Dawn taking chem makeup data at 385 km

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Re: Ceres now 128% of full moon, Dawn in picture-taking mode

Postby Marshall on February 12th, 2015, 3:00 am 

After the 12 Feb photo-shoot, apparently going on now, the next picture taking will be in one week, 19 Feb, at a range of 46 thousand km.
Ceres will be well over twice the size of the full moon by then. Should be pretty nice pictures.
As a reminder, since we just turned a page, here's the table of planned shoots up thru 15 April, taken from the January Dawn Journal
http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/

Relevant column headings:
Distance from Dawn to Ceres in (kilometers)
Ceres diameter in pixels
Resolution in (kilometers) per pixel
Resolution compared to Hubble
Illuminated portion of disk

Code: Select all
Jan 25   (237,000)   43     (22)   1.3   96%   
Feb 3   (146,000)   70    (14)     2.2   97%
Feb 12   (83,000)   121    (7.8)    3.8   98%
Feb 19   (46,000)   221    (4.3)   7.0   87%
Feb 25   (40,000)   253    (3.7)   8.0   44%
Mar 1   (49,000)   207    (4.6)    6.5   22%   
Apr 10   (33,000)   304     (3.1)    9.6   18%   
Apr 15   (22,000)   455    (2.1)    14   50%   


As I write this, current status now gives the range as 84.77 thousand km corresponding to an angular size for Ceres of 128% of the full moon.
Image
Marshall
 


Re: Ceres now 131% of full moon, Dawn in picture-taking mode

Postby Marshall on February 12th, 2015, 10:06 am 

That current status frame keeps getting updated, range is now 83.14 kkm so the planet looks 131% moonsize.

And I gather from comment on Marc Rayman's blog that we will in fact be seeing results from today's photo shoot.

For convenience here are some links:
Current status: http://dawn.jpl.nasa.gov/mission/live_shots.asp
Dawn Journal: http://dawn.jpl.nasa.gov/mission/journal.asp
http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/
Emily Lakdawalla: http://www.planetary.org/blogs/emily-la ... focus.html
http://www.planetary.org/blogs/emily-lakdawalla/
Marshall
 


Re: Ceres now 131% of full moon, Dawn in picture-taking mode

Postby BurtJordaan on February 12th, 2015, 11:40 am 

From the 15:20 UTC view, it looks like Dawn is communicating with Earth. Must take some time to download all the data. I wonder how much is it?
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Re: Ceres now 131% of full moon, Dawn in picture-taking mode

Postby Marshall on February 12th, 2015, 1:51 pm 

Jorrie, I see references to Deep Space Network (DSN). A network of large dish antennas all around the world that receives data from distant spacecraft. Apparently they have a website that tells which antenna location is receiving data from which source. So people consult the DSN website to find out if Dawn is communicating. I didn't check this out.

One thing we can always do is write a question to Marc Rayman's blog. I see a number of people have done this in the comments at the end of the 29 January 2014 blog post. I am a bit shy about doing this. But he seems to have the courtesy to answer at least some of the questions other people ask.
http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/

I also am wondering how many bits or more practically speaking how long does it take to transmit one photo. I expect the probe's voice is really faint over such a long distance so the bits per second transmission rate must be slowed way down

I see the current status view you may have been looking at!
http://neo.jpl.nasa.gov/orbits/fullview3.jpg
It shows the spacecraft oriented so as to point its main antenna at Earth. so we see its "back" end where the thrusters are. the distance given, to Earth, is
529 million km
I don't think we can trust these simulated views to be entirely accurate as to times and details but they are suggestive.
Marshall
 


Re: Ceres now 133% of full moon, Dawn in picture-taking mode

Postby Marshall on February 12th, 2015, 2:04 pm 

You got me curious enough to google Deep Space Network. Here is "DSN Now"
that shows the current activity of the various antennas
https://eyes.nasa.gov/dsn/dsn.html
http://eyes.nasa.gov/dsn/dsn.html

None were currently receiving from Dawn, you click the number under the antenna icon and over to the right it tells which spacecraft it's receiving from.

2 arcsin(.475 / 81.56) = 0.6674 deg
Marshall
 


Re: Ceres now 133% of full moon, Dawn in picture-taking mode

Postby BurtJordaan on February 13th, 2015, 12:56 am 

Marshall » 12 Feb 2015, 20:04 wrote:Here is "DSN Now"
that shows the current activity of the various antennas
https://eyes.nasa.gov/dsn/dsn.html
http://eyes.nasa.gov/dsn/dsn.html

None were currently receiving from Dawn, you click the number under the antenna icon and over to the right it tells which spacecraft it's receiving from.


At 04:50 UT, 13th, the big antenna DSS-43 (70-metre) at Canberra was communicating with Dawn.

I suspect this is data download as well as the programming for the reorientation for thrusting to follow.

--
Regards
Jorrie
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Re: Ceres now 136% of full moon, Dawn in picture-taking mode

Postby Marshall on February 13th, 2015, 1:17 am 

Thanks! your reporting some positive news prompted me to go look at
http://eyes.nasa.gov/dsn/dsn.html
and I saw that Canberra was actively in touch, as you say, and also another antenna was ready to continue the communication with Dawn, at Madrid. Presumably as the earth rolls around they will shift from Canberra to Madrid antenna.
Marshall
 


Re: Ceres now 136% of full moon, Dawn transmitting pix

Postby BurtJordaan on February 13th, 2015, 3:17 am 

Yup, both Canberra and Madrid are presently (07:16 UT) communicating with Dawn. Probably in the change over phase.

UT 07:19 and Canberra is now talking to GTL.
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Re: Ceres now 136% of full moon, Dawn transmitting pix

Postby BurtJordaan on February 13th, 2015, 4:04 am 

There are some more 'bits' of information on the Dawn data on the http://eyes.nasa.gov/dsn/dsn.html page (under 'more details' after you clicked the number 63): Madrid receives downlink data at 125 kbits/sec on a carrier frequency of 8.44 GHz. Power received is 4.24 x 10-20 kW, which explains the slow effective data rate.
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Re: Ceres now 139% of full moon, Dawn transmitting pix

Postby Marshall on February 13th, 2015, 4:16 am 

Nice details! In case anybody just started reading , here is the reason that Canberra dropped out when it got to be late afternoon in Australia, and Madrid took over the job when it was morning in Madrid
Image
If the Earth were between the Sun and Ceres, it would be the night-time hours when an antenna would be able to point at Ceres and communicate. But the diagram shows Earth situated at present so that an antenna would see Ceres mainly during daylight hours.

Current distance 78.53 kkm.
2arcsin(.475/78.53) = 0.693 deg
139% moon-size :^)
Marshall
 


Pix sent, thrust resumes--Ceres 141% moon-size

Postby Marshall on February 13th, 2015, 11:29 am 

2arcsin(475/77100) = .706 degrees

http://neo.jpl.nasa.gov/orbits/fullview2.jpg shows Dawn resumed normal thrusting after the 12 February photo shoot
Marshall
 


Re: Ceres now 144% full moon, pix sent, thrust resumes

Postby Marshall on February 13th, 2015, 1:17 pm 

I'm impatient to see the 12 Feb batch of pictures and have been checking the NASA Dawn twitter:
https://twitter.com/NASA_Dawn

The next two shoots will be at closer range but the planet's face will not be fully illuminated.
The 19 Feb and 25 Feb photos will be from 46 and 40 kkm with 87% and 44% of the disc lit. Here's that handy table from the 29 Jan journal.

Relevant column headings:
Distance from Dawn to Ceres in (kilometers)
Ceres diameter in pixels
Resolution in (kilometers) per pixel
Resolution compared to Hubble
Illuminated portion of disk

Code: Select all
Jan 25   (237,000)   43     (22)   1.3   96%   
Feb 3   (146,000)   70    (14)     2.2   97%
Feb 12   (83,000)   121    (7.8)    3.8   98%
Feb 19   (46,000)   221    (4.3)   7.0   87%
Feb 25   (40,000)   253    (3.7)   8.0   44%
Mar 1   (49,000)   207    (4.6)    6.5   22%   
Apr 10   (33,000)   304     (3.1)    9.6   18%   
Apr 15   (22,000)   455    (2.1)    14   50%   


So it looks like the pictures from yesterday are apt to be the best of Ceres we can expect until April
Marshall
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Marshall on February 13th, 2015, 1:19 pm 

Current status (10:30 PM pacific, 13 Feb) gives the range as 72.73 kkm, so angular size 0.75 degrees, 150% moon-size
2 arcsin(475 / 72730) = 0.7484 deg

We should be getting some pictures
For convenience here are some links:
Current status: http://dawn.jpl.nasa.gov/mission/live_shots.asp
Dawn Journal: http://dawn.jpl.nasa.gov/mission/journal.asp
http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/
Emily Lakdawalla: http://www.planetary.org/blogs/emily-la ... focus.html
http://www.planetary.org/blogs/emily-lakdawalla/
Marshall
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 14th, 2015, 11:09 am 

Hello all, just registered.

Like everyone else in this thread, I'm eagerly awaiting the latest photos from Feb 12th.

As to why they're late ... this is just personal speculation, but as the owners of the probe, I'm guessing the photos won't be released until the NASA lead scientist(s) complete their perogative of first crack at commentary on the (as yet) unreleased photos. Always fun to be the first to pee on virgin snow.

Given all the amped up scrutiny over the bright spots, and now that we're well in excess of Hubble resolution, I'm guessing there will be at least a day or two delay on all photos from here on out, and little or nothing on weekends (since the relevant people are salaried and usually posting on company time).

- $0.02
Darby
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 14th, 2015, 12:12 pm 

... As for the bright spots, I'd speculate they're probably old craters that have slowly filled with pools of captured frozen water (or some other volatiles) over the eons. Recall that most comets generally begin to de-gas and form tails as they cross the asteroid belt on their sunward plunges ... so to me it sorta makes sense that a large body (read: non-negligable gravity) whose orbit borders on a solar radiation driven thermal change in state boundary would tend to collect and form standing deposits of said materials in low lying areas. More shallow deposits would have long since sublimed or ionized away courtesy of the solar wind, but deeper deposits could linger in the craters for some time ... deposits perhaps slowly captured from the traces left by countless other degassing comets.

The reflectivity we've seen in the approach vids released thus far seems consistent with light reflected from the sun (which is located off camera to the left), and as postulated above, it's probably ice.
Darby
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 15th, 2015, 12:44 pm 

Been doing a little online reading on the thermal estimates for Ceres, and the change in state boundary I alluded to above seems more consistent with CO2 ice than Water ice.

Still looking to see if/when we can expect to see the release of the 2/12 photos ...
Darby
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Marshall on February 15th, 2015, 12:50 pm 

Darby » Sun Feb 15, 2015 9:44 am wrote:Been doing a little online reading on the thermal estimates for Ceres, and the change in state boundary I alluded to above seems more consistent with CO2 ice than Water ice.

Still looking to see if/when we can expect to see the release of the 2/12 photos ...


You called it right when you advised not to hold breath. Professionals want to take time analyzing new data if it's interesting before public release. Also don't necessarily work overtime on weekends. I'm quite impatient to see pix but realize might have to wait till monday.
Marshall
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 15th, 2015, 12:51 pm 

Here's the latest I've been able to find from the JPL Mission Director:

Marc Rayman says:
February 13, 2015 at 3:15 pm

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.


Monday's a Federal holiday here in the States, so it's looking like we wont see the 2/12 photos until 2/17 at the earliest.
Darby
 


Re: Ceres 170% full moon, pix sent, thrust resumes

Postby Marshall on February 15th, 2015, 12:59 pm 

By neat coincidence that reply by Marc Rayman was to a question by someone here at SCF!

I don't understand how you figure "not until 2/17 at the earliest" though. Are you reading something into Rayman's tone or account of details? they have a lot of other data to look at besides the pictures, true. but why couldn't they get the pictures out online today or tomorrow 2/16?

Oh! I see what you are saying. Monday is a holiday. That makes sense. *gloom*
Marshall
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 15th, 2015, 1:02 pm 

Hang on, lemme find it ... in his post at 4:21 pm (EST) on the main Blog page, he wrote

... Monday is a federal holiday, so some of the steps will not be possible before Tuesday ...


Sorry bout the crossed posts.
Last edited by Darby on February 15th, 2015, 1:23 pm, edited 1 time in total.
Darby
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Darby on February 15th, 2015, 1:11 pm 

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.


I havent read up on what future satellites are currently planned, but to me there seems to be a clear and obvious need for a deep space communications relay satellite, and the logical location for it would be at Legrange 2. Better still would be two satellites - one at L3 and another at L5, so that the latter would always be in line of sight with the Earth (and L3), and never occluded by the Sun.

If we had something like that in place, it could unblinkingly accumulate any/all data streams from multiple directions in one swell foop, without having to worry about the rotation of the Earth, and then it could compress and restransmit same with a strong high speed signal to the Earth Based DSN stations on the ground. Essentially, a cell tower in space, for all our inter planetary missions.

I'd even suggest a name for it ... the Sir Arthur Clarke Deep Space Relay.
Darby
 


Re: Ceres 150% full moon, pix sent, thrust resumes

Postby Marshall on February 15th, 2015, 1:32 pm 

Darby » Sun Feb 15, 2015 10:02 am wrote:Hang on, lemme find it ... in his post at 4:21 pm (EST) on the main Blog page, he wrote

... Monday is a federal holiday, so some of the steps will not be possible before Tuesday ...


Sorry bout the crossed posts.


I see, the comments/replies are arranged in THREADS so it isn't all latest first. That was from thread #4, in case anyone else wants to check it out.
==quote==
...is becoming far too interesting now.
Thank You very much :D
Andrew R Brown, Ashford, Kent, United Kingdom.
Reply
Marc Rayman says:
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.
In the meantime, it seems that the OpNav 3 images are continuing to provide plenty of material for interesting and entertaining discussions. If you think it’s becoming too interesting now, just wait! The views are going to improve throughout the year as Dawn spirals to lower and lower altitudes (just as we did at Vesta). By the end of this year, in the lowest orbit, the resolution will be almost 400 times better than the OpNav 3 pictures. You might find that even more interesting :-)
Marc
=============
http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/

About your CO2 ice idea, there was a comment in thread #5 from Matt about that:
==quote==
Matt Gibbons says:
February 12, 2015 at 9:51 pm
I am wondering why there is no discussion of carbon dioxide ice. I believe the published estimates of the surface temperature of 1 Ceres are (white) spot on for CO2 ice. There seems to be a bias in favor of water, but Marc has already confirmed that there isn’t enough water vapor based on data from Herschel. I previously wrote that “CO2 sublimates to a solid at 194 deg K, which is within the temperature range of Ceres (168-235 deg K), correct?” These temps seem to be a key…but I certainly could be wrong.
The albedo of 1 Ceres is very dark, so the “white” spot might just be light gray or some other gray scale value that stands out against the more or less black surface of 1 Ceres. It’s fun to speculate…but there is more than enough data to move to informed speculation rather than what we’d like to see. Sure would be cool if there was a lot of water ice, but it doesn’t seem like that boat floats :)
==endquote==
- See more at: http://dawnblog.jpl.nasa.gov/2015/01/29 ... anuary-29/
Marshall
 


Ceres 170% full moon, next shoot 19 Feb at 46 kkm

Postby Marshall on February 15th, 2015, 1:40 pm 

No worry about crossed posts, happens to me all the time. I don't necessarily agree or even follow what Matt Gibbons says but it's something to keep in mind.

Current status says range 64.1 kkm
so angular size about 70% larger than full moon
next photo shoot is scheduled for Thursday, 19 Feb, when the planet will look over twice as big as moon does to us.
Marshall
 


Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby Marshall on February 16th, 2015, 12:36 pm 

as of 9AM pacific time, range = 58.93 kkm, Ceres looking 185% of moon-size

An internet acquaintance has generated some numbers modeling Dawn's trajectory over the coming days. The dates/distances can differ fractionally from those in Marc Rayman's journal, as if a different time zone or time-of-day sampling were being used But by and large there seems to be a rough match.
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, 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.
Code: Select all
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


Marshall
 


Re: Ceres 170% full moon, next shoot 19 Feb at 46 kkm

Postby Darby on February 16th, 2015, 12:54 pm 

Neat.

BTW, here's JPL's small body database entry for ceres (I apologize if someone's already previously posted this).

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=c ... ;cad=1#orb

You can use that tool to see the current orbital data on any currently discovered object in the solar system, by entering the name in the search field, and then clicking on the orbital diagram button.
Darby
 


Re: Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby Marshall on February 16th, 2015, 1:10 pm 

Thanks for posting that, Darby
I'm currently having Java problems with my Mac, so can't avail myself of that resource, but others surely can.
I'd be curious to know Ceres present orbit speed.
As I recall the average speed is 17.9 km/s

But for example if she is near aphelion the speed would be considerably less than average.

Also Ceres orbit plane is inclined by some 10 degrees from the ecliptic, or from the regular solar system plane and I don't happen to know if Ceres is currently UP (i.e. north pole direction) off the ecliptic plane or not.

I wonder if the JPL small body data base has current information like that, or if it just has orbit elements. Wish I could get Java, pictures help a lot!
Marshall
 


Re: Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby BurtJordaan on February 16th, 2015, 1:43 pm 

Marshall » 16 Feb 2015, 18:36 wrote:as of 9AM pacific time, range = 58.93 kkm, Ceres looking 185% of moon-size

An internet acquaintance has generated some numbers modeling Dawn's trajectory over the coming days.

Great stuff!

Your acquaintance does not perhaps have access to software for those "transparent glass" cylindrical plots that we often see star and galaxy positions displayed in so well? I think this complex orbit around Ceres will look spectacular in such a plot!
--
Regards
Jorrie
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Re: Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby Darby on February 16th, 2015, 1:51 pm 

Marshall: There appears to be a sister site for near earth objects, which lists a java workaround. Hope that helps.

http://neo.jpl.nasa.gov/orbits/

I never took orbital mechanics, and I dont see a pre-crunched velocity value in the data pulled for today, but it looks like all the keplerian parameters required to compute it are present, if some one wants to take a stab at it.
Darby
 


Re: Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby Marshall on February 16th, 2015, 2:36 pm 

Let's try to get oriented with this diagram. I think 0 longitude is due "EAST." Is that right? So on March 21 (or whenever Equinox is) the dot representing Earth will be due "West" of the sun.
Image

The longitude angle is counter clockwise. So Ceres and Dawn are currently about 270 degrees or due diagram-"south".

Just eye-balling the diagram it looks to me like Ceres orbit is fatter on the "south-east" . Like it might have its aphelion anywhere between 270 and 360=0 degrees. Say halfway between which would make it 315 degrees.
But that could just be an optical illusion.

Jorrie and Darby please let me know if I have things completely backwards here :^D

It makes sense to me that Ceres should be approaching aphelion just now, i.e. at its slowest orbital speed.
because current status says dawn's speed relative to the sun is only 17.33 km/s and it is nearly keeping up with Ceres.

So ceres must be going a lot less than its average speed of 17.9
Marshall
 


Re: Ceres 185% moon-size, next shoot 19 Feb at 46 kkm

Postby Darby on February 16th, 2015, 2:51 pm 

Jorrie and Darby please let me know if I have things completely backwards here


Dont look at me ... I'm just a hobbyist. {whistle}

By the way, if you click on the date button at the lower left of the orbital disgram {with the applet open}, you can enter a future date and see the orbital posiitions change.
Darby
 


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