One
hundred kilometers above the Earth's surface space is starting to fill up with
debris, with hundreds of now defunct satellites and tens of thousands of
smaller bits of waste. As the cost for launching into space continues to
go down the volume of satellites will continue to rise. While we are
unlikely to see a dramatic loss of orbiting equipment as portrayed in the movie
Gravity, there is a risk that the volume of debris could reduce the overall
life expectancy of spacecraft in more crowded orbits. Researchers from
around the world have suggested various ways to clear orbits, ranging from
designing satellites that will intentionally fall back to Earth at the end of
their useful life, to using high tech harpoons, and using lasers to slow down materials
sufficiently for them to burn up
in the atmosphere.
As of May 2019, there
have only been handful of small-scale experiments intended to test some of the
proposed methods of eliminating space debris. While the results for these
removal methodologies appear to show positive results, humans have yet to
establish a standard for cleaning our space-based messes. While all
reasonable solutions to space debris should be given consideration, this
article will make an argument for the use of satellite-based laser platforms as
a way to control space debris.
Lasers can be used in
two primary ways to eliminate space debris ablation and vaporization. For
most readers when they think of using a laser to clear space debris, they are
likely thinking about vaporization. Vaporization is achieved by aiming a
strong laser at a piece of material as long as it takes to heat the material
enough for it to be broken down into microscopic components. This
requires a very strong laser, several megawatts, and as a result a large amount
of power. The approach preferred by researchers at NASA deals with
ablation. Laser ablation happens when a strong laser is focused on a
target for several hundred nano-seconds, this very short pulse is sufficient to
cause microscopic pieces of material to be ejected from the target material,
while leaving the remainder of the target seemingly unscathed. As
microscopic pieces are ejected from the target material, they create a small
amount of thrust that causes the space junk's orbit to change. Eventually
the changes in orbit caused by the ablation of the space debris are sufficient
to send the material back into the Earth's atmosphere, where the remainder of
the debris will burn up. Because ablation is only burning enough material
to change the orbit of the debris, the overall energy requirements are
drastically lower than vaporization, the tradeoff that it will take more time
to clear out materials.
Currently there are
proposals for both ground and space based laser platforms that could be used
for clearing orbit. According to this NASA paper, a single space based laser would
be massive, where the solar panels alone would need to be over 500 meters in
diameter to supply the roughly 108 Megawatts of power the laser would
require. At first glance a massive solar array in orbit would seem prohibitively
expensive, such a massive undertaking needs a longer-term perspective. Early
in the life of the Anti-Debris Laser System (ADLS), almost all power generated
by the solar arrays would be used to clear debris and maintain orbit.
Over the years the volume of debris would begin to drop off and soon our ADLS
would have a power surplus and the ability to transmit that energy over a long
distance. The primary debris clearing laser could be augmented by a
collection of smaller energy transmitters. Much as the International
Space Station now serves as energy source and orbital platform for a range of
experiments, the ADLS could serve both as platform and power source for
countless future scientific projects.
One extreme example of
the ADLS being used as a remote power source would be for low Earth orbit satellites proposed by the
European Space Agency. These air breathing ion engines are intended to
capture the rarified gases that orbit the Earth and use these materials to
supply fuel for their ion engines. A challenge facing current design
proposals is the added drag that their solar panels would supply. If the
satellites were designed with the ability to receive additional energy from a
directed energy source they would be able to get by with fewer solar panels,
which would both reduce the weight of the space craft and reduce drag, a nice
little win win.
Future Scenario
April 12th 2051
A new satellite
communications start-up has submitted a power purchasing agreement from the
United Nations Space Agency's ADLS division. According to their filing,
they are looking to buy sufficient power to supply a constellation of at least
2500 Ultra Low Orbit communication satellites. These satellites will have
some of the lowest orbits ever authorized to a non-governmental body. In
a press release yesterday their spokesbot said "Fastest Trade is looking
forward to working with the United Nations Space Agency to help provide 7G
Micro Latency communications to the global market of ideas. Our
technology will allow consumers around the world to shave critical nano-seconds
off of their communications." The press release was positively received
by several High Frequency firms. A researcher from the European Space
Agency noted that without the external power provided by the ADLS, the orbits
of the Fastest Trade satellites would need to be several kilometers* higher
than what they have filed for.**
(Scenario 2)
12 hours ago disaster
struck Bigelow Research Station El Dorado, due to a series of software errors
the station's on board solar panels stopped orienting towards the Sun.
Seven minutes after the error was confirmed support teams from available ADLS
platforms were able to add the El Dorado to the orbital power grid user
base. While investigators try to determine how and why the solar panels
ceased to function, researchers were able to continue their various
projects. Currently the software team is pointing fingers at an
unauthorized 3rd party addition to the solar control platform.
* yeah the scenario is
fictional, but I do want to say its on the hard science side of things and the several
kilometers value is basically random. That being said lower drag with a
better engine should mean a lower orbit I just don't know by how much.
** honestly high
frequency trading is the only reason I can think of as a long term use
for satellites at a really low orbit, that being said I hope there are more
generally beneficial uses of this concept.
I hope this idea was
interesting, it was inspired by a friend asking me about the potential for
using existing satellites and space debris as a source material for future
missions. If you are interested in ideas around re-using old satellites,
feel free to check out this post I did a few years ago
Questions and comments
are welcome
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