Re: {MPML} SpaceX Hardware - Booster observations

From: Bill Gray via Seesat-l <seesat-l_at_satobs.org>
Date: Thu, 8 Feb 2018 07:15:31 -0500
Hi Jaime,

    Well... not really.  The orbits I came up with,  based just on
the total energy (C3=12 km^2/s^2) or the q and Q given in Elon
Musk's tweet,  both turned out to be badly wrong.  The "correct"
guess,  based on C3,  was still about six degrees off.  We'd never
have found it without getting the state vector via Jonathan,
which is what I used for those predictions I sent you.

    All I had to go on was the TLE for launch to heliocentric burn,
plus the aforementioned C3 and q/Q values.  So I just took the
state vector as of 02:30 UTC (near the end of the burn),  and
increased it in magnitude so that it would have that value of C3.
(And for the alternative orbit,  I did the same thing,  except
giving it Q=2.61.)

    You would do that if you wanted to get exactly the maximum
amount of energy into the orbit.  However,  there could be some
other considerations (especially if your goal is to go to a
specific point in space,  which wasn't an issue here),  and
you wouldn't lose much energy if you were "misaligned" by several
degrees.  Which happened here.  My assumption of a "straight ahead"
burn was a big assumption... unfortunately,  with the info I had,
I didn't have much choice.

    It wouldn't surprise me if the Tesla really is exactly where
the Horizons ephems (based on a full-precision state vector) say
it is,  possibly within arcseconds.

    And as I wrote this,  I got some more astrometry,  from
Richard Kowalski at (703) Catalina... should have that posted
shortly,  after I check out some interesting objects that just
popped up on NEOCP.  All this,  and I've not even finished my
first cup of coffee...

-- Bill

On 2018-02-08 06:55, jimmy newman wrote:
> ... about only 20 arcmin of the Bill "predictions" !!
> Jaime
> 
> On Thu, Feb 8, 2018 at 11:47 AM, Bill Gray pluto_at_projectpluto.com <mailto:pluto_at_projectpluto.com> [mpml] <mpml-noreply_at_yahoogroups.com <mailto:mpml-noreply_at_yahoogroups.com>> wrote:
> 
>     __
> 
>     Hi all,
> 
>     Jaime Nomen at (Z66) in Spain and Cristovao Jacques at (Y00)
>     in Brazil both got this object, at a distance slightly greater
>     than the moon (390000 to 416000 km). With either of their data,
>     we'd have gotten a decent orbit. With both, we've got one that
>     will ensure it'll be easy to keep track of... looks as if we'll be
>     able to do that for at least a week before it gets too faint :
> 
>     https://projectpluto.com/temp/spacex.htm#eph <https://projectpluto.com/temp/spacex.htm#eph>
> 
>     I still don't know if this is just the booster, or if it's booster
>     plus car. It looks to me that if they were still attached to each
>     other, you wouldn't be able to tell from the camera images; the
>     booster would be "hidden" on the underside of the vehicle.
> 
>     On the other hand, the positions measured by Cristovao and Jaime
>     are almost a quarter degree from the Horizons ephemerides, which is
>     about the difference we often see between payload and booster. My
>     guess is that the car will, sadly, be several magnitudes fainter
>     and therefore not too likely to show up... still worth looking
>     through the images, though; it could be brighter than I'm thinking.
> 
>     -- Bill
> 
>     __._,_.___
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>     Posted by: Bill Gray <pluto_at_projectpluto.com <mailto:pluto_at_projectpluto.com>>
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Received on Thu Feb 08 2018 - 06:16:42 UTC

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