Tuesday, April 8, 2008

Preliminary Report on Jupiter Joint SDT

Ron Greeley from Arizona State University presented a status report on the Jupiter/Europa Joint Science Definition Team (JSDT) at last week's Spring OPAG Meeting. As reported earlier, the Jupiter JDST will be a combination of ESA's LaPlace and NASA's Europa Explorer and Jupiter System Observer mission concepts. The mission would be composed of three separate mission components: Europa Orbiter (provided by NASA), Jupiter Planetary Orbiter (provided by ESA), and Jupiter Magnetospheric Orbiter (provided by Japan's national space agency, JAXA). Greeley's presentation and Jean Paul Lebreton's Cosmic Visions presentation provide details on how this joint mission concept study is progressing.

First, it appears that the Jupiter Planetary Orbiter will not flyby Io as originally thought. This mission component will use solar panels for power and thus will likely stay in the neighborhood of Ganymede and Callisto. Very few details were provided on the Jupiter Planetary Orbiter component though the presentation states that its science goals will be focused on the Jupiter System as a whole.

The Europa Orbiter (EO) has evolved a bit since the Europa Explorer concept study. The mission has taken on more of the Jupiter System science goals from the Jupiter System Observer concept. This includes early orbital tour strategies that include as many as four close Io flybys, though none and one near orbit insertion are also possibilities. Four Io flybys would add 0.3 Mrad to EO's total radiation dosage, but this is offset by EO's shorter primary mission at Europa (60 days versus 6 months for last year's Europa Explorer concept). The flybys would also add 10-20 kg of mass to the Attitude Control Subsystem, though the JSDT notes that this mass trade ''looks favorable'' since less fuel would be needed compared to using Ganymede to slow EO down near JOI.

This cut in primary mission length is intended to reduce the total cost of the mission down to NASA's cost cap of $2.1 billion (from $2.4-2.6 billion). Other cuts include the removal of several instruments from the core payload. These cuts include the narrow-angle camera, which was baselined with the resolution equivalent to the camera on Galileo. The two remaining camera systems, the medium-angle camera and the wide-angle camera, will have resolutions 10 and 100 times coarser, respectively. This cut will reduce the effectiveness of EO to do distant Io science, but this could be made up if the Jupiter Planetary Orbiter retains Jupiter System Observer's superior camera systems. The core payload also omits the Thermal Imager, which will reduce EO's effectiveness to map lower temperature thermal emission on Io. The Near-IR Spectrometer has been retained so that should be fine for higher temperature hotspots.

Another note from the Greeley (and Lebreton) presentations is that these mission components will likely be launched separately, and not necessarily in the same launch window. It is also possible that the Magnetospheric orbiter and Planetary Orbiter will be launched on the same vehicle. However, this would push JPO to 2020 or later, since the Magnetospheric Orbiter will not launch before 2020.

This mission concept is competing with the Titan/Saturn System Mission to be selected as the next flagship mission to the outer planets. Selection of the mission to be launched in the 2016-2017 timeframe will come later in the year.

Link: Preliminary Report of the Joint Jupiter SDT [www.lpi.usra.edu]

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