# Tag Info

66

There is a very nice Myth Busters video about bouncing a laser off the Moon linked below. To answer your question, current work is done with an array of corner cube reflectors on the Moon roughly 50 x 50 cm in size. Pulsed lasers on Earth have traditionally been green frequency-doubled infrared Nd:YAG lasers, similar to the "classic" DPSS green laser ...

36

The University of Texas's McDonald Observatory performs laser measurements of the distance to the Moon using retroreflectors left by the Apollo astronauts. You can read all about it in the McDonald Laser Ranging page. Lots of technical details in this paper.

27

It absolutely could happen, but it would require a more precise pointing than 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 ...

17

Let's try and do some numbers. We will need to make a few assumptions.I'm going to choose ones which make the calculations easy, varying might produce variation of a factor of 10 or 100 in the answer. A near IR laser with a wavelength of $1 \mu m$ NH transmitting using the LORRI telescope with an aperture of about 20cm. We know NH can point accurately ...

12

Given that the interstellar medium (ISM) has a density of about 1 atom per cubic centimeter and given that laser propulsion could, in theory, accelerate a spacecraft to 30% of the speed of light in ten minutes, I'm going to say this one is plausible. They are talking about using several probes, so even if a few happened to get destroyed by particles, some ...

11

We're working on it. You do need a little telescope on the spacecraft to serve as the antenna. You can have two-way laser communications. It may in fact be essential to achieve the required pointing accuracy. There are many modulation schemes -- that's not an issue. Pulse position modulation is a front runner. The upside is much higher data rates with ...

9

This question was asked on Physics.SE with the question Amateur moon laser ranging. The answer is that in order to do so, you'd have to have a really precise laser beam (1 mRad divergence), along with a very accurate time measurement system (Nanosecond scale), and need a reasonably large telescope (On the order of a meter or two seems to be large enough). It'...

8

The Apollo 11 EASEP handbook gives basic information on the first version. Of the LRRR, it has just two pages of text... There are some (poorly reproduced) images labelling the main parts. It's correct there is a sun "compass" and a level. The large part labelled "B" in the question is a rear support, presumably so the folded device could be stood on the ...

8

No, you don't need "at least some photons per data bit". 13 bits per photon has been demonstrated with laser communications. You calculate the data rate capability the same way you do with any other wavelength, which is using the power, range, transmit and receive apertures, noise, modulation scheme, and coding gain. This paper summarizes detailed analyses ...

8

Here is a pdf studying techniques of laser debris removal. Summary: 1) Non-ablation laser debris removal (by light pressure and termal radiation) is ineffective. Only impulse laser ablation is feasible. 2) Large mirror is required (11-13 meters) to focus laser beam. 3) 0.75 kg aluminium piece of junk at 500 km orbit requires 9 months to be deorbited (...

8

All I could find was here which led to a variety of articles which explain the technology in depth. Not that Wikipedia is always reliable, however it stated that: The satellites will employ optical inter-satellite links and phased array beam-forming and digital processing technologies in the Ku and Ka bands, according to documents filed with the U.S. ...

7

Pulling some info from the Fact Sheet and this website. The formula, from Wikipedia, is $\theta \simeq \frac{\lambda}{\pi w_0} \qquad (\theta \mathrm{\ in\ radians}).$ I'm going to assume $W_0$ is the aperture width provided. That gives a beam width, assuming 1.1 um wavelength, of about 3.5 uRads Okay, at that value at the distance of the Earth will ...

6

Obviously the reason they have that amount of power on station is to use it to run the station. So the first obvious math hour is that you cannot have all the power for 15 seconds. Conversely the notion of using extra power that is unconsumed is valid. The Ad Astra guys with VASIMR plan to scavenge extra power to charge the batteries for their engine so ...

6

The technical challenges aren't the main barrier; several demonstration missions have demonstrated laser downlink to the ground. The main obstacles are: Operational: Clouds necessitate ground stations on mountain tops and in deserts, which generally means expensive + poor backhaul for the data as well as making it difficult to achieve 99% uptime without ...

6

Yes, it is entirely possible for lasers to give a propulsive power. In fact, there is a fairly commonly discussed idea of pointing a large laser at a solar sail to accelerate it faster than would be possible by just the sail itself. The key is, the lasers cannot be on the spaceship, they have to be away from the spaceship. And yes, given these laws, lasers ...

6

The solar sail idea just works, tested and true. Very powerful lasers are a reality. Very accurate, narrow-beam lasers are a reality too. Bringing these two together is absolutely doable. Powering that up requires just lots and lots of solar cells. We have these. Very reflective mirrors (so that the probe is accelerated and not obliterated by the laser) ...

6

If it took 10 years from our point of view, it would take 9.8 years from the point of view of the spacecraft travelling at 20% of the speed of light. So a little shorter, but not by much. A bigger effect would be that the spacecraft would be two light years away by the end of it's journey, so if we were watching though a telescope we wouldn't see it reach ...

6

The linked image is a 125mm telescope in a coarse-pointing hemispherical (two axis) mount. It has a field of view of about 2.5mrad in acquisition mode, which drops to 0.5mrad for data transfer. It’s backed up by fine-pointing optics with sub-10$\mu$rad pointing and sub-$\mu$rad co-linearity, consistent with a diffraction limited beam. The acquisition ...

6

Steve Linton's answer is excellent, although possibly a bit conservative. Information has been transmitted in the lab via laser at a rate of 1 bit per photon. For proposed uses, Error Detection and Correction codes are definitely indicated. Has anyone proposed, or indeed do we (4) already use, laser-style communications in space? Yes to both, although ...

6

Apollo 11 retro reflector was placed on the Moon on 21 July 1969, the first successful use of the reflector was on August 1 and 3 by the Lick Observatory. Returns were observed on August 20, September 3, September 4, and September 22, 1969, at the Mc­Donald Observatory. Attempts were made almost immediately but there was only a brief time available before ...

5

Well, for a laser to help in this situation, you'd need to vaporize the debris. That means heating the entire piece to its evaporation temperature. This needs either a very powerful laser, or enough dwell time at a lower energy level. Both are difficult to achieve. For high laser power, you're talking about the sort of power that is generated by the ...

5

The Mars 2022 orbiter is expected to have this capacity. From the Mars Telecommunications Orbiter wiki page, one can see the entire history, including the latest plans. See also SpaceFlightNow. This mission will be similar to MRO, in that it has a science mission, but doubles as a high speed data relay, although it will be a higher speed relay than MRO, as ...

5

The cannon will follow a process known as "laser ablation" to shoot down space debris. Energy from the cannon will heat space junk with a beam, which will then vaporize it. As a result, the space junk will evaporate. But surely that will just create lots more < 1cm particles to worry about? Evaporation turns things into a gas, so the particles will ...

5

This is closely related to the concept of Antenna gain, which for radio transmission measures how narrow a beam the antenna can focus. The narrower the beam, the more accurately you need to point it. However, any laser or radio beam will still be divergent - it will spread out the further away it goes. And it will spread out at the same rate, with the beam ...

5

It would have more TWR, the same efficiency, but the matter is almost irrelevant anyway. (If you're trying to build a weapon, not a thruster, the laser is better because it is collimated in a narrow beam and the lamp isn't.) Lasers are inefficient... and their inefficiency means they output heat. Which can only be disposed of in space by radiation. So if ...

4

The main reason for reduced received signal with radio communication in space is the spreading loss, that is intensity declines with the square of the distance from source to receiver. This is true even with beamed radio signals. Laser communications beams suffer from exactly the same loss once the cross-sectional area of the beam exceeds size of the ...

4

I'm going to borrow an analogy from Baron Münchhausen (see Fig. 1) later on to illustrate the Newton's three laws of motion that are in effect with such a system you're proposing and why it wouldn't be possible to create a propulsive force, if the lasers and the solar sail are a part of the same closed system (or a single body), but let's first go through ...

4

This is indeed possible. The US spent a fair amount of money in the 60s and 70s on beamed power. In recent years it has gotten some more interest for lunar rovers that can survive the 14 day lunar night (without RTGs). The losses are not negligible, and the pointing requirements are rather extreme but in practice there's no reason why this couldn't happen. ...

4

Arecibo can measure speeds with an accuracy on the order of 1% in scanning mode (i.e. just observing asteroids as they pass through the field of view). Distances can be measured to 10-8 (10 ppb), I suspect this is done in a different, more accurate mode. Emily Lakdawalla discusses this in her blog, inlcuding this graph that shows the position accuracy of ...

4

This would still cause debris, either immediately or eventually. Technically, an unresponsive satellite is 1 piece of space debris. But the real question is lots of small pieces.... Overheating could certainly cause the tanks to explode at the time. If left disabled, a satellite with non-empty tanks and charged batteries does pose a threat to explode/...

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