http://dawnblog.jpl.nasa.gov/2015/12/31 ... cember-31/
plus several updates including one from 8 Jan
==quote==
January 8, 2016 -Dawn to Perform Small Orbit Maintenance Maneuvers
After devoting much of the week to observing Ceres, Dawn will execute a pair of burns with its ion engine today to modify its orbit. Starting a little after 1:00 PM, the ship will thrust for less than two hours, wait about six hours as it continues to revolve around Ceres and then thrust again for less than two hours, finishing around 11:00 PM. With its uniquely efficient and gentle ion engine, these small orbit maintenance maneuvers will keep the explorers' orbital motion aligned with the plan the flight team has devised for systematically studying the alien world from this low orbital altitude of 240 miles (385 kilometers). Dawn will spend most of the weekend sending its pictures and other data to Earth. When it has finished on the morning of Jan. 10, it will begin collecting still more data.
==endquote==
Here's an interactive graphic you get (after a few seconds of animation) when you click on
http://www.jpl.nasa.gov/dawn/swf/GRAND/ ... mation.swf
It has 10 or more short explanations that pop up if you hover over parts of the picture or click on the picture's various written labels. You can learn which chemical elements in the surface material Dawn is now gauging the abundance of.
Here's from earlier posts:
==quote Rayman's status update==
December 7, 2015 -Dawn to Stop Ion-Thrusting Today in Low Altitude Orbit
Dawn is scheduled to conclude ion-thrusting for its spiral descent shortly before noon today. At that time, it will be orbiting about 240 miles (385 kilometers) above Ceres, closer than the International Space Station is to Earth. After it turns to point its main antenna to Earth, navigators will begin to measure its orbital parameters very accurately. During the next two days, they will analyze the orbit carefully and decide on Dec. 9 whether to make an adjustment at the end of the week. (It is likely such a trajectory correction maneuver will be needed.) The November Dawn Journal explains this in more details.
==endquote==
Here's the link to the November Dawn Journal:
http://dawnblog.jpl.nasa.gov/2015/11/30 ... vember-30/
====EARLIER POSTS====
The October Dawn Journal is out.
http://dawnblog.jpl.nasa.gov/2015/
Ceres was the subject of a session at the American Astronomical Society--Division for Planetary Sciences (DPS) meetings in Washington DC area 8-13 November.
Emily Lakdawalla has a report on the Ceres findings:
http://www.planetary.org/blogs/emily-la ... ceres.html
Dawn's altitude is now less than 800 km (500 miles). It is descending to final orbit LAMO altitude 375 km.
=========
Dawn has reached HAMO (its next-to-closest orbit) and started photography and sensor work around 10PM pacific time on 17 August. This phase lasts a bit over 2 months and will involve some 80 passes over the day side of Ceres from N to S pole.
LAMO, its *really* close final orbit, will not be reached unti mid-December. That's the orbit where Dawn will be able to detect the chemical elements in surface material (to a depth of about one meter) by their gammaray emission and neutron scattering.
==older post==
An anomaly developed on 30 June and Dawn's descent from 4400 km to 1450 km altitude orbit did not start as planned.
The craft was reconfigured and a successful test was performed around 15 July. Results were evaluated around 16 July. I only have estimates, no official report yet. The craft now seems to have resumed descent. DSN is no longer communicating. Simview shows the thruster is on. they may have changed thrusters, they had at least one usable backup unit.
==older post==According to the Mission Director's 30 June update, Dawn has made the last survey orbit at 4400 km and has now begun spiraling down to the next orbit at 1400 km altitude. The simulated view does not show the ion thruster beam turned on yet but it should soon. The schedule we have shows the craft taking about 5 weeks to make the descent
==older post==
I found the YouTube visually interesting and informative. It is for a wide audience--covers all it can, once over lightly--and as such is well done.
The conical mountain is in the upper right part of this picture:
http://photojournal.jpl.nasa.gov/tiff/PIA19574.tif
It's height is estimated at 5 km. Other mountains are showing up in the latest shots, most clearly when you get the arc of horizon in the picture.
===still older posts==
Check out the new version of simulated view. Dawn is shown orbiting a globe with its own photos of Ceres projected onto it. The current simview (19:59 UTC 2 June) shows the double bright spot. But what we see rotates, so other recognizable features will appear and those "headlights" will disappear in the next few hours.
Approach has proceeded far enough that my original opening post was obsolete. I've replaced it with images that others (thanks Faradave, Darby, Watson) have posted further along in the thread




==previous post==
Dawn retro-thrusting so as to spiral in closer. 23 May picture shows higher resolution, smaller pixel size.
http://dawn.jpl.nasa.gov/news/news-detail.html?id=4605
Horizontal scratches seem roughly aligned with Ceres rotation. East-West. Photo taken from about 5000 km.
http://www.jpl.nasa.gov/spaceimages/det ... d=PIA19065
Planned descent to altitude 4400 km orbit.
==some earlier tweets==
NASA's Dawn Mission @NASA_Dawn · 27 April
Am still in the "RC3" orbit, 8,400 miles (13,500 kilometers) from #Ceres.
NASA's Dawn Mission @NASA_Dawn · 27 April
Update: I began science operations on Friday night and spent the weekend collecting science data at #Ceres.
https://eyes.nasa.gov/dsn/dsn.html
====older posts=====
Here's an animation of pictures shot around 15 April from over Ceres N pole: Click on the image to get a coherent version.
If all goes as planned, Dawn will have slipped into circular orbit by 23 April. Target orbit radius is 14 kkm and the probe is now at 14.3 kkm so only about 300 km closer in to go, and a few m/s slower. To hold the target orbit, looping over N and S poles, speed must be 67 m/s and present speed is 72. So almost all the thrust vector is now aimed at slowing down.
Old post:
The first circular orbit will be at an altitude of 13.5 kkm or a radius of about 14 kkm which is the distance at which the Ceres disk will fill the full view frame of Dawn's camera. Any closer and we will not see the whole disk.
Dawn has rotated around to point its thruster tail at Ceres, so as to slow down. So it won't arrive too fast to curve into circular orbit. Approach is a tricky navigation thing. They will soon take a picture of Ceres against the background of known stars, for navigation purposes. Only a tiny crescent is illuminated because Dawn is approaching from the dark side.
Old post: In the current status (12 March) view of Ceres from Dawn's perspective, Ceres covers one of the stars in Orion;s belt. the Sun, not shown, is about 20 degrees up and to the left of Orion's belt, outside the view frame. Dawn arrived with excess speed which has carried it past Ceres. This one-minute video shows the plan to cope with this. It has distance maxing out between 15 and 20 March after which the spacecraft swoops back in and winds into a circular orbit.
You can see how the ion thruster is used to slow the probe's speed and shape its orbit.
The image of Ceres is exaggerated over-large and its rotation is far from realistic---but that's just details, the main thing is to show the trajectory.
Current status (12 March) shows the probe's distance from Ceres to be over 73 thousand kilometers.
Comparing that with the projections in our table I have concluded that Dawn will not make the turnaround as soon as originally expected. It will overshoot the 77 kkm turnaround goal.
Old post:
"Confirmed: I am in orbit around #Ceres"
https://twitter.com/NASA_Dawn
This announcement
http://www.jpl.nasa.gov/news/news.php?feature=4503
says that capture occurred around 4:39am pacific time
Here are some links
Current status: http://dawn.jpl.nasa.gov/mission/live_shots.asp
Dawn Journal: http://dawn.jpl.nasa.gov/mission/journal.asp
Emily Lakdawalla: http://www.planetary.org/blogs/emily-la ... focus.html
http://www.planetary.org/blogs/emily-lakdawalla/
Dawn Journal (DJ) is really informative. E.g. from November 2014 DJ one learns that the spacecraft is approaching from sunward direction, so sees a fully illuminated face, a "full-Ceres".
Ceres equatorial diameter is 950 km. So radius is 475 km. A formula for angular size (how big it looks in the sky, from the probe's distance R) is "2arcsin(475 km/R) in degrees"
You just plug in the current distance for R and paste that into google.
So if the current distance is given as 100 thousand km, R = 100,000 km and you paste in
"2arcsin(475 km/100,000 km) in degrees" Google gives you back 0.5443... degrees
For comparison, angular size of moon from Earth is half a degree
Back in September some electronics were disabled by a cosmic ray particle and the craft lost several days of thrusting until they managed to revive it. this was a cliff-hanger and is described in October 2014 DJ.
The lost thrusting time necessitated redesigning the approach trajectory. New trajectory described in November DJ
There are two diagrams, one looking down on Ceres north pole, one looking in direction of orbital motion. the new trajectory uses Ceres gravity to assist in making up lost orbital speed. It's interesting, might be worth a look.
If all works out, they plan to first get into a polar orbit at altitude 13,500 km above the surface, then if that is successful, spiral down to around 4400 km altitude, then around 1400 km, and finally around 375 km.
the exact altitudes are in the April 2014 DJ which also gives the schedule for spiraling down
Both Dawn and Ceres are orbiting the sun at a bit over 17 km per second, roughly neck and neck with Dawn trailing just slightly behind and since 24 February beginning to catch up.
Excess outwards and upwards speed is being reduced by both the crafts own thrust and Ceres gravity.