Welcome to the third post from the Science Geek. This post continues my previous two posts and discusses how we might get to Saturn’s moon Enceladus, which many scientists now believe is the most likely place in the solar system, other than the Earth, to harbour life.
Image from NASA
Types of mission
There are two types of mission to Enceladus: a one way trip and a return trip.
(a) the one way trip
As said in my previous post, NASA’s Cassini mission (http://saturn.jpl.nasa.gov/mission/introduction/) was launched in 1997 and arrived at Saturn in 2004 to study the planet and its moons. It has already flown past Enceladus a number of times. A few more flybys are planned before the mission ends in 2017 and one in particular, in October 2015, is scheduled fly only 50 km above its surface.
A new mission could fly much closer to the “water volcanoes” than the current Cassini mission, and might even fly through one while it was erupting. It could have specific experiments to look for life, and more up to date instruments to analyse the chemical contents of the volcanic plumes in more detail. The mission could land on the surface, perhaps near one of the water volcanoes and analyse material which had gathered nearby.
(b) the return trip
Another more exciting possibility would be to have a return mission which would land on Enceladus, capture some material, and then return it back to Earth. At the moment such a mission is sadly beyond the technical capabilities of any nation – a sample return mission has still not been attempted for the planet Mars which is much closer and thus far easier to get to than Enceladus. However, technology is continually evolving and such a mission might be feasible in 80 to 100 years time. The Science Geek is very unlikely to be around to see it!
How Long Would the Mission take?
The mission would probably take a similar amount of time to reach Saturn as did the Cassini space probe which is currently in the area. This was launched in October 1997 and arrived at Saturn in July 2004, nearly seven years later. Cassini’s trajectory is shown in the diagram below:
Cassini Trajectory (from the NASA website)
As you can see from the picture above, the mission used the gravity of the planet Jupiter (see Notes below) to attract the probe, speed it up and ‘slingshot’ it onto Saturn. Using the slingshot, or to be more precise, ‘gravitational assist’, means that the gravitational field of Jupiter does much of the work. This has cost implications for the mission: because the spacecraft needs to contain less fuel, it is much lighter, so the rocket required to launch it into space is smaller – and therefore cheaper.
There have been four missions so far to Saturn and all four spacecraft have used the gravitational assist. Indeed I would go so far as to say that, using today’s rocket technology, it would not be possible to launch a complex spacecraft to Saturn without using a Jupiter gravitational assist. The costs would be astronomical.
Limitations of the Gravitational Assist
The limitation of the gravitational assist is that Jupiter and Saturn need to be in the correct alignment for it work and this only happens every 20 years. The last time was in 2000, the next opportunity will be in the year 2020, and the one after will be in 2040.
Because it always takes at least five years to get from the financial approval of a mission to the actual launch date, plus up to three years to get to from Earth to Jupiter, we have missed the opportunity of using Jupiter to perform the gravitational assist in 2020. So any mission to Enceladus will have to wait until Jupiter is correctly aligned with Saturn in 2040, meaning that the spacecraft could leave Earth around 2037 in order to reach Jupiter in time. It would then arrive at Saturn around 2044.
At the moment although the Cassini spacecraft is performing a few more flybys of Enceladus, there are no further mission there planned by any nation. I think this is great pity since it is such a promising place where there could well be life. I hope that a mission to go there is given approval and that a space probe arrives at Enceladus in the mid 2040s, with all the instruments on board to see what kind of life exists.
* Cassini actually performed two flybys of Venus and one of Earth, bfore heading to Jupiter. Although this meant that the spacecraft took longer to reach Jupiter than if it had flown there directly, it meant that the amount of fuel needed was kept to a minimum, thus reducing the overall costs of the mission.