Lake lander probe TiME (artist's concept: Corby Waste/Jet Propulsion Laboratory) |
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| Operator | Under evaluation by NASA |
|---|---|
| Mission type | Lake-lander |
| Orbital insertion date | 2023 |
| Launch date | 17 January 2016 (proposed)[1][2][3] |
| Launch vehicle | Atlas 411 |
| Mission duration | Cruise: 7 years; science: 3 to 6 months |
| Power | ASRG |
Titan Mare Explorer (TiME) is a proposed spacecraft lander that, if launched, would probe Titan, the largest moon of the planet Saturn, and would perform the first exploration of an extraterrestrial sea.[1] TiME has been proposed to NASA by Proxemy Research as a scout-like pioneering mission, originally as part of NASA's Discovery & Scout Mission Capability Expansion (DSMCE) concept-study program.[4] TiME is one of three Discovery Mission finalists that received US$3 million in May 2011 to develop a detailed concept study. After another review in 2012, NASA will pick one to see through to launch. The selected mission will be cost-capped at $425 million, not including launch vehicle funding.[2]
It has also been proposed to delay TiME enough so it can be incorporated into the flagship-Titan Saturn System Mission proposed for launch in the 2020s.[4][5]
TiME is a low-cost, outer-planet mission that would directly measure the organic constituents on Titan and would perform the first nautical exploration of an extraterrestrial sea, analyze its nature and, if possible, a shoreline.
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The discovery on 22 July 2006 of lakes and seas in Titan's northern hemisphere confirmed the hypothesis that liquid hydrocarbons exist on it.[6] In addition, previous observations of southern polar storms and new observations of storms in the equatorial region provide evidence of active methane-generating processes, possibly cryovolcanic features from the interior of Titan.[5]
It is believed that Titan's methane cycle is analogous to Earth's hydrologic cycle, with meteorological working fluid existing as rain, clouds, rivers and lakes.[6] TiME would directly discern the methane cycle of Titan and help understand its similarities and differences to the hydrologic cycle on Earth.[5] The Principal Investigator of the lander mission is Ellen Stofan, a member of the Cassini radar team. The spacecraft concept is being developed by Lockheed Martin, Proxemy Research Inc.,[7] and the Applied Physics Laboratory at Johns Hopkins University.
TiME's launch would be with an Atlas 411 rocket during 2016 and arriving to Titan in 2023. The target lake is Ligeia Mare (78°N, 250°W). It is one of the largest lakes of Titan identified to date, with a surface area of about ~100,000 km². The backup target is Kraken Mare.[1][5]
The Titan Mare Explorer would undergo a 7-year simple interplanetary cruise with no flyby science. Measurements and data transmissions would begin only after splashdown. The science objectives of the mission are:[1][5]
Malin Space Science Systems, which builds and operates camera systems for spacecraft, has signed an early development contract with NASA to conduct preliminary design studies.[8] There would be two cameras. One would take pictures during the descent to the surface of Ligeia Mare lake, and the other would take pictures after landing.[8]
Titan's thick atmosphere rules out the use of solar panels like the ones that have kept the Mars rovers and landers functioning for years, while batteries would only provide some hours of power at most. If selected by NASA, the TiME lander would be the test flight of the new Advanced Stirling Radioisotope Generator (ASRG),[4] which is a prototype meant to provide availability of long-lived power supplies for landed networks and other planetary missions. For this mission, it would be used in two environments: deep space and non-terrestrial atmosphere. The ASRG is a radioisotope power system using Stirling power conversion technology and is expected to generate 140–160 W of electrical power; that is four times more efficient than RTGs currently in use. Its mass is 28 kg and will have a nominal lifetime of 14 years.[1]
The lake-lander would not be self-propelled and the wind will be expected to push this buoyant craft around the lake for months.[3]
The vehicle will communicate direct to Earth and, in principle, it could be possible to maintain at least intermittent contact for several years after arrival: the Earth finally sinks below the horizon as seen from Ligeia in 2026.[9] It will not have a line of sight to Earth to beam back more data until 2035.[10]
The capsule is expected to drift on the surface of the lake, pushed by currents and wind with typical speeds of 0.5 m/s, and not exceeding 1.3 m/s (4.2 feet/second).[9] Even if the vehicle's motion cannot be controlled, location sequences can be used to optimize scientific return, such as lake depth, temperature variations and shore imaging. Some proposed location techniques are measurement of Doppler shift, Sun height measurement, and Very Long Baseline Interferometry.[9]
The chance to discover a form of life with a different chemical basis than life on Earth has led some researchers to consider Titan the most important world on which to search for extraterrestrial life.[11] A few scientists hypothesize that if the hydrocarbon chemistry on Titan crossed the threshold from inanimate matter to some form of life, it would be difficult to detect.[11] This is because there is no way that terrestrial life could have originated or could prosper on Titan because of the fundamentally different chemistry of Titan's surface. Moreover, because Titan is so cold, the amount of energy available for building complex biochemical structures is limited, and any water-based life would freeze without a heat source.[11]
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