Posts by JeffyPoooh

Re: I wonder what the latency of this is?

In this thought experiment, it's more like 'reductio ad absurdum' memory.

Which is to say, if it were, it would be, but it obviously isn't. Which is the point of course.

Merry Xmas!

Re: Party Trick

NeilPost "...having to carry....20% more fuel..."

Mush is quoted as it's a 30% ***reduction in payload***. Not 20-30% "more fuel".

Payload to fuel mass ratio is a small fraction.

So extra fuel (and including vanes and legs) is 30% x a small fraction.

Cheers.

Re: Party Trick

NeilPost "Think of all the extra fuel needed to be carried all the way into space and back to allow this."

Much less fuel than your instincts are suggesting.

Musk has stated that the Return to Land approach (fuel and extra gear) imposes 30% reduction on payload. NOT 30% extra fuel mass, but 30% less payload. Payload mass is a very small fraction of initial fuel mass. So that's 30% multiplied by some very small fraction.

Although the 1st stage looks much the same landing as it did at launch, it's then nearly empty of fuel and is thus vastly less mass.

People are visual creatures, and one can't see that it's essentially empty at landing.

They should make it transparent so that everyone can more easily understand.

Merry Xmas!!

Re: Real numbers would be interesting (space debris)

I noticed that the shroud panels were jettisoned surprisingly (to me) early in the ascent. It made me wonder if that was intentional, in order to ensure that the panels were low enough and slow enough to ensure that they will definitely reenter quickly.

I've seen plenty of old NASA launches (videos) where the shroud panel were finally jettisoned after reaching the parking orbit. Meaning that those shroud panels will certainly become space junk for months or years.

If this detail is as I suspect, then kudos.

Re. "...the first footprints on Mars be made..."

Prediction. The first footprints on Mars be made by somebody from the NHK/Discovery Channel joint venture video crew that lands a few days before 'The Big Event' to set up. Actual first person will probably be some previously unknown caterer running outside to set up the snacks table.

It'll be months later before anyone twigs, "Hey, who videoed this 'first step' anyway? Oh. Oh my gawd..."

Re: Real numbers would be interesting

Credas: "...has to leave fuel unburnt to power it's descent. ...mass taken off the rest of the payload. You end up with a much bigger, and hence more expensive, launcher than a non-reusable one for the same payload. ..."

It's a bit unobvious, until you think about it, that the amount of extra fuel required is quite small when compared to the initial mass of fuel required for launch. Because the first stage mass is mostly fuel, once it's reached initial MECO, then it's much less mass. So the retro-burn and re-entry is dealing with a very low mass vehicle. Surprisingly so.

Also, even if the 1st Stage was twice the cost for the reason you've listed (but it clearly isn't twice), if it can be reused even just three times, then you're ahead on the deal. If it can be reused dozens of time, well - you do the math.

In summary, it's a*obviously* a very clever strategy. Your objections are all true, but are obviously swamped out by the basic math.

Re: Let's just say that...

I posted an obvious point about driverless cars vice congestion, and AceRimmer replied with some assumptions about "ride sharing" and essentially driverless taxi cabs. Ride Sharing with taxi cabs is as feasible now as it would be with driverless cars. Which is to say, not really (for many reasons); else it would be commonplace (which it isn't).

Plenty of muddled thinking on this topic.

Re: Let's just say that...

Cynic_999: on replacing private cars with driverless taxis

Replacing parked private cars with empty driverless cars driving back for more passengers points towards a DOUBLING of traffic congestion during rush hours.

Yes, the parking garages will be much less full. But the roads will be twice as jammed. By cars wandering around twice as much.

PS. Wasted fuel too.

If you doubt this common sense prediction, then go to Manhattan NYC and look at the swarming masses of yellow cabs, many empty of passengers, on their way somewhere.

Too much unthinking hype on driverless cars.

Re: Returned to Earth

ZSn offered "With a heavy load of fuel in the tanks..."

At launch, yes.

But at retroburn, much much less.

At landing, hardly any.

Re: Return to Earth

Chris: "...cargo of 11 satellites (i'm guessing tiny ones)..."

Their *smallest* dimension ('height') is reportedly about 0.5m. 380 lbs each.

So smallish, but certainly not "tiny".

"...spaceships land like this... ...Sci-i..."

Alister: "Isn't it curious how we've seen spaceships land like this for decades in Sci-Fi films and TV shows, but to see it actually happen for real somehow is just so much more awesome."

Space vehicles landing vertically has been done before.

At least six times.

On the Moon.

Starting in the 1960s.

Re: That's stage 1 sorted

Peter Ford asked about Stage 2.

It flames through the atmosphere at 17,000 mph and what's left splashes into the ocean in a traditional manner.

They mention that they intentionally deorbit it (retro-burn), which is nice since it was some 630 km up. Otherwise it'd be space junk for nearly forever.

How about we get them modern electricity grids and cheap reliable energy first?

That'd be those 2600+ Coal Fired power stations that are planned to be built over the next decade or so, thus ensuring a nightmare 4°C global average temperature rise (if we believe the predictions).

How about we invent something better FIRST?

Re: I you want a guarantee, get a toaster

So, how do you certify a Machine Learning system to Level 'C'?

Answer: You can't. Not practically.

In reality, the system might not recognize pedestrians wearing kilts. You just don't know.

Testing (vice Analysis) to the required level of safety will take a Very Long Time.

Re: @JeffyPoooh Silver badge

@Tom 13

You're confused. The original issue was with the phrase "sum of speeds".

With two cars in a head-on collision, you may SUM THE MASS, not sum the speeds.

So with two cars, each brings their own energy. But it's distributed between the TWO cars. Indistinguishable from each hitting a brick wall.

This is high school Physics.

If you know the Physics, then perhaps it's a reading comprehension problem on your part.

Re: @Charlie 9

@DaLo

Your discussion includes "an immovable Car2" which is a VERY poor choice of an example.

Do you mean that Car 2 is parked but ready to move with impact, or it's fixed in place like a 'brick wall' ? Does it have crumple zones? Is it in Neutral, or Park? How good are the tires on Car 2?

Makes your entire argument unclear.

Re: Here in California ...

jake "...you can be cited for this ... "

Citation are issued at the whim of the officer. I doubt that such a ticket would survive review by the prosecution, let alone a judge. A phone call to the prosecution would make it go away.

Many people are confused on this point. Similar to 'You can be sued...'.

Re: What's funny...

AC: "Strong AI does exist today..."

BS.

AI exists, arguably.

Strong AI is still a dream.

@Charlie 9

"Now you have two cars crashing at the sum of their respective speeds..."

That's not how Physics works. Summing non-relativistic speeds, which are squared in the energy formula, would lead to creation of energy from nothing.

If two cars (same mass) doing 100 kmh crash head-on, that's basically the same as each hitting a brick wall at the very same, non-summed, 100 kmh.

Using bold print and being wrong must be embarrassing.

Re: "thousand-qubit"

Quantum annealing is suppose to instantaneously consider all possible solutions at once, and then settle on the solution directly.

Factoring a big number becomes simple multiplication, f1 x f2 = given big integer

Assuming you'd have to use a legacy algorithm is obviously nonsense. Why on Earth would you make that assumption?

If a D-wave can't perform this simple canonical problem on demand, then it smells like BS-ware.

PS, your stackexchange link has a highly rated answer that supports my position.