Dr. Jerend Mesoman had established the first telescopic observatory a couple years ago, and often had students help her in the dome. Lenna was a math student, and Jerend was experimenting with a radical astronomy-based mathematics program. Observation was not one of Lenna's strong suits, so she took every opportunity she could to stay in the dome with the professor and learn firsthand how observing was done.
"Hey, um, Professor Jerend?"
"Hmm?"
"What's that in the dome?"
"Lenna, I already told you, these are space objects, they're not on the dome."
"No, no, that web thing."
"Huh?"
"You're aimed right at it."
"Oh, this? I'm examining this nebulosity. It's full of stars"
That didn't satisfy Lenna. But she didn't want to bother the professor while she was doing important work. Finally, Jerend looked away from the eyepiece.
"Oh. Huh. So that's why the contrast went--GET INTO THE HATCH!" Jerend stood up too fast, and went dizzy, falling back into her chair. Lenna got to the hatch, and opened it. Jerend didn't follow.
"Professor!" Lenna shouted, but there was no answer. She grabbed Jerend's arm and dragged her around the hatch, stuffing her in the airlock. 'One at a time,' she said, cursing under her breath. She closed the hatch and the airlock cycled. The vibration from the air pump beneath the observatory caused the dome to flex. Lenna looked at the crack again. 'It's full of stars,' she thought, as the crack opened up entirely.

There was a loud CRACK and a muffled hiss, and Lenna was exposed to Mesbin's exosphere. She exhaled. She couldn't speak, she couldn't breathe. She stumbled over to the cabinet, and tore out an emergency air mask. She smacked the mask over her face, high-strength glue caused it to stick. She squeezed the inlet valve with her last trickle of consciousness.

Lenna crawled through horrible joint pain to the airlock door. The indicator was red. She looked through the window. It was hard to see anything at all, but it seemed like someone was helping Jerend through. Lenna's eyes burned and it hurt to keep them open.

Finally the indicator turned yellow, and Lenna tried to pull the lever to open the airlock. It wouldn't budge. She banged on the door with her air tank. The air tank sprung a leak, but the door opened, and she scrambled into the airlock. And she then lost consciousness.
She woke up in a hospital with her sister by her side.
After recovering from vacuum exposure, she returned to university, and got an apology from the professor. "The observatory wasn't fail-safe. I should have known it."
Lenna nodded.
"No thanks to you not letting me know about the crack sooner," Jerend said.
Lenna's heart sank.
"Still, I wouldn't have been able to finish my observing report if you hadn't saved by life," Jerend said, but she didn't smile.
Lenna did.