Theory:

    There was a shrill whistle and Tilloo found himself the centre of attention. His father pulled him away roughly and restored the red button to neutral position. But the damage was done.
 
    The mechanical hand from the spacecraft ceased to work.
 
    At a press conference held by NASA, a scientist was briefing the world press:
          ... Everything has been going on smoothly with the Viking Mission. There is a small hitch. The mechanical hand which was to dig out the Martian soil for examination has developed a malfunction... We don’t know the cause but our technicians are confident they’ll sort it out...
Explanation:
 
Later, Tilloo's interest in pressing the most visible red button resulted in an uncomfortable high-pitched sound. Tilloo had found himself in the centre of attention. On the other hand, his father grabbed him roughly and tried to restore the machine to its normal position. Tilloo's father had done it because to avoid problems. Also, they should not reveal their existence because they did not know the motives and intentions of the spacecraft. As a result of his mischief, the mechanical hand stopped functioning.
 
On the other hand, a news conference was held by NASA on Earth, and a scientist started to explain why the mechanical hand had ceased moving. It meant that the spacecraft was sent from the Earth, and unfortunately, it stopped functioning. In most cases, while dealing with spacecraft, the scientist must answer his higher authorities and the press if any trouble occurs. So, when the mechanical hand was no longer moving, NASA held a news conference in which a scientist gave a brief explanation of why it had stopped moving.
 
It was evident from the press conference that Tilloo and the rest of the characters lived under the Martian surface. Aliens refer to people from another world. According to the Martians, people from the Earth seemed to be Alien.

While everything had been going smoothly with the Viking Mission, there remained a problem, though. The problem was occurred due to Tilloo. As a result, the robotic hand stopped functioning. The main motive of the mechanical hand was to dig up Martian soil for analysis. Unfortunately, it had failed, and they were not sure what's caused the issue. Later, the scientist reported to the press that they were unsure what the cause was, but he addressed that their experts were confident that they'd rectify the problem soon.
 
Viking1mars.jpg
Viking Mission I on Mars*
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Restore To return something or someone to an earlier good condition or position
2
Scientist An expert who studies or works in one of the sciences
3
HitchMove something into a different position with a jerk
Reference:
National Council of Educational Research and Training (2007). Supplementary. An Alien Hand - Jayant Narlikar (66-73). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.
 
Viking Mission I on Mars*: Public Domain, Wikimedia Commons.