Professor Tobias was showing the exploded view of a Battle Craft called Raider 01 with the help of a hologram. He was explaining its features to his students, "And the specialty of this Battle Craft is that it was one of the first models of craft that could successfully travel through a wormhole. The planet of origin of this model is C-31."

Spaceship Designs was Natalia's favorite class but today her mind was not present in the class. And the reason for her mind drifting away was that her father had not called her this morning.

Natalia glanced at her phone that had intergalactic reception but there was no call or text from her father. David would never fail to contact Natalia first thing in the morning and update her about where he was and what was going on in his ship. But today, however, the call never came.

"Did something happen to dad?" Natalia furrowed her brows and bit her finger nail while thinking about her dad. "No, he must be busy with something. He will call me when he is free. I'll just leave a message to him."

Then Natalia started to type something in her phone. Professor Tobias noticed that Natalia was not being attentive in the class. Natalia was one of the promising student of his class so he wanted to have her attention, "Natalia, will you tell me what kind of power source is used by Raider 01?"

This question from Tobias jolted Natalia out from her thoughts. But Natalia was not listening to the lecture so she replied with hesitation, "I'm sorry Professor. I do not know."

However, that was just a trick question from the Professor and its purpose was to get her attention. So he flicked his hand and said, "Correct answer. How would you know when I have not told you yet? Okay, the answer is, Raider 01 uses a radioactive isotope called Nickel 56 as a compact source of electrical power."

The Professor changed the image of hologram and displayed the virtual representation of Nickel 56. "While the standard source of energy in all other space crafts is another commonly found radioactive isotope called plutonium 238, Raider 01 uses Nickel 56. It is a rare radioactive isotope which is only produced when a star goes supernova, meaning when a star explodes."

The whole class was in awe when they heard that inhabitants of C-31 were able to extract the isotopes from supernova and use it as a power source for their crafts.

"I wish I was as intelligent as the scientists of C-31. How did they even come up with the idea of gathering such radioactive isotopes from an exploded star?" A student whispered to his friend in the class.

The Professor went on explaining to the students, "Because of its unstable form, Nickel 56 produces excess energy by naturally emitting radiation. And you all know how useful such energy is for spaceships."

Tobias adjusted his glasses and emphasized the next piece of information carefully, "And let me add, once the core was installed with Nickel 56, the designers of Raider 01 claimed that the power source would work for a hundred years."

Natalia was also amused by this piece of information. "Whoa! A hundred years? That means the core does not need to be changed for such a long time… that is just awesome."

One of the students raised her hand and asked, "Professor, I am curious as to how this Nickel 56 produces electricity."

Professor Tobias smiled and then answered, "Excellent question! As you all know, these radioactive isotopes have a very unique characteristic. They gradually decay, changing its form. Nickel 56 also decays to cobalt 56 and then to iron 56."

Tobias shifted his gaze at Natalia who was now really interested in the discussion and continued, "And I want to emphasize that in spaceships, the heat produced in such decay process is converted into electricity by using thermoelectric junction circuits."

Professor Tobias took a pause and then asked to the class, "Any more question?"

But the bell rang loudly indicating the class's time was up. Everyone rushed out of the room. Natalia also packed her bag and prepared to go outside of the class but the Professor called her to the front, "Natalia, will you come here for a minute?"

Natalia obliged and then walked towards the Professor. "Yes Professor."

Professor Tobias then asked her, "Is something bothering you today? You seemed to be distracted in the class."

Natalia hesitated to give the answer. The Professor was not her friend after all. She tried to smile and then simply said, "No Professor, I'm good."

Then Tobias smiled back and replied, "David is a good friend of mine. I know you must feel lonely at times because your father is mostly travelling. But trust me when I say this, he is a great captain and you don't need to be worried about him."

Natalia felt like the Professor was able to read her mind. But she was glad that he said those words. "Thank you Professor. I kinda needed to hear them."

"Then I'm glad I said them. Okay, I don't want to take much of your time. See you in next class, Natalia." Tobias waved his hand to say goodbye.

Natalia also waved her hand and left the class to find Alexis.

Alexis was waiting for Natalia outside her classroom. They both needed to get to their part time job at the Harper's.

"Hey Natalia, how was your class?" Alexis cheerfully asked Natalia when she saw her.

"It was good. We learned about a Battle Craft. And how was yours?" Natalia tried to put up a smile when she answered.

Alexis noticed that Natalia was not her usual self. She would normally go on and on about what she learned. So she tried to cheer her up. "Well it was far more interesting because you were not there to distract me."

"You are such an arse." Natalia jokingly slapped Alexis on shoulder and laughed. Alexis also joined in and laughed with her.

Alexis booked a cab for them and they started to walk towards the Academy's gate. Soon the cab arrived and took the girls to their destination in P-99 Street.

While Alexis was paying, Natalia got off and went to open the gate of the Harper's. However, it didn't budge. Alexis came near the gate and asked, "What happened?"

Natalia grunted while trying to open the gate and said, "It is not opening. I think it is locked." Then she shouted at the top of her lungs, "Mr. Harper… Mr. Harper… Hey, we are stuck outside. Will you open the door?"

They waited for a minute or so for Mr. Harper to reply or open the door but there was no answer.

Alexis looked at Natalia and suggested, "Well why don't you try calling Mr. Harper's cell phone. He might not have heard us."

"Yeah, okay." Natalia took out her phone and called Mr. Harper.

"Hello!" A weak voice answered from the other side.

"Mr. Harper?" Natalia was not sure if it was the right person.

"Yes. Who is this?" Mr. Harper coughed loudly after asking that question.

"Mr. Harper, I'm Natalia. Are you alright? You don't sound so good. Where are you?" Natalia was concerned for him because he sounded sick and he might have been lying down alone inside the office somewhere.

Mr. Harper finally recognized the voice and said, "Oh! Natalia, I'm sorry. I completely forgot that you two joined the work and forgot to inform you that I wouldn't come today. I was not feeling well so I'm at the hospital."

"What? What happened?" Natalia asked in a worried tone.

Hearing Natalia's worried voice Mr. Harper tried to console her, "You don't have to worry, it is nothing serious. I will be fine by tomorrow."

Natalia let out a sigh of relief. "That is good to hear. Well, I guess we'll return home today then."

Mr. Harper was getting old and his memory was not what it used to be. He felt bad that the girls came to his office just to return back without working. He took a mental note to make sure to pay them for today as well. "Sorry that I forgot to inform you. I will make sure to compensate you girls for today."

"You don't have to be sorry. It's okay. Take care and get well soon Mr. Harper." Natalia merrily wished good health to him.

"Sure. Thanks." Then he ended the call and got back to resting.

Natalia turned towards Alexis who was listening to the conversation and said, "He is not here today. He said he is sick."

Alexis puckered her lips and rested her back on the gate. "What do we do now? Shall we go back home or should we go somewhere else?"

Natalia also rested her back on the gate and started to draw some lines on the dusty road with her shoes. "I don't want to go home just yet. I'll be alone. Dad has not called me or texted me today, and if I'm alone I'll overthink about it."

Alexis knew that this would be her answer so she had already thought of a perfect place to visit while Natalia was talking to Mr. Harper.

"I think I have the perfect place for you Nat. But we will need to buy some masks before we go there."