Re: {MPML} Chang'e 4 launch schedule?

From: Bill Gray via Seesat-l <>
Date: Wed, 5 Dec 2018 11:38:08 -0500
Hi Marshall,

On 05/12/2018 05.39, [mpml] wrote:
> They have apparently put out NOTAM type restrictions for the launch :
> 1815-1834 UTC - Long March 3B/E carrying Chang'e 4 lunar lander and
> rover to the far side of Luna!
> Regards
> Marshall

    Thank you.  I'm not having any real success in getting ephems
for this launch.  The Chinese space program is something of an
enigma wrapped in mystery inside a cloak of invisibility.

    However,  I've not given up hope.  Cees Bassa pointed out some
characteristics of the Chang'e 5T1 orbit,  which look to be quite
similar to those for Queqiao and Chang'es 2 and 3.  (Though my data
for those last two is pretty rough;  we didn't start observing them
until after the hardware had passed the moon.)

    In each case,  the trajectory was an eminently sensible one :
launch due east with things timed so that you enter your transfer
orbit to the moon exactly at a point opposite where the moon will
be at your apogee.  This uses the least necessary amount of fuel.
That point is roughly at longitude W 179,  latitude -1,  and
occurred about 13 minutes after launch for Queqiao.  Your
inclination is then roughly the latitude of the launch site.
Queqiao's was 28.57 +/- 0.01;  the launch site is at 28.15 N.

    Once we've got a more exact launch time,  I'll come up with an
orbit with perigee 13 minutes later,  just above that spot near
the international date line,  with inclination 28.57 degrees,  and
tweak the apogee distance to result in the object encountering the
moon about four days later (possibly constrained if I can get
data on when it's "officially" supposed to reach the moon).  The
lunar approach will ideally be prograde,  and I think coming in
from below the lunar equator (the landing is supposed to be near
the south pole).

    Given this,  we may at least get ephems suitable for finding
spacecraft and booster.  Or not,  since it'll probably be at a
low elongation from the sun,  and it's not a given that anybody
will even look.

-- Bill
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Received on Wed Dec 05 2018 - 10:39:04 UTC

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