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"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL)
post Aug 3 2020, 03:33 AM
Post #136


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QUOTE (Explorer1 @ Jul 30 2020, 07:22 AM) *
There will probably be some condensation (even Huygens saw a droplet fall across the camera, I recall?). I'm sure they will do plenty of testing in a Titan simulation chamber once assembled, if that hasn't already been done for the individual components. We will know it is real when we see it flying in a chamber...

Is Curiosity real? Did you see the descent stage doing a skycrane manoeuvre in a chamber? No. And yet it is real.

And MSL was a flagship project, not a cost-constrained New Frontiers mission.

Validation and Verification on planetary missions relies, of physical and fiscal necessity, on much analysis as well as testing, because the testing can never completely replicate the planetary environment anyway (put a Titan chamber in the Vomit Comet to replicate gravity.....? Something close was done once - at the wheel level, not the rover level, to test wheel/soil interaction for the Apollo LRV. But never since.) Typically one tests some key aspects, and uses models to bridge that data to the planetary setting. There will be aerodynamic tests at relevant Reynolds numbers and densities (e.g. TDT and/or NTF wind tunnels at Langley) and we are building a Titan chamber at APL for thermal balance tests etc, but earth gravity is earth gravity.... so like other planetary projects we use a lot of analytic and computer models. (But unlike most, can fly a scaled-down and/or lightweighted vehicle)

The possible droplet detected in a Huygens image was likely the result of surface heating by a lamp, dumping 20 W of heat on a small patch of ground (20cm across)
That's actually a pretty strong degree of heating.

Dragonfly needs the heat from a radioisotope power source to stay warm (just as MSL) and (like MSL) uses a pumped fluid loop to pull the heat inside. (It of course is ultimately rejected to the environment through the insulation all over the lander body, but at a low power density.) The meteorological measurements need to take this into account and are being designed accordingly

See my papers

Lorenz, R. D., 2016. Heat Rejection in the Titan Surface Environment : Impact on Science Investigations, AIAA Journal of Thermophysics and Heat Transfer, 30, 257-265

R D Lorenz, Thermal Interaction of the Huygens Probe with the Titan Environment : Surface Windspeed Constraint, Icarus, 182, 559-566, 2006

R. D. Lorenz, H. Niemann, D. Harpold, J. Zarnecki, Titanís Damp Ground : Constraints on Titan Surface Thermal Properties from the Temperature Evolution of the Huygens GCMS inlet, Meteoritics and Planetary Science. 41, 1405-1414, 2006.

Lorenz, R. D. and K. S. Sotzen, Buoyant Thermal Plumes from Planetary Landers : Application to the Height of Meteorology Masts, Planetary and Space Science, 90, 81-89, 2014

Lorenz, R. D. 2018. Atmospheric Test Environments for Planetary In-Situ Missions: never quite "Test as you fly", Advances in Space Research, 62, 1884-1894

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post Aug 3 2020, 04:50 AM
Post #137

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Thank you for the very detailed response; I could have phrased the last sentence better. (I should have said I will know it's real when I see it!) My reply to Steve G was made with the Insight mole's troubles in mind (unusual physical properties in the environment impossible to predict ahead of time). Titan's surface is complex in an entirely different way, so I'm glad to hear of the lower power density. The next six years will be exciting no matter what....
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