[meteorite-list] DAWN drives up to Vesta

From: Matthias Bärmann <majbaermann_at_meteoritecentral.com>
Date: Sun, 17 Jul 2011 18:43:11 +0200
Message-ID: <BDCBBDED9D9B4D88A5B57BA76BC24EDF_at_thinkcentre>

Hi Doug, do you expect from this mission a precise calculation of Vesta's
mass before/after begin of meteorite and namely HED collecting down here?
Any secret mining there? When I've a look on my Green one: no single little
trace of fusion crust and completely fragmented. That's suspicious :-)

Best,
Matthias

----- Original Message -----
From: "MexicoDoug" <mexicodoug at aim.com>
To: <meteoritemike at gmail.com>; <Meteorite-list at meteoritecentral.com>
Sent: Sunday, July 17, 2011 6:29 PM
Subject: Re: [meteorite-list] DAWN drives up to Vesta


> Hi Mike,
>
> Clearly, orbit was achieved at least by yesterday, at some point probably
> while we were chattering about this. Since they basically drove up to
> Vesta and we don't know the outer limit with super accuracy there can be
> no real time congratulation announcement.
>
> So a few more significant digits will need to be calculated on the mass of
> Vesta and then some engineer will rubber-stamp with hindsight an "official
> time" of capture. But they will need to do a little more communication
> with the spacecraft to determine precisely where it is to get that super
> precise mass, and from that back out when orbit actually started which
> might only be an estimate with the best data, anyway. So that is why this
> is a different moseying up to Vesta capture that will be successful under
> a wide range of mass assumptions.
>
> I don't know if this is being maintained accurately to reflect the
> maneuver into orbit, here's the link though:
>
> http://neo.jpl.nasa.gov/orbits/fullview4.jpg
>
> seems to be a simulation noting the relative speed between the probe and
> Vesta as well as the distance. It shows ~50 m/s (104 mph) and 13,100 km
> 8,100 miles), and those numbers haven't changed much. That sounds like a
> fast approach already so if the proposed two week descent is still the
> plan and the image data accurate, at this point we are well past the
> capture and have already started the orbital transition to lower altitude
> (the two week decent into the first scientific orbit).
>
> Unless I'm doing something wrong, a normal satellite at that 13,100 km
> distance would have an orbital speed of 82 miles/h (132 km/hr) and in a
> circular orbit no relative speed toward Vesta instead of the 100 mph.
>
> The image numbers were 700 km further out and 3-5 km/h slower 10 hours ago
> so it doesn't exactly add up, but it shows the ion engine is currently
> thrusting and still approaching Vesta. Since the initial target orbit was
> 15,000 km and they are around 13,000 km now from Vesta according to this
> you might also imagine that either they decided to come in more closely,
> or Vesta was more massive than calculated.
>
> Best wishes
> Doug
>
>
>
> -----Original Message-----
> From: Galactic Stone & Ironworks <meteoritemike at gmail.com>
> To: Sterling K. Webb <sterling_k_webb at sbcglobal.net>
> Cc: Meteorite-list at meteoritecentral.com; MexicoDoug <mexicodoug at aim.com>
> Sent: Sun, Jul 17, 2011 9:34 am
> Subject: Re: [meteorite-list] DAWN drives up to Vesta
>
>
> Hi List,
>
> I fell asleep last night before 2:30am. So what is the good word on
> Dawn? Do we have orbit?
>
> As has it captured a photo yet of a mile-wide patch of diogenite
> exposed through the regolith? ;)
>
> Best regards,
>
> MikeG
>
> -------------------------------------------------------------------------
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> Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
>
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> -------------------------------------------------------------------------
> --------
>
> On 7/17/11, Sterling K. Webb <sterling_k_webb at sbcglobal.net> wrote:
>> Doug, List,
>>
>> I suggest the very detailed "Dawn Journal" postings
>> by Dr. Marc D. Rayman, Chief Engineer. Of course,
>> he's busy right now! The last Journal log was June
>> 23, 2011, but the earlier extensive Journals have a
>> lot of information. They can be found at:
>> http://dawn.jpl.nasa.gov/mission/journal.asp
>>
>> On June 1, Dawn was closing at 540 mph. By
>> June 23, about 250 mph. Currently, it's within
>> your local speed limit 55-65 mph. Hands on
>> the wheel and eyes on the road.
>>
>> "The spacecraft will glide into a very high orbit
>> in late July and continue thrusting, gently as always,
>> until early August, when it will arrive in its survey
>> orbit at an orbit at an altitude of about 2700
>> kilometers (1700 miles)."
>>
>> You will note that Dawn is AHEAD of schedule
>> now, gaining it more time at Vesta. Ion drive is
>> like a video game -- play it right, you get bonus
>> points.
>>
>> "In survey orbit, the probe will be about 2700
>> kilometers (1700 miles) above the surface. During
>> the approach phase, navigators will measure the
>> strength of Vesta's gravitational tug on the spacecraft
>> so they can compute the giant asteroid's mass with
>> much greater accuracy than astronomers have yet
>> been able to determine it. (The mass is calculated
>> now using observations of how Vesta perturbs the
>> orbits of other asteroids and even of Mars.) That
>> knowledge will allow them to refine the survey orbit
>> altitude, and they may target it to be somewhat higher
>> or lower, depending on whether Vesta is more massive
>> or less massive than the current calculations show.
>> The sequences for acquiring science data are being
>> designed to accommodate a reasonable range of masses.
>> Dawn will be in a near-polar orbit. Its trajectory
>> will take it over the north pole (which will be in
>> darkness, because it will be northern hemisphere
>> winter at that time), then over the terminator (the
>> boundary between the illuminated and unilluminated
>> sides), down over the equator, over the south pole,
>> and then across the terminator again to pass over
>> Vesta's night side. Such an orbit allows the spacecraft
>> to have a view of virtually every part of the lit surface
>> at some time. Each revolution in survey orbit will take
>> 2.5 to 3 days to complete. While this may seem like a
>> leisurely pace, the spacecraft will be busy the entire time.
>> The primary objective of survey orbit is to get a broad
>> overview of Vesta with color pictures and with ultraviolet,
>> visible, and infrared spectra. The camera will obtain views
>> with 250 meters (820 feet) per pixel, about 150 times
>> sharper than the best images from the Hubble Space
>> Telescope. The mapping spectrometer will reveal much
>> of the surface at better than 700 meters (2300 feet)
>> per pixel."
>>
>> Actually finding the Pole (so you can line up for a polar
>> orbit) has been a problem. North? South? East? West?
>> Front? Back? Which pole? Vesta's irregularity poses a
>> limit on "How low can you go?" Interplanetary Limbo
>> can be hazardous to your spacecraft...
>>
>>
>> Sterling K. Webb
>>
> -------------------------------------------------------------------------
> -------
>> ----- Original Message -----
>> From: "MexicoDoug" <mexicodoug at aim.com>
>> To: <Meteorite-list at meteoritecentral.com>
>> Sent: Saturday, July 16, 2011 11:36 PM
>> Subject: [meteorite-list] DAWN drives up to Vesta
>>
>>
>>> Hi everyone with a bit of Vesta fun,
>>>
>>> This is a different kind of encounter to visit Vesta, not like we're
>>> used to hearing about anyway from visits to the Moon, Mars. At the
>>> moment, it's about 13,000 km (9,000 miles) to Vesta and like a nice
>>> Chevy Camaro (or a Ford Mustang in a pinch) DAWN is cruising along
> the
>>> interplanetary highway (route I-5 in honor of Vesta's soon to be
>>> crowning as a dwarf planet, the fifth planet, considering all roads
>>> lead to and from Earth). Get ready to promote all of your HED
>>> meteorites ;-), even the moon isn't planetary according to the IAU
> ...
>>> because where the rock is matters to them for some fool reason.
>>>
>>> Is there really much risk to the Vesta orbital insertion? I'd say
> no,
>>> nothing to hold your breath over. Does anyone recall the Six-Million
>>> Dollar Man - he pretty much could could run the approach to Vesta -
>>> heck even we could, so I'm imagining DAWN tooling along in slow
> motion
>>> just as he would, for the effect of speed (of course by slowing down
> -
>>> I need a psychologist to explain why we are now all conditioned from
>>> television to feel speed when the film is slowed down with
> interesting
>>> sound effects).
>>>
>>> The real risk, I'm guessing has already been made and we are kind of
>>> stuck with it and most depends on the assumption of Vesta's mass
>>> barring mechanical steering failure which is very unlikely during
> this
>>> critical maneuver considering the long track record and minimum of
>>> moving parts and that it would have to be for a much longer time than
>>> a conventional propellant motor. If the target is an initial orbit
>>> around Vesta at 100 km altitude, for example, I'm thinking how close
>>> they will get to it since changing the course significantly on these
>>> incredibly weak ion engines is like trying to turn the Titanic on a
>>> dime - you can't. The real risk would be to basically know the mass
>>> of Vesta (or the product of G*M). I'm not sure how accurate that it
>>> was known and I'm betting that a lot of work has gone into refining
>>> the number for the purpose of navigation on this mission. It really
>>> wasn't that well determined before! So that is already one benefit
> of
>>> the mission - Vesta's mass.
>>>
>>> I don't know the initial altitude insertion target, let's assume it
> is
>>> between 100 km and 500 km and somewhat circular (though an eccentric
>>> orbit might be chosen), the spacecraft will accelerate to around 294
>>> to 377 mph (31 m/s to 168 m/s ; or, 474 to 606 km/h ) and the speed
>>> will determine the initial altitude. So as long as the spacecraft is
>>> within that speed range, I think, and has decent pointing capability
>>> (which is all happening in slow motion due to the nature of the
>>> engines), now, it is a done deal, whoever figured out a mass good
>>> enough to navigate to Vesta is a real hero here and deserves the
>>> congratultations - as the main power must be coming from the
>>> gravitational acceleration into Vesta now and the ion engine mostly
>>> secondary and primarily for (slow) steering manuevers.
>>>
>>> The other detail I see is that since Vesta isn't perfectly round, if
>>> they don't pick an "iso-radial" or whatever you call a constant
>>> diameter great circle in Vesta that happens to not be oblong, I think
>>> that even a circular orbit could be fun, like a ride at an amusment
>>> park - the ground could actually be going up and down below you 65 km
>>> during each orbit - at a 100 km orbit, that would be pretty awesome.
>>> And also a reason not to start with an orbit too low right away for
>>> fear of getting Vesta whipped. Being in a circular orbit but having
>>> it feel elliptical without doing anything! Charlie Sheen could make
> a
>>> better joke than I can here ...
>>>
>>> All this assumes no atmosphere. That seems like a good assumption
>>> since many spectra have been taken of Vesta - but, there
> theoretically
>>> could be a a few patches of dust floating around. With those huge
>>> (and beautiful work of art) solar panels that conceivable could be a
>>> consideration and would be a first instance of
>>> "micro-meteoroid-braking" a.k.a., sand-blasting.
>>>
>>> Lots of fun things to think about Vesta while they are still not
>>> confirmed, which won't last long ... just thought I'd note these
>>> thoughts in case anyone was interested while we all take a vicarious
>>> walk to Vesta and route for the home team. I guess I need a "blog"
>>>
>>> Best wishes
>>> Doug
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>
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Received on Sun 17 Jul 2011 12:43:11 PM PDT