

Pseudo-satellites: A cheap alternative to satellites is starting to take off - klearvue
http://www.economist.com/news/science-and-technology/21614095-cheap-alternative-satellites-starting-take-west-wind-blows

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btown
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
> 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!

[1]
[http://en.wikipedia.org/wiki/Space_debris](http://en.wikipedia.org/wiki/Space_debris)

~~~
seanflyon
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.

~~~
dredmorbius
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?

~~~
seanflyon
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](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.

~~~
dredmorbius
But higher LEO orbits _are_ pretty stable from what I understand. I'd have to
look up data, but we're talking centuries to thousands of years for decay, no?

Geosyncronous is a whole 'nother matter, and yes, anything placed there will
probably still be orbiting when the Sun goes supergiant. Ponder that.

~~~
seanflyon
After some quick searching I could not find any trustworthy numbers on how
long satellites stay up in higher LEO. My impression is that it's decades at
most, but I could be way off.

~~~
dredmorbius
Definitely not my area of expertise, but my understanding is that the upper
reaches of the atmosphere are quite dynamic, and various circumstances
(including possibly solar storms) may cause the atmosphere to reach out
further than it normally does. Density of the satellite in question, and
extent of any large surfaces (solar panels, etc.) which might tend to increase
drag or cause tumbling (a bird does no good if it doesn't point right) are
other factors.

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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.

------
fensterbrett
How do they compare with Google Loon?

[http://www.google.de/loon/](http://www.google.de/loon/)

~~~
seanflyon
More maneuverable, but more expensive.

~~~
dredmorbius
Also probably more durable. Loon is a one-shot mission lasting at best a few
weeks. I suspect the ultimate limit is UV degradation of the mylar balloon
envelope. The fact that you'd be littering the planet with yet more plastic
(though on a pretty small scale) also comes to mind.

------
trhway
one of the things that really can be resolved by technology here is re-fueling
in air. You don't need solar panels and batteries if your drone hanging at
20km can be automatically supplied by refueling missions of another drone.

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.

~~~
pavel_lishin
But if you can build a drone that can stay up nearly indefinitely, why bother
refueling it?

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?

------
qwerta
NASA patfinder has been around for some time already:
[https://en.wikipedia.org/wiki/NASA_Pathfinder](https://en.wikipedia.org/wiki/NASA_Pathfinder)

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

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

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nkozyra
Missed opportunity at "pseudollite"

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

~~~
T-hawk
"Quasi-satellite" already has a different astromechanical meaning:
[http://en.wikipedia.org/wiki/Quasi-
satellite](http://en.wikipedia.org/wiki/Quasi-satellite)

~~~
TeMPOraL
:(.

------
mturmon
Hmm, an un-crewed airplane for remote sensing applications:

[http://uavsar.jpl.nasa.gov](http://uavsar.jpl.nasa.gov)

[https://airbornescience.nasa.gov/aircraft/SIERRA](https://airbornescience.nasa.gov/aircraft/SIERRA)

------
nothiggs
As for using it for military purposes - wouldn't any country it flies over
that has the ability to detect it, just shoot it down?

~~~
seanflyon
At 70,000 feet it would be expensive to shoot down and quite possibly
difficult to detect.

~~~
dmd
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.

~~~
TeMPOraL
> _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 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).

~~~
leoedin
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.

------
nlkndlk
>That Arianespace, a French rival of SpaceX, announced on the same day that
two satellites it had tried to launch to join the European Space Agency’s
Galileo constellation (intended to rival America’s Global Positioning System),
had entered a “non-nominal injection orbit”—in other words, gone wrong—shows
just how difficult the commercialisation of space can be.

>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.

~~~
privong
> 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.

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.

~~~
ericd
He may have a point - it's locally optimal to decrease the cost of
applications, but it may be globally optimal to pay more for those
applications to increase space launch volume and decrease the marginal cost of
a launch.

