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Titan's surface pressure is about 1.5 bar and because the surface gravity is low pressure falls off much more slowly with altitude than it does on Earth. From Wikipedia's Atmosphere of Titan; vertical structure:

Titan's vertical atmospheric structure is similar to Earth. They both have a troposphere, stratosphere, mesosphere, and thermosphere. However, Titan's lower surface gravity creates a more extended atmosphere, with scale heights of 15–50 km (9–31 mi) in comparison to 5–8 km (3.1-5 mi) on Earth. Voyager data, combined with data from Huygens and radiative-convective models provide increased understanding of Titan's atmospheric structure.

The plot below suggests a scale height near the surface of about 15 km and the pressure of 1 bar (Earth's surface pressure) at about 6 km, though I don't know about the density which what matters more to its propellors.

A graph detailing temperature, pressure, and other aspects of Titan's climate. The atmospheric haze lowers the temperature in the lower atmosphere, while methane raises the temperature at the surface. Cryovolcanoes erupt methane into the atmosphere, which then rains down onto the surface, forming lakes. click for larger

A graph detailing temperature, pressure, and other aspects of Titan's climate. The atmospheric haze lowers the temperature in the lower atmosphere, while methane raises the temperature at the surface. Cryovolcanoes erupt methane into the atmosphere, which then rains down onto the surface, forming lakes. Source

Question: As I understand it, since the atmosphere is dense and tall and dragonfly comes with all these low-light cameras, navigation hardware and four pairs of propellors, there'll be no sky crane. At some point they'll just cut it loose and let it manage it's own descent.

  1. From what altitude will they cut the Dragonfly helicopter loose on Titan and make it descend and land by itself?
  2. What are the main factors that are determine the optimum "cut-loose" altitude?
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The Dragonfly Entry and Descent System, Wright et al. (NTRS entry #20190028683) gives this ConOps:

EDL ConOps Dragonfly

  • Entry Interface 1270 km: Spin stabilized to 2 RPM
  • Entry heat pulse: 250 sec: Peak heat flux 250 W/cm2 margined
  • Drogue deploy E+6 min, ~Mach 1.5: More than 80 minutes spent on drogue
  • Main chute deploy E+88 min: Low velocity & opening load
  • Lander Release E+105 min: Plenty of time to stage heatshield separation, activate radar & lidar, deploy landing legs

The ConOps indicates that the lander is released at 105 minutes, at a height of 1.2 kilometres. A later slide states that the delivery accuracy is an ~149 x 72 km ellipse at release.

Easily affords lander sufficient accuracy to navigate to selected landing zone

Dispersions sources

  • Latitude: navigation errors
  • Longitude: on-chute winds

Question 2 is a very good question that I have not found any information on (outside of what is presented here). I suspect that vigorous engineering work on this phase of the mission has not occurred yet. This paper (Selection and Characteristics of the Dragonfly Landing Site near Selk Crater, Titan, Lorenz et al. 2021) provides some insight in the form of topographic profiles near the proposed landing site that have variations of a few hundred metres: Topo profile

The maximum height variation could represent a minimum separation height constraint.

Cool EDL animation w/ velocity markers: Dragonfly Animation

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    $\begingroup$ Stack Exchange answers can't be images of text, they need to be contained in the text of your post itself. This is a good start but please go back to those slides, select, and copy/paste any information you want readers to have available as ASCII text. That makes it 1) searchable, and 2) available to those folks who use screen readers. There's nothing wrong with including screenshots of slides, but any information from them that is written should be also reproduced as actual text as well. Thanks! $\endgroup$
    – uhoh
    Jun 30 at 1:19
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    $\begingroup$ Thanks for the edit! I made a few additions, and the slide seems to say 1.2 rather than 1.5 km so I changed that as well. If they have a named height of 1.2 km then I don't believe that question #2 (asking What are the main factors...? ) "has no answer at the present time". Maybe you haven't found it stated explicitly in the sources you cite, but that doesn't mean it's necessarily fundamentally unanswerable. Too high and there's not much lift and the batteries will run out before it lands, too low and it won't be able to slow down fast enough. Either way it's end of mission, right? $\endgroup$
    – uhoh
    Jun 30 at 3:28
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    $\begingroup$ @uhoh oops, good catch. I will try to clarify what I mean by that statement. $\endgroup$ Jun 30 at 11:27

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