Hybrid Solar Electric Cars : Refueling With The Sun

What if you could charge an electric car simply by parking it in the sun? I’ve been keenly interested in the Tesla Model S, and was curious if it would make sense to incorporate solar cells into the vehicle body. I did the math on this, and was a bit surprised at the results.

Updated with footnotes below to address reader questions and critiques.

Using the Tesla Model S as an example, I estimated how much upward facing surface area is available for solar cells (about 6 square meters, assuming solar cells are crammed into every available space, plus another 2 to 4 square meters if the side panels are also lined with solar cells, also useful for collecting light when the sun is low in the sky). I used 8 square meters as an estimate of how much space is available including both upward and side facing solar surfaces.

Some readers commented that the area estimate is a bit high. I assumed that designers would be aggressive in maximizing the usable solar area.

Average solar insolation at sea level is 850 Watts per square meter. The most efficient solar cells that are commercially available convert 24% of this energy into electricity. Most of the southwestern US receives about 5.5 to 6 sun-hours per day on average. With that, we can estimate the power production of the vehicle integrated array by multiplying collecting area, efficiency and sun-hours to get between 9 and 10 kilowatt hours per day.

If we use higher efficiency solar cells (the current record is about 40% efficiency), we could boost this to almost 17 kilowatt hours per day. (Ultra efficient cells like this are quite expensive, and are currently limited to special applications such as powering space vehicles, however they’re coming down in price).

Output could be boosted by placing a flat, slide out solar panel or trailer in the space above or below the battery tray. This would slide out into a parking space behind the vehicle, and would double the collecting area and therefore daily charging potential (it would be straightforward to make this an expandable panel, like a dining room table, so it could be stowed compactly, but span out to cover a standard parking space, and maybe also pivot to the optimal collecting angle).

This is also an easy way to add solar to a car without embedding solar cells in the car body, perhaps a good first step (embedding solar cells in the car body involves a lot of design and technical tradeoffs whereas the solar trailer is easy, and it would be protected in its storage space).

The Model S consumes about 0.28 kilowatt hours per mile, so a vehicle mounted solar array would generate an average of about 35 miles per sunny day or 12,700 miles per year (using modules rated at 24% efficiency), well in line with average commute distances.

Note: this is a rough estimate, based on annual averages. Actual output will vary depending on the time of year, weather conditions, vehicle geometry, etc. So treat this as a rough estimate. Your milage may vary, as they say.

There are a number of benefits to integrating solar power into an electric vehicle, among them:

Range extension : driving range could be extended 10 to 15% with a vehicle like the Model S.

Low carbon power : when recharging an electric vehicle, you’re drawing from carbon fueled power plants. By enabling the vehicle to generate most or all of its power via integrated solar panels, you can further reduce your carbon footprint.

Off grid charging : wherever there is sunlight, you have a charging station. Next time you go on a weekend camping trip, you can pick up 50 to 100 miles of range just by parking your car in a sunny location.

It would also be interesting to find out if its possible for the Model S to operate in a slow speed, low acceleration solar only mode. Aerodynamic drag increases in proportion to velocity cubed. Acceleration could be limited to match the power output of the solar cells. Not a sporty ride, but if you can pull out your solar trailer and limp along to the nearest charging station or power outlet, its better than calling a tow truck.

What do the economics look like? At an average of 9-10 kilowatt hours per day, the vehicle would generate roughly $1.00 worth of electricity per day that would otherwise be purchased from the grid (I assume $0.10 per kilowatt hour as a rough number, about right for the California market). At current solar cell prices, it’s cheaper to buy electricity from the grid, however prices continue to drop rapidly, so by the time something like this reaches the market, that may change.

As an option, its pretty attractive for the reasons mentioned earlier. Being able to charge your car by simply parking it in the sun would be super convenient. Add the peace of mind of knowing that if you run out of juice, you can recharge anywhere or limp along to the nearest power source, and that seems like an option many EV owners would go for.

The math looks interesting today, and should only improve, for example when ultra high efficiency solar cells become cost effective, or new lithium-sulfur batteries slash vehicle weight and power requirements.

The important point is that it’s not necessary to design a car that runs solely on solar power, but simply generates enough power on average, to offset typical daily use. Then all you’d need to do is park your car in the sun to keep it topped up and ready to go (and tap into the grid only when you need to).

Performance Estimates Recap

Model S covered with 24% efficient cells (Sun Power used as example), approx 8 square meters of usable solar surface area via combination of upward and side facing surfaces, 5.5 to 6 sun hours per day. 9 to 10 kilowatt hours charge per day, 32 to 35 miles per day, approx 12,500 miles per year.

Pull out, expandable solar trailer, sized to cover a standard, small parking space (8' by 18', or approx 13 square meters). 14.5 to 16 kilowatt hours per day, 52 to 57 miles per day, approx 20,000 miles per year.

Combined solar-hybrid vehicle and pull out solar trailer. 23.5 to 26 kilowatt hours charge per day, 84 to 92 miles per day, approx 32,500 miles per year.

Reader Q&A and Critiques

Q: How did you calculate the surface area of the vehicle?

I used specs from Tesla Motors to get the physical dimensions of the vehicle (roughly 5 meters long by 2 meters wide). I subtracted a meter from the vehicle length to account for windows (in fact there are solar coatings for windows that are 10% efficient, but I treated the windows as unusable space. I assumed that at least part of the door and side panels could be covered in solar cells. So I went with 8 square meters is a safe estimate for the available area (adjust your estimates as desired). If a manufacturer actually builds this, they’ll almost surely adjust the geometry to maximize usable area.

Q: How did you calculate the power output and daily range potential?

This is pretty simple to do. The Earth’s surface receives, on average 850 Watts per square meter. The National Renewable Energy Laboratory publishes maps that depict solar insolation in terms of sun hours per day or kilowatt hours per day. Most of California gets 5.5 hours/day on average. To calculate average daily output, multiply surface area by 0.85 by solar cell efficiency (24% for the best Sun Power modules) and then by sun hours per day. That works out to 9 kilowatt hours per day.

The Tesla Model S consumes 0.28 kilowatt hours per mile, so that works out to 32.14 miles.

Q: How can you increase charging potential further.

There are three ways to do this. One is to modify the vehicle geometry to maximize surface area (make it a bit wider and/or longer), not much room to work with there. Another is to use ultra high efficiency solar cells, such as those used in satellites (expensive, but they’ll get cheaper). The simplest way is to store a removable solar panel or trailer that slides out from a compartment above the battery pack (which runs along the entire length of the underside of the car). Then when you park your car, you’d pull this out into the space behind you. This would double the collecting area and therefore charging potential (to about 60 miles a day, 80-90 miles per day if vehicle and trailer based charging is in use, more than most people drive).

Q: Wouldn’t the car get incredibly hot?

No more so than a car with a dark colored paint job (a black car converts nearly 100% of the light striking it into heat). On a hot sunny day, you could remotely turn on your A/C before you head to the car. The energy cost of running the A/C for a few minutes to cool the car down will be covered by the power generated by the solar cells if the system is designed right. The system could also run a simple fan to vent outside air to prevent overheating.

Q: Solar panels are fragile, this can’t be done, hand wave, hand wave, hand wave.

This article is about back of the envelope calculations to show that this can be done, not a proposal for a specific implementation of the idea. There would be lots of technical and design considerations to deal with in building an actual vehicle (such as what type of coating to use to protect solar cells), but the basic math in terms of how much power can be generated and the driving distance that equates to is sound and is derived from solar modules that are shipping commercially today. A pull out solar trailer is probably the place to start with the Model S as it sidesteps the issues associated with integrating solar cells into the vehicle body.

Next Story — The Big Book of Ideas — Black Rock City Reimagined
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The Big Book of Ideas — Black Rock City Reimagined

If you could design Black Rock City, what would you build?

Mother — by Sergio Bianchi, Simone Fracasso, Chiara Pellegrin (Italy)

That’s the question a group of long-time Burning Man participants posed last fall. Thousands of people from nearly every country in the world expressed an interest in submitting their ideas.

The result of this unofficial design competition is a free ebook of city plans from contributors in over 30 countries. These designs, ranging from rough sketches to beautifully detailed renderings, explore the concept of Black Rock City as an imagined space, from straightforward adaptations to the current plan to completely new and science fictional cityscapes.

Download and share your free copy today!

Next Story — We Need A National Police Safety Board
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We Need A National Police Safety Board

Law enforcement agencies could learn a great deal from aviation. Traveling by air was not always as safe as it is today. It used to be pretty dangerous. See the graph below which shows the fatal accident rate for general aviation from 1938–2009. While some of the improvements in air travel safety are the result of better technology, much of this is due to improvements in pilot education and the adoption of safety culture throughout the aviation system.

General aviation fatalities per million hours flown (1938–2009), logarithmic scale, source AOPA [1]

The graph above charts the number of general aviation fatalities per million hours flown from 1938 until 2009 (source: AOPA), an accident rate that has declined by 90% and continues to steadily improve to this date. Note that this plots the accident rate for small aircraft, not commercial airlines (which are even safer and have shown even greater improvements). What you can clearly see in the chart is a steady downward trend in the accident rate that has remained remarkably consistent over decades.

I’d like to show you a similar chart of police related injuries or fatalities per 911 call, but I can’t because we don’t collect this data, at least not in an organized and consistent way like the national aviation system has been doing for decades.

Most aircraft accidents are caused, at least in part by pilot error. This isn’t to say that the pilots involved are careless, just that they failed to avoid a known situation or chain of events that led to the accident. For example, flying into bad weather with inadequate training or equipment is a common cause of mishaps in small aircraft. (Talk to small aircraft pilots about the hazards of “scud running”).

The National Transportation Safety Board was formed in 1926 with the primary task of investigating the cause of civil aviation accidents. Its job is to investigate the cause of every serious aviation mishap, everywhere in the country. Not blame, but investigate and document what happened so people could learn from the mistakes of the people ahead of them. We need something like the NTSB for law enforcement, and the reason for this is pretty simple. What gets measured generally gets managed.

Citizen-police interactions can be measured in a similar way, from the start of an interaction with law enforcement personnel until the end of the encounter. As with air travel, the goal in policing should be as few deaths and injuries are possible per trip/encounter, with a clear understanding of which scenarios are risky, and learning about how those risks can be mitigated.

One of the morbid habits that many pilots share is reading NTSB accident reports. It’s a good way of learning what NOT to do, or what TO do. Sadly, the reports are filled with examples of obvious bad ideas, like taking off in bad weather when you are not instrument rated or proficient. But they also contain gems of information that will save your butt should you find yourself in a similar situation.

One of the most interesting findings in the investigation of aviation accidents was that many mishaps could have been avoided if subordinate crew members had spoken up in the lead-up to a wreck. Co-pilots and navigators would often defer to the captain even when he was making an obvious mistake. The Tenerife runway collision was a prime example of this. United Airlines flight 173 which crashed en route to Portland due to fuel exhaustion was another. The lessons learned from this and other incidents led to the development of Crew Resource Management, a system where everyone was expected to cross-check each others work, and where subordinate crew members could override more senior crew without fear of punishment.

How would an NTSB-like system for police operate? It should probably focus on collecting two different types of information: data about routine operations, along with data from investigations into incidents that resulted in the death or injury of someone during a police encounter.

Data from routine operations, which could be collected automatically from dispatch systems, would record information such as the location, date, time and duration of a police interaction, the reason for the encounter, the outcome, along with basic information about the officer and individuals involved. Statistics like this will reveal a lot about overall operational efficiency and safety, and allow researchers to identify patterns and problem areas to focus on. Consistently measuring performance across agencies will also allow law enforcement agencies to see how they are performing relative to peers.

Following incidents where an individual is seriously injured or killed during a police encounter, the safety board would investigate the series of events leading up to that incident and publish its findings. The NTSB investigates every serious aviation mishap, not just fatal incidents, so the fact that there is an investigation does not imply wrongdoing, it is just a routine process. The purpose of these investigations is not to assign blame, but to understand what happened, why it happened, and if the incident was avoidable.

A federal agency that does this makes sense for a number of reasons. First and foremost, it would enable data to be collected in a systematic and consistent way, and would also insure that incident investigations are conducted by personnel who are not affiliated with the parties involved. This agency, call it the Law Enforcement Safety Board, would not be anti-cop, but pro-safety (in the same way that the NTSB’s overall mission is accident prevention). Federalizing this would also relieve local law enforcement agencies (especially those in smaller communities) of the financial burden of conducting routine investigations.

Most aviation accidents are caused by human factors. Sometimes gross negligence is involved, but often it is more complicated than that. Air France Flight 447 is an example of an incident where a series of unlikely events led to a catastrophic outcome. In this accident, the aircraft lost its airspeed indicators (a critical instrument), which disabled the automatic pilot and automatic safety features (which prevent the pilots from putting the aircraft into an unsafe attitude). The pilots thought the aircraft was going too fast, and thought the safety system would prevent them from putting the aircraft into a dangerous attitude, and inadvertently went into a stall and crashed. If the pilots had been better trained on how to deal with this scenario, the crash would have been avoided, but until this incident the risks of this happening were underestimated.

It would not be surprising to discover similar situations in police encounters that go bad, as well as to learn from strategies that work well. The main question investigators should be asking when someone is killed or injured by police is “could this have been avoided without putting the officer or the public at risk?”

Safety culture in aviation is not about “good enough”, its explicit goal, especially in commercial aviation, is zero fatalities and zero injuries. You would never hear the CEO of an airline say that as long as we only lose one planeload of passengers a year that’s OK. Would you fly that airline? Of course not.

We should expect a similar focus on safety from the law enforcement agencies our taxes pay for.


[1] General Aviation Fatalities (1938–2009), AOPA, https://www.aopa.org/about/general-aviation-statistics/general-aviation-safety-record-current-and-historic#gaaccidents

Next Story — Traveling To Mars? Just Add Water!
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Traveling To Mars? Just Add Water!

An artist’s depiction of Ernst Stuhlinger’s “sun ship” which combined solar thermal powerplants and cesium ion drives for propulsion. Image credit: Frank Tinsley/American Bosch Arma Corporation, 1954

Since the Moon landings, we have eyed Mars as the next step in manned space exploration. In the nearly fifty years since, it still remains a distant location. We have sent many robots there, but sending people is a far more difficult goal. The challenge of reaching Mars is more one of logistics than technology. How do you keep people alive for years in space? How do you launch enough material to do so? at a reasonable cost? What if the key to reaching Mars and other worlds is to rethink what a spacecraft is made of? In short, what if a spacecraft was made mostly of water?

The Apollo program probably would not have happened if it were not for Lunar Orbit Rendezvous. Little known by outsiders, this technique was developed by NASA engineers Tom Dolan and John Houbolt. It made the difference between a mission that was just barely achievable given the technology of the day, and one that would have required a rocket so huge and so massive that the costs would probably have sunk the program. The breakthrough in LOR was logistical, not technological, and that’s an important point because the plans on the books for manned missions to Mars and beyond all have the same fundamental weakness that early moon mission designs had.

What LOR did was to replace one big rocket ship that flew all the way from Earth orbit to the lunar surface and back (as depicted in 1950s era sci-fi), with three smaller craft: the command/service module, which only flew from Earth orbit to lunar orbit and never landed and the lunar module, with its disposable descent stage. Essentially what this did was break one big craft into three smaller craft which each flew a segment of the trip and then were discarded. This greatly reduced the mass of the entire system, which in turn, reduced the size of the rocket required to launch them all from Earth’s surface to orbit at the start of the mission. As it was, the Saturn V was a giant rocket! If they had tried to do the mission with one large spacecraft, as envisioned in 1950s sci-fi films, the launch rocket would have had to be several times bigger, well beyond the realm of possibility then or today.

Moon’s surface as imagined by famous space artist Chesley Bonestell, early 1950’s. The same spaceship design was used in the movie “Destination Moon,” for which Bonestell was a technical advisor. A “half Earth” hovers over the mountains. Credit: http://www.faculty.virginia.edu/rwoclass/astr1210/moontop.html

Manned missions to Mars have a similar logistical problem. To travel from Earth orbit to Mars and back requires a larger change in velocity (delta v) than a trip to lunar orbit, a challenge in its own right. Further complicating the situation is the requirement to provide enough life support and supplies (consumables) to keep the crew alive and comfortable for roughly two years (as compared to two weeks for an Apollo mission). As a rough example, consider a 6 person crew on a mission to the Martian system. This will require roughly two years, so figure about 800 days to include some reserve margin, and about 5 kilograms per day per person allotment for water, oxygen, and food (which is also mostly water). That works out to 24,000 kilograms, or about 24 tons, just for consumables. And here’s why that’s a big problem.

That material is deadweight that has to be pushed along by yet another rocket motor and its propellant. In rough numbers, you end up needing ten to twenty times as much propellant to drive this deadweight mass from Earth orbit to Mars and back (even with half of it dropped off as waste at the destination). The amount of material needed ends up being comparable to the mass of the International Space Station, which took years and tens of billions of dollars to build. Never mind other considerations such as radiation protection. This is a major reason why manned trips to Mars have persistently remained 20 or 30 years in the future.

The International Space Station, as seen in 2010 by the Space Shuttle Atlantis as it departed the ISS during STS-132. Image credit: Wikipedia

When Alex Tolley and I started this project, we started with a simple question that we explored in a paper for the Journal of the British Interplanetary Society. What if you could turn all or nearly all of the consumables into propellant? Specifically, what if you could design the entire ship around electric engines that use reclaimed water and waste gases as propellant? It turned out that not only is this possible with existing technology, but it also completely changes the economics of manned interplanetary space exploration, as well as what a spaceship might look like.

Electric propulsion is not a new technology, and has been used on many unmanned spacecraft. The idea is to use an external power source, typically a solar photovoltaic array, to drive an engine that uses an electrical or magnetic field to heat and accelerate a gas stream to great speed (tens of kilometers per second). Because these engines can achieve much higher exhaust velocity than chemical rockets, 10x or better, they can achieve greater change of velocity (delta v) using the same amount of propellant. This means they can venture to more ambitious destinations, carry more payload, or a combination of both. It also turns out these engines can also use a wide range of materials for propellant, including water. Following are some helpful primers on rockets and the rocket equation.

Test firing of a T-140 Hall Effect Thruster. Hall Effect thrusters were first developed in the US and Soviet Union in the 1960s, and are now widely used for satellite orbit insertion and stationkeeping. Image credit: High Power Electric Propulsion Laboratory / Georgia Tech, http://mwalker.gatech.edu/hpepl/thrusters/t-140-het/

To understand why this is so important, let’s go back to the 24 tons of consumables we would need for our hypothetical six person mission. In a conventional spacecraft architecture, that deadweight, along with the dry mass of the hull, needs to be pushed by an external rocket many times as massive. By turning that material into propellant, you eliminate the need for an external rocket almost completely. This reduces the mass of the system by a factor of 10 to 20 or more, which in turn reduces overall mission complexity and cost by 90 to 95%. For details, calculations and more, we encourage you to read our original JBIS paper, this article on Centauri Dreams, and, if you have the time, our book for Springer Verlag about the spacecoach architecture.

Another question we asked was “Do we really need to send people to a planetary surface on most missions, or is getting them to the general vicinity good enough?”. This is another major flaw common to Mars missions. The primary motivation to go there initially will be scientific exploration, most importantly the search for evidence of past or present life. Mars colonies make for an exciting story, but realistically those will come well after initial exploration because we don’t want them to end up like Jamestown.

Sending people to the Martian surface is risky and expensive compared to putting them in orbit overhead. First there is the cost of all of the equipment needed to get people to and from the surface from Martian orbit, as well as the physical risk of flying to the surface and back. More importantly, there is the risk of biological contamination, not from Martians infecting us, but from us contaminating the Martian environment with Earth microbes. Humans are literally walking piles of bacteria and will contaminate any area they explore. Because of planetary protection concerns, early Mars expeditions will avoid locations thought to have liquid water. If that’s the case, what’s the point of going? And lastly, there is the risk that people just won’t care very much about “boots on Mars” and will be reluctant to fund an Apollo scale program. Pop quiz! Name the astronauts currently flying aboard the International Space Station.

Sending people to the vicinity of Mars doesn’t mean you can’t do anything on the surface. It turns out you can do quite a lot. Instead of people, you send robots to the surface which will be tele-operated by astronauts from orbit overhead. From Mars orbit, the communication delays induced by the speed of light are negligible, so astronaut operators would be able to control them in real-time. With VR and tactile feedback, they will have fine control over these robots, and will experience the surface environment and interact with it as if they are there, all while in a shirt sleeve environment and without the expense and risk of flying to the surface.

Small sample return rockets could deliver surface material back to local orbit for more detailed study. As an added bonus, astronaut operators will be able to control multiple robots at multiple locations on the surface, which means that mission planners will be able to hedge their bets by exploring many interesting locations in a single mission. A manned surface expedition will only be able to go to one location per sortie. This approach reduces risk and expense by another order of magnitude. Al Anzadua’s paper, “From Moon To Mons To Mars”, is worth a read, as it describes this pathway in detail.

The point isn’t that people should never go to the Martian surface, just that we can get a lot of mileage out of remote exploration from orbit before we need to do so and before we are ready. The argument for sending people straight to the surface in the immediate future just isn’t there if we can accomplish the same goals at less cost via tele-operation.

What Would A Water Based Spacecraft Look Like?

Alex and I started with the basic idea of using consumables as propellant, and let the analysis guide us toward a system design. We started with a few basic constraints, both to simplify the design process, and to avoid tying the design to a specific mission.

Among the main constraints were:

  • The ships are purely interplanetary vessels. Once built, they never land on a surface or enter a planetary atmosphere, but instead travel between orbit around Earth and other worlds. Any descent to a planetary surface is done via a separately designed module. This also means the ship can be reused for many missions, so its construction and launch cost can be amortized accordingly.
  • The ships are powered by large solar photovoltaic arrays. While other power sources, such as nuclear electric power plants, could be used, we assume that solar is the primary power source, for technical and political considerations, especially because solar PV is a well understood and continually improving technology.
  • The ships are propelled mostly by electric propulsion technology, and use water, carbon dioxide and gasified waste as propellant, essentially they convert the crew waste streams and reclaimed water into propellant after first pass use by the crew. Water and water rich material is used for other purposes, such as radiation shielding and heat management, while in passive storage.
  • Habitable areas are derived from inflatable structures, such as Bigelow Aerospace units, to allow large structures to be fit into existing launch systems and then be self-assembled in space with less manual intervention.
  • The system as a whole is modular, so external landers, chemical propulsion units, and other modules can be attached and detached as needed based on mission requirements.

This design pattern leads to a ship that looks like the rendering below. While this isn’t the only possible configuration, this “kite” pattern minimizes the materials required while providing a sizable habitable area, and while generating enough electrical power to generate useful amounts of thrust via electric propulsion. We coined the name “spacecoach” to describe them, as a nod to the Prairie Schooners of the Old West.

Rendering of the “kite” design pattern for a spacecoach, with a person shown to the right for scale. Image credit: Rudiger Klaen.

Because the ships are purely interplanetary, they can gradually change their orbit under electric propulsion rather than use high thrust chemical rockets. These engines generate low thrust for long periods of time, so the ships never experience extreme stresses or vibration, but rather gently accelerate and decelerate. They are more like the Mars Cycler concept proposed by astronaut Buzz Aldrin than a conventional rocket ship, and I suppose you can think of them as active cyclers. Because of this, the ships can be big, with a large surface area for solar arrays, and can be large enough to generate artificial gravity. They will also be able to fly many missions, with a useful life comparable to the ISS (20+ years) so their construction and initial launch cost can be amortized across 5 to 10 missions.

The use of water and waste gases as propellant, besides reducing the mass of the system by a factor of ten or more, has enormous safety implications. 90% oxygen by mass, water can be used to generate oxygen via electrolysis, a simple process. By weight, it is comparable to lead as a radiation shielding material, so simply by placing water reservoirs around crew rest areas, the ship can reduce the crew’s radiation exposure several fold over the course of a mission. It is an excellent heat sink and can be used to regulate the temperature of the ship environment. The abundance of water also allows the life support system to be based on a one-pass or open loop design. Open loop systems will be much more reliable and basically maintenance free compared to a closed loop system such as what is used on the ISS. The abundance of water will also make the ships much more comfortable on a long journey.

The design pattern also leads to extensive redundancy, and a ship that is safe by default. Take the electric engines as an example. In most of the configurations we looked at, there would typically be dozens of relatively small units grouped into arrays that collectively generate usable thrust. Similarly the electrical system would consist of many smaller units that collectively generate a large amount of power. The failure of a few units out of dozens would lead to a minor recalibration instead of a crisis.

Some of the design patterns we explored will also enable the ship to rotate to generate artificial gravity while cruising. Microgravity, along with radiation exposure, are the two primary health hazards associated with multi-year missions. The abundance of water, an excellent radiation shielding material, will make radiological exposure much less of an issue. Artificial gravity will enable the crew to spend most of their time in Earth like conditions, and will also simplify many aspects of ship design (furniture, showers, toilets, etc).

The design pattern also borrows an important lesson from the computer industry, that many small, incremental improvements in component technologies can compound to produce overall huge improvements in capabilities and costs. The basic technology used in computing and communication, the solid state transistor, was invented decades ago. The dramatic improvements we’ve seen resulted from making them smaller, faster and less energy intensive with each manufacturing cycle. The space coach will enjoy a similar effect as solar photovoltaic and electric propulsion technology improves, especially if ships are designed so that these components can be swapped out with each new mission.

Testing and Development

People typically assume that this spacecraft architecture will be prohibitively expensive to develop. In fact, it will be possible to validate most of the mission architecture without building a full scale spacecraft, and the most important work can be done without leaving the ground.

Electric propulsion technology is the fundamental driver in the system design and its cost model. In our research, we identified several technologies that should work with water and waste gases, and that will offer the performance required for missions throughout the inner solar system. Some of these systems are already in advanced stages of development, and a few, such as Hall Effect thrusters, are already flying. The next step then is to organize an engineering competition to test these engines with water, carbon dioxide and other waste gases, and to measure how they perform. This competition can be done in ground based facilities, and can be done very cheaply in the context of spaceflight.

The winners from that competition would move on to build small satellites that test these engines in actual spaceflight conditions, and that simulate the overall duration and profile of an interplanetary mission while remaining in near Earth orbit. They would do this by stepping up and down in orbital altitude to accumulate the total change in velocity and flight duration required for an interplanetary mission. Everything short of the crew habitat could be tested via small unmanned platforms like this.

The first crewed ships could simulate an interplanetary mission while remaining in near Earth space. A spacecoach would fly out to cislunar space to spend two years gradually changing its orbit around the moon to simulate both the delta-v and the duration of a subsequent mission to the Martian moons. During the mission, the crew would be able to fully test ship systems, tele-operate surface robots on the moon, and perform other activities anticipated in an actual Mars mission. Meanwhile they would be able to return to Earth within a few days via a crew return vehicle should an emergency arise. Once fully tested, the first ship would be ready to venture out from the Earth-Moon system to the Martian moons and eventually far beyond.

A Real World Starfleet

These ships will not be destination specific. They will be able to travel to destinations throughout the inner solar system, including cislunar space, Venus, Mars and with a large enough solar photovoltaic sail, to the Asteroid Belt and the dwarf planets Ceres and Vesta. They’ll be more like the Clipper ships of the past than the throwaway rocket + capsule design pattern we’ve all grown up with, and their component technologies can be upgraded with each outbound flight.

In effect, they will form the basis for a real world Starfleet, one whose range of operation will grow as their component technologies evolve and improve.

Further Reading

Reference Design For A Simple, Durable, and Refuelable Interplanetary Spacecraft”, Alex Tolley; Brian McConnell, Journal of the British Interplanetary Society (2010)

Spaceward Ho!”, Alex Tolley, Centauri Dreams (Jan 9th, 2015)

A Stagecoach To The Stars”, Brian McConnell, Centauri Dreams (May 1st, 2015)

A Design For A Water Based, Reusable Spacecraft Known As The Spacecoach”, Springer International Publishing (2015), ISBN 978–3–319–22677–4

Next Story — Burning Man : Blueprints For The Ephemeral City
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Burning Man : Blueprints For The Ephemeral City

Last Fall, the Black Rock City Ministry of Urban Planning, a group of long-time Burning Man participants, launched a design competition for the Black Rock City street plan. Many of us had wondered what sort of ideas for the city were out there, and since urban planning is an art form in its own right, why not create a forum for people to contribute and discuss ideas for the city itself?

“Connected Project” by Ludale of Hardel Lebihan (France)

You might ask “Why change the city plan?”. A better question to ask is “Why not?”. The ongoing experiment in Black Rock City is one of the few places on Earth where one can design and build an entire city from scratch. Meanwhile, the physical environment imposes almost no constraints on how the city can be laid out. Burning Man is all about participatory art, so we thought a forum like this would be a great way for urban planners, architects and artists to contribute and discuss ideas for the city’s development. For participants, changing the city plan would make each manifestation of Black Rock City new and unique.

The response to this was amazing, with over 1,600 registrants, all in response to a couple of blog posts that took on a life of their own. Since then, we’ve received over 70 submissions from 30 countries (submissions are open through June 30th, so if you have an idea to share, please do). In this article, I’d like to highlight some of the results so far (you can find the full gallery here).

We encouraged people to submit ideas in one of three categories.

  • Design Elements — stand alone elements, such as street lights, parks and intersection designs, that can be incorporated into larger city plans, including the existing arc/ring plan.
  • Conforming City Plans — adaptations to the existing city plan. We received a lot of these, some of them quite interesting.
  • Non-Conforming City Plans — radical departures from the existing plan. Completely scrapping the existing city plan may be a long shot, but its interesting to explore completely new geometries for the city.

Most of the plans submitted retained some reference to the current city plan, with the Man as the focal point of the city. The current city plan is essentially a circle around a campfire, writ large, and there is much good to be said about this configuration. But as you can see, there are many possibilities for adapting and extending this design pattern in interesting ways. Below are just a few of the submissions (the full gallery and submissions form are here).

“Mother” by Sergio Bianchi, Simone Fracasso, Chiara Pellegrin (Italy)
Untitled by Michael Colton (United States)
“A Simple Evolution” by Jeffrey Smith of designAIRING (United States)
“Ideal City” by Michal Dvořák, Ivan Gogolák, Lukáš Grasse of dvořák+gogolák+grasse (Czech Republic, Slovakia)
Untitled by MDX2 (Macedonia)
“Glowworm” by Scott “Glow Worm” Rogowski & Annika McPeek (United States)
Untitled by Nadica Pankovska, Joana Stojchevska from Macedonia

What surprised us the most was the geographical diversity of the submissions. People and teams from over 100 countries registered, far beyond anything we imagined. It says something about how far an idea can travel in today’s world, and about how fascinated people are with the idea of designing a new city.

Our hope is that this competition will become part of the annual planning process for Burning Man, as well as regionals. This type of competition format is a great way to get a lot of ideas on the table. Imagining what the city could be is an interesting exercise for its own sake, and if the early results are any indication, there is no shortage of talented people who want to contribute to the city plan.

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