# Tag Info

39

Sorry for the length of this, but it brings up some interesting facts and possibilities. The moons you mention, Titan, Europa, and Enceladus, are three very different places. Titan has a relatively large surface gravitational acceleration (as far as satellites go) and a very thick atmosphere; Europa has a relatively large surface gravitational acceleration ...

28

Simple. It was the easiest to land on. Titan has an atmosphere, which makes landing there quite a bit easier than landing on Europa, which does not. In addition, Europa has only been known as an object of interest since Galileo, which was the last mission that even had a chance of sending a lander there. It was suspected as an object in the Voyager flyby, ...

21

The "atmosphere" at $10^{-12}$ that of Earth's is entirely useless for landing. It would simply be retrorockets as you would for our Moon. Many types of landing gear could be considered, such as traditional legs, airbags, wheels a la skycrane, pallets, crushables, whatever. But to get to that point at a survivable velocity, it's all about rockets.

18

It's probably going to be less of a concern than you'd guess. The icy worlds of our solar system have essentially no atmosphere, so the surface materials will sublimate directly to vapor and be dispersed rather than melting and freezing the landing pads into place. Fairly little of the surface will be disturbed to begin with. The gas expansion which ...

18

Let's go back our old friend the Pork chop plotter. Earth to Jupiter using minimum fuel takes around 2 years and you get one opportunity per year, more or less, to get there. You can shorten the journey to perhaps 20 months with minimal extra fuel. The delta-V required at Earth (over and above escape velocity) is about 9.3 km/s (you can in theory aerobrake ...

13

Jupiter is 778,500,000 km away from the sun, on average. Earth is 149,600,000 km. Thus, the distance to Jupiter is always between 630-930 million km. So, let's take that range, and figure out what the time would be, given 1 g of acceleration, and ignoring for the moment relativity. Let's also ignore starting/ending velocity, as I'm feeling lazy... Okay, so 1 ...

11

I whomped up a spreadsheet to compare scenarios like this: Hohmann.xls. Typing Earth into departure planet cell and Mars into destination planet I get Launch windows open each 2.14 years (synodic period) Trip time .71 years Delta V Low Earth Orbit to Low Mars Orbit: 5.7 km/s Typing Mars into departure planet and Jupiter into destination: Launch window: ...

10

@PearsonArtPhoto's (excellent) answer doesn't consider efficiency. Direct travel – by accelerating directly toward the spot Jupiter will be at when you arrive, and then decelerating for arrival – is not the most efficient way to reach Jupiter. To date, no human-made spacecraft has used such a method. So taking the distance to Jupiter and calculating travel ...

10

A Europa lander would need much more shielding, and/or more radiation tolerant components. Juno's orbit avoids the main radiation belt, but Europa is right in the middle of it.

9

A wire would be needed to get any real amount of data out. Wikipedia has the state of the art communication with submarines. There are basically 2 ways to communicate with them. Using sound waves could work for short period distance, and that might be possible to use from a surface component to the underwater submarine. Very low frequency (3-30 kHz) can ...

8

The standard for any tidally locked body, of which Europa is a member, is to have the 0 longitude be the point at the center of the planet-facing side. That being the case, the middle of the map should be the portion facing Jupiter, the edges the part that never faces Jupiter. See Wikipedia for the referenced quote below: Tidally-locked bodies have a ...

8

We don't really know how the tidal energy that Europa gets from its orbit around Jupiter translates exactly to its surface or subsurface activity, so it would be hard to speculate on any possible power plant types that we might employ to produce electrical power, but Europa's orbit is kept elliptical (orbital eccentricity of 0.0094) due to the resonance with ...

8

Disclaimer: I'm going to attempt answering this question mostly out of my head due to lack of time, but will later equip it with references and correct my assumptions, if anything goes wrong... Ever since Voyager 1's fly-by back in 1979 and providing us with detailed enough photographs of the Europa to show these cracks on its surface (earlier Pioneer 10 ...

7

Francis' Python BOTEC looks at Hohmann orbits. To simplify he assumes circular coplanar orbits. Here is a pic comparing an earth-to-Mars Hohmann vs an earth-to-Jupiter Hohmann: At perihelion the Mars transfer orbit is moving 33 km/s vs earth's 30 km/s. Departure Vinf is 3 km/s. At aphelion the transfer is 21.5 km/s vs Mars 24 km/s. Arrival Vinf is 2.5 km/s ...

6

You would almost certainly need a wire. You have 2 things to contend with on Europa (besides the crippling radiation, extreme cold, vacuum, etc) and that is Ice and Water. Water absorbs radio waves, only extremely low frequency, very powerful radio waves can penetrate much water and these signals are terrible at carrying information as the rate at which data ...

6

The Hubble Space Telescope did an ultraviolet emission study of vapor plumes from Europa's southern hemisphere in 2012. It found that the emissions were consistent with $H_2O$. H2O freezes (19), and any enhancement must be localized to its source. In addition, electron impact on H2O (e + H2O) yields HI 121.6 nm and OI 130.4 nm, but has a lower cross ...

6

Adapting an existing rover design to work underwater would be extremely cost prohibitive and it would be cheaper, more effective, and all around a better idea to design a whole new rover with underwater capability in mind. In a general sense, there's a couple problems that an underwater rover needs to counter: Pressure: Most spacecraft and rovers function ...

5

Europa's surface gravity is just a bit less than that of our moon (0.134 g versus 0.165 g), and as Mark Adler notes, the atmosphere is negligible. Russia and China have already put unmanned rovers on the moon via unmanned rocket-powered landers; both of these rovers are roughly in Opportunity's weight class (Yutu a bit lighter, and Lunokhod about 4x heavier)....

4

TL;DR: We've all agreed to not do that, but there's no Intergalactic Police stopping you. But you would likely be stopped by earth police forces. Relevant Treaties and Organisations UN The UN's Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies has been signed ...

4

That depends on where the spacecraft lands. The radiation belts rotate faster than the moon so the trailing side of Europa gets a lot of radiation while the leading side gets relatively little. It also depends if the lander will be a separate spacecraft or a part of the orbiter. If it has to go multiple times through the radiation belt with the orbiter, ...

4

They landed on Titan because Titan is the only natural satellite in the Solar System that has a dense atmosphere. And it is the only object other than Earth where surface liquid has been found. Source: Wikipedia.

4

Yes, you would need to get higher resolution data than we have in order to pick a landing site, even if only for science reasons. You want to get to the "good stuff", which would be exposure of material somewhat recently brought up from the ocean. You would also need to pick a site that meets the requirements of the lander, which would be designed to be as ...

4

Simply, it is possible, but whether or not we can build a probe like that is up for discussion. This geyser occurs when Europa is at it's apoapse around Jupiter due to the weakening of the tidal forces on it's surface. All the pent up pressure under the surface shoots outward as a geyser, reaching heights of up to 125 miles. Now, to quote NASA, these ...

3

Terminal velocity is proportional to the square root of gravitational acceleration, if other factors are held equal. So it will be about 120 mph $\times \sqrt{0.1335} \approx$ 44 mph.

3

The ice layer is almost certain, in fact, it's not all that rare. Most outer solar system objects have an ice layer. The real interesting question is the potential water layer on Europa. From Wikipedia, we get a better overall picture of what's going on. It is almost certain that there is a layer of water underneath the ice. The size of that layer is the ...

3

It's possible to argue that the NEAR Shoemaker probe was the first landing beyond Mars. The probe landed on near-Earth asteroid Eros on 12 February 2001. On first encounter in February 2000, Eros was 1.7 AU from the Sun, outside of Mars' orbit. However, by the time of landing Eros was only 1.43 AU from the Sun; while Mars was near aphelion, so Eros was no ...

3

In our solar system the rocky planets/satellites which have atmospheres dense enough for flying are Venus, Earth, Mars, and Titan. I believe that after Mars the next thickest atmosphere on a rocky world would be on Triton and that is much thinner than that of Mars. It has detectable winds but probably is way too thin for flying. Of course no guarantee how ...

3

It won't be cataclysmic. Europa's ocean already vents to space, a probe would just add a small channel to that. A narrow channel several km long will also clog up quickly because the liquid water will freeze to the walls of the channel.

3

No. The water and ice are almost certainly under hydrostatic equilibrium. The ice is floating on the water. If you cut a hole in the ice, the water would fill the hole only part way, just like ice fishing. See this answer from someone who knows about these things. While there are observations of water geysers from some moons in the solar system, the water ...

3

It is easy to calculate. The ice is reported to be 15 to 25 km deep. Simply take the weight of the ice in Europa's gravity over one square meter of the top of the ocean. Calculation in Wolfram Alpha You get 24 MPa, or about 240 atmospheres for 20 km of ice. However that ice sitting on the ocean is in equilibrium, just as ice is floating in a glass of ...

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