How NASA is upgrading the International Space Station’s ancient power system

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Three upcoming spacewalks are part of a bigger plan to boost the aging space station’s power supply.

Large rectangular solar panels dangle in front of the curvature of the Earth. One, on the left, is in the process of being unfurled.
An ISS Roll-Out Solar Array (iROSA) is deployed in 2001. The solar arrays are slowly being added to the space station to boost its available power.
Image: NASA

In the next few weeks, astronauts will be heading out of the airlock on the International Space Station (ISS) on a series of three spacewalks, part of a long-term plan to upgrade the space station’s aging power system. 

The ISS uses large solar arrays to collect energy from the Sun and convert it into usable electricity for everything from life support and temperature controls to communications with Earth and propulsion systems to allow the station to dodge debris. 

The old ISS power system, including eight solar arrays that spread out from the exterior of the station like wings, had been able to meet the power needs of the station to date by generating an average of between 84 and 120 kilowatts of electricity. However, some of the arrays were more than 20 years old and were originally designed for a 15-year service life, so they were showing signs of degradation. 

That doesn’t mean that the old arrays will suddenly cut out or stop working — though the station has had power troubles in the past — but it does mean that they are gradually becoming less efficient over time. And with large numbers of increasingly complex science experiments being performed on the station, the power requirements are going up. 

“Those arrays are doing great for us and doing great science, but over time with normal wear and tear they get used up a little bit,” Anthony Vareha, spacewalk flight director for the upcoming November 15th spacewalk, explained in a press briefing. “And some of those strings that generate the power on those arrays just fall offline. That’s a standard thing that we have built into our power plans for years.”

To keep up with the station’s power needs, the ISS has been continuously upgrading its electrical system, including swapping out batteries on previous excursions. Now, new arrays need to be added — which is the main goal of the upcoming set of spacewalks.

The upgrades to the power system consist of adding six new arrays, which will sit in front of the older arrays with an offset, allowing power to be drawn from both. At 60 feet long and 20 feet wide, the new arrays, called ISS Roll-Out Solar Arrays, or iROSAs, are smaller than the old arrays, which are 112 feet long and 39 feet wide. However, developments in solar panel technology mean that the new arrays can generate about the same amount of electricity as the originals.

Adding new arrays isn’t a simple process, however. Before an iROSA array can be added, it needs support structures, called mod kits, to be in place on the exterior of the station. Vareha described a two-part process of first installing the scaffolding and then later installing an array. At the moment, the ISS has two of the new iROSA arrays already installed. Scaffolding is ready for two more, and scaffolding for the last two will be installed soon, starting with the upcoming spacewalk on November 15th. It will be the first-ever spacewalk for NASA astronauts Josh Cassada and Frank Rubio.

Two later spacewalks tentatively scheduled for November 28th and December 1st will then install two more arrays to the existing scaffolding, with the aim to have all six arrays installed and working by the middle of next year.

Chris Mundy, spacewalk officer, said the new arrays will arrive folded up on a carrier in the SpaceX CRS-26 resupply mission, which is to be launched on November 18th. Then the arrays will need to be installed, integrated into the power system, and deployed. The deployment involves rolling out the arrays like a blanket in a process that takes six to 10 minutes.

For integration with the power system, the spacewalkers need to install Y cables to link both old and new arrays to the power system. “Once those are fully connected, we’ll be able to route power from the legacy array and the new iROSA array into the ISS power system,” Mundy said.

NASA says these new arrays are being tested for potential use in future missions such as the Artemis Moon program as well as helping the space station continue operations. As for the space station, its precise future is still unclear. While NASA announced at the end of last year that it intends to continue operating the ISS through 2030, Russia, another major partner, has repeatedly threatened to withdraw its cooperation, leaving the ISS in a tenuous position even as it gets powerful new upgrades.   

“Each new array brings new power,” Fiona Turett, spacewalk flight director for one of the future spacewalks, said. “ISS continues to grow, and we have more science and more systems online. This additional power will ensure we can operate ISS to the fullest extent in the upcoming years.”

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