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Comment: Re:It doesn't work that way. (Score 1) 110

by DerekLyons (#49500315) Attached to: An Engineering Analysis of the Falcon 9 First Stage Landing Failure

what we're saying is that arranging for velocity AND position to be 'null' at the same time is harder than simply arranging for velocity to be null and position to be +/- 100m(or so).

*Sigh*
 
I understand what you're saying - but as with my previously reply, you don't grasp the problem.
 
The appearance of the vehicle "working hard at the last second" during the first attempt was a consequence of running out of hydraulic fluid - and would have occurred regardless of the size of the target. The appearance of the vehicle "working hard at the last second" during the last attempt was a consequence of the throttle valve not operating to spec - and would have occurred regardless of the size of the target.
 
From the point of view of the final landing sequence it's not all that much easier to arrange for velocity to be null and position to be +/- 100m than it is to arrange the same +/- 1m. Selecting a landing point occurs at a relatively high altitude (and on a, relatively speaking, relaxed timeline) and final trim starts around a kilometer or so up (AIUI). From there, jittering the variables (burn time and timing, gimbal angles, and throttle settings) a tiny amount one way or another to maintain targeting isn't a substantial burden (on the software or the hardware) compared to the much larger problem of nulling your velocities.

You're talking about some kind of articulated arm (which can survive being essentially inside rocket exhaust)

I think you're picturing something different. I'm picturing something pretty big that comes in from the sides, staying well away from the exhaust.

That just makes an already heavy, complex, and expensive system even heavier, more complex, and more expensive than I envisioned.

Comment: It doesn't work that way. (Score 1) 110

You're not getting what he was saying.

I do get what he's saying. What neither of you seem to grasp is that the size of the target isn't as relevant as you think, because you have to null your horizontal velocity regardless of the size of the target. It doesn't matter whether you're stopping on a postage stamp or anywhere in a given block - either way you still have to stop. It's the stopping that's problem, not the deciding where to stop. Stopping is very difficult for the Falcon 9 because it's T/W ratio is so far out of the optimal range and a larger target area won't make it all that much easier.
 

Though if they're that good at targeting, maybe programming up an adaptive 'catcher' robot would work? I'm thinking of something along the lines of 3 arms that have a range of motion, and when the rocket's within a few feet, they gently 'grab' the rocket using shaped and padded interfaces(I'm picturing a semi-circle matching that of the rocket) and provide stability.

That's "good at targeting" a couple of orders of magnitude better than what they've demonstrated to date (which is, pardon my french, already pretty fucking amazing). You're talking about some kind of articulated arm (which can survive being essentially inside rocket exhaust)... Which is, quite frankly, makes things much harder and more complicated and introduces a metric buttload of additional possible points of failure. Much easier to simply re-engineer the throttle valve.

Comment: Neither failure was due to target size (Score 1) 110

by DerekLyons (#49490349) Attached to: An Engineering Analysis of the Falcon 9 First Stage Landing Failure

The rest of what you say is generally true, although a larger target *would* help. The advantage of a larger target is that, while you still have to zero your horizontal velocity, you don't have to zero it anywhere terribly precise.

Yeah, you do. Given the narrow footprint and the low CG of the vehicle, if the horizontal velocity wasn't as close to zero as you can get at touchdown - it's very likely to tip over. (Even if you don't damage the landing legs in the process.) The upper part of the vehicle isn't heavy, but it has a very long lever arm.
 

You can pick an optimal set of thrusts that results in the correct orientation and velocities (horizontal and vertical) without worrying overmuch *where* that series of thrusts has you touching down.

In the end, that makes far less difference than you think because while you can reduce the amount of horizontal velocity that needs to be nulled you cannot eliminate it. (Not without launch criteria that include "near zero wind at the recovery site", which is beyond impractical.) The result is, with the current vehicle, you still have to null horizontal velocity at the last second before touch down. The basic problem is that the vehicle is badly designed for what it's being asked to do.
 

. Both attempts so far clearly demonstrate the ability to do an excellent good job of targeting a (relatively) tiny barge, but currently, if the rocket would come down even 100' (30m) to one side of its target spot, it needs to induce a horizontal momentum (which requires leaving a vertical attitude as well, it can't just translate sideways) and then null that momentum at the right moment (and fix its attitude). That's hard.

Both times they've hit the barge almost dead center - I fail to see how that's an arguement for a larger landing area since neither failure was caused by the landing area being too small. Both vehicles would have crashed regardless of the size of the landing area due to control system failures. (Attitude control on the first, throttle control on the second.) That's what neither you nor the OP seem to grasp.

Comment: Re:Video from the barge (Score 4, Informative) 110

by DerekLyons (#49489741) Attached to: An Engineering Analysis of the Falcon 9 First Stage Landing Failure

Kind of makes me wonder if using the barge as such a small target is contributing to the hard landings, simply because it's such a tiny target relative to the area that the rocket has to come down on

Since the first attempt hard landed because it ran out of attitude control gas, and the second hard landed because of a control valve problem... how would a larger target have helped? In case of the first attempt, you've still got to control your attitude regardless of the size of the field. In the second, the size of the field is irrelevant if you can't properly control the vehicle in the first place.

Seriously, don't be misled by the frantic activity in the final seconds of the most recent attempt. That burst of activity was the vehicle attempting to null it's horizontal velocity and then trim it's attitude before landing - something it has to do regardless of the size of the field.

The basic flaw in the landing sequence isn't the size of the target, it's the design of the vehicle. Its minimum T/W ratio is well over unity at landing, meaning it can't hover, can't ease itself down, and you have to take great care to not end up with positive vertical velocity. The only way it can land (with any reasonable sized target) is to approach at high speed, then at the last second try to null horizontal velocity without excessively reducing vertical velocity (I.E. bouncing), followed by a return to vertical and touchdown.

You could avoid this by having a circle of paved ground a quarter to half a mile in diameter - but that's not cheap to build or maintain given the need to resist a rocket's exhaust. Long term, given that the tests are essentially free*, it's cheaper and easier to figure out how to land precisely on a smaller target.

* The first stage is bought and paid for by the launch customer - and so long as the added equipment for landing poses no undue risk during ascent, they don't care what happens to it after separation.

Comment: Re:Larger landing area (Score 1) 340

It sure seems that if a larger landing area was available, so that the rocket didn't have to lean so far to adjust to a very small target and thus could prioritize staying vertical, it would be able to land successfully.

No so much as you might think - you still have to trim and eventually null your horizontal velocity, and null any horizontal residuals arising from trying to remain vertical. It's a complicated problem, even if you're just aiming for an arbitrary landing spot in a larger landing area.

On top of that, the crash seems to have been caused not by prioritization, but by a control valve operating sluggishly causing the response time to go out of limits. Even if you're just accepting a landing wherever you're coming down, if the control system gets out of phase you're screwed.

Comment: Re:Basement-dwelling Introverts (Score 1) 137

by DerekLyons (#49477837) Attached to: Road To Mars: Solving the Isolation Problem

So just send people who are happiest sitting at the same keyboard for days if not hours on end, with minimal human interaction.

The truth is, that kind of person is damn near the worst choice possible and the polar opposite of the kind of person you need.
 
You don't need someone who can't or won't deal with individuals. You need someone who can deal with forced close quarters interactions with individuals while also being able to deal with near complete isolation from society. These are two very different kinds of people.
 
The crew of a Mars-bound craft will invariably be forced into contact with each other due to the small size of the vehicle. On top of that, they must come together as a team because much of what they'll be doing will be done with close coordination in close proximity to each other. Someone who willingly isolates himself (or worse yet deliberately isolates himself) psychologically and socially from his crewmates over a long term is thus more of a liability than an asset because he'll have a hard time coming together and remaining as part of the team (if he can do so at all).
 
The latter (near complete isolation from society) is actually the difficult part. Unless they're truly out at the end of the bell curve (and thus edging on being mentally ill), all but the most introverted basement dweller has email, guild chat, chatrooms, forums and blog comments, social media, and other forms of real time or near real time communications. (Not to mention shared experiences and events as raids, game releases and updates, movie releases, etc...) They've isolated themselves from close physical contact with individuals, but they're still in close social and psychological contact and interaction with society. (Very few people actually willingly completely cut themselves off from society.) Onboard a Mars bound spacecraft, that close contact and interaction (fostered by real time and near real time communications) and those shared events and experiences will be nearly completely absent - not just due to speed-of-light delay, but due to limited communications bandwidth.
 
Disclaimer: Former SSBN crewman, been there, done that, got the t-shirt. (Or at least about as close as you can get without actually being an astronaut.)

Comment: Re:Olde-timey carbon fuel (Score 1) 362

by DerekLyons (#49473069) Attached to: Can Civilization Reboot Without Fossil Fuels?

Why does everyone assume we need to make more steel? There will be plenty of it around for re-purposing.

*Sigh*
Nobody is assuming that. That's why nobody has discussed iron ores - only fuels.
 

We may need fuel to help rework the steel into different uses, but certainly not to smelt the raw materials to make brand new stuff.

Yes, we'll fuels - in literally mountainous quantities. And fuel will be very hard to come by.

Comment: Re:Olde-timey carbon fuel (Score 1) 362

by DerekLyons (#49473017) Attached to: Can Civilization Reboot Without Fossil Fuels?

Last I heard we weren't anywhere close to running out of coal, there is literally mountains of the stuff still around and relatively easily available.

Welcome to 2015 - where coal isn't still "relatively easily" available. Surface deposits and those that can be mined without serious powered machinery have been gone for most of a century.
 

Steel and iron production would probably happen on a smaller scale but you'd have huge quantities of it still sitting around waiting to be recycled.

Without massive amounts of charcoal, coke, or coal - you aren't recycling significant amounts of anything.
 

The one thing that I can think of that could be problematic would be making plastics in a world with less available oil.

Then, frankly, while you may be thinking - you're not very well informed.

Comment: Re:Yes (Score 1) 362

by DerekLyons (#49469913) Attached to: Can Civilization Reboot Without Fossil Fuels?

If you're "re-booting" civilization, then you don't have an established market to upset, so there aren't the same issues.

Just because there aren't the same issues doesn't mean there aren't different and equally intractable issues - such as the lack of cheap long distance transport, and the lack of cheap fertilizers and high performance farm machinery. The result is that you still end up in the same place we are today - bio-diesel competing with food over scarce resources.
 

The first electric cars were made in the 1800's, but they didn't get much of a chance then, because fossil fuel powered cars were there. Without fossil fuels, they would probably have been developed faster and become much more significant.

Sure, so long as we handwave away the fact that electrical cars only existed because of the existence of a massive fossil fuel powered industrial infrastructure.

Comment: Re:Olde-timey carbon fuel (Score 5, Informative) 362

by DerekLyons (#49469815) Attached to: Can Civilization Reboot Without Fossil Fuels?

The classic multipurpose "biodeiesel" of old was charcoal, a renewable source of fuel for high-temperature furnaces suitable for making iron and high-quality steel.

Yes... and no. During the charcoal era, iron and steel were produced in very small quantities because the amount of fuel and labor needed to produce the charcoal was immense. (And resulted in massive deforestation.) What make iron and steel cheap and powered the industrial revolution wasn't charcoal, it was coke - a fossil fuel.
 

It [charcoal] doesn't require any process plant or chemicals to produce after all.

Yes... and no. Low tech methods of producing charcoal typically involve losing as much as 80% of the process material to produce mostly low quality (I.E. insufficient for iron and steel making) charcoal.
 

Lower-temperature needs such as locomotive and boiler steam could be met with simple logging of reforested areas without the extra step of turning wood into charcoal.

In a low population, charcoal powered scenario, you're unlikely to have locomotives and boilers - it would take literally decades and square miles of forest to produce sufficient iron and steel.

What most people don't grasp when they postulate post-apocalyptic scenarios is the synergistic nature of the advances that powered the industrial revolution - and that ultimately fossil fuels lay at the root of them all. Coke for cheap steel and coal for cheap long distance transportation in particular.

Comment: Re:Why a one-second launch window? (Score 3, Interesting) 77

by DerekLyons (#49466671) Attached to: SpaceX Launch Postponed

You're remembering wrong. Most ISS launches have windows a few seconds wide, at most. There's a lot of stuff in LEO, all moving very fast, If you want a course that will hit the ISS at exactly the right speed, and not come too close to anything else, you've got a narrow window to do it in.

You're explaining wrong. It has nothing to do with "other stuff" in LEO, and everything to do with the ISS's high inclination orbit. The plane of the orbit only passes over Cape Canaveral at intervals, and if you miss that window it will take excessive energy to match planes with the ISS.
 

You *can* launch outside that window (space is a big place), but it eats into your fuel and safety margins and usually there's no reason to do that.

Um, no. The width of the window is determined by the performance (available energy) of the booster and payload - you can't launch outside of it at all and reach the target. That's why windows exist in the first place.

Comment: Re:"Old" vs "new" trolling (Score 1) 278

I'd use "trolling" myself, because the action and the result of both"traditional" and "new" trolling are functionally indistinguishable. The "non-malicious" claim is a distinction without a difference as intentionally disrupting a list (or group, or forum, or whatever) is malicious on the face of it. In the end, both are intentional actions performed by and for the benefit of the troll to the detriment of the discussion.

Comment: Re:"Old" vs "new" trolling (Score 1) 278

Today the media conflates "trolling" with "abusive asshole." I think they misunderstand the word "troll." "Trolling" meant "fishing." To dangle bait for newbs to take and work themselves into a lather, and then laugh at those who don't get the joke. It was performance art.

*Sigh*. For as literate and educated (generally speaking, though not as much as they believe) as Slashdot is, one basic concept seems to continually elude them - words and their meanings do change. In this case, the so-called "classical" meaning of "troll" vanished not long after the start of Endless September. The "new" meaning (an individual that's deliberately abusive or deliberately fans the flames) has been the more commonly used one for a very long time.

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