"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL) Options

[rlorenz]

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, Titan’s 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

[Explorer1]

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....

[rlorenz]

A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

[vjkane]

A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

In the paper, there's a figure of the trajectory to Titan with the original launch date of 2025, which has now been delayed to 2027 per NASA's directive (as I understand, to spread out spending).

In the paper for the caption of the figure, there's a statement that states, "Phase A interplanetary trajectory with launch in 2025 and Titan arrival in 2034. The launch date has been prescribed to be 2027, although the arrival date and conditions remain the same."

I see two interpretations of this: 1) despite a two year delay in launch, Dragonfly still arrives at Titan in 2034; 2) the arrival date refers to local time on Titan relative to its orbit around Saturn but is a later Earth calendar year.

[rlorenz]

In the paper, there's a figure of the trajectory to Titan with the original launch date of 2025, which has now been delayed to 2027 per NASA's directive (as I understand, to spread out spending).
In the paper for the caption of the figure, there's a statement that states, "Phase A interplanetary trajectory with launch in 2025 and Titan arrival in 2034. The launch date has been prescribed to be 2027, although the arrival date and conditions remain the same."
I see two interpretations of this: 1) despite a two year delay in launch, Dragonfly still arrives at Titan in 2034; 2) the arrival date refers to local time on Titan relative to its orbit around Saturn but is a later Earth calendar year.

Yes, that wasnt quite clear. The arrival date will depend on the launch vehicle class that NASA assigns but will in any case be in the mid-2030s, and as you say the local time will be the same as shown.

[vjkane]

Yes, that wasnt quite clear. The arrival date will depend on the launch vehicle class that NASA assigns but will in any case be in the mid-2030s, and as you say the local time will be the same as shown.

I know you can't speak to this, Ralph, since launch vehicle selections are confidential. But here's hoping for a selection that limits the travel time, both so we are all younger when Dragonfly arrives and so there's a longer life for the MMRTG once on Titan.

[mcaplinger]

But here's hoping for a selection that limits the travel time...

See https://trs.jpl.nasa.gov/handle/2014/48626 for trajectory details.

The LV selection is obviously a tradeoff between LV cost and mission ops costs. Since the former is a lump sum up front and the latter is spread out over time, the latter tends to be favored by budgeteers, but we'll see.

[JRehling]

This is a fascinating read, Ralph. As a starting point, it's enlightening to understand that operational constraints and the basic dynamics of Titan's orbit and rotation favor a certain range of longitudes. This is also true, though the details are different, for Venus, which meant that seven Venera landers ended up in a fairly small fraction of the planet's surface. So, not only were Dragonfly landing sites relatively constrained, but future landing sites will either respect the same constraints or have to make some tradeoffs to go beyond them.

[vjkane]

A paper describing the factors in site selection for Dragonfly, and the datasets describing the target area, is now online

https://iopscience.iop.org/article/10.3847/PSJ/abd08f

I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky

[rlorenz]

I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky

Sadly true. I guess maybe Iapetus might be in the night sky at some point, havent looked into whether it would be detectable.

When we were working on the Titan Mare Explorer, IIRC even though Ligeia is on the anti-Saturn hemisphere, I think it was far enough north that Saturn would have been visible from the early part of descent..... but Selk is far too close to the anti-Saturn point.

[rlorenz]

See https://trs.jpl.nasa.gov/handle/2014/48626 for trajectory details.

That paper goes into the orbit design very nicely, but was written and presented at a stage during the New Frontiers competition when we werent comfortable disclosing the actual science target landing site..... hence no maps.

[rlorenz]

This is a fascinating read, Ralph. As a starting point, it's enlightening to understand that operational constraints and the basic dynamics of Titan's orbit and rotation favor a certain range of longitudes. This is also true, though the details are different, for Venus, which meant that seven Venera landers ended up in a fairly small fraction of the planet's surface. So, not only were Dragonfly landing sites relatively constrained, but future landing sites will either respect the same constraints or have to make some tradeoffs to go beyond them.

I guess the best example of the astrodynamics-->landing site mapping is the Soviet sample return missions, where there was basically just a point on the Moon where if you launch straight upwards and keep going, you get back to Soviet territory....

As for future Titan missions, the large atmospheric scale height means the aerothermodynamic constraints on entry angle allow the torus of locations for a given incoming asymptote to be quite broad. So the situation may be less constrained than at Venus. Furthermore, while the longitude of the asymptote on Venus is restricted for a given launch date, on Titan it sweeps around every 16 days, so for a given cruise trajectory you can just nudge the arrival back or forth by a week to get to a different longitude (although at the penalty of increasing your entry speed. Whether that matters or not depends on how fast the interplanetary trajectory is, and how close or otherwise you are to some heatshield material limit.)

It's a fascinating multidisciplinary problem.

[charborob]

I believe that the landing site is on the anti Saturn hemisphere, so no images of Saturn in the sky

Would Saturn actually be visible through the atmospheric haze? A quick Google search couldn't give me a definitive answer.

[Steve G]

Landing on the Saturn-side would be more than just for pretty pictures. It would offer some light during the eight-day-long nights.

[vjkane]

Would Saturn actually be visible through the atmospheric haze? A quick Google search couldn't give me a definitive answer.

One of the Titan spectral windows falls in the near infrared range that is commonly covered by visible-to-near-infrared imaging chips used for spacecraft instruments. I forget the specific band.