## Search found 126 matches

Sat Jun 02, 2018 2:35 pm UTC
Forum: What If?
Topic: What-If 0157: "Earth-Moon Fire Pole"
Replies: 30
Views: 13993

### Re: What-If 0157: "Earth-Moon Fire Pole"

One trick I'm studying is accelerating packets of Deimos dust to 2 km/s while it is travelling prograde relative to Mars orbit. With very high precision aiming and timing , the packets will smack into the heat shield of a vehicle arriving from Earth, and speed it up to match orbits with Mars; speci...
Sat Jun 02, 2018 5:21 am UTC
Forum: What If?
Topic: What-If 0157: "Earth-Moon Fire Pole"
Replies: 30
Views: 13993

### Re: What-If 0157: "Earth-Moon Fire Pole"

A Phobos-Mars descent is vastly easier. Mars-Phobos L1 is 2.5 kilometers "above" Stickney crater on Phobos, equivalent to a 50 centimeter high hill on Earth. If you use a 5 kW searchlight power radiator on your 500 kg vehicle, with a top speed of 100m/s, the descent takes 24 hours. Simila...
Sun Aug 19, 2012 3:07 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Sun Aug 19, 2012 2:58 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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
Sun Aug 19, 2012 1:41 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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, ...
Sun Aug 19, 2012 1:24 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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 ...
Sat Aug 18, 2012 4:11 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 11:47 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 10:13 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 10:06 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 3:18 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 2:52 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Fri Aug 17, 2012 6:59 am UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Thu Aug 16, 2012 10:22 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Thu Aug 16, 2012 7:58 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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...
Thu Aug 16, 2012 7:04 pm UTC
Forum: What If?
Topic: What-if 0007: "Everybody Out"
Replies: 350
Views: 59956

### 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 ...
Tue Jan 17, 2012 3:24 am UTC
Forum: Science
Topic: Temperature on the Moon
Replies: 9
Views: 2402

### 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...
Tue Nov 29, 2011 5:29 pm UTC
Forum: Fictional Science
Topic: Space Rocks
Replies: 8
Views: 4269

### 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 ...
Thu Nov 17, 2011 9:04 pm UTC
Forum: Science
Topic: Molten salt reactors
Replies: 19
Views: 9445

### 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.
Thu Nov 17, 2011 8:53 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7565

### 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...
Wed Nov 16, 2011 11:58 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7565

### 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...
Wed Nov 16, 2011 9:28 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7565

### 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...
Wed Nov 16, 2011 9:23 pm UTC
Forum: Fictional Science
Topic: Artificial Gas Giant Surface
Replies: 22
Views: 7565

### 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...
Sat Nov 05, 2011 10:14 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4921

### 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,...
Tue Nov 01, 2011 1:11 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4921

### 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 ...
Thu Oct 27, 2011 9:53 pm UTC
Forum: Fictional Science
Topic: Orbit-Surface Landing Craft
Replies: 17
Views: 4921

### 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 ...
Fri Oct 07, 2011 10:49 pm UTC
Forum: Science
Topic: What is the point of space colonies?
Replies: 11
Views: 1620

### 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....
Sat Sep 10, 2011 11:36 pm UTC
Forum: Science
Topic: good jobs for the study of space?
Replies: 9
Views: 1433

### 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...
Fri Sep 09, 2011 8:52 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5775

### 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.
Fri Sep 09, 2011 8:47 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5775

### 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...
Fri Sep 09, 2011 8:12 pm UTC
Forum: Science
Topic: Planet disassembly
Replies: 25
Views: 5775

### 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 ...
Tue Sep 06, 2011 2:28 pm UTC
Forum: Science
Topic: Capturing Asteroids in Earths' Orbit for Mining
Replies: 72
Views: 7240

### 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...
Sun Sep 04, 2011 7:42 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Fri Sep 02, 2011 9:49 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Fri Sep 02, 2011 7:15 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Fri Sep 02, 2011 4:42 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Thu Sep 01, 2011 8:54 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Thu Sep 01, 2011 8:48 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Wed Aug 31, 2011 11:15 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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...
Wed Aug 31, 2011 6:44 pm UTC
Forum: Science
Topic: Moon or Mars?
Replies: 42
Views: 5455

### 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 ...