Each of our highest priority targets in the outer Solar System offers something unique, from Europa’s internal ocean to the geysers of Enceladus. But Titan exerts the kind of fascination that comes from the familiar. The imagery of lakes and river channels reminds us inescapably of our home world, even if the temperature on the Saturnian moon averages a brisk 94 K, which works out to -291 degrees on the Fahrenheit scale. But because of its thick atmosphere we have options for exploring Titan that are unavailable on the other icy moons, and we’re working with a landscape that is a compelling frozen doppelgänger of Earth, a landscape we’d like to explore up close.
As we saw yesterday, part of the outer system puzzle is getting supplies of plutonium-238 up to speed, and there is at least some movement on that front. If we want to get aggressive about exploring Titan, one excellent way to deploy that plutonium is aboard AVIATR (Aerial Vehicle for In-situ and Airborne Titan Reconnaissance), a 120 kg airplane that could study the moon’s atmosphere from within and give us views of its geography on demand. Under study by a team led by Jason Barnes (University of Idaho), the airplane could do some things a balloon could not, including not being at the mercy of equatorial winds and being more flexible in studying some of the interesting terrain around high-latitude lakes and in the turbulent weather near the poles.
I’ve been thinking about AVIATR and other Titan options this week because last weekend I had the chance to speak with Mike Malaska, an organic chemist who has been collaborating with members of the Cassini team in research that involves characterizing the Sikun Labyrinth canyon-land region and hydrocarbon channels located near Titan’s South Pole. I discovered that Mike is also a volunteer artist for the AVIATR mission proposal. Like I said, Titan fires the imagination, and the idea of a human aircraft in operations there sounds too fascinating not to attempt. Mike’s image of the unmanned AVIATR vehicle flying over the surface of Titan is below.
Image: A rendering of the AVIATR airplane flying over Titan. Credit: Mike Malaska.
But back to that thick atmosphere, which helps us on Titan in so many ways. In an environment where gravity is seven times less than on Earth, we’re dealing with an atmospheric pressure one and a half times greater than Earth’s. It was Robert Zubrin who suggested, back in the 1990s, that humans with wings strapped to their arms would be able to fly in this thick and soupy environment. We’ve already seen evidence of this atmosphere’s effect on the Huygens probe, which took fully two and a half hours to descend to the surface in early 2005.
A paper on the AVIATR concept notes Titan’s advantages:
With an Earth-like surface shaped by rainfall and atmospheric interaction, a rich and complex chemistry, and the astrobiological potential of complex organic molecules interacting with liquid water, Titan is one of the three most interesting targets in the solar system for planetary exploration. Like Mars, but unlike Europa, Titan can be explored inexpensively. Although cruise times to Titan are long (∼7 years), arrival at Titan is easy. Titan’s dense atmosphere with a large scale height is perfect for decelerating landers and aerial elements cheaply and with low heating and acceleration loads. Orbiters at Titan can be mass-efficient, too, if they utilize aerocapture…
The plutonium-238 issue becomes still more interesting because the new type of radioisotope thermoelectric generators NASA is examining seem made to order for an airplane in Titan’s atmosphere, while they’re unlikely to function in alternative balloon proposals. Called Advanced Stirling Radioisotope Generators (ASRG), the new RTG’s are considerably more efficient than their predecessors, requiring less plutonium-238 and producing less waste heat. Barnes and team argue in their paper that a hot-air balloon would not work on Titan with an ASRG because of its lower heat production — balloon designs would need to function with the waste heat from an MMRTG [Multi-Mission Radioisotope Thermoelectric Generator]. In fact, Barnes’ calculations show that the 500 W of heat from an ASRG would support less than 10 kg in a balloon, which is actually less than the mass of the ASRG itself.
Contrast this with AVIATR, which can use the longevity of twin ASRGs for extended operations on Titan. Setting aside the power requirements for computers, actuators and instruments, Barnes and company find they have in the neighborhood of 80 W to power up the propeller for straight and level flight operations. From the paper:
The propeller’s thrust on an airplane with singly folded wings can keep aloft an airplane with a mass up to ∼120 kg. Other nuclear power sources, such as the MMRTG, cannot satisfy the physical requirements for heavier-than-air flight at Titan subject to appropriate engineering and risk constraints. Thus the use of an ASRG makes the AVIATR mission concept possible…
In fact, once deployed in Titan’s atmosphere, AVIATR should be in a benign environment:
Heavier-than-air flight on Titan is easier than anywhere else in the solar system. With over 4 times more air and 7 times less gravity than Earth, flight on Titan is 28 times easier than it is here (in the sense that a vehicle with the same contours flying at the same velocity on both planets could lift 28 times more mass). It is over 1,000 times easier on Titan than on Mars.
Long-duration flight is the name of the game, and AVIATR is seen as capable of carrying out a 1-year mission. The stability of the design would return the aircraft to straight and level flight in case the autopilot failed, in which case stabilizing vanes would deploy automatically to keep the aircraft in a stable position while pointing its antenna at the Earth to receive safe-mode instructions. The paper notes that the materials for the airframe are conventional and based on designs for unmanned aerial vehicles (UAVs) that operate here on Earth. AVIATR would also be more robust than a balloon in handling atmospheric turbulence and wind shear.
How would AVIATR be deployed, and how would it conduct flight operations? More on this tomorrow, when I want to dig a little deeper into the science and the unusual telecommunications strategy afforded by an aircraft on Titan. The paper is Barnes et al., “AVIATR—Aerial Vehicle for In-situ and Airborne Titan Reconnaissance: A Titan airplane mission concept,” Experimental Astronomy, Volume 33, Issue 1 (2011), pp.55-127 (full text).
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Leggendo la traduzione di questo articolo, ho notato che viene evidenziato che la durata di un viaggio di una sonda dalla Terra a Saturno, è di sette anni.
Ma non c’è un modo per ridurre i tempi di questo viaggio, magari utilizzando le tecniche più innovative che si conoscono e che si sono utilizzate di recente?
E la proposta di inviare una sonda, galleggiante in uno dei grandi laghi di Titano, non potrebbe essere abbinata insieme a questo affascinante aereo telecomandato da una sonda in orbita, o dalla Terra?
Mi rendo conto che i costi di una doppi missione(aereo in quota, e una sonda galleggiante su un lago di metano)sarebbero molto alti, però mi piace sognare…
Un saluto da Antonio
Superb write up and very interesting article Paul. I have also been reading about another proposed mission to Titan which is called TiME (Titan Mare Explorer). This is a probe which would land in Titans Ligeia Mare to discover more about Titans lakes. The thought came to my mind as to the possibilty of combining this mission with AVIATR, whereas the aircraft could carry TiME and release it by parachute to drop it into a lake. I understand the aircraft would have to be larger as would the launching rocket, but the cost should be evened out by having the two missions combined into one. Another plus would be better control over where TiME would splash down. Something to think about…if you like the idea and wish to pass it along to some of your contacts…..have at it!!!!!
Antonio’s comment above, via Google Translate:
Reading the translation of this article, I noticed that it is shown that the duration of a trip of a probe from Earth to Saturn, is seven years.
But there’s a way to reduce the time of this journey, perhaps using the latest techniques that are known and have been used recently?
And the proposal to send a probe, floating in one of the great lakes of Titan, could not be combined with this fascinating aircraft remote-controlled by a probe in orbit, or from Earth?
I realize that the cost of a double mission (aircraft altitude, and a probe floating on a lake of methane) would be very high, but I like to dream …
Greetings from Antonio
Interesting how Tom and Antonio came up with the combined mission idea at precisely the same time!
Hey Antonio…great minds think alike…we need to get together and patent this idea before Paul does!!!! LOL
Perhaps we should have some bumper stickers and T shirts made up with
the slogan ” It’s AVIATR TiME” ????
One thing I cant understand is , if we have this giant spacestation floating around in low orbit , why dont anyone even talk about using it for something worthwile ? The sugestion here by Tom and Antinio of a larger combined mision to Titan should be much erasier if the spacecraft could be refuelled at the ISS . If you follow the delivery scedules of the ferryboat activity to the ISS it seems that there are often spare lifting capacity not beeing used .
If every spaccraft ariving vere topped of weight-wise with fuel , it would have acumulated by now to a usefull quantity . Enven better would be if the ISS were equipped with electrical propulsion for orbital corrections . In that case there would ALWAYS be extra fuell to be stored for future refuelings . In the SF film “Armaggedon ” the Russisams had just the right idea of a fuel depott !
Burde, I see your point and readly agree. I understand that they are in the process of doing simulated experiments on board the ISS in fuel transfer. Your ideas have a lot of merit, but I wonder about the electrical engine power for an ISS reboost…..that is a mighty bit of tonage for an ion engine.
The ISS is in a high inclination orbit so it may not be useful as a launch point for lunar or solar systems probes. However, by the time we are ready to do this sort of thing I have a feeling that the ISS is not going to be the only manned space station up there and so other options will be available.
The biggest impediment to TiME and AVIATR is money. One of NASA’s biggest money drains is the ISS, so in a way you could say that the ISS (and the Space Shuttle – good riddance) have been holding back space exploration.
The ISS is (mostly) scientifically useless. It served as a fine political venture, a convenient sink for aerospace corporate welfare and it’s a good place to send 3 – 6 high tech janitors and the occasional super rich tourist. The “science” done on the ISS involves looking out the window and taking admittedly breathtaking photography and re-running microgravity experiments that have been done and redone and redone since Salyut and Skylab, if not earlier.
Don’t be too hard on the ISS, FrankH! Certainly, it’s been managed more as a jobs programme than a space one. But the unplanned effect is that it is now acting as a destination to help get private sector space transport companies like SpaceX up and running. When they can supply the ISS regularly, they’ll be able to branch out into commercial markets and increase traffic to orbit. Increasing traffic means falling costs and rising reliability (as people like Rand Simberg, and David Ashford in the UK, have been saying for years). These in turn will make science probes out into the rest of the Solar System less expensive, as a large part of their cost is their launch cost.
How does NASA fund this? or anything planetary? The SLS boondoggle eats the manned budget and the JWST incompetent program management over runs are killing the unmanned space budget. Read in Sky & Telescope that after years of state of the art science and engineering that the Keck interferometer loses funding in July. Between NASA’s self imposed (read SLS) budget crunch and Hawaiian religious superstition aversions to telescopes on holy mountains, Keck interferometer will shut down.
I think the often expressed view that the (perceived) boondoggles are keeping the money from (presumed) better missions is deeply flawed. These boondoggles are money magnets. Without them the entire budget would shrink, and funds for smaller (better?) missions might even dry up more.
In a better world everything would be different, but in THIS one , the ISS exists
,which means that a gigantic investment has been made . Hundreds of tons of high quality material and equipment of many different sorts has ben lifted into space , and if you are just a little bit of an optimist , it would seem a terrible waste to give up on all this without trying to find something usefull to do with it .
The only thing of real value that it can theoreticly be used for , is asemby of stuctures too big or complex to lift in one piece .
Electric propulsion is only getting started , and the russians are not hybnotized by politically correct anti-everything -nuclear bubbletalk.
What the ISS need is a nuclear MOTOR powerfull enough to get it to an orbit where it will be SAFE for a long time from the atmospheric drag , and eventually capable of reaching any kind of orbit usefull for asemby missions . Even if this kind of missions are not presently in the pipeline ., it should be possible to put the ISS into akind of “long term storage” orbit . For those that believe more and bigger and better spacestations will be build in the foreseable future , I would suggest trying a strict regimen of cold showers and a low fat diet…
About the size of the necesarry electric motor : a continous effect of 50 KW would be enough to raise the orbit 20 km a week , which is less than the total efect of intalled solar panels , so theoreticly the ISS could be mooved around by its own power if almost everything else were shut down , which would be without a crew . If the exhaust velocyty were as god as the best obtained in laboratory conditions for ionic liquids , it would only need something in the range of 15 kg a week of reaktion mass or “propellant” .