Find out more on NASA's New Horizons Mission page:

The space payload for New Horizons includes Ralph, Alice, REX, and LORRI. Yes, it's a SWAP, but why is PEPPSI involved - things could get sticky. After all that fooling around, somebody has to cleanup - who better than a student?

The science payload includes seven instruments:

Ralph: Visible and infrared imager/spectrometer; provides color, composition and thermal maps.

Alice: Ultraviolet imaging spectrometer; analyzes composition and structure of Pluto's atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects (KBOs).

REX: (Radio Science EXperiment) Measures atmospheric composition and temperature; passive radiometer.

LORRI: (Long Range Reconnaissance Imager) telescopic camera; obtains encounter data at long distances, maps Pluto's farside and provides high resolution geologic data.

SWAP: (Solar Wind Around Pluto) Solar wind and plasma spectrometer; measures atmospheric "escape rate" and observes Pluto's interaction with solar wind.

PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation) Energetic particle spectrometer; measures the composition and density of plasma (ions) escaping from Pluto's atmosphere.

SDC: (Student Dust Counter) Built and operated by students; measures the space dust peppering New Horizons during its voyage across the solar system.

Spacecraft instruments are selected to meet a mission's science goals. On New Horizons, for example, NASA set out a list of things it (and the planetary science community) wanted to know about Pluto: What is its atmosphere made of, and how does it behave? What does the surface of Pluto look like? Are there big geological structures? How do particles ejected from the sun (known as the solar wind) interact with Pluto's atmosphere?