Energy Supply Problem The Space Station Energy Supply Problem When you hang out with NASA engineers, often you will find a few who are Star Trek fans. The creator of Star Trek, Gene Roddenberry, conceived of a time 300 years in the future in which people from many nations would live and work in harmony on board a station for long periods of time away from Earth. That idealistic fantasy has come true with the building of the International Space Station. On board the star ship Enterprise, all the exploration, all the research, all the day-to-day living and working functions were dependent on one very important thing: dilithium crystals. With these crystals, the creators of Star Trek solved perhaps the most difficult problem of life in space--where to get an endless supply of energy. You see, according to the science behind the fiction, dilithium crystals provide an ideal source for regulating a reaction between matter and antimatter, thus producing a boundless supply of energy. When the crew of the Enterprise needed to replenish their supply of dilithium crystals, they had to travel to a planet far off in another galaxy. The crew of the ISS, on the other hand, does not have to travel nearly as far to obtain the energy source they need. They don’t even need to leave their solar system. In fact, the energy to power the ISS comes directly to them. It arrives in the form of solar energy from the sun. The sun, is responsible for nearly all the energy on earth. It is an average size star that’s been burning for a very long time and is expected to burn long into the future. It is a limitless energy source that delivers 1.52 X 1018 kilowatt hours per year of electrical energy to the earth. All of mankind’s total energy needs since the discovery and use of electricity total to less than 0.1% of this amount. A kilowatt hour (kWh) is one thousand watt-hours and is the unit of measure used on your household electric bill. Ten 100-watt light bulbs left on for one hour will use one kWh of electricity. The solution to the electric energy supply problem has been found in harnessing the sun’s solar energy. Scientists have developed ways to transform solar energy into electric energy using photovoltiac cells. These are electronic devices that collect the electrically charged particles of solar energy, just like the solar powered calculators we have all used. If only one small photovoltiac (PV) cell can only operate a single calculator, just imagine how many solar cells it would take to operate every electric appliance in your home. At completion, the electrical energy required to operate the ISS during one 95-minute orbit around the earth is about 78kW (Kilowatts). This is roughly the same amount of electrical energy required to operate an average household for one month. While the astronauts are in space working on experiments and maintaining the station the ISS is their laboratory and their home. In order to sustain life the ISS must have the capacity to provide essential elements necessary for survival like oxygen for breathing, water, light and heat. All of the equipment and controllers necessary to produce and deliver these elements require electrical energy to operate. In addition, the ISS must also have the ability to provide electric power to operate computers, communication equipment and many other systems aboard the spacecraft. The ISS Power Plant The ISS orbits the earth once every 95-minutes. Two thirds of this orbit is in direct sunlight. This portion of the orbit is called the “insolation” period. One third of every orbit is in the earth’s shadow and is called the “eclipse” period of the orbit. The scientists at NASA have developed huge PV arrays. These arrays can capture enough solar energy in the “insolation” period of the orbit to provide electrical power for the ISS and to charge on board batteries to provide power during the eclipse period of orbit. When the ISS is fully completed, the solar arrays will cover an area of nearly 27,000 square feet--almost one full acre. These battery systems have been designed so that at the end of the eclipse period, 35% of the battery’s stored energy has been used up. During the following “insolation” period the PV arrays will again supply power to the ISS and recharge the batteries. If there is a total failure of the PV arrays or the power system the ISS can only operate for one more complete 95-minute orbit in a low power consumption or power-saving mode. This could be a very serious problem! Illustration Power Management NASA scientists have been very aware of this potential problem and have designed the ISS with many safety features to conserve electrical energy. These features cannot however compensate for events outside the control of the ISS like a solar storm or coronal mass ejection. These solar events can eject extremely large amounts of highly electrically charged particles into space. The effects of solar storms have been studied for many years. High levels of solar radiation and electrical energy have actually disrupted or permanently crippled communications, tracking and many other types of satellites. This energy has also reached the earth and interrupted cross-country power transmission. The electric energy is attracted to anything that will conduct electricity. Metal power cables, towers, buried pipelines and even conductive minerals in the earth’s crust can become supercharged with electric energy from the sun. This energy can actually be absorbed into the existing power cables and cause them to overload sending far too much energy to transformers or other equipment. In some cases this solar energy has caused transformers to explode resulting in the total failure of entire power grids. In 1989 a solar blast from the sun hit North America in Quebec. This left millions of people without power for nine hours. Power plants, global positioning tracking systems, cell phones, pagers, radios and practically any type of electronic equipment is at risk during a solar storm. The effects of a CME are even potentially more dangerous at high altitudes where the protective cover of the earth’s atmosphere is a lot less. This energy can also affect integrated circuits or computer chips causing them to malfunction. This could result other serious types of problems as microcomputers are built into many devices we all use. The photons can penetrate into the heart of a microchip and cause the logic registers to “flip their bits”. This means that the memory registers in a binary logic chip can be randomly reversed. The zeros can be turned into one’s and vice versa rendering the computer useless. These facts have led NASA to develop ways to “harden” or shield the electronic components from dangerous solar energy levels. They have done their very best to harden the ISS against CME storms. However, the intensity and duration of a future solar storm could exceed the protective shielding any damage the ISS power systems or controls. If this happens, it could result in huge problems aboard the ISS. A computer controls practically every electromechanical device on the space station. If the output data from a computer becomes contaminated with bad data from “flipped bits” it would cause a malfunction in the system or systems that it controls. Within the power system grid of the ISS this could translate from a severe reduction in output to a total loss of power generated by the PV arrays. We have learned much about solar storms and other forms of space weather over the years. Several space weather stations have been deployed into deep space that can track solar storms and send the earth advance warnings. Data from these stations gives an indication of the level and possible duration of solar events. This is much like the TV news and satellite weather forecasting we use here on earth. Weather reports let us know if we need to take special precautions or just to be prepared.