You can get around this by using an array of lasers, each of which is individually rather harmless, but focused together would be enough to destroy such a target. The "danger area" would be restricted to the focal point. Anything outside/beyond/inside that point would receive much less laser power and likely escape damage.

Now if your drone is using active terrain masking, that makes it more difficult to hit at range. However, such a system would probably require a human remotely controlling it, making that susceptible to jamming. I don't think automated terrain avoidance (in real time) is practical just yet for anything a non-military entity could get its hands on. And in any event, such a terrain-avoidance system would likely need its own sensors (radar/lidar) which could be detected, jammed, or both.

Or you could have an array of relatively low-powered lasers that focus on a target point to collectively do their damage. Any misses would be harmless due to them being outside/beyond the focal point.

So what's your point? That a more capable drone is also bigger? So? So what? That's obvious. Do you think the added size/complexity of such a thing would be any impediment whatsoever to a determined aggressor? If you want to penetrate controlled airspace to do something nefarious, you're perforce going to want something that's difficult to detect, difficult to jam, difficult to shoot down, and has enough payload to carry whatever you need to cause the damage you're looking for.

Really? Then let's hear your alternative options. I already covered sensors and weapons, but let's recap. Radar is vulnerable to stealth, so it won't do the job alone. Lidar is too short ranged to do the job alone. Acoustic is even worse. But put together, a web of such sensors would be very difficult to overcome. If there are other sensors out there that are even remotely applicable, please enumerate them.

As for weapons, you have only three options: ballistic, missiles, or directed-energy weapons. Ballistic weapons have all kinds of downsides, from trajectory computation to wind to limited ammo, not to mention the inevitable collateral damage from misses (of which there will be MANY). Missiles have similar downsides. DEW's have (almost) none of these, the sole one being the potential for (minor) collateral damage in the case of a miss. You could even potentially mitigate this by using an array of low-power lasers, individually almost benign, but focused together to take down a drone.

This assumes you can get a good doppler signature on the rotors at all. I'm not an expert on radar/stealth construction, but I know a fair bit about it. A rotor made of radar-transparent (or absorbent) material would make it rather hard to detect, at least until it was well within range to do damage.

That's why God invented single mode fiber.

Forget outfitting it with a lawn dart. Any insufficiently powered heavier-than-air craft will BECOME a lawn dart due to that pesky "gravity" thing.

Small drones with significant non-metal construction will be more or less indistinguishable from birds. And it's not a stretch to imagine "stealth" drones specifically constructed or modified to mitigate radar.

Using a radar offensively, aka an EMP weapon, is a possibility, but shielding electronics is also a possibility. You'd need a very powerful signal to defeat that, and operating such a thing in a civilian area could lead to all kinds of unintended damage.

Radar, backed up by lidar and acoustic sensors, is the best route. Threat mitigation is best handled by a point defense laser. End of story.

Use this: www.youtube.com/watch?v=D0DbgNju2wE

Infinite ammo so long as you have power, instant hit, no ballistic fallout if you miss. And it's not like they can't afford it.

Not to go all Dr. Evil on the subject, but the Navy *does* have some recently-deployed point defense laser technology designed to shoot down incoming cruise missiles. These tiny drones aren't manned and they're violating what might be the most restricted airspace in the country outside of Groom Lake; there's nothing legally preventing them from being shot down by said laser. That's a far better course than trying to do it ballistically or with something like a Stinger missile, both of which would have a hard time hitting something small and have issues with what happens to the round if it misses (i.e. falls on a civilian).

Mars is also a nine-month journey with no practical prospect of a "turn around and go home if something goes wrong" option. The moon is three days away and a free-return abort is built into the flight plan (along with a direct abort if the situation is dire). The scale of the two missions is completely different, with Mars being vastly more difficult mainly due to time.

I'm a big fan of the lunar base idea. Start there and develop -- or re-develop, as the case may be -- the technologies needed to get us reliably to and from the moon. Lunar habitats can be inflatable, or built underground using locally available materials. Hell, we could put robots on the moon to BUILD the habitats before we ever go there in person, making the whole trip a lot safer. And remotely controlling robots on the moon is a helluva lot easier than doing the same on Mars. Water is present on the moon for rocket fuel. Solar power is reasonable, but a small fission reactor would be much better. The escape velocity for the moon is lower than Mars and vastly lower than Earth. And asteroid capture missions could redirect to the moon instead of Earth, where the risk of "losing" and asteroid and having it impact would be negligible compared to aiming one at Earth and hoping you don't hit a populated area.

In short, a sustainable lunar base could be used as a springboard for future manned missions to Mars and the outer planets. The moon is IDEAL for this for every reason except one: it currently has no infrastructure for building or launching anything. Let's remedy that as soon as possible instead of trying to figure out how to haul everything out of Earth's gravity well and dense atmosphere. Grab an asteroid, send it to lunar orbit, smelt it down in orbit and construct your spacecraft THERE instead of on the surface. Complex items that cannot be easily made in orbit can be made on the lunar surface and launched via magnetic catapults into lunar orbit for final assembly. Or, for that matter, a lunar space elevator. The lower gravity and lack of atmosphere means we can construct a lunar space elevator with existing materials RIGHT NOW. Forget the magical unobtanium needed to make one on Earth; we just turn the moon into our launch platform for the solar system. Long term, instead of just redirecting asteroids to the moon, we can get to Saturn and grab a few cubic miles of water ice from its rings. Sent to the moon, it could provide water, breathable oxygen, and fuel for thousands of missions.

The DC-X and NASP were cancelled because they were unworkable concepts. The prototypes you saw up until cancellation were about as space-ready as my toaster is. There were too many problems with materials and performance that we do not have the technology to overcome just yet. Boeing recognized this and that's why the ideas were shelved, not some Vast Corporate Conspiracy.

Except for the fact that it does nothing to spread out the human species. Right now, if a calamity befalls Earth such as an asteroid/comet impact, or the explosion of the Yosemite supervolcano, or global thermonuclear war, we get wiped out as a species. In the long run, we MUST leave Earth if for no other reason that to get all our eggs out of one basket.

And, if you want to be REALLY forward thinking, we have to eventually leave this entire solar system, as our Sun will eventually burn out, turn into a red giant, swallow Mercury and Venus, and probably Earth as well if it isn't burned to a cinder already.

Why land a rather large rocket? Seriously. This same discussion took place pre-Apollo when engineers thought we'd have to land a large rocket on the moon. Their solution then would work equally well now. Send a lander with a small, lightweight return-to-orbit ascent stage. Leave the Earth-return rocket in orbit awaiting the ascent stage with sample. Your landing/takeoff mass problem is thus solved.

Granted, you now need an automated docking procedure in Mars orbit, but I can't imagine that would be more difficult to engineer than trying to orchestrate a much heavier land-and-return rocket setup.

Remind me again who's been in charge of charge of the House, the Senate, and the White House for most of Obama's tenure? Sure, a Republican was pushing for this pork. But it passed a Senate and a White House both controlled by Democrats, either of which could have easily stopped it. Neither did. In fact, depending upon the timeline (which I'm too busy to fully look up at the moment), it's possible the Democrats were in control of the House as well at the time this was going on. I can't recall exactly when the Republicans took over the House.

The truth here is the entire system is contemptible. Both Republicans and Democrats bear equal responsibility for this debacle. And to suggest there aren't billions and billions of dollars of pork barrel projects championed by Democrats is disingenuous at best.

Yeah, just like Prometheus was the "best ever" sequel to Alien!