Space Solar Power X-Prize

NSS Space Settlement Advocacy Committee
December 2007


Spur development of Space Solar Power (SSP) with an X-Prize and a series of X-Challenges at the X-Cup.


Space Solar Power refers to collecting energy in space and sending to Earth. Most of today's spacecraft use solar power, and wireless energy transfer using microwaves has been demonstrated at high efficiency.

Long term, space solar power can deliver vast quantities of baseline electric power; more than enough for all of of Earth's centralized electrical energy needs, including all the peoples of the poor nations and power for future electric cars. Most if not all of the materials can come from lunar regolith, most operations can eventually be automated, and the total power available is many thousands of times that used today. As there are no fuel costs, in the long term SSP power should be extremely inexpensive.

Importantly, space solar power can have an extremely light environmental footprint. With sufficient development, the SSP space segment can be built from lunar or asteroidal materials with zero terrestrial environmental impact of any kind. Only the antennas to receive the energy need be build on Earth. Beam interaction with the atmosphere must be minimized for efficiency as well as environmental reasons. Although there is every reason to believe that this environmental impact will be very small, further study is required and the choice of frequency is important.

Besides replacing and increasing baseload electrical capacity in wealthy countries, such antennas are relatively easy to build in remote areas, such as Africa and Central Asia, to deliver large quantities of electric power to energy-poor regions.

As an energy source, space solar power has some significant advantages over existing options. For example,

However, SSP is not yet ready for prime time. An enormous amount of technology and infrastructure development is necessary before SSP can fulfill its promise of vast quantities of low-cost, environmentally friendly power. Prizes may be a good way to get some of the technology development done.

We propose an X-Prize for some tens of millions of dollars and a series of X-Challenges suitable for the X-Cup (1).

SSP X-Prize

  • Power must be generated from sunlight and come from an artificial object in space (100 km altitude or above) supplied by the contestant. The contestant can supply their own spacecraft or hitch a ride. No more than 20% of the prize money may be won by suborbital systems.
  • Contestant supplies the receiving antenna (rectenna), power conditioning and chooses the time and location.
  • Contestants may send an uplink signal from the rectenna's position to simplify pointing.
  • X-Foundation supplies a cable with a standard connector to receive and measure power.
  • The power delivered must be over a TBD threshold . Prize will be awarded for watt-minutes delivered at the rate of $TBD per watt-minute. The X-Prize Foundation will supply systems to illustrate the power received (lights, sound, electric vehicles, etc.).
  • Up to three contestants may receive prize money. No single contestant may receive more than 50% of the prize money. No two more than 75%. No three more than 100%.


    This will demonstrate the end-to-end system and prove that power can be delivered from space to Earth. To do it inexpensively will require innovative engineering and solutions to dozens of practical, nitty-gritty engineering problems.

    SSP X-Challenges

    As the X-Prize may take years to fund and win, it is advantageous to have smaller prizes that can be contested at the X-Cup. Here are two ideas:

    Operational Solar Power Wireless Transmission

    Contestants will deliver 10 kw solar generated power wirelessly over 700 meters. These parameters are chosen to match the requirements on La Reunion island to deliver electricity to a small isolated mountain village called Grand-Bassin without damaging the natural beauty of the environment (see


    1. All power must be generated by solar collectors.
    2. The 'space segment' may consist of solar collectors, power beam generating equipment, command reception antenna, command and control systems, and, potentially, repair robots. Contestants will not have physical access to the 'space segment' during the contest except in cases of vandalism.
    3. The 'ground segment' may consist of rectenna, power conditioning equipment, uplink antenna, command center staffed by humans, and, optionally, lighting displaying the names of the sponsors. Contestants will have physical access to the 'ground segment'.
    4. The maximum size of the rectenna is TBD square meters.
    5. 10 kw must be delivered to the grid continuously from two hours after sunrise to two hours before sunrise at least 95% of every day of the X-Cup. Exceptions can be made for weather.
      1. The winner is the one that delivers the most power per unit mass of the 'space segment' during this period.
      2. No person may come within 10 meters of the 'space segment' from midnight before the start of the contest to the end (one hour before sunset on the last day) or access the 'space segment' except through commands sent wirelessly.
      3. No battery power may be delivered to the beam during this period.
    6. The power beam must use frequencies where the atmosphere is transparent under most conditions, including heavy rain and snow.
    7. No contestant may interfere with cell phone, satellite TV, commercial TV, or satellite radio transmission.
    8. All contestants will receive payments equal to the value of the electricity delivered to the grid.
    9. The winner will receive $TBD.
    10. Future years will involve longer distances and higher power levels.


    This is a much easier challenge and can be located at the X-Cup. The end-to-end system must be developed but without the challenges of the space environment. Again, innovative engineering will be required to deliver a working system. Furthermore, the best system can be dismantled, shipped to La Reunion island and put into operation.

    Future versions of this challenge will require contestants to scale up their systems towards more realistic SSP parameters.

    Virtual SSP Construction

    The second challenge is a software challenge. The idea is similar to RoboCup where software robot teams play soccer on a virtual field. In the SSP X-Prize case the field is simulation of orbital construction of a solar power satellite. In each heat, each of four contestants build one quarter of the satellite from pre-defined components. Contestants are given a mass budget for robotic builders and a set of parts to construct them from. Energy and thermal limitations for the robots and realistic vision inputs are important parts of the playing field.

    Contestants are allowed software control without time delay and/or simulated teleoperation from Earth by human operators with a delay appropriate for geosynchronous construction. Time to completion is the competitive measure.


    This allows participation by those with nothing more than a computer, time, expertise, and enthusiasm. Furthermore, it can develop techniques needed to efficiently build large space structures.


    Long term, space solar power has the potential to end energy-driven war and supply vast quantities of power to everyone at very low economic and environmental costs; while significantly progressing our space capabilities, particularly launch, in situ resource utilization and construction of large space structures.

    An X-Prize of a few tens of millions of dollars and a series of X-Challenges suitable for the X-Cup are proposed. If funded and implemented, there is reason to believe that a large fraction of the people of Earth will benefit greatly in the long term.


    (1) A billion-dolar scale prize system was proposed in A U.S. Space Program for Space Settlement, Al Globus, 25th Internatioal Space Development Conference, National Space Society and the Planetary Society, Los Angeles, California, 4-7 May, 2006, but this is beyond the scope of this proposal.

    (2) For additional information, see the extremely extensive materials archived by the National Space Society at