increases. Thus the ;Jrocess of docking, or flying in formation
with a satellite already in a preceding orbit hec0mes a compli-
cated and difficult maneuver involving descent to a lower, and
therefore smaller, orbit with the lcsultaDt increase in angular
velocity causing the following orbiting body to appr~ach the preceding.
Atmospheric drag slows the satellite speed, especially near
perigee, and this causes the satell i te to swing out to a smaller
subsequent apogee. TIle urbit contracts and becomes more circular.
Eventually the satellite descends to an altitude where the drag
causes the satellite to reenter the earth's atmosphere.
Table 5 shows some calculated decelerations for a massive
object such as H satellite, and a small meteoritic particle of
-3 -4
0.1 ('m. di:.wleter anu density of 0.4 gm/cm (mass'= 2.0~ x 10
gram~J. At 160 km. (the perigee of many of the manned space-
cruft orbitH) the deceleration on the ~pacecraft is not trivial
_?
(0.017 cm/sec '-) and the orbit will slowly, but surely degrade
tu a reentry. Of lntercst in connection with the observation of
small particles by the astronauts is the differential acceleration
between the sp'1cecr e.ft ;::""j the particles. In a period of ten
seconds small part.icles will "drift" away from the spacecraft
a distance of some meters. Typical relative speeds of small
particl~s with respect to the spacecraft have been estimated by
the astronauts as 1 or 2 m/sec.
During reentry, the spacecraft Rnd fragments flaked off of
its surface become luminous, producing the di~j1lays sometimes
reported as UFUs. A s8tf'1lite reentry norlllully occurs along a
gl'J.::ing pe.th, but th t1'ajcctoril's of lJIeteorites are more radial,
anu then'fore the llUl'ation of luminosity is usually no Iwre than
two to three ~;ec()nd,.
TallIe' 6 shows tIlL' masses of Objects for given apparent stdlar
magnitudes and varying periods of luminosity, calculat.ed on the
as~'mption that all the orbital kinetic energy of the object is
281