[meteorite-list] Son of Rosetta?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat, 17 Nov 2007 21:33:00 -0600
Message-ID: <025c01c82993$b8749ac0$4b29e146_at_ATARIENGINE>


    Well, I asked the right questions anyway, even
if I didn't have the right answers! Once you start
tweaking the orbit with a burn here and a burn there,
your co-orbiting companion is off on its own, or you
are (depending on which one you're on). I scrounged
through the ESA site trying to find if they'd had burns
but I could not find it out one way or the other. FIVE
correctional burns would seem to make launch stage
follow-on a virtual impossibility.

    A reasonably reflective object the size of the EPS
(which has a 12 m^2 cross section) with 80% to 90%
albedo would be brighter than the "mystery" object.
If the EPS had an albedo of around 50%, it would
be the same brightness (which means nothing really,
except that besides it can't get there, it's too bright).

    It is darn spooky, though. For now, I'm going to
put an "X" in the "More Rocks Than You Think"
column (and a smiley face in the brand-new "Comet
Spies From Churyumov-Gerasimenko" column).

Sterling K. Webb
----- Original Message -----
From: "Rob Matson" <mojave_meteorites at cox.net>
To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>;
<lebofsky at lpl.arizona.edu>; "Meteorite List"
<meteorite-list at meteoritecentral.com>
Cc: <lebofsky at comcast.net>; <mexicodoug at aol.com>
Sent: Saturday, November 17, 2007 3:07 PM
Subject: RE: [meteorite-list] Son of Rosetta?

Hi Sterling,

> 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").

Yes -- the 1.5-meter f/2.0 at the Steward Observatory about 10 miles
north of Tucson.

> The Ariane 5 upper-stage ATV is 10.3 meters long and 4.51 meters
> in diameter; don't know how reflective it is.

Not that stage. The final stage on the Ariane 5 (the EPS), which is
much smaller:

Ariane 5-2. Gross Mass: 12,500 kg. Empty Mass: 2,700 kg.
Thrust (vac): 27.400 kN (6,160 lbf)
Isp: 324 sec
Burn time: 1,100 sec.
Diameter: 3.96 m
Length: 3.36 m
Propellants: N2O4/MMH. No Engines: 1. Engine: Aestus.
Empty mass without VEB payload fairing support ring and avionics is 1200 kg.

> 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.

There have been quite a few powered maneuvers -- at least five that
I'm aware of. You always do a burn before and after each planetary
gravity assist: one to fine-tune the approach, one to tweak the
post-encounter result. So there were burns before and after the
first earth flyby, and burns before and after the Mars flyby this
past March. There was also a "deep space" burn in between the
Mars encounter and this latest (second) earth flyby. The burns
themselves don't drastically alter the heliocentric orbit, but
they do have a significant impact on the closest approach to
each planet. Since small changes in planetary close approach
bring about large changes in gravitational bending, the orbits
of the booster and Rosetta would have significantly diverged
following the first earth flyby.

> 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.

They (ESA?) says they have, and that the EPS is nowhere near
Rosetta. To double-check, I provided several orbital gurus with
the JPL-Horizon's heliocentric ephemeris as it existed immediately
after shutdown of the Ariane 5 EPS. I was curious where that EPS
is today, and whether it could have had any close encounters with
earth or Mars in the last 3 1/2 years.

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

I think both of these are true! --Rob
Received on Sat 17 Nov 2007 10:33:00 PM PST

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