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"Dragonfly" Titan explorer drone, NASA funds Johns Hopkins University Applied Physics Laboratory (APL)
vjkane
post Jul 2 2019, 04:14 PM
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QUOTE (mcaplinger @ Jul 2 2019, 08:40 AM) *
Back in 2017 you were still speculating that it would be possible to fly from equator to pole. What changed? wink.gif

I think it's a little early yet to know what the baseline mission profile will look like, though conservatism is not an unreasonable assumption.

In the NASA Live discussions following the announcement, someone said that Dragonfly would land 180 km from the crater and take 2.5 years to get there. Also, it was either there or something I've read since that said Dragonfly would advance 10 km per flight. Assuming one flight per Titan day (which other documents suggest), that limits how far it can go in a year. My back of the envelope imagining suggested 15 km per Titan day if the goal was just to get to somewhere, similar to Opportunity's traverse from Victoria to Endeavour crater.

My earlier post was based on the craft doing little more than putting as many km on the odometer as possible. Once I did the research for my blog post on the mission, I realized that a better way to think of the mission is as a regional explorer that will explore 200 to perhaps 400 km.

It is a shame that Selk crater isn't closer to Adiri. There appears to be lots of interesting terrain and surface materials there.


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atomoid
post Jul 2 2019, 10:49 PM
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...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...
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vjkane
post Jul 3 2019, 03:02 PM
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QUOTE (atomoid @ Jul 2 2019, 02:49 PM) *
...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...

One of the technical articles on Dragonfly showed an example power budget over a Titan day. Between the one flight, science, and communications to Earth, the battery was drawn down to about 30%. The craft then went into low power mode for the night with just occasional science activities to recharge the battery.

Another reason for no nighttime flights is that the navigation depends on assessing images taken in flight, which requires daylight.

QUOTE (atomoid @ Jul 2 2019, 02:49 PM) *
...Dragonfly would advance 10 km per flight. Assuming one flight per Titan day ...

looks like that average 10km value already has baked into it having to operate largely within limited communication windows when Selk crater isn't occluded from comm link with Earth, which seems like it would consist of on/off 8-earth-day sessions as the 'Titan day' of activity, since despite autonomous abilities I suspect 'daily' uplinks are still going to be the basis of operation (and someone might do Celestia simulations to enlighten us on communications windows) so apparently no red-eye flights to increase that 10km, but in an extended mission scenario who knows, RTG power allowing.. seems the plan is to send Dragonfly purely on its own, no assistive communications relay or independent sister orbiter with its own suite of experiments, no MarCO analog with jumbo solar array.. but such are hopes and wishes and unlimited budgets...

One of the technical articles on Dragonfly showed an example power budget over a Titan day. Between the one flight, science, and communications to Earth, the battery was drawn down to about 30%. The craft then went into low power mode for the night with just occasional science activities to recharge the battery.

Another reason for no nighttime flights is that the navigation depends on assessing images taken in flight, which requires daylight.


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JRehling
post Jul 3 2019, 08:47 PM
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This is probably already in everyone's consciousness but day/night cycles and radio contact with Earth are almost equivalent, except for superior conjunction when the Sun will block radio contact.

A lander/flyer/floater at high latitudes, however, could spend several terrestrial years in continuous daylight and continuous radio contact with Earth. An equatorial landing site would mean almost uniform periods of day/night.

Terrain types on Titan correlate very strongly with latitude. The polar stuff and the equatorial stuff are almost literally two different worlds.
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climber
post Jul 3 2019, 10:27 PM
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Did you notice that launch will be 29 years after Cassini which means exactely 1 Saturn orbit?
Add another 29 years and I’ll be exactely 100 years old rolleyes.gif
Interesting coincidences


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elakdawalla
post Jul 25 2019, 05:06 PM
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The launch being 1 Saturn year after Huygens is sort of a coincidence but also a selling point and a helpful risk reduction factor. It means that Huygens descent data will be relevant for Dragonfly's EDL.


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Decepticon
post Jul 26 2019, 07:40 AM
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What is the minimum number of propellers needed to fly on titan?

I'm worried about damage or motor failures.
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rlorenz
post Jul 26 2019, 11:22 AM
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QUOTE (Decepticon @ Jul 26 2019, 03:40 AM) *
What is the minimum number of propellers needed to fly on titan?

I'm worried about damage or motor failures.

Dragonfly is an octocopter (quad layout of coax pairs) to provide resilience to failure. It can still fly fine with as many as three rotors out
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Jaro_in_Montreal
post Aug 19 2019, 01:46 PM
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With the high atmospheric density and low gravity on Titan, I'm thinking that Dragonfly might be able to "autogyro" unpowered to the ground, following reentry.
Has anyone looked at what the lading speed would be, unpowered ?
Could the quadcopter control system maintain level flight in such a case?
In the affirmative, maybe Dragonfly could dispense with the EDL parachute, saving mass for more science instruments or bigger battery?
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mcaplinger
post Aug 19 2019, 03:07 PM
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QUOTE (Jaro_in_Montreal @ Aug 19 2019, 05:46 AM) *
With the high atmospheric density and low gravity on Titan, I'm thinking that Dragonfly might be able to "autogyro" unpowered to the ground, following reentry.

I haven't worked out what the terminal velocity of the aeroshell would be before chute deploy, have you? The vehicle has to be slowed enough for the deployment/unfolding sequence to work in the first place.

That said, as a rule, autogyros require forward motion to generate lift. You may be thinking of what's called an autorotation in a helicopter. To do an autorotation, you need blade pitch control to reduce your descent rate from the fairly high rate needed to keep the blades turning to a rate low enough for landing, and of course you have very little choice about where you land (you have to commit to a landing spot pretty high up). Dragonfly has no blade pitch control and the small diameter props of a quad don't have enough momentum to do autorotations, on Earth anyway.

The battery is charged at the start of EDL so there's no particular advantage to landing unpowered anyway. The mission profile calls for a long flight traverse before the first landing to find the best landing site.


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djellison
post Aug 19 2019, 07:41 PM
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QUOTE (Jaro_in_Montreal @ Aug 19 2019, 06:46 AM) *
Could the quadcopter control system maintain level flight in such a case?
In the affirmative, maybe Dragonfly could dispense with the EDL parachute, saving mass for more science instruments or bigger battery?


Quadcopters maintain level flight by adjusting the RPM of all 4 ( or in the case of Dragonfly... all 8 ) rotors.

Also - without a parachute....how do you successfully separate the heatshield?
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vjkane
post Yesterday, 06:23 AM
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QUOTE (djellison @ Aug 19 2019, 12:41 PM) *
Quadcopters maintain level flight by adjusting the RPM of all 4 ( or in the case of Dragonfly... all 8 ) rotors.

Also - without a parachute....how do you successfully separate the heatshield?

Dragonfly has both a drogue and main parachute. It descends on the drogue from about 6 minutes into the entry until about 88 minutes and then is on the main chute until about 105 minutes. As the presentations says, "Plenty of time to stage heatshield separation, activate radar & lidar, deploy landing legs."

Presentation doesn't say how long after the lander release the actual landing would be, likely because the lander can search for a suitable location and that time is non deterministic.


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djellison
post Yesterday, 03:47 PM
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The great thing about Titan EDL...you've got PLENTY of time under your parachute.
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rlorenz
post Today, 01:49 AM
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QUOTE (djellison @ Aug 20 2019, 11:47 AM) *
The great thing about Titan EDL...you've got PLENTY of time under your parachute.


The talent on this forum is impressive. Mike, Doug and Van's responses are all correct (and well-reasoned,
I don't think all those details - like rotors being fixed-pitch - have been presented/published, but are obvious
when you start to think about them)

The EDL sequence as presently conceived (which can be adjusted, as Doug notes, we have oodles of time) is to
drop from the backshell and make the transition to powered flight about 1km off the ground to set up for
landing site search. More than a couple of minutes of flight, but less than a couple of tens of minutes..

Right at the very beginning of developing Dragonfly I had imagined we might land on a chute, and then do the
fancy new rotorcraft stuff after an initial landed mission, but then you are exposed to terrain risks (probably small,
but not controllable) for that first landing. And when you consider all the bits you need (hazard sensing, rotors etc.)
for flight, you might as well land with them from the get-go. Unlike a rocket-powered skycrane, you can test all
that stuff very effectively on Earth.
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