TiPS tether angular length

Robert H. McNaught, Anglo-Australian Observatory (RMN@AAOCBN1.AAO.GOV.AU)
Tue, 25 Jun 1996 8:16:25 +1000 (EST)

The following table gives the theoretical apparent angular length of the TiPS
tether based on

1) a tether length of 4.0 km.
2) circular orbit of height 550 nautical miles (1019 km)
3) tether pointing vertically down

 Elev.  Length       Elev.  Length      Elev.  Length
  deg   arcmin       deg    arcmin      deg    arcmin       
  0.0    3.16        30.0    5.93       60.0    5.15
  5.0    3.65        35.0    6.15       65.0    4.52
 10.0    4.17        40.0    6.24       70.0    3.77
 15.0    4.68        45.0    6.19       75.0    2.92
 20.0    5.17        50.0    5.99       80.0    1.99
 25.0    5.59        55.0    5.64       85.0    1.01
                                        90.0    0.00

The maximum apparent length is 6'.25 (0.104 deg) at an elevation of 41 degrees.
Note that the apparent length near the horizon is still substantial despite the
greatly increased distance.

Being site independent, one only need note the predicted elevation to derive
the length.

Paul Maley noted a length of 0.12 deg at 31 deg elevation, close to the
prediction above of 0.10 deg.  However Paul's maximum length of 0.17 deg is
much longer than the maximum predicted (0.104 deg).  I don't believe I have
made any error in the calculations (but someone may like to check), which
would imply one or more of the initial assumptions are in error.  Certainly,
if the tether were perpendicular to the line of sight when overhead, it
would subtend 0.42 deg, so a moderate tilt could happily accomodate Paul's
observation.

Cheers, Rob McNaught
aaocbn2.aao.gov.au