COS2035: Extending COS/FUV Operations Through the 2030s

Imagine the universe is a giant, dusty attic filled with stories written in invisible ink. To read these stories, astronomers use a special flashlight called a telescope, but some of the most interesting tales are written in a color of light our eyes can't see: ultraviolet. For decades, the Hubble Space Telescope has been the master librarian of this attic, using a tool called the Cosmic Origins Spectrograph (COS) to decode these UV messages. However, there's a catch. The "film" inside Hubble's camera is like a delicate, high-tech sponge. Every time a photon of light hits it, the sponge gets a tiny bit squished. If too many photons land in the exact same spot, that spot gets permanently damaged, losing its ability to see clearly. This is called "gain sag." For years, scientists had to move the camera's view around to avoid these squished spots, but they were running out of fresh spots on the film. If they couldn't find a way to keep the film working, the most popular way to study the universe's history would have to stop.

This paper, written by a team of astronomers in 2026, is the blueprint for a rescue mission. It explains how they are going to trick the camera into seeing fresh, undamaged spots on the film, even though the film is old and worn. They aren't just patching a hole; they are completely redesigning how the camera moves and how the film is used. By combining four clever technical tricks with two new rules for how much "squishing" is allowed, they have a plan to keep Hubble's UV vision sharp and productive all the way through the 2030s and beyond. It's like finding a way to rearrange the furniture in a crowded room so everyone can dance without stepping on each other's toes, ensuring the party can go on for another decade.

The Problem: The Squished Sponge

Think of the detector inside the Cosmic Origins Spectrograph as a giant, sensitive sponge. When light hits the sponge, it records the message. But if you keep dripping water (photons) on the exact same spot, that spot eventually gets soggy and stops working. This is "gain sag." For years, the team had to move the camera to a fresh, dry spot on the sponge every time the old one got too wet. They had found eight safe spots, called "Lifetime Positions" (LPs), but they were running out. The old rules said they couldn't use the top part of the sponge because of a "light leak" (a hole in the roof letting in too much rain) and a "soft stop" (a bumper that stopped the camera from moving too high). They were stuck in the middle of the sponge, and the most popular spots were getting too soggy to use.

The Solution: A New Way to Dance

The team came up with a strategy called COS2035. It's a mix of four technical breakthroughs and two new rules.

1. The "Split" Trick (SPLIT-wavecals)
Previously, the camera had to take a picture of the science target and a picture of a calibration lamp (to make sure the colors were right) at the exact same time. This was like trying to eat dinner and wash the dishes simultaneously. But above the "light leak" area, doing both at once would break the camera.
The new trick is to do them one after the other. They take the science picture, then quickly move the camera to a safe spot to take the calibration picture, and then move it back. It's like taking a quick break to check your map before continuing your hike. This allows them to use the "dry" spots at the very top of the sponge that were previously off-limits. The only cost is a tiny bit of extra time (about 15% more per orbit), but it opens up a whole new playground.

2. The "Hybrid" Dance Floor
Before, the whole camera had to stand on just one spot on the sponge. If one part of the sponge was wet, the whole camera had to move. The new "Hybrid-LP" architecture lets different parts of the camera stand on different spots at the same time. Imagine a dance floor where the slow dancers stand in one corner and the fast dancers stand in another. This way, they don't crowd each other, and they can use the specific spots that are best for their style. For example, one type of light filter can stand on a spot near the top, while another stands near the bottom, maximizing the use of the whole sponge.

3. The "Infinite" Numbering System (LP-infinity)
The camera's computer had a list of only eight spots it could remember. Once they filled the list, they couldn't add more without a massive, expensive computer update. The team built a "patch" that tricks the computer. They told the computer, "You only have eight slots, but we'll just keep swapping the numbers in the last slot." It's like having a hotel with only eight rooms, but the front desk keeps swapping the key cards so new guests can stay in Room 8 without ever needing to build Room 9. This means they can add new spots (like LP10, LP11, LP12) without needing to rewrite the camera's brain.

4. The "Smart" Damage Check
The team used to throw away a whole column of data if even one tiny pixel was a little soggy. That was like throwing away a whole pizza because one slice had a tiny crumb on it. The new method is smarter. It looks at the whole column and asks, "Is the total damage enough to ruin the picture?" If the damage is small and doesn't affect the final result, they keep the data. This allows them to use spots that have a little bit of old "soggy" history, as long as the new data is still clear.

The New Rules: Don't Overeat

To make sure the sponge lasts as long as possible, the team added two strict rules for how scientists can use the camera:

• The "Good Enough" Limit: Once you get a clear enough picture (a specific signal-to-noise ratio), stop taking more pictures of that same target. Taking more just squishes the sponge for no reason.
• The "2% Share" Rule: No single science project can use more than 2% of the sponge's total life at any one spot. It's like a pizza party where everyone gets a slice, but no one can eat more than a tiny piece of the whole pie. This ensures that one big project doesn't eat up all the fresh spots for everyone else.

The Future: Dancing into the 2030s

With these tricks, the team has already moved some of the most popular light filters to new, fresh spots (LP7 and LP10). They are currently testing two new spots, LP11 and LP12, which will open up even more room.

• LP11 will be used for a low-resolution filter (G140L) that can handle a bit more "soggy" history.
• LP12 will be used for the most popular filter (G130M/1291), placed in a spot that used to be considered too wet, but the new "smart check" says it's actually fine.

The paper concludes that with this strategy, Hubble's Cosmic Origins Spectrograph can keep working through the 2030s and even into the 2040s. This is crucial because it bridges the gap between Hubble and the next generation of space telescopes, ensuring that we never lose our ability to read the universe's ultraviolet stories. The team is confident that these methods will work, having already successfully tested them in simulations and early operations, and they are ready to keep the Hubble party going for another decade.