Search found 124 matches

by HopDavid
Sun Aug 19, 2012 3:07 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

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, google...
by HopDavid
Sun Aug 19, 2012 2:58 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

Max™ wrote:I'm not sure how you'd compare the energy costs of a rocket to an elevator, as we don't know what the manufacturing of elevator materials would cost, nor what it would take to move a counterweight into place, though if it is already made, then yes it wins handily.


Not necessarily
by HopDavid
Sun Aug 19, 2012 1:41 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

Routes to space range from the doable to wildly implausible. Orions and bean stalks belong to the latter category. The plausible proposals are a cry in the wilderness. They are drowned out by the din of wildly unlikely science fiction. And so we will remain below LEO. Until you educate yourselves, ...
by HopDavid
Sun Aug 19, 2012 1:24 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

For analogy: Q: What would be the least amount of only vegetables someone would need to survive for a year? Randall: Well, the lowest bound would be:... You: Randall is so stupid, because he didn't talk about how if you add some meat you would have a more well-rounded diet! A number of topics were ...
by HopDavid
Sat Aug 18, 2012 4:11 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

That Randall and the readers of this forum are unaware of them is deeply disappointing. It is a symptom of how deeply we've sunk into the Britney Spears zeitgeist. As we get dumber and dumber, our chances for breaking free of cradle earth grow dimmer and dimmer. Oh give us a fucking break. Routes t...
by HopDavid
Fri Aug 17, 2012 11:47 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

That is a huge mischaracterization of the article, which is discussing the energy cost of humanity (note, not humans) leaving the planet all at once. Whether we're sending 4 billion humans or 1000 is immaterial. There are more plausible ways to get beyond LEO than this outdated 1970s science fictio...
by HopDavid
Fri Aug 17, 2012 10:13 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

Tethers have the potential to do the same. But tethers are far more plausible than a full blown space elevator. Your earlier post seems to dismiss anything that's orbiting lower and faster than geosynch. I don't dismiss anything. I just pointed out that no alternative skyhook/tether system gets you...
by HopDavid
Fri Aug 17, 2012 10:06 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

There is a math error in Randall's article: Δv=v exhaust ln(m start /m end ) m start and m end are the total mass of the ship+fuel before and after the burn, and v exhaust is the “exhaust velocity” of the fuel, a number that’s between 2.5-4.5 km/s for rocket fuels. What’s important is the ratio betw...
by HopDavid
Fri Aug 17, 2012 3:18 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

For lower (and shorter) elevators, one idea is to spin the cable so it kind of "rolls" along the atmosphere, with higher the end of the cable moving at twice the orbital velocity, and the lower end almost stationary (all with respect to the Earth's surface). This is called a sky hook . Th...
by HopDavid
Fri Aug 17, 2012 2:52 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

His statement goes on to say " or it's moving at quite a clip relative to Earth's surface and you've got to catch up to it first, which means you need exactly as much energy as getting into orbit in the first place. " Which is completely incorrect, actually. What's wrong with that? Are yo...
by HopDavid
Fri Aug 17, 2012 6:59 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

His statement goes on to say " or it's moving at quite a clip relative to Earth's surface and you've got to catch up to it first, which means you need exactly as much energy as getting into orbit in the first place. " Which is completely incorrect, actually. What's wrong with that? Are yo...
by HopDavid
Thu Aug 16, 2012 10:22 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

Which means he is completely correct, actually. In order for the ring to stay in orbit below the geosynchronous line, it would have to be moving faster than the Earth's rotation. That's the first part of what he said. Of course orbits below geosynchronous move faster than earth's rotation. But read...
by HopDavid
Thu Aug 16, 2012 7:58 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

[(And in response to your other post about a ring lower down than GEO: space elevators have their center of mass so high because that way they don't have to move relative to Earth's surface. At any other height, you're either wasting energy keeping it synched with Earth's rotation, or it's moving a...
by HopDavid
Thu Aug 16, 2012 7:04 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 55822

Re: What-if 0007: Everybody Out

As mentioned, mass goes up exponentially with delta V. If hydrogen and oxygen is the propellant, each 3 km/s added to the delta V budget is a square on this chess board: http://clowder.net/hop/TMI/Rice.jpg However, if you could refuel along the way, you get to start over on each square on the chess ...
by HopDavid
Tue Jan 17, 2012 3:24 am UTC
Forum: Science
Topic: Temperature on the Moon
Replies: 9
Views: 2215

Re: Temperature on the Moon

Short question: What does it mean for the moon to have a temperature of -150 C? Elaboration: I've been trying to figure out what temperature looks like in space. Since it's a vacuum, you should only lose temperature by radiation. This would take a while and continue until you're hovering right abov...
by HopDavid
Tue Nov 29, 2011 5:29 pm UTC
Forum: Fictional Science
Topic: Space Rocks
Replies: 8
Views: 4095

Re: Space Rocks

I am currently in the middle of writing/editing a longer story, but I am running into some confusion with a certain plot point. In short, I am curious to know about what would happen if a 5-metre meteorite where to collide with the planet earth. While I wouldn't necessary need to know this for the ...
by HopDavid
Thu Nov 17, 2011 9:04 pm UTC
Forum: Science
Topic: Molten salt reactors
Replies: 19
Views: 9210

Re: Molten salt reactors

idobox wrote:and why it remained at the prototype level, even in countries that had independent nuclear programs, and didn't give a shit about American energy policy.


Look's like China's checking it out.
by HopDavid
Thu Nov 17, 2011 8:53 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7278

Re: Artificial Gas Giant Surface

Iit's not just the weight. Those 400lb people are living in a 1g environment so their heart doesn't have to work as hard as a 160lb person in a 2.5g environment. It may be technically possible for humans to live there but they'd have hideous health complications and I don't think you'd find many vo...
by HopDavid
Wed Nov 16, 2011 11:58 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7278

Re: Artificial Gas Giant Surface

It'd be a bit nippy out there though... Jupiter clearly wouldn't work. 2.5 gravities is an insane amount to live in permanently. You'd be lucky to reach the age of 30 with all that stress on your heart, and forget ever being able to stand up - even if you managed it, you'd probably pass out from al...
by HopDavid
Wed Nov 16, 2011 9:28 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7278

Re: Artificial Gas Giant Surface

This is a fantastic idea. I see no reason why a flexible balloon around a planet like Venus should not be stable. And if you had one earth atmosphere above the balloon, then you could live there I like it too. Rather than around a star, a mini Dyson sphere around a planet with a dense atmosphere. A...
by HopDavid
Wed Nov 16, 2011 9:23 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7278

Re: Artificial Gas Giant Surface

Power. That's why. The planet is a power source/ It also adds gravity. It can also be used for materials depending on what it is made of. Gravity.. are we talking about a solid shell we can walk on the outside of because of planetary gravity, possibly resting on the planet's unsolid "surface&q...
by HopDavid
Sat Nov 05, 2011 10:14 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4719

Re: Orbit-Surface Landing Craft

Wow, even if that doesn't become reality, it would be an awesome plot device for near science fiction stories. The Next Continent by Issui Ogawa uses something like Skylon. I highly recommend this book. Perhaps optimistic hard science fiction has fallen out of fashion in the english speaking world,...
by HopDavid
Tue Nov 01, 2011 1:11 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4719

Re: Orbit-Surface Landing Craft

One way reusable? How can a lander be reused if it doesn't make the ascent back to orbit? By plonking it on top of a rocket. The rocket parts aren't reusable, but there's no reason the command capsule can't be. Oh, okay. SpaceX recovered Dragon. If they successfully send it back up, this will have ...
by HopDavid
Thu Oct 27, 2011 9:53 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4719

Re: Orbit-Surface Landing Craft

Tech challenge - Design a dropship/landing craft that goes, one way (but reuseable) from an orbiting vessel to a planetary surface. Assume Earth conditions, i.e. Atmospheric heating, orbital velocity, altitude, and the whole 9 yards. Remember, one way reuseable transport. One way reusable? How can ...
by HopDavid
Fri Oct 07, 2011 10:49 pm UTC
Forum: Science
Topic: What is the point of space colonies?
Replies: 11
Views: 1508

Re: What is the point of space colonies?

ORLY? Since the Martian surface offers all the natural resources and elements necessary to sustain human society—unlike, for example the Moon—a permanent Martian settlement is thought to be the most effective way to ensure humankind becomes a space-faring, multi-planet species. True, Mars has CHON....
by HopDavid
Sat Sep 10, 2011 11:36 pm UTC
Forum: Science
Topic: good jobs for the study of space?
Replies: 9
Views: 1351

Re: good jobs for the study of space?

If you like planetary stuff you could also go for geology. A lot of the information that came back from the Mars rovers went right to university geologists for analysis. The upshot is that even if you don't get into extraterrestrial geology right away, a geology degree leaves you a lot more employa...
by HopDavid
Fri Sep 09, 2011 8:52 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5413

Re: Planet disassembly

Soralin wrote:Using the rockets we do now, taking off of Earth, it takes 9-10 km/s of delta-v, to get into low earth orbit, whereas without the drag it would be 7.8km/s. So you could add 15-25% or so because of that.


15-25% increase in velocity is 32-56% increase in kinetic energy.
by HopDavid
Fri Sep 09, 2011 8:47 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5413

Re: Planet disassembly

But we don't want the rockets going sideways? Unless I've misunderstood the diagram. Horizontal burn is minimum gravity loss. However achieving an 8 km/sec horizontal velocity vector in earth's troposphere is very bad. A vertical ascent is required before the rocket does the main horizontal burn. E...
by HopDavid
Fri Sep 09, 2011 8:12 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5413

Re: Planet disassembly

Can the two energies be compared though? Is the energy required to explode/vaporise the earth, and the energy required to disassemble it the same? The only difference between exploding and disassembling is the fact that explosions happen quickly. But the gravitational binding energy is what has to ...
by HopDavid
Tue Sep 06, 2011 2:28 pm UTC
Forum: Science
Topic: Capturing Asteroids in Earths' Orbit for Mining
Replies: 72
Views: 6744

Re: Capturing Asteroids in Earths' Orbit for Mining

I can't imagine it will be very cheap to safely bring the mined materials down to the Earth's surface. As I understand it, pretty much the only reason to do any mining outside of our gravity well is if the end product is also going to be there- but the things that you would want to put in space (li...
by HopDavid
Sun Sep 04, 2011 7:42 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

It is very easy to go to Home Depot and get a wide variety of materials. An appliance might have copper from Arizona, nickel from Canada, plastics from petroleum refineries, etc. It's so easy to get stuff it's easy to forget we're the beneficiaries of a vast mining, manufacturing and transportation...
by HopDavid
Fri Sep 02, 2011 9:49 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

Well, with a completely automated setup, you could always go for a lossy approach. I mean, if the automated miner can at least deliver enough resources to the automated factory to build a copy of itself, before it gets crushed in a cave-in or something, then you're still ahead. :) Everything additi...
by HopDavid
Fri Sep 02, 2011 7:15 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

Setting up the needed mining infrastructure with autonomous robots is well beyond the present state of the art. But how eagerly are we pursuing things like that? I mean, when you see things like big-dog, you start to wonder why you can't build a generic robot capable of building and maintaining sui...
by HopDavid
Fri Sep 02, 2011 4:42 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

i wonder if it would be possible to create a machine or robot that just runs along the desert, scooping up silica in the sand and churning out crystaline silicon solar cells. :D That would be a nice step towards some sort of self replicating machine, obviously it wouldn't be self replicating, but i...
by HopDavid
Thu Sep 01, 2011 8:54 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

A base on the Moon is better than footprints on Mars, but even better than both would be self replicating robots on the moon. If we could make just a handful of launches to put 5 or 6 robots on the Moon, and then those robots could replicate, and then build other things after a while, we'd be all s...
by HopDavid
Thu Sep 01, 2011 8:48 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

The question is pretty biased; do you want a fully sustainable awesome Moon Base with ROBOTS, or do you want to do a round trip with some people on Mars... I want a fully sustainable awesome Mars Base with ROBOTS. Issues with distance: light lag, bandwidth. Telerobots are much less plausible for Ma...
by HopDavid
Wed Aug 31, 2011 11:15 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

Hmm, maybe I do not understand your arguments or it was a bit unclear what I compared: a) EML1 -> "brake" 0.65km/s and go close to earth -> accelerate 0.5km/s and go to mars b) EML1 -> accelerate x and get close to the moon -> there, accelerate y and get close to earth -> accelerate <0.5k...
by HopDavid
Wed Aug 31, 2011 6:44 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

Maybe it is even more efficient to go from EML1 to the moon first - use an even smaller delta_v to go around it and another small one to adjust the orbit there. I did not calculate numbers, but I think it could help a bit. It is my strong opinion a stop at EML1 propellant depots would be much more ...
by HopDavid
Tue Aug 30, 2011 5:55 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

For reaching deep space destinations like Mars or NEOs, EML1 (Earth Moon Lagrange 1) has [an advantage of] about a 12 km/sec advantage over earth's surface. Aren't you discounting the Oberth effect here? Actually, I'm using the Oberth effect. Or can you make a trajectory past the Earth from EML1 th...
by HopDavid
Tue Aug 30, 2011 5:31 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5082

Re: Moon or Mars?

I generally tend more to option three: NEO's. In the long term NEOs offer much more resources and real estate than the big moons and rocky planets. They're also more accessible with their shallow gravity wells. I'm in the J. S. Lewis camp that decries planetary chauvinism. That said, the moon is th...

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