Index The Garwin Archive

"Defense is Easier From the Ground," Op-Ed piece by R.L. Garwin
published in Space News, March 11-17, 1991.

                       Richard L. Garwin
                          P.O. Box 218
                  Yorktown Heights, NY  10598
                         (914) 945-2555
                      FAX: (914) 945-4419

                                                 March 7, 1991


  At  a  Pentagon  press conference February 12, the Strategic
  Defense Initiative Organization's  Director,  Henry  Cooper,
  argued   that  a  system  of  1000  child-sized  space-based
  interceptors  (Brilliant  Pebbles  or  "BP")  could   defend
  against  the  stretched Scud missiles then being launched by
  Iraq against Israel and Saudi Arabia.

  But it is clear that the more urgent and important the  task
  of  countering  tactical  or theater ballistic missiles like
  the stretched Scud, the less one wants to rely on  Brilliant
  Pebbles,  and  the  more  one  wants to rely on ground-based

  Whether you need a new refrigerator or new software for your
  personal computer, the beginning  of  wisdom  is  comparison
  shopping.    What would a system of space-based interceptors
  need to do to destroy a stretched Scud (call it Scud-S), and
  how else might this be done?   As modified by  Iraq,  Scud-S
  has  a range of some 800 kilometers (500 miles) and a flight
  time of 480 seconds, with apogee (maximum height)  of  about
  200 kilometers (124 miles).

  The  1000  orbiting  BPs  would be pre-authorized to destroy
  missiles rising from a certain region, Iraq in  the  present

  So  the  BP  defense  against  a single Scud-S would need to
  observe the launch of  the  missile,  assign  a  BP  to  the
  intercept, orient the BP to project itself to near-collision
  with  the  predicted apogee of the Scud-S path, and maneuver
  during the last seconds of final approach,  at  a  speed  of
  some  10 kilometers  per  second  (22,000  miles  per  hour)
  through the rarefied atmosphere to collide with the  missile
  and  to  destroy it by impact.  During the 200 seconds or so
  from Scud-S launch to apogee intercept, the orbital speed of
  the BP would have carried  it  some  1600  kilometers  (1000

  Cooper  says the United States will not deploy the BP unless
  some invention makes it possible to solve the problem  posed
  by  (Soviet)  ICBM  warheads  equipped with countermeasures.
  These countermeasures might include enclosing  the  re-entry
  vehicle  or  missile  in  an  inflatable multilayer balloon,
  accompanied by similar balloons tethered at  a  distance  of
  10 meters  (33 feet)  or  so.    In  reality,  it  is highly
  doubtful that a BP could identify and reject tethered  decoy

  The interesting point is that the country should not want to
  deploy   Brilliant  Pebbles  against  Scud-S  even  if  that
  long-sought invention is forthcoming.  Because Scud-S  could
  be  flown  with  100 km  (62 mile) apogee with minor loss of
  maximum  range,  even  against   simple   missiles   without
  countermeasures  the  BP's  homing  sensor  must  be able to
  operate  in  the  residual  atmosphere  at  100   kilometers
  altitude, which at the BP's high velocity would rapidly heat
  the frontal area of the sensor.

  If  we  imagined  that  the BPs could somehow do the job, we
  could do it better, sooner, and more reliably  with  BPs  of
  lesser capability based on the ground in the target country:
  ground-based interceptors, "GBI".

  A  BP  homing  head  on  the  ground anywhere within 100-200
  kilometers (62-125 miles) of the expected  target  could  be
  launched at least as soon after the Scud-S launch as could a
  BP  cued  by  the  same  system with which the U.S. observed
  every  Iraqii  Scud  launch.    Instead  of   the   enormous
  additional  reachout  speed  provided the space-based BPs to
  compensate for their being in the wrong place  when  needed,
  the  ground-based  interceptor  would  require  maneuver and
  launch speeds each less than 3 kilometers per  second  (7700
  miles  per hour) to meet the Scud-S at apogee.  Needing less
  fuel than the BP, a GBI could carry a larger warhead with  a
  lethality-enhancement  device  such  as an umbrella or mesh.
  Furthermore, launching the interceptor from the ground could
  be done with a rocket in the 200-kilogram (440-pound) weight
  class; one would need a rocket five or 10 times as large  to
  launch  each  BP  to  orbit  (even  with  a  BP  homing head
  one-fifth the mass of the GBI's).

  The ground-based interceptor would need to detect its target
  only in a very limited uncertainty area at  a  distance  not
  exceeding  200  kilometers,  and  the  closing speed for the
  intercept would be less than half the closing speed for a BP
  intercept.    The  infrared  sensors  of  the   ground-based
  interceptor  would  operate  on  battery  power  without the
  necessity of an on-orbit solar power  system,  refrigerator,
  station-keeping, etc.  Rugged semi-active radar homing, with
  apogee   illumination   from  a  ground-based  radar  is  an
  alternative for a GBI provided good cueing information.

  Furthermore,  the  ground-based  interceptor  would  need  a
  sensor  operating  life  not  exceeding five minutes, versus
  five years in the  space  environment  for  the  space-based
  interceptor.    Its  infrared sensor has an easier task than
  the  space-based  BP;  it  does  not  need to see its target
  against the background of the Earth or the dense atmosphere,
  and the atmospheric  heating  for  the  slower  ground-based
  interceptor  is  about  1%  that suffered by the space-based
  interceptor at the same altitude.   In contrast to  the  few
  BPs  that could respond to any multiple launch, ground-based
  interceptors could be launched from  the  target  region  as
  many at a time as desired.

  The  conclusion  is  clear.    The  more urgent the need for
  protection against Scud-S and its more accurate  successors,
  the  less one wants to deploy a constellation of space-based
  interceptors for that task.  Against theater-range  missiles
  without     countermeasures,     dedicated,     ground-based
  interceptors with existing  radar-homing  sensors  could  be
  smaller  and  cheaper  than the existing Patriot air-defense
  interceptor that can destroy only  those  Scuds  that  would
  impact  close to the Patriot launcher.  If Brilliant Pebbles
  homing  technology  works  brilliantly,   the   ground-based
  interceptor  would  no  longer  need the Patriot radar.   If
  discrimination outside the  atmosphere  cannot  be  achieved
  (the  long-sought  invention does not emerge), one will have
  to fall back on intercept as the  missile  descends  through
  the   atmosphere,   and   for   that   purpose   space-based
  interceptors are even less suitable than they are for apogee

  Richard L. Garwin
  Richard Garwin is science adviser to the director of research
  at the Thomas J. Watson Research Center, Yorktown Heights, N.Y.
  These are his personal views.