Ykhjuy

There was just a question (actually, on Astronomy) about why the data rate from New Horizons is low.

Of course, even with the most directional radio antennas, the spread is enormous.

I guess conceptually, some sort of laser signaling system would have tremendously less spread. (Or zero spread? I don't know).

Since the Earth has crap seeing, I propose

• On New Horizons, some sort of laser modem




• On our moon, some sort of laser modem receiving base

What are the numbers here? If (1) New Horizons has a power available of 1 NHPU, how many NHPU would be needed on board for my scheme? Is it overwhelmingly too much, or just "a bit more"? (For that matter, is it much less? Like, "a really good LED" or some such? After all, directional is a fantastic energy saving in the abstract.)

How complex would Moon Base Laser need to be? What I mean is, (2) would it be "surprisingly small" rather than the huge sizes needed with radio antennas. Would it basically be ........... a telescope?? With a $200 nikon camera body glued on, or is "a laser receiver" different somehow than "a telescope with a CCD"?)

So, would Moon Base Laser be a natty device (I'm thinking, say, the size of a car) which we could easily throw on to the moon with current systems, or, would it more be "a large construction". i.e. somewhat like current large Earth telescopes??

I know we already have (tricky) devices which receive lasers bounced off a mirror on the moon ... would one of those be ready-made to do the job, or ...?

With our current awesome radio dishes, they need to get (much) bigger as the spacecraft gets further ... would (3) this be the case with Moon Base Laser or would the issue not be so bad? Would reception / data rate be pretty much the same as the craft moved through our solar system ("since lasers are directional!") or is that all wrong?

Has anyone proposed, or indeed do we (4) already use, laser-style communications in space?

Are there any other narrow-paradigm communication concepts I don't know about, other than "laser"? Which we could use instead of good old dispersing radio??

(I guess proposed multi-craft fleets like LISA indeed do this, right?)

Summary,

1. how many NHPUs of power would be needed on board for this scheme? what's the order of magnitude?




2. what size paradigm would Moon Base Receiver be? suitcase-sized? town-sized?




3. would Moon Base Receiver have to increase in size dramatically w/ distances in the solar system (as do radio dishes)




4. do we do this already?

PS I'm just assuming this would be worthless from Earth, so, I'm just assuming a Moon receiver (or I guess an orbiting receiver) is a must.

It absolutely could happen, but it would require a more precise pointing then New Horizons has. Lasers of some kind are the best for the high data resolution. The spacecraft to most heavily use lasers in communication is the Lunar Reconnaissance Orbiter. It has also long been talked about as a goal for a Mars communication satellite, which would allow for much more data back from Mars. The problem is the pointing requirements are pretty extreme, you even have to know which site on Earth you are going to target, the laser beam will not cover the entire planet Earth from Mars. For example, MRO has a pointing accuracy requirement of 0.0032 mrad. Pointing requirements for a laser system are in fact similar to this requirement, however, they require stability for much more time. HiRISE only requires it for a few milliseconds, while a laser communication system requires it essentially indefinitely.

In the case of New Horizons, it just isn't needed. Yes, it will take a long time to get the data back, but that isn't a problem, there's lots of time to wait.

As a reference, laser power systems generally require less power then radio based systems, because they broadcast power more directly and thus waste less power.