Will Vehicle Energy Use Increase or Decrease with Automation?

There is an ongoing debate within the transportation analysis community over whether automated vehicles will reduce energy use and greenhouse gas emissions, or increase them. On the one hand, automated vehicles can both drive more efficiently and be designed to be lighter, saving energy. However, the convenience of not having to pay attention on the road may lead people to use them more, increasing energy consumption. Which effect will tend to prevail?

An interesting new paper by Wadud et al. (2016) does an excellent job of trying to answer this question. They quantify the range of energy impacts of automated vehicles across 12 different effects, including eco-driving, platooning, and right-sizing. The work builds upon previous research in this area by Brown et al. (2014), Morrow et al. (2014), and a few others.

One of the most innovative things Wadud et al. do is provide a novel approach for estimating the increase in travel demand using a travel cost elasticity relationship. That is, they postulate that the change in distance a vehicle will drive annually depends on the ratio of total cost of vehicle ownership before and after automation, raised to an exponent called the elasticity.

While speculative, it offers a defensible way to estimate the increase in travel usage if the costs of insurance, fuel, and importantly, people’s time, decrease with automation. I applaud them for attempting to put more quantitative bounds on the potential of automation to increase or decrease transportation energy use.

To examine overall effects, they develop four scenarios that emphasize different groups of features, and conclude that future energy use may range from about a 40 percent decrease to a 100 percent increase relative to today. Both the studies by Brown et al. and Morrow et al. reached many of these same conclusions, though their estimated range of changes were higher.

How to reduce energy use with automation

However, I think that the study misses some important synergies that could further reduce energy use beyond what is captured in their analysis. In particular, they only estimate the effect of shared mobility on vehicle usage (vehicle kilometers traveled or VKT), without considering its potential to enable greater use of electric vehicles, which could result in large energy savings.

While they discuss the potential for automation to enable greater use of alternative fuels (including electricity), they stop short of making any quantitative estimates in this regard.

This is a significant shortcoming. In my paper published last year in Nature Climate Change, I focused on this effect, and concluded it has the potential to be strong because it is coupled with lower total operating costs, driving potentially large adoption.

Smaller (one- and two-seat) vehicles could further reduce costs, making shared electric vehicles even more appealing. Because electric motors are several times more efficient than gasoline-powered engines, it could result in significantly lower energy use per VKT.

Electricity already has lower greenhouse gas emissions per unit energy compared to petroleum, and potential policy changes encouraging more renewables and less reliance on fossil fuels, such as recent California legislation or the federal Clean Power Plan, could further reduce emissions.

Therefore, shared electric vehicles represent a very important way to lower greenhouse gas emissions from the vehicle transportation sector in a way that simply reducing petroleum use cannot. My study concluded that these vehicles combined with a greener grid could still result in lower greenhouse gas emissions even if travel demand due to vehicle automation were higher.

Do you think that automated vehicles will increase or decrease average energy use? How about greenhouse gas emissions? Share your thoughts in the comments section below.

Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.

How Much Energy is Needed to Send One Million Humans to Mars

While NASA is planning to send the first human explorers to Mars sometime in the 2030s, several non-governmental organizations, including at least one private company (SpaceX), are looking at more aggressive timelines starting in the 2020s. They are also setting a higher bar: rather than sending astronauts for a limited-duration mission, the goal is establishing a permanent human settlement.

My interest is in identifying new technologies that could be disruptive, and sending large numbers of people to Mars definitely qualifies. I have just completed a study entitled Energy and Resource Impacts of an Earth-Mars Human Transport System, which has been submitted for journal publication.

It describes the model I used to simulate the spacecraft and associated infrastructure needed to send one million people to Mars over the next century. In addition to estimating the mass, volume and numbers of spacecraft required, I calculated the energy and resource needs of such a system, in order to ensure that it would not put undue strain on resources both on and off of the Earth.

Mass estimates for sending humans to Mars

The mass and energy requirements overall are actually quite modest compared with what is consumed today globally. Building the fleet of spacecraft would require about 17 million tons of material, equivalent to 10 years of U.S. aluminum production, but spaced over about 100 years. The required propellant, or rocket fuel, needed to power these spacecraft would amount to approximately 100 times this mass.

I assumed rockets would use a combination of hydrogen and oxygen, or methane and oxygen, as propellant, which would mainly be produced on the Moon or Mars. The lower gravity of these locations would allow for large mass savings compared to making everything on Earth.

However, the choice of propellant is driven by available resources. There is very little carbon on the Moon, but it is likely that there is a lot of water ice. We could use some of that water for human needs, but convert most of it into hydrogen and oxygen for rockets, as well as oxygen to breathe. Methane and oxygen would be made from the abundant carbon dioxide and water ice on Mars.

Energy requirements for sending humans to Mars

My report estimated the energy required to manufacture spacecraft and propellant. Cumulative energy requirements would be 55 exajoules, or about four years of U.S. electricity consumption, again, a modest amount when spread over the course of a century. I even calculated the amount of solar photovoltaic (PV) capacity needed to generate this electricity, and found it was equal to 13 times the current global annual installation rate. Most of the solar power would be installed on Mars, not the Earth. So the impacts on Earth’s energy resources are small.

Limited water on the Moon

The study also found that between 18 and 78 percent of the water ice on the Moon might be depleted in providing rocket fuel for large spacecraft. This is a real problem. The water – if it is there at all – has probably been on the Moon for billions of years. If we build a base on the surface and use it to drink and bathe, we can recycle it almost indefinitely, but turning it into rocket fuel removes it permanently to space. It is irrecoverable.

As a consequence, the report warns that alternatives must be identified and explored early in the settlement process, to avoid undue resource depletion. One approach would be to build smaller, more efficient spacecraft. Another would be to find other sources of water, such as asteroids. A third way would be to develop alternatives to rockets, such as building a space elevator.

Space elevators as a propellant-saving alternative

A space elevator would consist of a cable extending from a gravitating body’s surface to more than 20,000 kilometers into space. Small electric “cars” would grip the cable and slowly ascend from the ground into orbit, where they could transfer their cargo to waiting spacecraft.

It sounds crazy, but this can actually be built on the Moon or Mars with existing technology. Building elevators on both bodies could reduce propellant energy needs by 69 percent. Propellant supplied from the Moon would be reduced by 51 percent.

Future challenges: Human settlement on Mars

To sum things up, many of the model’s parameters are not well constrained, so the results have a large amount of variability. There are still many questions, such as the assumed rate of population growth in the Mars settlement, the rate of people returning to Earth, or the masses of the spacecraft.

Once we see detailed spacecraft designs, we can constrain some of these parameters better, but other parameters, such as population growth, will have to wait until a Mars settlement begins to take shape to be better defined.

What do you think about the prospects for sending large numbers of people to Mars or other places to live? How will such developments change transportation and human culture? Share your thoughts in the comment section.


Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.

Space Mining: Building the Space Transportation Infrastructure

A commercial space transportation industry is growing rapidly. Private companies are competing for launch contracts for government, military and private customers, and prices are falling quickly. NASA is turning its human spaceflight attention from low Earth orbit to the Moon and beyond. Several companies are even thinking about building settlements on Mars.

All of these activities will require physical infrastructure in the form of spacecraft, space stations, refueling depots, and so on, but where will this hardware be built?

Initially, of course, on Earth – but it is energy-intensive and costly to lift anything out of Earth’s deep gravity well and into space: a rough gauge is about 10 kilograms of propellant for every kilogram of material; when one factors in the mass of spacecraft equipment such as propellant tanks, engines, communications, etc. the requirement is closer to 30 kilograms of propellant per kilogram of useful cargo. Would it make more sense to build things in space in the first place?

Indeed it would. Some forward-looking companies including Deep Space Industries, Planetary Resources, and Moon Express are examining the business case for mineral mining of asteroids and the Moon.

There are several advantages to doing this: 1. materials in space are abundant, 2. lower gravity means moving material from origin to destination in space requires far less energy than moving it from the Earth’s surface, and 3. many materials on Earth are running out, and mining damages the environment; both these problems would be solved if materials are mined in space.

A cosmic cornucopia

More than 12,000 near Earth asteroids have been discovered within easy reach of the Earth-Moon system, and it is estimated that more than 2 million asteroids may exist in orbits reasonably close to Earth. Many of these are rich in metals such as iron and nickel, and possibly precious metals like platinum. Others are endowed with water ice or other “volatiles” like ammonia or methane. All probably have rocky materials containing silicon, aluminum and oxygen.

It is estimated that every element available in the Earth’s crust is also present in asteroids, and possibly in higher concentrations since heavier elements on such a light body as an asteroid do not sink to the core as they do on Earth.

In November 2015, the U.S. Congress passed – and President Obama signed – the Commercial Space Launch Competitiveness Act, making it legal for U.S. companies to appropriate materials in space for commercial purposes. (It also uses the term “commercial space transportation industry” to describe these activities.)

This landmark legislation firmly opens the door to commercial space mining, paving the way for growth of commercial space activities.

Building infrastructure in space

Extracting pure metals from a metal-rich asteroid appears to be straightforward in space. The Mond process uses carbon monoxide to extract pure nickel and iron from asteroid material. The resulting product is a liquid that can easily be separated from other material, and the pure metal recovered by mild heating.

The carbon monoxide can be recycled indefinitely to extract more metal. The metal, which can be recovered as a powder, can then be fed to a 3D printer to fabricate parts of any desired shape.

3D printing has already been demonstrated in a zero gravity environment of the International Space Station, and recently a space mining company demonstrated the first 3D-printed object made with meteorite material. With a bit more effort, other metals such as aluminum can probably be recovered, opening the door to lightweight materials and alloys needed to build a wide variety of structures in space.

The promise of low-cost access to space

Even if complex machinery cannot be fabricated in space, many massive parts probably can. With a suitable assembly environment (perhaps inside a spinning spacecraft to simulate the effects of gravity, which might make assembly easier), either run by tele-operated robots or actual humans, one can imagine large structures being built in orbit.

The tremendous mass savings of such an endeavor could make space transportation much less expensive. Together with in-space propellant depots supplied from off-Earth resources, reusable Earth-to-orbit launch capability on Earth currently being pioneered by several companies, and a sufficient supply of raw materials from asteroids, the cost of space access could approach the cost of energy required to lift a person into orbit, which in the long term might be as little as 20,000 US dollars. Water, oxygen, and even food could be grown in space.

An ecological boon on Earth

Space mining could become so cost-effective that mines on Earth would shut down, along with their attendant pollution problems. In space there are no sensitive ecosystems to pollute. Though we should still be careful about generating toxic hazards in space, in principle it is easier to segregate pollution away from human activities, and there is vastly more room in space to put everything, unlike on Earth.

With sufficiently low-cost materials from space, we could ban all terrestrial mining, and focus instead on ecological restoration, relegating extractive industries to the heavens.

Asteroid mining: Turning threats into opportunities

The technology for asteroid mining shares much in common with detecting and diverting asteroid threats to Earth. The impact of a large (1 kilometer) asteroid could cause severe climate impacts globally. While large asteroids are easier to find and track, we are currently limited by our ability to detect threats from smaller asteroids (100 to 300 meters) that could still cause tremendous destruction if they impact cities on Earth.

Better detection equipment – probably space-based – will be needed, along with techniques to move their orbits enough to avert the threat. A timely example is the 27 million-ton asteroid Apophis that will pass with 30,000 km of Earth – below the orbits of geostationary satellites – in 2029, and may impact Earth in 2036 without intervention. Fortunately, we can leverage this technology to identify asteroids of high economic value, and even move their orbits to allow for the safe return of material to the Earth-Moon environment.

Thus, money spent on planetary protection could in principle be self-financed, if the material from some asteroids are recoverable and sold at profit on Earth or in orbit.

What advances do you think space manufacturing could engender? Please share your thoughts in the comment section.


Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.

Space Debris and Flying Garbage Trucks

What happens to orbiting satellites, spacecraft or other materials when they reach the end of their useful life? Sadly, they become space “junk” and may pose a serious hazard to other spacecraft for years, before eventually burning up in the atmosphere. As the use of space grows, so will this problem. What can be done to fix it?

For the past several years, about 80 rocket launches annually place an average of 300 metric tons, or 300,000 kilograms, of spacecraft into orbit around the Earth. As of 2008, there was more than 5,500 metric tons of orbiting space debris, with more accumulating each year. The problem is that the debris does not remain whole, but often fragments into tiny pieces due to accidental collision or deliberate destruction.

There are more than 20,000 objects larger than 10 centimeters in diameter, and over 100 million objects smaller than 1 centimeter. While NASA keeps track of more than 500,000 space objects, the U.S. Air Force actively tracks only 23,000 large objects (including debris) that pose the greatest threat to active spacecraft. To increase tracking capacity, the U.S. is developing a next-generation “space fence” that will track roughly 200,000 objects using high-resolution radar.

Solutions to deal with space debris

Because of their high speeds (several kilometers per second), even very small objects, such as paint flecks can damage or disable operational spacecraft. Currently, the main strategy for dealing with space debris is to avoid it. Tracking systems issue warnings when debris is likely to venture too close to operational spacecraft, which – with enough forewarning – can change their orbits slightly to avoid collision, a process known as “debris avoidance maneuvers.”

For human-occupied spacecraft such as the International Space Station, people can retreat to safer parts of the station, or, if necessary, evacuate entirely. For debris too small to track, spacecraft are designed to withstand impacts via protective outer layers, but it is no guarantee.

One of the greatest concerns over increasing levels of space debris is the danger of a “runaway” effect. First proposed by NASA scientist Donald Kessler in 1978, the “Kessler syndrome” is a hypothetical situation in which debris collides with itself or operational spacecraft, producing new debris whose numbers grows exponentially, until the process becomes unstoppable.

The result would render portions of orbital space too dangerous to use. Such an event was depicted dramatically in the 2013 movie “Gravity.” Avoiding such a situation is of paramount importance to the future of space transportation.

Flying garbage trucks

The alternative is to actively remove space debris, by redirecting their orbits so that they enter the Earth’s atmosphere and harmlessly vaporize (unless they are so massive that they remain intact until impact). Among the methods proposed to accomplish this include indirect (ground-based) and direct (space-based) approaches.

More than one group is investigating the use of ground-based lasers. Shining an intense laser on an object can create a jet of gas that will change its velocity. The object’s speed only has to decrease by about one percent for it to slow down enough to re-enter the atmosphere. However, this technique only works for smaller objects. NASA estimates that a five-kilogram object could be safely removed using a multi-kilowatt laser over a two-hour exposure.

Methods of contacting and removing space debris include sending “janitor” spacecraft into orbit to attach to an object and pull it back into the atmosphere. Multiple approaches to this concept exist. Another method involves releasing a cloud of inert gas in the vicinity of multiple debris targets; the resulting aerodynamic drag would slow them down enough to re-enter the atmosphere.

Still others are exploring the use of lightweight sails to create just enough drag from the thin atmosphere present at orbital altitudes to achieve re-entry.

While such techniques would not be inexpensive – scientists estimate that a laser system might cost several million dollars to build and operate – satellite insurance currently costs between 5 and 15 percent of a satellite’s value, or tens of millions of dollars each. If collision risk could be lowered through these approaches, it seems that the money is there to pay for it.

Space recycling

Some people are rethinking the idea of cleaning the skies of space junk, arguing that such objects may be more valuable if they stay in orbit, but can be re-purposed. The U.S. Defense Advanced Research Projects Agency is sponsoring the “Phoenix” project to reclaim intact hardware from non-functional satellites for re-use. Others are looking at extracting precious materials directly to use in space-based manufacturing.

Each kilogram launched into space costs an average of 20,000 US dollars, not including the cost of production on Earth. The more than 5,500 metric tons of debris currently in orbit therefore has a theoretical value exceeding 110 billion US dollars. Such materials consist of highly-refined metals, high-performance lightweight composites, and electronics containing precious elements. Examples of materials that can be recycled include aluminum alloys and other metals. Kevlar, a high-strength organic polymer used in bulletproof vests as well as space applications, is five times stronger than steel and can be recycled into new fiber.

However, space materials must meet several performance criteria, including dimensional stability (ability to maintain size and shape under large temperature swings that occur in orbit), mass efficiency (as light as possible without compromising structural integrity), durability (ability to withstand the harsh space environment, including radiation, atomic oxygen and vacuum), and strength or flexibility (the ability to resist or bend under force without breaking).

So it is unlikely that much material, if it could be captured, would be re-used, but if even a small fraction of this material were re-purposed for space-based manufacturing such as 3-D printing, it could be worth a lot of money.

What do you think about the threat of space debris and approaches for removing it? Share your thoughts in the comment section.


Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.

Fueling Stations in the Sky

Fast forward a few years from now: Several space companies have successfully and competitively reduced the cost of launch into low Earth orbit (LEO) by more than a factor of 10. The commercial space industry is thriving. There are soaring numbers of satellite launches, astronaut ferries to and from space stations, and forward movement in the human and robotic exploration of the inner solar system. How might all these spacecraft get around? The answer: Fueling stations in the sky!

As discussed in a previous blog post, the cost of sending propellant up into space along with a spaceship is very expensive for missions with destinations well beyond LEO, because the mass of propellant is so much greater than the spacecraft itself. For a journey to Mars, the ratio is roughly 10:1, but where else can this propellant be obtained than the Earth?

Depending on its chemistry, most common rocket propellants only need simple starting ingredients for manufacture: water, carbon dioxide and perhaps nitrogen. Water can be turned into hydrogen and oxygen, a very effective rocket propellant. (Note that in space, an oxidant – usually oxygen – must be supplied along with fuel, because there is no air in which to burn. Thus all rocket propellants are comprised of both fuel and oxidant.)

Adding carbon dioxide could provide a wide range of hydrocarbon fuels, including methane, methanol, ethylene – even kerosene. Most are familiar fuels on Earth, and they can also be used in rockets. Nitrogen provides still other possibilities, including hydrazine (a fuel) and nitrous oxide and nitrogen tetroxide (oxidants). The main issues are complexity of the chemical conversion process, energy requirements and storability.

It turns out that at least some of these basic chemicals are available on the Moon, Mars comets and some asteroids. The idea is to mine the raw materials in one or more of these places and manufacture propellant in space, then deliver it back into Earth orbit. Once a spacecraft arrives in orbit, it “tanks up” at a waiting fueling station and is on its way.

While at first glance it might seem like a crazy idea to ship propellant millions of miles across space, one has to realize that space transportation is VERY different from transportation on Earth. Because there is no friction in space, it often requires less energy to ship something a long distance, if the material originates on a body with low gravity relative to the Earth.

Energy requirements for future spaceships

For instance, the Moon’s gravity is about 1/6 that of Earth, meaning someone who weighs 200 pounds (about 90 kilograms) on Earth would only weigh 33 pounds (15 kilograms) on the Moon. Getting a spacecraft off the Moon and into orbit similarly requires about 1/6 the energy (technically, change in velocity or “delta-v”) as getting it into orbit from the Earth.

While it does require more energy to get back to LEO from lunar orbit, the overall energy requirement is roughly half that of launching it from the Earth’s surface. Serious companies have now proposed exactly this idea as a way to provide commodity-priced hydrogen and oxygen propellant for future spaceships.

While it requires almost as much energy to send material back from Mars as it does to launch it from Earth into orbit, making propellant on Mars for the return trip still makes a lot of sense, again due to the lower gravity (38 percent of Earth). So it is likely that along with fueling stations in orbit around the Earth, there will be stations on the surface of Mars or in Mars orbit to service routine spaceflight departing from (or refueling at) the planet.

Sending material into Earth orbit from asteroids or comets might require even less energy, because the gravity of these objects is almost negligible. If orbiting objects with the right composition can be found and reached, we might be turning them into propellant (plus other products – asteroids may also contain valuable and even precious metals, as well as rock minerals and perhaps volatile chemicals), ushering in a thriving space propellant logistics industry. The next “oil boom” would not be based on oil, and it may well be in the sky!

What do you think about the idea of fueling stations in orbit or on other planets? Share your thoughts in the comment section below.


Please note that this article expresses the opinions of the author and does not reflect the views of Move Forward.