Electrical power on-board a space vehicle is arguably one of the key functional requirements of a satellite, enabling the functioning of (scientific) equipment, propulsion and communication. With the steady enhancement of satellite capabilities, these power requirements have increased from around 1W for the Vanguard-1 [link] up to 100's of kW for manned missions. For example, the ISS has a power usage of around 110kW [link] which is generated by multiple solar arrays and balanced with fuel cells and batteries during its 90min orbiting period.
power in space
The majority of spacecraft orbiting the planet use photovoltaic (solar) arrays as their primary source of energy. The great benefit of this technology is that there is no need to bring fuel into orbit which reduces mass and therefore cost. Instead, the solar radiation functions as the 'fuel' with a power density of around 1367 W/m2 at the outer atmosphere [link]. A drawback however is the relatively low energy density and limited lifetime due to the harsh space environment. The use of photovoltaics is actually one of several technologies available to produce power in space. A more complete list can be summarized by:
- Chemical (batteries, turbines)
- Fuel cells
- Cryogenic engines
- Photovoltaics (PV)
- Radioisotope thermal generators (RTG)
- Nuclear dynamic systems (fission, fusion)
The exact choice for any of these systems will depend, among others, on the power level required and the mission duration. In general, short duration flights (e.g. launch systems) often use batteries and/or fuel cells, while long duration missions rely on solar arrays or nuclear systems. For example, the most distant still operating spacecraft, Voyager-1, contains 3 RTG's delivering 157W each (at its current distance of 1.8x1013 m, the incident solar radiation has dropped to below 0.1W/m2). Besides the power generation, two additional elements of the power system are of critical importance, which are the power control/distribution and storage. All three elements are interconnected as supply and demand may be unbalanced requiring a robust distribution networks to control the output over time. In most cases, the source output also changes over time as the fuel is depleted or the generating/conversion efficiency decreases.
The ongoing activities within the Advanced Concept Team span all the above elements by investigating novel methods for generation, distribution and storage of energy in space. By studying new scientific advancements, we aim to provide a first look on future operational capabilities. Several topics currently under investigation are:
- High energy density materials and devices (aerogels, superconductors)
- Wireless power transfer (earth-orbit, orbit-to-orbit)
- Solar power conversion (nano-antenna's)
Space and Terrestrial Synergies
Besides research on the development of advanced space power systems, the work at the Advanced Concept Team is also aimed to link with terrestrial energy applications. One of the questions here is how current and future space assets could contribute in the development of a sustainable world energy grid. In fact, observations from space are already being used today in the planning and monitoring of the grid infrastructure [link]. The goal of the ACT is to investigate new roles for space to contribute in a variety of areas:
- Space Power Station (SPS)
- Earth observation and monitoring (weather forecasting, planning, grid inspection)
- Communication networks (GPS, grid synchronisation)
- Distribution network (wireless power transfer)
For more detailed information on related activities you are invited to have a look at the currently ongoing projects below.