Theory:

‘The community of Nations Square,’ he told her. ‘People of different nationalities who work in Selenopolis come here after work. And there are some tourists. They’re walking towards the lake. It’s quite an exotic experience to have a swim on the Moon.’

‘I’m sure it’s better in the river Dnieper when you come to the Earth for your holiday.

When they looked at the astrodrome, where two spaceships the size of the Ostankino TV tower were pointed into the black void of the universe, she sighed again.
Explanation:

The son explained to his mother that the lily-shaped tent was known as 'The Community of Nations Square' and that people from many countries who worked in Selenopolis would gather there after their day's work. According to the son, even some tourists would pay a visit to the location.

As mother and son conversed, they noticed people travelling along a specific route. They were walking towards a lake where people might swim, the astronaut told his mother. He even suggested that having a swim on the moon would be an unusual experience. The astronaut's mother, on the other hand, told her son that swimming in the Dnieper River on Earth was preferable to swimming in the Selenopolis River. This tells us two things. To begin with, the astronaut's mother was determined to persuade her son to visit Earth. Her son was more important to her than anything.

The Dnieper River is an important river in Ukraine and Europe. Might be the astronaut and his mother were the inhabitants of Russia.

She then noticed two large spaceships which were pointed toward the black space of the universe. It is so huge, like the size of the Ostankino TV tower in Moscow, Russia. She sighed at its enormous size. An astrodrome is a place to launch spacecraft. The Ostankino Tower is a television and radio tower in Moscow, Russia, which measures $$540.1$$ metres tall. It is the world's 11th tallest tower and Europe's tallest free-standing structure.

Meaning of difficult words:

 S.No Words Meaning 1. Exotic Very strange or unusual 2. Sigh To let out a long deep breath 3. Astrodome A place to launch spacecraft 4. Black void Without light
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.