Today's writing: Changeling Space Program (Patreon)

The top line of the chalkboard had a series of numbers across it, one to twenty. Under the numeral 1 the word "Today" was scribbled in. A line drawn under the numbers thirteen through twenty marked these Reserved For Ship Retrieval. A shorter line ran under numbers nine through twelve, marking these as Transit Time, Equus to Moon. Only the numbers two through eight remained unlabelled- marking the days CSP and ESA had to train and prepare for the rescue of Rainbow Dash.

Twilight Sparkle finished the last stroke on the complex diagram of the three-person capsule with fuel tank and engine attached. Labels pointed to various points on the capsule, connected to a drawing of a not-quite-square box with multiple nozzles extending from it. "The primary goal of the mission is to rescue Rainbow Dash," she said. "But the secondary goal is to fully inspect Amicitas in preparation for a future repair, refueling and retrieval mission. The best way to do this is to have Mission Twenty-Three dock with Amicitas using our new docking port system and remain there during the entire inspection and close-out period."

"And why, exactly, should we bother with this?" Chrysalis asked. "I can understand you wanting to get the ship back. It's yours, after all. But why can't we use the hatch-"

"Airlock."

Chrysalis blinked. "What?"

"Amicitas has airlocks," Twilight said. "Two of them. One in the bridge compartment, behind the co-pilot position, and a larger one for engine repair on orbit."

"Really." Chrysalis gave Twilight a level look. "And you've repaired engines in mid-flight how many times now?"

Twilight blushed. "Well, we'll be able to some day!" she insisted. "And when that day comes, we'll be prepared!" She lifted a pointer in her magic and slapped the chalkboard with it, a little harder than necessary. "And as to why we can't use the airlocks, it's a question of orbital mechanics."

"You mean the orbital mechanics who are going to fix your engines mid-flight someday?"(468)

As Twilight snorted and huffed in indignation, Warner von Brawn rumbled, "The princess, I believe, refers to the fact that two objects in space, separated by any distance at all, technically occupy two different orbits. Over time they will drift together or apart, depending on relative velocity. Station-keeping with any safety would require repeated orbital correction burns, each with the potential for accidents. If you can make the two objects into a single object by linking them together, the need for constant piloting is removed."

"Exactly," Twilight said, having had a moment to calm down. "I want to spend a full day going over Amicitas, first diagnosing the problems that caused the accident, then performing a systematic close-out of the ship to prepare it for a long period of hibernation." Seeing Chrysalis's mouth opening, she added hurriedly, "Because we don't know when we'll be back again, NOT because winter is coming!"

Chrysalis shut her mouth and shrugged.

"So," Twilight continued, "in order to dock safely, the pilot of Mission Twenty-three will need to be able to maintain orientation with the target while controlling trajectory in all three axes of motion simultaneously." She tapped the chalk outline of the rescue ship's main engine. "While this can potentially be done with the main engine alone plus reaction wheels, it would be both inefficient and highly dangerous. Therefore instead we will be using the RCS- the Reaction Control System."

"Maneuvering thrusters," Cherry Berry said helpfully.

"So I had guessed," Chrysalis hissed back.

"ESA will provide eight RCS blocks to be arranged like the corners of a cube around the ship," Twilight continued. "Starlight Glimmer will coordinate with your ship construction team-"

"Could she not?" Chrysalis interrupted. 

Twilight snorted again. "What is this about now??" she snapped.

"Oh, it's nothing personal to your student," Chrysalis said. "I'd just rather not risk having an  unicorn whacking my rocket with a large rock in some desperate attempt to stop my evil scheme. Unlikely as the prospect is."

Now Chrysalis had every eye in the planning meeting on her. After several seconds of choked silence, Cherry Berry finally said, "I'm pretty sure you didn't intend to use your out-loud voice when you said that."

"Just humor me," Chrysalis said. "Have Moondancer oversee the modifications instead. It will help me keep my mind on the training."

"O... kay?" Twilight Sparkle had three kinds of worry on her face, fighting like three fat stallions over a two-mare train bench. "I... I guess Starlight can focus on preparing the simulator to handle docking exercises?"

"Much better," Chrysalis agreed. "The simulator is much less likely to explode and take the top of my castle off. That I don't have."

Twilight's three kinds of worry formed a united front and unbreakable alliance, using her eyes to silently signal Cherry Berry for foreign aid. 

Cherry shrugged. "Long story," she said. "You could try asking Luna about it."

"Oh. Okay." Twilight managed to pull herself together, then pushed on. "Moondancer for installing the thrusters and the docking port, Starlight to oversee simulations. Um... where was I?" She lifted up a stack of index cards in her magic and ruffled through them, muttering, "Covered that... did that... and that... oh!" She straightened up, using the pointer to tap the row of numbers up top. "Now, ideally we want to save four days of food for two ponies to use in the future retrieval mission," she continued. "That means we need to get to Rainbow Dash not later than twelve days from now. Allow four days from launch to lunar orbit and rendezvous, and that leaves us a launch date not later than eight days from now."

"Giving us seven days for training and prep," Cherry nodded. "We've done more with less time. And we've already had training for the other mission items on this flight."

"There will be some changes," von Brawn said. "We were originally going to put the science package on top of the lander. That way it could be jettisoned after the data was collected to lighten the load on the way home. But we can't use that configuration with the docking port. We'll have to contrive an experiments bay to ride below the crew capsule."

"At least this way we'll get the equipment back," Chrysalis muttered. "Less wasted money."

"This will make the ship substantially heavier," von Brawn continued. "All the more reason to test the return stage engines in lunar orbit, to make sure performance is adequate."

"So throw more boosters under it," Chrysalis snapped. 

"We may indeed need to do that," von Brawn agreed. "But we'll have to fabricate the cargo bay in less than five days to meet our launch date. I'll speak to Goddard about that."

Cherry shook her head. "Appleoosa's working full steam ahead just building the boosters for Twenty-three and Twenty-four," she said. "Plus the ESA parts restock order. We don't have the floor space, even if we added more skilled workers."

"We could build it," Twilight said. "We have a fabrication shop at Cape Friendship currently doing nothing. All we have to do is scale up the existing cargo bay module for the new tanks and engines, right?"

"And who are you going to get to build it?" Chrysalis asked. "You and Starlight Glimmer are your main engineers, and you're both going to be here."

"I can do it." Dragonfly, who had been in the meeting by virtue of not having been kicked out by the others, raised a perforated hoof. "I've worked with their facilities before on parachute and space suit development. And I've been thinking about redesigning the bay doors so they fold up and don't get bent or twisted if the rocket's lying on its side."

Chrysalis's eyes narrowed, but she said nothing about the interruption. Instead she asked, "Don't we have a fabrication shop here for you to use?"

"Not big enough," Dragonfly said. "We've been building so much for so long at Appleoosa that we never bothered to bring large component construction here. We mainly use it for computer component testing."

"Hmph," Chrysalis grunted. "What about that Jet Set pony? He keeps sending us passenger compartments to test. Can't he build a cargo one?"

"Not his company's field," Cherry put in. "He invests in pony flight, not freight." 

"All right," Twilight said, "then that's what we'll do. I'm sure we have copies of all the same scientific instruments and bays you've been using, so we won't need to ship anything there." 

For the first time Chrysalis looked taken aback. "Just like that?" she asked. "Not even thinking of saying no?"

"Why should I?" Twilight asked. "Those instruments will be doing important scientific work for all ponykind!" She smiled a little and added, "And it'll be ready in time. I know it."

Chrysalis gave a tiny shrug of her shoulders. "Very well. Are there any other issues we need to know about?" When no one spoke up, she nodded her head. "All right, let's get started. And let's see if we can't launch sooner than eight days from now, hm? I'd like to be back home in time for Nightmare Night."

Footnote:

(468) The time had passed when this question would have been asked by Queen Chrysalis in any sincerity. She knew what orbital mechanics were, even if she didn't give two figs about the math. But needling Twilight Sparkle was too fun to pass up.