Transportation Options for Getting Around on Mars
Another chapter in our Living on Mars series -- a collection of articles on what technology and systems will be needed to survive - and thrive - on Mars.
Other articles in this series include:
Most exploration ideas don't really discuss the problems of transportation on Mars, except maybe for the obligatory and iconic 'pressurized rover'.
But think about it -- when you get to Mars, how will you get around?
On Earth we take transportation for granted. We use different types of vehicle for different purposes:
... walking, or hopping on a bike perhaps, for traveling just a few blocks.
... catching a bus or driving a car when you need to go a little farther or do some shopping..
How about a plane for when we need to go even farther -- and a little faster?
There are plenty of options.
For a settlement on Mars, we should consider the same.
In other words,we shouldn't rely on just one big rover to do everything -- to take us everywhere and do everything. We will need multiple vehicles, each specific to the task.
And for that, we need to consider three different modes of travel:
Getting Around On Mars - Ground Travel
For ground transportation, we need to consider at least three different requirements:
- long distance, exploratory excursions
- construction, and
- short haul, quick trips
Pressurized rovers can work for both the long haul trips and some of the heavy duty construction work, but unpressurized rovers will be preferred for many of the construction activities and short haul trips.
Let's take a look at each.
Long Distance Travel
For long range trips, explorers will need pressurized vehicles that can sustain them while away from home. The solution?
The iconic pressurized rover.
There is no shortage of ideas on what a crewed rover would look like, but, in essence they are all similar: a pressurized cabin with an airlock on top of a wheeled chassis - not very sleek and not very fast -- but still pretty cool.
NASA's Space Exploration Vehicle
NASA's Space Exploration Vehicle (SEV) is designed to be flexible. Depending on the destination, the pressurized cabin can be used for space missions or for surface exploration.
The surface exploration version of the SEV has the cabin mounted on a chassis, with wheels that can pivot 360 degrees and drive about 10 kilometers per hour in any direction.
It's about the size of a pickup truck (with 12 wheels) and can house two astronauts for up to 14 days with sleeping and sanitary facilities.
Two versions of the SEV have been built for testing at NASA's Mars Yard -- an outdoor test range at the Johnson Kennedy Space Center in Texas. It's made to simulate the surface of Mars with rocks, sand, hills and valleys that can fully test the SEV capabilities.
In the test versions of the vehicles, the EVA suits are attached to the rear of the cabin and are accessed directly from the interior of the rover. This not only keeps martian dust out of the interior, but also means, since the suits are already inflated, astronauts can get into and out of them in about 15 minutes instead of the hours it takes to prep a suit in space.
In addition, there is a side hatch that is meant for docking directly to the habitat -- no need to actually get in a suit, go outside, and then climb into the rover.
Get in -- get out. In your shirtsleeves.
The SEV also has incredible mobility.
Each set of wheels can turn in place 360 degrees, which means the SEV can not only move forward and backwards, but also sideways and diagonally.
You can even pivot in a full circle if you want -- in place!
Overall -- pretty cool. In fact, NASA recently let a journalist from Business Insider, Jessica Orwig, take one of the SEVs for a spin to show off the complete range of motion. Needless to say, she was dutifully impressed. (Check out her report here.)
As in many NASA designs, the SEV is a multi-function system.
It is meant for use in all sorts of different situations, including deep space. In all scenarios, the cabin would essentially be the same and would allow the astronauts to work in comfort without actually having to step outside.
It's great for the long duration trips scientists and explorers will want to take on the surface of Mars (or for exploring an asteroid in the case of the deep space version), but it's overkill for the daily grind around a Mars base.
For puttering around the base for short periods of time or short distances, we will need something simpler.
Construction vehicles, for example. Trucks and tractors. Dozers and scrapers and excavators.
The work horses for building and maintaining a settlement.
Trucks and Tractors
As in the SEV, if you are working all day smoothing a pit for a new dome, or making a new road, wouldn't you prefer to sit in a warm cabin in your shirtsleeves rather than an EVA suit?
Of course you would.
But if you are simply working in and around your base, you don't really need a cabin capable of keeping you alive for a couple of weeks like the SEV.
Instead, you need something more ... utilitarian.
Something where you can sit and drive in comfort, but take back and dock at the hab when you need a break or at the end of the day.
Something where you can get out when you need to (EVA suits will still need to be available), but food, hygiene and cots? Probably not.
A vehicle with interchangeable parts and tools, just like some tractors here on Earth.
This type of 'work' vehicle for Mars has not been looked at in much detail, though. Many consider it a second generation technology for a Mars program.
In other words - explore first, then worry about settlement and construction.
But these type of vehicles will be needed the very first day for a settlement larger than just a handful of astronauts -- and they will be commonplace for a growing colony.
In fact, they should be delivered as part of the pre-supply missions prior to any human landing.
Short haul transportation
For those really short trips, why use a pressurized vehicle at all?
As on earth, if we are only going a short distance, or don't need to carry much with us, we don't typically need to take the family SUV.
A scooter or bike might do just fine. Or maybe an ATV.
Have you ever seen images of the Mars Society experiments at their research stations? The researchers often take ATVs for short jaunts around their base or even day trips to explore the surrounding area.
On Mars, we could do the same.
The vehicle could be electric, but it could also be gas. Methane production is a pretty simple process on Mars, if you have a little hydrogen or martian water. It's a well researched process first proposed by the Mars Society's Dr. Robert Zubrin for fueling Mars Ascent and Earth Return Vehicles.
But we could also use that fuel for a methane-powered internal combustion engine.
Since there is no oxygen in the atmosphere, however, we would need to supply some for the engine to work properly.
The first Martians will already be producing oxygen for the hab (using the the Mars Oxygenator). For methane-powered engines, simply make a little more and store it for later use. Add an oxygen tank to a vehicle along with a fuel tank, and there you go -- an old-fashioned internal combustion engine..
But would we really need -- or want -- a gas-powered vehicle?
The power to weight ratio for a gas engine is much better than an electric motor (batteries weigh a lot) and limiting the amount of mass delivered to Mars is critical. A methane-powered engine might be a really good idea.
Or better yet - a hybrid.
Combine the ability to recharge batteries directly from solar cells for the electric motor with natural gas-powered engines for speed and power when you need it and ...
This might be the best choice of all.
Getting around Mars on the ground will be the most common mode of travel for settlers, scientists and explorers alike. But what happens when you need to travel longer distances? Or need better views?
For those scenarios, we should look at alternatives to ground transportation and start thinking about air travel.
Getting Around On Mars - Air Travel
Mars has an incredibly thin atmosphere -- only about 0.6% that of Earth (6.1 millibars of surface pressure versus Earth's average sea-level atmospheric pressure of 1,013.25 millibars, according to NASA).
With an atmosphere that thin, you would think you couldn't possibly fly anything on Mars. After all, planes, helicopters and balloons all rely on atmospheric pressure to fly.
More precisely, they rely on differences in atmospheric pressure.
Planes and helicopters create a pressure differential using the shape of their wings or rotors to generate lift. Balloons and blimps use the atomic mass differentials of their gases (hot air or helium) to become 'lighter than air' and float.
So, with such a low atmospheric pressure on Mars, how could you possibly create a pressure differential that would allow a vehicle to fly?
NASA has been working on a few ideas ...
NASA has been testing a flying wing prototype called the Preliminary Research Aerodynamic Design to Land on Mars, or Prandtl-m for short.
It is a fixed wing aircraft that will hopefully be capable of flight in the thin martian atmosphere.
Initial flight tests this last year, with additional high-altitude balloon drops planned for 2016 and beyond, will demonstrate the flight capability and eventually open up extended access for future exploration missions to Mars.
This includes a piggyback ride to Mars on NASA's planned 2022 -2024 mission to demonstrate a working model.
Stay tuned ...
The problem with a fixed wing airplane, like the Prandtl-m, is not just the ability to fly in low-atmospheric pressures -- it's the ability to take off and land.
Airplanes need a smooth, horizontal strip of land, free of obstacles, get airborne.
On Mars, that's not going to happen (unless we get very lucky and find a nice patch of land or get busy and make a runway).
Could we use something that takes off and lands vertically instead? Like a helicopter?
That's the idea behind JPL's Mars helicopter, a proposed add-on to Mars rovers of the future that could potentially travel three times as far as current rovers drive in a typical Martian day.
The helicopter would fly ahead of the rover, checking out points of interest and helping engineers back on Earth plan the best driving route. It would have a limited range, but would recharge from integrated solar panels and be capable of several short 'hops' every day.
The key to its operation, though, seems to be in the shape and size of the counter-rotating rotors.
Designed specifically to operate in the low pressure atmosphere of Mars, these rotor designs could potentially have use back here on Earth as well -- perhaps in alpine search and rescue, or even delivering emergency supplies to disaster sites at high altitudes (like the Nepal earthquakes).
Take a look at this short video clip from JPL to see it in action ...
Balloons and Blimps
Another type of aircraft, which may actually be the best type of all for long distance travel on Mars, is the balloon.
Balloons were actually the first aircraft here on Earth, so why not try them out on Mars as well?
There have been a few proposals to do just that.
Balloons have been flying for decades in Earth's stratosphere (about 6-30 miles above the surface), which, at its upper altitudes, has an atmosphere as thin as that on the surface of Mars.
Conventional stratospheric balloons, though, only stay aloft a few days because of the daily heating and cooling of the balloon. Helium superpressure balloons, on the other hand, could fly for more than 100 days.
Even -- perhaps -- as long as an entire year.
It's research the Ultra Long Duration Balloon project (ULDB) is trying to perfect. In fact, smaller superpressure balloons carrying payloads of only a few kilograms have already flown for as long as a year.
NASA is now applying that same technology toward a balloon for Mars.
The Mars balloon would be deployed soon after a spacecraft enters the Mars atmosphere and would be rapidly inflated from a helium tank as the payload descends beneath a parachute.
After inflation is complete, the parachute and tanks would detach and the balloon and its science payload would float at a nearly constant altitude for the duration of its mission.
Include a couple of propellers, similar to the rotors proposed for the Mars helicopter, and it would be possible to steer the balloon and essentially make it an airship -- a blimp for Mars.
Although it would be slower than a fixed-wing craft like the Prandtl-m, it would still be faster than a ground rover. And it could cover a lot more territory.
Another type of balloon, called a solar Montgolfiere (after the French brothers who flew the first hot air balloon), does not have to be inflated with a light gas such as helium when it drops out of orbit. Instead, the balloon deploys upon entering the Martian atmosphere and an opening at the bottom of the balloon fills up with Martian "air" while the vehicle falls to the surface.
As the 'air' is captured, it would be quickly heated by the sun and the balloon would become buoyant.
Unfortunately, this type of balloon would only last a few hours -- as soon as the sun sets, solar heating of the air trapped inside would end and the balloon would drop to the surface.
Crewed? -- or non?
As you look at the ideas above, you'll notice that there are two common elements. They both are:
- relatively small, and
OK, OK -- the balloons are big, but their payloads are pretty small. Like just a few 'centimeters per side' kind of small.
The point is that to use these designs for long distance -- crewed -- travel on Mars, these concepts will have to be expanded and enlarged.
And that's not just a simple matter of increasing the scale.
When trying to make small prototypes bigger, engineers often encounter a common problem called the square-cube law -- which basically states that as you increase the size of an object, its volume increases faster than its surface area.
(The volume increases by the power of two -- squared -- while the surface area increase by the power of three -- cubed)
For planes and rotor blades, this implies that, as their sizes increase, the load increases much faster than it's ability to create lift. In order to maintain lift, therefore, you need to dramatically increase the vehicle's speed.
In turn, this dramatically increases mass, which means even more lift will be required, which means even more speed.
It can be done -- just look at how this company from Hungary is scaling a tricopter toy drone into a personal 'speeder' (talk about a fun way to get around on Mars!), but simply thinking we can quickly scale planes and helicopters is just not that simple.
Balloons, on the other hand, actually benefit from an increase in size.
As the size of a balloon is increased, the surface area increases quadratically but the lift generated from volume increases cubically.
In other words, bigger balloons generate more lift.
NASA has been studying this exact concept as a possible way to explore Venus (just take a look at the concept vehicle in the image below), so why wouldn't it also become a favorite method for traveling around Mars?
All these vehicles, once scaled up. have the potential to open up the entire planet to the first settlers.
But for extended exploration the best choice may be something completely different ...
Getting Around on Mars - Planet Hopping
What is it?
Planet hopping is a long distance travel method that is unlike anything we have on Earth.
Basically, a 'hopper' takes off like a rocket and begins a ballistic trajectory that shoots it into space, but not into orbit. The planet's gravity pulls the vehicle back down to the surface where it can perform a powered landing, refuel and do it again.
In other words, it can jump up and 'hop' to another spot on the planet-- over and over again.
You can cover large distances this way -- hundred, even thousands of kilometers -- and do it really fast.
There have been proposals for just such a vehicle here on Earth using space planes (see London to New York in 45 minutes). Although technically 'planes', the flight path is essentially the same ballistic path as a hopper. Only the take off and landing profiles are different.
And -- at least from a physics point of view -- it's a pretty simple concept.
Give a ballistic vehicle an initial velocity, shoot it off at the proper angle and it will follow an arc and land at a predetermined point far, far away.
For exploration, however, and vehicles that can carry a crew, the challenge is in the landing -- and in the reusability.
These both can be extremely tricky in a heavy gravity environment like Earth but, as both SpaceX and Blue Origin have demonstrated, clearly doable.
On Mars, with only 38% of Earth' gravity, it should be much easier.
So how do we do it?
The Nuclear Hopper
In his book The Case for Mars, Dr. Robert Zubrin presented the concept of the nuclear hopper, which he called the NIMF (Nuclear rocket using Indigenous Martian Fuel)
Powered by a small nuclear reactor, the vehicle was a robotic exploration craft that used the power of the reactor to compress CO2 from the martian atmosphere, and, when ready, superheat that gas and turn it into rocket exhaust.
It is definitely not the most efficient rocket engine (it would only have an ISP of 260 seconds or so) but being able to refuel itself constantly from just the atmosphere meant it's range was virtually unlimited.
Hop -- refuel -- hop -- refuel -- all the way across the planet.
And during each stop, while the reactor was busy pressurizing the fuel tanks, small, robotic rovers would be dispatched to explore the surrounding area. Once the vehicle was fully pressurized and ready for its next 'hop', the rovers would return and the hopper would jump to the next site.
It was an interesting idea that you don't often hear about in today's exploration plans - probably because of the need to use a Nuclear Thermal Reactor (NTR) to power the vehicle.
There is one group in the UK, however, that has not let that deter them.
A research team from Leicester University and the Astrium space company have proposed a slightly different type of nuclear hopper that could be used for robotic exploration. This one uses a radioisotope thermal generator for the rocket engine rather than the more complex NTR, but the basic operation is exactly the same as the NIMF.
Pull carbon dioxide from the Martian atmosphere and compress it until it is liquefied. When ready to 'hop', pump the gas into a chamber and expose it to the intense heat from the RTG. The CO2 would explosively expand through a nozzle, and -- you have a rocket.
The designer's calculations suggest the thrust achieved could enable a one metric tonne (1,000 kilos or 2,200 lbs) craft to leap a distance of up to 900m at a time.
As Hugo Williams, from Leicester's Space Research Centre said:
The advantage of this approach is that you have the ability to traverse more aggressive terrains but also that you have wider mobility - the possibility of traversing much greater distances than we have with even the very successful rovers
There is one problem with these ideas, though, mentioned it above. At least it's a problem for a non-governmental, non-military settlement program. And it can be described in one word:
Despite the advantages of nuclear power for a Mars settlement, an NTR, or even a radioisotope thermal generator (RTG), would be a problem for a civilian program. Nuclear material is carefully monitored and is not available for civilian use.
And it's not just a regulatory issue.
Protestors would more than likely come out in force if anyone were ever to plan to launch a nuclear reactor from Earth -- at least from American soil. Environmentalists have long worried about how much worse a disaster like the explosion of the Challenger shuttle would be if the rocket also carried nuclear material.
So is there another way to use a 'hopper', but with more traditional fuels?
Absolutely. We call it ....
The Mars Exploration Vehicle
The Mars Exploration Vehicle (MXV) is a single stage spacecraft currently under development here at Mars for the Many -- and it's BIG.
With an outside diameter of 15 meters (roughly 50 feet), it's bigger than anything that's ever landed on Mars.
The MXV is an all purpose vehicle designed to get the first crews and settlers to Mars. But it's also designed to be reusable -- to launch crews and supplies back into orbit and to transport exploration teams to regions of interest far away from a main settlement.
Once on the surface, or from a refueling depot in orbit, the MXV could be used as a 'hopper' to explore other regions of Mars and then return to the settlement's main base.
It wouldn't have the range to explore the entire planet in one jump, nor would it be capable of refueling itself from the martian atmosphere once on site like the NIMF, but it could refuel at the base, hop to an area of interest and then hop back.
And once back at the main base, it could refuel, hop to another location, and come back -- and do it over and over again.
Current designs predict it could travel up to 2100 km and back in one trip.
To extend that range, the MXV is also capable of reaching low Mars orbit, but there it would need to be refueled if you wanted to go anywhere else on the planet besides back to the main settlement.
Want to know more about the MXV?
Get instant access to a free copy of the MXV datasheet with exclusive information straight from the designers.
It's the ultimate planet hopper -- and one of the reasons a refueling station in Low Mars Orbit (or perhaps on Phobos) is one of our 10 'must have' technologies for settling Mars.
Simply put, with the ability to refuel in orbit, the entire planet becomes accessible.
Which makes the MXV a vital part of our 'settle - then explore' strategy for Mars -- and a key component of getting around on Mars.
How do you think we will get around on Mars? Share your thoughts in the comments below. And if you like what you saw, please, share with your friends.