SpaceBased Solar Power

1
Space-Based Solar Power

• James Harkins, Dan Livingston, Alex Wong, Aaron
  Sanders

2
How it works

• Solar panels on satellite capture light, sends
  power to earth using microwave wireless power
  transmission technology

Signal sent from receiving antenna on earth
(green) allows satellite to pinpoint its
microwave beam.
3
History

• Producing electricity in space from sunlight is
  used by hundreds of satellites in operation
  today.
• In 1968, Dr. Peter Glaser, formerly of NASA,
  introduced the concept of a solar power satellite
  system with square miles of solar collectors in
  high geosynchronous orbit to collect and convert
  the sun's energy into a microwave beam to
  transmit energy to large receiving antennas
  (rectennas) on earth.
• In 1999 NASA formed SERT, the Space Solar Power
  Exploratory Research and Technology program to
  perform design studies and evaluate feasibility.

4
Design Ideas

• Thrusters must be used to counteract solar winds
• The space-based antenna needs to be at least 1 km
  in diameter, making it far larger than any
  satellite ever proposed.
• Recieveing antenna (an array of wires) must cover
  20,000 acres.
• Sidebands not worth capturing
• Laser alternative to microwave power transmission.

Sage-Hall Thrusters
5
Technology obstacles to overcome

• NASA estimates a SSP will need to operate
  at 1000v or higher, which leads to
  self-destructive arcing. Current
  experimentation is at 300 v.
• Wireless power transmission only
  recently became a reality, with
  small amounts of power over a few
  feet.
• Lots of design work left regarding the high
  temperature characteristics of the transmitting
  antenna and the solar array.

Example of self destructive arcing
Image http//gltrs.grc.nasa.gov/reports/2000/TM
-2000-210210.pdf 
6
Solar Arrays

• Weight between 0.5 kg/kW to 10 kg/kW
• Lifespan is about 20 years
• Exposure to charged particles can reduce the
  lifespan drastically
• Naturally degrades about 1 to 2 percent per year
• Efficiency up to 30
• Solar radiation is 5-10 times greater in space

7
Power

• Efficiency of power transmission is about 50
• Microwave transmission will diffract greatly
• Total efficiency is about 7
• Power yield from rectenna is about 90 W/m2
• Lasers are an alternative to microwaves
• Rectenna will only need to be 180m in diameter

8
Benefits of SSP
9
General Benefits

• No pollution after construction
• No ghg during power generation
• Source of energy is free
• Large amount of energy potential.

10
Space Advantages

• Less atmosphere for sunlight to penetrate for
  more power per unit area
• Any location on Earth can receive power
• Satellite can provide power up to 96 of the time
• Solar panels do not take up land on Earth
• Lots of space in space
• Promote growth of space, solar, and power
  transmission technology

11
Problems with SSP

• VERY expensive initial cost
• Microwave/lasers may be harmful?
• Cosmic rays can deteriorate panels
• Maintenance Problems
• Very large receiving antennas on earth
• Solar winds could kick it off course
• Would need a complex propulsion system

12
VERY Expensive Initial Costs

• Cost of Lifting Cargo Into Space using Space
  Shuttle is currently 10000/kg
• Reusable Launch Systems looking to reduce this
  cost are underdeveloped
• Space Elevator

13
Microwave Concerns

?

• At the earth's surface, the microwave beam has a
  maximum intensity in the center of 23 mW/cm2
  (less than l/4 the solar constant) and an
  intensity of less than 1 mW/cm2 outside of the
  rectenna fenceline
• Retrodirective phased array antenna/rectenna

http//ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.g
ov/19800022396_1980022396.pdf
14
Very large antennas/rectennas

• The distance between the antenna and rectenna
  will be roughly the distance from Earth to
  geosynchronous orbit (22,300 miles)
• For best efficiency the satellite antenna must be
  circular between 1 and 1.5 kilometers in diameter
• The ground rectenna would need to be elliptical
  and around 14 kilometers by 10 kilometers

http//ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.g
ov/19800022396_1980022396.pdf
15
Very large antennas/rectennas (cont.)

• Anything smaller would result in excessive
  losses due to sidelobes.
• To collect and convert the
  desired energy the satellite would
  need between 50 and 100 square
  kilometers of collector area using
  standard 14 efficient monocrystalline silicon
  solar cells making this much larger than most
  man-made structures on Earth.
• Though not unfeasible, such an enormous
  undertaking in orbit has never been attempted
• image http//www.spacefuture.com/archive/concept
  ual_study_of_a_solar_power_satellite_sps_2000.shtm
  l  

Microwave power distribution on the ground
surface.
16
Targets

• Launch costs
• Currently 10,000/kg
• Not feasible with chemical rocket technology
• Space elevator
• SSP array costs
• Must be very efficient
• Currently 2.4 million/kW
• Ground-based 5,000/kW
• Operation and Maintenance