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

[marcus]

LPetrich,
I printed off your numbers, and I am trying to judge the difference in scale. For Ceres the upper X1 and lower X2 are 238 and 321
that is, in the lower image the planet is farther to the right. So if I take Ceres as my origin, or zero, then the farthest right the probe goes is around 20 March
Say 582 - 238 = 344 on the upper
and 560 - 321 = 239 on the lower
As I interpret it, this determines the relative scale of the two diagrams. that is "239" on the lower is the same distance as "344" on the upper diagram.
Does this make sense to you?

You are doing the work, so maybe I should not make suggestions. But my inclination would be to subtract off the Ceres coordinates and make Ceres the origin. And then multiply the lower diagram distances by 344/239 to scale them up to be the same size as in the upper diagram. I wonder if this seems reasonable to you?

BTW the originals of the two diagrams are in the November Dawn Journal, as far as I know.
http://dawnblog.jpl.nasa.gov/2014/11/28/dawn-journal-november-28/
The date labels are figured out from taking the capture date to be 6 March, which is what Marc Rayman estimated it would be. this is marked on both trajectories

 

[lpetrich]

Those are raw pixel coordinates, right off the images. I did it that way so that it's easy to compare with others' measurements. Yes, it's a raw-data release. :)

My measurement of Ceres is in the second row. So you can subtract that out, at least if you think that it's not grossly in error.

I found that the first diagram has a true distance per pixel about 3/2 the second diagram, without a large error. So my measurements of Ceres's position in the pictures is not far off. I also found that 1 kkm = 3.22 second-diagram pixels, also without great error. I guess I should upload my adjusted version.

 

[OmCheeto]

Om,
Impressive bit of animation, thanks for sharing it. The figure in your post #87 rotates! I'm curious: what type of account puts a storage limit on this? Is it a PF limit, or one connected with your ISP (internet service provider)? Or has it to do with some "cloud" thing that you upload to, analogous to YouTube for videos or SoundCloud for music.

The limit is from my ISP. I've had my own webspace since around 1996.
I broke my 50 megabyte limit a while back from all the images I was posting to PF.
I didn't realize until today, that my $5/month upgrade bumped me up to a 750 mb limit.
I guess I'm still kind of stuck in my 4 kilobyte ram and 300 baud mindset, from when I got my first PC.

That little "movie" just bumped my usage from 90 mb to 120 mb.

 

[marcus]

Om, Petrich, Mfb,
as of right now Ceres is 50% larger than the full moon. This is the according to the current status report as of 10:30 PM pacific on 13 Feb
which is the same as 6:30 AM UT on 14 Feb. this is as I am posting this
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
says distance is 72.73 kkm which corresponds to 0.75 degree or 150% of moon's angular size

I'm impatient to see the photos that were taken yesterday.

 

[OmCheeto]

Om, Petrich, Mfb,
as of right now Ceres is 50% larger than the full moon. This is the according to the current status report as of 10:30 PM pacific on 13 Feb
which is the same as 6:30 AM UT on 14 Feb. this is as I am posting this
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
says distance is 72.73 kkm which corresponds to 0.75 degree or 150% of moon's angular size

I'm impatient to see the photos that were taken yesterday.

My guess is, that they are going to wait until 1 minute after midnight, such that it will be a Valentines day present.
Set your alarm, and take a nap! :D
That's what I'm doing.

 

[lpetrich]

Standard gravitational parameter - Wikipedia

In celestial mechanics, the standard gravitational parameter μ of a celestial body is the product of the gravitational constant G and the mass M of the body.

μ = GM

For several objects in the Solar System, the value of μ is known to greater accuracy than either G or M. The SI units of the standard gravitational parameter are m³s⁻².

For Ceres, it is 63.1(3) km³s⁻², or an error of 1/20.

I've included my calculations in my latest attachment. It's another TSV text file, and I've zipped it to save space.

In addition to my raw positions, I've calculated:
Positions in pixels with Ceres's position subtracted out
Scaled and combined 3D positions - kkm
Distances for them -- kkm
Smoothed 3D positions (5-point with quadratic fit) -- kkm
Distances for them -- kkm
3D velocities (2-point differences) -- m/s
Velocity magnitudes -- m/s
Orbital velocities -- m/s
Escape velocities -- m/s

I get capture at March 5 - 6, and the last velocities are close to the circular-orbit velocities for their distances.

 

[marcus]

Thanks Petrich! I just printed it out and will have a look. Almost midnight here, so may not get back to you until tomorrow.
It looks like you ran a successful check because capture worked out right (around 6 March) and the final orbit velocities are right.
I don't understand what you did very well at present, but I think it will become clearer after a little time.

 

[mfb]

I used your numbers to calculate accelerations from gravity and from Dawn. And while the second derivative of those numbers is not very reliable, the data points are good enough for an interesting result: gravitational acceleration from Ceres exceeds the average acceleration from Dawn's ion drives during the fly-by end of this month, probably 2-3 days before Feb 20 where you have the first velocity data.

Expressed in (Mm)^2*m/(s*day), GM=5450. That leads to 3m/(s*day) at 42.5km distance, while I get ~2m/(s*day) average for the ion drives, increasing to 4m/(s*day) close to RC3 (but there I would need a better integration scheme to get more reliable values).

Quick cross-check: Using the values of 3000 I_sp and 1 kW estimated power I found, continuous thrust would allow ~5800kg*m/s momentum change per day. Dawn is lighter than 1000 kg now, so those velocity changes look reasonable.
Also, most of the time the calculated ion drive acceleration is against the direction of motion, something you would expect from an enery/fuel-saving approach.

 

[lpetrich]

I used for smoothing a quadratic function fitted to 5 points with equal weight. That resulted in this filter kernel: (1/35)*{-3,12,17,12,-3}

For derivatives, I used this filter kernel: (1/2)*{-1,0,1}

I calculated Dawn's orbital energy, and it declines until about March 17, then it levels off until about April 7, then it starts declining again. Since Dawn's ion engines are typically run for long stretches of time, I conclude that there will be a gap in its running between March 17 and April 7, a gap that will let Dawn fall toward Ceres.

Orbital energy:
$$ E = \frac12 v^2 - \frac{\mu}{r} $$
Strictly speaking, energy per unit spacecraft mass. It changes at this rate:
$$ \frac{dE}{dt} = {\mathbf v} \cdot {\mathbf a} $$
for acceleration a. Doing the case of going from one circular orbit to another in an orbit that is as circular as possible, I find:

(Final orbital velocity) - (initial orbital velocity) = +- (propulsion delta-V) (+ for inward, - for outward)

Also, Dawn will get to about 40 kkm at about February 23, giving Ceres an angular size of 1.5 degrees or 3 times the Moon's from the Earth. It will then move away to about 80 kkm at about March 18, with Ceres being 0.75d across or 1.5 times the Moon's.. Late in April, it should be less than 20 kkm away, giving an angular size greater than 3d or 6 times the Moon's.

Dawn should reach its lowest Ceres-relative velocity at about March 21, a little more than 10 m/s (36 km/h, 22 mph). It is currently traveling at 90 m/s (320 km/h, 200 mph) relative to Ceres. Late in April, it should get up to about 60 m/s (220 km/h, 130 mph).

It will spend some time in a high-altitude orbit before going into a low-altitude orbit. The lowest possible one is for a surface satellite, and that sort of satellite will have orbital velocity 360 m/s (1300 km/h, 800 mph) and period 2.3 hours. So after getting into a high orbit, Dawn will expend about 300 m/s delta-V for getting into a low orbit. But it's not expected to do any more traveling, since escaping Ceres will require a similar amount of delta-V and going to some other sizable object will require even more delta-V.

I've uploaded the Mathematica notebook that I've been working on for these calculations.

 

[OmCheeto]

Just for the record, I fully approve of your numbers, lpetrich.

Ceres and Dawn are moving "into" the image.

Dawn and Ceres are moving "up" in the image​

Except for the apex, our numbers are very close.
And I should mention that your apex numbers are better than mine.
I think I massaged mine a bit too much, as my raw data at that point matched yours much more closely.

I used for smoothing a quadratic function fitted to...

You apparently know your maths...
I, unfortunately, have lost too many brain cells to figure out how to interpret some of this "magic".

 

[marcus]

To get a rough idea of how it shapes up in 3D I have copied Petrich's X,Y,Z, and distance numbers (smoothed where available.) X is distance out from sun with Ceres X = 0, and Z is the lag behind Ceres, which at first increases until probe begins catching up. We want Z to be small because that means Dawn has caught up with Ceres Z = 0.
Y is a bit unintuitive, it is the distance BELOW the orbit plane (i.e. roughly in Ceres South pole direction) so when it becomes more negative that means the probe is rising in the North pole direction, above Ceres orbit plane Y = 0.

I will fill in some more of Petrich's numbers in this abbreviated table later as time permits.

date      X          Y          Z        distance from Ceres
F17   -45.9972    -6.4086    27.2882    53.86518747                  
F18   -38.555    -9.71627    28.2185    48.75630903
F19   -32.3324    -12.4392    29.202    45.30865911                  
F20   -26.169    -14.8491    29.9728    42.46976656
F21   -19.6171    -17.2648    30.4689    40.14047582
F22   -13.2794    -19.4975    30.6993    38.71617222
F23   -6.73346    -21.6416    30.593    38.07400666
F24   -0.502056    -23.4431    30.212    38.24390071
F25     5.62894    -25.0851    29.7158    39.29345973
F26     11.407    -26.4613    29.1488    40.98746867
F27     17.2899    -27.6663    28.1919    43.11783881
F28     22.8583    -28.5286    27.0313    45.46508635
M1      27.9985    -29.1842    25.6846    47.90962543
M2      32.8862    -29.7513    24.1873    50.51403254
M3      37.6439    -30.1647    22.7166    53.31994232
M4      41.9734    -30.4246    21.3167    56.05197848
M5      45.8274    -30.5605    19.8726    58.55779181
M6      49.5028    -30.6491    18.2955    61.02966376
M7      52.8252    -30.4896    16.7451    63.24963112
M8      55.7681    -30.3242    15.1946    65.27261258
M9      58.5427    -30.0761    13.6441    67.21592802
M10     58.5427    -30.0761    13.6441    67.21592802
M11     63.2886    -29.4796    10.5963    70.61710331
M12     65.1256    -29.1961    9.32939    71.97772953

 

[mfb]

As Dawn is within the Hill sphere of Ceres, the meaning of Z and Y do not matter much. Total distance matters. And X relative to the total distance, because it determines how much sun we see on the surface.

 

[lpetrich]

Except for the apex, our numbers are very close.
And I should mention that your apex numbers are better than mine.
I think I massaged mine a bit too much, as my raw data at that point matched yours much more closely.

Thanx. Good that two independent measurers agree.

(my smoothing algorithm)

You apparently know your maths...
I, unfortunately, have lost too many brain cells to figure out how to interpret some of this "magic".

It's a rather standard sort of procedure. For each point, find a smooth curve that goes through it and its neighbors. Then find the curve's value at the point's location.

If the curve is a linear function of its parameters, like a polynomial with its coefficients, and if one does least-squares fitting, then one can do much of the fitting work in advance. The smoothed point's value then becomes a weighted sum of its original value and its neighbors' values. One finds those weights by doing that advance fitting work.

 

[marcus]

Hi Mfb, glad you are contributing to the discussion!
Om and Petrich, thanks so much for the numerical and graphic work! It makes a big improvement.
Besides ourselves, I don't know who else might be reading. In case others are, I'm thinking that since we are studying one approach trajectory it might be interesting to make a comparison with the earlier one that was planned before the accident in September caused several days loss of thrust.

The second approach, developed after the accident, takes more than five weeks longer. So it shows what a difference a slight deficiency in orbit speed can make. Timing is sensitive.
In the first approach Dawn had all the necessary orbit speed so it was not lagging behind the planet, and the time-consuming gravity assist was not needed. This figure from the November Journal shows the comparison. In both cases "capture" occurs on 5-6 March. So you can count the day circles thereafter and see how much longer it takes to reach the initial target orbit (labeled RC3).

The sun is off to the left--Dawn approaches from sunward. Their common solar orbit direction is into the page.
In the first case, Dawn would have been up to speed and able to use thrust to slow down (short spacing between day circles as it enters diagram). So it slips right into RC3 orbit. Clean and direct
In the second case, Dawn is still needing its thrust to match Ceres' orbit speed, so it has not been able to slow down its sideways approach from sunward (long spacing between day circles as it enters) and moreover it is still falling behind as it approaches!
So it overshoots and uses Ceres' gravity to help slow down. It is also using Ceres' gravity to help it catch up. (the falling behind is up out of the page and not shown, nor is the crucial catching up, which is what takes such a long time).

These additional maneuvers, and the additional navigation photo shoots, consume the attitude control propellant (hydrazine) which has become the critical factor which could limit successful completion of the mission. Dawn was launched from Earth carrying a 45 kg supply of hydrazine and the mission team has had to budget that supply carefully. Planned navigational photoshoots have been canceled because they require rotating the orientation of the spacecraft .

Before the temporary loss of thrust in September, the planned arrival in RC3 orbit was 17 March.
After the necessary change of approach trajectory, projected arrival at RC3 will be over 5 weeks later.

BTW current status puts the range at 68.23 kkm at the moment (4PM pacific 14Feb, or midnight UT) making Ceres 160% of moonsize

 

[OmCheeto]

...
I wrote an image measurer for myself since I couldn't find a good one that enters a position with each click on the picture being measured. It's OSX-native, so to port it to Windows or Linux, you'll need GNUstep.

I was wondering how you did that so fast.
Is that X-code?
Not only do I need to relearn maths, I need to relearn how to code.

 

[lpetrich]

I was wondering how you did that so fast.
Is that X-code?
Not only do I need to relearn maths, I need to relearn how to code.

My image measuring was fast, but not the coding of my Image Measurer. I'd written it some months back, though I'd recently improved it to add some more types of rescaling.

I had indeed written it with Xcode, Apple's IDE for Cocoa apps.

 

[OmCheeto]

My image measuring was fast, but not the coding of my Image Measurer. I'd written it some months back, though I'd recently improved it to add some more types of rescaling.

I had indeed written it with Xcode, Apple's IDE for Cocoa apps.

Ok. After about 14 hours, Xcode is now installed. Marcus's "original trajectory" problem looks like fun, but hand digitizing images is a pain in the b***!
I went to bed last night and thought about this for about an hour before I fell asleep.
This will give me something to do while waiting for the images to be published.

ps. I got tired of waiting, and photographed my log again.

This is not Ceres!
This is Om's log, sitting in the back of his truck, photographed from a distance of 17 feet.
This is only a predictive indicator of the resolution we are to see from the static images.

 

[mfb]

A beautiful log! Are those impact craters? :D

How do you adjust for the different camera quality?

 

[OmCheeto]

A beautiful log! Are those impact craters? :D

How do you adjust for the different camera quality?

Experimentally, of course.
Since I couldn't understand what:

Framing Camera (FC) Instrument
...at an angular resolution of 93.7 µrad px-1...

meant. (Fowla Deutschern! Immer mit der hoch-gesrpachen...)
From the previous "Ceres" thread:

Today I took my baseball out and photographed it at the appropriate distance: 83 feet
I blew it up, and it only had a resolution of about 13 pixels diameter. Since the Dawn team claims the resolution they will be taking should be 26 pixels, I replaced the baseball with a log.
...

Looking at the moon/Ceres/baseball from a certain distance, gives us a human perspective, but doesn't give you a resolution, if you had eagle eyes, or camera eyes.

 

[mfb]

Ah.
93.7 µrad/pixel are 10600 pixel per rad or 186 pixel per degree.

 

[OmCheeto]

Ah.
93.7 µrad/pixel are 10600 pixel per rad or 186 pixel per degree.

I suppose, I could have done the math...

Fowla Om!

ps. For those who don't speak Kraut, my mother, a native of Germany, used to call me and my siblings; "Faule affen!" Which sounds a lot like "Foul apes!". But, it really means, "Lazy apes".

Es stimmt. (= I agree)

pps. Wait a minute. Who's holding up these images?

JPL manages the Dawn mission for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. The University of California, Los Angeles (UCLA) is responsible for overall Dawn mission science. Orbital Sciences Corp. in Dulles, Virginia, designed and built the spacecraft . The Dawn framing cameras were developed and built under the leadership of the Max Planck Institute for Solar System Research, Gottingen, Germany, with significant contributions by German Aerospace Center (DLR), Institute of Planetary Research, Berlin, and in coordination with the Institute of Computer and Communication Network Engineering, Braunschweig. The Framing Camera project is funded by the Max Planck Society, DLR, and NASA/JPL. The Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team.

This appears to be, an international conspiracy!

Faule missgeburt*!

*This is what mom called us, when we were really, really bad.

Thank god, google translates this word, mildy, as "Freak".

 

[marcus]

Om, I'm reluctant to offer any rational excuse because your cussing out NASA helps make the delay bearable. However Monday is *Presidents Day* a federal holiday and there may be key technical personnel at JPL who go home for long weekends leaving facilities shut down that the scientists need for analyzing data.
Down at the end of comment thread #5 of http://dawnblog.jpl.nasa.gov/2015/01/29/dawn-journal-january-29/
Marc Rayman says:
==quote==
February 13, 2015 at 4:21 pm
Hi Andrew,

We will post pictures on this website and elsewhere as soon as all the necessary steps are complete. After receiving the data, the team has to process the images before making them public, following established processes. Monday is a federal holiday, so some of the steps will not be possible before Tuesday.
==endquote==

I was also interested by what he said here:
==quote==
February 13, 2015 at 3:15 pm
Hi Jorrie,

The time to transmit a picture depends on the details of the image, because the spacecraft compresses the data, but generally it is between one and two minutes. The full analysis of the pictures for scientific purposes, however, requires additional information from the spacecraft . In addition, to keep our distant robotic explorer healthy, we scrutinize myriad measurements of currents, voltages, temperatures, switch positions, pressures, valve positions, software states, instructions it has executed, decisions it has made, and much more. Following RC1, it took Dawn about 16 hours to download all of its Ceres observations plus this additional information.

As you know, no one antenna can point at Dawn for 16 hours, just as you cannot point at the sun, moon or a star for that long. Earth rotates too quickly. To return the data yesterday and today, we used the three largest antennas of the Deep Space Network, each 230 feet (70 meters) in diameter. We started with the one in Canberra, Australia, then moved over to the one in Madrid, Spain, and concluded in Goldstone, California.

Thank you for your interest!

Marc

- See more at: http://dawnblog.jpl.nasa.gov/2015/01/29/dawn-journal-january-29/#comment-8599
=endquote==

So there is the unspoken rule that in-house professionals get "first crack" at new data (given which understanding I think JPL is pretty generous) and there is the thing of "established procedures" for releasing photos, which I guess makes sense if you don't want variants to flood the media ahead of more reliable copy. And the more interesting observation, I thought, was that sending pix takes only a couple of minutes! But the whole communication session took 16 HOURS! It's intriguing to think of all that other stuff going on. Reminds me of going into the doctor's for a complete medical exam with all the blood tests and the poking and tapping on the knees and listening to the lungs etc etc.

Classic comment on excessive use of technical jargon:
Fowla Deutschern! Immer mit der hoch-gesprachen...
Behind every really funny humorist there is a Mom

 

[OmCheeto]

Om, I'm reluctant to offer any rational excuse because your cussing out NASA helps make the delay bearable...

As Red Green once said; "If you can't figure out why the the 4th power polynomial interpolation of a radian graph fits so well, you may as well attempt, to make a funny"

Feb 16 thru Mar 3, radian vs pixel distance.
Upper JPL image.​

...
Behind every really funny humorist there is a Mom

And sometimes, a dad.

 

[OmCheeto]

Om, I'm reluctant to offer any rational excuse because your cussing out NASA helps make the delay bearable. However Monday is *Presidents Day* a federal holiday and there may be key technical personnel at JPL who go home for long weekends leaving facilities shut down that the scientists need for analyzing data.

Not sure if you're aware of this, but I retired last May, so I no longer know what day of the week it is, nor worry about long weekends.
My bad.

...

I was also interested by what he said here:
==quote==
February 13, 2015 at 3:15 pm
Hi Jorrie,

The time to transmit a picture depends on the details of the image, because the spacecraft compresses the data, but generally it is between one and two minutes. The full analysis of the pictures for scientific purposes, however, requires additional information from the spacecraft . In addition, to keep our distant robotic explorer healthy, we scrutinize myriad measurements of currents, voltages, temperatures, switch positions, pressures, valve positions, software states, instructions it has executed, decisions it has made, and much more. Following RC1, it took Dawn about 16 hours to download all of its Ceres observations plus this additional information.

As you know, no one antenna can point at Dawn for 16 hours, just as you cannot point at the sun, moon or a star for that long. Earth rotates too quickly. To return the data yesterday and today, we used the three largest antennas of the Deep Space Network, each 230 feet (70 meters) in diameter. We started with the one in Canberra, Australia, then moved over to the one in Madrid, Spain, and concluded in Goldstone, California.

Thank you for your interest!

Marc

- See more at: http://dawnblog.jpl.nasa.gov/2015/01/29/dawn-journal-january-29/#comment-8599
=endquote==

So there is the unspoken rule that in-house professionals get "first crack" at new data (given which understanding I think JPL is pretty generous) and there is the thing of "established procedures" for releasing photos, which I guess makes sense if you don't want variants to flood the media ahead of more reliable copy. And the more interesting observation, I thought, was that sending pix takes only a couple of minutes! But the whole communication session took 16 HOURS! It's intriguing to think of all that other stuff going on. Reminds me of going into the doctor's for a complete medical exam with all the blood tests and the poking and tapping on the knees and listening to the lungs etc etc.

...

I understand all that. But, "I'm a TAXPAYER"! They should know what I want, and give it to me, when I want it.

Anyways, I digitized the alternate original flight path, tried to figure it out, and have decided that I am brain dead.
Switching between Cartesian and Polar coordinates is making me crazy.
It's no wonder Newton went mad.

Wait!

​

He wasn't mad. I've done spectral experiments, also. And I'm not mad.
I'm sure it's just a mild case, of ADD.


Oh... Never mind.
The new pictures are up...

 

[marcus]

Heh heh, Newton (mad or not) would have been delighted by the new pictures, Om. Thanks for posting them! To me she's still looking like a ball of grimy ice, which is what I want her to be

 

[marcus]

Om, you remember the abbreviated table I made from Petrich's good XYZ trajectory numbers? I was playing around with that table to see if I could make it more readily intuitive. He is using a right-handed coordinate system: OUT--UP--Backwards (from Ceres orbital motion). So that Z becomes more positive as Dawn lags farther behind.
And RH is conventional orientation. But suppose we use a left-handed XYZ: OUT (from the sun) UP (off the orbital plane) and FORWARDS (with the planet motion)
All it means is changing the sign of his Z numbers.
When I hold up my left hand and think of the sun as far to my left (as in Rayman's diagrams) then thumb is X (pointing right, out from the sun) and indexfinger is Y (pointing up) and the third digit is Z (pointing forward or into the page of Rayman's upper diagram). So X and Z define the orbital plane. And Y is up off the plane in roughly the Ceres North pole direction. Actually the N pole is currently tilting slightly outwards (by about 3 degrees they estimate) away from sun, but basically it is up off the plane.

Petrich, I'm trusting that it is acceptable for us to play around with the numbers you posted. They're definitely helpful in understanding the approach trajectory. For looks I truncated some surplus precision in the rightmost column, and changed the sign of Z.

To review:
X Y Z are coordinates relative to Ceres, which is (0,0,0), measured in kkm---thousands of km.
X is directed out from sun, in Ceres orbit plane
Y is directed perpendicularly up off the orbit plane, approximately in Ceres' north pole direction
Z is directed forwards in Ceres orbit plane, the direction Ceres is moving, a negative shows the probe trailing behind.

date      X          Y          Z        distance from Ceres
F17   -45.9972    6.4086    -27.2882    53.86                
F18   -38.555    9.71627    -28.2185    48.75
F19   -32.3324    12.4392    -29.202    45.30                
F20   -26.169    14.8491    -29.9728    42.46
F21   -19.6171    17.2648    -30.4689    40.14
F22   -13.2794    19.4975    -30.6993    38.71
F23   -6.73346    21.6416    -30.593    38.07
F24   -0.502056    23.4431    -30.212    38.24
F25     5.62894    25.0851    -29.7158    39.29
F26     11.407    26.4613    -29.1488    40.98
F27     17.2899    27.6663    -28.1919    43.11
F28     22.8583    28.5286    -27.0313    45.46
M1      27.9985    29.1842    -25.6846    47.90
M2      32.8862    29.7513    -24.1873    50.51
M3      37.6439    30.1647    -22.7166    53.31
M4      41.9734    30.4246    -21.3167    56.05
M5      45.8274    30.5605    -19.8726    58.55
M6      49.5028    30.6491    -18.2955    61.02
M7      52.8252    30.4896    -16.7451    63.24
M8      55.7681    30.3242    -15.1946    65.27
M9      58.5427    30.0761    -13.6441    67.21
M10     58.5427    30.0761    -13.6441    67.21
M11     63.2886    29.4796    -10.5963    70.61
M12     65.1256    29.1961    -9.32939    71.97

The table starts today 17 Feb and it shows the probe overshooting Ceres in the X direction (it has not had time to slow its X motion and will need Ceres gravity to pull it back in line)
likewise it shows the probe overshooting in the upwards Y direction (Ceres inclination is 10 degrees and it just recently passed its descending node, so it is "plunging down" relative to the ecliptic and Dawns prior orbit, again Ceres gravity will help bring Dawn in)
meanwhile it shows the probe at first falling behind in the Z direction (to a minus 30.7 kkm!) but then beginning to catch up.
It shows the Z lag being reduced to a minus 9.3 kkm.
That's important. As I understand it, much of Dawn's thrust, since October, has been devoted to catching up with Ceres' 17 km/s orbit speed, and the probe is still coming in with a slight deficiency in that department. It has had to concentrate on getting its Z velocity right which is why it has not had time to kill more of the excess X and Y and is overshooting in those departments.

 

[marcus]

If I wanted to boil down the narrative of that 3 week table of Petrich numbers, from 17 Feb to 12 Mar, I could say
The X overshoot continues out to 65 kkm past Ceres
The Y distance up from Ceres maxes out at 30.6 kkm on 6 March, and begins to subside.
The Z lag behind Ceres maxes out at -30.7 kkm on 22 February, and shrinks to -9.3 kkm by the end of the period.

Maybe I should add a few more rows to the table to see if the trends continue. I'll start with 5 March which is sort of a nominal "capture" date when the probe velocity finally falls below the scape velocity at its then-distance from the planet. Y distance up off the Ceres orbital plane also peaks about that same time.

date      X          Y          Z        distance from Ceres
M5      45.8274    30.5605    -19.8726    58.55
M6      49.5028    30.6491    -18.2955    61.02
M7      52.8252    30.4896    -16.7451    63.24
M8      55.7681    30.3242    -15.1946    65.27
M9      58.5427    30.0761    -13.6441    67.21
M10     58.5427    30.0761    -13.6441    67.21
M11     63.2886    29.4796    -10.5963    70.61
M12     65.1256    29.1961    -9.32939    71.97
M13     66.8636    28.8417    -7.90296    73.24
M14     68.4790    28.2510    -6.38793    74.35
M15     69.7223    27.7726    -4.80202    75.20
M16     70.7383    27.1819    -3.57051    75.86
M17     71.5002    26.8275    -2.34785    76.40
M18     72.0023    26.5440    -1.37327    76.75
M19     72.3581    26.2900    -0.12403    76.98
M20     72.4098    25.8411     1.05432    76.88
M21     72.2873    25.4277     2.33013    76.66
M22     72.0303    25.0319     3.22497    76.32
M23     71.7734    24.5653     4.24385    75.97
M24     71.1281    23.9983     5.08554    75.23
M25     70.1580    23.3604     6.02468    74.18
M26     68.9840    22.7402     6.74232    72.94
M27     67.6521    22.1023     7.46883    71.56

We can see that the distance UP off the Ceres orbit plane continues to subside over this next period. More significantly the X overshoot finally maxes out at around 72.4 kkm by 20 March. Dawn gets as far past Ceres, away from sun, as it is ever going to get, and Ceres gravity begins to pull it in. Also by 20 March, Dawn has not only made up all its lag but has actually gotten out a little ahead of the planet.

These projected coordinates, with minor changes, are copied from some prepared by L. Petrich. I believe they were derived from figures shown in Marc Rayman's Journal. The dates/distances can differ fractionally from those in the journal, as if a different time zone or time-of-day sampling might have been used But by and large they seem to match up.

 

[OmCheeto]

Marcus, I'm pretty sure I've posted somewhere in the forum, that I'm both vertically and horizontally dyslexic. So no matter what convention you use, I'll be confused.

My Mac "Grapher" software doesn't let me delete data sets, but does let me hide the ones that are wrong.

Here's what it looks like with nothing unhidden:

​

Looks like the bags of Mardi Gras beads I have hanging in my closet.
hmm... google google google
Ah!
Mark this on your calendars! This is the first year, I've missed partying, on Fat Tuesday, in about 40 years.

ps. I think I'll add this to my list of proofs, that god exists.

 

[OmCheeto]

Latest tweet:

NASA's Dawn Mission ‏@NASA_Dawn 27m27 minutes ago
Happy Lunar New Year, #Earthings! No moons detected at #Ceres [so far] http://dawn.jpl.nasa.gov
​

I was worried about moons.

 

[marcus]

Today 19 Feb is another planned navigational photoshoot. This current status view refers to earlier today (around midnight pacific time or 8h UT) but I just checked more recently and current status for 10AM pacific (18h UT) gives the range as 45.83 kkm and speed relative to the planet 81.4 m/s. (Its velocity is not directly at Ceres so it isn't closing in that fast.)
Ceres seen from the probe is now 238% moon-size. 2 arcsin(475/45 830) = 1.1877 deg
http://neo.jpl.nasa.gov/orbits/fullview2.jpg

They take photos of Ceres against the background of known stars in order to help locate the probe for navigation purposes. These photos are not necessarily posted on line. They may be taken either with a lower-resolution "navigation camera" or with the larger higher resolution camera that will be used to study the planet. I think this time the shots will be with the "navcam".