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if Earth gravity is necessarily optimum for human longevity
I'm not convinced that's been satisfactorily proven.
Common sense would suggest to me that mildly higher gravities (say, 1.1g or 1.2g) would correspond to constant workout, making us very athletic, low-fat and less prone to cardiovascular diseases since every time we moved it'd be like carrying some dumbells.
acce4pting premise 2, wouldn't say, 1/2 g, or mars g be better?
I don't see that it is. If we intend to provide non-Earth gravity, I think heavier gravity (forcing greater exertion and keeping us in better health) would be better than lighter gravity (allowing us to slack and develop cardiovascular diseases).
Like I said, simple physics. Gravity increases as you move towards the center of a body of mass, and decreases as you move away from the center.
Like I said, that's oversimplified and inaccurate physics. When you get all the way down to the center, you'll actually get 0g. The gravity will be dropping towards the center of the planet, because you're starting to have the same mass all around you, pulling you equally in all directions and cancelling each other out.
I haven't calculated what the tip-over depth is, where gravity will start decreasing with depth rather than increasing with depth, but that will happen at some point.
Of course, 300+ km inside Mercury might be very uncomfortable due to heat...not to mention the sheer difficulty of creating a 300+ km long tunnel. It's so far beyond any current technology we can conceive it's not even funny. We're not even able to dig 10km deep on our homeworld, let alone 30 times deeper on another celestial body by remote operated probes.
Might be doable someday, but definitely not in our lifetimes.
I also question whether Mercury has enough atmosphere to provide that 1 bar...is there enough atmosphere on the surface to fill that hole entirely?
I did a quick and dirty calculation that suggests that if you gathered up the entire atmosphere of Mercury (for which I got a rough figure of 560 000 kg) and placed it over one spot, that spot could be a maximum of 5.6 square meters if we wanted to provide 1 bar...any larger than 5.6, and the mass is insufficient to provide 1 bar anymore.
(Although, this NASA page says the total atmosphere mass is in fact less than 1000kg, which is even worse...)
Light has no rest mass, because light is never at rest.
There are many things that are never at rest, yet do have rest mass. For example, every single atom in your body. Unless they have been chilled to absolute zero, they are not at rest currently, nor is it likely they will be at rest for millions of years to come. Thermal vibrations (temperature) will keep them moving perpetually. Yet, the atoms do have rest mass.
I would rather prove it in the inverse direction:
If light *did* have rest mass, then when light traveled at the speed of light, its mass would be increased to infinity. Since we have observed light traveling at the speed of light, it should have infinite mass when traveling at that speed. Momentum is mass times velocity. Infinite mass times velocity of light is a quite considerable number. By the law of conservation of momentum, when light hits something, it should impart an infinite amount of momentum onto whatever it hits. Since we are not blown apart whenever light hits us, it must be assumed that light has negligible momentum. If its momentum is negligible, either its mass or its velocity must be negligible. Since it is traveling at the speed of light, we know its velocity is not negligible. Therefore, light's mass must be negligible. Negligible = very small or zero. Since very small would have been increased to infinity by the velocity, only the zero option is valid. Therefore, light has zero mass. QED.
Well, since you'd have 0.5g upwards and 0.5g downwards, it would all balance out to 0g. After all, if you're in the centerpoint, which direction are you going to fall in? Up or down? Answer: neither. Centerpoint has 0g, and you'd stay floating there, because there's equal mass in every direction, cancelling out the opposite directions.
I don't think you'll get 1g anywhere on Mercury, no matter how deep you go.
In fact, if you dig all the way to the exact centerpoint, you will have 0g.
By mass and luminosity, planets, even Jupiter sized planets, are a mere fraction of stars.
Kind of it like asteroids are harder to detect than planets. People were able to track Venus as long as humans have been looking up, but tracking Pallas and Vesta was much harder.
We're pretty much in the infancy of detecting extrasolar planets. Throwing in the monkeywrench of them being in a nebula would only be an added complication and most likely would make it harder, not easier.
Wouldn't the nebula give off certain characteristics that would be different from a planet the size of Jupiter or Saturn?
Yes, visual appearance the most obvious one of course. A nebula will look very different from a planet.
Would the gravitational variations be noticeable since the nebula functions one way and a planet another way.
I'm not sure how massive the average nebula is. But there would definitely be a different distribution of the gravity, as the mass of a nebula is widely spread out while a planet's is tightly concentrated in space. I suppose between a planet and nebula of equivalent mass, the difference might not be substantial for an outside observer, but to someone traveling inside the nebula, I have to wonder if they'd experience any significant gravity.
Are there any programs currently either operating or being developed whose main emphasis is to study NEOs?
Knowing which ones have the valuable volatiles would be really important information to have. Do we have this information, or do we have a program for finding out this information?
cIclops is right. You will need math almost *everywhere* in science, and quite complex and painful math at that. Especially if you want to get into something like physics (the math makes me want to shoot myself in the head every day). Become as good at math as humanly possible, and university majoring at a science will be MUCH easier...
Several reasons.
Nebulae are the remnants of a supernova, and planets tend to get blown apart by supernovas. It's like asking why there's nothing but dust and ashes in ground zero.
Nebulae are accretion disks, and planets have not coalesced yet.
So depending on whether a nebula is the "birth" or a "death" of a solar system, the planets might not have formed yet, or might have been blown apart.
Of course, these are not the only possibilities. There are many nebulae that do house stars. (These are often called "stellar nurseries".) It's entirely possible that if a star has coalesced, planets might have as well.
Even if there are planets within nebulae, they'll be orders of magnitude more difficult to detect than the stars within nebulae. It could simply be that they are too difficult to detect.
Just like the rest of us, you have no choice.
But it's good that you're so optimistic about getting to hold the bigger purse strings.
Building a little on terraformer's initial idea, here's a thought:
Not magnetic acceleration rings in space, but in the atmosphere.
Have n balloons at altitude y, spread out in an equidistant ring of radius r.
Repeat formation at altitude y+1, y+2, y+3, y+4, ... , until max altitude of balloons.
Each balloon ring generates an electric field to push projectiles upwards towards the center of the next higher ring.
In effect, a mass driver without a tube, and with a 30km launch "rail".
Is a tube or a rail needed, or could you construct a pseudo mass driver like this, with empty air as the acceleration track?
Unfortunately, even if this would be feasible, it still wouldn't be enough for humans, as a 30km launch track would still require 200g of acceleration to reach escape velocity at the end of it. Unless you wanted a hybrid launch, continuing with rockets once ejecting out of the balloon tunnel.
Total power required during acceleration = 2.5GW/Kg.
That's a lot of power pouring into a very small projectile. The odds are that it would melt within the barrel.
Of course, you could just take it easier and use a mere 8MW of power, which would still fire off the projectile in 7.6 seconds.
Even just 10, maybe even just 1, probes that could direct asteroids/comets to targets would be an improvement on the current stasis.
True, it would be. But a very trivial improvement. There would be no tangible return on the investment. Basically, to the ones that have the money, it would be like throwing away money on something that doesn't do anything noticeable. Of course, it's arguable that the current missions don't do anything noticeable either...with a few notable exceptions. Mars rovers and Huygens lander were/are some amazing stuff.
Multiple targets to get round the disagreement?
Which would only mean being able to do even less on each separate front. If we can't even muster enough money to terraform Mars, how well would it work out if we tried to terraform Mars, Moon, Venus and Titan at the same time, and Mars got only a quarter of the funding it would have otherwise gotten? We'd get nowhere even slower.
I'm in favor of the 'bombard it with objects' approach to terraforming. And the 'scorch it!' approach. It's the quickest.
And there's a lot of objection to such tactics from those holding the purse strings. Today's world is all about pussyfooting around and being wimps, not men.
A 10g (centrifugal) launch ring would be able to launch bulk goods as fast as desired. A bulk delivery could be accelerated tangentially at 1,000,000 g if we felt like it, that's not a problem. Big accelerations can be achieved however we like. It's the small accelerations (for humans and non-bulk goods) that have high requirements.
Probes that cheap wouldn't be able to do anything.
Plus, I don't think there's agreement on what the first target should be, how the terraforming should be conducted, nor even if terraforming *should* be conducted.
So it's both a matter of a) money; huge amounts are needed to terraform, and b) disagreement; nobody can agree on what to do.
Building for example an asteroid-pushing tug will be much more expensive if it's man-rated than if it is automated. You'd have to have an atmosphere circulation system, food, bathrooms, waste recycling, all kinds of extraneous stuff that would add huge amounts of weight that an automated tug wouldn't need to implement.
I suspect you've been making incorrect assumptions if you've been assuming people think early tugs would be manned.
Only if the 10g one can go to 10000gs.
And what use would that be? Why would you want to accelerate something faster than you'd have to?
Are you sure you're not confusing centripetal acceleration and tangential acceleration?
Human space flight has always involved a lot of risk. If that level of was unacceptable, nobody would fly.
Right, that's what I was saying. That 98% was acceptable.
Sure hasn't stopped the most recent missions. They sure are accepting the risk.
It'd be suicide *not* to use automated mechanisms in the beginning. I think it'd be more apt to ask if anybody's actually seriously thought about starting terraforming by going there yourself.
There's no realistic way to get the gs down to merely tens with a mass driver. Even hundreds of gs is pushing it.
Maybe as a nationwide megastructure, barely.
For the record, here are the numbers:
For a 10 g force pressing you against the launch ring's outer wall, you will need a launch ring 1230km in radius (2470km in diameter).
100g, 123km radius.
1000g, 12.3km radius.
10000g, 1.23km radius.
I could see a 10000g mass driver being built, but beyond that is going to get real expensive, real fast.
And there's no reason to build multiple mass drivers. If you built a 10g one, you could also use it for the medium and bulk goods.
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And... 98% reliability... Is that considered man-rated internationally?
It would not be considered man-rated by current US standards, but the risk would be considered acceptable for the Chinese.It must be close. How reliable is the shuttle?
1 - 2/120 = 98.3%
Seems to be acceptable for the Americans too.
The power supply need not be heavy at all. In fact, theoretically (assuming a vacuum and superfluidic mass driver tube, so no friction losses), you can build a mass driver powered by a shaft cranked by a single human. Friction losses will give us a minimum level of power input necessary, but it should be trivial.
Something accelerated at as low as 0.01g will reach escape velocity after 31.2 hours of continuous acceleration. 0.0001g (a ten thousandth of a g) would reach escape velocity in about a third of a year of continuous acceleration. Since (by Newton) F=ma, then the force needed is directly proportional to the acceleration we use. By putting the acceleration suitably low, we can put something to escape velocity with very little force (and resultantly, watts) needed. It will just take time, and an acceleration track of infinite length (i.e. a ring, like particle accelerators use).
So the launch costs would be the construction of the launch ring in the first place, plus electricity costs.
The friction losses will be pretty extreme inside the launch tube at high speeds, you'll definitely want to have a spherical delivery system which can roll inside the tube for rolling friction, i.e. shooting giant marbles upwards.
Not taking into account the non-trivial friction losses, accelerating 1000kg of mass to escape velocity inside our circular accelerator would require 0.5mv^2 of energy. Let's say we have a solar power plant 200m by 200m for a total of 40000m2, each square meter giving us, say, 200W of power. That would give us 8 megawatts for the acceleration during peak daylight.
t = E/P = mv^2/2P ~= 2.1 hours
So you could launch several 1000kg loads during peak daylight, let's say 6-8 hours are good light, so we could fire off 3-4 loads a day with our 8MW solar power plant.
So your costs are the initial ring/tube construction, the solar power plant construction, and then just maintenance. Basically, once it's built, launches are free of cost.
Friction's the only thing that messes this up...air friction inside the tube can be pretty much eliminated by vacuuming the tube...but rolling friction can't really be eliminated and it's gonna add up at high speeds.
(Incidentally, at escape velocity and assuming 10000g centrifugal acceleration pressing the sphere against the launch ring outer wall, the rolling friction would be approximately 500 kN of force dragging on the sphere, or about 50g of tangential backward acceleration to beat. Whatever force we're using to accelerate the sphere inside the tube would have to be able to push at least 50g of tangential forward acceleration in order to maintain the sphere's escape velocity until launch.)