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Comment: Re:NO, NO, NO, NO, this is a BAD idea (Score 1) 272 272

Nuclear powered craft are ONLY used for spacecraft which will be leaving earth orbit and not returning.

Those nuclear reactor powered probes I mentioned (SNAP-10A and TOPAZ reactor series) are in orbit. But I see what you mean and in Earth orbit, solar power seems to be good enough for most use cases.

First, you can physically render a nuclear device inert by removing parts of it.

Of course you can. All you need to do is distort any part of its ignition mechanism. You could do that on orbit even.

I believe they call it a "pill"

Precisely. It's usually a central part of the first stage. Without it in, upon ignitor detonation, the nuclear material won't compress correctly and will instead tend to be flung out of the pit, rather than achieve criticality.

So keep your nuclear devices UNDER ground, keep them disabled by storing that last bit of fissionable material in a totally different area.

And this is precisely what we already do and what even this asteroid defense plan would do.

Setting a device off in LEO is going to be a mess and it's going to affect a huge area.

The points on EMP blasts and radiation damage on detonation in LEO is quite correct. In no case would asteroid defense, however, entail doing that. By the time the object got close enough for LEO detonation to be a factor, we're toast anyway. A few seconds to minutes to impact - no amount of nuking is going to turn an asteroid around or stop it dead in its tracks. Asteroid defense always talks about deflection when the object is very far away, way past the orbit of Mars even. I think you got the wrong impression from some shitty Bruce Willis movie :)

Comment: Re:NO, NO, NO, NO, this is a BAD idea (Score 1) 272 272

1. Nuclear devices are ineffective in space.

Not the case. See Project Orion.

will have to use them early to nudge the object onto a different path

This would be the case for any asteroid defense and we're already capable of detecting and track most objects large enough to cause serious concern. With more investment, we'll only be getting better and be able to detect smaller and smaller objects.

banned by multiple international agreements

Banned due to potential for a space arms race over a potential war. Doesn't apply in case of joint global asteroid defense.

We don't put nuclear power generators in space for a reason

We can and regularly do send nuclear power generators into space, including fully-featured nuclear reactors. In related the news, we haven't all died yet.

4. Nuclear devices are pretty fragile devices & 5. Nuclear fission devices require regular maintenance

Just send many smaller ones. Even if some don't work, all you want to achieve is deflection. Pro tip: when not required, don't park the things in space. Keep them on the ground and launch them should the need arise. Any asteroid early-detection program gives notice years in advance (e.g. we learned about the close pass of 99942 Apophis a good 2 decades in advance).

6. An accidental malfunction would be a SERIOUS problem for the near by earth

Same problem applies for weapons stored on Earth. Fix is simple: keep the device disarmed and design in fail-safes. This has already been done. I 7 decades of nuclear weaponry, number of inadvertent nuclear detonations, even in case of accidental weapons drops: zero.

Comment: Re:How does "drone time" look like on your logbook (Score 1) 298 298

an officer pilot would never let a flight hour go uncounted because it directly affects their pay

I mean in the civilian sector. You can't log simulator hours (except maybe the absolute top-tier type 7 ones) into your logbook as full value flight hours, so how would this crap count?

Flying drones actually does teach a pretty valuable skill in that it requires being able to fly purely via instrumentation.

Which is in no way different to your standard IR, which all airline pilots are required to have anyway. Moreover, first thing they teach you in IR training is "don't trust your sense of motion". If anything, these static control stations are even worse, because they don't teach you to ignore conflicting motion sensations.

I knew a man who was a commercial airline pilot and it didn't really seem like that great of a gig

That is quite true. Pilots are paid atrociously, yet the training demands and responsibilities are as high as they've ever been.

Comment: How does "drone time" look like on your logbook? (Score 0) 298 298

My guess is, many of these aviators don't like the look of this shit on their logbooks (if it even gets logged at all). "Oh yeah, I totally played a video game for 1500 hours". I somehow have a hard time imagining this will land you an airline job after you're out of the airforce.

Comment: Re:HÃ? (Score 4, Interesting) 419 419

What bollocks is that? What has an RTG in space to do with a nuclear (fission) reactor on earth?

Pu238 is produced in reactors here on Earth. Due to all the restrictions and red-tape put up by (supposedly) anti-nuclear activists, it's difficult and very costly to keep producing it, so everybody who had been producing it, simply shut down.
Now to be honest though, this is a poorly constructed argument. Strict regulation of nuclear materials isn't in itself a bad thing and besides, the lack of Pu238 is mainly due to the shutdown of the nuclear weapons industry, not the power industry (which never produced it anyway). Moreover, Philae was a low-value part of the mission to begin with and an RTG wasn't really necessary (needless to say that it can weigh quite a bit, potentially sacrificing other experiments that could be carried in its stead). Regardless, the comet was scheduled to make a close pass by the Sun regardless, so there was always the possibility of getting more power later on in the mission. Where the RTG argument *can* make sense is in missions like Juno. Juno had to go to some pretty serious compromises to be able to explore Jupiter without an RTG, such as having oversized solar panels for its relatively meager scientific payload. Had Juno had an RTG, it would likely have been able to pack a lot more equipment that is also more power-hungry, allowing us to get more out of the mission. Anything beyond the orbit of Jupiter without an RTG is an outright non-starter using solar power, as the scientific return quickly diminishes to zero simply due to the lack of power. Even Mars missions without RTGs were compromised (one of the principal reasons Curiosity got an RTG was so that we could get more power-hungry experiments on it, cause being able to snap pretty pictures only gets you so far).
Overall, it's a soapbox article and sadly, it starts out with the wrong premise.

Comment: Re:If it was political, that is sad (Score 1) 419 419

A few of reasons this is not political:
1) Pu238 is *extremely* hard to come by. Pretty much all we had has already been used up.
2) Even if there was some available, getting through all the red tape to handle anything labeled "nuclear material" is a massive PITA.
3) RTGs are not very light-weight. This mission was enormously weight-conscious and philae was only an add-on. If it were RTG powered, it would likely have meant that some other experiments couldn't go on the main probe (which was the higher scientific value to begin with).
Philae was only a small extra and weighing all pros and cons, my guess is the scientists on the mission simply said "ah, screw it, it ain't worth all the trouble".

Comment: Re:We can't have this! (Score 1) 830 830

I know both about the short ton and the "metric ton" and that it is not a standard unit, however, it's in common usage and a perfectly acceptable shorthand, kinda like how you can say "I weigh 80 kilos" and everybody knows you're talking about kilograms, or how in Japanese centimeters are commonly referred to as "centi" - it's just a common shorthand.

Comment: Re:What tech challenges? (Score 2) 54 54

Lack of modern istrumentation, radar transponders, and other equipment which is normally used by modern air traffic control systems.

That's just BS. First of all, the instrumentation to fly an assigned heading and altitude must already be there, otherwise they just wouldn't be certified to fly. Secondly, there's no problem installing a modern radio stack in an old airplane - you can even have it tucked away in the cockpit so it doesn't interfere with the "old style" cockpit look too much. Tons of old airplanes are retrofitted with new avionics all the time. All you really need is the two boxes near the bottom of this instrument panel (retrofitted to a 1940s era Piper Cub with an admittedly quite pimped out instrument retrofit, the original had far fewer instruments, but still at least a compass and an airspeed and altitude indicator).

The primary issue won't be in the corridor itself, it'll be getting into and out of it from shared public airspace

You do know that ATC doesn't control all aircraft, right? Do you know what VFR means? How about class G airspace? Instruments aren't needed for all navigation and many pilots aren't even certified for instrument-only flight (look up "Instrument Rating") - in fact, these pilots are 100% self-reliant. ATC can provide traffic advisories and suggested headings if you ask them, but they don't have to and aren't even obligated to (if ATC is overloaded, VFR traffic gets dropped first).

and avoiding collisions between the aircraft themselves, many of which do not have anti-collision systems or even radars.

Tons of privately owned aircraft do not have TCAS and civilian aircraft radar isn't even intended to and cannot show other aircraft. Still, people manage to survive fly-ins and other large-scale GA gathering events even at uncontrolled airports. The key, that every pilot knows, is: look before you turn, say intentions before you act.

Comment: Re:Hype pain (Score 1) 75 75

Their design trades chamber pressure and engine Isp for lower pumping power requirements. They have 9 engines with pumps in the 50HP range, so around 350kW of pumping power. That really isn't able to give much more than 3-4MPa, which also roughly meshes with their claimed Isp figures (~270s at SL). The required power for self-feeding of fuel to the turbine engine is comparatively tiny, perhaps less than 1% of the overall output power requirement. As for cooling, they said they're using regenerative.

Comment: Re:DAB or DAB+? (Score 1) 293 293

112k mono

Is perfectly workable. The lack of a second channel almost cuts bitrate requirements in half. Then again, it's mono, so yuck!

99% of DAB radio is in mono

That's just f'ing atrocious.

The other stereo station on DAB reduced from 192k to 128k

If it's MP2, then yuck again! AAC at 128k is near transparent. MP2 is definitely not!

in no way is that an FM replacement, the dropping bitrate makes even the mono stations sound bad

It would be an FM replacement, *if* they were to use it right. Unfortunately, it seems most stations are hell-bent on crapping all over sound quality to save a few bucks on bandwidth.

Comment: Re:Hype pain (Score 1) 75 75

You can in fact just "dunk" the rotor in LOX.

Have you see this demonstrated on 1000HP-scale motors? Again, scale is the big question here.

Using AC Induction

They're using DC motors. The additional weight of inverters would be quite a cost. And an AC motor would heat up internally as well, away from the cooling liquid. You just can't get around it, as soon as you induce any current, you get losses and heat production. At your 5HP, it may be a non-issue. At >1000HP maybe not so much any more.

They have made the motor. It performs to their specifications.

Yes, and in other posts I have also calculated their specifications. OK performance for a modern hydrocarbon engine, but certainly not amazing. Very power limited (9 engines for only a 10 ton rocket?!) Less efficient than a much larger Merlin 1D and far less efficient than a staged cycle engine. So yeah, compromises, exactly like I said.

The next hardest part is controlling the rocket, which is going to be a damn sight easier with electric fuel pumps (Think fuel injection for your car, same principle).

Eeh, what? Rocket control (by which I presume you mean flight control) has almost nothing to do with engine cycle and everything to do with aerodynamics. Car control also has dick-all to do with fuel injection. A car is equally controllable whether it's fuel injected, carburated, naturally or forced-induction aspirated, etc. Moreover, my point wasn't that they didn't have a working engine. Of course I knew they had. But there's an awful lot of engineering that goes into rocket design besides the engines. It isn't "just a bunch of tubes around the engine". It takes an enormous amount of effort to take an engine which runs on a test stand and building a flyable piece of hardware using it. Take airplanes for instance. Yeah, 25% of the cost is in the engines, but that doesn't mean the remaining 75% doesn't exist. It just means that it's subdivided into millions of other parts, which together mean you've still got a lot of work ahead of yourself. And that's before we get to the regulatory and red-tape stuff that everything with the label "aerospace" is totally swamped with.

They are not using *rechargeable* batteries.

That's what I've been saying all along and I used it in my calculations. See about 4 posts back.

Comment: Re:Hype pain (Score 1) 75 75

Thanks, all of those I already read. Like I said, it's a compromise between cost/complexity and performance. Because their turbopump is so small (50HP really isn't much), they're running 9 engines on the 1st stage. Let that sink in. 9 engines on a 10-ton rocket. 450HP total will also give you quite low chamber pressure (probably in the 3-4MPa range), which pretty much meshes with the Isp I calculated for their first stage (272s at sea level). That's less than a much larger Merlin-1D can manage (282s at SL) and a far cry from what large staged combustion engines can do (RD-180, 311s at SL).
Also, their statement that they can build a Rutherford in 3 days is somewhat dishonest. First of all, they need to build 9 of them (so 27 days) for the 1st stage and one of the main reasons why building rocket engines takes so long is because large engines need custom machining, fitting, welding and subsequent assembly testing. These guys are 3D-printing their parts, so it's a lot simpler. It's really significantly a function of size. If they tried building something the size of a Merlin 1D, I can guarantee you they wouldn't be doing it in 3 days.

We have a equal opportunity Calculus class -- it's fully integrated.