Re: {MPML} Alternative Tesla/booster ephems

From: Bill Gray via Seesat-l <seesat-l_at_satobs.org>
Date: Wed, 7 Feb 2018 20:01:53 -0500
Hi Sam,

    I'll take the liberty of copying some data Rob Matson sent me :

----------- snip --------------------
Some specs on the roadster:

Dimensions are 1.873 m (W) x 3.946 m (L) x 1.128 m (H)

So looking down from above, the area is 7.39 m^2. Paint reflectivity for
a dark red paint is around 12% (ignoring the specular component, which
may be significant for some geometries).
------------ snap --------------------

    We can then consult with

https://www.minorplanetcenter.net/iau/lists/Sizes.html

    7.39 m^2 at 12% should roughly match 3.6 m^2 at 25%,  which is
what you'd get with a rock with a radius just a bit over one meter,
or diameter over two meters... puts us in the neighborhood of H=30.4.

    I don't think we know yet if we're looking at a Tesla
combined with the stage that boosted it into heliocentric
orbit,  or if they separated and there ought to be two
different objects.  In the latter case,  I'd think the underside
of the Tesla would _not_ be painted red,  and might be a little
brighter.

-- Bill

On 2018-02-07 19:24, Sam Deen wrote:
> Hi Bill,
> 
> I honestly never expected I would say this in my life, but what is the approximate absolute magnitude of a tesla roadster in space?
> 
> ~Sam
> 
> 
> On Wednesday, February 7, 2018 10:08 AM, "Bill Gray pluto_at_projectpluto.com [mpml]" <mpml-noreply_at_yahoogroups.com> wrote:
> 
> 
> Hello all,
> 
> In my previous message, I assumed that C3 really was 12 km^2/s^2.
> Following is what you get if the q/Q values are roughly correct.
> 
> They lead to _very_ different ephemerides, unfortunately. Both,
> unsurprisingly, favor observing in southern morning skies.
> However, they're about 20 degrees apart.
> 
> If anybody got observations _after_ the final burn, we might be
> able to settle the matter pretty quickly. Ideally, an RA/dec measured
> from an image at a particular location at a particular time. Even a
> single such observation ought to rubbish one of these orbit solutions
> (hopefully, not both of them!)
> 
> Anyway. _If_ it's actually the q and Q from Mr. Musk's tweet that
> are right, and (as before) we assume the objects sped up at 02:30
> UTC along their existing velocity vector until they were going fast
> enough to have those elements, we get...
> 
> Orbital elements: Sped-up
> Perihelion 2018 Jan 28.639832 TT = 15:21:21 (JD 2458147.139832)
> Epoch 2018 Feb 9.0 TT = JDT 2458158.5 Earth MOID: 0.0000 Ma: 0.0934
> M 4.63650 (J2000 ecliptic)
> n 0.40813685 Peri. 168.57287
> a 1.79997100 Node 317.89354
> e 0.4554736 Incl. 3.36051
> P 2.41/882.04d q 0.98013165 Q 2.61981035
> 
> Orbital elements: Sped-up
> Perigee 2018 Feb 7.107275 TT = 2:34:28 (JD 2458156.607275)
> Epoch 2018 Feb 8.0 TT = JDT 2458157.5 Gray
> q 7133.54306km (J2000 equator)
> Peri. 148.15635
> Node 285.92927
> e 1.7405665 Incl. 28.92091
> 
> (called 'Sped-up' because it requires a boost in speed over the
> earlier C3=12 km^2/s^2 solution.)
> 
> And, as before, the following synthetic astrometry can be pushed
> through Find_Orb to get customized topocentric ephemerides.
> 
> -- Bill
> 
> Sped-up C2018 02 07.50000 13 09 49.141-28 13 37.84 SynthE12
> Sped-up C2018 02 07.51000 13 10 00.415-28 16 51.34 SynthE12
> Sped-up C2018 02 07.52000 13 10 09.875-28 19 55.93 SynthE12
> Sped-up C2018 02 07.53000 13 10 17.643-28 22 51.71 SynthE12
> Sped-up C2018 02 07.54000 13 10 23.830-28 25 38.73 SynthE12
> Sped-up C2018 02 07.55000 13 10 28.549-28 28 17.06 SynthE12
> Sped-up C2018 02 07.56000 13 10 31.903-28 30 46.74 SynthE12
> Sped-up C2018 02 07.57000 13 10 33.997-28 33 07.83 SynthE12
> Sped-up C2018 02 07.58000 13 10 34.929-28 35 20.39 SynthE12
> Sped-up C2018 02 07.59000 13 10 34.796-28 37 24.47 SynthE12
> Sped-up C2018 02 07.60000 13 10 33.691-28 39 20.14 SynthE12
> Sped-up C2018 02 07.61000 13 10 31.706-28 41 07.47 SynthE12
> Sped-up C2018 02 07.62000 13 10 28.928-28 42 46.56 SynthE12
> Sped-up C2018 02 07.63000 13 10 25.443-28 44 17.48 SynthE12
> Sped-up C2018 02 07.64000 13 10 21.334-28 45 40.35 SynthE12
> Sped-up C2018 02 07.65000 13 10 16.684-28 46 55.28 SynthE12
> Sped-up C2018 02 07.66000 13 10 11.569-28 48 02.41 SynthE12
> Sped-up C2018 02 07.67000 13 10 06.066-28 49 01.87 SynthE12
> Sped-up C2018 02 07.68000 13 10 00.248-28 49 53.83 SynthE12
> Sped-up C2018 02 07.69000 13 09 54.186-28 50 38.45 SynthE12
> Sped-up C2018 02 07.70000 13 09 47.948-28 51 15.92 SynthE12
> Sped-up C2018 02 07.71000 13 09 41.599-28 51 46.43 SynthE12
> Sped-up C2018 02 07.72000 13 09 35.202-28 52 10.19 SynthE12
> Sped-up C2018 02 07.73000 13 09 28.818-28 52 27.42 SynthE12
> Sped-up C2018 02 07.74000 13 09 22.502-28 52 38.35 SynthE12
> Sped-up C2018 02 07.75000 13 09 16.310-28 52 43.23 SynthE12
> Sped-up C2018 02 07.76000 13 09 10.292-28 52 42.32 SynthE12
> Sped-up C2018 02 07.77000 13 09 04.497-28 52 35.86 SynthE12
> Sped-up C2018 02 07.78000 13 08 58.969-28 52 24.14 SynthE12
> Sped-up C2018 02 07.79000 13 08 53.750-28 52 07.43 SynthE12
> Sped-up C2018 02 07.80000 13 08 48.881-28 51 46.01 SynthE12
> Sped-up C2018 02 07.81000 13 08 44.396-28 51 20.19 SynthE12
> __._,_.___
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> Posted by: Bill Gray <pluto_at_projectpluto.com>
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Received on Wed Feb 07 2018 - 19:02:52 UTC

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