Exploring moon Triton
Authors: Sanmartin Juan , Pelaez Jesus 
Published: July 2022

&lt;p&gt;&amp;#160;&amp;#160;&amp;#160; The NASA program exploring habitability places in the outer Solar System searches for simple forms of life in &lt;em&gt;icy moons&lt;/em&gt; of Giant Planets, with internal &lt;em&gt;oceans&lt;/em&gt; &lt;em&gt;off thermal&lt;/em&gt; &lt;em&gt;equilibrium&lt;/em&gt; between cold, iced surface and rocky center warmed, possibly by dissipation of tides from the Planet; &lt;em&gt;H&lt;/em&gt;&lt;sub&gt;2&lt;/sub&gt;O molecules might lose oxygen to &lt;em&gt;reduced &lt;/em&gt;bottom minerals, and get oxygen back when moving upwards. This &lt;em&gt;Ocean World&lt;/em&gt; concept was confirmed in Jupiter&amp;#8217;s moon &lt;em&gt;Europa&lt;/em&gt;, and Saturn&amp;#8217;s moons &lt;em&gt;Titan&lt;/em&gt; and &lt;em&gt;Enceladus&lt;/em&gt;, the last one ejecting a local plume through ice, though not &lt;em&gt;Titan, &lt;/em&gt;with the &lt;em&gt;Europa&lt;/em&gt;-plume case apparently confirmed. In 2017, &lt;em&gt;H&lt;/em&gt;&lt;sub&gt;2&lt;/sub&gt; molecules, considered sign of &lt;em&gt;life&lt;/em&gt;, were detected at the &lt;em&gt;Enceladus plume&lt;/em&gt;. We here propose a mission to explore the only large Neptune moon, &lt;em&gt;Triton&lt;/em&gt;, which is usually considered an important &lt;em&gt;Kuiper Belt Object&lt;/em&gt; as captured &lt;em&gt;dwarf planet&lt;/em&gt;. More relevant, here, is that &lt;em&gt;Voyager&lt;/em&gt; 2, in 1989, found evidence of &lt;em&gt;Triton&lt;/em&gt; ejecting a kind of plume.&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160; &amp;#160;Ice Giants, however,&lt;em&gt; &lt;/em&gt;have only received &lt;em&gt;flyby &lt;/em&gt;missions, at difference with Gas Giants: An effective &lt;em&gt;orbiter-&lt;/em&gt;type mission to faraway Neptune is acknowledged as extremely expensive, trip-average solar power is almost nil, chemical capture leads to high &lt;em&gt;wet-mass, &lt;/em&gt;with scientific&lt;em&gt; &lt;/em&gt;load and orbital maneuvers very constrained. NASA had set a nuclear reactor in space for on-board S/C power in April 1965 but afterwards, for safety considerations, it always used a &lt;em&gt;Radioisotope&lt;/em&gt; Pu 238 power system (helpful in mission &lt;em&gt;Cassini&lt;/em&gt;)&lt;em&gt;.&lt;/em&gt; In a sense &lt;em&gt;constraints&lt;/em&gt; trade occurred in 2009, between proposed &lt;em&gt;Triton &lt;/em&gt;missions &lt;em&gt;a&lt;/em&gt;) with full modern technology but just a &lt;em&gt;flyby&lt;/em&gt; (&lt;em&gt;EPSC&lt;/em&gt;/&lt;em&gt;Potsdam&lt;/em&gt;) and &lt;em&gt;b&lt;/em&gt;) &lt;em&gt;captured&lt;/em&gt; &lt;em&gt;orbite&lt;/em&gt;r though with minimum technology (&lt;em&gt;National Research Council / Planetary Science Decadal Survey&lt;/em&gt;). &lt;em&gt;Aerocapture&lt;/em&gt; and &lt;em&gt;Radioisotope&lt;/em&gt;, for propulsion and power, have been considered for Neptune missions, but decayed consideration.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Magnetic Solution to Power and Propulsion Issues&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160; &lt;em&gt;Icy moon&lt;/em&gt; missions could use, however, thin, multi-kilometer conductive tethers, with no power or propulsion needs, available to a S/C if passing near the planet. The planetary magnetic dipole allows free &amp;#8211;thermodynamically dissipative- S/C capture, and afterwards maneuvering: The relative S/C velocity induces a &lt;em&gt;motional&lt;/em&gt; electric field &lt;strong&gt;&lt;em&gt;E&lt;sub&gt;m&lt;/sub&gt;&lt;/em&gt;&lt;/strong&gt; (in the tether frame) in the highly conductive plasma around, which polarizes the tether and drives a &lt;em&gt;current&lt;/em&gt; &lt;strong&gt;&lt;em&gt;I&lt;/em&gt;&lt;/strong&gt; inside, with &amp;#160;&lt;strong&gt;&lt;em&gt;I&lt;/em&gt;&lt;/strong&gt; &lt;strong&gt;&amp;#183;&lt;em&gt;E&lt;sub&gt;m &lt;/sub&gt;&lt;/em&gt;&lt;/strong&gt;&gt; 0, &amp;#160;the field &lt;strong&gt;&lt;em&gt;B&lt;/em&gt;&lt;/strong&gt;&amp;#160; then exerting &lt;em&gt;Lorentz&lt;/em&gt; drag on the current. Driving, however, was ineffective in tethers standard in the 90`s such as TSS1 and TSS1R, insulated all along, with a conductive sphere large enough at the anodic end, typically implying radius much greater than ambient Debye length and thermal electron gyroradius, strongly reducing electron collection. &lt;em&gt;Bare &lt;/em&gt;tethers [1]&lt;em&gt;&amp;#160;&lt;/em&gt;eliminated sphere and insulation to allow electron collection over a resulting &lt;em&gt;anodic&lt;/em&gt; tether segment, as a giant cylindrical Langmuir probe, in the optimal OML (&lt;em&gt;orbital-motion-limited&lt;/em&gt;) regime. Laframboise and Parker [2] had proved that OML current to cylindrical probes of convex cross-section and equal perimeter &lt;em&gt;p&lt;/em&gt; are equal. Thin tape cross-section will reduce tether mass when compared to an equal &lt;em&gt;p&lt;/em&gt; tether with round cross-section. Bare tethers, which made standard tethers rapidly obsolete, will thus be characterized by all 3 dimensions, length, width and thickness, widely differing, allowing particular design easier.&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160; &amp;#160;Lorentz drag decreasing as the inverse 6&lt;sup&gt;th&lt;/sup&gt; power of radial distance to dipole, capture &lt;em&gt;periapsis&lt;/em&gt; would need be very close to the Planet. Keeping current on following capture would hardly affect it, whereas &lt;em&gt;apoapsis&lt;/em&gt; could be lowered to finally reach 1:1 Laplace resonance of S/C and moon of interest.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Bare Tether Validation and Use&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160;&amp;#160; &amp;#160;&amp;#160;Bare-tether analysis was validated in early 2001 in an unintended way [3]. Measurements at the &lt;em&gt;International Space Station&lt;/em&gt; involving 3 NASA Centers, &lt;em&gt;NOAA&lt;/em&gt;/Boulder. &lt;em&gt;Univ-Houston&lt;/em&gt; and &lt;em&gt;SAIC&lt;/em&gt;, showed on-board plasma&lt;em&gt;-&lt;/em&gt;contactors ejecting substantial electron current as if &lt;em&gt;ISS &lt;/em&gt;structure&lt;em&gt; &lt;/em&gt;had become very negative. Authors acknowledged in the Abstract that tensioning rods of solar array masts could collect ambient electrons as &lt;em&gt;bare-wire &lt;/em&gt;tethers, with modeling &amp;#8220;&lt;em&gt;based upon J.R. Sanmartin&amp;#8217;s &amp;#160;bare-wire collection theory&lt;/em&gt;&amp;#8217;, which was incorporated into the complex &lt;em&gt;ISS&lt;/em&gt; computer code, &lt;em&gt;Environment Work Bench&lt;/em&gt;, including models of &lt;em&gt;Station, &lt;/em&gt;orbital motion&lt;em&gt;, &lt;/em&gt;earth&amp;#8217;s magnetic field, and ionosphere.&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160;&amp;#160; Further, in 2007, &lt;em&gt;Vlasov-&lt;/em&gt;code simulations in the high&amp;#8211;bias OML regime, at an Unuversity of Michigan PhD Thesis by E. Choini&amp;#232;re on the electron density versus radial distance [4] were shown equal to a high approximation when compared [5] with detailed results from the bare-tether theory.&lt;/p&gt;
&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160; To date, the bare tether analysis has been applied in considering missions to moons Europa [6] and Enceladus [7], and to Ice Planet Neptune&amp;#160; [8]}&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;[1] JR Sanmartin, M Martinez-Sanchez, E Ahedo, &lt;em&gt;J. Prop &lt;/em&gt;&amp; &lt;em&gt;Power&lt;/em&gt; &lt;strong&gt;9&lt;/strong&gt;, 353-360, 1993&lt;/p&gt;
&lt;p&gt;[2] JG Laframboise, LW Parker, &lt;em&gt;Phys. Fluids &lt;/em&gt;&lt;strong&gt;16&lt;/strong&gt; 629-636, 1973&lt;/p&gt;
&lt;p&gt;[3] EA Bering &lt;em&gt;et al&lt;/em&gt;, &lt;em&gt;Paper &lt;/em&gt;2002-0935, 40&lt;sup&gt;th&lt;/sup&gt; AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 14-17 Jan 2002&lt;/p&gt;
&lt;p&gt;[4] E Choini&amp;#232;re, BE Gilchrist, &lt;em&gt;IEE Trans on&amp;#160; Plasma Science&lt;/em&gt; &lt;strong&gt;35&lt;/strong&gt;, 7-22, 2007&lt;/p&gt;
&lt;p&gt;[5] JR Sanmartin, E Choini&amp;#232;re, BE Gilchrist, J-B Ferry, M Martinez-Sanchez, &lt;em&gt;IEE Trans in&amp;#160; Plasma Science&lt;/em&gt; &lt;strong&gt;36,&lt;/strong&gt; 2851-2858, 2008&lt;/p&gt;
&lt;p&gt;[6] JR Sanmartin &lt;em&gt;et al&lt;/em&gt;, &lt;em&gt;J. Prop &lt;/em&gt;&amp; &lt;em&gt;Power&lt;/em&gt; &lt;strong&gt;33&lt;/strong&gt;, 338-342, 2017&lt;/p&gt;
&lt;p&gt;[7] JR Sanmartin, J Pelaez,&amp;#160; &lt;em&gt;Acta Astronautica&lt;/em&gt; &lt;strong&gt;168&lt;/strong&gt;, 200-203, 2020&lt;/p&gt;
&lt;p&gt;[8] JR Sanmartin, J Pelaez,&amp;#160; &lt;em&gt;Acta Astronautica&lt;/em&gt; &lt;strong&gt;177&lt;/strong&gt;, 906-911, 2020&lt;/p&gt;