Undergraduate Team Space Design Competition
Conceptual Design and Architecture for Space-Based Solar Power System
The Sun has the capacity to be Earth’s primary source for renewable energy. The Sun radiates 2.3 billion times more energy than currently received on the Earth; therefore, the energy propagated by the Sun in just one hour could provide all of Earth’s population the energy it needs for an entire year. However, reliable solar energy of this magnitude cannot be created simply by installing more solar cells on Earth due to impeding cloud, rain, or snow coverage. Unlike earth-based solar power stations, space-based stations can collect and transmit solar power, using microwave energy, regardless of weather conditions. This is a key factor in northern climates with minimal sun exposure. In addition, the higher altitudes of space-based power stations experience shorter eclipse periods, which allows higher energy collection.
Since 1968, scientists have researched methods for collecting the Sun’s energy in space and converting it to usable power. Japan, one of the technological giants of the 21st century, has committed to the development and installation of a space-based system by 2020. In the USA, several studies have been conducted on developing a space-based solar power system [1-3]. A system that consists of a power station is proposed to be lofted into geostationary orbit (GEO) by 2016 and begin collecting 200 megawatts of sunlight under a 15-year contract with San Francisco-based Pacific Gas and Electric Company (PG&E). The solar energy from this station will be converted into radio waves, beamed to a ground station in Fresno, transformed back into electricity, and fed into PG&E’s grid.
To date, the main method proposed for harvesting and transmitting solar energy has been via space structures in GEO, at about 37,000 Km altitude, equipped to transmit accumulated energy to the earth via microwave. Earth receivers are then proposed to collect the transmitted energy and convert it to usable electricity.
The goal of this project is to develop architecture and a conceptual design for a space-based solar power system (SBSPS). The SBSPS will include one (or more) harvesting satellites and one (or more) power receiving ground stations. The goal is to receive one gigawatt on earth. The one gigawatt could be transmitted to one spot on earth, or divided to as many spots on earth as needed.
The mission statement is as follows: “There is an increasing demand for energy while natural resources are declining. Solar energy is a viable clean energy alternative source. A space-based solar power system that provides electric power to one or more ground stations in the United States is needed. Delivering electric power to ground stations in other nations is desirable but not required.”
The SBSPS may have one or more satellites. A satellite in the SBSPS may be in a medium altitude orbit, or a geostationary orbit (GEO). Satellites in GEO have certain limitations: 1) GEO is congested; 2) the launch cost to GEO is high compared to lower orbits; and 3) the transmitted energy is subject to high path loss due to the 37,000Km distance. In addition, part of the transmitted energy is absorbed or reflected by the ionosphere and atmosphere layers through which it must pass. Another alternative is a solar power network that consists of a constellation of satellites. Each satellite in the constellation may transmit power to ground receivers directly, relay to another satellite, or store then transmit power to ground receivers. The moon could be another alternative for harvesting solar power and then transmitting power to the earth. Other novel concepts may be investigated.
Satellite communication channels are affected by the ionosphere’s layers, water vapor, oxygen, and reflectors located in the proximity of the ground power receiving station. The signal pathloss is mainly a function of free space pathloss, as well as ionosphere and atmosphere attenuations which vary with frequency, time of the day, and the position of spacecraft.
Each team is to develop an architecture and conceptual design for the overall system configuration, including the conceptual design of the vehicle(s) and ground station(s). The vehicle’s conceptual design will include definitions for the propulsion, power, navigation, and communication systems. The team is to perform trade-off studies: 1) between a constellation of satellites at medium altitude orbits, at GEO orbit, the moon, and any other novel concept for space-based power harvesting and transmission; and 2) different launch options including conventional launch, build in space, or unconventional launch concepts. These trade-off studies should include the amount of power received at ground stations, the total cost of the project, the price per kilowatt, the system power transmission efficiency, risk analysis, and sustainability analysis.
Major design criteria include:
1- Minimizing the total mass of the vehicle(s) and the power consumption.
2- The space vehicle dimensions and mass must be compatible with the selected launch vehicle.
3- The cost for the mission should not exceed $21 billion U.S. dollars, including launch cost.
4- Safety: address the safety issue associated with beaming power to a spot on the earth.
The team will go through the process of space mission design to produce an architecture and conceptual design for the space-based solar power satellite system. This includes the conceptual design of the space power harvesting unit(s) and the ground power receiving unit(s). The team is encouraged to become familiar with the material in references [1,3]. The space-based solar power system shall be designed for an initial operation in 2040. The design shall specify the lifetime for the space vehicle(s) and design replacement schedule if applicable. The selected architecture and design will include a commercial business case justification. This justification shall explain the economic advantages for the selected architecture.
Where specific data (e.g., solar panel efficiency) are needed, the team shall use data of a current available technology. The team shall complete and document an analysis of requirements to the level required to support their design decisions and include the results in their report. If applicable, the team shall identify all needed critical technologies, their current technology readiness level (TRL), and estimate the time of developing it to the necessary TRL.
This project may require a multidisciplinary team of students including aerospace engineering disciplines such as mission analysis, orbital mechanics, optimization, and electrical engineering disciplines.