Dawn dead in Ceres orbit, ran out of fuel Oct 2018

[mfb]

From January last year.

Is "region A" the one with the two bright spots? That would be very interesting.

 

[Dotini]

"the bright spot is located at 20 degrees north, 240 degrees east, near the middle of the blue hemisphere."
http://www.planetary.org/blogs/emily-lakdawalla/2015/03191629-lpsc-2015-dawn-at-ceres.html

 

[Dotini]

A crater with water ice at the north pole of Mars.

http://www.esa.int/spaceinimages/Im..._view_of_crater_with_water_ice_-_looking_east

 

[mheslep]

A crater with water ice at the north pole of Mars.

http://www.esa.int/spaceinimages/Im..._view_of_crater_with_water_ice_-_looking_east

What distinguishes water ice from CO2 ice? Color of visible light?

 

[marcus]

Since we've turned a page I'll bring forward the timetable for the rest of the primary mission, regarding planned descent to closer orbits, to have handy for reference.
Table from Rayman's 31 March journal:

http://dawn.jpl.nasa.gov/mission/journal.asp

orbit     dates     altitude(km)    pixel(m) XHubble  period   analogy
RC3    April 23–May 9    (13,500)    (1,300)    24    15 days   (3.0 meters)

Survey    June 6-30     (4,400)      (410)    72    3.1 days    (1.0 meters)

HAMO    Aug 4–Oct 15     (1,450)      (140)    215    19 hours    (33 cm)

LAMO Dec 8–end of mission  (375)    (35)     850    5.5 hours    (8.5 cm)

Columns:
Orbit code name
Tentative dates
Altitude in (kilometers)
Resolution in (meters) per pixel
Resolution compared to Hubble
Orbit period
Equivalent distance of a soccer ball

It looks like it will require almost a month to descend from the present RC3 orbit to the "survey" orbit. From 9 May to 6 June.

 

[marcus]

The simulated view of Ceres from Dawn's perspective now includes the Sun and Mars. A couple of bright Gemini stars are in the background.
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
this is the first time i can recall seeing the views merged like that
usually the sun, Mars, Earth only show in http://neo.jpl.nasa.gov/orbits/fullview1.jpg
and fullview1 does not include Ceres.

DSN says Dawn is now sending data to Goldstone antenna #25 at around 125 kilobit/second, it is 8AM Goldstone time

 

[OmCheeto]

The simulated view of Ceres from Dawn's perspective now includes the Sun and Mars. A couple of bright Gemini stars are in the background.
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
this is the first time i can recall seeing the views merged like that
usually the sun, Mars, Earth only show in http://neo.jpl.nasa.gov/orbits/fullview1.jpg
and fullview1 does not include Ceres.

Thank you for mentioning this, Marcus. I grabbed this morning's shots and noticed that the Earth, Sun, and Mars were just out of the "Ceres-Dawn" graphic.

​

Perhaps Dr. Rayman was getting tired of all my lame attempts at aligning the images.

Ah ha! I was worried that my initial date stamping of the trajectory from months ago was a bit off, but it looks like Dawn had its ionic pedal to the metal, and arrived a bit early.

Note the shift in the angle of OpNav 7.

 

[marcus]

She has been a great craft so far. Indeed she had her "ionic pedal to the metal". I'm very hopeful now that survey orbit will be achieved and that we are going to find out some magnificent things about this little planet!
Sun, Mars, the two bright stars of Gemini, and the dark side of Ceres in the same view:

Having the other bodies in the simulated view tells us north is up. Dawn just passed under Ceres' S pole and is heading north. I suppose it will be over N polar region in another 4 days from now. Should be able to get some pictures on its next pass down over the sunlit side.
Then, on 9 May it will fire up the thruster and start spiraling into the closer "survey" orbit.

 

[marcus]

NEW TWEETS (saw them at 4:30 PM pacific)

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 3h3 hours ago
Am still in the "RC3" orbit, 8,400 miles (13,500 kilometers) from #Ceres.

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 3h3 hours ago
Update: I began science operations on Friday night and spent the weekend collecting science data at #Ceres.

 

[marcus]

Seen Tuesday 28Apr, at 1:54PM pacific:
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 44 minutes ago
Flying north over the night side of #Ceres, I passed over the equator early this morning.

 

[marcus]

fullview2 shows the upper rim (around the N pole) of Ceres beginning to light up as it should if the craft just passed the equator going north.
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
DSN shows Canberra conversing at 200 kilobit/sec and 125 kilobit/sec---around 7AM in Canberra.

 

[Dotini]

Dotini, depending on the time of day I'll be plumping either for salt flats or "some combination of the the above". I've read that the rest of the surface is very low albedo (10%, didn't Emily Lakdawala say something like that?) So the bright spots might not actually need to be very bright by ordinary standards--I expect they could still show up very bright by contrast.

I'm having a fraught time with albedo, pixels and calculation.

Emily did indeed mention 10% for Ceres in her blog of 2/26. However, the wiki for Ceres suggests an albedo of just under 1%., with Enceladus at 99% and our own Moon 12%.

Dr. Rayman mentioned a minimum 40% albedo for the #5 bright spots on April 8 at the Silicon Valley lecture, noting the features were too small to resolve, based on 3.7 kilometers/pixel.

Dr Chris Russell noted April 20 that the bright spots still could not be resolved, even at the current 1300 meters/pixel.

Members of the Planetary Society forum discussed an unusually high new albedo calculation for the bright spot before agreeing to wait for new observations.

 

[Jimster41]

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA18310when you look at two, or four of the larger "craters" in this image, they look different than the smaller ones, qualitatively. Their edges almost seem like "subsidence" features, rather than the rounded bowl-like ejecta craters? Or is that just normal for older and or larger craters. It just makes me wonder, if there was a water ice layer and big enough impacts were to temporarily melt it, I can imagine you might see "subsidence" events, where as the smaller ones are just knocking dust off the ice ball.

 

[marcus]

Jimster, thanks for posting that shot of the surface of Rhea, with your comment! Rhea is the second largest moon of Saturn, after Titan:
http://en.wikipedia.org/wiki/Rhea_(moon)
It could have a lot in common with Ceres.
I just noticed a new photo of Ceres at the NASA website, taken fairly recently around 24-26 April

 

[Jimster41]

Sorry I thought that was Ceres. I got lost on the NASA website.

There are worse places to get lost.

 

[marcus]

Both Ceres and Rhea seem to me to be very nice places to get lost
assuming you have good environmental protection while you are exploring.
Both are iceball orbs.
Rhea might have a subsurface ocean. Here is that Emily Lakdawalla graphic I like so much. we just turned a page so I'll bring it forward to have handy for reference:

Jimster, we need a general term for a solar system body that can be either a planet or a moon or a dwarf planet. The only word I know is orb how does that sound? Can you think of anything better. We need a general term that would include these iceballs.

Things that are ROUNDISH, with enough mass to have achieved hydrostatic equilibrium (that is what is required of both planets and dwarf planets). the dwarf planets category is orbs which are roundish like planets but haven't cleared the debris and other stuff out of their path. Ceres hasn't cleared its path so they call it dwarf planet. I want a general term. Maybe orb?

 

[Jimster41]

Very interesting. I had no idea we were expecting so much ice and water at this point! How long ago would that have been a pretty wild claim?

 

[marcus]

They can tell the size optically and they can tell the size from how small objects veer as they pass, so they can tell the density. If an orb's density is much less than that of rock then it probably has a good bit of water(ice)

For instance common silicate rock tends to have density around 3.5, and Ceres has density around 2.0.
So it should have about 30% of its mass be water(ice).

There is also a way to tell how likely an orb is to be differentiated into layers of varying density. Dense core and less dense mantle surrounding it. Ask about that if you get curious. Someone will doubtless explain the method used to tell. Has to do with rotation (something else that can be observed remotely.)

 

[Jimster41]

How about "Plorb", "Plicenet", "Orcoon"

Wait, I think that's Barsoomian for "bring me another beer please".



Honestly though I really had no idea we were that good with identifying ice and water in our solar system. Makes complete sense. Do we think water is likely to be a common compound in most main sequence solar systems? Why wouldn't it be? If yes, seems like another marker on the table - for "we're not special enough to feel lonely as we do..."

 

[marcus]

Jimster, all the other iceballs are in the OUTER solar system---Jupiter moons or even farther out.

that is what makes Ceres so unique. It is the only icy orb this side of Jupiter.

In the inner solar system it is hot enough that water tends to get cooked out of things. Venus is dry, Mars is mostly dry. The Earth and Ceres are the two exceptions in the inner S.S. that have plentiful water.

Think about why that is: UV can split H₂O in the atmosphere. Temperature is what gives atoms and molecules their speed, by determining their average kinetic energy mV²/2, so at any given temperature something with 1/9 the mass will have 3 times the speed. on average.

At inner S.S. temps, any loose hydrogen in the upper atmosphere is apt to acquire escape velocity and fly off into space, never to be recovered. It is moving so much faster than the other atoms and molecules. The "solar wind" helps dry planets too, if they don't have their own magnetic field to deflect the wind from directly blowing past their upper atmosphere. It can help give extra velocity to any hydrogen up there.

I think the Earth has been lucky and (I'm not sure but) I think photosynthetic LIFE has helped to keep Earth wet.
Photosynthesis converts CO₂ into O₂ which is not a greenhouse heat-trapper.
If CO₂ builds up it can raise the temperature enough to cause the release of more CO₂ and trigger a self-reinforcing runaway greenhouse effect. Over the long term that would tend to dry the planet. I think Venus suffered a runaway greenhouse and so has an atmosphere that is mostly hot CO₂. Any water in the atmosphere would tend to be split by UV, letting the hydrogen escape into space.

So in the inner SS it is unusual for an orb to retain its supply of water.

 

[marcus]

GAUSS AND CERES
Ceres was observed only briefly in early 1801 and then disappeared in the glare of sunlight. Gauss took the observations (spanning only 9 degrees of sky angle, during the first 40 days of that year) and calculated from them where to look at a later time, around the end of the year, when it would be out of the glare. Here are excerpts from a nice student term paper about this (at a Rutgers History of Science website)
Thanks to Leorah Weiss and http://www.math.rutgers.edu/~cherlin/History/Papers1999/weiss.html
===excerpts===
Then,on January 1, 1801, the Italian astronomer Joseph Piazzi discovered a planetoid, working from an observatory in Palermo, Italy. This object, which he christened Ceres, was moving in the constellation Taurus. Astronomers were only able to observe the planetoid for 41 days, during which its orbit swept out an angle of only 9 degrees. Ceres was then lost to sight when its light vanished in the rays of the sun, and the astronomers could no longer find it. There was now a challenge of calculating Ceres' orbit using only the observations Piazzi made, so that astronomers would be able to sight Ceres when it reemerged. [1,5,6,8,10]
...
...
The technical execution of Gauss's method is very involved, and required over 100 hours of calculation for him. His first tactic was to determine a rough approximation to the unknown orbit, and then refine it to a high degree of precision. Gauss initially used only 3 of Piazzi's 22 observations, those from January 1, January 21, and February 11. The observations showed an apparent retrograde motion from January 1 to January 11, around which time Ceres reversed to a forward motion. Gauss chose one of the unknown distances, the one corresponding to the intermediate position of the 3 observations, as the target of his efforts. After obtaining that important value, he determined the distances of the first and third observations, and from those the corresponding spatial positions of Ceres. From the spatial positions Gauss calculated a first approximation of the elements of the orbit. Using this approximate orbital calculation, he could then revise the initial calculation of the distances to obtain a more precise orbit, and so on, until all the values in the calculation became coherent with each other and with the three selected observations. Subsequent refinements in his calculation adjusted the initial parameters to fit all of Piazzi's observations more smoothly [11].

In September of 1801, Zach published several forecasts of the prospective orbit, his own and Gauss's among them; Gauss's prediction was quite different from the others and expanded the area of the sky to be searched [1]. Using Gauss's ephemeris for Ceres (astronomical almanac showing its predicted location at various times), astronomers found Ceres again between November 25 and December 31. Zach, on December 7, and then Olbers, on December 31, located Ceres very close to the positions predicted by Gauss. Between the discovery of Ceres in 1801 and the present day, over 1,500 planetoids have been identified, with Ceres remaining the largest [5,10]. While continually improving and simplifying his methods, Gauss calculated ephemerides for the new planetoids as they were discovered. When Olbers found Vesta in 1807, Gauss calculated the elements of its orbit in only 10 hours. His calculations of parabolic orbits were even faster, as is natural. He could calculate the orbit of a comet in a single hour, where it had taken Euler 3 days using the previous methods [5,6].

Gauss published his methods in 1809 as "Theoria motus corporum coelestium in sectionibus conicus solem ambientium," or, "Theory of the motion of heavenly bodies moving about the sun in conic sections." [1,2,3,5,6,11]. Gauss first wrote this work in German, but his well-known publisher, Perthes, requested he change it to Latin to make it more widely accessible (sic). In fact, the astronomical methods described in Theoria Motus Corporum Coelestium are still in use today, and only a few modifications have been necessary to adapt them for computers [11]. Gauss's determination of Ceres's orbit made him famous in academic circles worldwide, established his reputation in the scientific and mathematical communities, and won him a position as director at the Gottingen Observatory. [5,10]
==endquote==
Gauss was born in 1777, so in 1801 when Piazzi first observed Ceres and Gauss made the first successful calculation of its orbit, he was 24 years old....

 

[Jimster41]

Very interesting. Is there any hypothesis as to why Ceres still appears to have water ice, in the inner S.S? Is it a case of just the right UV (solar wind) and temperature zone for it to remain H2O (whether liquid or solid) over whole solar disk evolution? Unlikely it has an EM field right?

 

[Dotini]

Unlikely it has an EM field right?

"Dawn was scheduled to carry a magnetometer to measure any magnetic fields around Vesta and Ceres, but cost overruns forced Dawn investigators to drop the instrument from their final design."
http://news.sciencemag.org/2012/10/eternal-youth-asteroid-vesta

 

[Jimster41]

GAUSS AND CERES
Ceres was observed only briefly in early 1801 and then disappeared in the glare of sunlight. Gauss took the observations (spanning only 9 degrees of sky angle, during the first 40 days of that year) and calculated from them where to look at a later time, around the end of the year, when it would be out of the glare. Here are excerpts from a nice student term paper about this (at a Rutgers History of Science website)
Thanks to Leorah Weiss and http://www.math.rutgers.edu/~cherlin/History/Papers1999/weiss.html
===excerpts===
Then,on January 1, 1801, the Italian astronomer Joseph Piazzi discovered a planetoid, working from an observatory in Palermo, Italy. This object, which he christened Ceres, was moving in the constellation Taurus. Astronomers were only able to observe the planetoid for 41 days, during which its orbit swept out an angle of only 9 degrees. Ceres was then lost to sight when its light vanished in the rays of the sun, and the astronomers could no longer find it. There was now a challenge of calculating Ceres' orbit using only the observations Piazzi made, so that astronomers would be able to sight Ceres when it reemerged. [1,5,6,8,10]
...
...
The technical execution of Gauss's method is very involved, and required over 100 hours of calculation for him. His first tactic was to determine a rough approximation to the unknown orbit, and then refine it to a high degree of precision. Gauss initially used only 3 of Piazzi's 22 observations, those from January 1, January 21, and February 11. The observations showed an apparent retrograde motion from January 1 to January 11, around which time Ceres reversed to a forward motion. Gauss chose one of the unknown distances, the one corresponding to the intermediate position of the 3 observations, as the target of his efforts. After obtaining that important value, he determined the distances of the first and third observations, and from those the corresponding spatial positions of Ceres. From the spatial positions Gauss calculated a first approximation of the elements of the orbit. Using this approximate orbital calculation, he could then revise the initial calculation of the distances to obtain a more precise orbit, and so on, until all the values in the calculation became coherent with each other and with the three selected observations. Subsequent refinements in his calculation adjusted the initial parameters to fit all of Piazzi's observations more smoothly [11].

In September of 1801, Zach published several forecasts of the prospective orbit, his own and Gauss's among them; Gauss's prediction was quite different from the others and expanded the area of the sky to be searched [1]. Using Gauss's ephemeris for Ceres (astronomical almanac showing its predicted location at various times), astronomers found Ceres again between November 25 and December 31. Zach, on December 7, and then Olbers, on December 31, located Ceres very close to the positions predicted by Gauss. Between the discovery of Ceres in 1801 and the present day, over 1,500 planetoids have been identified, with Ceres remaining the largest [5,10]. While continually improving and simplifying his methods, Gauss calculated ephemerides for the new planetoids as they were discovered. When Olbers found Vesta in 1807, Gauss calculated the elements of its orbit in only 10 hours. His calculations of parabolic orbits were even faster, as is natural. He could calculate the orbit of a comet in a single hour, where it had taken Euler 3 days using the previous methods [5,6].

Gauss published his methods in 1809 as "Theoria motus corporum coelestium in sectionibus conicus solem ambientium," or, "Theory of the motion of heavenly bodies moving about the sun in conic sections." [1,2,3,5,6,11]. Gauss first wrote this work in German, but his well-known publisher, Perthes, requested he change it to Latin to make it more widely accessible (sic). In fact, the astronomical methods described in Theoria Motus Corporum Coelestium are still in use today, and only a few modifications have been necessary to adapt them for computers [11]. Gauss's determination of Ceres's orbit made him famous in academic circles worldwide, established his reputation in the scientific and mathematical communities, and won him a position as director at the Gottingen Observatory. [5,10]
==endquote==
Gauss was born in 1777, so in 1801 when Piazzi first observed Ceres and Gauss made the first successful calculation of its orbit, he was 24 years old....

It truly boggles the mind, what these people were able to figure out, before calculators, electric lights, and modern dentistry even existed... But then I guess, the night sky was still pretty dark, and it's not like you could watch TV.

 

[marcus]

Dotini, thanks! I didn't know that they originally wanted to carry a magnetometer.

Jimster, good questions! I hope someone with reliable expert knowledge replies. Off hand I would say your guesses are right. the main factor would be the temperature. She is at 2.8 AU so the equilibrium temperature is much colder.

My guess is that pure water ice exposed on the surface would sublime slowly. Slowly turn to vapor without passing thru a liquid phase. Dissolved salts might change details, but basically I don't think any ice can last on typical Ceres surface. Of course in a crater at the N pole where never exposed to sun might be different. Even on Mercury there can be ice in permanently dark craters

But the ice on Ceres is not, I think, directly exposed to vacuum. It is covered by a thin "regolith" (is that the right word?) debris rubble residue from earlier evapoporation of salty mud, whatever. There is a "skin" covering the Ceres ice mantle, that protects from or retards evaporation.

I think you are also right that the solar wind would have thinned out some, at 2.8 AU, and not be quite as drying as it is elsewhere in the inner solar system. So that would be a factor. Just as with temperature, the extra distance from the sun helps.

 

[marcus]

New Dawn Journal!
The new entry http://www.jpl.nasa.gov/blog/2015/4/getting-down-to-science-at-ceres
is dated 29 April and is titled "Getting down to science at Ceres"
The back issues of the Marc Rayman's journal are here:
http://dawn.jpl.nasa.gov/mission/journal.asp

It's no longer possible to post comments and questions like on a blog. Evidently too busy to reply so when they redid the website just recently they eliminated that feature. All the more reason for us to have room for comments etc. here at PF.

 

[OmCheeto]

Ugh. My modem went out last week, and I've discovered that I can't function without it.
Anyways, Dr. Rayman graciously responded to my last silly question to the Journal:

OmCheeto says:
Your comment is awaiting moderation.
April 29, 2015 at 8:13 am
Hi Dr Rayman!

I read on Dawn’s Twitter page the other day, that Dawn’s total change in solar powered velocity was around 24,000 mph or 39,000 kph. Does this make Dawn the fastest man made solar powered vehicle in the known universe?

Thanks!

Om

Hi Om,

Your comment came in while our web team was transitioning the website to a new system that does not allow blog comments (in compliance with the JPL Blog). It wasn’t my idea, but it is what it is. I would have been happy to answer this one for everyone, because this kind of question comes up so often, but now I’ll reply only to you.

The information on Twitter now comes from me but it may be reworded by the person who actually does the tweeting. So sometimes it may be a little misleading. Nevertheless, it is quite correct that the total delta-v now exceeds 24,000 mph. As of today, it is 10.8 km/s, and since you are technical, I’ll stick with metric.

Your question shows a common misconception. Missions that travel to higher orbits (in this case, higher solar orbits) generally go slower. Dawn’s heliocentric velocity today is 17.1 km/s. You and I are traveling around the sun today at 29.5 km/s. So we have not used the ion propulsion system to accelerate but rather to decelerate (as well as to accomplish other changes in the orbit, including inclination).

I have written about this quite extensively in my Dawn Journals. See http://dawn.jpl.nasa.gov/mission/journal_02_28_13.asp for one discussion. Also, every September 27, my Dawn Journal described how much faster Earth travels than Dawn. Of course, all objects on Earth travel at essentially the same heliocentric velocity, and spacecraft sent to the inner solar system travel still faster. MESSENGER traveled at Mercury’s heliocentric velocity, so it was much faster than Dawn. Most (but not all) spacecraft sent to the outer solar system, such as Cassini, Voyager 2, Juno, and others, travel even more slowly than Dawn. But to answer your question more directly, Dawn is one of the slowest man made solar powered vehicles. (As all man made objects are in the known universe, that qualification isn’t important.)

Of course, in orbit around Ceres (and Vesta), Dawn uses its ion propulsion system to accelerate (relative to the central body) so that it can go to lower orbits. Then at Vesta it decelerated relative to Vesta to climb to higher orbits and escape before resuming its heliocentric travels.

I hope that answers your question.

I also hope that my previous email answered your questions, but I have no idea. You don’t need to acknowledge my responses, but if you do, you might find me to be even more helpful (or, at least, happy to help) in the future. Everyone (or, at least, I) likes to know their efforts are worthwhile. Once again, however, it is not necessary.

By the way, I took a quick peek again at the physicsforums again not too long ago, as you had invited me to some time ago. I didn’t have time for more than a minute or two there. There are far too many points to comment on (and virtually every question had already been answered in my Dawn Journals, although I know they are impractical to scour or even search). I don’t have time now to look it up again, but I will reiterate a comment I believe I made to you once before, although I may have posted it on the blog. The Mystic simulator, as one of the forum participants observed, is consistent. Consistency does not equate to accuracy, however. It is never based on actual flight data. The numbers in my Dawn Journals, now the information in tweets (because it comes from me), and the mission status reports are more accurate. I love the Mystic simulator, but one needs to be careful about using it to conclude what the spacecraft is really doing. It is based on a design reference trajectory.

Regards,

Marc

I responded, with my usual Omic

ps. I also apologized for not being able to make it to Pasadena on the 9th, as I'd received a sign from god, implying I shouldn't go. (Modem gave me the red light. Couldn't get ahold of Captain Kirk!)

 

[OmCheeto]

First there was Einstein.
Then there was the Death Star.

And now...

Emily Lakdawalla @elakdawalla · 2 hours ago
Now that I've seen this on Ceres, I can never unsee it:

It's no wonder you've been so keen on Ceres, Marcus.

 

[mfb]

Oh, the joys of orbital mechanics, where you thrust forwards to slow down.
We just need the right reference frame, then Dawn is fast again. Dawn is the fastest man-made object with ion drives in the reference frame of Earth.

Dawn is between Ceres and the Sun again, which means we will reach the end of RC3 soon (scheduled: Saturday May 9). 3 times better resolution in one month (also faster orbits, 3 days instead of 15).

 

[marcus]

Oh, the joys of orbital mechanics, where you thrust forwards to slow down.
We just need the right reference frame, then Dawn is fast again. Dawn is the fastest man-made object with ion drives in the reference frame of Earth.

Dawn is between Ceres and the Sun again, which means we will reach the end of RC3 soon (scheduled: Saturday May 9). 3 times better resolution in one month (also faster orbits, 3 days instead of 15).

For now here's a shot taken 4 May one day before it crossed the equator flying south.
So there is some of the dark side near N pole showing.

As you say, descent to lower orbit is scheduled to start tomorrow 9 May, so in the simulated view we should see the thruster on tomorrow.
Crossing the equator 5 May was tweeted.
https://twitter.com/NASA_Dawn/status/595770021864992769
Hopefully they got a shot on 5 May as well as this one.
Schedule:
https://www.physicsforums.com/threads/ceres-at-rc3-13500km-above-surface.793140/page-20#post-5089960

Orbit    dates      altitude(km)  pixelsize(m) res/HST  period  soccerball at
RC3    April 23–May 9    (13,500)    (1,300)    24     15 days    (3.0 meters)
Survey    June 6-30      (4,400)      (410)     72     3.1 days    (1.0 meters)
HAMO    Aug 4–Oct 15     (1,450)      (140)     215    19 hours    (33 cm)
LAMO Dec 8–end of mission  (375)      (35)      850    5.5 hours    (8.5 cm)

 

[marcus]

Mfb suggested this orbital mechanics paradox: In the opposite sense from his example, to spiral in the craft points its ion thrust beam ahead in the direction it is going, thrusting in reverse as if to slow down. But as it spirals in it actually speeds up. So braking speeds you up.
As it moves in closer, the planet's gravity is stronger. The craft moves faster and in tighter spiral loops. It takes more work to cancel the gravitational energy difference between orbit levels.

Supplementing the timetable in the previous post:
http://dawnblog.jpl.nasa.gov/2014/04/30/dawn-journal-april-30-2/#more-527
So four weeks (5 loops) to get from RC3 down to Survey
Five weeks ( nearly 30 loops) from Survey down to HAMO
Nearly eight weeks (around 160 loops) from HAMO to LAMO

I didn't find a diagram for the descent from Survey to HAMO, taking some 5 weeks and 30 loops, but here's a diagram of the final descent to LAMO.

According to the timetable, it will take around 8 weeks, and some 160 loops, to spiral into LAMO

 

[OmCheeto]

Mfb suggested this orbital mechanics paradox: In the opposite sense from his example, to spiral in the craft points its ion thrust beam ahead in the direction it is going, thrusting in reverse as if to slow down. But as it spirals in it actually speeds up. So braking speeds you up.
As it moves in closer, the planet's gravity is stronger. The craft moves faster and in tighter spiral loops. It takes more work to cancel the gravitational energy difference between orbit levels.
...

Last time I tried to figure out something impossible, I popped a blood vessel.

Anyways, I wasn't able to make it down to Pasadena for the show today, but they are having live feeds starting at 12:30 pm (PDT):

i C Ceres Presentations (JPL)

Small Worlds 101 – All About Asteroids, Comets and Dwarf Planets

12:30-1:30 pm PDT

Vishnu Reddy: Research scientist at The Planetary Institute and a member of Dawn's Framing Camera team.​

To Boldly Go ... Well, You Know: NASA's Dawn Mission to the Asteroid Belt
2:00 - 2:30 pm PDT

Marc Rayman: Chief engineer and mission director for NASA's Dawn mission to orbit two objects in the asteroid belt.
(YAY! My newest pen pal, and bff. )​

You Want to Go Where? Exploring New (Icy?) Worlds in our Solar System

2:30 - 4:30 pm PDT

Jim Green: Director of the Planetary Science Division at NASA Headquarters.

Carol Raymond: Manager of JPL's Small Bodies Program and the Deputy Principal Investigator on NASA's Dawn asteroid/dwarf planet orbiter mission.

Claudia Alexander: Research scientist specializing in geophysics and planetary science.

Dante Lauretta: Professor of Planetary Science and Cosmochemistry at the University of Arizona's Lunar and Planetary Laboratory and the Principal Investigator on NASA's OSIRIS-REx asteroid sample return mission.

Alan Stern: Planetary scientist, space program executive, aerospace consultant, author and the Principal Investigator of the New Horizons mission to Pluto.

Emily Lakdawalla: Session's moderator, is a passionate advocate for the exploration of our solar system.
(If you have to follow anyone on Twitter, follow Emily. She's the best space bloodhound in the universe. She misses nothing! )​

 

[mfb]

The MYSTIC simulator didn't update for more than a day. Is the thrusting mode to Survey orbit missing in its code?

Probably no iron core: https://twitter.com/NASA_Dawn/status/597167449557991424

 

[marcus]

More detail on one of the bright spots.

 

[marcus]

there's an animation of a sequence of shots taken around 4 March. I don't know if I can copy it here:
it's from http://dawn.jpl.nasa.gov/multimedia/images/index.html?view=list_view&start=0
which links to here:
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547
and from there:
http://photojournal.jpl.nasa.gov/archive/PIA19547.gif (this gets the animation)
Copying the animation here doesn't seem to work or I simply don't know how to do it.