Theory:

     ‘Wouldn’t it make more sense to settle properly on the Moon first, and then on the planets in the solar system, before going further?’
 
     It was now his turn to sigh. ‘You may be right, but…’
 
     ‘But what?’
 
     ‘How do I know?’
 
     He longed to tell her about the flight he was longing for and about how nervous he had been when confronted by the selection commission. But he checked himself. It was their last meeting before his departure, so why spoil it?
Explanation:
 
The astronaut's mother meant to ask her son why people wanted to explore or move to other planets, as she believed it would be better for people to stay and settle on the Moon first, then move on to other planets in the solar system. People were aware of things like soil, water, air, and so on (at least a theoretical knowledge) of planets in the solar system, she reasoned. However, details about a galaxy other than the Milky Way have yet to be discovered, and mankind may encounter peril where they have the least possibility of returning.
 
Milky way.jpg
The Milky Way
 
Previously, the astronaut's mother sighed when she looked at the two large spaceships. Then the astronaut sighed as he listened to his mother's speech and was about to tell his mother something, but he couldn't. He knew he will not have a chance again to meet his mother. His mother began to inquire about what he was about to say, but he remained silent. He couldn't tell his mother the secret that was causing him so much agony.
 
In actuality, the son's name was also on the list of spaceships voyage set to travel in one of those two spaceships, which was a tragic thing. It was either his ambition or a burning yearning to visit another planet. And he was worried that he would not be chosen for such a voyage to another galaxy when the selection commission was deciding who would be chosen. He wanted to tell his mother about those nerve-wracking moments. But he restrained himself from doing so. After all, it was their final meeting, and he knew he wouldn't come back after such a trip, and he wouldn't get to meet his mother. As a result, he didn't want to ruin such a meeting.
 
Due to the greater distance and a lack of technical advancement, the astronauts will not be able to return from another galaxy.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
ConfrontTo face or meet a challenge
2.
DepartureThe act of leaving a place, job etc.
Reference:

State Council of Educational Research and Training (2018). Term-3 English Standard-9. Mother’s Voice - Vasil Berezhnoy (pp. 170-173). Published by the Tamil Nadu Textbook and Educational Services Corporation.