Part 8/12:
Suppose we imagine that a spacecraft could decelerate enough to just "fall into" the sun. To do so, it would need to reduce its orbital velocity to nearly zero relative to the sun. This would involve burning enormous amounts of fuel to counteract its inherited velocity.
But can we "crash" into the sun?
The sun lacks a solid surface—its atmosphere consists of plasma at millions of degrees Fahrenheit, making any spacecraft disintegrate before reaching the inner layers—the photosphere, chromosphere, or corona.
In other words, even if a spacecraft could be directed inward perfectly, it would vaporize before any impact, making traditional "landing" or "crashing" impossible.