NASA's Human Exploration Rover Challenge isn't for the faint of heart. The critical thinking that goes into designing rovers and the hours spent building them require dedication from teams of students from high schools, colleges and universities around the world.

The 26th annual challenge, managed by the Office of STEM Engagement at NASA's Marshall Space Flight Center in Huntsville, Alabama, will be held April 17-18, 2020, at the U.S. Space and Rocket Center in Huntsville. It is one of six Artemis Student Challenges that NASA hosts to engage, inspire and help develop the next generation into science, technology engineering and math. The competition requires the students - members of the Artemis Generation - to design, build, test and develop a human-powered rover and innovative technologies, tools and plans needed to succeed on a difficult course mimicking features seen on other worlds and moons across the solar system.

Piloting the student-built rovers are one male and one female driver from each team, simulating the exploration forays of the first Artemis crews on the lunar surface beginning in 2024 when the first woman and next man will land on the surface of Earth's celestial neighbor.

2 people on a human-powered rover with rockets in background
The demanding half-mile Rover Challenge path is dotted with scientific challenges and terrain and obstacles simulating that found on the Moon, Mars and other solar system bodies - terrains astronauts will likely explore one day. The course is littered with rock outcroppings, sand traps and simulated "lava rilles," like those the original lunar explorers faced during the Apollo 15, Apollo 16 and Apollo 17 missions.

For the uninitiated, there's bound to be questions about the inner workings of the rovers themselves. "It's always exciting to see what design tweaks teams develop to take on the course," said Julie Clift, education program specialist at Marshall. "Their creativity and ability to innovate are hallmarks of our students and young people - the Artemis Generation."

On this challenging course, only the strongest rovers survive. Chains break. Frames snap. Wheels buckle. And nearly every new team exits the course saying the same thing: "That was a lot tougher than we expected."

So what does it take to conquer the Rover Challenge? Following is an in-depth look at the rover itself - an opportunity to learn more about these amazing machines and what it takes to win. Let's break it down element by element.

The Chassis
The vehicle's core is the chassis - the framework or skeleton that supports the whole structure. It is typically composed of a metal frame - usually steel or a combination of metals - supported on springs or some other type of suspension system, which buoy the vehicle and its occupants. A Rover Challenge win or loss can be decided right here.

The frame or central truss requires some thought. Steel is strong and durable but heavy; aluminum is lighter but requires reinforcement to withstand the abuse of the course. There's no weight constraint, but teams do receive points based on the weight of their rover - reflecting the critical weight constraint every crewed space exploration mission faces.

Teams often consider a combination of steel and aluminum, using tube-shaped metal struts to fashion a conventional rectangular frame for four-wheeled vehicles or a more creative configuration for three-wheelers. Teams might even consider using composite materials to fashion the chassis. But the frame alone does not make the machine. Teams must also wisely choose suspension options. Again, it's all about what rovers are going to face on the field.

The Drivetrain
The drivetrain is basically everything between the rider's feet and the road, including pedals, gearing, axles, tires and wheels. It transmits human power from the riders' pedaling legs to the vehicle's drive wheels. Most have a gearing system to convert speed and torque. Typically, rovers employ a simple series of gears, or a fancier, direct-drive system with a driveshaft and transmission to transmit torque and rotation.

The rover is human-powered, but it's really not like a bicycle at all. A rider's legs can put upward of 300 pounds of force on each pedal per stroke. Add a second rider, a lot of adrenaline and awesome prizes and bragging rights waiting at course's end, and now there's nearly a half-ton of force hitting those drive chains on every obstacle. Standard bike chains can't handle that kind of force.

Teams using chains must employ tensioners and chain guards, particularly where the bottom of the vehicle contacts the terrain. Event experts also caution against employing derailleur gears - a kind of variable-ratio transmission system that includes a chain and sprocket system to change gears and widen the range of applicable torque and power.

Being able to change gears to increase speed isn't the goal anyway. Because of all the turns and obstacles, the fastest rovers on the course usually only clock about 15 mph on straight sections. On straightaways, rover drivers want gearing conducive to speed. On harder sections, they want gearing conducive to torque. Winning vehicles tend to maintain a fairly steady top speed across the course, without a lot of gear changes.

"Think beyond a regular bicycle," said Rover Challenge supervisor Dennis Gallagher, a Marshall astrophysicist. "I like planetary gears, gearboxes designed specifically and fabricated by teams aware of the requirements of the course." Organizers also suggest designing a system that uses nearly all-modular hardware - enabling drivers to quickly and easily take off broken or damaged parts and pop on replacements.

Suspension
Suspension is the catch-all term for the network of springs, shock absorbers and linkages used to connect a vehicle to its wheels. These contribute to good handling and braking and protect the drivers from jarring changes to the driving surface.

Most rover suspension systems - simple cart axles that keep each pair of wheels parallel and perpendicular to the axle - employ passive springs to absorb impact and shocks to control spring motion. Independent suspension systems add a certain amount of self-governing rise and fall to each wheel, bracing drivers against uneven terrain.

Any typical off-road vehicle suspension system, such as that found on a dirt bike or ATV, provides a good jumping-off point for rover design, experts say. The best systems keep the frame fairly level and spare rover operators most of the rough shocks, letting the wheels take the punishment. The real challenge is to maintain control of the machine through the bounces and jolts - which is why the Rover Challenge insists every driver be firmly belted and buckled in for the ride.

The 'Folding Mechanism'
A folder rover for NASA Human Exploration Rover Challenge Nobody wins this competition based on course speed alone. Every team first must demonstrate how quickly they can fold out or otherwise reconfigure their collapsed rover. It's a historic aspect of the challenge, based on the need to fit the original lunar rovers in a 4-by-4-by-4-foot cube aboard the Lunar Excursion Module - all the room Apollo-era engineers could afford them. Competition rovers must fit in a 5-by-5-by-5-foot cube reflecting the volume constraints of NASA's Orion capsule system.

When the competition began in the mid-1990s, assembly times could be 20 minutes. Today, teams typically use hinges, a pivoting chassis frame with a handy batch of cotter pins or even elaborate pump systems to collapse and pop their rover back into ready position. Modern assembly times can be as quick as two seconds.

Whatever the folding mechanism, Gallagher reminds teams to ensure their machine has sufficient strength to handle the stresses experienced by those hinge or fold points once the rover is assembled or unfolded.

The Wheels
NASA will no longer accept pneumatic tires or other commercially purchased wheels on any competing vehicle. Each team must design and fabricate their wheels, with the exception of the central hubs. Wide wheels work best, like those on track bikes and ATVs.

Teams are encouraged to augment their pedals in a way that helps riders keep their feet firmly planted on the pedals but without making it difficult to remove their feet quickly if necessary. Using a way to anchor rider feet to the pedals is not required, however.

Steering
Steering configurations are as varied as any other element, but hardware is relatively simple: upright or drop handlebars or a simpler straight handle or riser bar, like that on a mountain bike, which turn the fork and front wheels via a stem rotating in the headset. But that simplicity shouldn't cause teams to underestimate its importance or the stress experienced by the steering system as surface obstacles on the course are encountered.

Design is paramount. Drivers may sit side by side, or one in front and one behind. They may share steering duties, or one may take point to guide the vehicle. Regardless, the type and position of the handlebars should inform seating design. Drivers seated low at a backward angle for better pushing power, for example, can't properly use upright handlebars that force them to awkwardly lean up or forward to maintain control.

For the most aerodynamic rider profiles and ergonomic seating designs, officials suggest teams study recumbent bikes, with under-seat or over-seat steering arms or joysticks at the sides, and mountain bikes, which have wider handlebars or risers to improve handling. Rigorous testing is key. Ensure the system responds properly and ascertain how much power is needed to coax the rover around a sharp turn.

Brakes
The only thing more important than steering, experts agree, is braking. From crude rim brakes like those on regular bicycles, to internal hub or disc brakes for sturdier off-road or tandem bikes and direct-pull or linear-pull brakes like the V-brakes found on many BMX and mountain bikes, there are pros and cons everywhere.

With rim brakes, friction pads are compressed against the wheel rims themselves. With internal hub brakes, they're contained within the wheel hub. The highest marks from competition officials typically go to disc brakes, which have a separate rotor for braking, or linear-pull brakes, which deliver the most hardware flexibility. These tend to stand up best to hard, abrupt braking.

Seats
Seating is among the most important rover elements. Rover Challenge veterans say quality bucket seats which conform to the lower back and rear end are ideal. Drivers should be able to seat themselves solidly to provide lots of lower-back pushing power. Bicycle-style saddle seats won't suffice, as they have no pushing power at all, and simple folding seats or rigged chairs can snap under riders' mass and pushing energy.

Whatever style of seat is used, strong, buckling seat belts must be included. "No Velcro, no rope, no duct tape," Gallagher warns. "Seat belts are not optional."

Accessories
Last but not least comes the rover facade, accessories that put the finishing touches on this homage to NASA ingenuity and can-do spirit. Each rover must have a national or school flag. Elaborate paint jobs, creative "dust abatement" devices or wheel covers and spirited school apparel reflect the teams' creativity and personality while looking cool on the Rover Challenge course.

The Best Reward: Experience
Clift, Gallagher and other Marshall organizers all say they're excited by the event. They enjoy the mix of creativity, problem-solving and pure adrenaline it sparks in nearly every participant. More important, they say, is the professional experience students are gaining, the practical value that lasts long after the adrenaline has faded.

"Most don't yet have a lot of computer modeling experience, or a background in stress analysis, or a thorough understanding of how a certain tension steel will behave in a particular application," Gallagher said. "What the Rover Challenge offers is a clearer understanding of the way engineers work. This is hands-on, professional experience: design work, speccing out requirements, fabrication, welding, rigorous testing."

Which isn't to say it's a dispassionate profession. Like the NASA and industry engineers tapped to deliver the original Lunar Roving Vehicle in a mere 17 months from 1969-1971, today's rover teams come to recognize that a professional engineering challenge is pure passion.

"I have yet to see a team come in here and get beaten by the course who didn't get right back up, eager to tackle it again," Clift said. "It's the real deal, and it leaves an impact."

The impact will be a lasting one as the student competitors are members of the Artemis Generation, which, like the Apollo generation that came before, will be the thrust for unparalleled space exploration. With the Artemis program, NASA will land the first woman and next man on the Moon by 2024, using innovative technologies developed by innovative minds to explore more of the lunar surface than ever before. NASA will collaborate with its academic, commercial and international partners and establish sustainable exploration by 2028, using what is learn to take astronauts to Mars.

In just a few short months, the Human Exploration Rover Challenge will once again test participating students' mettle and lay their foundation for the exploration of the cosmos.

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