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SPACE: EGGBEATERS ON MARS


Inch - epaper ⋅ Ausgabe 2/2019 vom 06.06.2019

Engineers have perfected the art of rovingon Mars – now its time to take off. The car-sized Mars 2020 rover will carry a small helicopter drone. DubbedScout, it will test if its possible to fly in Marsthin air. If it works, we might soon be exploringthe skies of Mars, Venus or Titan.


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Bildquelle: Inch, Ausgabe 2/2019

Ingenieure haben die Kunst, auf dem Mars herumzufahren, inzwischen perfektioniert – jetzt ist es an der Zeit abzuheben. Der Mars 2020 Rover wird eine kleine Helikopterdrohne mit sich führen. Der sogenannte Scout soll testen, ob es möglich ist, in der dünnen Luft des Mars zu fliegen. Falls alles klappt, ...

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... werden wir vielleicht bald die Himmel von Mars, Venus oder Titan erkunden


< ILLUSTRATION: NASA/JPL-CALTECH >

Proposals for new space missions sometimes sound like “engineering fiction”: catching and redirecting asteroids, shooting tiny spaceprobes to distant stars with lasers or landing on the Moon within the next five years. Projects like these may be based on science facts but their engineering is stillfictitious – not tomention theirbudgetary approval .

When, in 2015, NASA’s Jet Propulsion Laboratory proposed a small helicopter drone that would fly the Martian sky it sounded like just another one of these engineering fiction stories: clever, cool … but far in the future.Granted , Mars is one of the fewcelestial bodies with an atmosphere, andaerial flight should therefore be theoretically possible. But engineers have just learned how to rove on Mars and now they want to send a toy-sized drone there? Theodds for approval seemed as thin as the air on Mars.

The story, however, took a serious turn in May last year when NASA officially announced that a small helicopter wouldindeed be part of the Mars 2020 rover mission.Recently , the helicopter’s flight model, the actual vehicle going to the Red Planet, passed critical tests. It looks like, in spring 2021, a human-made object will, for the first time in history, lift off and fly through the sky of another world.

The idea of flying “off-world” is probably as old as space flight itself. Aerialexplorers fill in the middle ground between satellites and landers or rovers: They provide a higherresolution than orbiters and have an extended mobility compared to rovers.Accompanying robotic or human explorers, drones can act as scouts to look over hills and craterrims , tomap thesurrounding terrain, or to reach otherwiseinaccessible places.

FLYING ANDFLOATING IN FOREIGN SKIES

Venus, with its thick atmosphere and Earth-likegravity , is anobvious candidate for aerialsurvey – were it not for the 400-kph-winds and theacid rain. Despite thesedrawbacks , in 1986, the Russiansdropped two balloons into this hellish sky, and they lasted for several hours. Otheraerostatic probes have beensketched for Venus including giant airships and even empty rocketstages which would actually float in its thick atmosphere.

Flying on Mars is a bittrickier , though. Its atmosphericdensity is very low, equivalent to about 30 kilometres inal-titude here on Earth. There aren’t so many aircraft flying in these regions. Mars’ low gravity, 38 percent of that of Earth, might be a bonus, but you still need the air to createlift . The answer to the problem is speed. 500 kph would have been the necessary speed to lift the rocket-powered ARESfixed-wing Marsaircraft , which in the late 2000s came quite close to the selection as an actual mission.

What aboutrotary aircraft ? The idea of a Marschopper has been around for quite a while. Firstconceived in 1993, a more detailed study from 2000concluded that it should theoretically be possible – given a low mass and a high enough rotor speed. These main variables were confirmed by Mimi Aung, project manager for the upcoming Mars Helicopter mission at JPL, in an interview with Spaceflight Now: “The biggestchallenge of having a thin atmosphere is you have tospin much faster, and you can lift less. I would say the secret sauce to making something like a helicopter fly at Mars is to make the vehicle as light as possible, and it has to spin very fast.” In the case of the Mars helicopter, 2,900 revolutions per minute or about ten times faster than a regular helicopter here on Earth.

In addition to fighting the laws of physics, Aung’s team was alsochallenged by theallowances from their colleagues of the Mars 2020 rover team. The Mars helicopter would be travelling as a technology demonstrator with very little scientificvalue , which, if it were tofail , should have noimpact on the main mission. 1.8 kilograms and a place on the rover’sbelly with room for a 14-centimetre cube and a 1.2-meter-diameter rotor was all the rover people wouldspare .

Fitting a system capable of autonomous operation complete with computer, navigation sensors, cameras, transmitter, solar cells, batteries and heater into such a small and light package is afeat in itself. Then adding a rotor and making it fly is something else. To save weight, Aung’s teamopted for a coaxial rotor design with two horizontalblades made from carbon fibre rotating inopposite directions. This eliminates the need for atail rotor tocounteract theangular momentum and also simplifies the rotor control mechanics.

THE CHAMBER OF TRUTH

With physics andrequirement specifications checked, it was time to set the theory aside and see if the little drone could actually fly. “Rotorcraft are very hard to model,” explains Håvard Fjær Grip, a fixed-wing pilot who leads theguidance , navigation, and control team for the Mars Helicopter, in an Air & Space interview. “When we flew the vehicle, weanticipated that it wasn’t going tobehave exactly as the computer model, and it didn’t. But it did what it wassupposed to do, showing that it could produce enoughthrust to get off the ground.” The engineers had stuck ascaled model of the Mars helicopter into JPL’s famous Space Simulator, a 7.6-meter-wide vacuumchamber , whichrecreated the atmospheric conditions on Mars. The chopper ultimatelywent haywire and crashed – but only after it hadhovered for a few seconds.

A couple of years ago, the Mars helicopter was just a computer graphic (left), now the real thing (below) is travelling to the red planet with the Mars 2020 rover.


The little hop was thetipping point for the project; suddenly the Mars helicopter, now dubbed “Scout”, was a real thing. The rest was rocket science as usual: simulating and testing, simulating and testing again whileshaving off weight gram by gram andscouting the industry for cheapoff-the-shelf components, i.e. cellphone cameras, batteries from electronic cigarettes, automotive processors or laserrange finders from industrial robots. The engineering modelevolved andgained a small solar panel on top of the rotors and fourspin-dly carbon-fibre legs as a low-techlanding gear .

Finally, in January 2019, it was time for the ultimate test. Scout’s flight model, the actualitem going to Mars, was placed into the Space Simulator, the air replaced with a thin, minus-90-degree-cold Martiancarbon dioxide atmosphere. “Getting our helicopter into an extremely thin atmosphere is only part of the challenge,”recalls Teddy Tzanetos, testconductor for the Mars Helicopter at JPL. “To truly simulate flying on Mars we have to take away two-thirds of Earth’s gravity, because Mars’ gravity is that much weaker.” The teamaccomplished this with a gravity offload system – a motorizedlanyard attached to the top of the helicopter to provide anuninterrupted tug equivalent to two-thirds of Earth’s gravity.

Logging agrand total of one minute of flight time at an altitude of five centimetres, more than 1,500 individual pieces of carbon fibre,flight-grade aluminium, silicon, copper,foil andfoam have proven that they can work together as acohesive unit .

“The next time we fly, we fly on Mars,” said Aung. “Watching our helicoptergo through its paces in the chamber, I couldn’t help but think about the historic vehicles that have been in there in the past. The chamberhosted missions from the Ranger Moon probes to the Voyagers to Cassini, and every Mars rover ever flown. Seeing our helicopter in therereminded me we are on our way to making a littlechunk of space history as well.”

SPACE HISTORY IN HOPS

Space history that will happen in small, careful hops. First, of course, the little Scout will have to survive the “seven minutes of terror”, thefiery entry into Mars’ atmosphere,mounted on the belly of the one-ton rover which, after entry, will belowered onto thesurface dangling from a sky crane. Then, in spring 2021, after the rover has finished system checks and the mosturgent of science experiments, it will look for a nice flat area, drop the Mars helicopter and drive away a safe distance to watch space history unfold. First a careful little hop, no more than three meters straight up and just 30 seconds long. From there engineers will work their way up.Scheduled areat least five flights withincreasing complexity up to 90 secondsduration , heights of 5 meters and distances of up to 150 meters. Thefootage and the sensor data from the helicopter will berelayed via the rover back to Earth, where scientists willattempt to create 3D maps of the surrounding terrain. In between the flights, Scout has to rest torecharge its batteries.

No-one really knows what will happen during these flights – even NASAconsiders the mission high risk, highfail . The helicopter might crash ortopple over but even if it performs exceptionally and the engineers manage more than the initial five flights, after 30 days, Mars 2020 will rove on leav -ing his little companion behind. There are more important things to do on Mars than watching little drones fly.

Final checks for the Mars helicopter Scout: On its next take off it will stir up some Martian dust in the Jezero crater. The technology demonstrator will only perform a few short hops but it could pave the way for larger and more capable aerial probes in the future.


Of course, compared to the rover’s actual mission to finally prove the existence of past or present life on Mars, these little hops of a technology demonstrator might seem pretty trivial. Then again, the mighty Mars rover itself cantrace itsheritage back to a little technology demonstrator: In 1997, the shoe-box-sized Sojourner rover travelled just 100 meters. Today, Mars 2020 has the size of a small car, weighs a ton and is capable of operating for yearscovering tens of kilometres.

What could the future hold for flying vehicles at Mars? “The next generation of helicopters in the 5- to 15-kilogram class could have direct communication to an orbiter and would not need a lander, or could continue to work with a landedasset ,” says Bob Balaram, the Scout mission’s chief engineer. “The overall small mass of these helicopters could lead to small fleets of vehicles that couldsupport new kinds of science and exploration mission across large sections of the Mars surface. It is alsoconceivable that a helicopter couldfetch samples one at a time from a samplecache back to a Marsascent vehicle.”

The Mars helicopter isnt the only aerial explorer: HAVOC is a concept for a crewed airship which would float above the cloud tops of Venus.


< PHOTO: JOHNS HOPKINS APL >

The nuclear-powered Dragonfly multicopter, designed for Saturns moon Titan, might, in 2019, actually be selected as a real mission.


< PHOTO: NASA/SADC >

ONWARDS TO TITAN

These are just the possibilities on Mars. There’s another celestial body that’s absolutely perfect for aerial flight: Titan. Saturn’s moon has it all: a thick,dense atmosphere and an even lower gravity than Mars. The proposed mission “Dragonfly” is engineering fiction turned up to the max: A nuclear-powered dual-quadcopter the size of Mars 2020 capable of exploring hundreds of square kilometres on its two-year mission in the mid-2030s. Who knows, if the little Mars Scout does its job well, Dragonfly might become a real mission as early as this summer when it’s up for selection. The skies, even those of foreign worlds, are no longer the limit.<<< Matthias Meier >>>

https://mars.nasa.gov/news/8424/nasas-mars-helicopter-completes-flight-tests
Eine aktuelle Pressemitteilung zur Flugerprobung des Mars Helikopters. Eine eigene Webseite gibt es noch nicht.
https://spaceflightnow.com/2018/05/14/helicopter-to-accompany-nasas-next-mars-rover-to-red-planet
www.airspacemag.com/space/helicopter-dreams-of-mars-180971739
Die beiden im Text zitierten Artikel mit weiteren Informationen zum Mars Scout Helikopter.
https://rotorcraft.arc.nasa.gov/Publications/files/Balaram_ AIAA2018_0023.pdf
Wissenschaftliche Arbeit mit einer genauen Beschreibung des Mars Helikopters.
https://vtol.org/news/vertical-flight-society-applauds-nasa-s-mars-helicopter-selection
Artikel, der die Geschichte der Mars Helikopter beleuchtet.
https://youtu.be/w3y7iJEe7uM
Video, in dem Projektmanagerin Mimi Aung den Mars Helikopter vorstellt.
https://mars.nasa.gov/mars2020
Alle Informationen zur Mars 2020 Rover Mission.
https://sacd.larc.nasa.gov/smab/havoc
Das HAVOC Konzept für Venus Luftschiffe ist „engineering fiction” vom Feinsten.
http://dragonfly.jhuapl.edu/What-Is-Dragonfly
Details zur unglaublichen Dragonfly Mission. Der duale Quadrocopter für den Saturnmond Titan könnte schon diesen Sommer zur Ausführung gewählt werden.

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