Frequently Asked Questions
Please see below our most frequently asked questions. If you don’t see the answer you need, please don’t hesitate to get in touch
The trend for RF communications is to move to ever-higher frequencies and wider bandwidths. Space-based solar power requires just one-or two narrow spot frequencies for the whole world to use. These are below 10 GHz, at relatively low intensity (compared to radar, say), and well below the currently popular Ku and Ka bands and so are unlikely to cause problems for other well-designed equipment.
Rectennas are also likely to be positioned well away from areas of human habitation, reducing this risk even further.
A space-based solar power system in a geostationary orbit would appear stationary in the sky to a ground observer but would track across the starfield as the Earth turns. The solar power satellite design intentionally maximises the collection of sunlight, rather than reflecting it to Earth.
Despite the large size of the solar power satellite, because of the high orbit its visual angle when viewed from earth is less than 1/5 of the International Space Station (currently the largest satellite orbiting earth).
The capabilities needed for space-based solar power, including low-cost space access, could also facilitate further space-based astronomy, or systems located on the RF-quiet far-side of the Moon.
No, it won’t heat up the atmosphere. There is minimal absorption of the radio frequency energy by the atmosphere at frequencies below 10 GHz.
Most space-based solar systems use either 2.45 Ghz or 5.8 GHz. On a dry day there will be negligible absorption, and hence heating, by the atmosphere. On an overcast day with heavy precipitation, there may be up to 2% energy absorbed by the atmosphere. For safety considerations the maximum beam intensity will be limited to 245 W/m2, thus the atmospheric heating will be less than 5 W/m2.
A study by Andrew Ross-Wilson, atmospheric scientist at Strathclyde University, calculates the local maximum temperature rise to be in the order of 0.006ºC due to this heating.
That’s the exact opposite of what we’re trying to do! Fossil fuels and other non-sustainable energy sources are heating the world, space-based solar power will not.
In terms of direct heating from the beam that comes from the system, this will have a very minimal heating effect. It is insignificant compared to the sun’s power absorbed by the atmosphere and ground.
The sun delivers approximately 113,000 TW into the earth’s energy budget, absorbed in the atmosphere and on the earth’s surface. The total world primary energy usage (to generate electricity, provide heat, drive transport and industry etc) is of the order of 19 TW. Assuming 10% of all the world’s energy was derived from space-based solar power, this would only be an additional 0.002% addition to the earth’s energy budget. To put that figure in context, the sun’s output varies by about 0.1% over the course of a solar cycle.
The maximum power density at the centre of the beam is 230W/m2, which is less than one quarter of the intensity of the sun at noon (1,000 W/m2).
The beam density is a Gaussian distribution and the average power density across the beam is around 30W/m2.
As part of the development programme, international agreement on safe power levels for space-based solar power systems will be sought, based on the best scientific advice available.
No. Utilising fully reusuable launch capability with carbon-free propellants, and subsequent lift to MEO with a reusable space tug for assembly, will mean that within 23 days of operation, we will have paid back all the energy used to manufacture the propellants to place the system in orbit.
ESA has had occasional but significant scintillation issues on satellite communications downlink in 2.1 to 2.3 GHz frequency range, and this area that would benefit from further study. Adaptive optics could mitigate this problem in the same way that they do for visible light astronomical telescopes.
The energy beam is controlled by a retrodirective pilot communications beam from the rectenna to the satellite. This could work in a similar way to adaptive optics in visible light telescopes – distortion of the pilot beam would be compensated by the phase conjugation (time-reversal) performed at the satellite. Of course, this depends on the ionospheric turbulence having a time constant longer than the lightspeed delays and the pilot/power beam frequencies to be similarly affected.
Each receiving antenna (rectenna) is like a large net, strung out horizontally over an elliptical area occupying about 6 km x 13 km at UK latitudes. (Nearer the equator the rectenna can be more circular). In highly populated countries like the UK the best location for them is offshore, perhaps adjacent to offshore wind farms where they can pick up on the existing grid interconnections. For less densely populated countries, it is possible to place the rectennas on land, and potentially have dual use of the land, with arable farming underneath the rectenna.
Frazer-Nash Consultancy is currently doing a study for the European Space Agency at present to assess the costs and benefits of Space Based Solar Power for European nations, including some initial thoughts on where the rectennas would be sited.