Re: CLIO satellite launch on Sept 16

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Mon, 15 Sep 2014 16:04:15 +0200
Based on the coast period and the ground trace shown in the mission
overview, it is clear that CLIO will go to some sort of medium height
earth orbit, not geosynchronous.
(http://www.ulalaunch.com/uploads/docs/Mission_Booklets/AV/av_clio_mob.pdf)

The Centaur upper stage will launch the payload into an elliptical
orbit, with MECO-1 about 18 minutes after launch. It will then coast
for 2.5 hours after which a second burn is performed. CLIO will
separate from the upper stage shortly after that. This trajectory is
different from the trajectory typically flown for geostationary
payloads, where the upper stage will coast to the first descending or
ascending node, and then perform the second burn to inject the stage
into the geostationary transfer orbit. The coast time of 2.5 hours
resembles that used on GPS launches into 55 deg orbits; these last
about 3 hours.

The mission overview contains enough information that we can estimate
orbital elements for the transfer orbit. From the ground trace shown
in the mission overview, the coast period extends between these two
points:
 34W,  9N at  1078.1s after launch (MECO-1)
 90E, 20S at 10072.9s after launch (MES-2)
Here the latitude and longitude are approximate, and they assume the
ground trace is correct.

If we further assume that the second burn of the Centaur upper stage
occurs at apogee of the transfer orbit (zero radial velocity), we can
compute a set of transfer orbits that satisfy the boundary conditions
given three parameters; the apogee altitude, apogee velocity and
direction of velocity. By numerically integrating back from the MES-2
position and time to MECO-1 position and time, I obtain the following
approximate transfer orbits:

# 15000 km apogee
1 82301U 14999A   14260.02214449  .00000000  00000-0  00000-0 0    08
2 82301  34.6956 125.4827 3436967 149.3206 168.2153  4.30685461    04
# 16000 km apogee
1 82302U 14999A   14260.02214449  .00000000  00000-0  00000-0 0    09
2 82302  34.6997 125.4822 4205739 147.5971 170.1859  4.37681794    03
# 17000 km apogee
1 82303U 14999A   14260.02214449  .00000000  00000-0  00000-0 0    00
2 82303  34.7035 125.4825 4977685 146.4071 171.6579  4.44139369    05
# 18000 km apogee
1 82304U 14999A   14260.02214449  .00000000  00000-0  00000-0 0    01
2 82304  34.7069 125.4839 5751391 145.5372 172.8519  4.50105857    06

These elements are valid for a launch at the start of the launch
window, 2014-09-16T21:44:00UT.

For orbits with a higher apogee, the solutions are no longer realistic
as these predict an altitude at MECO-1 which is smaller than the
radius of the Earth. This table below gives the apogee altitude,
velocity and direction of velocity as well as the MECO-1 altitudes for
a set of solutions.

Apogee                 MECO-1
Alt.  Vel.    Dir.     Alt.
(km)  (km/s)  (deg)    (km)
15000   3.51   27.63   4188.8
16000   3.22   27.63   2887.1
17000   2.93   27.64   1604.1
18000   2.64   27.64    337.8
19000   2.34   27.64   -913.6
20000   2.02   27.64  -2152.4

These calculations show that the coast period is too short to insert
CLIO into a geosynchronous orbit, and suggests it is going to a medium
altitude orbit instead. Within the assumptions, if the payload is
inserted into a circular orbit at these apogee altitudes, they rule
out an orbital period that repeats twice a day, like that of the GPS
satellites (20300 km), unless the payload manouvres to a higher orbit
itself.

As usual with CCAFS launches, Greg Roberts has the best seat in the
house. For his location the elements above predict eclipse exit
between 22:30 and 22:45UT at elevations of 60 deg and
above. Unfortunately the MES-2 burn occurs at only 10 deg elevation in
his Eastern horizon.

Regards,
   Cees
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Received on Mon Sep 15 2014 - 09:05:02 UTC

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