(CNN) -- Here's something you don't want to hear aboard a 20-year-old space station hurtling through space at 17,000 miles per hour: Something has gone wrong with the power supply.
The rocket company was supposed to drop off a bundle of hardware and supplies to the six astronauts on board the ISS as part of an uncrewed launch Wednesday. But that launch was called off and the crew is working to restore the station's full power supply. NASA now says that if all goes well, the cargo capsule could launch Friday at 3:11 am ET.
The space station's crew is not in immediate danger, NASA said in a blog post.
The astronauts will spend Wednesday and Thursday working to replace a piece of hardware that routes the power generated by the space station's solar panels all over the station. The device failed earlier this week, leaving the space station running on about 75% of its usual power supply, according to NASA spokesperson Gary Johnson.
Parts of the football field-sized space station went dark Monday, but the crew was able to keep the lights on and continue running experiments by rerouting power from other lines while they work to restore full functionality, NASA said in a Tuesday statement.
SpaceX's Dragon 1 — the spacecraft that is supposed to make the trip — also relies on a giant robotic arm attached to the ISS that latches on to the capsule as its approaches. But the power supply issues left the robotic arm without a back-up power source. That caused safety concerns, so NASA asked SpaceX to delay its mission.
The power problem throws a wrench into what has otherwise become a routine mission for SpaceX. The company is one of a couple commercial businesses that NASA partners with to occasionally ferry cargo and supplies to ISS crew members. SpaceX has contracts worth billions of dollars to do so.
This upcoming resupply mission will mark SpaceX's 17th for NASA. The uncrewed Dragon 1 capsule will carry about 5,500 pounds of luggage, including hardware that will map carbon dioxide levels in Earth's atmosphere, a piece of equipment that could help communicate with deep-space exploration probes, and a host of science experiments.
Even once the power is returned, there is a separate issue that could throw another curveball into SpaceX's plans: Where to land Dragon 1's rocket boosters after the spacecraft launches.
SpaceX is the only company in the world that lands and reuses rocket boosters after missions to orbit, and it frequently does so. The company says reusing hardware is at the core of its plan to drastically reduce the cost of spaceflight. And the booster, the largest piece of the rocket and the part that gives it the initial thrust at liftoff, accounts for about 60% of the rocket's cost, according to CEO Elon Musk.
The problem is that SpaceX used one of its ground pads in Florida for an April 20 test of its new Crew Dragon spacecraft. That test ended in fiery disappointment, and the site is out of order. SpaceX said the ground pad needs to be quarantined while it investigates what went wrong with the Crew Dragon test.
SpaceX has a backup plan for the Dragon 1 launch, at least. The company can use a seaborne platform, or droneship, to serve as a landing side for its reusable rocket booster.
Typically, droneships are only used for SpaceX missions that require the rocket to travel so far out over the ocean that the booster doesn't have enough fuel left to return safely to terra firma. The Dragon 1 doesn't have that issue, so the droneship will only need to travel 20 miles off the coast.
The Crew Dragon mishap is still concerning for other reasons, though. That spacecraft is built to carry humans, and is a critical part of a separate, multibillion-dollar contract SpaceX has with NASA to eventually begin flying astronauts to the space station. Boeing has a similar contract. But both companies are already years behind schedule.
An investigation into what caused SpaceX's Crew Dragon to misfire is underway. It could derail plans to fly astronauts aboard the spacecraft later this year.
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