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

[marcus]

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

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

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

 

[Jimster41]

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

 

[marcus]

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

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

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

 

[Jimster41]

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

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



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

 

[marcus]

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

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

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

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

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

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

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

 

[marcus]

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

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

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

 

[Jimster41]

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

 

[Dotini]

Unlikely it has an EM field right?

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

 

[Jimster41]

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

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

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

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

 

[marcus]

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

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

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

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

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

 

[marcus]

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

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

 

[OmCheeto]

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

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

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

Thanks!

Om

Hi Om,

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

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

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

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

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

I hope that answers your question.

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

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

Regards,

Marc

I responded, with my usual Omic

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

 

[OmCheeto]

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

And now...

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

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

 

[mfb]

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

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

 

[marcus]

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

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

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

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

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

 

[marcus]

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

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

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

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

 

[OmCheeto]

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

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

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

i C Ceres Presentations (JPL)

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

12:30-1:30 pm PDT

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

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

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

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

2:30 - 4:30 pm PDT

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

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

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

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

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

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

 

[mfb]

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

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

 

[marcus]

More detail on one of the bright spots.

 

[marcus]

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

 

[mfb]

It is 16 MB large, better don't include it here directly.
A structure in the smaller spot! Very nice.

 

[marcus]

Dawn tweeted that it is thrusting and spiraling down
https://twitter.com/NASA_Dawn/status/597880787111956480
‏@NASA_Dawn (as of 3PM pacific on 11 May)
Update: Today I am about 8,000 miles (13,000 km) above #Ceres, and using my ion engine to spiral down to my next mapping orbit

This agrees approximately with fullview2
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
the simulated view also shows it on the night side of Ceres going north, with the ion beam pointed north, so as to apply braking
the simuated view is as of 2AM 12 May UT, which is I think 6pm pacific 11 May
the simulated view says 12700 km altitude. So roughly consistent

 

[marcus]

Good point!
These are simple ideas but very good to understand, if any newcomers see post #435 figure out how that works, or ask or both. Give Janus and Mfb something to do. Otherwise we have to rely on imagined hypothetical or future newcomers which we think may exist, and tailor our posts to.

If you are a spacecraft in circular orbit then braking speeds you up so if you thrust in reverse, like Dawn is now doing with its solar electric ion drive, you will spiral in slightly and speed up. And we can SEE THIS in the simulated view of Dawn
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
this is a concrete example.
while in its first circular orbit, for about 15 days, Dawn was at altitude 13,500 km and going at speed right around 150 mph.
On the 10 May it began a braking thrust with its ion beam pointed in the direction it was going.
Now simulated view says it is going 153 mph. Return tomorrow to see if that speed has increased!
And it says the altitude is now (7PM pacific on 12 May) about 11.7 kkm that is almost 2000 km nearer the surface than it was to start with.
Because of a delay in refreshing, this image as it currently appears is out of date. Click on REPLY to see the current sim-view version. You don't have to reply you can just cancel or back out of replying, if you want, but when you click "reply" at the bottom of this post it will show you the current version of the sim-view graphic. It is now as of 10PM pacific 12 May and the speed is 154 mph (more than what the outdated version the system provides currently shows).
UPDATE: As of now 7AM 13 May pacific, when you press "reply" the updated version says 158 mph. So quite a lot of speeding up has happened.
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
This image shows an earlier version but it will change to an updated one if you click "reply", so i am describing the situation for 7PM pacific on 12 May when I say she is flying up the night side of Ceres heading for the N pole, and thrusting to slow down. The Sun and Mars are visible so we can see the plane of the solar system currently in this sim-view.
UPDATE: Currently it says altitude 11.7 kkm and speed 154 mph, for 8PM pacific on 12 May. So we see speed continuing to climb in accordance with the reverse thrust braking by the craft.
Click on the link to get the latest sim-view figures.
UPDATE: as of 7AM 13 May, altitude 11.2 kkm and speed 158 mph.

 

[OmCheeto]

The good^[1], the bad^[2], and the ugly^[3]...

...

Marc Rayman...
(YAY! My newest pen pal, and bff. )​

[1] Dr. Rayman Marc apparently saw this post, and now insists, via his last communication, that in my future email salutations, I use his first name.

[2] I got antsy on Saturday, waiting for the live broadcasts, and went out to mow my lawn. I have apparently lost my ability to tell time by the position of the sun, and missed his live speech, by 10 minutes. I didn't cut my throat, as, well, I'm patient enough to know that very interesting things are in our near future.

[3] Marc informed me, that I was correct, that 50,000 people usually show up for a JPL open house event. He then informed me, that only 2200 people showed up for Saturday's event. I almost had another stroke.

My latest email:

Hi Marc,

That, is simply incomprehensible. In a metro area with over 18 million people, only 2000 showed up.

I’m glad you agree that it wouldn’t have been worth my time, as I calculated that the $500 to fly down and stay the weekend would have come out to $1000/hr for your 30 minute talk.

Though, meeting you, and all the rest, would have made it worth it.
...

And, back to the good, and another reason not to cut my throat:

• [/PLAIN]
  Chris GriffithsHow long before the lectures become available to download?
  Like · Reply · 1 · 9 May at 15:14
  • https://fbcdn-profile-a.akamaihd.net/hprofile-ak-xap1/v/t1.0-1/c1.0.32.32/p32x32/11178264_676875095792285_1139312566101433848_n.jpg?oh=73d1d942899dbb5183da99a4e4d51a3b&oe=55C2A783&__gda__=1443227839_8b9e04c822c47b7aa2e7020f8dbc174c
    NASA Dawn MissionMassive files, we are downloading from Caltech this week, hope to get them up by end of week.
    Unlike · 3 · 11 May at 12:07

Yay!

 

[marcus]

This was the official word on 13 May:
"Today's altitude is between ...10,000 and 11,000 km above #Ceres"
3:00 PM pacific - 13 May 2015
Now the sim-view says for 10PM UT on 14 May, which would be 2PM pacific on 14 May
that the speed is 179 mph and the altitude in 9.44 kkm
So if official twitter and sim-view are consistent (which I suspect they are at this point) then the probe is currently descending roughly at the rate of 1000 km per day and noticeably speeding up, now 179, while in the 13,500 kkm orbit it was always going right around 150 mph

UPDATE: Official tweet for 14 May:
" Today I will spiral down from an altitude of... 10,000 km to ...8,900 km with respect to #Ceres
2:20 PM - 14 May 2015"

 

[marcus]

there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif

 

[OmCheeto]

there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif

Interesting. It's looking flatter than before.

 

[marcus]

I agree. More like flat patches of ice or salt residue, level with the crater floor.

Sim-view shows the probe crossing over the N pole from dark side to light. Reverse thrusting to slow down. Thanks Mfb for updating the title!
It has already descended quite a lot.
Down from 13500 km a few days ago to (sim-view says) 7840 km, and speed has risen from 150 mph (in initial orbit) to 204 mph.
That's the current view, as of 7PM pacific on 15 May ( i.e. dated 3AM on 16th UT)

Since we turned a page, i should bring the orbit schedule forward.

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

There's some explanation of the table at:
https://www.physicsforums.com/threads/ceres-at-rc3-13500km-above-surface.793140/page-20#post-5089960
But it seems fairly self-explanatory. The more you descend, the faster you are going and the more work is required to descend further. At 7,800 km Dawn is more than half the way down from 13.5 to 4.4 kkm
but it is going to still take 3 weeks to come down the rest of the way.

 

[mfb]

Can we discuss Mars and space elevators in a different thread, please?Edit: The Mars/Ceres discussion got split out. There is some overlap, so some content appears twice and some references might be less clear without the other thread, but I tried my best.

 

[marcus]

Can we discuss Mars and space elevators in a different thread, please?

I hope we can. I was interested in some of the things people had to say about getting stuff into orbit from Ceres and Mars.
So I started a thread about the feasibility of manufacturing (e.g. chemical manufacturing) on Ceres as compared with Mars.
https://www.physicsforums.com/threads/ceres-mars-as-manufacturing-outposts-analytic-exercise.814235/

 

[mfb]

Did you notice the bright spots in http://neo.jpl.nasa.gov/orbits/fullview2.jpg ?
Also. Ceres grows notably in size from day to day.

7110km (about one transatlantic flight), 218 mph

 

[marcus]

I'll bring forward the sketch of the descent down from RC3 (15 day orbit) to Survey (3 day orbit)

It looks to me as if, in the diagram, distance to Ceres can actually increase or stay constant for a while after she goes 3/4 of the way around in the first loop.
Descent starts around 4 o'clock and goes counter clockwise, always closing in, until about 7 o'clock.

By then the probe is probably in an elliptical orbit (if she stopped thrusting) and she has excess kinetic and needs to swing out to apogee. So the thruster is fighting a tendency to swing out and it is a "draw" for a while. It does not get any closer in from, say, 7 o'clock to, say 3 or 2 o'clock. Then it starts to fall in again.

I'm probably over interpreting the diagram, which could be just a rough sketch to give the idea of a spiral, and not accurate in detail. Just a tentative interpretation.

I think sim-view has show some slowing and actual increase of the Ceres distance during the past couple of days, can't be sure, just my impression.

EDIT: Yes at least according to sim-view, I just looked and it say altitude 7.45 kkm and speed 205 mph, farther off and slower than it has been recently That was 8PM 17 May pacific time.

EDIT: noon pacific time, 18 May, 7.9 kkm and 191 mph, still farther off and still slower than yesterday.
according to sim-view.

 

[mfb]

Looks quite spirally to me, but even in the sketch the distance does increase a bit in between. The red circles are 50 pixels or about 2500km apart (with the inner one at about 5000 km).

We are bit outside the second smallest ring.

 

[marcus]

Thanks for the red circles. I think I see the outwards swing between 7 o'clock and 3 o'clock.
Simview says distance is 7.9 kkm and I think it's time for it to start approaching again.
Probe seems to have just passed over the S pole

 

[Dotini]

there is an animation that focuses specifically on one of the bright spots:
http://i.imgur.com/tsm3wN0.gif

Below are two stills from the animation. What are these artifacts in the images?

 

[marcus]

Dotini, thanks for picking out those frames with the curious spots. I don't even have a guess as to what they could be. Hopefully someone else can offer a suggestion.

 

[newjerseyrunner]

I have a theory. The bright spot is supposedly highly reflective and it's nearly white in this image. Is it possible that the sun is directly behind the spacecraft and that is the probe's shadow?

 

[marcus]

A couple of tweets today, I saw about 7:40 pm pacific time, so they were shortly after noon pacific today:
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
That means I'm going from altitude 7,600 to 8,200 km with respect to #Ceres today #orbitalmechanics

18 retweets32 favorites
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
My planned trajectory is temporarily increasing in altitude b/c my orbit is slightly elliptical...

14 retweets40 favorites

 

[marcus]

I have a theory. The bright spot is supposedly highly reflective and it's nearly white in this image. Is it possible that the sun is directly behind the spacecraft and that is the probe's shadow?

The pixel size is currently between 410 meters and 1300 meters per pixel. Those pictures were taken 4 May at altitude of 13,600 km.
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547

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

Very roughly the 4 May pictures were taken at 1300 meters per pixel. The dark spots would be several kilometers wide. Too wide to be the shadows of the probe.

 

[OmCheeto]

Dotini, thanks for picking out those frames with the curious spots. I don't even have a guess as to what they could be. Hopefully someone else can offer a suggestion.

I'm guessing dust on the camera lens.
The donut shaped anomaly can be seen in two other frames.

frame #14

frame #17

frame #18

The only other explanation: Aliens.

 

[Jimster41]

Do we know the frame frequency? And does the different angular relationship to the ice fort coincide with possible rotation of the camera? I have a hard time picturing loose dust, inside the instrument. Are those the only frames that show it?

 

[newjerseyrunner]

It's very unlikely that there would be dust inside the instrument, however stuck to the surface of the lens or floating above it because of static electricity I could see.

 

[mfb]

Do we know the frame frequency?

Ceres rotates once every 9 hours, if you track something on the surface (e.g. the bright spots) you can calculate it for this specific animation.

A dark spot that moves across the surface is clearly something camera- or spacecraft -related.

Dawn does not have a proper shadow, by the way. The sun has an angle of ~1/250 rad, to make a full shadow Dawn would have to be less than 500 m above the surface. Currently it is reducing illumination in a ~30 km x 30km spot by less than one part in a million.

 

[Janus]

The pixel size is currently between 410 meters and 1300 meters per pixel. Those pictures were taken 4 May at altitude of 13,600 km.
http://dawn.jpl.nasa.gov/multimedia/images/image-detail.html?id=PIA19547

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

Very roughly the 4 May pictures were taken at 1300 meters per pixel. The dark spots would be several kilometers wide. Too wide to be the shadows of the probe.

Besides which, at 13,000 km, the probe would only have an angular size of 0.298 seconds of arc, while the Sun still has an angular size of ~11 minutes of arc. Thus the probe would not cast a discernible shadow of any size.

 

[OmCheeto]

Do we know the frame frequency? And does the different angular relationship to the ice fort coincide with possible rotation of the camera? I have a hard time picturing loose dust, inside the instrument. Are those the only frames that show it?

On the full size animated gif, I can see anomalous dark spots in every frame.

One thing I haven't been able to determine is the sensitivity of the cameras, so I don't know how long the exposures are.

The Camera System – Dawn's Eyes (MPS)
The Cameras in Numbers

Exposure times: 1 millisecond to 3.5 hours
Field of vision: 5.5 dregrees times 5.5 degrees
Memory: 8 GBit dRAM
CCD-sensor: 1024 pixel times 1024 pixel
Filter wheel: seven narrow-band filters and one clear filter

While looking for information on "dust" yesterday, I also ran across a book edited by Christopher Russell, Carol Raymond.
The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres
The section on the framing cameras starts on page 263. The next chapter starts on page 328.
TMI! And lots of pages are missing.
But there are other interesting things in the book.
Electrostatic charge levitation of dust particles on the surface of dwarf planets and asteroids? (page 276)
574 pages in all. Good grief!
Fortunately for me, they hid pages 29 through 260, and 303 through 574, amongst other random page sets, or I'd still be snooping around for clues.

In the following image, "QE", stands for "Quantum Efficiency". (page 284)
Since it contains the word "Quantum", I have no idea what it means.
But I suspect it's a clue to the sensitivity of the CCD image sensors used in the cameras.

Wiki has the following to say:

Quantum efficiency
This article deals with the term as a measurement of a device's electrical sensitivity to light. In a charge-coupled device (CCD) it is the percentage of photons hitting the device's photoreactive surface that produce charge carriers. It is measured in electrons per photon or amps per watt. Since the energy of a photon is inversely proportional to its wavelength, QE is often measured over a range of different wavelengths to characterize a device's efficiency at each photon energy level. The QE for photons with energy below the band gap is zero. Photographic film typically has a QE of much less than 10%^[2], while CCDs can have a QE of well over 90% at some wavelengths.
...

[2]

Springer Handbook of Lasers and Optics
...
Speed (page 604)
The speed of photographic films can be characterized
assuming that the grain must absorb a certain number
of photons to become developable [9.64]. The referred
number of photons depends on the grain size. Thus,
there is a correlation between the speed and the grain
size. For bare silver halide emulsions (which are sen-
sitive below 500 nm), the whole volume of the grain
absorbs and the speed of the film is the grain vol-
ume times the absorption coefficient.
...

Obviously, a rabbit hole of complexity, which I should not have ventured down...

But this reminds me of trying to explain a non-functioning solar panel powered bilge pump volleyball court watering systems to an electrical laymen, who kept saying; "It all has to do with the Amps".

 

[marcus]

Dawn has reached the apoapsis (far point) of its quasi-elliptical loop and will start closing in again this evening, according to this tweet of about 2PM pacific on 19 May
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 4h4 hours ago
Today I am orbiting #Ceres between ... (8,200 and 8,400 km) in altitude. Tonight I will resume descending.

These tweets originate from Marc Rayman, we are told. He is providing update info and someone else relays it. The probe did swing pretty far out, it seems. From less than 7.2 to more than 8.2 kkm.
Here were some previous tweets about this, posted around noon pacific on 18 May

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
That means I'm going from altitude 7,600 to 8,200 km with respect to #Ceres today #orbitalmechanics

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 7h7 hours ago
My planned trajectory is temporarily increasing in altitude b/c my orbit is slightly elliptical...

 

[OmCheeto]

Dawn has reached the apoapsis (far point) of its quasi-elliptical loop and will start closing in again this evening, according to this tweet of about 2PM pacific on 19 May
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 4h4 hours ago
Today I am orbiting #Ceres between ... (8,200 and 8,400 km) in altitude. Tonight I will resume descending.

These tweets originate from Marc Rayman, we are told. He is providing update info and someone else relays it.
...

Do you think I"m making it up?

Emails from this morning:

May 19, 2015 12:45 PM
Hi [Om],

In addition to a new image every day, I now post a mission status update one or a few times a week, as I did at Vesta. I don’t tweet, but I provide information to someone else who tweets for Dawn every day.

[The one and only] Marc [Rayman, JPL, Om's hero]

bolding and bracketed items mine.

May 19, 2015 12:42 PM
Hi [Om],

I don’t have time now to look at the forum (I have only ever visited it very briefly), but the images do have artifacts. Some are the result of dust that occasionally separates from the spacecraft and, being small and out of focus, can look larger than it really is. We have observed this throughout the mission, but the flux of dust is very low and it does not compromise the scientific value of the images. There are also electronic artifacts from the CCD. Most spacecraft experience both, and image processing removes them. We are releasing images that have not yet gone through the (time-consuming) full processing, although ultimately all the data, both uncorrected and fully corrected, calibrated, will be released. Of course, all images are scrutinized for moons and other real phenomena, but we know with 100% confidence that none of the stuff we see is anything other than an artifact.

We post a new image every (work) day.

Regards,
marc

I told him about the alien space crafts we were seeing in the images.
Then I got kind of bossy, and told him to post more often.

Bad Om! Bad, bad, Om!

 

[OmCheeto]

Hey! Is someone else tweeting?

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 18 hours ago
Some of you were asking about little black spots or triangles on some of the images. Those are image artifacts, i.e. not part of #Ceres​

18 hours ago would have been about 2 pm PST. About an hour after I received my email.

 

[OmCheeto]

Marc, has, apparently, been listening, to me.

NASA's Dawn Mission ‏@NASA_Dawn 54 minutes ago
My closest image yet of the bright spots on #Ceres, taken from 4,500 miles away http://go.nasa.gov/1efEpyW

Now, I see, a big angler fish, eating a small fish.

 

[OmCheeto]

Along with "Conway's Game of Life".

I'm pretty sure, I've seen that binary formation, before.