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In regards to Europa, what are the limitations regarding current data transmission technology.

Say we were to have an orbiter circling Jupiter, a lander on the surface of Europa and a "swimmer" [submarine] that somehow got under the ice, and liquid water existed under the ice.

Using current technology, how could the "swimmer" talk to earth? (Aka "phone home") Would a wire be needed to penetrate the 2-8km of ice? (Can radar penetrate that far?) How far could the "swimmer" communication penetrate?

  • From the bottom of the Europa ocean, to the surface?
  • Through the ice, and to an orbiter?
  • All the way to the deep space network?

I am specifically curious about the limits of current data transmission capabilities of an object buried under 2-8km of ice. (Is the thickness of the ice relevant?). Data transmission rate isn't necessarily relevant, just distance through various mediums such as ice, water, and open space.

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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 communicate a few meters into water, while ELF can communicate using 3-300 Hz waves. Neither can transmit significant data, nor can one be built underwater. They also can't be focused very well, so they would at best communicate to the surface, from there to Earth.

Ice is somewhat better at transmitting RF than water, but it too, has difficulties. Radar is successful at penetrating large depths of ice, unlike water.

The only practical way to get data from under the water is to have a lander relay communications between Earth and the submarine, possibly via an orbiter, using either sound waves, or a wire.

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  • $\begingroup$ Alternatively, you could have a rover that is autonomous and reports back to its base station. Assuming, of course, that you are able to get through planetary protection protocols. $\endgroup$ – Phiteros Aug 2 '16 at 4:37
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    $\begingroup$ Not much you can do to "beam" those low VLF/ELF frequencies in any particular direction either, unless you use the geologically sized features of the moon to focus somehow. At many frequencies higher frequencies, the saltiness of the water will have an impact as well. $\endgroup$ – uhoh Aug 2 '16 at 5:19
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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 is carried is very low, like one character ever few seconds. ELF is used to communicate with submarines, but it's one way as the transmitter is huge, and the receiving antenna is very long - over a kilometer if I remember. Not practical for a space probe to carry, and there's no way we could send a transmitter to Europa as it's enormous. The probe would only be able to receive, and not send data using an ELF system.

Sonar is also a very bad carrier for information, it goes pretty far but there's too much attenuation and distortion.

The surface ice is a real problem as well, as it also absorbs radio and it will prevent a probe underneath from being able to expose an antenna.

To understand how we would do this on Europa you don't have to look any farther than how we do it on earth. While there are autonomous probes the vast majority of unmanned undersea exploration is done using tethered probes as it's the only way to supply the probe with power, and the only way to get data from the probe in quantity while it is under the surface. Even the autonomous probes have to surface to send information. Navies across the world have spent a great deal of money to find ways to transmit data through water so that submarines can communicate while submerged, but they still have to send data through an antenna exposed to the surface.

So any probe we send will require a wire of some sort to send data back.

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  • $\begingroup$ A wire with a tiny hose to bring home samples :-) Might be used as a power cord from the surface unit too. $\endgroup$ – LocalFluff Aug 2 '16 at 17:04
  • $\begingroup$ A sample would be amazing, but since the ice is supposedly over 15km deep that might be problematic. $\endgroup$ – GdD Aug 3 '16 at 7:11
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    $\begingroup$ Didn't Congress earlier this year force NASA to dedicate an SLS (Block I) to a lander on Europa? That's a three times larger mass budget than any other space probe, like a Viking orbiter/lander, but just for the lander. Another SLS for the orbiter. So there's room for ambitious concepts. Such a heavy orbiter should facilitate a sample return. (But lack of space nuclear power is still a decisive bottleneck). $\endgroup$ – LocalFluff Aug 3 '16 at 9:30
  • $\begingroup$ Even if you can't return a sample of liquid water from below the ice a core sample of the ice would be a fantastic source of data. $\endgroup$ – GdD Aug 3 '16 at 10:00

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