By far the most famous method of extraterrestrial transport is the rover. Their story starts with the Lunokhod 1 (Луноход meaning ‘Moon-buggy’: very inventive! ), which, you guessed it, trundled on the Moon.
On 17th November 1970, Lunokhod 1 was put onto the lunar surface in Mare Imbrium (the Sea of Rains), just north of the Copernicus crater, rolling out of the Luna 17 lander. It would become the testbed of rovers to come, on the Moon but also on Mars. With eight wheels and a polonium-210 radioisotope heater (a portable nuclear power station) for when the Sun set from the view of its solar panels, it went a staggering 10km in just 10 months (NASA’s Mars Opportunity rover took 7.2 times longer to do the same distance!). It set a precedent that would be carried forward into future rovers, taking 20,000 pictures and 200 panoramas, and conducting over 500 lunar soil tests .
Lunkhod 1 from the Lunar Reconnaissance Orbiter. Credit: NASA/LRO
Following this space-race icon, NASA brought out their own fleet of lunar rovers in the form of jeep-like vehicles with a pair of seats for Apollo astronauts to sit in, known as Lunar Roving Vehicles (LRVs); no more inventive than their Soviet counterparts! Restricted to a 9.5km radius due to their Portable Life Support System (PLSS), astronauts could ride on the untouched lunar landscape, picking up lunar samples, taking pictures and other scientific measurements along the way. However, can’t a robot do the same ?
Back then, yes, although the amount taken back robotically then was orders of magnitude less than that of the crewed missions to the Moon, such as the Apollo 15, 16 and 17 missions using the NASA’s LRVs. Luna 20, from the USSR, brought a light 55g of soil down to Earth in February 1972, whilst NASA’s Apollo 15 mission, employing the trusty LRV, collected 77kg (1400 times more than the Soviet’s mission) .
Apollo 17 LRV with astronaut Eugene A. Cernan. Credit: NASA
However, as technology quickly advanced, it became evident that the better way was robotic missions: enter the Mars rover! It all started with the Soviet’s Mars 2 and 3 missions, landing a PrOP-M rover… twice. Launched in May 1971 and arriving at Mars in November and December, Mars 2 and 3 attempted to make the perilous landing onto the Martian surface, but they’d picked the worst date to do it… during one of the worst dust storms in recorded history (unfortunate)! That meant Mars 2 crashed and Mars 3 lasted just 14.5 seconds (thought to be because the lander was blown over). If it were to have gone to plan, PrOP-M would have skated out over the lengthy 15 metre maximum distance (due to its ‘umbilical cord’ like tether attached to the lander), carrying a penetrometer (measuring the strength of the surface below) and gamma-ray densitometer (determining the density of the soil below) .
Instead of the Soviets taking the title of first Martian rover (although the title for first human-made object on Mars was claimed with the Mars 2 crash landing -take the rough with the smooth ), it was NASA with their humble Sojourner aboard the Pathfinder mission that took it. Landing in 1997, Sojourner wondered around Ares Vallis (an ancient, and more importantly safe, flood plain, with lots of rocks to analyse). ‘Barnacle Bill’ was the first rock to be analysed by Sojourner, discovering that silica was present: a compound found in igneous rocks (made at high temperatures), suggesting an interesting geological history on Mars, warranting further study . This call hasn’t been forgotten, with the trusty rover having been used in five NASA missions so far .
Sojourner on Mars. Credit: NASA
The success of this technology has then lent itself to use on other places apart from the Moon and Mars: namely Mar’s moon Phobos, where the German Aerospace Centre (DLR) are looking to send a four wheeled rover onto the Martian moon to get a better understanding of its origins. The MMX (Martian Moons eXploration) mission is scheduled for a drive on the alien moon in late 2026 to early 2027 .
The Phobos Rover. Credit: DRL, CC BY 3.0 DE
The Methane Submarine
Unlike the Yellow Submarine, this next method of transport hasn’t got a song to go with it, but what it does have is a destination with a very cool name: NASA’s Titan Submarine is going to be immersed into the depths of the Kraken Mare on Titan (one of Saturn’s moons). As a liquid methane sea, the Kraken Mare is a challenge for scientists to model for testing, with nothing remotely like it on Earth. At 1,000km wide and 300m deep, the sea will serve as a fantastic location for the first mission to an alien sea, with the aims of: measuring ocean currents, sampling the liquid to find out its chemical composition, and inspecting the seafloor features .
Titan Submarine. Credit: NASA
This mission could be a ‘pathfinder’ for another submarine mission to yet another moon: a submarine set for Europa (a Jovian moon). This mission, not seen as feasible at the moment, could one day wriggle its way through 10-20km of ice into the liquid ocean below to investigate what’s down there. The hope is that extra-terrestrial life could be found, with the ocean being home to not liquid methane but liquid water: an ingredient we know is imperative for life .
NASA’s Europa Clipper (scheduled for a 2020s launch) and ESA’s JUICE mission (JUpiter ICy moons Explorer, scheduled for a 2029 arrival) hope to get a better understanding of this icy moon, to find out if missions such as that of the Europa submarine are feasible, as well as to unlock the deep interior of Europa from above (much cheaper!) .
A Miniture Martian Chopper
Another exciting way to travel is, however, closer to the present. The modestly named Mars Ingenuity Helicopter has taken flight as the first helicopter on another planet. Having now carried out two test flights (one on 19th April and the other on 22nd April), the 1.8kg drone has now conquered Mars’ thin atmosphere (at just 1% that of Earth’s) to a 2m height (in its most recent flight), with its 1.2m blades wizzing around at a dizzying 2,500 revolutions every minute (terrestrial helicopters spin at just 400-500 revolutions per minute!). The aim is to help us study cliffs, craters and other locations on Mars that are hard to get to for the traditional rover .
The Ingenuity Helicopter in its second flight. Credit: NASA/JPL-Caltech/ASU/MSSS
Again, it will also act as another ‘pathfinder’ mission, leading the way for a possible new mission to… Titan. Apart from liquid methane, Titan also has a really interesting surface. NASA hopes to launch the Dragonfly helicopter in 2026 for a 2034 touchdown, using its flight capability to move between places, with journeys of up to 8km to take samples at each stop, before reaching the Selk impact crater: a location where there’s evidence of past liquid water, along with complex carbon-containing molecules, hydrogen, oxygen and nitrogen (all ingredients for life!).
The helicopter could then travel a staggering 175km (nearly double the combined distance all Mars rovers have travelled!), exploring the origins of life as well as the beautiful and complex landscapes of the alien moon .
Dragonfly on Titan. Credit: NASA/JHU-APL
A Space Bunny!
The final category of modes of transport on other worlds is the hopper. Like the rover, the hopper has its sights on the Moon and Mars.
NASA have proposed the Mars Geyser Hopper as a potential mission to the Martian south pole. With automatic detection systems in place, the Mars Geyser Hopper may be able to detect the first signs of a Martian geyser beginning to erupt and hop to it, taking images along with a chemical analysis of the plume of material emitted (which is moving at 160km/h up hundreds of metres into the sky). Hundred of geysers have been spotted from orbits of Mars already (with around one geyser found every 2km), caused by the ice at the Martian south pole cap melting during the summer, causing high pressure below the surface .
Dark dune spots: a sign of geysers on the polar icecaps.
Credit: NASA/JPL-Caltech/University of Arizona
And then there’s the University of Manchester’s fleet of hopping robots, hoping to become the mission selected by ESA to explore the lunar lava tube system on the Moon (you can read more here) .
However, as there is with all these transport methods, there’s a goal to send a mission to somewhere really exotic, even for space agencies like ESA and NASA: a comet. The Comet Hopper is a concept mission to land on comet 46P/Wirtanen. A Jupiter-family comet orbiting between Earth and Jupiter, comet 46P/Wirtanen has volatiles (molecules which evaporate easily at the outside temperature) within it, not possible to study from Space. The hopper would mean scientists could explore the entire surface of the comet (never done before) and collect some volatiles for future study in a sample return mission. However, it’s the hope that some in-situ physical and chemical testing of the nucleus (the comet’s rocky/icy centre) and inner-coma (the comet’s ‘atmosphere’ of ice, gas and dust produced by the comet’s interaction with solar wind), improving our understanding of these small and difficult worlds to explore .
NASA's Comet Hopper mission. Credit: NASA/GSFC/University of Maryland
There is certainly a lot to look forward to in terms of new Space based transport, along with the discoveries that they bring, and who knows what the future holds for how machine, and human, can get about on other worlds.
by George Abraham, ADAS member.
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Click here to watch a video on the University of Manchester's lunar mission proposal
Click here to track comet 46P/Wirtanen on JPL's Small Body Database
Click here to watch a video on NASA's Titan Submarine proposal
Click here to watch a ride on an LRV as part of Apollo 15
Click here to watch Ingenuity's first flight on Mars, viewed from Perseverance (the rover that Ingenuity arrived to Mars with
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