put on hold since. NASA says the company plans to resume missions later this year, but an exact date isn't yet set.

Additionally, the European Space Agency recently ended its role as a supplier for the space station, with its fifth and final cargo mission in February. And SpaceX could potentially put future launches on hold while this recent problem is investigated, perhaps delaying its scheduled September launch.

That would mean that the number of resupply options for the space station would have quickly dwindled to two: Russia and the Japanese Space Agency.

This puts a lot of pressure on their missions to run smoothly. It could force them to carry extra food at the expense of planned scientific equipment.

And in the extreme worst-case scenario, if there were problems with both the Russian or Japanese missions, it could even force the space station's occupants to evacuate — which, among other things, would ruin the ongoing experiment in which a pair of astronauts are spending an entire year in orbit.