Cassini's Saturn Mission Goes Out In A Blaze Of Glory (npr.org)

An anonymous reader shares a report: Controllers at NASA's Jet Propulsion Laboratory sent a final command Friday morning to the Cassini spacecraft orbiting Saturn. Not long after, accounting for the vast distance the message traveled, the order was received, putting the craft into a suicidal swan dive, plummeting into the ringed planet's atmosphere. Flight Director Julie Webster called "loss of signal" at about 7:55 a.m. ET, followed by Project Manager Earl Maize announcing "end of mission" as the spacecraft began to break up in Saturn's atmosphere. "Congratulations to you all," Maize announced to applause. "It's been an incredible mission, incredible spacecraft, and you're all an incredible team." With Cassini running on empty and no gas station for about a billion miles, NASA decided to go out Thelma & Louise-style. But rather than careen into a canyon, the plucky probe took a final plunge into the object of its obsession. Just how obsessed? Its 13-year mission to explore the strange world of Saturn went on nearly a decade longer than planned. It completed 293 orbits of the planet, snapped 400,000 photos, collected 600 gigabytes of data, discovered at least seven new moons, descending into the famed rings and sent its Huygens lander to a successful 2005 touchdown on the surface of yet another moon, Titan. Also read: Cassini's Best Discoveries of Saturn and Its Moons.

Comments

RIP

[gerrythegreat]

RIP Cassini you done good stuff for them science folk.

Re: RIP

[Anonymous Coward]

Here you go: http://www.21stcentech.com/money-spent-nasa-not-waste/

And this: https://www.sciencefriday.com/articles/meet-the-researchers-behind-the-cassini-mission/

And from here: http://www.airspacemag.com/flight-today/team-cassini-180960062/

"one of more than 5,000 people who have worked on the project over the years"

Maybe next time do research on your own and get educated about the subject before you bitch about it.

Cassini

[tquasar]

Some mission scientists were cheering and others crying when the final signal was lost, confirming the end of the craft and mission. It was launched in 1997! https://en.wikipedia.org/wiki/...

Re:Cassini

[magusxxx]

And yet phones aren't expected to last past their year warranty. ;)

Re:Cassini

[Arnold Reinhold]

NASA-TV showed displays of the S-band and X-band carriers prior to loss of signal, sharp spikes above a noise background. The S-band signal faded out first, as the spacecraft began to lose pointing accuracy for its high gain antenna when the thrusters could no longer keep up with the atmospheric forces. The X-band signal persisted for a few more seconds (more antenna gain at the shorter wavelength, presumably) before it faded out, but then it reappeared briefly above the noise before going away forever. It was as if the spacecraft gave one last effort to stay in touch with home. A very sad moment.

Re: Cassini

[Anonymous Coward]

You have it backwards. The upper display was x band. It faded first because the antenna has higer gain at the higher x band frequency, so the pointing is more critical. S band was on the bottom and faded a bit later because the dish has a wider beamwidth at 2 GHz than it does at 11 GHz.

Contamination

[lazarus]

TFA states that plowing the craft into Saturn was necessary to prevent contamination of the moons, but the mission began with dropping a Huygens Lander on Titan.

Seems like nobody has make the distinction between bacterial contamination and radioactive contamination. I suspect that the latter is actually the concern as the probe used an RTG for power and thus it was safest to de-orbit it into Saturn.

RIP Cassini. Thanks for all the science.

Re: Contamination

[Strider-]

It was a worry over biological contamination. JPL (and NASA) have very specific protocols for planetary protection. Huygens went through some extreme decontamination prior to launch. Cassini, as an orbiting probe, not so much. Also, at launch we didn't know as much about the Saturn system and it's moons. The RTGs aren't really a concern, as they're not all that radioactive. Pu-238 is primarily an alpha emitter, and is mostly just toxic.

Re: Contamination

[almitydave]

It was a worry over biological contamination. JPL (and NASA) have very specific protocols for planetary protection. Huygens went through some extreme decontamination prior to launch. Cassini, as an orbiting probe, not so much. Also, at launch we didn't know as much about the Saturn system and it's moons.

Specifically, we learned that Enceladus has a large subsurface ocean, at the bottom of which may lie hydrothermal vents. Since those on Earth are often teeming with life, we didn't want to risk contamination of Enceladus' oceans.

Re:Contamination

[SuiteSisterMary]

The problem with statements like this is that every time we've pointed at somewhere on Earth and said 'That part is missing some essential Requirement for Life,' turns out we've been wrong.

Life needs water (our kind of life, anyway)

[XXongo]

TFA states that plowing the craft into Saturn was necessary to prevent contamination of the moons, but the mission began with dropping a Huygens Lander on Titan. Seems like nobody has make the distinction between bacterial contamination and radioactive contamination. I suspect that the latter is actually the concern as the probe used an RTG for power and thus it was safest to de-orbit it into Saturn.

It was a worry over biological contamination.

Exactly. Huygens was battery powered: after the battery died, it dropped to a temperature of about 90K, barely above liquid nitrogen. No terrestrial life will contaminate anything at that temperature.

Cassini, on the other hand, contained several RTGs. In the unlikely case that it did impace into Titan, the RTGs would keep a tiny fraction of the probe debris above the liquidus point of water, and hence in principle terrestrial contamination could survive and even multiply.

The scenario is absurdly unlikely, of course, but it can't be absolutely ruled out, and since it can't be ruled out, it triggers the planetary protection protocol.

Re:Life needs water (our kind of life, anyway)

[Tablizer]

dropped to a temperature of about 90K, barely above liquid nitrogen. No terrestrial life will contaminate anything at that temperature.

Not necessarily. Spores could survive in a frozen state, and then later if a liquid water volcano or similar erupts, the spores could awake and seep toward the core. Unlikely and/or many years away, but not impossible.

Re:Life needs water (our kind of life, anyway)

[Baloroth]

Yet it doesn't stop us from dropping dozens of probes and landers onto Mars and Venus...

All of which followed pretty strict decontamination procedures. Well, maybe not the Venus probes, but if Earth bacteria manages to survive on Venus, I say more power to them.

Re:Life needs water (our kind of life, anyway)

[XXongo]

The scenario is absurdly unlikely, of course, but it can't be absolutely ruled out, and since it can't be ruled out, it triggers the planetary protection protocol.

Yet it doesn't stop us from dropping dozens of probes and landers onto Mars and Venus...

Mars probes are sterilized and follow a rigorous planetary protection protocol. This has a large and annoying effect on the Mars program: we're not allowed to land on the spots on Mars that have even a slight likelihood of having life or an environment where any possible form of Earth life could survive.

Venus probes-- well, the surface of Venus is hostile to any possibly terrestrial forms of life, and while the upper atmosphere could possibly harbor extreme acidophiles, not anything that's likely to contaminate a probe. In any case, though, the missions to Venus went there before planetary protection protocols were put in place.

Nor did it stop the even more microscopic risk of contaminating life on Saturn itself

Cassini hit the Saturn atmosphere at a velocity of 34 km/sec-- 76,000 mph. No microscopic life is going to survive.

Think of it as hitting with the energy of a 1/3 kiloton bomb.[ref]

- slingshoting Cassini at the sun or outer space would have been even "safer".

"Safer" but utterly impossible. The reason the mission was over was it was pretty much out of fuel.

I have a suspicion that the real goal was to go out in a spectacular "suicide", in order to create publicity. Nothing wrong with that, but be open about it.

Uh, no.

Re:Life needs water (our kind of life, anyway)

[Strider-]

Yet it doesn't stop us from dropping dozens of probes and landers onto Mars and Venus...

As I mentioned above, there is an entire policy (and in fact a portion of the organization) dedicated to planetary protection. Surface landers, such as what are sent to Mars (and in the future Europa and/or Enceladus) are required to go through very strict decontamination regimens before they are launched. In addition to being assembled in clean rooms (as are all the probes), they are baked/irradiated/cleaned with caustic chemicals/etc... prior to launch to sterilize them as much as possible. They don't want to discover life on another planetary body, only to realize that it's life they brought with them.

Venus is a slightly different beast, its surface conditions are so inhospitable (sulfuric acid rain, 400+C temperatures, etc...) that there is not much of a worry about possible contamination. The conditions would denature/destroy all known forms of life present here on Earth.

The larger orbiters (Cassini, Galileo, and Juno) are a) a lot harder to sanitize to the same degree and b) are orbiters not intended to settle on a planetary body that could possibly harbor life. They're not cleaned to the same degree, so the general policy is to dispose of them safely so that there is no chance that they will impact a protected body. Due to the complexity of the Saturn system, the safest way was to drop it into Saturn itself.

The other reason for this was that it is realistically a consequence of the final mission. For the past several months, Cassini has been plunging through the gap between Saturn and its rings. It did not have the fuel left to get out of that. This mission design gave the planetary scientists a wealth of new data on the rings, their mass, and composition.

Re:Life needs water (our kind of life, anyway)

[Ranbot]

I have a suspicion that the real goal was to go out in a spectacular "suicide", in order to create publicity. Nothing wrong with that, but be open about it.

I don't think the goal was publicity, but I'm sure they don't mind the publicity either. If you read the article at the end it mentions there was science to be done that could only be obtained [hopefully] by a suicidal plunge through the atmosphere. Previously the probe could never get close enough to Saturn to record its exact magnetic tilt or directly analyze the atmosphere, both of which they are hoping to get readings of from Cassini's final descent. With the limited fuel remaining the suicide run was probably the most reliable means to safely "dispose" of the probe which obtaining new scientific data they couldn't before. If it gets a little public attention too, all the better, but I don't think that was the main goal.

Furthermore, in my personal pessimistic opinion, I think saying this is a publicity stunt is giving the general public's interest in NASA/science way too much credit; and any positive PR made will fade long before there is any near-term benefit for NASA. The general public will forget about Cassini (if they paid attention at all) as soon as a Kardashian tweets something, or some athlete throws/kicks/carries a ball to score a point, or Putin says "boo!"...

You don't "spiral" into the sun.

[XXongo]

Yep. They could either have sent it out of the solar system (when it had enough juice left) or spiraling into the Sun. Didn't necessarily have to crash land on a planet.

You don't "spiral" into the sun. You watch too much star trek. Orbits are not spirals.*

Dropping into the sun would have required escaping Saturn's gravity well-- which Cassini didn't have the fuel to do-- and then cancelling out Saturn's orbital angular momentum around the sun, which requires 9.6 km/sec, well beyond anything remotely possible with Cassini even if it had full fuel tanks on its main braking engine.

Going "out of the solar system" would require "merely" 4 km/sec after escaping Saturn's gravity well. Still not even remotely possible.

--
*(unless you have ion engines, which Cassini didn't)

Re:You don't "spiral" into the sun.

[Strider-]

Dropping into the sun would have required escaping Saturn's gravity well-- which Cassini didn't have the fuel to do--

Actually escaping Saturn's orbit and going into solar orbit was one of the possible end-of-mission scenarios. When they were looking at the options, it would only have required 5-35m/s of delta-v, well within Cassini's capabilities. However, having a planetary probe in heliocentric orbit doesn't get you much science, as its instruments aren't designed for that kind of thing. At most they would have had a semi-long term observation of the solar wind, which can be done with missions that are much easier to maintain and control.

In the end, the wealth of data obtained by the final proximal orbits to Saturn were considered to be the best bang for the buck at the end of the probe's lifespan. The final retirement option chosen required about the same delta-v as an escape from Saturn, but achieved a whole lot more than just drifting around for ever.