Today is a milestone for the New Horizons probe. The spacecraft, which launched nearly nine years ago, has just begun its official six-month countdown. From this point forward, NASA will guide the probe based on the position of Pluto, rather than using strict radio tracking. It’s the first Earth probe to visit the most distant planitesimal known in the solar system — the closest analog to its mission would be the Voyager missions in the late 1980s, which visited both Uranus and Neptune.
Part of what makes the New Horizon’s mission fascinating is that the entire project is being coordinated by a MIPS-based Mongoose-V CPU. The Mongoose-V is derived directly from the MIPS R3000, which powered the original Sony PlayStation.
The MIPS R3000 was a 32-bit workstation and console processor with a dedicated FPU unit and a very small set of instructions with minimal pipelining. The CPU lacks a conventional L1 cache design but does have instruction and data caches of 2KB and 4KB respectively. The space-hardened Mongoose-V does vary compared to the conventional terrestrial version in one respect — it’s actually significantly slower. Where the PS1 clocked in at 33MHz, the New Horizons probe runs at just 12MHz.
The New Horizons probe actually carries more than one Mongoose-V CPU, but the second unit is kept as a backup control system and isn’t used simultaneously to provide additional compute power to the total probe. The reason for all this redundancy, and for the relatively anemic hardware in the first place, is power consumption and radiation hardening. At this distance from Earth, the New Horizons probe needs an efficient system to avoid taxing limited power reserves — but it also needs a CPU that can withstand substantial bombardment from cosmic rays and other stellar phenomena. Conventional high-end devices, like smartphones, wouldn’t last any length of time at all — so companies take considerable pains to radiation-harden their various designs.
By May, New Horizons will be close enough to Pluto to image the planet more clearly than the Hubble Space Telescope, meaning we should be able to resolve. Right now, the best image we have of Pluto that isn’t an artist’s rendition looks like this:
In four months, that will change. On 14 July, New Horizons will conduct a flyby of Pluto, Charon, Hydra, Nix, Kerberos, and Styx. Most of you have likely heard of Charon, the moon of Pluto discovered in 1978, but recent work has found three other natural satellites in orbit around the dwarf planet.
New Horizons will map the day and night terminators of the Pluto-Charon system, examine the surface of each planet for atmospheric conditions (if any), hydrocarbons and other nitriles, characterize the surface composition, and examine the area for moons, rings, and other features too small to be seen from Earth.
Following this mission, New Horizons will head into Kuiper Belt. NASA is currently searching for one or more targets that the probe might explore, shedding new light on some of the most distant objects in the solar system.
And no,
Mass Effect fans, there’s no word on what NASA intends to do if the moon Charon turns out to be a large, ice-covered alien structure
of unknown origin.