Option 2: Cassini is a spacecraft.

Cassini is the only option among the given choices that qualifies as a spacecraft. Here`s the detailed reasoning:

1. Apophis: Apophis is not a spacecraft but an asteroid. It is a near-Earth asteroid named after the Egyptian god of chaos. Apophis gained attention because initial observations indicated a small possibility of impact with Earth in 2029, but subsequent calculations ruled out the possibility of a collision.

2. Cassini: Cassini is a well-known spacecraft that was launched in 1997 by NASA in collaboration with the European Space Agency (ESA) and the Italian Space Agency (ASI). It was designed to study Saturn, its rings, and its moons. Cassini reached Saturn in 2004 and spent more than 13 years exploring the planet and its fascinating system.

Cassini carried a suite of scientific instruments, including cameras, spectrometers, and other detectors, which provided valuable data about Saturn`s atmosphere, magnetosphere, rings, and moons. One of its significant accomplishments was the discovery of liquid water on Saturn`s moon Enceladus and evidence of a subsurface ocean, making it a prime target for future astrobiological investigations.

In 2017, Cassini ended its mission with a spectacular dive into Saturn`s atmosphere, transmitting valuable data until its very last moments. The mission was a remarkable success and significantly expanded our understanding of Saturn and its celestial environment.

3. Spitzer: Spitzer, also known as the Spitzer Space Telescope, is not a spacecraft either. It was an orbiting infrared observatory launched by NASA in 2003 and operated until 2020. Spitzer`s primary mission was to detect and study objects that emit infrared radiation, such as distant galaxies, young stars, and dust disks around stars. However, it was not a spacecraft intended for deep-space exploration like Cassini.

4. TechSar: TechSar does not correspond to a known spacecraft. It might be a fictional or non-existent entity as of my knowledge cutoff in September 2021. If it refers to a recently developed or announced spacecraft, I`m not aware of it.

In conclusion, among the given options, Cassini is the only spacecraft. It was a highly successful mission that provided us with valuable insights into Saturn and its complex system of rings and moons.