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20

Currently all spacecraft start out on Earth and while fairly stringent measures are taken during manufacture to keep them clean it is pretty much impossible to guarantee that no bacteria, viruses, spores or other biological material get in somewhere. Certainly anything which is exposed to untreated air at any point is quite likely to be contaminated with ...


16

Cassini's INMS, the Ion Neutral Mass Spectrometer, is an in situ instrument that measures the neutral and plasma gas composition of what it ingests. It was intended for the measurement of Titan's atmosphere, Saturn's magnetosphere plasma, ring composition, and in fact the composition of icy satellite effluents. Here is a good presentation on the basics of ...


15

If we were going to send a probe into Saturn's atmosphere and were concerned about contamination of a potential ecosphere there, we would sterilize the probe first, e.g. with dry heat microbial reduction, to make sure that nothing viable was on the probe. Cassini has no protection from the entry heat like a probe would, and will be entering at an incredible ...


14

Your guess is correct. To quote NASA's page, The mosaics each consist of multiple narrow-angle camera (NAC) images with data from the wide-angle camera used to fill in areas where NAC data was not available.


13

I'm not up to a complete exhaustive survey of every possible contestant, so I've focused on relatively recent orbiters. I found a few that beat Cassini. The figures I've found so far are occasionally a bit contradictory or squirrelly -- masses are rounded differently here and there, some sources give the design tankage while others give the actual flown ...


10

Define "destroyed". It will no longer be able to maintain attitude control due to torque from the atmosphere at a radius of about 61,700 km. From there we will get no more data from the spacecraft since it can't point the antenna. From our point of view, at that moment, Cassini is buh bye.


10

First off, what's done is done. Don't make it worse. Second the main concern is Enceladus, not Titan. Enceladus is an ocean world whose ocean regularly and significantly interacts with its surface. Titan may be an ocean world, but it is unlikely that that ocean interacts significantly with the surface.


9

To answer the question, 'is Cassini running out of fuel': As you'd expect, NASA has monitored Cassini's fuel levels. In 2014 JPL published a study, 'Ensuring Cassini’s End-of-Mission Propellant Margins': With three years left and only 2.5% of its loaded bipropellant and 37% of its loaded monopropellant remaining, the Cassini project actively manages the ...


9

As far as I can tell, Huygens would not have been able to take a picture of Cassini. Huygen's camera was part of the Descent Imager/Spectral Radiometer instrument package. As seen in this cutaway from GSFC, the DISR port is on the side of the spacecraft. This port would have been entirely covered by the heat shield. Therefore, the very design of Huygens ...


8

This is purely a speculation, as I have not found any official sources to confirm it, but I think they want to be able to view Saturn's pole during the fly by. The trigonometry works out at least: If you want to get a close-up of the polar regions with a lower inclination, like 40, 50 or 60 degrees, the altitude required is larger than the gap between ...


7

Not only are they canted, they are gimbaled in two axes. The gimbals are used to fine tune the pointing through the CG that moves as propellants are expended.


7

Titan. This is all done using gravity assists from Saturn's largest moon, Titan. Only tiny amounts of propellant are used to target the Titan flybys.


7

The paper itself (I have access) says and shows that they are detecting the bottom of some lakes with their radar with a maximum depth of 105+/-6 meters. The radar reflection off the bottom is much fainter than off the surface, but still distinct and clear. The attenuation (17 dB/us) fits a mostly-methane composition (best fit 69% methane, the rest mostly ...


7

From Cassini observations the methane-ethane mixture (with methane by far the largest component, maybe with some dissolved nitrogen) appears so pure that its absorptivity at the RADAR instrument's Ka-band frequency is quite low. That's how it could see so deep — not just 100 m, but 160-170 m. The paper The Bathymetry of a Titan Sea by Marco Mastrogiuseppe ...


6

It's some other force. In particular, it's that last approach to Titan on September 11 that will send Cassini deep enough into Saturn's atmosphere so as to make the spacecraft burn up on September 15. Notice that your graph shows that Cassini will make several somewhat close approaches with Titan during the next several months. Some will raise Cassini's ...


5

It is modeled that the dunes must form from chips of Titan's bedrock. Whether those chips are primarily hydrocarbons or primarily water ice, depends on what Titan's crust is presumed to be composed of. There are varying models, depending on what is known of Titan (such as the moment of inertia), and one model with a reasonable level of support involves a ...


5

Concise version from the pre-flyby media teleconference announcement: Cassini scientists are hopeful the flyby will provide insights into how much hydrothermal activity is occurring within Enceladus, and how this hot-water chemistry might impact the ocean’s potential habitability for simple forms of life. If the spacecraft’s ion and neutral mass ...


5

According to Wikipedia Some of the options examined include collision with Saturn atmosphere, icy satellite, or rings; another is departure from Saturn orbit to Jupiter, Uranus, Neptune, or a Centaur. Other options include leaving it in certain stable orbits around Saturn, or departure to a heliocentric orbit. Each plan requires certain amounts of time ...


5

Any picture of Cassini in space is an artist's conception, probably a computer rendering, although the Saturn backdrop may come from real Cassini photographs. I had thought it possible that the Huygens probe carried by Cassini to Titan might have taken one or more pictures of Cassini as it departed, but it's not possible, as the camera was enclosed under ...


5

The raw images of Cassini can be viewed online in reverse order https://saturn.jpl.nasa.gov/galleries/raw-images?order=earth_date+desc&per_page=50&page=0


5

The International Astronomical Union is the most official source on this matter. Among other surface features on Titan the IAU recognizes 81 lakes (lacūs, "small dark plains with discrete, sharp boundaries") of 5km to 240km diameter (median 36km), and three larger seas (maria, "large expanses of dark materials thought to be hydrocarbons"): Kraken Mare, ...


5

It boils down to: how much spacecraft resource is required by the attitude control method you propose using? And sometimes the mission's pointing requirements play a significant role. Thrusters use propellant. Reaction wheels (and momentum wheels) use electric power. Spin stabilization uses neither, as long as you don't need to repoint the spacecraft — but ...


4

They are very narrow passband filters with FWHM pass-through of usually only a few nanometers and a sharp cutoff. Say, a red continuum filter might be centered on ~ 620–740 nm with a FWHM of, say, 5–20 nm. They can be used standalone to only pass through emissivity in that narrow spectral band, or to use produced images as a mask for other exposures and then ...


4

According to Wikipedia, the probe lasted only a short time beyond touchdown: The probe was designed to gather data for a few hours in the atmosphere, and possibly a short time at the surface. It continued to send data for about 90 minutes after touchdown. It remains the most distant landing of any human-made craft. This was expected: The spacecraft ...


4

tl;dr: The September 15, 2017 end for Cassini is part of the second mission extension (XXM, or Solstice Mission) proposed in 2009. The plan was approved. above: "Choosing the XXM Tour: Cassini project manager Bob Mitchell demonstrates the features of the Cassini spacecraft to the XXM senior review panel at JPL on February 10th 2009, watched by project ...


4

Hard to say. Cassini's "main engine" is a modernized version of the attitude thrusters used on the Apollo spacecraft: MMH/NTO bipropellant thrusters delivering about 440N thrust. Every maneuver made by the Apollo CSM or LM would have used several of these thrusters in short bursts. It would not surprise me if that amounted to several hundred fires per ...


4

You'd need to get to Jupiter to get an assist to Earth. It might be possible. See Saturn Escape Options for Cassini Encore Missions and Cassini End-of-Life Escape Trajectories to the Outer Planets. You can certainly escape Saturn with multiple Titan flybys. Getting to Jupiter is trickier, and requires the right timing and a lot of patience. Low-energy Saturn-...


4

Some of those are the Ku-band antenna feeds for the Radar. The high-gain antenna also serves (served) as part of the Radar science instrument. The HGA was pointed at Titan many times to get synthetic-aperture radar images of the surface of Titan, otherwise obscured by the haze in the atmosphere to visible light instruments.


4

A "flux tube" is a magnetically-confined conduit that allows charged particles to flow between one place in a planet's magnetosphere and another. An "L-shell" is a subset of a planet's magnetic field lines that cross the planet's equator (for most planets, anyway) at the specified number of planetary radii from the planet's center. In a uniform magnetic ...


3

According to Sutton, both blow-down and conventional pressurization use a pressurant (like helium in this case). Conventional systems have a pressure regulator between a pressurant tank and fuel tank, so they yield constant pressure and constant thrust until out of pressurant. In blow-down, per Sutton: Here the gas is stored under pressure inside the ...


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