John Mankins, a longtime U.S. SSP advocate, presented an update on an advanced concept under study with NASA funding known as Solar Power Satellite by means of Arbitrarily Large Phased Array (SPS-Alpha). The idea “represents a very different architecture for SPS, using a hyper-modular approach in which all platform elements can be mass-produced, and none are larger than a ‘smallsat,’” he writes. “This could enable significantly lower development time/cost, much greater ease of manufacturing at lower cost, and significantly higher reliability.”
Basically, mass-produced “intelligent” spacecraft weighing 100-300 kg (220-660 lb.) would assemble themselves into a constellation shaped to collect, convert and transmit solar energy through the “hive” of other spacecraft to a transmitter array assembled in the same fashion. Mankins says the idea is based on the behavior of bees and ants.
Mass Production (at Low Cost) of All Platform Elements.
The potential economic viability of SPSALPHA depends on mass-producing all elements of the system. The highly modular architecture will allow the use of manufacturing analogous to that currently used for satellites in large constellations (such as the Iridium), or in the manufacture of Remotely Piloted Vehicles (RPVs) rather than typical spacecraft. (With hardware costs of less than $500-$1,000 per kg.)
Robotic Assembly in Highly Structured Space Environments.
SPS-ALPHA depends on the use of in-space robotic assembly at a scale unprecedented previously. However, the requirement is for robotic assembly in a highly structured environment – not an unstructured environment such as that found in planetary surface exploration. The type of technology needed is currently in use in terrestrial applications such as automated mining operations and large commercial farming.
The current state of the SPS-ALPHA concept incorporates a total of some 8 elements – achieving an overall project goal. These elements include the following principal parts, each of which may be integrated in various implementations to realize the overall SPS-ALPHA SPS platform:
• HexBus Module
• HexFrame Structural Module
• Reflectors & Deployment Module
• Solar Power Generation Module
• Wireless Power Transmission (WPT) Module
• Modular Robotics / ISAAC Module
• Propulsion / Attitude Control Module
Conventional In-Space Transportation Cases
• Case 1: Conventional Large CommSat; power @ 8 kW, mass @ 3,000 kg; aperture @ 2 x 300 m2
• Case 2: CommSat-ALPHA; power @ 8 kW, mass @ 3,000 kg15; aperture @ 180 m
Advanced In-Space Transportation Cases
• Case 3: CommSat-ALPHA; power @ 16 kW, mass @ 6,000; aperture @ 600 m2
• Case 4: CommSat-ALPHA; power @ 32 kW, mass @ 12,000; aperture @ 1,200 m2
SUMMARY AND CONCLUSIONS
The SPS-ALPHA concept represents a very different architecture for space solar power, involving a hyper-modular approach in which all platform elements can be mass produced, and none are larger than a “small sat”. If proven feasible, SPS-ALPHA could enable significantly lower development time and cost, much greater ease of manufacturing at lower cost, and significantly higher reliability.
During the past 40 years, space solar power for Earth has remained little more than a vision. Power for space missions has remained both scarce and expensive: most satellites operate on less powerthan that needed to run a typical home in the U.S., many on considerably less. If SPS-ALPHA can be developed, solar power in the range of 100s MW to 100s GW could be harvested in space and delivered efficiently to markets on Earth, and to enable energy-rich operations throughout the inner solar system –transforming all aspects of government and commercial space.
Systems analysis results from the 2011-2012 NIAC Phase 1 study project suggest that SPS-ALPHA may be able to achieve economic viability. Following technology maturation and systems-level demonstrations, the SPS-ALPHA concept delivered close to commercial results (e.g., less than 20¢ per kW-hr) with technologies currently in the laboratory, and competitive commercial energy (e.g., less than 10¢ per kW-hr) with selected improvements in key technologies.
Solar power satellites based on SPS-ALPHA could deliver power on demand to more than 90% of Earth’s population at locations across the globe. It would have a near zero “carbon footprint” and facilitate reaching greenhouse gas (GHG) emission reduction goals. Affordable and continuous solar energy delivered on large scale affordably from SPS to the U.S. and other markets would transform terrestrial power since no other “green energy” technology has similar potential to provide sustainable and “dispatchable” baseload power that is essentially immune to diurnal variations or to weather. SPSALPHA could enable a more rapid, effective and affordable response to natural disasters and calamities (e.g., the 11 March 2011 disaster in Japan).
As has been found in past studies and for other SPS concepts going back to the 1970s, ETO transportation remains a critical factor in realizing economically viable SPS for terrestrial markets. Inspace transportation costs are also important, but appear closely tied to ETO cost; in other words, low-cost in-space transportation (from LEO to GEO) cannot be realized without low-cost ETO transportation.
In addition, there are a number of prospective civil, commercial and security related applications of the SPS-ALPHA space systems architecture. These range from power for permanently shadowed regions at the lunar poles, to near-term applications in various Earth-orbiting satellites where a large, lowcost aperture is required.
In most locations across the Inner Solar System solar energy is available, sometimes continuously. This project would advance the capability to deliver power (at less than $1/kW-hour) to civil or commercial space missions in space, on the Moon, Mars, or small bodies. The availability of reliable, inexpensive and continuous power at levels of 100s kW to 10s MW or higher would forever change the character of space systems, missions, and goals. Moreover, high power large apertures would be of great value for U.S. security space missions. And, recent studies (e.g., for DOD NSSO) concluded that development of SSP systems and technologies, including SPS, would significantly benefit the security of the U.S. and its allies. Not only would space systems benefit, but benefits would also result from delivery of assured, affordable power to forward bases, military operations, markets, and allies.
Finally, ancillary SSP technologies – in areas such as space transportation, space communications, in-space construction, robotics, lightweight structures, etc. – would be of immense value to a wide range of civil / commercial space missions.
The roadmap for SPS-ALPHA appears quite tractable programmatically: the hyper-modular architecture should enable fast-paced, relatively inexpensive steps forward, with a total cost for a scalable solar power satellite pilot plant of about $5B and the first full-scale SPS of roughly $20B. These numbers are substantial, but compare well to the reported $100B cost of the ISS or the earlier 1980s era estimates of roughly $1,000B to reach the first SPS.
In summary: the SPS-ALPHA advanced concept is extremely promising and warrants future consideration.