Flying Over Another World

There are currently 26 active NASA spacecraft that have left low Earth orbit (LEO) to explore the solar system and beyond. This site lists 28, but it includes the Hubble Space Telescope which is in LEO, and the Opportunity Mars rover, which has not been heard from since a planet-wide dust storm several months ago.

What of future missions? What’s on the drawing boards?

NASA recognizes three classes of space missions, separated mostly by how costly they are. The most expensive are Large Strategic Science Missions, but most people still call them by their former name of flagship missions. A recent example of such a mission would be the Cassini/Huygens spacecraft, a Saturn orbiter and Titan lander that spent 13 years vastly expanding our knowledge of the planet, its rings, and its moons.

Medium class missions fall into the New Frontiers category. These are neither the least expensive missions, nor are they as costly as the flagship missions. The New Horizons spacecraft that flew by Pluto in 2015 and just this month past the Kuiper Belt Object 2014 MU₆₉ falls under this classification.

The least expensive missions are Discovery class. There is a competitive process for the funding required, and the cost restrictions encourage creativity and innovation. The Kepler Space Telescope that discovered over 2600 extra-solar planets shows that you can do amazing science without breaking the bank.

I’m going to focus this post on one particular proposed mission. It is one of two remaining proposals for the New Frontiers program. Whether it wins out over its competitor (a sample return mission from the comet 67P/Churyumov-Gerasimenko) should be announced by this summer. Both of these missions would do great science. But as I think you will see, this one definitely wins out on the cool factor.

DRAGONFLY

How would you like to fly a quadcopter drone with double rotors over another world, scout out interesting places to land, take samples of the surface for analysis, then take off to the next location? If this mission is funded, this will be a reality in the mid-2030s. Well, maybe not for you. But for somebody.

TITAN

The largest moon of Titan was targeted by the first of the two Voyager probes (which rendered it unable to aim itself for Uranus and Neptune; that was undertaken by the second Voyager), and the results were frustrating. The surface of Titan is hidden from view by a thick layer of atmospheric haze.

It was with the arrival of the Cassini Saturn orbiter and its hitchhiking Huygens probe that descended to the surface that we learned so much about this world. Cassini’s infrared cameras were able to penetrate the haze to reveal surface features.

Some quick facts:

• Titan is larger than the planet Mercury, but far less dense and therefore less massive. While Mercury is metallic and rocky, Titan is icy and rocky.
• The surface gravity at Titan is only 14% that of Earth, even less than on the Moon.
• Uniquely among moons of the solar system, Titan has a significant atmosphere. It is mostly nitrogen, with methane composing about 3-5%.
• The surface atmospheric pressure at Titan is 50% greater than at sea level on Earth.
• So far from the sun, it is very cold. Average surface temperature is only 94 Kelvins (-290 Fahrenheit).
• It has a “hydrologic” cycle similar to that of Earth, except where water exists on Earth as vapor, liquid, and solid, on frigid Titan that role is taken on by methane.
• The analog of Earth’s bedrock—composed literally of rock—is water ice on Titan. At these temperatures, water ice on Titan is as hard as rock is on Earth.
• Titan has ice mountains, and rivers and lakes of liquid methane.
• There is occasional methane “rain.”
• It has dunes made of organic sand—particles of complex and largely unknown organic material.

The atmosphere allowed the Huygens probe to descend to the surface via parachute in 2005, taking a series of images that have been combined to create this video.

And the only image taken from the surface of a world more distant than Mars shows pebbles and “rocks” of water ice.

Dragonfly is fairly large—each rotor would be a meter in diameter. At such a great distance from the sun, and under Titan’s perpetual haze, solar energy is simply too feeble a source of power. Dragonfly would rely on a radioisotope thermal generator (RTG), a simple device with no moving parts that converts the heat from a radioactive source directly to electricity. Even given its SUV size and mass, the combination of low surface gravity and thick atmosphere make flying on Titan relatively easy.

No disrespect to the comet nerds competing for NASA dollars, but I am really pulling for this one to be funded!