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Pseudo-satellites: A cheap alternative to satellites is starting to take off

economist.com

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Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#41

Post by winfred »

jessriedel wrote: post #40

Why is this better than a balloon? (Most use cases don't need maneuverability, which usually isn't possible with satellites either.)

The main uses for satellites are observation and communication. Both are appealing markets for HAPS. Hovering drones could act as relays for telephone calls and internet traffic in places that do not have good enough infrastructure on the ground. And there is never a shortage of customers who would like to snoop on various parts of the Earth’s surface, whether for commercial or military reasons.(fta)

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#42

Post by neolefty »

jessriedel wrote: post #40

Why is this better than a balloon? (Most use cases don't need maneuverability, which usually isn't possible with satellites either.)

Probably can control position more easily, to stay over your service area. Balloons relying on air currents for position may not be as reliable.

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#43

Post by TeMPOraL »

T-hawk wrote: post #29
TeMPOraL wrote: post #17

Earlier quoted context omitted.

Maybe "quasi-satellite" or just "quasilite"? It's like "pseudolite" but without the negative connotations.

"Quasi-satellite" already has a different astromechanical meaning: http://en.wikipedia.org/wiki/Quasi-satellite

:(.

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#44

Post by aptwebapps »

electromagnetic wrote: post #39
damian2000 wrote: post #33

Earlier quoted context omitted.

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.

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 abou…

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.

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#45

Post by TeMPOraL »

th0br0 wrote: post #38
TeMPOraL wrote: post #25

Earlier quoted context omitted.

Let me clarify what I meant. Sure, SpaceX is profitable. It has to be. But Elon right now seems to be using the economy to pursue his own goals with Tesla and SpaceX, but those goals are not dictated by what is profitable. He had to amass some capital and then basically force the economy to accept his visions. Tesla Motors pretty much created the market for electric cars that don't suck. SpaceX and Tesla were not eco…

Wonderful comparisons; I might have to steal them from you at some point. Thanks!

You might enjoy reading [0] - one of my favourite articles that dwells upon economic/game-theoretical concepts I addressed in my comment. It's rather long and somewhat specific, but IMO well worth the time to read.

[0] - http://slatestarcodex.com/2014/07/30/meditations-on-moloch/

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#46

Post by sesqu »

electromagnetic wrote: post #11

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 wi…

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?

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#47

Post by dredmorbius »

seanflyon wrote: post #15
btown wrote: post #9

If a network of these aircraft becomes a viable alternative to satellites, this could be a partial solution to the imminent problem of growing space debris, whose quantity and danger posed are decidedly super-linear to the number of objects launched into space: > 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 occ…

Relatively low flying satellites are also a solution space debris as they only stay up a few years. The are much cheaper to launch so the fact that they don't last as long is not prohibitive.

Most of your cost-to-orbit is achieving orbital velocity itself. So a marginally lower orbit (LEO is already ~100-250 miles) doesn't seem like it would offer that much in the way of launch cost savings.

Can you substantiate your "much cheaper to launch" statement?

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#48

Post by leoedin »

TeMPOraL wrote: post #27
dmd wrote: post #22

Earlier quoted context omitted.

Why would it be expensive to shoot down? Just send another one of these up after it, and crash into it. Why would it be difficult to detect? It's fairly hard to hide when your entire purpose is to transmit a signal.

> It's fairly hard to hide when your entire purpose is to transmit a signal. 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…

If you have a directional antenna (which would be needed to actually locate the transmitters location anyway) it's actually quite easy to spot GPS signals. It's only because conventional GPS antennas need to receive signals from all directions at once (or at least half of a sphere) that the signal drops below the noise floor. Any signal which can communicate a reasonable amount of data will have to be high powered enough to be easily detected and located by third parties.

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#49

Post by seanflyon »

dredmorbius wrote: post #47
seanflyon wrote: post #15

Earlier quoted context omitted.

Relatively low flying satellites are also a solution space debris as they only stay up a few years. The are much cheaper to launch so the fact that they don't last as long is not prohibitive.

Most of your cost-to-orbit is achieving orbital velocity itself. So a marginally lower orbit (LEO is already ~100-250 miles) doesn't seem like it would offer that much in the way of launch cost savings. Can you substantiate your "much cheaper to launch" statement?

The Falcon9 for example has a payload of 13,150 kg to LEO and 4,850 kg to GTO so that is nearly 3 times the cost (http://en.wikipedia.org/wiki/Falcon_9). Every rocket I have checked has a similarly small payload to GTO compared to LEO.

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.

Re: Pseudo-satellites: A cheap alternative to satellites is starting to take off

#50

Post by electromagnetic »

aptwebapps wrote: post #44
electromagnetic wrote: post #39

Earlier quoted context omitted.

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 abou…

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.

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.

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