RIP Dawn spacecraft

[lpetrich]

NASA’s Dawn Mission to Asteroid Belt Comes to End | NASA

NASA’s Dawn spacecraft has gone silent, ending a historic mission that studied time capsules from the solar system’s earliest chapter.

Dawn missed scheduled communications sessions with NASA's Deep Space Network on Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its pointing. Dawn can no longer keep its antennas trained on Earth to communicate with mission control or turn its solar panels to the Sun to recharge.

From a month before, NASA Jet Propulsion Laboratory Blog | Dear Dawnniversaries

Today Dawn is celebrating its 11th anniversary of spaceflight. This is the last dawnniversary the spacecraft will see. The venerable adventurer's mission will end very soon. Indeed, it could happen at any moment. In the meantime, Dawn is making the most of its remaining lifetime, performing exquisitely detailed measurements of dwarf planet Ceres. It will do so right to the very last moment.

The spacecraft was launched on 2007 September 27, atop a Delta II chemical rocket, and it used its ion engines the rest of the way. The two kinds of engines are as different as night and day.
[TABLE="class: grid"]
[TR]
[TD]What
[/TD]
[TD]Delta II First Stage
[/TD]
[TD]Dawn spacecraft
[/TD]
[/TR]
[TR]
[TD]Energy type
[/TD]
[TD]Chemical
[/TD]
[TD]Electric
[/TD]
[/TR]
[TR]
[TD]Energy source
[/TD]
[TD]In propellant
[/TD]
[TD]Solar panels
[/TD]
[/TR]
[TR]
[TD]Acceleration
[/TD]
[TD]Heating
[/TD]
[TD]Electrostatic
[/TD]
[/TR]
[TR]
[TD]Propellant
[/TD]
[TD]Kerosene+LOX
[/TD]
[TD]Xenon
[/TD]
[/TR]
[TR]
[TD]Thrust
[/TD]
[TD]1,054,000 N
[/TD]
[TD]0.090 N
[/TD]
[/TR]
[TR]
[TD]Exhaust velocity
[/TD]
[TD]3 km/s
[/TD]
[TD]30 km/s
[/TD]
[/TR]
[TR]
[TD]Run time
[/TD]
[TD]4 minutes
[/TD]
[TD]Several years
[/TD]
[/TR]
[/TABLE]
Dawn got about 11.5 km/s of delta-V (velocity change) from its ion engines, a bit less than what it got from its Delta II booster rocket.

Dawn traveled by Mars in 2009, and went into orbit around Vesta in 2011. After 14 months of observing there, it departed for Ceres, going into orbit around there in 2015. It then spent the rest of its mission observing that dwarf planet.

While Dawn was in orbit around Vesta, its radio broadcasts and optical-navigation pictures made it possible to find the asteroid's gravity-field shape. This gave some clues about its interior, and revealed evidence of a greater-density core. Dawn's spectroscopic measures of the asteroid's surface also clinched the identification of some asteroids as "Vestoids", pieces of Vesta, and also of the HED meteorites as pieces of Vesta. These meteorites are igneous rocks, rocks formed by solidifying molten rock, unlike most other stony meteorites, which are conglomerates of rock grains, including grains older than the Solar System.

So over its first 5 million years, Vesta melted, and over its next 5, it solidified again. The asteroid shows no evidence of more recent geological activity.

Turning to Ceres, Dawn observed mysterious white spots in a crater that got named Occator. These are likely carbonate deposits left behind from evaporating water. Ceres's surface is mostly craters, but they seem curiously shallow, suggesting a rather soft surface. Ceres also has one non-crater mountain, Ahuna Mons, and it may be a water volcano.

There was some discussion of sending Dawn to a third asteroid, but Dawn was low on fuel, and that idea was nixed.

 

[lpetrich]

Two previous threads here:
Dawn headed to its Final Orbit around the World Ceres
Dawn arrives at the world Ceres

Dawn Journal: Final Transmission | The Planetary Society Mark Rayman repeats his final entry in Dawn Journal | Mission – Solar System Exploration: NASA Science, which he titled Dear Dawntasmagorias (Nov 11).

Dawn's operators were lucky enough to be using the Deep Space Network on the spacecraft in its final moments. The DSN alternates between active interplanetary spacecraft, so it listens to each one only part of the time.

By observing changes in the strength and some other characteristics of the signal (and knowing the likely explanation), engineers were able to reconstruct some of the spacecraft's final actions. Around 20 minutes after it was at peridemeter, still quite low but with its momentum starting to carry it back up to high altitudes, the hydrazine thrusters became ineffective. Dawn recognized that it could no longer control its orientation (although it did not know the reason) and systematically proceeded through all the contingency procedures possible, such as swapping to backup equipment and even rebooting its main computer. It made valiant attempts and continued to operate with the professionalism of a dedicated, veteran space explorer, but without hydrazine, there was nothing it could do. The outcome was inevitable. Dawn was up against an unsolvable problem.

Although the spacecraft's depletion of hydrazine and subsequent inability to communicate had been predicted for quite some time, your correspondent considered it worthwhile to verify the diagnosis. It was possible, albeit highly unlikely, that some other problem had befallen Dawn and that after the scheduled session with the Goldstone antenna, the sophisticated robot would solve it and try to reestablish radio contact.

The plan then was for the flight team to look for Dawn at night. Hours after young trick-or-treaters everywhere had finished extorting sweets from their elders, when Earth had rotated so that another 230-foot (70-meter) antenna, the largest at the Madrid Deep Space Communications Complex, could point at Dawn's location in the sky, controllers listened again. Not even the faintest whisper was heard. The remote spacecraft was orbiting Ceres as silently as the cold vacuum of space itself.

After more than 11 years of an incredibly exciting, fantastically fruitful, extremely difficult, deeply rewarding, super fun and just totally awesome interplanetary adventure, your correspondent declared the mission over shortly before 1:30 am PDT on Nov. 1.

The DSN antennas still had some time committed to Dawn on November 1 and 2, and they received nothing. The spacecraft had become a derelict.