Frequently Asked Questions

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.

No, the system by design cannot be used as or converted into a weapon.

The aperture size of transmitter and receiving antenna are sized to keep the maximum beam intensity at or below 245 W/m2. This is only one quarter of the intensity of sunlight at midday, which is around 1,000 W/m2.

Lacking a common power bus, it would not be possible to re-purpose the power distributed across the platform to power a separate laser or particle weapon.

The system will be designed so that it is safe in the event that humans or birds or animals strayed into the beam.

The aperture of the transmitter and receiving antenna are sized to keep the maximum beam intensity at or below 245 W/m2. This is only one quarter of the intensity of sunlight at midday, which is around 1,000 W/m2.

The system also requires co-operation from a secured and encrypted pilot beam at the intended rectenna target to form and steer the power beam to itself. Without it, the power beam would immediately cut off.

The beam density is too low to do physical harm to aircraft or spacecraft.

Any risk of interference with communication, guidance or navigation equipment will be addressed through the development of international compatibility standards, and through regulation in a similar way that operational and compatibility standards are defined for civil aircraft today.

These standards are well established across all terrestrial and aviation systems to ensure interoperability of different systems without interference.

Space-based solar power will use continuous (not pulsed) wave beaming, at peak intensities less than emitted by a mobile phone held to an ear. Receiving antennae on earth will also be sited away from centres of habitation. There is empirical evidence to suggest that this is unlikely to be a problem.

Historically it has always been seen as too expensive, but recent developments in low-cost launch, maturing technology and more modular space-based solar power concepts are changing the economics. The global imperative to decarbonise economies is also prompting nations to invest in clean energy technologies.

A number of factors have encouraged a resurgence of interest in the concept, including:

• The cost of space launch reduced by 90% from $20,000/kg to under $2,000/kg, with that trend set to continue.
• Advances in semiconductor technology leading to improving efficiency for space use.
• New modular Solar Power Satellite designs (SPS Alpha, CASSIOPeiA) are much lower in mass and production cost.
• Increased concern about climate change has led to a renewed imperative by governments to study all clean energy technologies.

Space-based solar power can provide continuous base load and dispatchable power, day and night all year round, irrespective of the weather. It thus overcomes the intermittency of terrestrial renewables. space-based solar power could offer competitively priced baseload energy. Baseload energy generation is essential for grid stability.

A Solar Power Satellite in GEO can see the sun for well over 99% of the time. It is only in the earth’s shadow for a few hours each year around the spring and autumn equinox. Using a suitable microwave frequency such as 2.45GHz, the transmitted energy can be beamed through the atmosphere with negligible loss, even through clouds and rain.
Existing studies of space-based solar power economics claim that the Levelised Cost of Electricity could be around £50/MWh, which is competitive with intermittent renewables, and considerably less than nuclear power.

Intermittent terrestrial renewables place an additional burden on the grid to ensure security of supply. Analysis carried out for the Climate Change Committee estimated the cost of these measures to be £10/MWh to £25/MWh for generation mixes with 50% to 65% of variable renewables, rising to £25 to £30/MWh for a system with 75% to 90% of variable renewables.

A space-based solar power programme will provide the market demand for development of a vibrant competitive reusable launch market.

Any space-based solar power programme, national or more likely international, needs very substantial low cost – and hence fully reusable – space lift requirements, in the order of many times the current global launch capacity. SpaceX has led the way in reusable launch, and it is likely that this will spur competition from other providers. A space-based solar power programme will provide the market demand signal for these capabilities to be developed, though it may also need government support to develop the underpinning technology for reusable spaceplanes.

Already there are two fully reusable heavy lift launchers in development – SpaceX Starship and Blue Origin New Glenn. RocketLab has announced the development of the Neuron fully reusable launch vehicle. Reaction Engines is developing the SABRE airbreathing engine which is designed for a future reusable single or two stage to orbit spaceplane. This is in the absence of a declared space-based solar power programme, and these efforts would only accelerate if space-based solar power were pursued with a substantial and well-funded programme.

Space-based solar power systems are highly resilient, having no single points of failure and being highly modular it would be difficult to degrade by a kinetic projectile.

Weaponisation of space is also prohibited by International Treaty.

The space-based solar power system and its retrodirective beam steering would also be protected by secure encrypted protocols to prevent disruption or theft of the energy by an adversary.

The satellite architecture is highly resilient to damage from space debris or micrometeorites, with no single point of failure and a highly modular design. In the event of a collision, the satellite would continue to function with minimal performance degradation and repair or replacement of modules would be designed into the operational concept. The choice of operational orbits can also reduce the risk of space debris damage.

One operational architecture is for the satellites to be assembled in a Medium Earth Orbit, just above the inner Van Allen belt and with reduced space debris risk. CASSIOPeiA proposes the use of a Geosynchronous Laplace Plane orbit, which is free from congestion and with potentially lower space debris risk. Additionally it can use Highly Elliptical Orbits, which could be chosen to minimise the risk of space debris.

It is intended that the launch trajectory will be designed to largely avoid the Van Allen belts.

Instead, we will transit around it using an inclined elliptical transfer orbit to MEO assembly 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.

The energy beam at microwave frequencies produces a heating effect, just like microwave ovens but at much lower intensity, equivalent to one quarter of the midday sun at the equator. So it is safe to humans and wildlife. NASA has conducted long term studies on birds which confirm this. The receiving antennas are large and would need to be placed offshore or in remote areas, so they would not be co-located with centres of human habitation.

Nevertheless, safety is paramount with any new technology and there will need to be in-depth studies, together with suitable safety regulation to reassure the public.

No, the independent techno-economic assessment by Frazer-Nash Consultancy (summary report attached), concluded that a development programme would cost around £17Bn, including the first of a kind commercial power station in space. Thereafter the capital cost of the subsequent production systems is about £3.6 Bn for a 2GW system, or about one quarter of the cost of an equivalent nuclear plant.

No, it doesn’t, and efficiency is not the only measure of practicality.

Because the energy source (the sun) is limitless and free, the efficiency only matters because it affects the size, mass and cost of hardware. There are losses in energy conversion down the energy chain through the Collect, Convert, Transmit and Receive elements. This governs the size of the Solar Power Satellite, and hence its production and deployment cost, but not the practicality of operation of the system.

Overall efficiency from sunlight to AC power into the grid is therefore a notional 18%. Accounting for these factors, cost modelling analysis by Frazer-Nash shows that the LCOE (levelized cost of electricity, used to compare different methods of electricity generation on a consistent basis) falls between £37 and £74/MWh, which is competitive with terrestrial renewable technologies.

The utilisation (another broader measure of ‘efficiency’) of space-based solar power is nearly 100%, delivering power day and night year-round, compared to an average of 11% for terrestrial solar farms and 47% for offshore wind farms in the UK. Moreover, SPACE-BASED SOLAR POWER delivers baseload power, improving grid stability and reducing the need for other energy balancing systems on the grid.

For a given area of land or sea, space-based solar power produces 2.4 times more annual mean power than terrestrial solar farms and 12 times more than offshore wind farms.

In theory it could supply all of the world’s energy in 2050. There is sufficient room in orbit for the solar power satellites, and the Sun’s supply of energy is vast – a narrow strip around Geostationary Earth Orbit receives more than 100 times the amount of energy per year that all of humanity is forecast to use in 2050. In practice for resilience we will always seek to have diversity of energy supply, and Space Based Solar Power integrates really well alongside the intermittent technologies like wind and ground solar.

Whilst this is a very ambitious engineering development programme, the laws of physics are well understood and there are viable commercial concepts. It is not as difficult as Nuclear Fusion.

There are challenges; the main one is building the very large structure in space, which has not been done before. Secondly the wireless power beaming has not been done at this scale from space, though experiments on earth have repeatedly proven the principles. Thirdly, establishing the international regulations and standards which will be required to develop and operate these systems sustainably and responsibly will require major international collaboration.

But, nothing worth doing, and with the expected impact of space-based solar power, has ever been easy. This is an era-defining programme, which will change our future.

These very large satellites are quite different from existing monolithic satellites. They are made up of hundreds of thousands of small identical modules produced in factories on earth (think iPhones or laptops), and will be assembled in space by autonomous robots. The same robots would carry out periodic maintenance by replacing failed modules. The satellites are designed from the outset to be serviced in this way. This assembly technology is already being tested in space by a number of companies.