Cassini flyby

Randy John (skysat@home.com)
Tue, 22 Jun 1999 01:16:15 -0700

I can't help Ed with Giotto, but I can with Cassini.

Cassini will make an earth flyby at 1999-Aug-18 03:28 UT nearly
over Easter island at an altitude of 1173 kilometers.

Observers in South America will have a near view of the space-
craft.  Those in North America will have a not so near view.
Europe will be in morning twilight.  Other areas will be in
daylight.

The TELNET version of Horizons gives this state vector (the WWW
version doesn't know about state vectors):

pfile_redesign_v2m189d.n
2451408.500000000 = A.D. 1999-Aug-18 00:00:00.0000 (TDB)
  -.1846909838200464E+06 0.7967070634416329E+05 0.4263070908016452E+05
  0.1417157944366931E+02 -.6815065498345841E+01 -.3603906365487077E+01

Horizons can be found at http://ssd.jpl.nasa.gov/horizons.html.

Here is the same vector in SKYSAT format:
CASSINI
1 XYZ KM 99230.00000000     -184690.98      79670.706      42630.709
2                          14.17157943   -6.815065498   -3.603906365X

Since Cassini will be in a hyperbolic orbit there will be NO TLE.  Standard
TLE's do NOT support eccentricities greater than or equal to 1 so you must
use a program like SKYSAT or Horizons.

Here is the Horizons output for my location.
 Date__(UT)__HR:MN     R.A.__(r-apparent)__DEC Azi_(r-appr)_Elev      delta
deldot
 1999-Aug-18 04:30 Ar  23 17 46.54 -11 53 50.9 106.7806   1.9938
0.0004149237  15.91196
 1999-Aug-18 04:40  m  23 19 31.97 -11 02 13.1 107.4146   4.1022
0.0004786968  15.89621
 1999-Aug-18 04:50  m  23 20 44.84 -10 21 33.7 108.2975   6.1934
0.0005424102  15.88230
 1999-Aug-18 05:00  m  23 21 38.73 -09 49 01.6 109.3600   8.2506
0.0006060727  15.87077
 1999-Aug-18 05:10  m  23 22 20.14 -09 22 29.1 110.5609  10.2726
0.0006696939  15.86163
 1999-Aug-18 05:20  m  23 22 52.74 -09 00 26.8 111.8747  12.2609
0.0007332833  15.85474
 1999-Aug-18 05:30  m  23 23 18.85 -08 41 51.8 113.2856  14.2165
0.0007968495  15.84988
 1999-Aug-18 05:40  m  23 23 40.01 -08 25 58.9 114.7838  16.1399
0.0008604002  15.84688
 1999-Aug-18 05:50  m  23 23 57.32 -08 12 15.2 116.3636  18.0310
0.0009239425  15.84553
 1999-Aug-18 06:00  m  23 24 11.56 -08 00 15.8 118.0219  19.8889
0.0009874828  15.84569
 1999-Aug-18 06:10  m  23 24 23.33 -07 49 42.1 119.7577  21.7122
0.0010510268  15.84723
 1999-Aug-18 06:20  m  23 24 33.08 -07 40 19.3 121.5713  23.4992
0.0011145799  15.85001
 1999-Aug-18 06:30  m  23 24 41.17 -07 31 56.2 123.4641  25.2475
0.0011781468  15.85393
 1999-Aug-18 06:40  m  23 24 47.87 -07 24 23.4 125.4384  26.9546
0.0012417319  15.85891
 1999-Aug-18 06:50     23 24 53.41 -07 17 33.8 127.4969  28.6174
0.0013053394  15.86486
 1999-Aug-18 07:00     23 24 57.98 -07 11 21.2 129.6428  30.2325
0.0013689729  15.87170

"Delta" is in AU's so at 6:00 the elevation is 20 degrees and the range
is nearly 148,000 km.  Almost as bad as Giotto.

In Austin, Ed will have a nice view with a range of 50,000 km, elevation 20
degrees at 4:20.

An observer at -75.0000, -15.0000 (near Lima, Peru) will have a much more
reasonable range of 3485 km at 3:33 and an elevation of 42 degrees.

                Randy

p.s.  A nice web page by Troy Goodson (a member of the Cassini
Flight Path Control Group) is at : http://www.csun.edu/~kg46825/cassini/.

p.p.s.  Horizons doesn't know about Giotto.