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

[OmCheeto]

I'd be most interested in knowing more about the time-table and manner of Dawn getting into the right orbit plane.

From my calculations, it occurred at around 6 am this morning, PST.
4/4/2015 13:00:00 UTC.

But, as everyone knows, my math sucks.

ps. I was going to submit the question to Dr. Rayman, but the dawnblog is down, again...
Stinkin' Californians. How dare they, take weekends and holidays off. Pfft!

 

[OmCheeto]

The current view:

Slightly askew, but close enough for me.
Directly below Ceres, in the above image, is Sirius.

Here's a digitization I did over the weekend:

I don't know the names of the stars, but they are in some obscure constellation called Monoceros.

 

[mfb]

44.32 Mm at 21:17 UTC (101 mph) - probably less as we know the web interface is not accurate.
That is close to the previous closest approach at ~38 Mm.
The next picture is scheduled for April 10 at ~33 Mm - just a crescent, but closer than ever before.

 

[marcus]

Thanks for the update, Mfb. I'll bring forward Om's timeline trajectory to have it handy for reference. The diagram gives two different views of the same trajectory, from different angles. In each case the sun is way off to the left, in the upper picture Ceres' orbit motion is INTO the page, in the lower picture we are looking down on Ceres' orbit plane and Ceres' motion is upwards on the page.

...
The next picture is scheduled for April 10 at ~33 Mm - just a crescent, but closer than ever before.

If you are just joining us, the red dots on the timeline are where photos of Ceres are taken and transmitted back to Earth. So in the upper picture you can find the red dot that comes three day-circles after 7 April, and is labeled 33 thousand km, or 33 kkm.

The picture will be taken from the dark side of Ceres, so it may not show very much. Main interest might be simply for navigation purposes, because it will show the stars in the background and help the navigators figure out where the spacecraft is in relation to Ceres.

 

[marcus]

Dawn now sees Ceres right beside the star Sirius. Recall just a short while ago it saw Ceres in the belt of Orion? It has changed the angle of view quite a bit. (As I understand it, getting ahead of in Ceres orbit direction)
I can't believe that Dawn is in the final orbit plane yet.
The sliver of sunlit edge on Ceres is up and increasingly the right, like in the ONE o'clock position.

As I understand it, when Dawn finally gets in the correct orbit plane, and is approaching from outwards (anti-sun direction) then the sun must be on the Dawn's left, 5 degrees to the left of Ceres. The crescent sliver will then be more in the ELEVEN o'clock position, not the one o'clock. To me the position of the sunlit sector of the rim is a sign that she is not yet in the proper plane

the simulated view is looking good. Ceres is bigger.

Om, notice that in simulated view http://neo.jpl.nasa.gov/orbits/fullview2.jpg the blue green ion tail looks much SHORTER now. This is due to foreshortening because it is pointed much more at Ceres now. Dawn is trying to slow down so as not to arrive too fast to slip into orbit.
The tail is also a little down and to the right.
To the right because Dawn wants to get over to the left so that it will see the Sun 5 degrees to the left of Ceres. Only then will it be in the proper orbit plane.

 

[OmCheeto]

Dawn now sees Ceres right beside the star Sirius. Recall just a short while ago it saw Ceres in the belt of Orion? It has changed the angle of view quite a bit. (As I understand it, getting ahead of in Ceres orbit direction)
I can't believe that Dawn is in the final orbit plane yet.

According to my last PM from Dr. Rayman, it appears you are correct:

Sent to his blog:

Hi Marc,
Do you happen to know when Dawn entered the orbital plane?
Thanks!
Om​

His last response (he's apparently forgotten that I warned him no to correspond with me, as I can be a bit of a pest):

Hi Om,
I prefer not to take the time to explain your question to readers of the blog, so with your permission, I'll simply give you a quick response here. Dawn's ion thrusting to RC3 changes the plane along with the radius right to the very end of thrusting. So, Dawn reaches the RC3 orbital plane when it reaches the RC3 orbital radius.
Is that what you are asking?
Marc​

Then I yelled at him; "No!"
Probably not a good idea.

The sliver of sunlit edge on Ceres is up and increasingly the right, like in the ONE o'clock position.

As I understand it, when Dawn finally gets in the correct orbit plane, and is approaching from outwards (anti-sun direction) then the sun must be on the Dawn's left, 5 degrees to the left of Ceres. The crescent sliver will then be more in the ELEVEN o'clock position, not the one o'clock. To me the position of the sunlit sector of the rim is a sign that she is not yet in the proper plane

the simulated view is looking good. Ceres is bigger.

Om, notice that in simulated view http://neo.jpl.nasa.gov/orbits/fullview2.jpg the blue green ion tail looks much SHORTER now. This is due to foreshortening because it is pointed much more at Ceres now. Dawn is trying to slow down so as not to arrive too fast to slip into orbit.
The tail is also a little down and to the right.
To the right because Dawn wants to get over to the left so that it will see the Sun 5 degrees to the left of Ceres. Only then will it be in the proper orbit plane.

Orbital mechanics is probably over my head.

As I explained to Dr. Rayman, all I wanted to know when Dawn reached the "red dot".

Sirius and Saiph have been tracking linearly since around April 3rd.

How much more planer(?) 2 dimensional can this get?

 

[marcus]

Om,
have an appointment and must go out momentarily---just saw your post. Can't answer but will give my own impressions:
distance is now 35 kkm something, under 36.
Dawn is retrothrusting, you almost cannot see the ionized tail because it is pointing nearly at Ceres.

Ceres is to the LEFT of Sirius for the first time today (if I remember correctly). Remember it used to be way over to the right in Orion belt?
Ceres still moving left against background means Dawn is still drifting RIGHT, which means it is still getting ahead in Ceres orbit direction. This has to stop. To be in the correct orbit plane it has to come in slightly from behind (by about 5 degrees).
So at sometime in next 10 days Dawn will have to start drifting left, in the picture, which will make Ceres drift right against the starry background.

But for now the main job is retrothrusting, to slow the fall towards the mini-planet.

 

[mheslep]

Can Dawn by imaged at all by Hubble, perhaps with the ion thruster on? Resolution is nowhere close (the moon is 43 meters/pixel HST), but I can't lay hands on the information to determine the ion luminosity could light up a pixel.

 

[mfb]

Ceres emits some tens of terawatts of light power and still is at best at magnitude 6.6.
I guess the "most" visible would be the few kW of thermal power emitted by the probe itself, making Dawn a magnitude ~30 (?) object but in infrared only. Hmm, not so far away from the visibility limit, but Ceres is probably way too bright compared to Dawn nearby.

The emitted xenon is too thin to be relevant (Dawn has ~1kW of power and most of it is used for thrust, not for heating the exhaust).

We reached 300% moon size by the way.

 

[marcus]

Mfb, thanks for the update!
I see they have Goldstone antenna #25 talking with Dawn now:
https://eyes.nasa.gov/dsn/dsn.html
and Canberra #45 is standing by for Dawn later today.

The simulated "fullview2" shows the spacecraft with thruster off, oriented in that characteristic way associated with picture-taking and communication.

 

[OmCheeto]

Mfb, thanks for the update!
I see they have Goldstone antenna #25 talking with Dawn now:
https://eyes.nasa.gov/dsn/dsn.html
and Canberra #45 is standing by for Dawn later today.

The simulated "fullview2" shows the spacecraft with thruster off, oriented in that characteristic way associated with picture-taking and communication.

Same situation when I checked 3 hours ago, except that Canberra was not standing by. It is now receiving.
Doh!
Goldstone just shut off.
Canberra is now in two way communication.

I'm going to have to start time stamping my posts when I start them.
Things happen rather quickly around shift change.

 

[marcus]

They do that! I just checked fullview2 and it shows Dawn back in normal orientation. Picture shoot done. It has probably resumed thrust but we can't see the ion tail in the simulated view because it would be aimed almost directly at Ceres, and thus hidden by the spacecraft itself. Ceres sure looks big for a change! Even see some known surface details.

 

[mfb]

They do that! I just checked fullview2 and it shows Dawn back in normal orientation. Picture shoot done. It has probably resumed thrust but we can't see the ion tail in the simulated view because it would be aimed almost directly at Ceres, and thus hidden by the spacecraft itself. Ceres sure looks big for a change! Even see some known surface details.

You can see the tail in the http://neo.jpl.nasa.gov/orbits/fullview1.jpg .
I guess the bright greenish thing in the Ceres view is supposed to be the tail, too.

11:17 UTC: 31450km, 117mph (~340% moon)

 

[OmCheeto]

You can see the tail in the http://neo.jpl.nasa.gov/orbits/fullview1.jpg .
I guess the bright greenish thing in the Ceres view is supposed to be the tail, too.

11:17 UTC: 31450km, 117mph (~340% moon)

It's also visible in the Earth view.
I was thinking about mheslep's question yesterday, as I knew I'd asked a similar question before.

Can Dawn by imaged at all by Hubble, perhaps with the ion thruster on? Resolution is nowhere close (the moon is 43 meters/pixel HST), but I can't lay hands on the information to determine the ion luminosity could light up a pixel.

It turned out to be from January 27th! I can't believe I've been watching this for almost 3 months.

...my question as to why Hubble took such a crumby picture of Ceres...

So I did the maths for Dawn:

____________________________________________size relative to Ceres
Object________pixels_________degrees________when viewed with Hubble
Andromeda_____284151_________3.16___________15,400
Moon___________46602_________0.52____________2,520
Ceres_____________18_________0.00021_____________1
Crab Nebula_____8727_________0.097_____________472
Dawn_______________0.00038___0.0000000026________0.000021

I'm not sure why my pixel numbers are off by a factor of two.
Somewhere they compared the resolution of Dawn to Hubble, and Hubble came out to 33 pixels for Ceres.
I've seen proclaimed resolutions for Hubble from 0.1 to 0.04 arcseconds.Anyways, I'm getting very excited. Less than two weeks!

There will be work to do before photography begins however. The first order of business after concluding ion thrusting will be for the flight team to perform a quick navigational update (this time, using only the radio signal) and transmit any refinements (if necessary) in Dawn’s orbital parameters, so it always has an accurate knowledge of where it is. (These will not be adjustments to the orbit but rather a precise mathematical description of the orbit it achieved.) Controllers will also reconfigure the spacecraft for its intensive observations, which will commence on April 24 as it passes over the south pole and to the night side again.

 

[OmCheeto]

Two new (old but different) images were posted today on NASA's Photojournal.

These images, from Dawn's visible and infrared mapping spectrometer (VIR), highlight two regions on Ceres containing bright spots.
The top images show a region scientists have labeled "1" and the bottom images show the region labeled "5."
Region 5 contains the brightest spots on Ceres.

VIR has been examining the relative temperatures of features on Ceres' surface.
Preliminary examination suggests that region 1 is cooler than the rest of Ceres' surface, but region 5 appears to be located in a region that is similar in temperature to its surroundings.

Images taken using blue (440 nanometers), green (550 nanometers) and infrared (920 nanometers) spectral filters were combined to create the map.
The filters were assigned to color channels in reverse order, compared to natural color; in other words, the short-wavelength blue images were assigned to the red color channel and the long-wavelength infrared images are assigned to the blue color channel.​

I have no idea what any of this means.

 

[Dotini]

Not all of the puzzling bright spots on the dwarf planet Ceres are alike. The closest-yet images of the gleams, taken from 45,000 kilometres away, suggest that at least two of the spots look different from one another when seen in infrared wavelengths.
http://www.nature.com/news/mystery-of-ceres-bright-spots-grows-1.17313

NASA/JPL-Caltech/UCLA/ASI/INAF
Infrared images suggest that Spot 1 (top row), an area on Ceres, is made of ice. But the pair of bright gleams known as Spot 5 were invisible to an infrared camera (bottom right).

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
The surface of the dwarf planet Ceres (shown here) has fewer large craters than researchers expected.

Edit: Treed by Om!

 

[OmCheeto]

...
Edit: Treed by Om!

I have no idea what that means either.
But thanks for pointing out that Nature has a "BREAKING NEWS" section.

And now, for the moment, I'm bored with the bright spots.

What's with the infrared dark bands below the circled spot?

 

[mfb]

The bands look like some artifact from image taking/processing. I would be surprised if they are real features, and if I understand the orbit geometry correctly they should not be aligned with the rotation (as Dawn should approach a position above one of the poles now). There are similar bands in the visible light images.

Cold bright spots make sense - reflect more light = absorb less light, similar to a white versus a black car on earth.

 

[OmCheeto]

The bands look like some artifact from image taking/processing. I would be surprised if they are real features,

Not me, after seeing the images of Vesta's troughs/valleys/rings/rifts/whatevers.

​

and if I understand the orbit geometry correctly they should not be aligned with the rotation (as Dawn should approach a position above one of the poles now). There are similar bands in the visible light images.

Cold bright spots make sense - reflect more light = absorb less light, similar to a white versus a black car on earth.

That does make sense.

 

[mfb]

Not me, after seeing the images of Vesta's troughs/valleys/rings/rifts/whatevers.

Those are not exactly aligned with the camera pixels, and they don't have a width of exactly one pixel.

 

[Dotini]

NASA's Mars Reconnaissance Orbiter took this image of the larger of Mars' two moons, Phobos, from a distance of about 6,800 km (about 4,200 miles).
Credit: NASA/JPL/University of Arizona

Phobos is covered in numerous parallel, channel-like grooves. Over the years, researchers have come up with many hypotheses to explain the odd features, but the origin of the satellite's grooves are still heavily debated today.

 

[OmCheeto]

NASA's Mars Reconnaissance Orbiter took this image of the larger of Mars' two moons, Phobos, from a distance of about 6,800 km (about 4,200 miles).
Credit: NASA/JPL/University of Arizona

Phobos is covered in numerous parallel, channel-like grooves. Over the years, researchers have come up with many hypotheses to explain the odd features, but the origin of the satellite's grooves are still heavily debated today.

Any idea where I could find a list of the hypotheses?
I've my own, and would like to jump onto someones bandwagon.

ps. I'm keeping this brief, as I have something wonderful to share. hint:

 

[Dotini]

Any idea where I could find a list of the hypotheses?
I've my own, and would like to jump onto someones bandwagon.

ps. I'm keeping this brief, as I have something wonderful to share. hint:

No, please don't do it! Not the obelisk!

 

[OmCheeto]

No, please don't do it! Not the obelisk!

Ha ha! Good one!

No, this has nothing to do with the Phobos Monolith.

Though, it is a message, from the good Dr. (Floyd?).

 

[Dotini]

Any idea where I could find a list of the hypotheses?
I've my own, and would like to jump onto someones bandwagon.

ps. I'm keeping this brief, as I have something wonderful to share. hint:

Please find the makings of a list of hypotheses here for grooves on Phobos : http://www.space.com/25971-mars-moon-phobos-grooves-origin.html
Ejecta from Mars is the likely suspect.

Emily has a different idea for the grooves on Vesta:http://www.planetary.org/blogs/emily-lakdawalla/2011/3128.html

 

[OmCheeto]

Please find the makings of a list of hypotheses here for grooves on Phobos : http://www.space.com/25971-mars-moon-phobos-grooves-origin.html
Ejecta from Mars is the likely suspect.

Emily has a different idea for the grooves on Vesta:http://www.planetary.org/blogs/emily-lakdawalla/2011/3128.html

I see no hypotheses, that match mine.
Mine, is based, as I mentioned before, on my observations of the Philae lander incident, and other stuff.

 

[marcus]

Dawn is nearly over the north pole of Ceres. fullview1 and fullview2, the simulated views, from Dawn's vicinity, of Sun and Ceres, show that there is a close to 90 degree angle between the Sun and Ceres.

The line along Dawns solar panel "wings" points right at Ceres.
The panels face the Sun, and the illuminated half of Ceres (she is in nearly a halfmoon phase) faces in the same sunward direction
so those two views combine give a rather satisfactory 3D idea.

http://neo.jpl.nasa.gov/orbits/fullview1.jpg
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

Mfb is doing us a real favor by updating the headline!

BTW as announced earlier Dawn is in picture taking mode. If you glance at the fullviews you can see that thruster is turned off and the craft is oriented so that one of the cameras is aimed at Ceres.

The lower one of Om's timelines shows 15 April picture taking more or less over Ceres north pole

 

[OmCheeto]

As promised:

Dr. Rayman responded to my email 4 days ago. (I would check my email more frequently, if I thought he was actually foolish enough to respond to my foolish questions.)

I've inserted my questions into the text for clarity. I removed the part where I yelled at him:

4/11/2015 8:35pm

4/8/2015 3:56pm
...
We understand that Dawn will be adjusting its orbit, constantly.
We are interested in the timing of the big red dot point:

Hi Om,

Remember, this is an artist's rendition. The graphic is based on a design reference trajectory that we are not flying for many reasons: gravity errors, OD errors, execution errors, updates to the DSN schedule which affect thrust on/off times, and periods of forced thrust to reduce hydrazine consumption during periods set aside for statistical thrusting. So you are trying to extract precision information from a representation that doesn't support it. Even the width of the white line is large and hence it conceals details of the plane. I don't have time to dig up the details of the design reference trajectory, so to try to answer your question, I took a quick look at the time derivative of the plane angle of the actual profiles we uplink. I think the break you are seeing is a result of the interruption in thrust for OpNav 6 and the associated DSN pass. That would make sense too, because our thrust vectors (even in the reference trajectory) generally change more at the boundaries between segments than within segments. There are several reasons for this, but a big one is that we represent the inertial thrust vectors we transmit to the spacecraft as Chebyshev polynomials, and we (prefer to) use a single polynomial for a complete thrust segment. So putting the bigger changes between segments reduces the size of each polynomial and hence increases the accuracy for a limited number of coefficients. I hope that makes sense.Since I'm not sure I really answered your question, maybe I can make it up to you with a brief comment on your other questions. I don't have time for thorough answers, but perhaps this will be of some interest.

1. Apodemeter
I don't mean to sound like Sgt. Friday, but why was Dawn communicating with the DSN between the hours of approximately:
Mar 17, 2015, 06:25 UTC: Start
Mar 18, 2015, 11: 00 UTC: Stop
28.5 hours!
Parallax?
Doppler shift in carrier signal?

1) We were communicating from Mar 17 at 14:50 UTC to Mar 18 at 10:55 UTC. It was for routine uplink and downlink plus routine radiometrics (Doppler and ranging). This was to refine the orbit knowledge to get a good delivery to RC3. We do this all the time, and there was nothing special about what we did at that time. What was special, however, was that our Monte Carlo analyses had shown that we were a bit more sensitive to the OD accuracy then than usual. This was not a significant effect, but it was noticeable. The DSN does a terrific job, but it is a very, very complex system of systems, and performance is not guaranteed. Glitches occur. High winds, strong rain, a mechanical or electrical problem, another spacecraft declaring an emergency all could have caused us to lose a pass. It happens, and all projects have to learn to live with it. In this case, because it affected our deliver accuracy to RC3, I had us schedule multiple sequential stations in case one station or even one complex had a problem. That made the communications session last longer. As it turned out, everything went perfectly, so we got more radiometrics than the minimum we needed. I hope Sgt. Friday buys that alibi, because it's true!

2. HAMO altitude changed from 1470 to 1450 km in this blog.
Is this a change of plans, or just non-nerd number smoothing?

2) The short answer is that it is what your fearless leader would call non-nerd number smoothing, but there is a little more to it than that. I did indeed decide for the purposes of the table that 910 miles and 1470 km were too many significant figures, so I rounded to 900 and 1450. However, my orbit altitudes are always rounded. We don't design on the basis of a single number for altitude, nor would that really make sense. I explained this in one of my Dawn Journals at Vesta, but it's actually pretty obvious. Vesta, Ceres, Earth, and virtually all other solar system bodies are not spherical, so a single altitude is not a good description, especially for a polar orbit. Inside the Dawn project, we talk not about altitude but rather about orbit radius. So every time I present an altitude, I make a choice about how to present it, and usually I just subtract the mean geometrical radius of the body. Then I round it to something reasonable, because specifying an altitude at the implied precision of 1 mile or 1 kilometer makes no sense when the actual altitude varies by so much more than that with our targeted circular orbits. There is another effect as well. I have mentioned in several blog comments that I will give an updated Ceres mass in my May Dawn Journal. I'll leave you in (mild) suspense, but my choice for how to specify the HAMO altitude in the table was influenced by an expectation for what is going to be the new design altitude when we account for what the actual mass is.

I hope some of this information is helpful.

Regards,

Marc

#4 was kind of a joke. so you can ignore that one.

4. Ice Carrots.
Is there a possibility that the headlights are "Ice Carrots"?
(Yes, we've all googled "complex impact crater morphology", but Easter is coming up!)

He ignored that one.

Not "thorough answers"? hmmm...

------------------------------
Current status of Dawn:
4/15/2015 14:17 UTC (07:17 PST)
2 way communication with Goldstone #25
Canberra #45 standing by

 

[mfb]

Interesting answers :).

Current status of Dawn:
4/15/2015 14:17 UTC (07:17 PST)
2 way communication with Goldstone #25
Canberra #45 standing by

In the old expected size comparison, we should get something like the last image now. Less than a factor 2 to go in terms of distance.

21550km, 136 mph about 2 hours ago.

 

[OmCheeto]

Interesting answers :).

Someone will have to translate them for me...
Though I understand the jist of his answers, the details are all too mathy for me.
Actually, never mind.
I googled both "Monte Carlo" and "Chebyshev polynomials", and I don't feel I have enough time left to understand such things before I die of old age.

In the old expected size comparison, we should get something like the last image now. Less than a factor 2 to go in terms of distance.

21550km, 136 mph about 2 hours ago.

Mission update:
4/15/2015 15:22 UTC
Dawn is now in exclusive two way communication with Canberra #45

There is also an interesting new comment by Dr. Rayman on his blog, which kind of freaks me out, for personal reasons:

Dawn Journal | March 31
April 14, 2015 at 3:14 am
Hi Marc,
from the latest media releases it shows in infrared light that the two bright spots do not show up and yet other less bright areas thought to be ice as well, do show up. How is this possible? ...

Dr. Rayman;
...
It should not be surprising that at this early stage, we do not have enough detail to reveal the answers.
...
But with regard to your question about how it can be possible, for a change our common experience here is quite applicable: different materials in our everyday experience have very different thermal properties (and may even be at very different temperatures under the same illumination conditions). There are myriad examples, including the difference between the temperature of sand and water on a beach...

I was at the beach a couple of months ago, and measured the temperature of the sand and water with my new infrared thermometer.
The temperatures were all wrong. They all read below freezing.

I noticed a month earlier, that my IR thermometer could read the temperature of pretty much everything fairly accurately, except for my stainless steel cooking pot, where it also read low.

 

[marcus]

Canberra antenna #45 is conversing with Dawn
EDIT that was at 10AM pacific time, when I posted earlier, now it is 3PM pacific and antenna#45 is still talking two-way with Dawn
the incoming power is 2 x 10^-17 watts (I like the danish word "atten" for eighteen, 20 attowatts)
the outgoing power is 20 kilowatts..

the incoming frequency is about 8 Ghz. so that is the frequency Dawn likes to broadcast.

It seems to me that because of the position of our two planets, Canberra should lose sight of Ceres by around noon there.
but I see that it is 8 AM in the morning in Canberra, so they have plenty of time to continue their conversation. I think they have Ceres in the sky sort of midnight to noon, maybe not the full 12 hours maybe 1AM to 11AM

Madrid would be the next one up. It is shortly past midnight there
https://eyes.nasa.gov/dsn/dsn.html
they have two antennas unassigned

 

[OmCheeto]

A new image was posted a couple of hours ago.

This animation shows the north pole of dwarf planet Ceres as seen by the Dawn spacecraft on April 10, 2015.
Dawn was at a distance of 21,000 miles (33,000 kilometers) when its framing camera took these images.
The spacecraft was maneuvering toward its first science orbit, which it will enter on April 23.​

 

[marcus]

Larger version here:
http://dawn.jpl.nasa.gov/multimedia/Ceres_north_pole.asp
showing more detail around the north pole. You can see which craters mark the north pole, they stay roughly in the same place as the planet rotates, and turn or move in tight circles.

Fullview2 http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows Dawn coming around on the sunlit side!
It is slightly under 19 kkm from Ceres, has passed over the north pole, is coming around so that much of planet is now illuminated, and seems to be approximately in the right orbit plane!

If Fullview2 is at all accurate, they have done a very creditable job guiding the thing. I did not expect things to go as smoothly as the simulated view suggests they have, especially about veering the polar orbit plane so it would not align with the Sun.

Looking down on north pole, the polar orbit plane as to be rotated off of the sunline in a clockwise sense by a few degrees, like 5 degrees. then the probe will not fall in Ceres shadow during its months-long mission.
I'll try uploading the same animation Om just did in case it turns out larger:

Somehow I lost the animation feature

 

[OmCheeto]

...

Fullview2 http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows Dawn coming around on the sunlit side!
It is slightly under 19 kkm from Ceres, has passed over the north pole, is coming around so that much of planet is now illuminated, and seems to be approximately in the right orbit plane!

That will teach me to capture images 5 minutes after getting up in the morning.
I didn't notice until now that JPL had replaced their picture of my log (which they shamelessly stole and gave me no credit for) with an actual representation of Ceres.

If Fullview2 is at all accurate, they have done a very creditable job guiding the thing. I did not expect things to go as smoothly as the simulated view suggests they have, especially about veering the polar orbit plane so it would not align with the Sun.

Looking down on north pole, the polar orbit plane as to be rotated off of the sunline in a clockwise sense by a few degrees, like 5 degrees. then the probe will not fall in Ceres shadow during its months-long mission.
I'll try uploading the same animation Om just did in case it turns out larger:
View attachment 82127
Somehow I lost the animation feature

Has anyone done the calculations on how out of skew Dawn will have to be at the other orbits yet?
As I recall, she'll be almost nose to nose with Ceres at LAMO.

Maybe I'll go find my baseball. I'm tired of maths*.

*I was up till 11pm last night, doing my taxes.

 

[marcus]

...
Has anyone done the calculations on how out of skew Dawn will have to be at the other orbits yet?.

My understanding is that Dawn can stay in the same orbit plane for duration of mission, which takes about one quarter of a Ceres year, as long as it gets the plane right for the first orbit (RC3).
If it is clockwise skew by 5 degrees for RC3 then it is OK for RC3 (at which altitude Ceres ≈ 4 degrees)
then by the time it wants to spiral down to "survey" orbit the skew will have increased naturally for the simple reason that Ceres is at a different place in its orbit . It moves counterclockwise so the sun moves counterclockwise wrt Ceres, which increases the skew angle the sun makes with a constant plane.

I think they planned the descent schedule so that they would not have to change the orbit plane. the skew angle would grow just as fast as the angular size of Ceres grows and Dawn always stays out of shadow.

I think they planned it that way, in part, because as you get closer to a planet it becomes more COSTLY in energy terms to change the orbit plane.

I could be wrong of course. I think they are going to be able to coast thru this rather smoothly because the whole mission plan has signs here and there of being well thought out. But they did have that bad cosmic ray stunning the electronics accident in September and something like that could happen again.

Thanks to Mfb for updating the header! Five times the size of the moon, and Dawn has swung over to the sunny side!

 

[OmCheeto]

My understanding is that Dawn can stay in the same orbit plane for duration of mission, which takes about one quarter of a Ceres year, as long as it gets the plane right for the first orbit (RC3).
If it is clockwise skew by 5 degrees for RC3 then it is OK for RC3 (at which altitude Ceres ≈ 4 degrees)
then by the time it wants to spiral down to "survey" orbit the skew will have increased naturally for the simple reason that Ceres is at a different place in its orbit . It moves counterclockwise so the sun moves counterclockwise wrt Ceres, which increases the skew angle the sun makes with a constant plane.

I think they planned the descent schedule so that they would not have to change the orbit plane. the skew angle would grow just as fast as the angular size of Ceres grows and Dawn always stays out of shadow.

I think they planned it that way, in part, because as you get closer to a planet it becomes more COSTLY in energy terms to change the orbit plane.

I could be wrong of course. I think they are going to be able to coast thru this rather smoothly because the whole mission plan has signs here and there of being well thought out. But they did have that bad cosmic ray stunning the electronics accident in September and something like that could happen again.

Thanks to Mfb for updating the header! Five times the size of the moon, and Dawn has swung over to the sunny side!

Oh.
5° did seem like an excessive skew for the orbit at RC3, but I hadn't even thought about the rest of the mission.
This all makes sense now.
Thanks!

 

[OmCheeto]

I suppose I can stop capturing these images now.
Things are getting a bit too dynamic.

And, just so I don't feel I wasted my time yesterday.
Here's an image of Ceres from a distance where Dawn was yesterday, which is conveniently my eye height to ground, of Dawn at LAMO orbit.

Ceres is my baseball, Dawn is some yellowish thing that fell out of my big leaf maple tree, and my toes are in the general direction that Ceres is moving in.
Dawn is not to scale.

And as Dr. Rayman says; "This is only a simulation."

 

[marcus]

Om, you realize we are almost there? The RC3 orbit radius (from planet center, not altitude) is roughly 14 kkm and fullview2 says 14.7 kkm
They give the speed as 160 mph. That is what we want to see reduced, RC3 orbit speed is something like 67 m/s which is 150 mph. So hopefully in the next 2 or 3 days they can get the speed down from 160 to around 150 mph.

About the orbit plane tilt. It looks like they have the thruster tail pointed mostly in the direction the craft is going but also just slightly Ceres-aft to push Dawn slightly Ceres-forward while it is still on the sunward side---that combined with Ceres gravity should nudge the orbit plane just enough.

 

[mfb]

The April 14 pictures are still missing, and we might get RC3 pictures within a week.

3 more days for circularizing the orbit according to the latest dawn blog entry.

"intensive observations, which will commence on April 24 as it passes over the south pole"

14500km, 730% of full moon now.

 

[OmCheeto]

Om, you realize we are almost there?

Yes, Marcus!

The RC3 orbit radius (from planet center, not altitude) is roughly 14 kkm and fullview2 says 14.7 kkm
They give the speed as 160 mph. That is what we want to see reduced, RC3 orbit speed is something like 67 m/s which is 150 mph. So hopefully in the next 2 or 3 days they can get the speed down from 160 to around 150 mph.

About the orbit plane tilt. It looks like they have the thruster tail pointed mostly in the direction the craft is going but also just slightly Ceres-aft to push Dawn slightly Ceres-forward while it is still on the sunward side---that combined with Ceres gravity should nudge the orbit plane just enough.

I haven't had time to figure out what stars we are looking at. The sun view shows the sun in Gemini, so Dawn should be looking at the southern region of Sagittarius.
And has anyone noticed that they are updating the simulation images much more frequently?
Here are the last three image time stamps:

4.20.2015 13:31:09 UTC
4.20.2015 14:07:07 UTC
4.20.2015 15:27:05 UTC

The April 14 pictures are still missing

They're here!

There's also an animated gif.

 

[marcus]

...3 more days for circularizing the orbit according to the latest dawn blog entry.

"intensive observations, which will commence on April 24 as it passes over the south pole"

Since we've turned a page, I'll bring forward some possibly useful references. Om's timeline trajectory has been remarkably useful and even though made on 2 Feb, over 2 months ago has proven accurate within a day or two! Imagine the day-spot labels in the upper figure advanced by one or two on the last leg (say 24 March to 24 April) so that 24 April falls directly below the planet. It's easy to make that mental adjustment to what is still a useful map and record of the approach.

The RC3 orbit speed needed is 67 m/s or 150 mph and the simulated view says speed is currently 72 m/s or 161 mph. So slowing down the last little bit is clearly the main order of business. Fullview2 shows the ion tail pointed almost exactly in the direction the craft is going. Here are simulated view links:
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
http://neo.jpl.nasa.gov/orbits/fullview1.jpg
Dawn is roughly between Ceres and the Sun so in the view of Ceres, looking from sunwards, we see Dawn's main antenna dish.
In the view of the Sun (including Earth and Mars, with recognizable constellations such as Gemini and the upper part of Orion), Dawn's dish is on the other side from us, hence not visible.
The probe has its thruster beam pointed slightly Ceres-aft so that (besides slowing down) it will drift slightly Ceres-forward (in the direction of Ceres orbital motion) while it is on the sunlit side of the planet. this is part of adjusting the plane of Dawn's polar orbit around Ceres to keep it out of the planet's shadow when it rounds the S pole and comes up on the dark side.

Mfb mentioned the Dawn Journal, a blog kept by mission director Marc Rayman. It's been remarkably informative and fun to read over the past few months. Here's the link to the mission journal's index:
http://dawn.jpl.nasa.gov/mission/journal.asp
Here's the Ceres part of the Dawn photo/image gallery:
http://dawn.jpl.nasa.gov/multimedia/Ceres_science_gallery.asp
If anyone is curious, Om's original posting of that timeline trajectory is post#47 on page 3 of this thread:
https://www.physicsforums.com/threa...-size-of-full-moon.793140/page-3#post-4996800
Quite simply, it was adapted from a couple of figures in Rayman's November journal which did not have the day-circles labeled. Tagging the days with dates made the whole thing easier to read and use.

 

[marcus]

Speed went down for the first time! since the probe started spiraling into circular orbit. At least on the simulated view. This morning it had crept up to 161 mph, but a new fullview2 update as of 19:30 UTC shows it eased back to 160 mph.

I guess this means we can proceed with our plans to colonize the planet, Om. We need to figure out how to best to excavate air-tight bubbles deep in the ice for the colonists to live in. And how to provide cheerful lighting and amusement facilities.

 

[OmCheeto]

Speed went down for the first time! since the probe started spiraling into circular orbit. At least on the simulated view. This morning it had crept up to 161 mph, but a new fullview2 update as of 19:30 UTC shows it eased back to 160 mph.

hmmm... I'm not sure how to interpret the following:

NASA's Dawn Mission ‏@NASA_Dawn 1 hour ago
Today's orbit speed: 155 mph with respect to #Ceres, accelerating as I get closer

Should they have said decelerating? Or do rocket scientists only speak of positive and negative acceleration?
On the other hand, a change in speed is always an acceleration.
Ha! I don't think I've ever thought about that before.
Never mind.

I guess this means we can proceed with our plans to colonize the planet, Om. We need to figure out how to best to excavate air-tight bubbles deep in the ice for the colonists to live in. And how to provide cheerful lighting and amusement facilities.

Grand idea, Marcus! And perhaps the Cereans have already done it for us. Those headlights might be domes of ice, covering grand cities. I think I spotted another one in todays image. Though it is more of a splat than a headlight, and quite a bit dimmer.

 

[marcus]

I think it is just a discrepancy between the simulated view, which said 160 today, and the tweet which says 155.
I'm inclined to trust the tweet.
if I'd realized there was such a large discrepancy I would have held off posting about the speed, or used the Twitter information.

Thanks for pointing that out.

BTW they seem to agree better about the distance "less than 9000 miles" and a bit under 14.4 kkm.

 

[OmCheeto]

Ceres will be completing its first RC3 orbit right around my birthday.
Thank you, Marcus, for inviting me along for this ride.

I think it is just a discrepancy between the simulated view, which said 160 today, and the tweet which says 155.
I'm inclined to trust the tweet.
if I'd realized there was such a large discrepancy I would have held off posting about the speed, or used the Twitter information.

Thanks for pointing that out.

BTW they seem to agree better about the distance "less than 9000 miles" and a bit under 14.4 kkm.

I don't recall seeing a reason behind why the statistics in the images don't match what is really going on.
And I don't think I noticed until just now, that RC3 is just one orbit. It will start its descent down to the "survey" orbit, right around my birthday.
I don't think I could have asked for a better birthday present.

Thank you, Marcus, for inviting me along for this ride.

ps. Today is the first time in 6 days that a question has passed moderation on Dr. Rayman's blog. I can only imagine, that he is quite busy. I wonder when his birthday is. I'd like to send him something. Though, Tim Berners-Lee turned down my offer of chocolates, in appreciation for the WWW, many years ago. Probably a good thing. Can you imagine getting 3+ billion boxes of chocolate on your birthday every year?

 

[OmCheeto]

Has anyone noticed that the simulated images are already showing shadowing on the southern edge of Ceres?
This would mean that Dawn has already passed the equator.
Though the speed is still listed as 158 mph, and the tweet said 155 mph, 17 hours ago.

I wish I knew how to make a moving gif. The simulation images are being updated almost every hour. It's quite a bit of fun to scroll through them.

4.21.2015.140707
4.21.2015.152313
4.21.2015.163913

Here's a funny tweet from the other day:

NASA's Dawn Mission retweeted

Angela Gibson @AgilistaAG · Apr 19
Dr Green "Here is our best wrong model for Ceres" probably within a year thru @NASA_Dawn mission will know #NEAF

I think I missed the word "wrong" in there yesterday.

I'm still not fluent in twitter speak, so it took me a few minutes figure out that they weren't talking to someone/something called "NEAF".
NEAF = Northeast Astronomy Forum
They held a conference at SUNY Rockland Community College in Suffern, New York, April 18 & 19, 2015
2015 Speakers: Jim Green, Dir. of Planetary Science, at NASA Headquarters

 

[Dotini]

Some nice lights and shadows on this processed image,

A processed still image of Ceres from the above animated sequence of images.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Full Image
- See more at: http://dawn.jpl.nasa.gov/news/Ceres...k_into_view.asp#sthash.S27bW4aj.QmWqgwXm.dpuf

 

[OmCheeto]

NASA's Dawn Mission ‏@NASA_Dawn 31 minutes ago
...and 8,500 miles is about 14,000 kilometers #metricsystem​

Teasers!

8710 miles & 14020 km
157 mph & 0.07 km/sec
(from http://neo.jpl.nasa.gov/orbits/fullview2.jpg : 4/21/2015 21:22:49 UTC)

 

[Dotini]

What are the bright spots?

I've heard some ideas:
1. ice
2. salt flats
3. cryovolcanoes
4. water vapor
5. a combination of the above
6. it's better to remain baffled for a little while longer

We may well be on the edge of discovery. Is Marcus still plumping for salt flats?

 

[marcus]

At this point the ambiguity of altitude vs radius begins to make minor trouble. Rayman and/or the Dawn tweeter may like to talk to public in terms of altitude (RC3 = 13,500 km) distance from the closest point on the surface.
While the guy who does fullview2 and the other simulated views may like to use orbit radius (more conventional physicsish , RC3 = 13,975 km)