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NASA's LLCD Tests Confirm Laser Communication Capabilities In Space
An anonymous reader writes "This week, NASA released the results of its Lunar Laser Communication Demonstration's (LLCD) 30-day test carried out by its Lunar Atmosphere and Dust Environment Explorer (LADEE) that is currently in orbit around the Moon. According to the space agency, the LLCD mission proved that laser communications are practical at a distance of a quarter of a million miles and that such a system could perform as well, if not better, than any NASA radio system."
cat, just because we dont have a large manned space program does not mean we dont have a space program. I would say that we have found out more about space and moons and planets and stars in the previous 10 years than at any time in the past. Sure it is not as flashy as sending an astronaut to the moon or mars, which I am in agreement with you that we need to be working harder on our manned missions, but to say our space program is dead is just simply wrong
have you seen my sig? there are many others like it but none that are the same
...dealing with telepathic cats.
The earth orbits where the sun is right now. It takes light about 8 minutes to travel from the sun to the earth.
No. It also takes 8 minutes for changes in the gravitational field to travel from the sun to the earth.
The earth orbits, where the Sun appears to be; as the Sun appears to move, the gravitational field changes.
These changes are delayed by 8 minutes.
The constant 'c' from special relativity is not just the speed of light in a vacuum -- it is also the highest possible speed for any physical interaction within nature, and the conversion factor from changing units of time into units of space.
Gravitational waves, Gluons, Photons, and other massless particles travel at a maximum speed of c.
It is impossible to convey information at a speed faster than c.
There are cases where a wave can propagate faster than c, but no information can be conveyed faster than light.
Wrong. The sun is orbiting the galactic core at about 828,000 km/h, giving it a non-inertial reference frame. In the eight minutes it takes sunlight light to reach us the sun has moved 110,400 km within the galaxy. Then there's the velocity of our galaxy within it's cluster (and our cluster within its super-cluster, etc)
--- Most topics have many sides worth arguing, allow me to take one opposite you.
It has to do with the difference between phase and group velocities when dealing with groups of waves. You can have a phase velocity greater than c but information is transferred via the group velocity. One place to start is here, another here. You can find some nice applets around that will show it to you graphically. The topic comes up from time to time because it is at the heart of the misunderstanding of faster-than-light "photons".
I don't know anything about physics, but I have heard this quote:
When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong. - Arthur C Clarke
I have heard this. I've also heard that it's an urban myth. And that it's a real phenomena, but that the discrepancy only exists when analyzing the system in terms of Newtonian gravitation, and disappears when analyzed in terms of Relativity. Take your pick.
Regardless, we *are* looking for gravity waves - we've found tightly-orbiting binary star systems that are losing energy at precisely the rate predicted by the emission of gravity waves propagating at light speed (a different speed of gravity wave propagation would mean a different rate of energy loss). And we've built gravity wave detectors so sensitive that they should be able to detect the asymmetric spatial distortions created by gravity waves far weaker than those that the are being emitted by the binary stars.
And so far they have detected *nothing*. Not even a ripple. Which is a rather major mystery that, to me at least, suggests there's something important we don't yet understand about gravity.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Not that anyone has figured out yet anyway. I wouldn't wish to preclude the possibility.
Yeah, I had a sig once; I got bored of it.
No, he's mostly correct. The Earth is also moving around the galactic core with the sun, so the relative motion is just the Earth's orbit around the sun.
The distinction here is between linear and rotational movement. The sun's movement for the year (i.e. relative to background stars) is a linear movement (changes in relative position between observer and subject) and thus is affected by relativity and the 8.3 min travel time of light. Since it's only traversing a bit less than one degree per day (360 degrees in 365.24 days), this motion is very small. In 8.3 minutes the sun's actual position changes an almost imperceptible 0.0057 degrees.
Nearly all of the sun's "movement" across the sky is caused by the Earth's rotation (change in orientation of the observer) and thus is not affected by relativity and the 8.3 min travel time of light. The sun is where it appears to be right now, even though the sun appears to have moved 2.1 degrees in the sky during the 8.3 minutes it takes its light to reach us. If this weren't the case, if you spun around 360 degrees in 1 second, a star 1 million light years away would have traveled 2*pi*1 million light years in 1 second, far exceeding the speed of light.
There is no absolute reference frame for linear motion. If I'm on a spaceship moving at 10 km/s relative to your spaceship, we cannot tell if I'm stationary and you're moving at 10 km/s, or if you're stationary and I'm moving at 10 km/s. But there is an absolute reference frame for rotation. If I'm rotating I'll experience centrifugal (centripetal) forces, which disappear when I'm no longer rotating.
That's always been a cute fairy tale put forward by the Pentagon fantasy factory, but it's never been true. The military assisted in the space race, especially in the beginning when they had the only functional launchers, but the necessities of space exploration quickly surpassed the really rather primitive needs of the military. The Apollo 1 booster was already larger and more powerful than any ICBM would ever need to be, and took so long to assemble, prep and fuel that it could never be useful as a weapon. The Pentagon never needed a booster powerful enough to send a 700 kilo spacecraft to the edge of interplanetary space, much less send two spacecraft and an electric car to the moon, nor did the Kremlin.
Von Braun and Korolev worked on military projects during the first part of their because that was the only way they could get funding. They achieved their greatest accomplishments working on the civilian programs. Von Braun made no secret that the Moon had always been his goal, and Korolev upbraided a Kremlin general that wanted to usurp some of his funding by telling him, "These rockets are much more important to our future than your missiles."
"Think about how stupid the average person is. Now, realise that half of them are dumber than that." - George Carlin