> As the chance of collision is influenced by the number of objects in space, there is a critical density where the creation of new debris is theorized to occur faster than the various natural forces remove them. Beyond this point, a runaway chain reaction may occur that would rapidly increase the number of debris objects in orbit, and therefore greatly increase the risk to operational satellites. Called the "Kessler syndrome", there is debate if the critical density has already been reached in certain orbital bands. A runaway Kessler syndrome would render a portion of the useful polar-orbiting bands difficult to use, and greatly increase cost of space launches and missions. Measurement, growth mitigation and active removal of space debris are activities within the space industry today. [1]
(Anyone remember that scene from WALL-E where they need to punch through the debris to get out of Earth's orbit? It's not too far from the truth, and it would definitely make space travel a lot more difficult for future generations!)
On the other hand, an alternative to satellites for private industry means that there will be a lower demand curve for commercial launches, which may limit the amount of research and innovation that private space companies can support.
But of course Earthlings, in their infinite wisdom, have found a solution to low demand curves: government regulation! So the real question is: can our governments find a good balance between debris-proliferation and innovation? Only time and politics will tell!
Can you substantiate your "much cheaper to launch" statement?
Training gliders weigh about 600kg, and they have a 41kw gas engine to self propel and have a wingspan of 18m (based on the one linked on the wikipedia article). Average weight is about 80kg for a male. So these can likely get 160-200kg airborne with ease. RTGs produce about 500w/kg.
Basically we could have done this in the 1960s with a payload of about 80-120kg of equipment.
I wish we could get over our fear of nuclear. It would be very easy and efficient to build one of these with an RTG and you would have the ability to include redundancies and even in the event of engine failure you're not at risk of losing equipment and it can be glided to land. It could also carry its own landing gear and you could automate take off and landing schedules so you need minimal overlap on craft. One goes up to take the place while another gets serviced. With redundancies you could keep them flying with a fixed pitch for potentially years.
The New Horizons craft had the largest space based RTG at about 50kg. The dimensions roughly 0.5m in diameter and over 1.1m long. This means it would end up roughly 6.6m underground, or about 20ft deep. As long as the craft are kept above abandoned land, I honestly don't see a problem with it.
As far as I see they'll be an inevitable choice in areas above 40 degrees latitude. If winter nights are too long to recharge batteries they'll never happen in those areas. I mean by their current proposal the whole UK is out of their market as well as Canada, Alaska and all of northern Europe.
An RTG at 2 kg/kW would be so ridiculously good value that it makes you wonder what has changed about aviation drones to make this viable only now. Is it really just the radiation thing?
Say 40kg of batteries would contain 14KWh, ie. equivalent of 1.5 liter of gas or with adjustment for the thermodynamic efficiency of a gas turbine - 4 liter. Thus 30kg (lets allocate 10kg for the gas turbine and other stuff) of gasoline is a 10 day supply of fuel. Thus your re-fueling drone would need to make 1 trip/week.
Would it make more sense to perpetually spend money on fuel (and the fuel it takes to launch the fuel), or to spend more money up front to design a robust HARP that only comes down in case of severe fault, and is cheap enough that it's easier to just replace it?
Why would it be difficult to detect? It's fairly hard to hide when your entire purpose is to transmit a signal.
>If spacecraft are so precarious, then perhaps investors should lower their sights. But not in terms of innovation; rather in altitude.
As if constraining ourselves to low-earth orbit were too ambitious. It is absolutely disgusting to suggest that, after we gutted NASA in order to make opportunities for private enterprise, we should just stop sending stuff to space altogether. We need to face it: we're never going to become a interplanetary, space-faring civilization under this current economic system.
I do not think that was the point of the article. Some things do not absolutely need to be beyond the atmosphere, they only need to be up high. In the past, the technology to keep things at what might be termed "moderate" altitudes has not been available, so we pushed things above the atmosphere. But when you have technology to do the job better, it does not make sense to continue sending things up to space simply because that is what has been done in the past.
Not to mention, retrievable technology means it can be upgraded, rather than junked (as many satellites are). So this could very well reduce space junk (or at least reduce its rate of increase) and result in more rapid technology development.
There are certainly there are things which will still be easier or better served by the use of satellites up, and so that technology will continue to be developed.
http://scottlocklin.wordpress.com/2011/07/22/good-riddance-t...
This has nothing to do with our economic system. It's basic economics, in the sense that it's resource-intensive to put stuff into space and some resources are scarce. Regardless of how your domestic economy is organized or what sort of monetary policy you favor, the physical resources required for space projects are steep.
I disagree. Just look at SpaceX's development of reusable rockets. We are closer than ever before to becoming interplanetary [OK, that's basically a tautology] and developing space technology faster than any point after landing on the moon.
Well... almost as much as the NASA being a rival of SpaceX, Arianespace being the French/European initiative for space access. Arianespace was founded in 1980 to commercialize the Ariane launcher (planned in 1973 after the europa launcher failure).
While it's true that we might have had them sooner if we were willing to use RTGs, it seems like solar tech is good enough now.
And I don't think an ejectable RTG would go down well with the public, although passive guidance onto a radio source would work and guided munitions sit for potentially decades and have to remain workable.
I wonder how feasible it would be to produce an aerostat that can reach 70,000ft. The DHS(or DEA, the networks shifted hands a few times due to budget cuts, etc) is operating radar based systems with one tonne payloads at 15,000ft. They have a system wide 98% operational efficiency despite being subject to extreme weather.
Carrying on my RTG love, the thermal output of shorter half-life materials could easily out produce the BTUs produced by a hot air balloon burner (800w/kg of vehicle weight) as the space based RTGs can already approach this and have longevities in the centuries. So I wonder if a hot air aerostat would have a longer longevity than the current helium based ones.
I wonder if this would be possible to solve by going "the GPS way". As far as I understand how the system works, GPS signal as received on the ground is 20dB below thermal noise. We can still find and amplify it because we know the seeds and algorithms of random number generators on the satellites. But if you were an alien that just came to Earth, you wouldn't be able to find those transmissions. To read them, you need to know that they are there and what to look for (i.e. have a synced RNG).
I'm not sure if these move fast enough to chase each other down; I bet it takes a while to get up to elevation. Even if that works it's still the same cost to shoot down as it is to replace.
when your entire purpose is to transmit a signal
The problem is that even though its not that much fuel to get from LEO to GTO, you have to haul all that fuel up to LEO first.
Geosyncronous is a whole 'nother matter, and yes, anything placed there will probably still be orbiting when the Sun goes supergiant. Ponder that.
Eh, what? SpaceX is profitable.
And you can't get away from basing your space program on the economy, either because it determines your tax base or (potentially) because companies do space things for profit.
The thought I wanted to express is that our economic system is an optimization process that shapes (and is shaped by, in a feedback loop) the progress of technology. It's the economy that decided we won't be having moon bases or jetpacks anytime soon, even though we could. It's the force that decides that a random photosharing app is worth more than feeding the poor or curing cancer.
Current economy as an optimization process was aligned with human values pretty well so far (though not perfectly; government regulations are one of the tools we use to try and fix that alignment). But as a greedy process (in the CS sense of the word), it often gets stuck in local optimas. That's where Elons, Brins, etc. come in - they have enough cash and vision to force us out of the local optimum and help find a better one.
I don't mean to pass moral judgement here. I only observe that some of the most important problems we have don't yield themselves well to capitalism (which is sort of obvious - the ones that were important but compatibile with greedy optimization are the ones we already solved).
[0] - http://slatestarcodex.com/2014/07/30/meditations-on-moloch/