Ungula

The environment collar was created through a culmination of just about every race's magic.

Pegasus meteorological magic formed the basis, providing oxygen to the wearer along with a sheathe of atmosphere. Indeed, the earliest designs were entirely based on pegasus magic.

Unicorn magic kept that atmosphere pressurized, preventing it from being torn away. Without that stabilization, it would be constantly fighting against the vacuum, drastically reducing its reliability. Atmosphere was released from the field as needed to allow for cooling. It also kept it clean and added a shield against radiation, because the unicorns involved weren't about to let themselves be shown up.

Earth pony magic provided a pinch of gravitational adjustment. Gravimancy wasn't most ponies' first thought when it came to earth pony magic, but it formed the foundation of a great deal of their strength by adjusting their mass. In the environment collar, it allowed the wearer to survive in most high-gravity environments, prevented bone and muscle decay, and allowed the wearer to actually walk on bodies with gravity ordinarily too low to really stand on.

Thestral psionics formed the interface to control all the rest. Rather than wastefully run every function all the time and risk running out of operating time right when it was needed, or require manual activation that may not be fast enough in an emergency, each function was turned on the moment the wearer consciously or subconsciously felt the need for them. They also provided translation, so that diplomatic contact could be made with any new race encountered, and transmitted speech mentally to allow communication even through a vacuum.

Crystal pony magic provided longevity. There was a reason the greatest of legendary artifacts were all crystalline in form or in origin. Without crystallizing the magic, the enchantments would wear down over time, lasting perhaps a few years under normal circumstances – long enough, perhaps, but normal circumstances were far from guaranteed. With crystal magic the collars would last indefinitely, with the only restriction on their lifetime being how long they could operate continuously.

Thus was created the environment collar, by a collaboration of many races working together aboard Cadenza Station. Before, space exploration was a terribly risky endeavor; now, when all a spacefarer needed to travel safely was a moderately expensive collar, more ponies than ever before had their eyes to the stars.

"Rrrrgh! Why! Isn't! This! Working!"

All this is to say that the environment collar was horribly densely packed with enchantments, and Twilight Sparkle was having a hell of a time trying to pack in even more.

She was trying to create a countermeasure for the false friendship field that the blank pony created, and she was as of yet having little success.

Her problems were threefold: How to block the effect, how to cram it into the collar, and how to test if it worked.

She had so far solved exactly one of those problems, by rigging up a roomba to cast a charm spell based on the effect.

"Youuuu! Youuuuu are my friend. Why are you my friend? You're a robot! You can't think! And I cast five mental barriers!"

It wasn't a good charm spell. It was hacked together to create as close an approximation of the specific effect as she could manage, at the expense of basically all actual strength of the effect. It was only working at all because she was deliberately not fighting it, relying only on the magic she was trying to develop. But it did approximate the effect.

Twilight sighed and flopped onto her back. "Ohhh, why isn't this working, Roombella? I've tried everything I can think of. Why is there so little literature on blocking compulsions? Everything just says 'cAn Be ReSiStEd WiTh WiLlPoWeR'. You can't! Resist it! If you don't know it's there because it's subtle!"

Her roomba friend bumped into her in reassurance. Or because it wanted to mate with her. Or because it was trying to clean and she was in the way. One of those.

"You're right, I'll come back to it later. Time to beat my head against cramming something into the collar again…"

As Twilight started trying to get the collar to make the wearer see everything in shades of magenta, there was a knock at the door of her quarters.

"What? We're busy!"

"We…? Twilight, ya been holed up in there fer the better part of a day, and ya haven't come out to eat once. Take a break." (Applejack was fully aware of the irony of this advice coming from her.)

"I'll take a break when I know that's not going to happen again!"

Applejack opened the door.

"Y'all look like shit, sugarcube."

"Thanks Applejack! You're such a supportive friend." Twilight did in fact look like shit and she knew it.

"I'll support ya in making sure ya eat enough. Come on, you can tell me bout what you've been up to on the way to the mess."

Twilight sighed, and got up to follow. She knew she couldn't escape.

Applejack opened her mouth with a look to Roombella, as if to drag it along as well. Then she shook her head to clear off the compulsion, and led Twilight away, closing the door behind her. "So what's yer problem, exactly?"

Twilight took a deep breath, about to launch into a technical rant, only to remember her audience and simplify a bit. "There's almost no literature on resisting compulsions. Everything just says to resist using willpower but that effect was subtle enough that you don't know to resist it! And even if I had a way to block it the collars are packed! There's no room for it!"

Applejack nodded. "Why's it gotta be part of the collar?"

"Because the collar reads our emotional states to know when to turn things on. Hooking into that is the best way I can think of for detecting artificial feelings like that to turn on the countermeasures."

"Why not make somethin else that reads em? And if ya can't block it but ya can resist it if'n ya know it's there, why not just have it let ya know to resist?"

Twilight stopped in her tracks. "B… Because it takes thestral magic to read emotions like that, and I could get by without the crystal magic but it would be so much better with it," she grasped.

"Fluttershy's part thestral, and Rarity's part crystal."

Twilight slumped, approached the nearest bulkhead, and applied her head to it, making an incoherent strangled sound in which she expelled the entire contents of her lungs. It sounded something like "rrrrghhh" mixed with a wheeze and a sob. Then she turned to go find Rarity and Fluttershy.

"Food first, sugarcube."

"...Mmkay."

The final product was a set of tags for the collars in the form of a crystalline acorn each, coaxed from the reactor and containing an ember of friendship. As it would naturally heat up in the presence of genuine friendship, the thestral component would detect if any such feelings were not accompanied by the ember heating up and signal the unicorn component to make the tag cool down sharply instead. Twilight went to bed.