What you're talking about is a so-called "game mod"; a modification of an existing game.

What you would need is the following:

• a modeling application to build the environment (spaceship, planets etc)
• a tool to convert those models to a format that Half-Life can import
• a tool to create particle effects for the exhaust flames of the spaceship
• a tool to record the animation you make.

The import/conversion tool are available from the Half-Life community.
The modeling can be done using a standard modeling application.

There is no need to write a single line of C/C++

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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