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Two astronauts aboard the International Space Station (ISS) are ready for a spacewalk to begin the process of increasing the station’s electrical power output.
The spacewalk, US EVA-71, will be conducted by NASA astronauts Kate Rubins and Victor Glover, who officially began their stay at 06:12 EST (11:12 UTC).
Solar array background:
The ISS is equipped with eight solar array wings (SAW), each of which was designed to produce around 30 kilowatts (kW) of power, for a total of approximately 250 kW across the eight arrays.
The older array, attached to the P6 armor, was launched in 2000 on Shuttle Endeavor’s STS-97 mission, and additional arrays were launched in 2006, 2007, and 2009 aboard the STS-115 and STS-117 missions of Atlantis and Discovery’s STS-119 mission, respectively.
Due to the degradation, which was expected, the power generation arrays now only produce around 160 kW of power. At the same time, the station users, including the recently added Nanoracks Bishop airlock and the Bartolomeo European external platform, require more power than was originally envisioned at the time of the outpost design.
While the station’s solar panels were originally designed to be removed and replaced entirely via the space shuttle, the removal of that vehicle forced the ISS program to find an innovative solution to increase the amount of energy available.
As a result, the ISS Power Augmentation (IPA) program was born. The plan calls for adding six additional solar panels to the ISS to increase its power generation and restore it to original levels.
Specifically, six new ISS Roll Out (IROSA) solar arrays will be added. IROSAs are a new type of die technology, which differs from the station’s original dies, which were folded and unfolded in an accordion shape.
Developed by Deployable Space Systems of California, IROSAs unfold in a carpet shape from inside a cylindrical container.
Its solar cells are mounted on a very thin and flexible blanket instead of traditional rigid panels, and it features a compound arm that adds rigidity and allows deployment without the use of complex motors or mechanisms.
This allows large arrays to be stored very compactly, which is important given the current release options available for the Station program.
The solar cells themselves have an efficiency of around 30%, compared to the 14% efficiency of the original arrays. This allows the IROSAs to generate roughly the same amount of power as the original arrays, despite being only half their size.
The placement of the new IROSAs on the solar panels of the existing station. (Credit: NASA / Boeing)
IROSAs will be installed on six of the station’s existing solar panels. Although the IROSAs will partially shade the existing arrays, the original arrays will continue to generate power together with the IROSAs.
Installing the IROSAs on top of the existing arrays allows them to use the existing solar tracking motors (the Beta Gimbal set) from the current arrays and allows each IROSA to connect to the electrical system used by the current arrays to increase their power. .
Each IROSA will produce 20 kW of additional power, for a total of 120 kW in the six arrays. The unshaded portions of the original arrays will continue to produce 95kW, making a combined total of 215kW of power that will be available to the station, close to its original level.
This is an increase of almost a third compared to the outpost’s current available 160 kW of power. When combined with the recently completed effort to replace the station’s batteries with new lithium-ion units, this will ensure that the ISS has adequate power to support its increasing demands for the remainder of its useful life.
A subscale version of the IROSA was successfully tested at the station in 2017, and the technology is already planned for use in the Lunar Gateway’s Power and Propulsion Element (PPE), as well as in the Human Lander System (HLS) of Dynetics, for the Artemis Moon program.
The six IROSAs will be launched two by two on a pallet inside a SpaceX Cargo Dragon 2 trunk beginning on flight CRS-22 in June 2020. The new arrangements will be installed through spacewalks.
The “mod kit” to be built and installed on the mast vessel assemblies. These kits will serve as docking platforms for the new dies. (Credit: NASA)
EVA procedures:
The IROSAs will be structurally mounted on the base of the Station’s existing Mast Canister Assemblies, which housed the current arrangements during launch and now serve as its “base”.
However, as it was never imagined that the IROSAs would be added to the ISS, there is currently no structure on which to mount them.
Building this will be the goal of today’s spacewalk.
A “retrofit kit” will be installed on the mast and vessel assembly, consisting of several struts that will be connected together to form a structural frame on which the IROSAs will be mounted in the future.
The mod kit will be physically bolted to the mast vessel assembly using the existing connection points of the unnecessary ground handling accessories and the removed robotic pins.
The goal of today’s activities is to complete the construction of the modification kit on the 2B mast canister assembly and to begin the construction of the modification kit on the 4B mast canister assembly, both located on the P6 truss, the solar panels. oldest of the station. .
Today’s work location on arrays 2B and 4B on truss P6. (Credit: NASA)
The first task for the spacewalkers after commuting to the P6 job site, taking some very large work bags with them, will be to build an A-frame structure called a top bracket, which in turn will be mounted in the center of the ship’s boat. mast 2B Mounting.
Next, a left lower strut and a left center strut will be connected between the upper bracket and the left side of the mast bowl assembly. A right lower strut and a right center strut will be installed on the opposite side.
This will complete the 2B mod kit installation.
Next, the upper bracket will be built and connected to the 4B mast canister assembly, as will its lower right strut.
This is where the spacewalk is scheduled to end due to time constraints; However, if the duo get ahead of the planned timeline, construction on the 4B mod kit will continue.
If the pre-spacewalk plan is followed, the completion of the 4B Mast Vessel Assembly mod kit will be completed in a future spacewalk, and the pair will return inside the Quest airlock.
(Lead image: NASA astronaut Scott Parazynski on the arm of the Orbiter Boom sensor system while repairing an active solar panel outside the station in November 2007. Credit: NASA)
