The researchers at NORAD*, which is located under Cheyenne Mountain in Colorado Springs, Colorado, are currently tracking 20,000 objects in space as big as a softball or bigger.  Most of these orbiting objects are space debris fragments that can pose a collision hazard to other orbiting satellites such as the International Space Station.

Tracking these fragments of debris is complicated and expensive.  Preventing collisions is expensive, too.  So, too, is designing and building space vehicles that can withstand high-speed impacts.  A cheaper alternative may be to sweep some of the debris out of space to minimize its hazard to other orbit-crossing satellites.

When two orbiting objects collide with one another, the energy exchange can be large and destructive.  Two one-pound fragments impacting each other in a solid collision in low-altitude orbits intersecting at a 15-degree incidence angle can create the energy caused by exploding two pounds of TNT!!

One scientific study showed that returning substantial numbers of debris fragments to Earth with a hydrogen-fueled spaceborne tug would cost approximately $3 billion for each percent reduction in the fragment population – which has been increasing by about 12 percent per year, on average.

Fortunately, a powerful, but relatively inexpensive laser on the ground pointing vertically upward can be used to deorbit fragments of space debris traveling around the earth in low-altitude orbits.  The radial velocity increment provided by such a ground-based laser causes the object to reenter the earth’s atmosphere as shown in  the sketch in the upper left-hand corner of Figure 1.

The total required velocity increment can be added in much smaller increments a little at a time over days or weeks.  Drag with the atmosphere was neglected in the case considered in Figure 1, but, in the real world, atmospheric drag would help the object return to Earth.

Radiation pressure created by the assumed 50,000 watt laser beam is equivalent to 40 suns spread over the one square foot cross section of the object.  The total photon pressure equals 1/13^th of a pound per square foot.__________

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*  NORAD = North American Aerospace Defense (Command)

The researchers at NORAD*, which is located under Cheyenne Mountain in Colorado Springs, Colorado, are currently tracking 20,000 objects in space as big as a softball or bigger.  Most of these orbiting objects are space debris fragments that can pose a collision hazard to other orbiting satellites such as the International Space Station.

Tracking these fragments of debris is complicated and expensive.  Preventing collisions is expensive, too.  So, too, is designing and building space vehicles that can withstand high-speed impacts.  A cheaper alternative may be to sweep some of the debris out of space to minimize its hazard to other orbit-crossing satellites.

When two orbiting objects collide with one another, the energy exchange can be large and destructive.  Two one-pound fragments impacting each other in a solid collision in low-altitude orbits intersecting at a 15-degree incidence angle can create the energy caused by exploding two pounds of TNT!!

One scientific study showed that returning substantial numbers of debris fragments to Earth with a hydrogen-fueled spaceborne tug would cost approximately $3 billion for each percent reduction in the fragment population – which has been increasing by about 12 percent per year, on average.

Fortunately, a powerful, but relatively inexpensive laser on the ground pointing vertically upward can be used to deorbit fragments of space debris traveling around the earth in low-altitude orbits.  The radial velocity increment provided by such a ground-based laser causes the object to reenter the earth’s atmosphere as shown in  the sketch in the upper left-hand corner of Figure 1.

The total required velocity increment can be added in much smaller increments a little at a time over days or weeks.  Drag with the atmosphere was neglected in the case considered in Figure 1, but, in the real world, atmospheric drag would help the object return to Earth.

Radiation pressure created by the assumed 50,000 watt laser beam is equivalent to 40 suns spread over the one square foot cross section of the object.  The total photon pressure equals 1/13^th of a pound per square foot.

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*  NORAD = North American Aerospace Defense (Command)

Figure 2:  These engineering calculations show that the 20,000 space debris fragments now circling the earth in low-altitude orbits could, on average, each be deorbited with ground-based lasers for approximately $40,000 worth of electrical power.  Those same ground-based lasers could be used in a different mode to reboost valuable or dangerous payloads in low-altitude orbits or to send those payloads bound for geosynchoronous orbits onto their transfer ellipses.  (SOURCE:  Short course “Fundamentals of Space Exploration”.  Instructor: Tom Logsdon.

Seal Beach, CA)