[meteorite-list] Son of Rosetta?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 16 Nov 2007 17:27:27 -0600
Message-ID: <01b101c828a8$403f82e0$4b29e146_at_ATARIENGINE>

Hi, All,

    Was it the CSS's Mt. Lemmon scope? (There are two big
scopes on Mt. Lemmon; three, if you count the one downhill
a bit on "Mt. Bigelow"). The size estimate of a 9-meter ball
for 10% albedo becomes a 1.5 meter ball (or equivalent
area) if shiny reflective metal. (If it's a "stealth" alien spy ship
with 1% albedo, it's 30 meters across!) The Ariane 5 upper-
stage ATV is 10.3 meters long and 4.51 meters in diameter;
don't know how reflective it is.

    While Rob and Larry know roughly 100 times more
about this than I do, I wonder why there is only an
"extremely remote" chance of it being the Ariane upper
stage?

    Trying to Google up Rosetta's flight plan (which has
changed more often than some people change underwear)
suggests (but does not state unequivovally) that there are
no powered maneuvers until the middle of 2011 when the
engine will fire to shift the new eccentric orbit acquired by
this recent (and earlier) flybys to one that will match 67P/
Churyumov-Gerasimenko's orbit.

    Therefore, I assume that all the gravity assist maneuvers
were performed entirely by "ballistic ballet"! Since "launching"
a probe from its upper stage requires only that the probe move
away just fast enough to clear the launch vehicle -- 10 cm/s?
or less? -- it would seem that they would have very similar
initial orbits.

    In addition to the big humping engine Rosetta has (capable
of 2300 m/s delta-v), it has 24 little thrusters for trajectory and
attitude control. Have they been fired? The Mars flyby was
a "blind" darkside pass; the probe was in safe mode shutdown
(but the lander took a look at Mars). Usually, you tweak orbits
at the bottom of the gravity well (closest approach) where your
money's worth more, so I guess there was no "thrusting" at Mars.

    I wouldn't rule out the launch stage vehicle unless somebody
had taken a copy of the Rosetta flight data up to launch and run
a stimulation on it with the upperstage velocity deficit (10 cm/s)
applied to Rosetta and seen where it would be by now. Maybe
they've done that already; don't know. There's hardly been time.

    Assuming the launch stage would be "trailing" the spacecraft,
it would have flown by Earth (first time) and Mars too, a little
later than the spacecraft. This would have changed the "altitude"
of the flyby (but I can't even find whether the flybys were "leading"
or "trailing" the respective planets). Would such delayed flybys
"twist" the inclination this much?

    Oh, wait, I'm beginning to get it. If the launch stage had its
inclination altered by the past flybys, it wouldn't show up for
this last Earth flyby at all. It has to have come from some
other point in solar space than Rosetta did. Gee, I hafta do
trigonometry now? Two orbits, tilted at 4.6 degrees, a million
miles out from their future intersection point... scribble, scribble.
The two objects are separated by some 80,000 miles vertically,
between the planes of their orbits. That's definitely planet-missing
distance...

    Unless... If the upper-stage vehicle's inclination was altered
right at the starting point, it would have had a different orbit, but
would made the same flybys at slightly different angles, since
the orbit begins at a node and all future flybys occur at nodes?
That's pretty unlikely, too, I guess, but it sounds more plausible,
even if it isn't.

    Rob's suggestion of a probe from Churyumov-Gerasimenko
is looking better all the time! It's supported by the fact that the
trailing object's inclination of 6.5144 degrees is similar to 67P/
Churyumov-Gerasimenko's inclination of 7.1205 degrees instead
of Rosetta's "flatter" 1.9156 degrees. Checking out the nosey
Earthlings...

    Maybe there are just a lot more objects out there than we
think there are. Or maybe the Universe just likes to tease us.


Sterling K. Webb
-----------------------------------------------------------------------
----- Original Message -----
From: "Rob Matson" <mojave_meteorites at cox.net>
To: <lebofsky at lpl.arizona.edu>; "Meteorite List"
<meteorite-list at meteoritecentral.com>
Cc: <lebofsky at comcast.net>; "Sterling K. Webb"
<sterling_k_webb at sbcglobal.net>; <mexicodoug at aol.com>
Sent: Friday, November 16, 2007 2:06 AM
Subject: [meteorite-list] Son of Rosetta?


Hi Larry and List,

Just when the "asteroid" Rosetta case of mistaken identity was finally
starting to settle down, things took a turn for the bizarre earlier
today. Another object has been discovered on a very similar trajectory
trailing Rosetta (see Minor Planet Electronic Circular MPEC 2007-V119
for object 2007 VF189).
Link: http://cfa-www.harvard.edu/mpec/K07/K07VB9.html

It was picked up November 12th at Mt. Lemmon. Compare the orbital
elements of it with those of Rosetta when it was mistakenly reported
as minor planet 2007 VN84 (designation now retired):

2007 VF189 Earth MOID = 0.0014
AU
Epoch 2007 Oct. 27.0 TT = JDT 2454400.5 MPC
M 302.93114 (2000.0) P Q
n 0.75186100 Peri. 84.69614 -0.72209792 -0.68599714
a 1.1977817 Node 51.95276 +0.58124996 -0.67166613
e 0.3857965 Incl. 6.51444 +0.37513076 -0.27977230
P 1.31 H 28.3 G 0.15 U 6

Orbital elements:
Rosetta Earth MOID = 0.0001
AU
Epoch 2007 Oct. 27.0 TT = JDT 2454400.5 MPC
M 302.66563 (2000.0) P Q
n 0.76181070 Peri. 79.69236 -0.65353221 -0.75645089
a 1.1873297 Node 51.14851 +0.68070296 -0.60243373
e 0.3412776 Incl. 1.91562 +0.33096698 -0.25466771
P 1.29 H 26.3 G 0.15 U 9

The main difference between these two is ~4.6 degrees in orbital
inclination. Nevertheless, the coincidence was a bit of an eye-opener
when the MPEC was issued this morning: two objects that passed inside
the Moon's orbit on similar trajectories in the space of a few hours!

One possibility that was initially considered was that the trailing
object could be the Ariane 5 upper stage that deployed Rosetta in
March 2004. But the chances of this are extremely remote, given
that Rosetta had undergone two gravity assist fly-bys (one of earth,
one of Mars) ~prior~ to the most recent earth flyby this past Tuesday.

In order for the object to be associated with Rosetta, it would have
to have been shed more recently -- certainly after the first earth
flyby in 2005, and probably after the Mars gravity assist earlier
this year. And yet, if it had, the inclinations would match
better.

So, crazy as it sounds, the second object appears to be just a
"rock" ... or maybe it's a probe launched by the curious inhabitants
of 67P/Churyumov-Gerasimenko... ;-) --Rob

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com]On Behalf Of
lebofsky at lpl.arizona.edu
Sent: Tuesday, November 13, 2007 7:39 AM
To: Sterling K. Webb
Cc: lebofsky at comcast.net; Meteorite List; mexicodoug at aol.com
Subject: Re: [meteorite-list] Rosetta gravity assist flyby


Hi Sterling, et al.:

The "asteroid" (Rosetta) was discovered near midnight on November 7 and
was confirmed the next night at 2 other sites.

I did a calculation of size vs magnitude for the "asteroid" at discovery.

Its H magnitude (how bright it would be at 1 astronomical unit, 1 AU, from
the Earth) was 26.3. That would make it 23 meters in diameter with a 10%
reflectivity (gray). The darkest asteroids reflect 5% of the light the
hits them which would give a diameter of about 30 to 35 meters.

At the time of discovery, it was 0.04 AU from the Earth (about 6,000,000
km) was magnitude 19.7 (about 1,000,000 times fainter than the faintest
stars one can see with the naked eye) and was moving at a little less than
2 arc-minutes a day (mostly north to south).

The diameter of the Moon is 30 arc-minutes (1/2 degree) for comparison. It
turns out that the main belt asteroid Ceres was in the same area of the
sky and was moving about 1/2 as fast north to south, but 15 times faster
west to east at this time. Why the difference? Ceres is moving in its
orbit around the Sun while Rosetta was aiming right at the Earth (nearly
so), so even though is was much closer to Earth, it was going almost
directly toward us! (if an object is getting brighter but with no apparent
motion, duck!)

The whole idea behind discovering Earth-approaching asteroids is to find
them not when they come by the first time (not much you can do about them)
but to get an "early warning" for when it might be coming by the next
time, as in the case of Apophis. For comparison, I think that Apophis was
moving at several degrees a day at the time of discovery. At that point
you have a chance to do something about it (beyond just running for
cover).

So, to answer Sterling's question, VN84 was not discovered because of its
fast motion OR brightness, but more for how slow it was moving west to
east relative to its north-south motion! I will try to track this down.

Larry

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Received on Fri 16 Nov 2007 06:27:27 PM PST