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#1 Re: Life support systems » Solar panel operating limits » 2008-03-11 22:11:22

Okay, so the wattage intake is not an issue but the heating is. Thanks! That solves one problem for me.

#3 Re: Life support systems » Solar panel operating limits » 2008-03-11 21:17:28

I've googled a bit and can't seem to find the information so I thought I'd ask here.

What kind of limits do solar panels have, regarding how close to the sun can we put them?

At 0.1AU the solar constant is approx. 137200 W/m2 which is a hundred times the energy as we get here on Earth. But can solar panels take that kind of energy in, even if we get that close? Or are they limited by some kind of maximum intake?

Also, something that close will heat up quite significantly. Are there solar panels that can stand being heated up to hundreds of degrees, or will putting stuff that close to the sun effectively burn them to a crisp?

Some unmanned space craft have used solar gravity assists. How close to the sun did they get and how did their solar panels function during the close approaches?

#4 Re: Terraformation » Terraforming the Moon - Your opinion, please » 2008-02-18 16:11:41

Thank you, Midoshi. I will certainly review your sources! Thanks ever so much for providing them!

#5 Re: Terraformation » Terraforming the Moon - Your opinion, please » 2008-02-18 11:30:01

More reliable than a source that is continuously fact-checked and fixed by thousands of people?

Right, keep living in your cloud castle.

Wikipedia is dozens of times more reliable than any non peer reviewed message board can ever dream to be. When it's been scientifically verified to be on the same order of accuracy as the damn Encyclopedia Britannica, I think slandering its accuracy isn't going to gain you any points.

#6 Re: Single Stage To Orbit » SSTO » 2008-02-18 11:28:44

I don't see anybody counting the extra assist from the low latitudes at Kourou as one more stage. If it's on the ground, separate from the vessel going to orbit, I don't see why it should be counted.

You're just fudging semantics because you apparently don't want to accept it as a SSTO.

#7 Re: Terraformation » Terraforming the Moon - Your opinion, please » 2008-02-18 11:22:07

Well, that's from Wikipedia, the most unreliable source on the net.

And then you go on, and cite a *New Mars thread* as contradicting evidence?

You have the *gall* to dismiss Wikipedia and then suggest I should listen to anonymous posters on a New Mars thread?

Get some *real* sources before you try to ridicule Wikipedia. Your source as it currently stands is *far* more unreliable than Wikipedia was even three years ago.

#8 Re: Space Policy » Primary space politics » 2008-02-18 11:16:15

And that's why I'm in Clinton's corner for this fight.

#9 Re: Interplanetary transportation » Project Orion » 2008-02-16 21:53:29

I'm not talking leaving LEO, I'm talking about bridging interplanetary distances, for which 0.1c velocity can help a LOT. Going to Mars in days instead of months is a whole different ball game and you're not gonna get that out of current conventional rockets.

It's like, if your workplace is 60 miles away, you either have the option of walking the entire way (conventional rockets) or you can walk to the train station to catch the Orion which whisks you maglev express to the city, where you disembark the Orion and go down to the workplace with conventional rockets again.

What kind of an idiot walks the entire 60 miles?

#10 Re: Interplanetary transportation » Project Orion » 2008-02-16 19:25:42

No, its claim to superiority is its immense thrust, which works just as well in space as in atmosphere, except in space the pollution is much less dangerous. If you're going to use it where its negatives do the least damage, go ahead and bother.

#11 Re: Human missions » Space stations beyond ISS » 2008-02-16 16:54:12

I'm pretty sure there are *some* g-loc medicines, but I have no idea about how effective they are.

Incidentally, a "Titan Jr." station training astronauts for Titan gravity would only need a 31m radius of rotation. I suppose it'd be a good test bed/scale model to try out before building a full-on 1g habitat.

#12 Re: Terraformation » Terraforming the Moon - Your opinion, please » 2008-02-16 16:11:34

I do not believe we can tolerate that much CO2.

Here's from Wikipedia:

http://en.wikipedia.org/wiki/Carbon_dioxide#Toxicity

"It is dangerous when inhaled in high concentrations (greater than 5% by volume, or 50,000 ppm). The current threshold limit value (TLV) or maximum level that is considered safe for healthy adults for an eight-hour work day is 0.5% (5,000 ppm). The maximum safe level for infants, children, the elderly and individuals with cardio-pulmonary health issues is significantly less.

"Concentrations higher than 1,000 ppm (0.1%) will cause discomfort in more than 20% of occupants, and the discomfort will increase with increasing CO2 concentration. The discomfort will be caused by various gases coming from human respiration and perspiration, and not by CO2 itself. At 2,000 ppm (0.2%) the majority of occupants will feel a significant degree of discomfort, and many will develop nausea and headaches.

Also remember that O2 levels have to be kept below 30% or so to reduce flammability.

Given those two factors, we'd still need 70% of the atmosphere from some other source.

#13 Re: Human missions » Space stations beyond ISS » 2008-02-16 16:05:08

How about anti-sicknes drugs to tolerate higher RPM?

I'm definitely interested in any and all research into such medicines, so if you have any new info to share, I'm all ears.

And it doesn't neccersarily have to be a torus. A central Cylindar with spokes coming of it that are connected to habs would work, wouldn't it?

Correct.

Say about 0.75g and 3 RPM, how big would it have to be?

75m radius, 150m diameter.

#14 Re: Interplanetary transportation » Project Orion » 2008-02-16 15:51:08

I think Orion would probably be feasible as interplanetary transportation but never landing. Constructed in orbit, used to ferry back and forth between, say, Earth and Titan, but at those ends it would just transfer its cargo to other ascent/descent mechanisms in orbit rather than landing. It can dock with a space elevator and send cargo down via it, or it can have smaller shuttlecraft in bay to take things up and down, but an Orion should never get into a planet's atmosphere, IMO.

I'd definitely like to see some research done into an Orion-based heavy cargo transport with the mission to bring a bar of nitrogen from Venus to Moon or Mars.

#15 Re: Interplanetary transportation » Jules Verne » 2008-02-16 15:47:07

You won't get out of a big gravity well by thinking small.

#16 Re: Terraformation » Terraforming the Moon - Your opinion, please » 2008-02-16 15:43:43

Also, if the buffer gas atomic mass is much higher than oxygen, then won't it displace the oxygen, like a heavier liquid sinks to the bottom of the glass? Thus completely depriving the surface of oxygen.

Nitrogen is roughly the same as oxygen, so it doesn't displace the oxygen and the two mix at the surface. But if we had some really heavy buffer gas, it would create pressure, sure, but it would also separate all the oxygen away from the surface.

#17 Re: Interplanetary transportation » Jules Verne » 2008-02-16 13:32:15

Nah not really, getting it up to escape velocity is useless if there is no means of circularizing its orbit after launch. What sort of guidance & propulsion system could survive that sort of G-force?

"Fiske points out that the US military uses electronics in laser-guided artillery, which survive being fired out of guns at up to 20,000g."

http://www.launchpnt.com/Detail_View.43 … c30.0.html

Also, there can be catcher craft in orbit waiting to pick them up. Even if they are completely guidance-less (which isn't a given) it can still be done.

The system would likewise need to be more reliable if the number of launches increases... remember, at Mach 20+ even a small glitch could be very destructive.

And I really don't want to even think about making or moving that much electricity.

It's a good thing the builders of the first trains or battleships weren't scared of "moving that much mass".

You wanna stay in the safe zone, feel free. Me, I'm headed to the future. We can't get to the future if we don't go bigger.

#18 Re: Human missions » Space stations beyond ISS » 2008-02-16 12:18:37

Depends on how big a shipyard. If it takes 1 cubic meter, sure. If it takes a million cubic meters, no. How many cubic meters does a shipyard need? Answer that, and you have the answer to your question. smile

#19 Re: Interplanetary transportation » Jules Verne » 2008-02-16 12:14:59

For payloads that are *extremely* resistant to g-forces, mass drivers are a particularly viable alternative.

If, for example, payload x can survive 20,000 gs, it could be launched to escape velocity with -- get this -- a 314 meter long linear track. Something that small, you can put damn near anywhere. You could build the goddamned thing on an aircraft carrier and have it mobile around the world.

So it'd be a great launch mechanism for bulk goods like raw metals, liquids, gases and so on.

Hit something with a sledge hammer. If it still works after that, it should be orbited with a mass driver. wink

#20 Re: Interplanetary transportation » Jules Verne » 2008-02-16 11:32:20

A gas expansion cannon strikes me as wasteful (though I haven't done the math to verify), but a mass driver certainly has been considered a valid idea at least as far back as that Clarke or Heinlein book about the Moon.

I was actually just doing mass driver calculations yesterday (hence why I mentioned the idea in the SSTO thread) and I'd say there's definitely promise in the idea as a *supplement* to launch, but putting something in LEO or GEO *just* by mass driver would require too long tracks to be built in our lifetimes. However, we could definitely build launch tracks that'd add 1000-3000 m/s to launch which would help quite a bit.

Lemme go get my calculations and I'll get right back to you.

One of the things I seem to recall is that using a linear launch track will be able to provide a roughly 4x better exit velocity for the projectile than a circular (infinite length) launch ring. This is because a circular mass driver will exert pretty significant centrifugal forces. Given the same amount of physical construction materials (1km diameter launch ring = 3.14km of constructed length versus a 3.14km linear track), if you are limited by, say, 10g -- then in the launch ring where you'll be able to get n exit velocity, in a linear track you'll be able to get 4n.

I'll need to verify that with some more calculations but that's what I seem to recall from yesterday's math.

Edit: Okay, back with some math.

The factor of difference is 3.544908. A linear accelerator will be able to give you 3.5x better exit velocity than a circular one, assuming the same amount of construction materials and the same g-force tolerance in both designs.

In a launch ring, you are limited by a = v^2/r. That's the centrifugal acceleration, the g-force you're experiencing: v^2/r

Taking as an example, a ring that is 1000m in radius (total 2000*pi construction length), and a g-force tolerance of 10g (98.1 m/s/s).

v = (ar)^0.5 = 313 m/s

At the point when you're going 313 m/s, you will feel a 10g centrifugal acceleration. Now, a launch ring, with an infinitely long track, *will* be able to accelerate you for infinitely long, to ten times escape velocity if need be, but the g-forces will only get more intense the faster you're going, so you'll be dead long before you reach escape velocity.

A linear track, comparatively, is limited by its length (since it doesn't have infinite room to accelerate you in) and again, your g-force tolerance.

Taking again the same 10g g-force tolerance, and the same amount of construction materials (2000*pi length) we'll have an acceleration track of some 6300 meters, and 10 gs to pull in it. In a straight line track, we're limited by:

x = 0.5at^2
t = (2x/a)^0.5
x = 6283m
a = 98.1 m/s/s
t = 11.31802 s

It'll take a little over 11 seconds to travel that 6+ kilometers at 10g, and when you exit the track, you'll be traveling at:

v = at = 1110.298 m/s

v (linear track) / v (launch ring) = 1110/313 = approx. 3.5

So you can get 3.5 times the speed off a linear track. If you have the materials and money to build 6km of acceleration track, it makes more sense to build it straight than in a circle.

Incidentally, a 63km launch track at 10g would take 36 seconds from end to end, and you would exit at a velocity of 3511 m/s -- nearly half of what you need to reach ISS. I think ~60km is just about the top end of what might be achievable in our lifetimes. The smaller scales, a few kilometers in length and giving ~500-1000 m/s boost should *definitely* be achievable.

A 630km launch track at 10g would take 113 seconds (under two minutes) to travel, and you would exit at a velocity of 11,102 m/s. That's the kind of megaengineering scale you'd need in order to not have any significant rocket boosters on the projectile itself at all, just minor thrusters for precision.

So at dozens of km of launch track, you can get half orbital velocity...but you'll need *hundreds* of km to get to actual escape velocity. It's a factor of ten or so.

#21 Re: Human missions » Space stations beyond ISS » 2008-02-16 10:48:23

Here's a thought experiment following Bigelow's big idea -- inflatables.

If we wanted to construct a 450m diameter torus in space, bringing the rigid construction materials from Earth would require many many loads. You couldn't stuff the entire 450m diameter thing into the Space Shuttle cargo bay and just offload it in one fell swoop.

However, with an inflatable, you *can* get a 450m size torus in space with *one* Space Shuttle cargo bay, because it's compressed, and then inflated when it is out of the cargo bay.

Here's some rough calculations.

A torus that is 225m in radius, with the tunnel 5m in radius, with 5mm (1/5 inch) thick Vectran walls, would consist of 222 cubic meters of Vectran.

The Space Shuttle cargo bay is roughly 4.5m x 18m, which is 286 cubic meters. So, dimensionwise, you could compress the torus, stuff it in the cargo bay, launch, exit it in orbit, and then inflate it to full size.

However, 222 cubic meters of Vectran would weigh 311 tons while the shuttle's maximum payload is 25 tons...that's what shoots us down. Not the dimensions but the mass.

In order to fit the shuttle's maximum payload mass, the Vectran walls would need to be 0.4mm thick, at which point the torus would compressed be 18 cubic meters, and mass 25 tons.

If such thin walls would be viable, we could launch the torus whole and inflate it to 450m diameter in space. This would be just the air bladder of the station. After inflation, it should be coated both inside and outside with other materials to shield it from damage. On the outside, shielding against micrometeorite damage, and on the inside, against the mechanical scuffing resultant from human activity. Materials for the interior and exterior coating could have been launched prior to the air bladder launch and been left floating in space waiting for the air bladder to arrive. The interior and exterior coatings would not need to be airtight, their purpose is just to mechanically shield the air bladder. This reduces the shielding construction complexity. Theoretically, we could just spray the outside of the air bladder with layers and layers of hardening foam or whatever.

The key chokepoint of this technique is the required wall thickness for the air bladder to be able to contain a 1000mb (or 500mb, if we want to try working in low pressure) pressure differential with the vacuum. The wall thickness factors directly into the launch mass of the air bladder. If the construction material requires a high wall thickness, then you can't launch because it's too heavy. A high tensile strength material that can contain a 500-1000mb pressure differential at extremely low thickness is mission critical to the concept of building a 1g space station as an inflatable torus.

I'll try to look into the burst strengths of Vectran and other materials another day unless somebody can work that sooner.

One problem I see with inflatables is installing windows, or any other expansions. I don't see cutting holes in the air bladder as a particularly good idea. As such, an air bladder construction may be suitable for quick short-term setup, but long-term, a different architecture might be best.

In other words, first inflate an air bladder as a skeleton, then once you can shirtsleeve inside the "bicycle tire", construct an improved new airtight shell from the inside, and finally ignore the air bladder once the new airtight shell has been finished.

#22 Re: Human missions » Space stations beyond ISS » 2008-02-16 10:09:28

BTW, where did you get your figures for the amt. of m^2 /person (foodwise)

The "Eat like a Martian" thread (the link is right there in the post where I discussed the matter).

I'm confused. Is it about space stations orbiting Earth, or space colonies orbiting the sun?

Either or. General space colony rather than a moon or planet colony. You can discuss heliocentric or geocentric ones, either works.

#23 Re: Single Stage To Orbit » SSTO » 2008-02-15 21:03:38

SSTO is achievable with ground assist.

Mass driver acceleration track + rocket engines fired once clear of the track.

(Or at megaengineering scales -- probably not in our lifetimes -- just the former would be sufficient.)

#24 Re: Human missions » Shipyard? » 2008-02-09 18:52:15

So...if they could be used to build a shipyard...then couldn't they also be used to build ships? Making them, by definition, a shipyard?

So, in essence, you want to build the shipyard out of Bigelow modules. Okay, I suppose there's nothing in principle preventing that.

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