What-if 0007: "Everybody Out"

What if there was a forum for discussing these?

Moderators: Moderators General, Prelates, Magistrates

Eutychus
Posts: 448
Joined: Mon Jan 25, 2010 6:01 am UTC
Location: France

What-if 0007: "Everybody Out"

Postby Eutychus » Tue Aug 14, 2012 12:11 pm UTC

http://what-if.xkcd.com/7/

Urban France in mid-August can kind of feel like everybody's left the planet already.
Be very careful about rectilinear assumptions. Raptors could be hiding there - ucim

User avatar
ryzvonusef (1151717)
Posts: 34
Joined: Tue Feb 10, 2009 6:16 pm UTC
Location: Pakistan

Re: What-if 0007: Everybody Out

Postby ryzvonusef (1151717) » Tue Aug 14, 2012 12:23 pm UTC

Lame pun at end, why didn't I expect that?

Vroomfundel
Posts: 118
Joined: Wed Sep 29, 2010 7:36 am UTC

Re: What-if 0007: Everybody Out

Postby Vroomfundel » Tue Aug 14, 2012 12:31 pm UTC

Why lame? I liked the pun.

Anyway, I was short of wonder-struck by the scientific revelations of this one - I could have more arrived more or less the same conclusions myself - but my fascination with atomic spaceflight was once again rekindled by the mention of Project Orion. There is a film about it (http://www.imdb.com/title/tt1039992/) that I have been frantically looking for but failed to find - so any leads are welcome - and of course I'm buying the book :-) I won't be surprised if there is a peak in the sales after this post - the XKCD audience is both vast and probably interested in projects that are 1) capable of sending 10,000 people to Mars, 2) probably feasible and 3) find some use of the world's more than 30,000 nuclear warheads (other than destroying humanity several times over)
lexicum.net - my vocabulary learning platform

User avatar
AvatarIII
Posts: 2098
Joined: Fri Apr 08, 2011 12:28 pm UTC
Location: W.Sussex, UK

Re: What-if 0007: Everybody Out

Postby AvatarIII » Tue Aug 14, 2012 12:35 pm UTC

So the answer is that while sending one person into space is easy, getting all of us there would tax our resources to the limit and possibly destroy the planet.

So what? We've already assumed that we can't stay on Earth any more,
we’ll assume we don’t have to find a new home, but we can’t stay here.

What does it matter how (in what state) we leave the planet, as long as we're off it.
Last edited by AvatarIII on Tue Aug 14, 2012 1:22 pm UTC, edited 1 time in total.

Retsam
Posts: 57
Joined: Tue Aug 18, 2009 5:29 am UTC

Re: What-if 0007: Everybody Out

Postby Retsam » Tue Aug 14, 2012 12:41 pm UTC

Today's comic has a soundtrack.

Raph
Posts: 6
Joined: Fri Apr 13, 2012 4:37 pm UTC

Re: What-if 0007: Everybody Out

Postby Raph » Tue Aug 14, 2012 1:26 pm UTC

There's also various mass drivers and catapults, like StarTram (http://en.wikipedia.org/wiki/StarTram). The cool thing about nuclear-powered spaceships is that it's a pretty feasible way of achieveing interstellar travel at at least 10% of c. That'd mean 40 years to Centauri and 200 years to Gliese 581 (http://en.wikipedia.org/wiki/Interstellar_travel#Nuclear_rocket_concepts), not all that improbable in a reasonable timeline! Especially of you first construct the StarTram or something else more efficient to get stuff into space, and then construct the starship in space.

Eutychus
Posts: 448
Joined: Mon Jan 25, 2010 6:01 am UTC
Location: France

Re: What-if 0007: Everybody Out

Postby Eutychus » Tue Aug 14, 2012 2:08 pm UTC

Retsam wrote:Today's comic has a soundtrack.


I submit that this (inspired by this) is a much better one.
Be very careful about rectilinear assumptions. Raptors could be hiding there - ucim

User avatar
eran_rathan
Mostly Wrong
Posts: 1846
Joined: Fri Apr 09, 2010 2:36 pm UTC
Location: in your ceiling, judging you

Re: What-if 0007: Everybody Out

Postby eran_rathan » Tue Aug 14, 2012 2:35 pm UTC

No love for the nuclear lightbulb, I see (sigh).
"Does this smell like chloroform to you?"
"Google tells me you are not unique. You are, however, wrong."
nɒʜƚɒɿ_nɒɿɘ

Patrik3
Posts: 112
Joined: Tue Aug 14, 2012 1:45 pm UTC

Re: What-if 0007: Everybody Out

Postby Patrik3 » Tue Aug 14, 2012 2:47 pm UTC

Three things I thought about in response to the What-If

I have many ideas and inventions of my own, no way of knowing if any of them are plausible, but I'll post 3 such which were triggered back into memory by their relevance to this post -

When he mentioned "Space elevator", but that no material is yet strong enough

I have a solution to this - just build it from much higher up! Find a plateau of generally high ground, any upland area, possibly near the Himalayas or in the middle of Africa.

Then my idea is to build a pyramid of arches - if you had 3 arches in a triangle formation, the 2 base arches would have to support their own weight, + 0.5 of the top arch. So, 1.5x their own weight in total. Extrapolate until you get a many-layered triangle, and you'll find that the limit to how much each base arch will have to support will only tend to 2x its own weight. In a 3D pyramid structure, the limit would be even less. So theoretically, if you had enough steel, and a large enough area to build the base upon, you could build a tower of arches infinitely tall as long as each could support twice its own weight.

So build this pyramid, with each arch about 1-2km tall, build it 150 layers or so high, and then you've halved the distance of cable that the space elevator needs. (The ISS orbits at around 370km, so building the tower 150km high would mean the cable only has to be 170km long, minus the counterweight.) Also, the gravity and adverse weather systems might have decreased significantly by that point, so the cable could possibly be made out of today's materials.

Of course, building a triangle 150 layers high means that it would have to have 150*(150+1)/2 = 11,325 arches, each 1km tall, or 2,850 arches if they could each be built 2km tall. Starting the project a few kilometers above sea level would reduce the number of arches by a few hundred. Not sure if the design would be made more, or less, efficient by making it a pyramid instead of a triangle. Still, it would cost trillions to build, and although it would be of great value to NASA, and probably become the #1 tourist attraction in the world, it would take years to make any profit on it.

You heard it here first though. I dunno if it would work outside of theory, but if it did, it takes the space elevator idea out of the realms of pure fantasy and into just being very implausible - maybe it could be a nice monument to world peace, when we come to achieve it!

I promise not to write so much on this one. What Randall says about the "Orion project" is a terrifying prospect.

Just that, surely in all the nuclear testing, weapons manufacturers have been able to refine the technology to produce slightly smaller bombs?

So instead of blasting the ship into space with one big explosion, they could detonate many small explosions, still relying on nuclear fuel, but in a much more controlled way? Using huge bombs seems rather backward to me - you'd have to carry masses of armour to withstand the blast, most of it would be lost outwards, and the acceleration would be rather instant, so you'd have to have some major advance in g-suit technology or the pilot would be flattened against the back of his chair as soon as the bomb went off behind him. Is there not a way of producing many smaller controlled detonations, or even a continuous detonation to launch rockets into space?

Rather, I thought that the reason it was banned was not because of the size of the explosions, but that no one really wanted radioactive debris falling out of space at all.

Finally, a qualm I've had about rockets in general, seems to have been skipped over in the "what-if".

Why not catapults?

I see that missiles have the potential to travel at speed for longer than cannon projectiles - I assume this is because a cannonball reaches its greatest speed initially, so the resistances are also greater than a missile, which keeps a slower but more constant speed. Missiles have greater accuracy, and missiles traveling in the atmosphere don't have to hold their weight because they can act like planes.

However, as for space rockets, the largest speed is needed at launch - once you escape the gravity field, there's no need for excessive speed (and no resistances to slow you down). The point about missiles acting like planes is also irrelevant because space rockets only travel upwards, so they won't encounter any situation that can rely on uplift. Finally, the accuracy problem can be solved by having a secondary propulsion system on the projectile.

Here's what I'm getting at. I'm a big roller coaster enthusiast (in fact, I will hopefully be starting an Engineering degree soon in order to get a job in the industry!) and I've seen these new "rocket" coasters - Stealth at Thorpe Park, Kingda Ka and Top Thrill Dragster over the pond, to name a handful. Except that they aren't rockets. All of the energy is provided by a separate system at launch. Therefore, they don't take any "fuel" up the track with them.

So why not apply that to rockets? Keep some fuel, as propulsion in space, and for the thrusters, to maneuver. But how about building a big tunnel, filled with MagLev magnets, and evacuated of air, with one end of the tunnel curving upwards to vertical. Sit the actual rocket on a launch car, launch it, then detach the launch car at the end of the tunnel, and fling the rocket into space. The tunnel would provide very little resistance whilst the carriage accelerates, and the rocket would need much less energy to accelerate to escape velocity. Why don't space programs do this??? It seems obviously more efficient than using rockets!

---

So yeah, sorry for the long-post. This always happens when I'm on ritalin... I'd be thrilled if anyone replies to it! Other people have probably already had my ideas already, but just in case I have hit a novel, genius idea, can I ask that everyone's nice and doesn't steal it from me? I've no idea how to patent this stuff but please don't nick it :P !

EDIT: Just realized I made a horrible slip up in my "Arches" calculation - the mass that the base arches would have to bear would only limit at 2x its own weight IF it the layers halved in size each layer, NOT if they followed the triangular numbers sequence. So the amount of arches that would be needed would not be the 150th triangular number (11,325) but the sum of 2^x between 1 and 150 (approx 2.9e+45, I think?) which would be a probably a little less feasible.
Last edited by Patrik3 on Tue Aug 14, 2012 4:41 pm UTC, edited 1 time in total.

User avatar
The Moomin
Posts: 359
Joined: Wed Oct 13, 2010 6:59 am UTC
Location: Yorkshire

Re: What-if 0007: Everybody Out

Postby The Moomin » Tue Aug 14, 2012 2:59 pm UTC

My friend randomly managed to answer the question "Is the explosion caused by Yoda expending the energy to make a vaccuum appear spontaneously in half of a glass of water enough to simultaneously spread the water out over a wide enough radius to short circuit the uprising robots while propelling the remainder of the glass attached to a platform containing the entire human race upwards at a velocity of 0.9c towards a batter on a planet formed of moles" on his SAT correctly.

*edited to include the word SAT and a batter.
I'm alive because the cats are alive.
The cats are alive because I'm alive.
Specious.

User avatar
PolakoVoador
Posts: 1028
Joined: Fri Jun 10, 2011 11:11 pm UTC
Location: Brazil

Re: What-if 0007: Everybody Out

Postby PolakoVoador » Tue Aug 14, 2012 3:44 pm UTC

The Moomin wrote:My friend randomly managed to answer the question "Is the explosion caused by Yoda expending the energy to make a vaccuum appear spontaneously in half of a glass of water enough to simultaneously spread the water out over a wide enough radius to short circuit the uprising robots while propelling the remainder of the glass attached to a platform containing the entire human race upwards at a velocity of 0.9c towards a batter on a planet formed of moles" on his SAT correctly.

*edited to include the word SAT and a batter.


Well played sir, well played :D

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 4:56 pm UTC

Patrik3 wrote:You heard it here first though. I dunno if it would work outside of theory, but if it did, it takes the space elevator idea out of the realms of pure fantasy and into just being very implausible - maybe it could be a nice monument to world peace, when we come to achieve it!

I imagine that the moment from rotation and air friction are going to be causing a significant amount of the wear on the tether, maybe I'm wrong...would this design be able to account for that?

So instead of blasting the ship into space with one big explosion, they could detonate many small explosions, still relying on nuclear fuel, but in a much more controlled way? Using huge bombs seems rather backward to me - you'd have to carry masses of armour to withstand the blast, most of it would be lost outwards, and the acceleration would be rather instant, so you'd have to have some major advance in g-suit technology or the pilot would be flattened against the back of his chair as soon as the bomb went off behind him. Is there not a way of producing many smaller controlled detonations, or even a continuous detonation to launch rockets into space?

Randall doesn't communicate it very clearly, but yes, the design is to detonate multiple nukes at regular intervals.

Others argue that when you think about what they were trying to do—put our entire nuclear arsenal in a box, hurl it high into the atmosphere, and nuke it repeatedly—it’s terrifying that it got as far as it did.


Why not catapults?
...
So why not apply that to rockets? Keep some fuel, as propulsion in space, and for the thrusters, to maneuver. But how about building a big tunnel, filled with MagLev magnets, and evacuated of air, with one end of the tunnel curving upwards to vertical. Sit the actual rocket on a launch car, launch it, then detach the launch car at the end of the tunnel, and fling the rocket into space. The tunnel would provide very little resistance whilst the carriage accelerates, and the rocket would need much less energy to accelerate to escape velocity. Why don't space programs do this??? It seems obviously more efficient than using rockets!

There is some work on it, with launching shuttles from high-altitude planes I think, but the resistances and minimum kinetic energy needed are going to be approximately the same. Rockets already make their main push to escape the atmosphere, then keep some mass in reserve for deceleration if they need to land somewhere. All using a sealevel catapult would do is require that an incredible portion of the energy be put in at launch for the impulse needed so that the rocket is at the correct momentum when it leaves the atmosphere. Using rockets, while requiring more energy to lift the extra mass of the fuel, allows for a more gradual burn that doesn't liquidate the ship and crew.

Now, there ARE designs for ground-based propulsion systems, if the ship is already launched. For example, propelling a satellite with the pressure applied by a laser. This would have the same gradual burn as a rocket, while removing the extra fuel mass from the object to be moved. The main drawback is designing a laser that is both powerful enough to get you out of the atmosphere, and weak enough that it doesn't also incinerate your ship. It's a working design for satellites that are already in space, though.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

User avatar
Whizbang
The Best Reporter
Posts: 2238
Joined: Fri Apr 06, 2012 7:50 pm UTC
Location: New Hampshire, USA

Re: What-if 0007: Everybody Out

Postby Whizbang » Tue Aug 14, 2012 5:42 pm UTC

Ooh, a laser! How come you don't have a laser, Woody?

Sorry. Automatically plays in my head any time someone uses the word "laser".

Patrik3
Posts: 112
Joined: Tue Aug 14, 2012 1:45 pm UTC

Re: What-if 0007: Everybody Out

Postby Patrik3 » Tue Aug 14, 2012 6:01 pm UTC

@KrytenKoro

Neat, thanks for replying!

The Space Elevator idea is not a new one. There's a great sci fi book on the subject, called The Fountains of Paradise, by Arthur C Clarke, which explains how it would work - basically, the weight of the structure would be offset by a counterbalance in space, pulling outwards due to "centripetal force". I can't remember if it goes into the details of twisting torsion or not, but it begins to sound like a plausible idea. Unfortunately, it can only work if someone invents a cable that is has an insane tensile strength:weight ratio.

My idea was basically to build it on the peak of an enormous artificial mountain of arches, to reduce the necessary length, and thus tension, on the cable, until it could be made out of a 'real' substance. Unfortunately, as per my edit, I've since realized that this mountain of arches is in itself much less feasible than I had originally calculated.

---

As for the nuclear launch, "nuke it repeatedly" still carries a connotation of using large nukes. I was talking about trying to make nuclear weapons as small as they can efficiently be, or even to have a continuous form of reaction.

---

And I'm afraid I don't quite understand the reply about the rockets. I'm saying, if you have a ship with only the fuel needed for piloting it in space (which, for the sake of the "What-If", is nothing, since there's no target except to be outside the Earth!) then it doesn't need to carry all the complex systems and fuel needed to take it to escape velocity. The projectile that is launched from the catapult at sea level will only weigh a fraction of what the rocket weighs, so it will only require a fraction of the energy to get into space. I don't see how this carries a chance of liquidating the crew?

The laser satellite thing sounds fascinating though - I've thought before of transforming the energy from a laser into electrical energy, to fuel, i.e. a plane's propellers with energy, but using the heat pressure from the laser is definitely a new one. I'm guessing we're still just talking about launch here, though? As in, the laser can't propel it with air pressure unless it's still in an atmosphere.

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 6:21 pm UTC

Patrik3 wrote:As for the nuclear launch, "nuke it repeatedly" still carries a connotation of using large nukes. I was talking about trying to make nuclear weapons as small as they can efficiently be, or even to have a continuous form of reaction.

You may derive that implication, but I'm telling you that that's not what the design is about.

A continuous form of reaction would be very nice, yes. However, we have not been able to develop it (cold fusion) yet.

And I'm afraid I don't quite understand the reply about the rockets. I'm saying, if you have a ship with only the fuel needed for piloting it in space (which, for the sake of the "What-If", is nothing, since there's no target except to be outside the Earth!) then it doesn't need to carry all the complex systems and fuel needed to take it to escape velocity. The projectile that is launched from the catapult at sea level will only weigh a fraction of what the rocket weighs, so it will only require a fraction of the energy to get into space. I don't see how this carries a chance of liquidating the crew?

While a costly amount of mass and required energy IS added by carrying the fuel on board, the major portion of the energy cost is still the constant that Randall covers, that needed to achieve the necessary delta-v. Using a catapult like you suggest grants slightly lower energy requirements at the cost of delivering ALL of that energy right at the launch, which would liquefy the crew.

It's important to note that using nuclear propulsion or even antimatter propulsion still requires the fuel to be on-board as mass--all it's doing is using more exotic fuels which have a better mass/propulsive force ratio, which tops out at 1 for antimatter.


The laser satellite thing sounds fascinating though - I've thought before of transforming the energy from a laser into electrical energy, to fuel, i.e. a plane's propellers with energy, but using the heat pressure from the laser is definitely a new one. I'm guessing we're still just talking about launch here, though? As in, the laser can't propel it with air pressure unless it's still in an atmosphere.

Radiation pressure, not heat or air pressure. Photons have energy/mass (just not rest mass), and so their collisions can exert pressure and thus momentum like anything else.

And no, this is for in space, as I said. I do not believe we have been able to design laser/material combinations that could provide the necessary force to escape Earth's gravity without incinerating the craft.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

Thorbard9
Posts: 44
Joined: Mon Feb 15, 2010 7:42 pm UTC

Re: What-if 0007: Everybody Out

Postby Thorbard9 » Tue Aug 14, 2012 6:22 pm UTC

KrytenKoro wrote:
Patrik3 wrote:You heard it here first though. I dunno if it would work outside of theory, but if it did, it takes the space elevator idea out of the realms of pure fantasy and into just being very implausible - maybe it could be a nice monument to world peace, when we come to achieve it!

I imagine that the moment from rotation and air friction are going to be causing a significant amount of the wear on the tether, maybe I'm wrong...would this design be able to account for that?

So instead of blasting the ship into space with one big explosion, they could detonate many small explosions, still relying on nuclear fuel, but in a much more controlled way? Using huge bombs seems rather backward to me - you'd have to carry masses of armour to withstand the blast, most of it would be lost outwards, and the acceleration would be rather instant, so you'd have to have some major advance in g-suit technology or the pilot would be flattened against the back of his chair as soon as the bomb went off behind him. Is there not a way of producing many smaller controlled detonations, or even a continuous detonation to launch rockets into space?

Randall doesn't communicate it very clearly, but yes, the design is to detonate multiple nukes at regular intervals.

Others argue that when you think about what they were trying to do—put our entire nuclear arsenal in a box, hurl it high into the atmosphere, and nuke it repeatedly—it’s terrifying that it got as far as it did.


Why not catapults?
...
So why not apply that to rockets? Keep some fuel, as propulsion in space, and for the thrusters, to maneuver. But how about building a big tunnel, filled with MagLev magnets, and evacuated of air, with one end of the tunnel curving upwards to vertical. Sit the actual rocket on a launch car, launch it, then detach the launch car at the end of the tunnel, and fling the rocket into space. The tunnel would provide very little resistance whilst the carriage accelerates, and the rocket would need much less energy to accelerate to escape velocity. Why don't space programs do this??? It seems obviously more efficient than using rockets!

There is some work on it, with launching shuttles from high-altitude planes I think, but the resistances and minimum kinetic energy needed are going to be approximately the same. Rockets already make their main push to escape the atmosphere, then keep some mass in reserve for deceleration if they need to land somewhere. All using a sealevel catapult would do is require that an incredible portion of the energy be put in at launch for the impulse needed so that the rocket is at the correct momentum when it leaves the atmosphere. Using rockets, while requiring more energy to lift the extra mass of the fuel, allows for a more gradual burn that doesn't liquidate the ship and crew.

Now, there ARE designs for ground-based propulsion systems, if the ship is already launched. For example, propelling a satellite with the pressure applied by a laser. This would have the same gradual burn as a rocket, while removing the extra fuel mass from the object to be moved. The main drawback is designing a laser that is both powerful enough to get you out of the atmosphere, and weak enough that it doesn't also incinerate your ship. It's a working design for satellites that are already in space, though.


It is much more efficient to launch a (sub-orbital at least) craft from altitude by dropping from a conventional carrier aircraft before using rockets than it is to launch from the ground using rockets all the way. This is why the Virgin space ship one is so much smaller than the equivalent shuttle would be.

I don't see why a couple of shuttle sized aircraft couldn't launch from a strategic bomber sized aircraft and go orbital.

It would at least be a simple way to get large quantites of material orbital to build a bigger spacecraft that wouldn't have to escape Earth's atmosphere in addition to Earth's gravity.

I think the reality of the "everyone out" scenario would be that every variation of launch craft would be employed to get to the orbital stage.

JudeMorrigan
Posts: 1266
Joined: Tue Jan 26, 2010 1:26 pm UTC

Re: What-if 0007: Everybody Out

Postby JudeMorrigan » Tue Aug 14, 2012 6:24 pm UTC

Patrik3 wrote:As for the nuclear launch, "nuke it repeatedly" still carries a connotation of using large nukes. I was talking about trying to make nuclear weapons as small as they can efficiently be, or even to have a continuous form of reaction.

Allow me to encourage you to read up on Project Orion. Wiki is a reasonable enough starting place.

http://en.wikipedia.org/wiki/Project_Or ... propulsion)

In particular, note this bit:
The optimal Orion drive bomblet yield (for the human crewed 4,000 ton reference design) was calculated to be in the region of 0.15 KT, with approx 800 bombs needed to orbit and a bomb rate of approx 1 per second.

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 6:37 pm UTC

Thorbard9 wrote:It is much more efficient to launch a (sub-orbital at least) craft from altitude by dropping from a conventional carrier aircraft before using rockets than it is to launch from the ground using rockets all the way. This is why the Virgin space ship one is so much smaller than the equivalent shuttle would be.

I'm a bit confused as to how this is possible...are we comparing the spacecraft to spacecraft, or launching assembly (spacecraft+fuel) to launching assembly (spacecraft+fuel+carrier).

I believe that you're right, and I know I've gone over this concept before, I just can't remember how flying the rocket up to a certain height with a conventional craft would be cheaper than flying the rocket up to the same height by itself. It seems rather counter-intuitive, as you'd expect that it should act like the extra mass of the carrier is being added...perhaps it's a practical difference due to the materials and technology we have available, and an ideal carrier with an ideal rocket would indeed be more expensive.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

Patrik3
Posts: 112
Joined: Tue Aug 14, 2012 1:45 pm UTC

Re: What-if 0007: Everybody Out

Postby Patrik3 » Tue Aug 14, 2012 6:39 pm UTC

KrytenKoro wrote:A continuous form of reaction would be very nice, yes. However, we have not been able to develop it (cold fusion) yet.


How about... cold fission? :D

JudeMorrigan wrote:In particular, note this bit:

The optimal Orion drive bomblet yield (for the human crewed 4,000 ton reference design) was calculated to be in the region of 0.15 KT, with approx 800 bombs needed to orbit and a bomb rate of approx 1 per second.


Ah ok, sorry, I was still thinking about blasting weapon-sized bombs behind the craft.


KrytenKoro wrote:While a costly amount of mass and required energy IS added by carrying the fuel on board, the major portion of the energy cost is still the constant that Randall covers, that needed to achieve the necessary delta-v. Using a catapult like you suggest grants slightly lower energy requirements at the cost of delivering ALL of that energy right at the launch, which would liquefy the crew.


What liquefies the crew? You mean, if the launch was instantaneous, the amount of linear g-force would turn them to mush?

Yes, it would, but that's not what I'm saying. As I mentioned in my first post, I'm a big fan of roller coasters, and I'm using the same sort of concept for the launch.

http://www.youtube.com/watch?v=olaMD9adB4E <- A video of "Stealth" at Thorpe Park.

In the link, the ride accelerates horizontally, before exiting the launch and curving upwards. So too would the ship - it would safely accelerate to escape velocity, before pulling up to vertical and shooting out the top of the tunnel. The crew would not be liquefied.


And no, this is for in space, as I said. I do not believe we have been able to design laser/material combinations that could provide the necessary force to escape Earth's gravity without incinerating the craft.


Wow that sounds even more impressive, the radiation pressure pushing it. Surely the force caused by the particles must be tiny compared to the heat of the laser? I see why there's such a danger of burning the craft.

jgh
Posts: 146
Joined: Thu Feb 03, 2011 1:04 pm UTC

Re: What-if 0007: Everybody Out

Postby jgh » Tue Aug 14, 2012 6:43 pm UTC

Baby elephants!

Роберт
Posts: 4285
Joined: Wed May 14, 2008 1:56 am UTC

Re: What-if 0007: Everybody Out

Postby Роберт » Tue Aug 14, 2012 7:13 pm UTC

Railgun assisted launches, maybe?
The Great Hippo wrote:[T]he way we treat suspected terrorists genuinely terrifies me.

User avatar
bmonk
Posts: 662
Joined: Thu Feb 18, 2010 10:14 pm UTC
Location: Schitzoed in the OTT between the 2100s and the late 900s. Hoping for singularity.

Re: What-if 0007: Everybody Out

Postby bmonk » Tue Aug 14, 2012 7:23 pm UTC

KrytenKoro wrote:
Thorbard9 wrote:It is much more efficient to launch a (sub-orbital at least) craft from altitude by dropping from a conventional carrier aircraft before using rockets than it is to launch from the ground using rockets all the way. This is why the Virgin space ship one is so much smaller than the equivalent shuttle would be.

I'm a bit confused as to how this is possible...are we comparing the spacecraft to spacecraft, or launching assembly (spacecraft+fuel) to launching assembly (spacecraft+fuel+carrier).

I believe that you're right, and I know I've gone over this concept before, I just can't remember how flying the rocket up to a certain height with a conventional craft would be cheaper than flying the rocket up to the same height by itself. It seems rather counter-intuitive, as you'd expect that it should act like the extra mass of the carrier is being added...perhaps it's a practical difference due to the materials and technology we have available, and an ideal carrier with an ideal rocket would indeed be more expensive.


If you consider the carrier as a new stage, there might be no difference at all. That is the primary reason for multi-stage rockets, after all: they allow a large engine to do the initial lifting, but once that engine is out of fuel, you drop it and move on to a smaller engine. Same here: by using the carrier to lift the rocket to a significant height, and likely adding some velocity at least, you allow the rocket portion to be smaller. And then you can re-use the carrier for the next rocket.
Having become a Wizard on n.p. 2183, the Yellow Piggy retroactively appointed his honorable self a Temporal Wizardly Piggy on n.p.1488, not to be effective until n.p. 2183, thereby avoiding a partial temporal paradox. Since he couldn't afford two philosophical PhDs to rule on the title.

User avatar
eran_rathan
Mostly Wrong
Posts: 1846
Joined: Fri Apr 09, 2010 2:36 pm UTC
Location: in your ceiling, judging you

Re: What-if 0007: Everybody Out

Postby eran_rathan » Tue Aug 14, 2012 7:32 pm UTC

KrytenKoro wrote:A continuous form of reaction would be very nice, yes. However, we have not been able to develop it (cold fusion) yet.


Well, not cold fusion, certainly, but you don't need to. Fission and hot fusion work just fine - check out 'nuclear thermal rocket' on Wikipedia.
"Does this smell like chloroform to you?"
"Google tells me you are not unique. You are, however, wrong."
nɒʜƚɒɿ_nɒɿɘ

rmsgrey
Posts: 3655
Joined: Wed Nov 16, 2011 6:35 pm UTC

Re: What-if 0007: Everybody Out

Postby rmsgrey » Tue Aug 14, 2012 8:01 pm UTC

bmonk wrote:
KrytenKoro wrote:I believe that you're right, and I know I've gone over this concept before, I just can't remember how flying the rocket up to a certain height with a conventional craft would be cheaper than flying the rocket up to the same height by itself. It seems rather counter-intuitive, as you'd expect that it should act like the extra mass of the carrier is being added...perhaps it's a practical difference due to the materials and technology we have available, and an ideal carrier with an ideal rocket would indeed be more expensive.


If you consider the carrier as a new stage, there might be no difference at all. That is the primary reason for multi-stage rockets, after all: they allow a large engine to do the initial lifting, but once that engine is out of fuel, you drop it and move on to a smaller engine. Same here: by using the carrier to lift the rocket to a significant height, and likely adding some velocity at least, you allow the rocket portion to be smaller. And then you can re-use the carrier for the next rocket.


The main benefit of an aeroplane-launched rocket is that the aeroplane is more fuel-efficient in air than the rocket is (which is why we use jet-engines and wings rather than rockets for commercial flights).


One of the cooler alternatives to a space elevator is the space-fountain - rather than a tensioned cable lowered from orbit, fire a stream of solid projectiles upwards. Catch them in a magnetic field when they fall back to the ground and bend their path so they end up travelling upwards again with comparatively small losses in speed. A platform can be supported by the twin streams (up and down) at approximately zero net energy cost - it draws energy from the up-stream (decelerating the particles with a corresponding 3rd law force pushing the platform upwards) and uses that energy to accelerate the down-stream (again, creating an upwards reaction force on the platform). To a first approximation, the platform has no measurable effect on the streams below it - the speed lost by the up stream is pumped back into the down stream - it merely reduces the altitude of the apex - the place where the up stream turns and becomes the down stream. While running, the whole thing only needs enough energy input to cancel losses.

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 8:11 pm UTC

Patrik3 wrote:What liquefies the crew? You mean, if the launch was instantaneous, the amount of linear g-force would turn them to mush?

Yes, it would, but that's not what I'm saying. As I mentioned in my first post, I'm a big fan of roller coasters, and I'm using the same sort of concept for the launch.

http://www.youtube.com/watch?v=olaMD9adB4E <- A video of "Stealth" at Thorpe Park.

In the link, the ride accelerates horizontally, before exiting the launch and curving upwards. So too would the ship - it would safely accelerate to escape velocity, before pulling up to vertical and shooting out the top of the tunnel. The crew would not be liquefied.

I'm very concerned about that pulling up to vertical bit. Escape velocity is what, approximately 7 km/s? And you're having them suddenly turn a corner to go vertical. Regardless of prior acceleration in other directions, you still need that 7 km/s AWAY from Earth, and doing that with any sort of ground-based system all on the ground, instead of the 11 km height of the atmosphere, is going to result in extreme impulse compared to a regular rocket (which already pushes the human limits for g-force).


And no, this is for in space, as I said. I do not believe we have been able to design laser/material combinations that could provide the necessary force to escape Earth's gravity without incinerating the craft.


Wow that sounds even more impressive, the radiation pressure pushing it. Surely the force caused by the particles must be tiny compared to the heat of the laser? I see why there's such a danger of burning the craft. The force at any one instant is going to be pretty small, yes, but the beauty of it is that there's almost no friction in space; therefore, you can continuously accelerate the craft by shining the laser at it. You would need another laser at the landing target to slow it down, but it's a very cost efficient way to deliver momentum.

The main benefit of an aeroplane-launched rocket is that the aeroplane is more fuel-efficient in air than the rocket is (which is why we use jet-engines and wings rather than rockets for commercial flights).


THAT's what I was forgetting, aerodynamics. So yeah, it has to do with practical effects, rather than an idealized rocket in a frictionless infinite plane.


Also, space fountains are hella cool. My only question is, what do you do when you have to perform maintenance?
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

User avatar
eran_rathan
Mostly Wrong
Posts: 1846
Joined: Fri Apr 09, 2010 2:36 pm UTC
Location: in your ceiling, judging you

Re: What-if 0007: Everybody Out

Postby eran_rathan » Tue Aug 14, 2012 8:29 pm UTC

Earth's escape velocity is close to 11 km/sec (depending on location and direction of launch - the closer to the Equator you are, the lower the velocity, plus you can pick up some speed by pointing east, essentially adding the speed of the rotation of the Earth to your velocity).
"Does this smell like chloroform to you?"
"Google tells me you are not unique. You are, however, wrong."
nɒʜƚɒɿ_nɒɿɘ

User avatar
AdmiralGreene
Posts: 100
Joined: Sun Jul 29, 2012 3:44 pm UTC
Location: Virginia! Hooray for the south!

Re: What-if 0007: Everybody Out

Postby AdmiralGreene » Tue Aug 14, 2012 8:30 pm UTC

Eutychus wrote:
Retsam wrote:Today's comic has a soundtrack.


I submit that this (inspired by this) is a much better one.


I read that book!
I suppose I should state something clever, no?

Dragons!

Patrik3
Posts: 112
Joined: Tue Aug 14, 2012 1:45 pm UTC

Re: What-if 0007: Everybody Out

Postby Patrik3 » Tue Aug 14, 2012 8:52 pm UTC

I'm very concerned about that pulling up to vertical bit.


Hmm, okay, I'll do the maths then, and see if it's anywhere near plausible.

The maximum safe sustained G-force vertically, even with a G-suit, is about 9G*. However, from experiments, it has been shown that even untrained humans can withstand at least sustained 17G in the 'linear' axis*, i.e. when the direction of the force is perpendicular to the spine. (Wikipedia doesn't specify whether this is with the aid of a G-suit. For the sake of the calculation, we'll be conservative and assume not.) So, if we just put the pilots in a supine position, we can safely exert almost twice the sustained force upon them.

Your estimate of Earth's escape velocity is actually a lot lower than the figure found on Wikipedia - 11.2 km/s.

The shape of an upward curve on a roller coaster is not actually circular at all: it has a much higher curve radius at the base than at the vertical. This is because 1) The train has lost some speed from climbing to the top of the curve 2) the component of gravity is much less at the top of the curve.

To give an accurate estimation of the height of our launch curve, I would have to calculate the radius of the curve all the way up. However, the safe radius depends partially on the speed of the train, which in turn depends on the height it has reached; but the height it reaches at any given angle in turn depends on the radius of the curve. So you get a circle of dependencies: safe radius -> speed -> height -> radius. For this reason it becomes very complicated to work out the exact size of the curve needed and I have absolutely no idea how to start deriving this formula. However, I would be very interested to know how it's derived in simple terms, (and as an aside, I'd also really like to see how the formula for a perfect teardrop loop is derived) so if anyone has any good explanations...?

Anyway, since I can't do that maths, I'll just assume that the curve is circular, so I just have to work out the radius at the base (which is obviously where it will be greatest.) Our 'safe' acceleration is 17*9.8 m/s^2. Our initial speed is 11.2*10^3 m/s. The formula for radial acceleration from a linear velocity is a = v^2/r*, or r = v^2/a

So, r = (11.2*10^3)^2 / 17.9.8 = 752,941

Ah.

Ok, so maybe that's why my catapult idea isn't feasible - no one wants to be building a launch ramp 753 kilometers into space... may as well just stick with the space elevator. Still, maybe you could launch the ship at a low angle, almost a tangent to the surface of the Earth. Hell, how about just sticking with the rocket idea but giving it a little 50mph boost out of the ground? Even that would probably save a couple tonnes of fuel...




*Data found on Wikipedia.

Thorbard9
Posts: 44
Joined: Mon Feb 15, 2010 7:42 pm UTC

Re: What-if 0007: Everybody Out

Postby Thorbard9 » Tue Aug 14, 2012 8:59 pm UTC

KrytenKoro wrote:
Thorbard9 wrote:It is much more efficient to launch a (sub-orbital at least) craft from altitude by dropping from a conventional carrier aircraft before using rockets than it is to launch from the ground using rockets all the way. This is why the Virgin space ship one is so much smaller than the equivalent shuttle would be.

I'm a bit confused as to how this is possible...are we comparing the spacecraft to spacecraft, or launching assembly (spacecraft+fuel) to launching assembly (spacecraft+fuel+carrier).

I believe that you're right, and I know I've gone over this concept before, I just can't remember how flying the rocket up to a certain height with a conventional craft would be cheaper than flying the rocket up to the same height by itself. It seems rather counter-intuitive, as you'd expect that it should act like the extra mass of the carrier is being added...perhaps it's a practical difference due to the materials and technology we have available, and an ideal carrier with an ideal rocket would indeed be more expensive.


Basically, as far as I know based on a couple of different lectures by the people associated with the Virgin Galactic project its to do with making each stage as efficient as it can be to do its own job.

A winged craft is much more energy efficient at low altitudes where the air is dense than a rocket is. The air density means you can use lift to work for you to move vertically. As the air gets less dense then the rocket doesn't have to work so hard against air density (air resistance) and if you design your capsule with wings of its own it can build up speed horizontally while still climbing before going into a vertical climb.

Part of the advantage is that the 1st stage is reusable as well as the payload stage and a single 1st stage could ferry more than one payload to sub-orbit for less material expenditure than doing it all with rockets.




Hmm... I don't know if that makes it any clearer... its been that sort of a day...

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 9:08 pm UTC

eran_rathan wrote:Earth's escape velocity is close to 11 km/sec (depending on location and direction of launch - the closer to the Equator you are, the lower the velocity, plus you can pick up some speed by pointing east, essentially adding the speed of the rotation of the Earth to your velocity).

Yeah, I uh, googled it instead of rerunning the calculations.

This.

So, lesson learned. Google doesn't know escape velocities.

Ok, so maybe that's why my catapult idea isn't feasible - no one wants to be building a launch ramp 753 kilometers into space...

Basically, yeah. Anything that could be described as a "ground-based launch" compared to a rocket traveling through the atmosphere is going to induce gs far, far outside of human limits. I'd be surprised if it would be within limits of current materials for the craft OR launcher, actually.

EDIT: Wikipedia also brings up the whole atmosphere problem:
Because of the atmosphere it is not useful and hardly possible to give an object near the surface of the Earth a speed of 11.2 km/s (40,320 km/h), as these speeds are too far in the hypersonic regime for most practical propulsion systems and would cause most objects to burn up due to atmospheric friction or be torn apart by atmospheric compression.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

MTGradwell
Posts: 67
Joined: Tue Aug 14, 2012 6:17 pm UTC

Re: What-if 0007: Everybody Out

Postby MTGradwell » Tue Aug 14, 2012 9:28 pm UTC

"No matter how we do it, whether we use rockets or a cannon or a space elevator, moving a 65-kilogram person—or 65 kilograms of anything—out of the Earth’s gravity well requires at least this much energy.
Gravitational potential energy=1/2*65kg*(Earth escape velocity)^2"

Not quite. First of all, suppose we need to accelerate to Earth's escape velocity. We do indeed require that much energy. However, if we start at the equator then we already have a velocity of 464 m/sec, thanks to the Earth's axial rotation. Escape velocity is 11,186 m/sec, but we only need to increase our velocity by that minus 464 i.e. 10,722 m/sec. That's why spacecraft are launched close to the equator.

Second, do we really need to worry about escape velocity? Do we need to escape? If we climb a space elevator to its top, putting us in a geostationary orbit, surely that counts as being "off-planet". In geostationary orbit our speed is 3066 m/sec, and our change in speed compared to equatorial ground level is that minus 464, i.e. just 2602 m/sec. Plugging that into the equation gives us 1/2*65*(2602)^2 = 220,038,130.

That's the energy we need to get our speed up to geostationary orbit *speed*. 220 million Joules is a lot, but still a lot less than 4 billion. Of course we also need to climb up to geostationary orbit *height*. I was going to calculate the energy required for that climb, but the maths looks complicated and I'm fundamentally lazy. Still, I'm sure that the total energy required to reach geostationary orbit is significantly less than that required to escape the Earth completely.

Why should it suffice to reach geostationary orbit? Because we can park as much stuff as we want in that orbit, enough to support all of humanity; and the stuff doesn't have to be lifted from the Earth's surface at tremendous expense in energy. It can be manufactured on the Moon, or on some other moon, or in the asteroid belt, or wherever, using raw materials obtained locally.

Finally, the energy required to lift a person to orbit could be obtained by the controlled lowering of a person-sized rock from orbit. The space elevator could be like a looped conveyor belt, with spacesuited people ascending one side and rocks, obtained from an asteroid, descending on the other side.

User avatar
Yakk
Poster with most posts but no title.
Posts: 11129
Joined: Sat Jan 27, 2007 7:27 pm UTC
Location: E pur si muove

Re: What-if 0007: Everybody Out

Postby Yakk » Tue Aug 14, 2012 9:33 pm UTC

KrytenKoro wrote:
Thorbard9 wrote:It is much more efficient to launch a (sub-orbital at least) craft from altitude by dropping from a conventional carrier aircraft before using rockets than it is to launch from the ground using rockets all the way. This is why the Virgin space ship one is so much smaller than the equivalent shuttle would be.

I'm a bit confused as to how this is possible...are we comparing the spacecraft to spacecraft, or launching assembly (spacecraft+fuel) to launching assembly (spacecraft+fuel+carrier).

I believe that you're right, and I know I've gone over this concept before, I just can't remember how flying the rocket up to a certain height with a conventional craft would be cheaper than flying the rocket up to the same height by itself. It seems rather counter-intuitive, as you'd expect that it should act like the extra mass of the carrier is being added...perhaps it's a practical difference due to the materials and technology we have available, and an ideal carrier with an ideal rocket would indeed be more expensive.

Easy. Airplanes don't have to carry their propellant with them.

They can just push off against air. So the rocket equation, with all of its massive blowup, does not apply. They can carry energy with them (in the form of fuel), then shove air down (or back) at a relatively sedate speed (note: pushing things slower gives more efficient momentum-per-energy) without having to lose mass. You then proceed to lift yourself out of the lower atmosphere and get a starting velocity up (well, really, it is about lifting yourself out of the lower atmosphere), then drop your rocket and have it fly away with your "cheap" boost.
One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision - BR

Last edited by JHVH on Fri Oct 23, 4004 BCE 6:17 pm, edited 6 times in total.

User avatar
eran_rathan
Mostly Wrong
Posts: 1846
Joined: Fri Apr 09, 2010 2:36 pm UTC
Location: in your ceiling, judging you

Re: What-if 0007: Everybody Out

Postby eran_rathan » Tue Aug 14, 2012 9:37 pm UTC

The easiest ways around this, I think are 1. use a spiral curve and 2. don't use the rails for the full escape velocity - just get the craft about 2/3rds of the way up and then ignite the rockets.


Additionally, while 'straight up' is the fastest way through the atmosphere, practical engineering would consider a far more shallow angle to be acceptable, assuming you used the #2 method, above.
"Does this smell like chloroform to you?"
"Google tells me you are not unique. You are, however, wrong."
nɒʜƚɒɿ_nɒɿɘ

m1el
Posts: 13
Joined: Wed Aug 01, 2012 5:38 am UTC

Re: What-if 0007: Everybody Out

Postby m1el » Tue Aug 14, 2012 10:31 pm UTC

I don't know why, but there is a very effective space launch method which is not mentioned in this "what-if". And, IMO, it's easier than nuclear propulsion.
http://en.wikipedia.org/wiki/Launch_loop

Patrik3
Posts: 112
Joined: Tue Aug 14, 2012 1:45 pm UTC

Re: What-if 0007: Everybody Out

Postby Patrik3 » Tue Aug 14, 2012 11:26 pm UTC

@KrytenKoro Yeah, the launch ramp idea really isn't sounding feasible to me anymore...

I talked with some friends about the topic, and they reminded me that most rockets actually use a curved trajectory, achieving orbital speeds above the atmosphere, instead of pushing directly upwards. Is this accounted for in the What-If?

m1el wrote:I don't know why, but there is a very effective space launch method which is not mentioned in this "what-if". And, IMO, it's easier than nuclear propulsion.
http://en.wikipedia.org/wiki/Launch_loop


Again, a really intriguing method. I love these "What-If"'s and I'm really glad I joined the forum today, because I've had one of the most interesting and amusing discussions I've had in ages - thanks, guys!

- I also thought up a couple more solutions, too:

1) Create a huge floating rig, suspended by balloons, miles up in the atmosphere, and launch the rockets from there.

2) (Silly) The Earth's already unsuitable to live upon, right? (according to the "What If"). So why not use nukes to blast a chunk of the moon out of orbit, and then use the landed chunk (which will form a gigantic 1000 mile high mountain) to climb into space from there?

As another aside, the whole 'evacuated tunnel MagLev launch' thing, I was also considering for use as a means of easy supersonic, intercontinental transport...

Ashtar
Posts: 24
Joined: Sun Jun 03, 2012 5:56 am UTC

Re: What-if 0007: Everybody Out

Postby Ashtar » Tue Aug 14, 2012 11:29 pm UTC

The Moomin wrote:My friend randomly managed to answer the question "Is the explosion caused by Yoda expending the energy to make a vaccuum appear spontaneously in half of a glass of water enough to simultaneously spread the water out over a wide enough radius to short circuit the uprising robots while propelling the remainder of the glass attached to a platform containing the entire human race upwards at a velocity of 0.9c towards a batter on a planet formed of moles" on his SAT correctly.

*edited to include the word SAT and a batter.

Turns out I wanted to do just that. Only my question was:
Would the explosion caused by Yoda's Force power suddenly forming a vacuum in half a glass of water destroy the uprising robots who have forced the entire human race to leave the Earth by launching themselves at 90% light velocity toward a batter on the mole-of-moles planet who has gotten a perfect score by guessing on the SAT?

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Tue Aug 14, 2012 11:37 pm UTC

eran_rathan wrote:The easiest ways around this, I think are 1. use a spiral curve and 2. don't use the rails for the full escape velocity - just get the craft about 2/3rds of the way up and then ignite the rockets.


Additionally, while 'straight up' is the fastest way through the atmosphere, practical engineering would consider a far more shallow angle to be acceptable, assuming you used the #2 method, above.

I don't see how a spiral is going to solve the problem of acceleration, only exacerbate it. For example, you experience more g's going a set speed on a roller coaster than you do going at the same speed on flat ground, because you are constantly accelerating in new directions.

Also, viewed from the frame of the larger orbit (so, not rocket-based), the launch is at quite a shallow angle due to the rotation of the Earth...and you have to maintain that curvature in order to actually get anywhere near where you are targeting. That's why launch windows are so important.

I talked with some friends about the topic, and they reminded me that most rockets actually use a curved trajectory, achieving orbital speeds above the atmosphere, instead of pushing directly upwards. Is this accounted for in the What-If?

Yes, it is. It depends on your frame of reference, and the mechanic is similar to that behind apparent retrograde motion.

From the point of view of the rocket, it is traveling directly "away" from Earth. This makes the launch as cheap as practically possible. From the point of view of Earth, the rocket quickly starts curving due to the Earth's rotation, and from the point of view of the Sun (if the rocket is going to, say, Mars), the rocket was already curving due to the motion of the Earth.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

nowhereman
Posts: 68
Joined: Thu Apr 15, 2010 5:46 pm UTC

Re: What-if 0007: Everybody Out

Postby nowhereman » Wed Aug 15, 2012 12:16 am UTC

@jgh. I am really glad that i am not the only one who thought of that book while reading his mention of nuclear impulse propulsion. I think everyone should read "Footfall".

As for the idea to send launch vehicles to space, I believe that a 'roller coaster' method could work. However, it would be best done by using sub escape velocities and augmenting the launch trajectories with additional propulsion around 20km once atmospheric leeching has significantly dropped. I estimate that a vehicle launched at mach five would easily do the job of reducing lift energy.

On a side note, i estimate a projectile launched a little over mach six will reach the altitude of the ISS. I have a new use for rail guns ;).

{ disclaimer: I am not advocateing the use of high energy weapons for the purpose of
playing a game of super size NES duck hunt. I am merely pointing out that that would be awesome}
"God does not play dice with... Yahtzee!" - Little known quote from Einstein

KrytenKoro
Posts: 1487
Joined: Tue Apr 05, 2011 2:58 pm UTC

Re: What-if 0007: Everybody Out

Postby KrytenKoro » Wed Aug 15, 2012 12:37 am UTC

nowhereman wrote:@jgh. I am really glad that i am not the only one who thought of that book while reading his mention of nuclear impulse propulsion. I think everyone should read "Footfall".

As for the idea to send launch vehicles to space, I believe that a 'roller coaster' method could work. However, it would be best done by using sub escape velocities and augmenting the launch trajectories with additional propulsion around 20km once atmospheric leeching has significantly dropped. I estimate that a vehicle launched at mach five would easily do the job of reducing lift energy.

Well, yeah. That's an orbital elevator.
From the elegant yelling of this compelling dispute comes the ghastly suspicion my opposition's a fruit.

AllenMS828
Posts: 1
Joined: Wed Aug 15, 2012 1:13 am UTC

Re: What-if 0007: Everybody Out

Postby AllenMS828 » Wed Aug 15, 2012 1:22 am UTC

Patrik3 wrote:2) (Silly) The Earth's already unsuitable to live upon, right? (according to the "What If"). So why not use nukes to blast a chunk of the moon out of orbit, and then use the landed chunk (which will form a gigantic 1000 mile high mountain) to climb into space from there?

To take your "silly" idea a step further... what if we built a huge seesaw and placed a spaceship containing all the humans on the low end of it, and have it positioned to where the chunk of the moon would land on the high end and fling us into space? That would sure save a lot of fuel. :D


Return to “What If?”

Who is online

Users browsing this forum: No registered users and 6 guests