Friday, August 21, 2009

White Paper: Titan Geophysical Network

This blog entry will begin a series of summaries of Decadal Survey White Papers. These position papers are submitted by members of the planetary research community to make the case to prioritize specific lines of inquiry, measurements, and missions. Because the papers are meant to be read by a wide audience, they generally are not too technical on either the science or engineering sides. This makes them readable by interested members of the general public such as myself and probably most of the readers of this blog. The papers are also short. The papers are limited to seven pages and 12 point font. All papers are due by September 15, meaning that there will soon be a flood of publication to the White Paper website. Drafts of a number of papers have been posted, and I'll begin summarizing these.

A couple of notes, though. I cannot publish summaries in anything approaching real time (the penalties of a family and career). You can probably expect that I will still be writing summaries for the next several months. Nor am I likely to read and summarize all the papers -- there is likely to simply be too many. However, all the White Papers are available at this website, so you can read the ones of greatest interest to you.

I'll start this series with a White Paper written by Ralph Lorenz (with a number of co-authors). Lorenz is a much published scientist who focuses on Titan and also has led or participated in a number of task forces exploring mission options for future Titan exploration. He has published a couple of books on Titan for the general public. Ralph is also a good guy to share a beer with at a scientific conference.

Lorenz's paper is, "The Case for a Titan Geophysical Network Mission." The goal of the paper is to have the Decadal Survey prioritize this mission high enough that it would make the list of potential missions for a future New Frontiers ($650M) class mission. A second goal is to make the development of small plutonium powered energy sources a priority. (NASA is considering developing such a power source to enable small probes to a number of solar system targets.)

This proposal is one of a number of proposals to establish long-lived (at least months, preferably years) networks of fairly small landers on a moon or planet. A number of fields of study such as meteorology, seismology, and rotational state require measurements from multiple locations on a surface. This paper lists several areas of study that could be advanced with simple Titan landers:

  • Measure near-surface meteorology for both short-term changes, medium-term changes from the atmospheric gravitational tide as Titan orbits Saturn, and potentially long-term changes with the passing of the seasons
  • Variations in Saturn's magnetic field on the surface of Titan to explore the properties of the water-ammonia ocean beneath Titan's crust
  • Track changes in Titan's rotation and tilt to explore the interior structure
  • Possibly make seismic measurements (which would require a relay orbiter)

The paper points out that the basic measurements could be made with sensors common in many high end watches: "a pressure sensor, a magnetometer, a light sensor, and a thermometer." If budgets allow, the landers could also carry a tiltmeter to study tidal deformation of the crust, a wind instrument, a seismometer, a communications system that allows precise doppler tracking, and a wind measurement instrument. A descent camera could take images of the landing site.

The paper is short on specifics, leaving the detailed definition to the proposers of an actual New Frontiers mission. Instrument mass could be as low 1.5 kg to 20 kg. The mission would fly four probes to Saturn on a carrier craft that drop the probes off without entering Saturn or Titan orbit. Communications would be direct to Earth, which would limit the bandwith to as little as 1 bit per second.

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