[electromagnetic]

I wonder what the lower weight limit is on these. The solar panels produce 1kw/kg the batteries store 350 watts per kg. The whole thing weighs 50kg and has a 23m wingspan.

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.

[damian2000]

I agree, but hundreds of nuclear power sources hovering around the planet controlled by a single corporation ... sounds like the plot of a James Bond movie.

[electromagnetic]

It definitely does! However, if one of these did go uncontrolled and break up, it's a kinetic impactor. The Uranium core should act like a DU penetrator if the craft disintegrated, meaning it should penetrate ~6 times its length.

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.

[aptwebapps]

Planes don't always fall straight down. From that height they could go a long way. It would be hard to keep them over empty land and still close enough to enough people to use them.

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.

[electromagnetic]

I would assume if it has to stay above the weather its wings would be very prone to breaking. However at a descent rate of 0.5m/s and a 40:1 glide ratio. Descending the ~20,000ft before hitting weather would mean 150 miles travelled before being at risk of breaking up.

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.

[sesqu]

Note that the batteries do not store 350 W/kg, but 350 Wh/kg. That means the majority of weight is batteries, since you need 1 kg/kW for the day but 1 kg/kW + 12 h * 1 kg / 350 Wh for the night, giving a total of 36.3 kg/kW of continuous power. The article implied that these things could not store enough power for the nighttime, which is easy to believe from those numbers.

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?