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

[marcus]

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

 

[marcus]

I now think fullview2 speeds have been more reliable after all. Just a hunch. The tweeter seems to me to have been calculating the speed gain as the radius shrank, and reporting that without counting the effect of thrust.
fullview2 seems to me to have embodied consistent physics and it now says 153 mph as the probe is beginning to pass over the S pole.

We will know it's passing over S pole when we see a "half-Ceres" phase.

And then the probe should not be crossing the terminator at 90 degrees, from light into dark. It should be crossing into the leftthand dark quadrant. Like at an angle of 95 degrees, instead of 90. That way when it comes back over the N pole, from dark into light, it will be heading into the righthand light quadrant, say at an angle of 85 degrees. (usual counterclockwise angle convention taking terminator as x axis)

By that time it may be going only 150 mph, which would be 67 m/s or RC3 orbit speed assuming the Ceres mass of 943 billion billion kg. Just guessing.
Of course fullview2 could be using the wrong mass and be wrong many ways, but so far it is telling a consistent story and I haven't seen a good reason to doubt it.

 

[OmCheeto]

Fun trivia tweet from the Dawn team:

https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 1 hour ago
Fact: My total delta-V -- the total sum of velocity changes that this spacecraft has done since launch -- is now more than 24,000 mph
​

Ahh... the power of solar motivated ion drive.

 

[mfb]

= 10.7 km/s

Distance to Ceres seems to be very stable at 13.990 km. Once it switches off the ion drives we can see the final velocity, cover the "distance to surface or distance to center" issue, and make guesses what Marc Rayman will announce as mass in May.

 

[OmCheeto]

What are the bright spots?

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

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

7. Ice Tardises

​

 

[marcus]

= 10.7 km/s

Distance to Ceres seems to be very stable at 13.990 km. Once it switches off the ion drives we can see the final velocity, cover the "distance to surface or distance to center" issue, and make guesses what Marc Rayman will announce as mass in May.

Quite true. That said, it's still exciting to watch the simulated view (which has been fairly close to reality so far.) View shows half-Ceres phase. speed 151mph (nominally we expect 150 so very close) and as you say distance steady at about 14 kkm. The dateline is 2AM, 23 April. UT.

I would say that if you trust fullview2, give or take a few hours and time zones, it IS now in circular polar orbit. With the orbit plane angled off the sun direction by a few degrees. And it is passing over the Cerean south pole region. Yahoo!

I don't expect them to stop and take pictures any time soon. They might. But it seems more likely that they will be be extremely busy doing all kinds of checks and making all sorts of preparations. Might even see them in radio (doppler) navigation contact. Does anybody know when a photoshoot is scheduled?

 

[marcus]

fullview2 now indicates Dawn is in the planned circular orbit at radius 14 kkm (steady for a couple of days) and speed 150 mph (67 m/s)
passing over S pole
and crossing the terminator at a sufficient angle to keep the craft out of Ceres' shadow as it comes up north on the dark side.
We see the solar panels edge-on because they are facing the sun, which is at right angles to our line of sight.

The dateline on fullview2 is currently 23 April, 8 AM UT
http://neo.jpl.nasa.gov/orbits/fullview2.jpg
This image is the the first one I've seen showing 150 mph for speed relative Ceres,
which is what it has to be for circular orbit at this radius, assuming Ceres mass 943 billion billion kg.
(G*943e18 kg/14000 km)^(1/2) = 67.05 m/s
or 149.98 mph

https://eyes.nasa.gov/dsn/dsn.html Deep Space Network currently shows Dawn in 2-way radio communication with Goldstone antenna #24 (as of 4:35 AM pacific, around 12 hours UT)
the power received is shown varying around 18 attowatt.
125 kilobit per second at 8 GHz.
to me this suggests that the craft has turned off thruster and aimed its main antenna at Earth

 

[OmCheeto]

...
to me this suggests that the craft has turned off thruster and aimed its main antenna at Earth

Does this mean someone should say shout; "We're here"!
Within the last few minutes, Goldstone stopped communicating, and Canberra dish #35 is receiving data.
Currently: 4/23/2015 14:23 UTC (7:23 am PST)

 

[marcus]

It's official in a sense
fullview2 shows thrust off and the probe re-oriented to point antenna at Earth, confirming the Deep Space Network activity we saw earlier this morning.
Also fullview2 changed its range reporting format from "distance to Ceres" which had been 14 kkm
to "altitude above Ceres" which is 13.52 kkm, close to the expected 13500 km.

It's significant and it resolves for us the minor ambiguity about distance (from center) and altitude (above surface).
And it makes sense to change over: altitude above surface is going to be the optically pertinent range as time goes on and the probe gets closer.
People may want to check the DSN site to get an idea of the information flow
https://eyes.nasa.gov/dsn/dsn.html now that Dawn is apparently in its planned initial destination orbit ("RC3" for "rotation characterization")
Here are the tentative plans, orbitwise, from the mission director's journal of 31 March
http://dawn.jpl.nasa.gov/mission/journal.asp

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

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

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

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

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

 

[marcus]

Even though we are looking at the beginning of the most interesting part of the mission the first-time study of one of the solar system's ice-ball orbs, I'm inclined to reflect on what I think are already significant innovative achievements in several directions:
solar powered ion propulsion (10-fold more efficient than chemical rocket)
a different kind of trajectory (smooth steady-thrust curves)
precision remote navigation in and out of orbits at several AU distance
the extent to which the craft seems robotic, to have intelligent control delegated to it

I don't know enough to judge the level of innovation on the last point but was impressed by the extent of independent operation, the probe was thrusting much of the time unsupervised (70% of the time it has been abroad, most of that time un-monitored and under its own guidance)

 

[Jimster41]

Yes, what the heck is solar powered ion propulsion and what does hydrazine have to do with it?

 

[mheslep]

make guesses what Marc Rayman will announce as mass in May.

Wouldn't that already be known precisely from Ceres' solar orbital period and solar distance?

 

[mheslep]

Even though we are looking at the beginning of the most interesting part of the mission the first-time study of one of the solar system's ice-ball orbs, I'm inclined to reflect that this is has been a significant innovative achievement in several ways:
solar powered ion propulsion (10-fold more efficient than chemical rocket)
)

Ion propulsion has been routinely used in Earth orbit sats for years, so I'm not sure the ion drive itself qualifies, though it's application and mission and scale on Dawn certainly qualify as a first.

 

[marcus]

Yes, what the heck is solar powered ion propulsion and what does hydrazine have to do with it?

hydrazine has no direct connection. In Dawn it is not used for main propulsion, only little-bitty attitude control, adjusting the angle and orientation (for picture taking, pointing the antenna etc

the propellant is xenon, which is used very efficiently: from a kilogram of xenon they get 10X the momentum that a chemcical rocket gets from the same amount of chemical fuel.
because the xenon is ionized and accelerated to 10X the speed that rocket fuel chemical reactions produce

they still have plenty of xenon left, even now.

some concern about running low on hydrazine for occasional angle adjustments (especially now that a couple of "gyro" reaction wheels have worn out)

 

[OmCheeto]

...
It's significant and it resolves for us the minor ambiguity about distance (from center) and altitude (above surface).
Altitude above surface is going to become the much more pertinent quantity as time goes on and the probe gets closer.

Hmmm...
Marcus, should we go?
I'm pretty sure I could knock Dr. Rayman down on the lawn and sit on him, while you ask him all the hard questions.
Tell him you're "Joe Friday".
I'm sure Ms. Lakdawalla would join in.

i C Ceres Celebration

Saturday, May 9, 2015 | Caltech, Pasadena, CA​

After a seven year journey that included a fabulous year in orbit around asteroid Vesta, Dawn has arrived at its second destination in the main asteroid belt, dwarf planet Ceres. The Dawn mission will host a flagship I C Ceres community event at California Institute of Technology in Pasadena, California.

Fun on the Lawn
Beckman Auditorium Lawn

10:00 am - 2:00 pm
​

Science and Engineering Presentations
Beckman Auditorium

12:30 p.m. PDT

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

• Science Saturday with Vishnu Reddy​

1:30 - 2:30 p.m. PDT

Break
​

2:00 p.m. PDT

Dawn's Journey to Vesta and Ceres• Marc Rayman; Dawn Mission​

2:30 - 4:30 p.m. PDT

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

• Introduction:

Jim Green, Director of Planetary Science, NASA Headquarters​

• Panel:

Claudia Alexander, Rosetta Mission
Carol Raymond, Dawn Mission
Dante Lauretta, OSIRIS-REx Mission
Alan Stern, New Horizons Mission​

• Moderator:

Emily Lakdawalla, Planetary Society​

A virtual "who's who" of people I want to bow before.

ps. I'm currently checking on flights, and specials on PF t-shirts.

 

[mfb]

Wouldn't that already be known precisely from Ceres' solar orbital period and solar distance?

This just gives you the sum of solar mass plus Ceres mass (neglecting other planets). As the mass of Ceres is negligible compared to the solar mass, it does not help.
It is the same reason why ISS and approaching spacecraft s can have the same orbit, for example - negligible mass compared to Earth.

You get a rough estimate if other asteroids come close enough to see a change in their orbit from Ceres' gravity.
Asteroids with moon are much easier. Dawn is like a moon now, its orbit allows a precise mass estimate.

 

[Jimster41]

Are there PF t-shirts?

 

[mheslep]

This just gives you the sum of solar mass plus Ceres mass (neglecting other planets). As the mass of Ceres is negligible compared to the solar mass, it does not help.
It is the same reason why ISS and approaching spacecraft s can have the same orbit, for example - negligible mass compared to Earth.

You get a rough estimate if other asteroids come close enough to see a change in their orbit from Ceres' gravity.
Asteroids with moon are much easier. Dawn is like a moon now, its orbit allows a precise mass estimate.

Yes, thanks.

 

[OmCheeto]

Are there PF t-shirts?

Yes. You can buy them at the PF store. I have 2. I purchased 3, but one ended up being too small, so I gave it to my niece.

ps. I just noticed that if you click on the "Tweets & replies" button on Twitter, you get a lot more chatter.

[URL='https://twitter.com/NASA_Dawn']https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_bigger.jpeg NASA's Dawn Mission‏@NASA_Dawn​

@pareek_kunal Hi, for the newest image set the resolution is about 1.3 miles (2.1 kilometers) per pixel
9:18 AM - 21 Apr 2015​

[/URL]

 

[marcus]

So it is official, as we expected:
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 5h5 hours ago
Big day for me: I am in the "RC3" mapping orbit, which is 8,400 miles (13,500 kilometers) from #Ceres
https://pbs.twimg.com/profile_images/3502834940/2f750377e236127f02d96e270510d727_normal.jpeg NASA's Dawn Mission @NASA_Dawn · 2h2 hours ago
My current orbit goes over both poles, providing the opportunity to see all of the surface as #Ceres rotates on its axis.

Om, thanks for pointing to the Dawn mission twitter. I think that 21 April post must refer to the shots taken of the N pole region on the 15 April. They would be the latest available? For future shots, RC3 and later, we have the table from Rayman's 31 March journal:

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

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

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

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

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

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

It looks like the next batch of pictures will be from RC3 at resolution of 1.3 km per pixel.

 

[marcus]

Dawn and Canberra #34 are still talking! That's over 14 hours---could be 14-18 hours, I only noticed it had started with Goldstone by 4AM pacific. could have begun earlier, like by 12. https://eyes.nasa.gov/dsn/dsn.html

EDIT @ 7PM pacific: Just now as I looked, a Madrid antenna #65 was re-assigned to Dawn, and is standing by to take over when Ceres is out of sight from Canberra, it is almost noon at Canberra.

It is 4AM in the morning in Madrid. With the current positions of Earth and Ceres it seems like the good hours for communication are 4AM to noon. Goldstone was certainly talking with Dawn at 4AM pacific, which is Goldstone time.

EDIT @ 8:30PM pacific: Madrid took over at 8PM (5AM local time) and Canberra quit around 1PM local time. The good hours seem to be in the window of 4AM to 1PM, or more restrictedly 5AM to noon.
they've been talking for at least 18 hours and Madrid just came on so it looks like a long session.

 

[marcus]

Strange. At 7AM pacific, this morning, I happened to check DSN and there were two antennas assigned to Dawn, Goldstone #25 and Canberra #34. Goldstone was receiving. Then a few minutes later both were inactive.
It was 7AM at the former and around 12AM at the latter.

OK it makes sense, now at 7:30 AM Goldstone has been un-assigned. I just happened to look during a transition. Presumably Canberra will start receiving soon and will continue for part of today. I'm not sure what they are doing, maybe it is simply continued doppler tracking to gain a more precise determination of the orbit.
https://eyes.nasa.gov/dsn/dsn.html

 

[OmCheeto]

Strange. At 7AM pacific, this morning, I happened to check DSN and there were two antennas assigned to Dawn, Goldstone #25 and Canberra #34. Goldstone was receiving. Then a few minutes later both were inactive.
It was 7AM at the former and around 12AM at the latter.

OK it makes sense, now at 7:30 AM Goldstone has been un-assigned. I just happened to look during a transition. Presumably Canberra will start receiving soon and will continue for part of today. I'm not sure what they are doing, maybe it is simply continued doppler tracking to gain a more precise determination of the orbit.
https://eyes.nasa.gov/dsn/dsn.html

Good morning Marcus,

Were you watching the DSN during the Vesta orbits? I'm afraid I don't know enough about Dawn to make an educated guess as to what is going on.
Do the solar panels rotate?

In the latest Dawn blog, Dr. Rayman said this;

March 31, 2015

Controllers will also reconfigure the spacecraft for its intensive observations, which will commence on April 24 as it passes over the south pole and to the night side again.

So I would imagine that Dawn is busy taking pictures right now.

hmmm... I guess I could check the old blogs:

September 1, 2011 (re: in "survey orbit")

As Dawn follows its course, it passes over the north pole, then heads south on the day side of Vesta. On each orbit, it trained its sensors on the illuminated surface and filled its memory with the spectacular sights. On the other half of its orbit, gliding high above the dark landscape, it radioed its findings to distant Earth.

(just checked a slew of old blogs & logs)

Did Dawn not have an "RC" circular orbit before descending to "survey" orbit over Vesta?

 

[OmCheeto]

I love polls. Sorry...What's the spot on World Ceres?

ps. I voted for JPL on the Webbies last night.

 

[Dotini]

I love polls. Sorry...What's the spot on World Ceres?

ps. I voted for JPL on the Webbies last night.

There's more than one glowing spot on Ceres, and apparently they have differing thermal signatures, so they may have differing causes. Of #5, the big double spot, I recall Emily suggesting it must be some sort of outgassing plume, since it could be seen over rim of the crater. If so, it will require an explanation as to the energy source, I would think.

 

[lpetrich]

Here's something curious about Ceres, at least so far. Aside from those mysterious bright spots, its surface is all impact craters. No lava plains or other such features that would suggest internal geological activity. Not even the sort of grooves that Vesta has. Because of its size, one might expect some features that suggest internal activity, but none are evident other than those bright spots.

Interestingly, Vesta is at least partially composed of igneous rocks, rocks that had melted and solidified. When Dawn visited there, it collected lots of spectra of its surface, and that strengthened the identification of that asteroid as the source of the HED meteorites (Dawn; the Vesta–HED connection; and the geologic context for eucrites, diogenites, and howardites - McSween - 2013 - Meteoritics & Planetary Science - Wiley Online Library). But Vesta was likely melted only very early in its history, and it does not have any lava plains with a low crater density, as the Moon and Mercury do.

 

[marcus]

Now it's 4AM in Madrid and Madrid antenna #55 is in two-way communication with Dawn.
The Canberra antenna #34 remains assigned but inactive, no idea why.

This is disconcerting I looked again at 4:04AM Madrid time (7:04 pacific) and the Madrid antenna was also inactive. Is Dawn having trouble communicating? Or are they just doing doppler measurement intermittently from both locations?

EDIT 9:30PM pacific: all seems well and back to normal. Madrid#55 is sporadically receiving data at a good rate like 200 kilobit/second, on a strong signal of about 10^-16 watt. The inactive Canberra antenna has been re-assigned.
https://eyes.nasa.gov/dsn/dsn.html

 

[marcus]

Here's something curious about Ceres, at least so far. Aside from those mysterious bright spots, its surface is all impact craters. No lava plains or other such features that would suggest internal geological activity. Not even the sort of grooves that Vesta has. Because of its size, one might expect some features that suggest internal activity, but none are evident other than those bright spots.
...

Could what you are describing be normal for planets with an ice mantle?
That is, if Ceres is in fact covered with an icy layer that is 100 km or more thick, wouldn't the signs of geological activity be different from a differentiated rocky planet? One wouldn't necessarily expect lava plains, would one?

My understanding is that Ceres is differentiated into a denser core and less dense outer layer(s), with ice mantle covered by a thin crust (impact debris, residue of evaporation, regolith.) Differentiation implies some internal geological activity at least early on. But geological activity in an ice-ball planet could be of a different, lower-temperature sort maybe.

Do you have any geology/planetary science sources? Links?

 

[OmCheeto]

...
Do you have any geology/planetary science sources? Links?

While looking for information on "complex craters", I ran across the following:

Predicted crater morphologies on Ceres: Probing internal structure and evolution
Received 7 March 2013​

Two years old, so there are a lot of "ifs".
I only understood about 5% of the paper, but what I did understand, was interesting.

Castillo-Rogez and McCord (2010) argue that, if Ceres formed shortly after the formation of CAI’s, then short-lived radiogenic heating is sufficient to completely melt the body, leaving a pure water ice surface layer.

 

[Monsterboy]

Because of its size, one might expect some features that suggest internal activity, but none are evident other than those bright spots.

What kind of geological activity can we expect when it's mass is 0.0128 times that of the moon(from wiki) .Our moon is geologically dead right?

 

[Dotini]

There is a poorly documented category of observations known as Transient Lunar Phenomena (TLP) which would seem to suggest some outgassing. Many of these observations are associated with the crater Aristarchus.

Aristarchus Crater
Mike's Astro Imagery UK Rotated Left 90 degrees.
Caught during flow glow December 17th 2005

Note the bright flare near the middle of the terminator, between Pallas and Schröter.
Image photographed: 11/15/1953 0200 U.T. by Leon H. Stuart – Tulsa, OK USA
Photo courtesy the estate of Leon H. Stuart. 8" Reflector

http://www.cmf.nrl.navy.mil/clementine/clib/
http://www.vgl.org/webfiles/jon/clemltp.htm

 

[OmCheeto]

What kind of geological activity can we expect when it's mass is 0.0128 times that of the moon(from wiki) .Our moon is geologically dead right?

Ice planet type activity!

The hydrothermally altered core could later dehydrate, with the associated volume changes causing disruption of Ceres’ surface (i.e., geologic activity) (McCord and Sotin, 2005).

ref

 

[OmCheeto]

omg, omg, omg.

not... "SAFE MODE !"

April 24, 2015
Dawn Enters Science Orbit
Dawn Mission Status Report

NASA's Dawn spacecraft entered into its first science orbit on Thursday, April 23, as scheduled. Following a delay in communicating a command sequence, the spacecraft briefly entered into safe mode and awaited further instructions, which were sent by mission controllers. As of early Friday, April 24, the spacecraft returned to normal operating mode and the mission team continues to prepare for science data collection.

Last Updated: April 25, 2015
Editor: Tony Greicius

hmmm...

What's up with the DSN and Dawn?
Currently, Canberra is receiving the carrier signal from Dawn, and is transmitting instructions to Dawn.

 

[Dotini]

Ice planet type activity!

ref

From the abstract of your primary reference:
"if Ceres is primarily a rocky body, we expect crater relaxation to be negligible."

There's not much sign of relaxation, so what we have may be a rocky body, and not an icy one.

 

[Dotini]

...so what we have may be a rocky body, and not an icy one.

Dear Dotini, please do not be in such a rush to conclusions.
"Scientists using the Herschel space observatory have made the first definitive detection of water vapor on the largest and roundest object in the asteroid belt, dwarf planet Ceres.

"This is the first time water vapor has been unequivocally detected on Ceres or any other object in the asteroid belt and provides proof that Ceres has an icy surface and an atmosphere," said Michael Küppers of ESA in Spain, lead author of a paper in the journal Nature."
http://science.nasa.gov/science-news/science-at-nasa/2014/22jan_ceres/
http://science.nasa.gov/media/medialibrary/2014/01/22/data_strip_.jpg
This graph shows variability in the intensity of the water absorption signal detected at Ceres. [More information]