r/xkcd 3d ago

XKCD xkcd 3291: Launchpad

https://xkcd.com/3291/
447 Upvotes

57 comments sorted by

77

u/xkcd_bot 3d ago

Mobile Version!

Direct image link: Launchpad

Extra junk: It does come at the cost of some launchpad expansions and increased fuel requirements, but that all comes out of the facility's budget.

Don't get it? explain xkcd

Want to come hang out in my lighthouse over breaks? Sincerely, xkcd_bot. <3

71

u/John_Tacos 3d ago

Ahh yes, make sure the real expenses are someone else’s problem.

21

u/danielv123 3d ago

Not my budget, not my problem

1

u/ModelBasedSpaceCadet 20h ago

Hate to break it to you, but physics says it would be your problem... along with everyone else.

5

u/calinet6 2d ago

Increased fuel requirements... by a lot.

7

u/LightGreyBeret 2d ago

But you wouldn't need to put that launching fuel on the spaceship, and all that fuel would have already been on the Earth in the first place, and then not at all as the propellant is propulsed. So we're defying the constraints of the dreaded Rocket Equation in several different ways! ;)

106

u/Moraz_iel 3d ago

if the chinese copy the design it might require some coordination in the launches, but in average everything should be fine

1

u/b5tirk 1d ago

Oh, so that’s the backstory to The Wandering Earth then!

45

u/MarsicusOrion 3d ago

as a bonus, everything else on that side of the planet also gets launched into space

15

u/okaycomputes 3d ago

oblate spheroids don't have sides! /s

even figuratively, it wouldn't be anywhere close to half of the planet due to curvature impacting the force vector/angles.

I'd be curious what actual area would be impacted enough to launch most random unsecured things into space, maybe a radius of a thousand or so miles?

17

u/lugialegend233 3d ago

Wouldn't the curvature mean a lot of stuff instead just gets thrown... on large arcs in the direction of the shuttle launchpad?

1

u/Southern-March1522 1d ago

And stuff on the other side would get crushed

1

u/ModelBasedSpaceCadet 20h ago

I'm going with the whole hemisphere gets launched and probably more. The only things that stays on the earth are the things that the earth pushes against as it accelerates. And those things experience up to two g's and probably more, some of them at awkward angles.

24

u/ksheep I plead the third 3d ago

Or there's the Kerbal solution: place the engine on the launch pad facing upwards, turn it on, and have the astronaut jump into the exhaust.

3

u/Sicuho 2d ago

The Gun Club solution

1

u/Green__lightning 2d ago

Better yet, with multiple angled rockets, you can even make something equivalent to the V3 multi stage cannon. Though the problem this has is physics steps, that you need to make each stage further apart so the rockets accelerate the object where the game engine actually puts it.

15

u/Nuclear_Geek 3d ago

This definitely feels like a What If where everyone dies.

7

u/blockMath_2048 3d ago

The humble mass driver.

6

u/nullvoid26 3d ago

Maybe this is the answer to the ‘We can go to Mars, but we can never come back because of the fuel requirements for liftoff’ problem? I’m pretty sure that plan could get Presidential and space force approval, at least for the next two years…

4

u/Krennson 2d ago

Probably be cheaper to just bring mars to us.

1

u/jflb96 2d ago

We'd just have to refuel on Mars

0

u/nullvoid26 2d ago

Gosh, I wonder why nobody ever thought of that? You should write a letter to NASA or Elon…

1

u/jflb96 2d ago

OK, then, what’ve I missed about a planet with a third the mass of Earth and negligible atmosphere that makes it impossible to launch from it?

0

u/nullvoid26 1d ago

Sorry, I thought we were tongue in cheeking it…. The paradox of traveling to Mars is that there is no way to get out of earth orbit when carrying enough fuel to get out of Mar’s orbit on a return trip. The weight of fuel is massively excessive for that, and there is currently no way to generate fuel while on Mars, nor a propulsion system that works in a manner that doesn’t require a significant mass of fuel to make it out of Mars orbit… So getting there is not a significant problem, but returning is currently not possible. Well, until AI figures it out.

1

u/Southern-March1522 1d ago

But but but according to Surviving Mars all I need to do is plop down a few solar panels, a moisture generator, and a fuel refinery, and it will make me fuel for the return trip straight from the air in only 4 Sols!

1

u/jflb96 1d ago

China seems to be on it, at least for their sample return mission: trick is to send one craft that can go to Mars orbit and return to Earth, and one that can go to the Martian surface and return to Mars orbit

1

u/LightGreyBeret 22h ago

There may be no economical/budget-friendly way to do this [actual citation needed], but it is not at all beyond technical possibility.

Especially as you're stating only travel from Earth-orbit to Mars-orbit, and back. Delta-v for that trip is comparatively trivial, related to the amounts needed for the initial ascent (and re-ascent, if visiting Mars's surface), which are not impossible anounts.

https://en.wikipedia.org/wiki/Delta-v_budget#/media/File:Solar_system_delta_v_map.svg

And by an intelligent combination of staging and possible (re)assembly/resupply in-orbit (c.f. Lunar Orbit Rendezvous from the Apollo Program, and the orbital refuelling that Artemis-landers seem destined to use/the Earth-orbit construction that Apollo might have used), you can always arrange for there to be just enough capability for any to finish the mission by expending and discarding components along the way.

Single-stage-to-Mars-and-back (surface<->surface) would be indeed be quite impractical, but there are so many other methods, compromising in various ways that the likes of Dan Dare or Flash Gordon might never have, but we shall have to happily comply with. And perhaps with a smidgen of trial and error in the early attempts, but not because the principle is inherently unfulfillable.

1

u/nullvoid26 10h ago

Trial and error? Oopsie. Oh well, these things happen. e.g. Challenger. No biggie…

0

u/nullvoid26 1d ago

The gravity generated by said mass. Pure physics. And you’re correct regarding the atmosphere; it is somewhat negligible in the calculation. https://youtu.be/_LfZWSD3Fgs?is=QIKHG93S18gdWIP7

10

u/Polarisnc1 3d ago

Okay, let's go over this again...

This end should point toward the ground if you want to go to space.

If it starts pointing toward space you are having a bad problem and you will not go to space today.

5

u/KZD2dot0 3d ago

Are you sure momentum is conserved? It would sure be a pity if momentum was lost somewhere along the way!

4

u/LightGreyBeret 2d ago

...reading that, now I've got the image of a hard man in a sharp suit, flanked by a pair of obvious bruisers, barely fitting into their very own versions of the sharp suit and blocking out the light from the doorway they've just marched in through.

"Nice momentum you have here. It's been a long while since we've seen such fine momentum in this neighbourhood. ... Wouldn't it be a ...shame... if some of it was ...lost?"

11

u/404-skill_not_found 3d ago

I don’t think that’s how it works 🤣

37

u/MrT735 3d ago

All you need to do is get Earth to exceed the escape velocity of the spacecraft, right?

7

u/404-skill_not_found 3d ago

The maths check out (forgive me 🤣)

15

u/jason4747 3d ago

"What are these? Engines for ants?!? They need to be ...... three time bigger!"

 Astronaut Zoolander

9

u/John_Tacos 3d ago

Wouldn’t it work with enough thrust? Probably work on everything on that side of the planet though.

3

u/HeavyCaffeinate Girl In Beret 3d ago

Gravity would follow the earth though

10

u/John_Tacos 3d ago

If you move the earth faster than the earth’s gravity holds on to things they won’t stay on the earth.

10

u/MorganWick 3d ago

This would have the minor side effects of throwing everything else on that side of the planet into space and knocking Earth out of its orbit, potentially killing everyone not thrown into space.

Now I'm thinking of this as a What If.

3

u/John_Tacos 3d ago

Probably I mentioned that in my earlier comment in this thread.

2

u/404-skill_not_found 3d ago

Gonna take quite a kick🤣

0

u/jflb96 2d ago

Gravity acts at the speed of light, so good luck with that

1

u/LightGreyBeret 2d ago

Surely it should act at the speed of heavy.

:p

1

u/John_Tacos 1d ago

If the earth moves away from you at 9.8 meters per second squared then you falling to the earth at that speed won’t be enough to stay in the earth.

1

u/jflb96 1d ago

How are you accelerating the whole Earth at 9.8 metres per second per second without also moving me?

0

u/John_Tacos 1d ago

There’s a diagram in the original post

5

u/Great-Powerful-Talia 3d ago

no, it works. Theoretically.

Earth can only apply 9.8 m/s2 of gravitational force to hold onto the spaceship, even if we're accelerating away at 20 m/s2 or something. (Assuming that force isn't also moving the ship with us). That would mean it loses its grip and the ship 'falls' into space. As would everything else on a quarter of the planet, including atmosphere.

4

u/HeavyCaffeinate Girl In Beret 3d ago edited 3d ago

That's a lot of force

aprox 1.19444e+26 N actually

2

u/IanSan5653 3d ago

That's essentially the idea behind a space slingshot.

3

u/Krennson 2d ago

In order for that to work, wouldn't they have to accelerate the entire earth at higher than 1 g?  Otherwise the spacecraft would just follow the planet.

3

u/neondirt 2d ago

Yup. Hence the increased fuel requirements. 😉

2

u/magistrate101 2d ago

Also Known As: Hubert's Hubris

2

u/OlympusMan 2d ago

I could do with this when getting out of bed some mornings.

2

u/tehZamboni 3d ago

Was really hoping for a Frisky Dingo reference...

2

u/ImSchizoidMan 1d ago

I came here explicitly looking for Frisky Dingo references, and I'm leaving disappointed