The nuts and bolts
New Horizons accomplishes all this with a small spacecraft that weighed just 943 pounds (428 kilograms) at launch, including fuel. The Johns Hopkins University Applied Physics Laboratory in Maryland built and operates the probe. (The lab previously built trailblazing explorers including NEAR-Shoemaker, which orbited and landed on the asteroid Eros, and the MESSENGER orbiter of Mercury.) My institution, the Southwest Research Institute, based in San Antonio, Texas, has been responsible for mission management, payload development and operations, mission science planning, as well as science data reductions and analysis.
New Horizons carries on board propulsion, power generation, guidance, pointing, command and data handling, and thermal control systems. All of these are redundant except for power generation. A single Radioisotope Thermoelectric Generator — a refurbished spare from NASA’s Galileo and Cassini programs — produces just over 200 watts to power the entire spacecraft and scientific payload during the Pluto encounter.
We designed New Horizons to take maximum advantage of its time at Pluto and, later, any KBOs. The team accomplished this by equipping it with a sophisticated and comprehensive sensor suite to study its targets, fast bus speeds that allow several instruments to operate simultaneously, large solid-state memories to store much more data than earlier Pluto mission concepts could, and fast “turn rates” that allow the spacecraft to point back and forth at various objects in the Pluto system with agility.
Thanks in part to the march of technology, the seven-instrument payload aboard New Horizons is more capable than any other sent on a first reconnaissance mission. Yet the entire instrument suite weighs less than just the camera system on Cassini, and it draws less power while operating than a single 30-watt light bulb.
Our payload includes color and panchromatic imagers, a pair of spectrometers — detectors that break light into its component colors, one operating at infrared and the other at ultraviolet wavelengths — and two radio science instruments to probe Pluto’s atmosphere and measure its surface temperature. Additionally, two onboard plasma spectrometers will measure charged particles to determine the density and composition of material escaping from Pluto’s atmosphere. And rounding out the suite is a dust impact counter to trace the density of debris in the outer solar system.
To get a feel for the greater capabilities of New Horizons compared with the legendary Voyager spacecraft, consider this: Its composition mapping spectrometer, called Ralph, has more than 65,000 pixels; Voyager’s had one. New Horizons’ ultraviolet spectrometer, called Alice, has 32,000 pixels; Voyager’s had two. And its solar wind plasma instrument, SWAP, detects charged particles at about 1,000 times the rate of Voyager’s most equivalent instrument.
Although New Horizons is much smaller and lighter than Voyager, in most respects it is more powerful — and the project cost almost five times less than Voyager. When comparing 1970s-era Voyagers with 2000s-era New Horizons, I like to make the analogy of 1970s mainframes to today’s tablet computers: Tablets — like New Horizons — are far smaller but also far more powerful and far less expensive. The mission not only is going to new horizons at the solar system’s frontier, but it also is opening new horizons for how to do outer planet exploration less expensively.