1626: "Judgment Day"

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Re: 1626: "Judgment Day"

Postby orthogon » Thu Jan 07, 2016 1:09 pm UTC

Copper Bezel wrote:Why does Ronald Reagan owe you five pounds?

Mutually assured destruction: not to be confused with mutually assured distraction, which is what happens when you send somebody a TVTropes link. You send them on a wild click chase, but you can't resist being sucked down the rabbit hole yourself.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1626: "Judgment Day"

Postby ijuin » Thu Jan 07, 2016 1:19 pm UTC

I think that CB means that he doesn't get the "You are X and I claim my five pounds" reference.

Anyway, I forget the name of the guy, but there was a famous promotion where he would be seen traveling about England, and fans who recognized him could claim a prize of five pounds by speaking to him and declaring that they were claiming it.

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Re: 1626: "Judgment Day"

Postby gmalivuk » Thu Jan 07, 2016 1:36 pm UTC

ShuRugal wrote:I found the rollover text more intriguing than the main subject of the comic. It got me thinking, what wold be the requirements of a rocket to achieve same-day lunar delivery?

If this post begins to ramble, please forgive me. I am going to tackle this question using this post as my scratch-work page, so my number can be double-checked by someone more studied in rocketry than I:

Spoiler:
Conditions:
1. Package arrives the same day it was ordered
2. Package arrives in same condition it departed the warehouse
3. Amazon specifies a minimum delivery window of 9 hours for same-day service.

Givens:
1. Earth-Moon distance: 384,400 km
2. Moon orbital velocity ~= 1.022 km/s
3. Gravity of Earth (surface) 9.8 m/s/s
4. Gravity of Earth (lunar orbit) 271.72 cm/s/s

If we assume the rocket is launched within 30 minutes of payment, and the package arrives at its final destination within 30 minutes of lunar touchdown, we get an 8-hour trip.
To make this trip, our rocket must have an average velocity of:
384400 / 8 = 48050
48050 / 60^2 = 13.34722 km/s

If we split the time in half, and use 4 hours to accelerate toward orbital altitude, and another 4 hours for braking and orbital insertion (this is the easiest way for me to break down the calculations. Would love to see a more efficient solution) then our peak velocity while achieving orbital altitude is 26.694 km/s.

So, our bare-bones Delta-V requirement (ignoring gravity) appears to be:
--26.694 km/s up
--26.694 km/s brake
+1.022 km/s match speed with moon
= 54.41 km/s + whatever gravity adds

Since our window for delivery is so short, we can't really take advantage of efficient orbital paths, we basically have to go screaming straight up against gravity the whole way (at least until we are close enough for lunar gravity to be dominant). Our average gravitational resistance is 5.036 m/s/s. Applied over our 8-hour trip, and gravity adds:
5.036 * 8 * 60^2 = 145.037 km/s to our delta-V requirements, bringing us to a total of 199.447 km/s of delta-V required to achieve same-day delivery.

using the Tsiolkovsky rocket equation, we can estimate the fuel required to get us this Delta-V. I will assume the following variables:

Delta-V: 199.447 km/s (from calculations above)
exhaust velocity 4.5 km/s (wiki value for bipropellants)
final mass: 5,000 kg (1/3 mass of lunar lander from apollo missions. Amazon now uses remote-piloted lunar rockets)

re-arranging the Tsiolkovsky rocket equation to solve for initial mass is beyond my level of mathematical education (how do i distributive property logarithms?), So i plugged the numbers into Wolfram Alpha and got an initial mass of 8.863e22 kg, about 1.5% the mass of the earth. unfortunately, this much mass is impossible to accelerate that quickly with such a slow exhaust stream...

If we build a rocket with an exhaust velocity of 10 km/s, we only need an initial mass of 2.426 trillion kilograms. If we get our exhaust velocity up to 50 km/s, we now only need 273 metric tons of rocket, and our hit time becomes achievable.

Of course, i'm not entirely certain what would happen if we pointed a 50 km/s exhaust plume at our planet, but i feel like the launch site would not survive.


Needless to say, I don't think Amazon will be offering same-day delivery to the moon any time soon.
While it's true it would be prohibitively propellant-expensive to send something to the Moon in 8 hours, your math is wrong. You're not fighting gravity for 8 hours if you' re slowing down for half of that time, but rather gravity is *helping* you with the deceleration.

Also you can't just add the starting and ending gravitational accelerations and treat that as the average over time, because the acceleration doesn't change linearly with distance and distance doesn't change linearly with time.
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Re: 1626: "Judgment Day"

Postby orthogon » Thu Jan 07, 2016 2:16 pm UTC

ijuin wrote:I think that CB means that she doesn't get the "You are X and I claim my five pounds" reference.

Anyway, I forget the name of the guy, but there was a famous promotion where he would be seen traveling about England, and fans who recognized him could claim a prize of five pounds by speaking to him and declaring that they were claiming it.
[pronoun fixed :-)]

It seems as though it was a different person and name each week, although apparently there were a number of similar competitions run by different newspapers.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1626: "Judgment Day"

Postby Apeiron » Thu Jan 07, 2016 2:25 pm UTC

Sentience wouldn't be enough for a decision like that. My cats are sentient and have no opinions on nuclear weapons. They could never understand what they do.

A SAPIENT entity might be smart enough to realize the folly of mutually assured destruction.

We have different words because they have different meanings.

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Re: 1626: "Judgment Day"

Postby Elroydb » Thu Jan 07, 2016 3:14 pm UTC

I thought SMBC had this one figured out with comic #1852
(I can't post links yet apparently without being flagged as spam :( )

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Re: 1626: "Judgment Day"

Postby Stargazer71 » Thu Jan 07, 2016 3:46 pm UTC

Minutes after the comic, North Korea, having outdated computers still running Windows 10 and functioning nuclear weapons*, then goes to town like a bull in a china shop.

( *though just barely :D )

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Re: 1626: "Judgment Day"

Postby cryptoengineer » Thu Jan 07, 2016 3:50 pm UTC

orthogon wrote:
Copper Bezel wrote:Why does Ronald Reagan owe you five pounds?

Mutually assured destruction: not to be confused with mutually assured distraction, which is what happens when you send somebody a TVTropes link. You send them on a wild click chase, but you can't resist being sucked down the rabbit hole yourself.


The other part is explained here: ...And I Claim My Five Pounds. On the net, it has become shorthand for "you're acting like <an identifiable other person>", and is often abbreviated to AICMFP.

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Re: 1626: "Judgment Day"

Postby orthogon » Thu Jan 07, 2016 3:51 pm UTC

Stargazer71 wrote:Minutes after the comic, North Korea, having outdated computers still running Windows 10 and functioning nuclear weapons*, then goes to town like a bull in a china shop.

( *though just barely :D )

Apparently their "hydrogen bomb" was just slightly more powerful than their previous fission bomb. I can't help wondering whether somebody missed the point and they used the fission device to set fire to some hydrogen gas.
xtifr wrote:... and orthogon merely sounds undecided.

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Re: 1626: "Judgment Day"

Postby Copper Bezel » Thu Jan 07, 2016 3:53 pm UTC

Windows has those mandatory update pushes now, though.

orthogon wrote:[pronoun fixed :-)]

Danke. = ]

It seems as though it was a different person and name each week, although apparently there were a number of similar competitions run by different newspapers.

Yeah, I didn't think to Google the "and I claim my five pounds" and thought maybe sfmans had made a bet with Reagan over MAD or something. Also, Reagan was a nuclear disarmament advocate. = ,

But eidako's prediction is also just too cynical not to love. It's awkwardly true that the last total war we ever had was immediately prior to the arms buildup.
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Re: 1626: "Judgment Day"

Postby dbam987 » Thu Jan 07, 2016 4:03 pm UTC

That will teach the sun for those pesky solar flares!

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Re: 1626: "Judgment Day"

Postby gmalivuk » Thu Jan 07, 2016 4:09 pm UTC

Apeiron wrote:We have different words because they have different meanings.
Then why do we also have so many synonyms and homonyms?
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Re: 1626: "Judgment Day"

Postby wumpus » Thu Jan 07, 2016 4:31 pm UTC

ShuRugal wrote:I found the rollover text more intriguing than the main subject of the comic. It got me thinking, what wold be the requirements of a rocket to achieve same-day lunar delivery?


Oddly enough, the whole topic reminded me of this video: https://www.youtube.com/watch?v=uNS6VKN ... A&index=19
[explanation: Scott Manley, a famous youtuber and ksp guru, decides to help a fellow youtuber who suggests sending all copies of a bad video game into the Sun]

The problem here is that the delta-v needed to launch something into the Sun is roughly equal to the delta-v needed to launch something out of the solar system*. Scott first tries a massive rocket, and fails miserably. Second try Scott does a "reverse" slingshot around Jupiter with delta-v to spare. Oddly enough, not only is [as RAH once said] "Earth orbit [is] halfway to anywhere", but getting out to lunar orbit (and particularly Lagrange point 2) is pretty much all the delta-v you need (plus a ton of CPU time and patience): https://en.wikipedia.org/wiki/Interplan ... rt_Network

So never mind say-day lunar delivery: assuming the computers can make sure that nobody is able to retrieve the missiles, you can launch the missiles to the Sun for the same price as 3-day lunar delivery (assuming you are willing to wait a few years for final delivery).

* Roughly assumed by knowing that delta-v to Earth escape is roughly double the delta-v to orbit the Earth. In any event, going to the Sun is harder than it looks.

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Re: 1626: "Judgment Day"

Postby gmalivuk » Thu Jan 07, 2016 6:07 pm UTC

Additional delta-v to escape is only 41% of circular orbital velocity, and so a smaller fraction of the total delta-v needed to get into orbit in the first place (because getting to orbit in the first place is where you have to deal with gravity drag and atmospheric drag).
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Re: 1626: "Judgment Day"

Postby eidako » Thu Jan 07, 2016 7:53 pm UTC

sfmans wrote:You are Ronald Reagan and I claim my five pounds

#####

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Re: 1626: "Judgment Day"

Postby Copper Bezel » Thu Jan 07, 2016 8:05 pm UTC

gmalivuk wrote:
Apeiron wrote:We have different words because they have different meanings.
Then why do we also have so many synonyms and homonyms?

Look, nobody said it's a good idea, but it's the idea. = .
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

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Re: 1626: "Judgment Day"

Postby kelly_holden » Thu Jan 07, 2016 8:47 pm UTC

Elroydb wrote:I thought SMBC had this one figured out with comic #1852
(I can't post links yet apparently without being flagged as spam :( )

New accounts can't post links.
http://smbc-comics.com/index.php?id=1852

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Re: 1626: "Judgment Day"

Postby Bicycle Bob » Fri Jan 08, 2016 2:54 pm UTC

Those warheads are on ICBMs, people, not IPBMs. They only have enough range to reach Earth.

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Re: 1626: "Judgment Day"

Postby The Moomin » Fri Jan 08, 2016 4:07 pm UTC

Moose Anus wrote:
rhomboidal wrote:
The Moomin wrote:Isn't this Superman IV?

Supercomputers would do as Superman did. It's only logical.
No, not like this. There's not a computer like this in the whole world anyplace. It doesn't exist. You see, we have to build it.


Now that was Superman III wasn't it?
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Re: 1626: "Judgment Day"

Postby Stargazer71 » Fri Jan 08, 2016 4:22 pm UTC

gmalivuk wrote:
Apeiron wrote:We have different words because they have different meanings.
Then why do we also have so many synonyms and homonyms?


Because linguists hate us and want us to be miserable.

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Re: 1626: "Judgment Day"

Postby gmalivuk » Fri Jan 08, 2016 4:39 pm UTC

Bicycle Bob wrote:Those warheads are on ICBMs, people, not IPBMs. They only have enough range to reach Earth.
Hence the booster rockets.
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Re: 1626: "Judgment Day"

Postby ShuRugal » Fri Jan 08, 2016 5:11 pm UTC

gmalivuk wrote:
ShuRugal wrote:I found the rollover text more intriguing than the main subject of the comic. It got me thinking, what wold be the requirements of a rocket to achieve same-day lunar delivery?

If this post begins to ramble, please forgive me. I am going to tackle this question using this post as my scratch-work page, so my number can be double-checked by someone more studied in rocketry than I:

Spoiler:
Conditions:
1. Package arrives the same day it was ordered
2. Package arrives in same condition it departed the warehouse
3. Amazon specifies a minimum delivery window of 9 hours for same-day service.

Givens:
1. Earth-Moon distance: 384,400 km
2. Moon orbital velocity ~= 1.022 km/s
3. Gravity of Earth (surface) 9.8 m/s/s
4. Gravity of Earth (lunar orbit) 271.72 cm/s/s

If we assume the rocket is launched within 30 minutes of payment, and the package arrives at its final destination within 30 minutes of lunar touchdown, we get an 8-hour trip.
To make this trip, our rocket must have an average velocity of:
384400 / 8 = 48050
48050 / 60^2 = 13.34722 km/s

If we split the time in half, and use 4 hours to accelerate toward orbital altitude, and another 4 hours for braking and orbital insertion (this is the easiest way for me to break down the calculations. Would love to see a more efficient solution) then our peak velocity while achieving orbital altitude is 26.694 km/s.

So, our bare-bones Delta-V requirement (ignoring gravity) appears to be:
--26.694 km/s up
--26.694 km/s brake
+1.022 km/s match speed with moon
= 54.41 km/s + whatever gravity adds

Since our window for delivery is so short, we can't really take advantage of efficient orbital paths, we basically have to go screaming straight up against gravity the whole way (at least until we are close enough for lunar gravity to be dominant). Our average gravitational resistance is 5.036 m/s/s. Applied over our 8-hour trip, and gravity adds:
5.036 * 8 * 60^2 = 145.037 km/s to our delta-V requirements, bringing us to a total of 199.447 km/s of delta-V required to achieve same-day delivery.

using the Tsiolkovsky rocket equation, we can estimate the fuel required to get us this Delta-V. I will assume the following variables:

Delta-V: 199.447 km/s (from calculations above)
exhaust velocity 4.5 km/s (wiki value for bipropellants)
final mass: 5,000 kg (1/3 mass of lunar lander from apollo missions. Amazon now uses remote-piloted lunar rockets)

re-arranging the Tsiolkovsky rocket equation to solve for initial mass is beyond my level of mathematical education (how do i distributive property logarithms?), So i plugged the numbers into Wolfram Alpha and got an initial mass of 8.863e22 kg, about 1.5% the mass of the earth. unfortunately, this much mass is impossible to accelerate that quickly with such a slow exhaust stream...

If we build a rocket with an exhaust velocity of 10 km/s, we only need an initial mass of 2.426 trillion kilograms. If we get our exhaust velocity up to 50 km/s, we now only need 273 metric tons of rocket, and our hit time becomes achievable.

Of course, i'm not entirely certain what would happen if we pointed a 50 km/s exhaust plume at our planet, but i feel like the launch site would not survive.


Needless to say, I don't think Amazon will be offering same-day delivery to the moon any time soon.
While it's true it would be prohibitively propellant-expensive to send something to the Moon in 8 hours, your math is wrong. You're not fighting gravity for 8 hours if you' re slowing down for half of that time, but rather gravity is *helping* you with the deceleration.

Also you can't just add the starting and ending gravitational accelerations and treat that as the average over time, because the acceleration doesn't change linearly with distance and distance doesn't change linearly with time.



You know, I completely forgot to account for gravity braking. When I started mathing, I had intended to, but it slipped my mind by the time i got there.

Anyway, do you know/would you care to share a solution to account for the errors?

wumpus wrote:Oddly enough, not only is [as RAH once said] "Earth orbit [is] halfway to anywhere", but getting out to lunar orbit (and particularly Lagrange point 2) is pretty much all the delta-v you need (plus a ton of CPU time and patience): https://en.wikipedia.org/wiki/Interplan ... rt_Network


I remember reading this article years ago. Fascinating stuff.

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Re: 1626: "Judgment Day"

Postby BillGawne » Fri Jan 08, 2016 7:50 pm UTC

May as well just launch them out of the solar system. It takes less energy.

For getting to the sun delta v = 31.8 km/s
For getting out of the solar system delta v = 16.65 km/s

Of course that assumes you have a booster capable of providing that much delta v.

(I made the same mistaken assumption once, myself. It's easy to do.)

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Re: 1626: "Judgment Day"

Postby Eshru » Sun Jan 10, 2016 9:50 am UTC

If Amazon was delivering packages to the moon same day, they'd build a space elevator, duh.


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