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Frequently Asked Questions - General Information

Frequently Asked Questions - General Information

What is Cassini-Huygens?

Cassini is a robotic spacecraft that is scheduled to arrive at Saturn on July 1, 2004 Universal Time (June 30 in U.S. time zones), and to orbit the planet for four years. The Huygens Probe is attached to Cassini, but will separate from it in December, 2004, fly to Titan (Saturn's largest moon), and descend through Titan's atmosphere to its surface in January, 2005.

The Cassini-Huygens mission is an international collaboration among three space agencies. The Cassini orbiter was built and is managed by NASA's Jet Propulsion Laboratory. The European Space Agency (ESA) built the Huygens Probe. The Italian Space Agency provided Cassini's high-gain antenna. Seventeen countries had contributed to the mission at the time of launch. More than 250 scientists worldwide are involved in studying the data coming in from the Saturn system.

For further information, visit

Where can I find basic information on Cassini? How can I get updates as the mission progresses?

Cassini and Saturn
Cassini and Saturn
You can find a lot of information right on our website: Be sure to explore the great stuff listed under "Multimedia."

For weekly updates of significant events, visit .

There are also several electronic mailing lists you can subscribe to, free of charge. The Cassini mailing list provides weekly status reports, image advisories, press releases and science news via e-mail. To subscribe, go to

By signing up at you can receive newsletters on the Cassini mission, Cassini "E-postcard" images, and information on other missions and events related to NASA's Jet Propulsion Laboratory.

For downloadable fact sheets and press kits, visit:

Cassini's orbits seem to become more and more rounded and less "egg shaped." Why is that?

The first few orbits were quite eccentric ("egg shaped") because they had longer orbit periods, but since then, they've stayed more or less the same in this metric, and generally will for the rest of the tour.

The orbit's shape will vary from orbit to orbit, depending on how close to Saturn the Cassini spacecraft comes and what the duration of the orbital period is. However, while the closest approach distance doesn't vary substantially from orbit to orbit, the orbital period does, ranging from 120 days for the first orbit down to seven days later in the tour. Thus, the longer period orbits are more elliptical ("egg shaped") because they go out farther from Saturn while the shorter period orbits are more nearly circular.

What were the fastest speeds reached by the Cassini spacecraft?

The maximum speed clocked by Cassini was 44.0 kilometers per second (98,346 miles per hour) relative to the Sun on June 25, 1999.

Relative to Saturn, the spacecraft reached 30.7 kilometers per second (68,771 mph) during the Saturn Orbit Insertion maneuver on July 1, 2004.

With respect to Earth, the maximum speed reached by Cassini is 19.0 kilometers per second (42,561 mph) on Aug. 18, 1999, as the spacecraft flew past our home planet at an altitude of 1,171 kilometers (727 miles).

During the second Venus flyby, Cassini zoomed by the planet at 13.6 kilometers per second (30,523 mph) on June 24, 1999.

The spacecraft flew by Jupiter at a speed of 11.6 kilometers per second (25,951 mph) on Dec. 30, 2000.

How fast is Cassini traveling today?

To find out today's speed, go to "Where is Cassini Now" and click the frame at the lower right. The spacecraft speed (relative to Saturn) is indicated in kilometers per hour next to Cassini's position.

By the way, Saturn's average orbital speed around the Sun is about 34,700 kilometers (21,561 miles) per hour.

How much longer are you expecting Cassini's batteries to last?

Cassini uses nuclear power, so it will have electrical energy available for many years. Propellant used for navigation and orbit control is likely to be the life-limiting resource, and it will last well beyond our prime mission that goes to June 30, 2008. After this, presuming we are approved for an extended mission, the rate of propellant usage depends on the mission profile that is chosen for an extended mission. It could be used up in a year or so, or extended for several years. A mission intensively focused on Saturn's moons -- typically done with targeted flybys -- will use propellant at a much greater rate than simply making magnetospheric measurements. In any event, it is almost certain that electrical power will be available well after we run out of propellant.

Does it make sense to point the cameras on the Cassini spacecraft toward Comet 17P/Holmes?

Nov. 6, 2007

First of all, quite a few of the project members have been following Comet 17P/Holmes, and are very excited about this unique astronomical event.

However, there are three principal difficulties with pointing Cassini's cameras at Comet 17P/Holmes. First, it is quite close to the Sun as seen from Cassini. We cannot point our cameras very close to the Sun or sunlight will damage the instruments. Comet 17P/Holmes may be far enough from the Sun to target it - just barely - in about a week, but stray light from the Sun may make it impossible to take any useful measurements.

Second, Cassini is about six times as far away from Comet 17P/Holmes as the Earth is. Remember, Saturn is nearly 10 times as far from the Sun as the Earth, and the comet is still in the inner solar system. Ground-based telescopes and orbiting platforms like Hubble are much closer than Cassini is, and generally more able to conduct better science.

Third, since our spacecraft carries twelve instruments with twenty-seven associated investigations, we must design and build our sequences many months in advance to plan the detailed and optimized measurements our scientists (and the public) deserve. In order to add a new observation days or weeks in advance, we must work very hard to rebuild a piece of a sequence and test it thoroughly to make sure we don't make a mistake. Also, we have very little idle time on board the spacecraft, so observations of 17P/Holmes would have to replace interesting observations of some other very fascinating body in Saturn's system - and those are the measurements Cassini was built to take. We almost never do this - outside of responding to an anomaly - and only for the very highest priority activities.

Having said all that, however, there actually are Cassini scientists that are looking into the feasibility of taking some observations of Comet 17P/Holmes. It really is a very interesting astronomical event, and Cassini carries an Ultraviolet Imaging Spectrograph which could make observations that Earth-based instruments could not (since Earth's atmosphere blocks nearly all of the UV part of the spectrum). Also, imaging the comet and its tails from a different perspective could also be scientifically useful (as well as pretty cool!).

These potential observations are in a very primitive stage, and would have to be justified against the interference in our existing sequences, the added workload they would cause, and any risks associated with pointing close to the sun. But stay tuned, and perhaps we'll have something to add to the excitement in the coming months.