Neptune Orbiter
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Neptune Orbiter is a proposed NASA unmanned planetary spacecraft to explore the planet Neptune. It would be launched sometime around 2016 and take 8 to 12 years to reach the planet. The Neptune Orbiter is designed to answer many questions that still surround the planet. Its main mission is to study Neptune's atmosphere and weather, its ring system, and its moons, particularly Triton.
California Institute of Technology has proposed one mission plan while University of Idaho and Boeing have proposed an alternate approach.
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[edit] Mission Summary
Neptune Orbiter's primary mission is to go into orbit and perform scientific analysis on the planet. The mission was first picked up from NASA in 2005. The planned orbiter is to be launched some time around 2016. Its launch vehicle is yet to be determined, and it is also undetermined whether the probe will be launched directly toward Neptune, or will use a more complicated trajectory to get gravity assists from Jupiter (like New Horizons) and possibly Venus and Earth as well (like Cassini-Huygens). All of these would require a cruise stage of 8 to 12 years. One proposed idea even includes a Uranus fly-by although this seems unlikely. After arriving, it will begin Neptune Orbit Insertion. After adjusting its orbit to its regular science orbit, the orbiter will carry out studies of Neptune and finally release its Triton landers and atmospheric probes. The main phase of the science operations may take as long as 3 to 5 years with an extended mission phase lasting 3 more years.
[edit] Current status
As of 2006, the construction of the Neptune Orbiter is still under debate, and the launch date, trajectory, and payload are all still speculative. Although NASA administrators and the public propose a flight toward Neptune, current budget controls continue to threaten the proposal along with other NASA science operations. Right now, Neptune Orbiter is in early planning stages and funding is planned to begin sometime around 2008. In addition, a large amount of radioisotope thermoelectric generators would likely be required for this mission, but NASA has a short supply of remaining radioisotope thermoelectric generators. Nevertheless, radioisotope thermoelectric generators remain the most likely choices of power.
[edit] Power Sources
[edit] Radioisotope thermoelectric generators
The Caltech mission would be similar in design to previous NASA outer solar system missions. It would use Radioisotope thermoelectric generators for electrical power. As of 2006, this power source is the most likely choice for the mission. It would also reduce the costs of building the spacecraft, which is important with NASA's limited current science budget. Based on this propulsion, the spacecraft design may be similar to Galileo, Cassini-Huygens, Voyager, and New Horizons, with conventional thrusters for propulsion.
[edit] Solar Panels
Another proposal calls for using solar panels to provide electrical power to the spacecraft. The panels would also be inflatable reducing their mass. Although advancements in solar panel technology means it should be possible to achieve sufficient power at the distance of Neptune, the high cost of providing the solar panels would possibly eliminate the idea of using solar cells. As of 2006, this proposed power source would probably require significant technological advances and may add risk to the development schedule. This design would presumably also use conventional thrusters, as the dim sunlight in the outer solar system would probably be insufficient to power an ion propulsion system.
[edit] Nuclear Electric Fission
For propulsion it is proposed that the Orbiter use a nuclear electric propulsion system that was planned for the now cancelled Jupiter Icy Moons Orbiter. This would take up to 20 years to reach the planet but would leave the mission with a large supply of fuel and electrical power for the orbital phase of the mission, allowing the spacecraft to orbit multiple bodies and to carry a greater variety of instruments. But this method of propulsion seems unnecessary and, considering the opposition radioisotope generators have elicited, launching a nuclear reactor into space may be too controversial with the public. Also, the development time and cost needed for this idea may be too much for NASA's budget. But, nuclear-powered spacecraft cannot be ruled out as there have been many proposals for missions to use nuclear reactors in space in associating with power for manned spaceflights to Mars and for deflecting asteroids that threaten to collide with Earth in the near future.
[edit] Instruments
[edit] Orbiter
The orbiter is considered the main part of the mission which will carry out the main mission objectives. Instruments that the Orbiter is planned to carry include a multispectral imaging system, to image the planet from ultraviolet to infrared. A magnetometer will be carried to investigate why the Neptune's magnetic field is oriented so far from the planet's axis of rotation.
[edit] Triton lander(s)
NASA scientists and engineers have planned to send one or two mini-landers to Triton's surface and analyze the composition of the surface, the interior, and the possible nitrogen atmosphere, as well as to search for any liquid water and microscopic life forms. Although detailed exploration of Triton is a high priority for mission planners, NASA's current budget may threaten the ability to launch the Triton landers and possibly cancel them from the mission. Suggested landing sites focus on the north and south poles of Triton where large amounts of frozen water ice may be discovered. The landers' normal operational lifetime is estimated to be from 2 weeks to a month with a possible extended mission phase on Triton.
[edit] Atmospheric probe(s)
Along with Triton landers, at least two atmospheric probes have also been proposed to go into Neptune's atmosphere and study the climate and weather of the stormy planet. Similar to the Galileo probe that descended into Jupiter's atmosphere, it would take about 30 minutes to an hour of detailed analysis of the atmosphere. Then it would be planned to continue its descent until the planet's mass and strong gravitional pull would crush it and thus destroy them.
