Today's writing: Changeling Space Program (Patreon)

(reminder: ESA is confident they can still beat the changelings to the moon, but one distraction after another has eaten their time advantage, and very little of it remains...)

"All right, Rainbow Dash," Starlight Glimmer's voice echoed over the comms, "we're all go for main engine test. Stand by for simulated liftoff."

"Yeah, yeah," Rainbow muttered irritably, and then louder, "Amicitas copies, standing by."

Not that she was actually sitting in Amicitas. The ship which would take her into space in eight days' time, and to the moon three days after that, currently rested in the VAB undergoing final flight refit. Rainbow Dash sat instead in the much smaller cockpit mockup room attached to the immense rocket engine testing center, situated in its own two-mile radius no-go zone well away from everything else at Cape Friendship. 

On the other side of a double-layered reinforced wall stood reproductions of six engines- the three liquid-fueled main engines used in launch, and the three much smaller engines powered by the single, massive block of enchanted diamond behind them, all of which bolted to a gantry whose base extended down into the concrete foundations of the building itself. 

A laypony, at first glance, would have thought the wall and the reinforced mount overkill on an absurd level. Rainbow Dash, having taken part in several of these tests(446), knew better. Hard experience had demonstrated the heavy engineering to be both necessary and adequate(447). For her own part, she would have preferred to conduct the exercise by radio from mission control, or from her own house back in Ponyville. But she also wanted to be able to hear the sounds the engines made when in operation, and this was the best way.

"We're going to start a simulated launch countdown from t minus twenty seconds," Starlight said. "Fuel and oxidizer pumps active." 

Off a significant distance from Rainbow's simulated cockpit, and separated from the test building by a freestanding blast wall, giant refrigerated pressure tanks holding liquid oxygen and liquid hydrogen began to creak and knock as internal mechanisms passed the dense fluids into pipes which, on the switch of a few valves, would feed them into the engine mechanisms, Rainbow couldn't hear it, but she'd seen them tested before, and the creaking never failed to worry her... not that she'd let anypony see it.

"Fifteen seconds."

The systems Amicitas used had grown too complicated for the old system of allowing the pilot to launch the rocket just whenever. The rocket engines had to be ignited and checked for thrust balance before releasing the clamps which held the giant imbalanced stack on the pad. Only after the ship left the ground would Rainbow Dash take control; until then, launch control on the ground ran the show by wire.

"Ten. Nine. Eight. Seven."

Rainbow wiggled a little in her flight spacesuit, placing her forehooves on the mock flight yoke and throttle. Behind her she heard faint clanks as the valves opened, pumping high-pressure fuel and oxygen into the reaction chambers of the three main engines.

"Main engine start. Four."

The wooshing sound of fuel got drowned out almost instantly by a roar that still threatened to deafen Rainbow Dash, despite thick walls and her communications headset. Her cockpit shook with vibration transmitted through the test facility's walls.

"Three. Two. One. Zero. Liftoff!"

Under her hoof the throttle shifted itself forwards to full power, and the roar grew louder. The mission clock began ticking on the console of mocked-up controls. 

"Twenty seconds! Throttle down to eighty percent for max Q."

"Copy eighty percent for max Q." This was the first actual thing Rainbow had to do. She pulled the throttle back a bit, just as she would in an actual flight about this point as the rising ship approached the sound barrier. Behind her, the roaring reduced slightly. 

"Forty seconds," Starlight said. "Performance nominal..." The words, begun with certainty, trailed off towards the end. "Amicitas, read me mana battery power level."

Rainbow Dash glanced over the mockup controls for the readout. "Uh... mana battery at one hundred, repeat full charge."

"Huh. Guess we have a bad gauge here. Past max Q and go for throttle-up."

"Roger, go at throttle-up." Dash pushed the throttle forward again until it wouldn't move any farther.

Through the roaring there came a faint crunching sound, followed by a loud BANG. Instantly every light in the mockup capsule, including the interior illumination, went red.

"SHUTDOWN! ABORT, ABORT, ABORT!" Starlight's voice shouted over the comms. "Fire crews stand by! Do NOT enter the testing facility until ordered!"

The roaring ceased, replaced by the almost but not quite totally muffled sound of an ordinary fire. 

"Fuel shutoff confirmed! Fire teams, go go go!"

Rainbow Dash sighed, slumping back in the mock flight couch and slapping open the latch of her flight harness with one hoof. "Control, Amicitas," she called. "Starlight, what the hay just happened?"

"I think it was your gauge that was faulty on the mana battery, Dash," Starlight said. "In here we were showing a rapid drop-off of power levels. Either the enchantment was faulty or the mana engines were sucking down more power than they should have. Either way, the battery was overdrawn and had a critical failure."

"In other words, it blew up," Dash said.

"In about a million tiny pieces," Starlight agreed glumly. "I guess diamond is just too brittle for this size of battery after all. It doesn't look like the engines are actually damaged, but we'll have to spend a couple days inspecting them to be sure."

"We haven't got a couple of days!" Rainbow Dash insisted. "Those engines need to be inside Amicitas five days from now so we can get the ship on the stack!"

"I know, I know," Starlight said. "But there's no point in launching until we know the battery works. And a fifty percent failure rate just isn't acceptable. I don't want to strand you in moon orbit."

Rainbow Dash sighed again. "All right, that's it. As soon as you give me the all-clear to get out of this thing, you and I are gonna go talk to Twilight about this."

Half an hour later Rainbow Dash kicked in the door of Twilight's office in the Cape Friendship administration building, shouting, "Twilight, we gotta talk about- huh?" She froze mid-rant(448) as she saw Twilight Sparkle, head bowed in utter depression between two immense stacks of paperwork. "Hey, Twilight, what's wrong?" She fluttered into the room, circling around Twilight's desk like a worried mother bird. "Did the changelings launch a sneak mission to the moon already?"

"No," Twilight said miserably. A quill slowly danced across the page in front of her, idly lifting itself over to the inkwell for a dip.

"Don't mind her," Spike said as he peeled himself off the wall behind the door Rainbow had slammed open. "It's just that she just got a letter from her parents. They won an airship cruise for the whole family, and she THINKS she can't go."

"But I CAN'T!" Twilight insisted, showing life at last. "There's the friendship school to work on! There's the map back at the castle, which could summon somepony at any time for a friendship mission! There's the administration of this space program! There's the tests of the magic rocket engines, the moon lander-"

"Um, about that," Starlight Glimmer said as she poked her head around Rainbow. Rainbow pushed her back with a quiet shushing noise.

"-and flight sims, and the cruise leaves dock in seven days! Launch day is in eight! I'd miss the launch!"

"I told her," Spike grumbled, "that's why we have backups."

"I'm not going to make Moondancer take my place just so I can have a fun vacation!" Twilight snapped. 

Spike looked at Rainbow. "Make her go to the moon?" he asked. "Make her?"

"You know what I mean!" Twilight snapped. "I'm a princess! I have responsibilities! I can't just go around handing things off to other ponies!"

"You mean, like Celestia does?" Starlight asked, exchanging knowing nods with Spike.

"That's totally different!"

"All right, I've heard enough," Rainbow Dash said, dropping down directly in front of Twilight. "Look at yourself, Twily," she continued, waving a forehoof up and down at her friend. "You're working yourself to exhaustion and thinking yourself to a frazzle! You're in no shape to fly! You need rest!" She waved both her forehooves as she stated, "Everypony, this is the face of the pony most in need of a vacation in all Equestria!"

"I do NOT need a vacation!" Twilight insisted.

Rainbow Dash looked her in the eyes. "Twilight," she said, "somewhere in Equestria is the pony who loves lists of things more than anypony else except you."

"Harsh," muttered Spike.

"But not wrong," whispered Starlight.

"And someone among their fifty gazillion lists," Rainbow Dash continued, "they have a list labeled, 'Ponies Who Need a Vacation.' And just under the title, it says, 'Number One: Twilight Sparkle!'"(449)

"But... but I can't!" Twilight shrieked. "I know Moondancer's been doing her best, training as my backup, but if something goes wrong with the magic engines she can't fix them! And she's not strong enough to power them by herself!" She waved a hoof at Starlight Glimmer. "Starlight could, but she's not trained as an astromare yet! And there isn't anypony else, Dash!"

"That's all right," Dash said. "Because I'm flying alone."

"WHAT?"

"Well, I'm certainly not flying with you," Dash insisted. "Like I just said- you're not fit to fly. You're worn out, your mental state is a wreck, you haven't had the time to put in the training you really need... the way you are now, you'd be more of a hindrance than a help!"

"But-"

"And besides," Rainbow Dash pressed on, "we don't really need you, or Moondancer really, because we're not taking the magic engines up on this flight. We've had too many system failures on the ground, Twilight. They're not going to be flight-ready in time!"

"But if we use sapphire or amethyst instead of-"

"Not ready in time!" Rainbow repeated. "We still need weeks of tests! Weeks without a single failure! Not weeks where we keep hoping for best two out of three! Yeah, the engines work great when they work, but when we're up around the moon we need to know, for certain, that when the throttle goes forward the battery isn't going to explode or the oscillation crystal isn't going to shatter or the thrust bell isn't going to crack and disintegrate. Will we know that in time, Twilight?"

Twilight hung her head. "No," she said quietly. "But the changelings are going to launch in three weeks. We have to launch on schedule."

"I know," Rainbow said. "So here's my plan. We take Amicitas to low orbit over Equus. We launch the moon lander, dock it there, and do those tests close to home. Then we launch another probe, a Mission Fifteen, with a huge tank of fuel to refill Amicitas's internal tanks. We put fuel and oxidizer refill ports inside the engine bay and put a couple of fuel hoses in the ship kit that I can use to link up with the probe's fuel tanks through the docking port. Then I go out to the moon, see how low I can orbit, take photos of landing sites, and come home. Pack extra food so I can make some aerobraking maneuvers to slow down before final re-entry. It's not as simple as the old mission plan, but it's a thing we can do reliably and safely. Right?"

"But Amicitas is the future," Twilight protested. "The magic thrusters will revolutionize space travel."

"Yeah, but not right now," Rainbow Dash said. "And what we can do in five days is remount the liquid fuel engines, and ONLY those engines, put extra fuel tanks in instead of the mana battery, and work out how to build and launch a refueling probe in about a week. And however important it is to show the world how wonderful Amicitas is," she finished, "it won't make a darn if Chrysalis gets to the moon before we do!"

"Well... but..." Twilight looked Rainbow Dash in the eyes. "Even so, I don't want you to go alone. Remember how rough the ride back into atmosphere was on Amicitas's first flight?"

Dash nodded. To the outside world, that re-entry had looked uneventful. In reality, Dash had wrestled the controls of the tail-heavy ship and fought like a mare on locoweed to keep the ship from tumbling out of control during aerobraking. "Yeah. So?"

"If it had gone wrong," Twilight said, "I could have saved you. Shield, teleport, I'd have managed it. If something goes wrong around the moon, and I'm not there..."

"Yeah, stop right there," Rainbow Dash said. "To tell the truth, I'd rather have you here on the ground. Because if something does go wrong, and I get stranded around the moon... who else could I trust to make sure somepony came to rescue me?"

"Princess Celestia..."

"Princess Celestia would try," Rainbow Dash agreed. "But Princess Twilight Sparkle would know how to do it. And she'd make it happen if she had to walk to the deepest pit in Tartarus and fight her way back out. And I know it." She smiled and added, "Because I know you'd never leave me hangin'."

Twilight shook her head. "That's right," she said. "And thank you for saying that. But I still want to go with you, Dash."

"Not the way you are now," Rainbow insisted. "It's time you took some time off. Moondancer will take care of space program stuff while you're gone."

"I can work on the friendship school," Starlight volunteered. 

"And I can keep up the friendship log and answer your fan mail!" Spike added. 

"And when I get back," Rainbow Dash said, "you'll be rested and relaxed, we'll know how Amicitas and the moon lander work, and we can finish training for the actual moon landing. Before the changelings can do it!"

"But... Rainbow Dash, Starlight, you're my friends," Twilight said. "And Spike, you're part of the family too. You ought to go on the cruise too! I can't just leave all of this work for you!"

"What's that?" Spike asked. "I can't hear you. Because you're on VACATION!"

Twilight turned to Starlight. "Starlight?"

Starlight looked at Spike. "You know, I could swear I just heard Twilight's voice," she said. "But that can't be, because she's ON VACATION!"

"I know, right?" Spike asked.

Twilight looked at Rainbow Dash, who hovered with her forelegs crossed. Sighing, she gave in. "I guess I could use some time off," she said. "And I can use the days before the cruise to sketch out the refueling ship and-"

"Aaaaap, aap aap aap!" Rainbow Dash scolded, reaching down and yanking Twilight out from behind her desk and into the air. "Vacation! Behind desk is not vacation! Drawing spaceship blueprints is not vacation! VACATION is vacation! So VACATE!"

"All right, all right, I'm going!" Twilight said. "I'll fly straight to Ponyville and pack my suitcases! One for visiting my parents in Canterlot, and one for the cruise!"

"Sounds like a plan!" Rainbow said, allowing Twilight to descend back to the floor. "Have a good time!"

"Thanks, everypony," Twilight said. "And good luck with the launch. I'll be listening from the cruise." With that she turned and, with a spring in her step she hadn't had before, marched down the hall to the administration building lobby.

"WHEW!" Rainbow Dash sighed, slumping in midair. "I thought she'd never give in."

Spike held up a warning claw. "Wait for it," he said. He held up three fingers, then two, then one...

"CRUISES HAVE ACTIVITIES, RIGHT?" Twilight shouted from halfway down the hall. "GIMME SOME PAPER! I NEED TO MAKE A SCHEDULE!"

"There it is," Spike said, smiling smugly.

"Really?" Rainbow Dash asked. 

"You've known her longer than I have," Starlight said. "But even I know that no power in the world will stop Twilight from organizing things."

Footnotes:

(446) Rainbow Dash only took part in those tests which were more involved than "turn it on, turn it off", a distinct minority of rocket engine tests. But even this limited experience had made a deep and lasting impression on Rainbow Dash... and, on two occasions for which she was present, a deep impression in the concrete and steel as well.

(447) Adequate, that is, up to that point. The thing about the word "adequate" as regards testing rockets and other explosive devices is that you can only truly learn if the word should have been "inadequate" the hard way. Oh, math could say this or that, but math didn't know everything.

(448) Totally blocking the doorway and preventing Starlight Glimmer from entering behind her. Not that Starlight minded that much, since it gave her a chance to catch her breath after her desperate gallop across miles of empty space center grounds attempting in vain to keep up with Equestria's fastest mare.

(449) Rainbow Dash didn't know it, but the hypothetical pony she was talking about was Princess Celestia, and she did indeed have a list of Ponies Who Need a Vacation. However, number 1 on that list belonged to Celestia herself. And, because Celestia knew more ponies than Rainbow Dash did and had a broader perspective on things, Twilight actually came in well down the list at #17, behind the Royal Palace Pastry Chef (#4), Raven Inkwell (#8), Tempest Shadow (penciled in at #12.5), and Pinkie Pie (#15).