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Vesta departure and journey to Ceres, A new phase of Dawn adventure
dilo
post Aug 26 2012, 05:45 AM
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As suggested by "TheAnt", is time to start a new thread!

Due to lack of updates from "Mystic simulator", I asked directly to Marc Rayman for an update and he kindly sent me the following "unofficial" plots, showing evolution of distance, radial velocity and sub-spacecraft latitude (radius trend is splitted in two plots with different scales due to huge variation of the distance):
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I did not publish them immediately because I wanted to integrate them with my previous plots but, due to the lack of time in last week, I decided to post them directly with only minimal changes.
As you can see, third engine stop occurred on Aug 8-18 at almost 2300km above Vesta while next (final) one is just started and, as reported by Marc in his latest journal, will be used to map North polar regions from 6000km distance. Thereafter thrust will resume and, based on plots, on Sept 5 total speed will overcome escape velocity (almost 45 m/s), so total energy balance will be zero; definitive exit from Vesta Hill sphere should occur after 20 days but consider that the times could slighty change due to orbit refinement and thrust plan changes.


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Sarunia
post Aug 26 2012, 11:17 AM
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Thanks Dilo for the updating. I was little worried. Last spice spk file (25 august) shows that Dawn will not escape form Vesta indicating an another problem. But it seems now that this file was only a test.

My little contribution with this video created thanks to spice data from NAIF.
http://www.youtube.com/watch?v=EL5nbFU3xl8
Since SPICE doesn't indicate the states of engines, the orbital parameters are only "guessed" assuming a Vesta like a point mass of 2.59^20 kg.
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tedstryk
post Aug 26 2012, 05:18 PM
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Departure was not supposed to happen until the 26th.


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Sarunia
post Aug 26 2012, 11:41 PM
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Sorry, I meant the date of spk file releasing (25 august) not the date of depart which is scheduled on 5 september as dilo wrote.
The initial departure was planned on 26 august but after the problem with wheels reaction it was postponed as we know.
But i remain concerned: the last spice ck file shows that the observation of Vesta to mapping north pole didn't occur sad.gif
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Sarunia
post Aug 27 2012, 06:15 PM
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I must apologize for my previous post.
According to the spice files released today, there was an attempt to observe Vesta as planned.
The ck file shows that the probe has problem to maintain her orientation but i don't know if this effect is due to the ck files (always under construction) or the problem of lack of one reaction wheels.
From now, I will avoid any speculations useless alarmist and I will wait the official update of wonderfull Dawn journal and Dilo states plots (specially the states of engine propulsion wink.gif ) (from Mystic or Marc).
And of course hope of beautiful images of Vesta's north pole smile.gif
Again very sorry.
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dilo
post Aug 28 2012, 04:59 PM
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I had a private comunication from Mark, he confirmed that they successfully imaged Vesta over the weekend.
Moreover, he said there wasn't any problem with the SPK file. As explained in several Dawn Journals (including November 29, 2011), they generate a reference trajectory that goes all the way to the next destination but then, as they fly along, they generate updated flight profiles to account for all the usual error sources (orbit determination accuracy, unmodeled perturbations from RCS, deviations in IPS thrust from the modeled value, etc.). Each time an updated thrust plan is sent to the spacecraft, they only send the next thrust segment, not the full reference trajectory; in this way, in case of failure, they don't have onboard ephemeris based on thrusting that didn't occur. So when they upload the new thrust segment, they upload a new ephemeris as well. Probably, SPK issue Sarunia found is for an isolated thrust segment which then is followed by a ballistic propagation...


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Explorer1
post Aug 31 2012, 07:48 AM
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A farewell animation:
http://www.youtube.com/watch?v=84vz6J8cnc8
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TheAnt
post Aug 31 2012, 08:52 PM
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Thank you for posting that one Explorer1.
Next stop Ceres in 2015, so lets find out what that bright spot is then. biggrin.gif
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Decepticon
post Sep 1 2012, 04:08 PM
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It looks like a peak of a crater to me.
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Marz
post Sep 2 2012, 02:39 AM
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Looks like an informative Hasta La Vesta hangout:

"We’re celebrating this milestone with a live Google+ Hangout featuring the Dawn mission team September 8, 2012 at noon PDT.

During the Hangout, moderated by Dawn’s education and public outreach (E/PO) liaison to the science team, Dr. Britney Schmidt, we’ll hear stories from Dawn scientists and engineers and get updates on latest mission findings.

Pose the questions you’ve always wanted to ask. Submit your questions for the Dawn team by leaving them in the comments section below, on Dawn’s Facebook page, or by using the hashtag #HastaLaVesta on Twitter."

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dilo
post Sep 5 2012, 05:00 PM
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Based on last Dr Rayman (unofficial) comunication, this morning at 6.45 UT, Dawn definitively leaved Vesta gravitational field when his speed exceeded escape speed (45 m/s at 18000 km height). Curiously, in the same hours MISTIC simulator went back online... rolleyes.gif


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belleraphon1
post Sep 6 2012, 01:17 AM
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A Last Look Back at Vesta ....bye Vesta...

http://dawn.jpl.nasa.gov/feature_stories/d...parts_vesta.asp

http://dawn.jpl.nasa.gov/multimedia/last_look_back.asp

From Protoplanet to Dwarf Planet.... Ceres here we come.

Craig
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Explorer1
post Sep 6 2012, 02:40 AM
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The pole at last! I'm assuming it's in the largest crater, right?
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Adam Hurcewicz
post Sep 6 2012, 08:42 AM
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Hi

I see some difference in Dawn - Vesta position at Mystic Simulator and Eyes of the Solar System

Date and time is 9:43 UTC - 06 Sep 2012
See screens below. What's wrong ? What distance are good ?

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Added:

In HORIZONS JPL is 64 540 km huh.gif
http://ssd.jpl.nasa.gov/horizons.cgi

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Also in Solar System simulator is 64 549 km
http://space.jpl.nasa.gov


Attached Image


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Adam Hurcewicz from Poland
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dilo
post Sep 6 2012, 10:27 AM
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QUOTE (Adam Hurcewicz @ Sep 6 2012, 09:42 AM) *
I see some difference in Dawn - Vesta position at Mystic Simulator and Eyes of the Solar System

Adam, I can say Mystic is perfectly in line with Marc Rayman plots, as showed in these plots where I merged the two sources:
Attached Image

(consider that Mystic hiatus ended yesterday and lasted 1 month; moreover, you will not see distance/velocity modulations due to elliptic orbit during third engine stop because I reported only average info in this period).
Moreover, both Marc/Mystic data are in agreement with last Nasa updates about Vesta depart milestone (see links from bellarophon1); in my plots (left/bottom in particular) you can see that total energy becomes positive only on Sptember,5 while, if Dawn really lies at 64500 km from Vesta, this means he surpassed this point many days ago and is already half-way to Vesta Hill sphere margin!


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