“Good question. We don’t try to hit the planet as we follow it. We point to the side a little so the planet does two things. It makes us go faster, and it turns or steers the spacecraft in the direction we want to go. The trick is approaching the planet just right.”

“Kayla squinted her eyes a little and pinched her chin.

“Here, let me make it a little easier. Picture our big round trampoline at home. Now imagine it with a bowling ball resting right in the center. Now, suppose you and I are standing on opposite sides of the tramp. To roll a soccer ball from me to you, I would roll it along the trampoline so it passes just to the side of the bowling ball. What will the soccer ball do as it rolls along?”

“It will turn toward the bowling ball because that’s down hill.”

“Right. If it rolls too slow, it will turn too much toward the center, and hit the bowling ball. If it rolls fast, it will pass by the bowling ball while turning toward it a little. If I roll it even faster, it will turn a little and then roll off the far side of the tramp. Picture every planet as a bowling ball in the center of a trampoline causing things that come near to steer toward the planet. We can use these gravity pulls to turn and steer the ship where we want it to go.”

“Cool,” Kayla picked up a different model and held it high as she flew it around a globe in the corner of the room.

“And let’s suppose the trampoline was orbiting around the house…”

Kayla’s raised her eyebrows. “Sorry dad, I can’t imagine a trampoline orbiting our house.”

Tom looked up for a moment. “Okay, try this. Remember when we all went skating? Suppose you and I were skating along and I was a little ahead of you. Now if I reached back and grabbed your hand, then pulled on you and swung you out in front of me, you would speed up and I would slow down a little,  you would be going faster than you were before, and I would be going a little slower. That’s what the planet does to the spacecraft.”

Kayla closed her eyes half way. “It sounds like a lot math.”

“Yes, and physics and other important school subjects. But it’s really powerful to know how to…”

“Dr. Dixon,” A man in his early twenties with a red face, out of breath, stood in the doorway of Tom’s office.

“Hi Ben, how is your internship going?”

“I’ll tell you about that later. We have a serious problem and I came to get you.”

“What are you talking about?”

“There’s been a solar flare, larger than expected. As programmed, Vector1 automatically shut down for radiation protection.”

Tom stood and moved quickly toward the window and parted the blinds.

“They’re not sure if the solar panels retracted in time, the radio signal has gone quiet; anyway, the solar wind gave us a nudge, and they say she’s approaching earth high and wide.”

“No!” Tom turned from the window, distinct wrinkles across his forehead. “This can’t be. Everything was going well. We’ve worked so hard for this.”

Ben opened the door wide. “The director wants the best orbital mechanic, in the control room, right now” Ben pointed at Tom and raised both eyebrows. “That means you.”

Tom grabbed his laptop and headed for the door. “Kayla, come with me. It looks like ‘Bring Your Child to Work Day’ is not going to be routine.” Tom pointed at the spacecraft Kayla was flying around the office. “Bring that model.”

Kayla lowered the spacecraft and followed the two men quickly down a long hall.

“What happened Ben? We’ve experienced solar flare’s before. Why is she off course? Why do you think the solar panels are still extended?”

“That’s the only explanation for the change in trajectory. And there’s another problem; we don’t know Vector1’s attitude…”

“A spacecraft with an attitude?” Kayla thought out loud, but the two men did not hear her. “Well if I had just been hit by solar wind, my attitude would be bad.”

Tom and Ben entered the control room, with Kayla gravitating right behind. Her father pointed to a chair in the corner. “Ben, would you sit by my daughter? She’ll probably have questions and I’ll be too…”

“You got it Dr. TD.” Ben replied.

“Dr. Dixon, the timing couldn’t have been worse.” A man with a dress shirt and loose tie sighed a small measure of relief when Tom entered the room. He pointed at a computer monitor. “From all we can tell, the solar wind had enough effect on Vector1 to put our periapsis burn altitude too high.”

“Kayla.” Ben leaned over and spoke quietly. “Ask me anything you want.”

“Why did you call my dad an orbital mechanic? That sounds like someone with wrenches on the space station that goes around fixing broken satellites.”

Ben grinned. “An orbital mechanic uses math and physics to predict how planets, asteroids, and spacecraft react to the gravitational pull of each other.”

“Oh. So that’s how he can plan trips to Jupiter.”

Tom leaned over and examined the screen. We’re off by a few arc-seconds. “We’re on the wrong approach trajectory to earth. We need a course correction burn immediately,” Tom pronounced with a very serious tone, “or we’ll be on the wrong departure trajectory leaving earth; we’ll be headed no-where at high speed.”

“We can’t maneuver within an hour,” Another man, plaid shirt and blue jeans yelled from across the room.  “Vector1 is in radiation shutdown for fifty-five more minutes. And when she comes back on line, if she comes back on line, we don’t even know her attitude, we could make things worse with a hasty burn. We could come in low and have aerodynamic drag in the earths atmosphere…

Kayla looked at Ben.

Ben whispered. “A burn means to fire the on-board rockets to change it’s direction or speed. It’s often called a Delta-V or Delta-velocity.”

“What are you talking about?” Dr. TD raised his voice.

“Tom, it’s very possible that the solar panels were damaged by the flare. They weren’t designed to take this much radiation. They were supposed to retract temporarily for events like this.”

“I know all that. Are you telling me that our billion dollar mission is gonna fail because…”