NASA Is a VTOL Electric Aircraft Feasible for Titan Exploration?

[mfb]

Not personally, of course... or not yet?[/size]

The Dragonfly mission was selected as fourth mission in the New Frontiers program (the previous missions were New Horizons, Juno, and OSIRIS-REx). Dragonfly is a helicopter that can fly in the dense atmosphere and low gravity of Saturn's moon Titan. The planned launch is 2026 with a landing in 2034.

Here are various images

Dragonfly has 8 rotors for redundancy and flies with a battery charged by a radioisotope thermoelectric generator. It will charge the battery over night and inspect its environment and make flights during the day - something like 20-30 km at a time (we'll get better estimates once the design is more advanced). The light speed delay makes direct control from Earth impossible. To have humans look at landing sites in advance it is planned to fly "two steps ahead, one step back": Fly ~15 km forwards, take images of a potential new landing site, then fly backwards to a previously inspected landing site. 5-10 km in a Titan day (2 Earth weeks) - a factor 100 faster than the Mars rovers, despite a larger delay for signals and the much more challenging terrain (Titan has rivers, lakes and large dunes). Over its 2 years of planned lifetime it can make ~50 flights, and we know from the Mars rovers how conservative these lifetime estimates can be.
We'll get direct inspections of 50+ landing sites and high resolution images and other measurements of large areas from the flights. This is not just 50 times the same thing - with its range Dragonfly will be able to fly to many different places on Titan.

Whatever we might know about Titan today - it will all be completely outdated by the time Dragonfly has been there.

(It will not be the first atmospheric flight outside of Earth - that will be the Mars Helicopter Scout, flying to Mars next year. It is much smaller and will mainly fly up to take pictures - it won't fly longer distances).

 

[YoungPhysicist]

Not personally, of course

Maybe Cessna is not a good idea. Maybe something else.

We'll get direct inspections of 50+ landing sites and high resolution images and other measurements of large areas from the flights.

Just my thought: Is using a quadcopter the only way to achieve that? I know satellites won't work, but can't a fix-winged plane do something similar?

 

[MikeeMiracle]

A quadcopter can take off and land in a single spot, also the ability to hover to study a specific area over time could also be beneficial if you want to study any potential geological process occurring.

A fixed wing plane needs a runaway, how can we be sure there would be somewhere suitable to land a plane? In the above studying a specific location example, youwould have to be doing constant loops and hope to be in the right place the next time you want to take a picture.

It just doesn't make sense to use a fixed wing plane for this purpose in the same way we resure stranded people with holicopters and not planes due to their hovering abilities.

 

[YoungPhysicist]

A quadcopter can take off and land in a single spot, a fixed wing plane needs a runaway.

How can we be sure there would be somewhere to land a fixed wing plane?

Yeah, of course. But if they are sure there is somewhere to land a quadcopter, they probably know somewhere to take off/land a fixed wing plane. probably.

 

[MikeeMiracle]

If we have a 1m square quadcopter you need to find a space 1m square to land and take off. This does not even have to be perfectly flat and level. A fixed wing plane would need FLAT runaway and a runwaway long enough to take off and land.

Which are we more likely to find? :)

Have you ever flown a drone? They can land and take off practically anywhere so long as nothing is impeeding the rotation of the rotors. You can land on the side of a large boulder at a 60 degree angle and still take off (assuming it does not fall off.)

 

[YoungPhysicist]

If we have a 1m square quadcopter you need to find a space 1m square to land and take off. This does not even have to be perfectly flat and level. A fixed wing plane would need FLAT runaway and a runwaway long enough to take off and land.

Which are we more likely to find? :)

Have you ever flown a drone? They can land and take off practically anywhere so long as nothing is impeeding the rotation of the rotors. You can land on the side of a large boulder at a 60 degree angle and still take off (assuming it does not fall off.)

Alright, I guess my argument is completely wrong this time. Thanks!

Have you ever flown a drone?

Yes, I had. But it ended dramatically.

 

[berkeman]

Dragonfly is a helicopter that can fly in the dense atmosphere and low gravity of Saturn's moon Titan.

Just curious -- if it is a low-gravity environment, how can there be a dense atmosphere?

 

[MikeeMiracle]

I guess the "dense" part is relative :)

So long as designed weight and propolsion system of the craft has taken into account the presumed density of the atmonsphere we expect to find, it "should" fly.

 

[mfb]

Just curious -- if it is a low-gravity environment, how can there be a dense atmosphere?

The two are not directly related as long as the escape velocity is high enough to keep any sort of atmosphere. See e.g. Venus, slightly lower gravity but much thicker atmosphere. Titan is cold, the molecules don't have much energy so they are very unlikely to escape. Despite Titan's smaller size its atmosphere has more mass than the atmosphere of Earth.

We are not talking about a small asteroid here. Surface gravity is 0.14 g and the escape velocity is 2.6 km/s.

Edit: Considering the fixed-wing idea: Both that and a hot "air" balloon were also considered, but a helicopter is much more flexible. The fixed-wing design would need to fly continuously, there is no way to land. Here is an overview.

 

[berkeman]

Ah, I didn't think of the temperature aspect. Thanks @mfb

 

[Klystron]

JFTR fixed wing VTOL aircraft can hover, take off and land vertically as the acronym -- vertical take-off and land -- indicates. NASA tests a variety of propulsion sources including jet engines with variable directed thrust, ducted fans, fixed horizontal fans and variable geometry propellers. Many of these designs are used in practical VTOL aircraft with fixed wings. One advantage of fixed wings over helicopter rotors is the ability to glide longer distances trading altitude for distance. Ground effect craft also hover, lift off and touch down without runways albeit at restricted altitude.

Assume NASA evaluates Titan aircraft designs based on many factors including payload and mission requirements; but fixed wing aircraft can launch, hover, and touch down on hard surfaces and liquids on Earth.

 

[mfb]

That is possible, and I'm sure it was studied, but apparently the downsides are too important. The fixed-wing design that got more attention would have flown continuously. It would have covered even larger areas, but wouldn't have been able to study samples in direct contact.

 

[MikeeMiracle]

Fixed wing VTOL aircraft can hover but they use a lot of fuel in doing so as they have to support the entire weight of the aircraft as opposed to just pushing it forward and letting the lift generated by the wings handle keeping the aircraft in the air.

This is fine for take off and landing but you would not want to hover for an extended period of time this way. Any electricity generated by this craft has to be used efficiently and I am sure we would rather they spend it observing than hovering.

In fact, is a VTOL aircraft even viable using just electricity for propulsion?