At 02:57:31 UT today, Cassini passed 30-million-kilometer line from Saturn. The spacecraft is now no more than 30 million kilometers from the planet.

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I think the next major milestone (after 30 million km) is next week when Cassini enters the Saturn system, and is under the influence of its gravity.

That makes me wonder. Where is the Saturn/Sun L1 point? I have never even thought of how to calculate an L1 point. Does that statement (from the JPL website) "Cassini enters the Saturn system in Mid-May" mean that it has crossed the L1 point?

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Well, obviously, it's not going to cross the L1 point itself; that's a point, not a spherical surface around the planet. But it was as far from Saturn as the L1 point is back when it was about 64,330,000 km out. I suspect they're using the point at which the force of Saturn's gravity is equal to the Sun's, which would be at... let's see... 24,170,000 km. That looks like that would probably be happening next week or so, so that's probably what they mean.

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What is L1 point?

According to my work, on May 19 at 10:55 UTC, the gravity from the Sun will equals to the gravity from Saturn. But hours before the moment, the gravity from the Sun and its planets equals to the gravity from Saturn and its moons.

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Saturn's sidereal orbit is 10,759.22 days. For a satellite with that period in orbit around Saturn I'm getting an SMA of about 58.6 million miles or 94.3 million km. But that's ignoring the fact that the L1 point is a little closer to the Sun and receiving slightly more pull... I don't know if that's negligible or not.

I knew Cassini would not cross the L1 point. I should have said something like: ...when Cassini crosses a spherical boundary of radius equal to the distance from Saturn to its L1 point with the Sun with the center of the "sphere" at Saturn... or something like that. ops:

Oh, and since I posted that post, I thought about it in more detail, and at least I figured out (at least conceptually) how to calculate an L1 point, so that made me happy.

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Well, just so you know, here's how I figure it. Unfortunately, I haven't found a way to isolate the r_1, so I have to use reiterative Newton's method (well, my calculator does it for me, anyway).

G = gravitational constant (I used 6.67259*10^-11 m^3/(s^2*kg)
m_1 = mass of Sun (1.9891*10^30 kg)
r_1 = distance of L1 from Sun
m_2 = mass of Saturn (5.688*10^26 kg)
r_2 = distance of L1 from Saturn
r_12 = semimajor axis of Saturn's orbit (1.4294*10^12 m)
T = orbital period of Saturn (I was using a 10,785.97 day sidereal year calculated from the semimajor axis and the masses of the Sun & Saturn and the gravitational constant; there's probably enough uncertainty in G & r_12 to account for the difference between this and the 10,759.22 days mentioned above)

r_1 = T^2*G/(4*pi^2) * ((m_1/r_1^2) - (m_2/(r_12-r_1)^2))

It's basically a standard orbit calculation like where m_1 is known and T is known and you solve for r_1, except you have to substitute (g_1 - g_2) for (g) (or for a_centripetal, if you prefer), and because both g_1 & g_2 depend on the radius and hence the answer (whether r_1 or r_2), you can't isolate the r_1 and have to take the roundabout number-crunching approach.

Just curious, got any easier ways to work it out? Or is your (cityboy916's) way pretty similar in approach and complexity? Of course, I suppose I'd also be wondering a bit about why I got 64.3 million km vs. your 94.3 million km. And given that you also gave it in miles, I can't think it was just a typo, despite the similarity after the first digit there.

Added: Oh, I see now! You were just treating it as a simple orbit with the same sidereal period. As you can see, that's pretty far off. As I pointed out above, once you're more than about 24.2 million km from Saturn, the Sun's gravity is stronger than Saturn's, so that'll throw your results off considerably.

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If you use GM instead of G * M, you may get a much more precision.

GM of the Sun = 1.3271243994E+20 m^3/s^2
GM of Saturn = 3.79312845E+16 m^3/s^2

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I used my own astronomy program to get those figures. It does the distance readout in both miles and kilometers. Obviously the added pull of the sun makes a lot more difference than I thought!

Thanks for the tip (I should have thought of using GM, I pointed it out myself in a post about the mass of the Sun not long ago) and the figures! Using those, and some other more precise figures I looked up since then (some of mine seem a bit dated), I'm now getting 62.75 million km for the L1-Saturn distance.
r_1 = T^2/(4*pi^2) * ((Gm_1/r_1^2) - (Gm_2/(r_12-r_1)^2))

BTW, where do you get those G*M figures? I rarely or never see them listed in the usual data tables and such on astronomical bodies.

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I got the GM figures from JPL's HORIZONS System at telnet://ssd.jpl.nasa.gov:6775

After you logged in, enter "Sun" under "Horizons>" prompt to get basic information about the Sun, enter "Saturn" for Saturn.

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Ooo, very nice ToSeek. It looks like Venus a bit... can't wait to see what lies underneath!
It's going to be a great summer.

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WOW new pics:

http://sci.esa.int/science-e/www/obj...objectid=35039

00oo000 sorry, didnt see ToSeek ops:

This is not in visible light, is it? Titan would look orange, would'nt it? So what manner of light is it?
They're naming features already? Cool!
This summer will be the summer of Saturn.

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The article mentions 938 nanometers as the midpoint wavelength, which would indicate infrared. (700 nanometers is about the limit for visible light.)

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The image looked to be infared. I didn't know infared could penatrate that atmosphere and reveal topography.
The image reminds my of an early photo of Ganymede taken by Voyager 1. Looked similarly blurry as Titan did in this image. I just imagine the details that Cassini will see at the Saturnian system.

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Godspeed, John Glenn. - Scott Carpenter

And these atomic bombs that science burst upon the world that night were strange even to the men that used them.
- H.G Wells, The World Set Free

To the conspiracy crowd, radiation is a big Boogey Man that inspires terror and death in all who encounter it. - JayUtah

1) In the article that accomanied the picture, it said:
This band is in the infra-red.

2) Any image taken through a single band will appear monochrome (black and white). True-color imaging requires images through red, green and blue broad-band filters.

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Cassini picture of the week: Bands of Clouds and Lace.

PS. The photo was taken from a distance of 38.5 million kilometers. Cassini is now almost a half closer .

Anyone else here thinking that those JPL/CICLOPS guys are a bunch of sadists, giving us only one picture a week? Sure, this will hopefully change soon, but... Aaaarrrrggghhhhhhhhh!

Time to start a "You Know You Are A Cassini Addict When"-thread...

Harald

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Calm down

They'll start to release pictures more often by the end of May.

Its like a long distance marathon, not a 100m. We have to build up our strength.

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Cassini will be 25 million kilometers from Saturn in instantaneous at 16:06 UTC on 2004-May-14 in SCET.

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A thread in the space.com forums:

http://uplink.space.com/showflat.php...art=3&vc=1

They plan to realese an image every day, 5 times a week starting later in the month and continuing for the remainder of the mission.

Cassini Significant Event Report
For Week Ending 05/14/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, May 12. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" web page located at http://saturn.jpl.nasa.gov/operation...t-position.cfm .

The final sequence approval meeting was held this week for S01, the first tour sequence. The background sequence, Ion and Neutral Mass Spectrometer (INMS) mini-sequence, and instrument expanded block loads have been processed and radiated to the spacecraft. The sequence will begin execution on Friday May 14.

Final activities in C44, the last Approach Science sequence, included uplink and execution of commands to reset the Imaging Science Subsystem (ISS) narrow and wide-angle cameras, uplink of Reaction Wheel Assembly (RWA) bias commands to execute in S01, and continuation of C44 science data collection activities.

Sequence development of S02 continued this week with release for review of the S02 Preliminary Sequence Integration and Validation 1 (PSIV) background sequence products, and Sequence of Events /Space Flight Operations Schedule products with a Saturn Orbit Insertion (SOI) burn sequence merged in for reference.

The Spacecraft Team completed a second Operational Readiness Test (ORT) on Saturday, May 9, 2004. This ORT involved Spacecraft Operations, Navigation, and Uplink Operations (ULO). The goal of the test was to demonstrate that these teams could recover from an anomalous SOI and perform a large correction maneuver in less than 3 days. The Navigation analysts were given simulated SOI Doppler data and the Spacecraft team was given an interrupted burn with an underperforming engine. Both teams, with ULO support, were able to diagnose the faults in a timely manner and complete the required work to get to the nominal Orbit Trim Maneuver 1 time.

Three SOI Critical Sequence regression tests were performed on May 10-12, 2004. These regression tests were to ensure that the Critical Sequence would work correctly with the two new ACS mask commands. The mask commands are the response to an ACS fault protection issue that surfaced last month. All tests were successful.

The ACS team completed end-to-end pointing analysis for tour sequences S27 and S28 as part of the Science Operations Plan Implementation process. Preliminary port 1 occurred for S29 and S30. The products have been merged, checked, and reports issued to the teams.

A Project Briefing and Waiver Request Disposition Meeting was held for S03. All waiver requests were approved. The handoff product has been given to the Sequence Team for the start of the SSUP process on May 17.

The S05 aftermarket process began this week with an assessment meeting to discuss proposed changes to the integrated plan. The integration teams will be evaluating these requests over the next couple of weeks, but initially it appears that requested changes fit within available resources. A final decision meeting to disposition the requested changes will be held on May 26.

The total number of ISS images acquired since the start of Approach Science is now 5855, and the number of Visual and Infrared Mapping Spectrometer (VIMS) cubes is 781.

Two items were approved this week in an effort to alleviate downstream workload and increase performance. A request for an update to the Multi Mission Image Processing Laboratory uplink software is now accepted as it will assist in reducing workload downstream on ULO, and after evaluation of Pointing Design Tool (PDT) performance testing, approval was given to release client-server versions of PDT for Mac and Linux platforms.

Instrument Operations, Science Planning, the Spacecraft Operations Office, and the Mission Support and Services Office participated in a Saturn Orbit Insertion (SOI) Playback Assessment Test. The rehearsal was intended to exercise end-to-end SOI Ground System procedures. Data loading into the TDS was expedited, to reflect planned SOI operations, making bested data available to instrument teams within 45 minutes versus 4 hours during normal operations. Team instrument data accountability reconciled with SCO Telemetry Input Gap Analyzer & Reporter data accountability and the teams showed they can easily meet their post SOI 20 hr deadline to evaluate the release of the SSR.

A delivery coordination meeting (DCM) was held for the ISS Pointing Tool (ISSPT) V2.5. ISSPT is a program that allows the user to design imaging observations using the Imaging Science Sub-system on the Cassini spacecraft. ISSPT allows the user to adjust and optimize camera settings, calculate image brightness and content based on pointing, and produce an Instrument Operations Interface output file suitable for building camera command sequences.

DCMs were held for PGT V9.1 and Mission Sequence Subsystem D10.3.1.

The Cassini Literacy Team hosted a booth at the International Reading Association convention in Reno, Nevada. Interest in "Reading, Writing, and Rings" was very high among the teachers in attendance. In addition, several publishers spoke with the team about Cassini products and incorporating Cassini images and products in upcoming publications.

A Saturn Observation Campaign member demonstrated the "What Is Synchronous Rotation?" activity and answered Cassini and Saturn related questions at Space Day 2004. The event, held at the Udvar Hazy Aerospace Wing of the Smithsonian Institution's National Air and Space Museum was part of the nationwide Space Day event.

Recent images of Titan returned by the Cassini spacecraft may be seen at http://saturn.jpl.nasa.gov

In an article in the Honolulu Advisor on May 7, it was reported that astronomers using Near Infrared Imager of the Gemini North Telescope on Mauna Kea have observed 10 objects circling Jupiter and four others circling Saturn providing evidence suggesting that clusters of satellites circling Jupiter and Saturn may be pieces of asteroid-like objects that were shattered in collisions early in the existence of the solar system. For more information go to: http://the.honoluluadvertiser.com/ar.../ln/ln03a.html

Additional information about Cassini-Huygens is online at http://saturn.jpl.nasa.gov.

Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Office of Space Science, Washington, D.C.

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Cassini-Huygens was only 23 million kilometers from Saturn at 20:41:26 UT on May 18, 2004.

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The smog moon Titan? Probably the alien equivalent of L.A...

Seven Years to Saturn

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