'Urgent need' to remove space debris
There is now so much debris in
orbit that the space
environment is close to a
cascade of collisions that would
make space extremely
hazardous, a major
international meeting has
concluded.
Its summary position stated there
was an "urgent need" to start
pulling redundant objects out of
the sky.
Scientists estimate there are
nearly 30,000 items circling the
Earth larger than 10cm in size.
Some are whole satellites and
rocket bodies, but many are just
fragments.
These have resulted from
explosions in fuel tanks and
batteries, and from the high-
velocity impacts between objects.
Upwards of 10cm is trackable with
radar, but there are tens of
thousands more pieces that are
smaller and move unseen.
And it is the prospect of an
increase in the frequency of
catastrophic collisions among all
this material that now worries the
experts.
"There is a consensus among
debris researchers that the
present orbit debris-environment
is at the rim of becoming unstable
within a few decades, a
phenomenon that is commonly
known as the Kessler Syndrome,
and that only active removal of
five to 10 large objects per year
can reverse the debris growth,"
Prof Heiner Klinkrad, the head of
the European Space Agency's (Esa)
Space Debris Office told reporters.
Prof Klinkrad was the chairman
for the 6th European
Conference on Space Debris in
Darmstadt, Germany.
Insufficient compliance
The meeting was presented with
a study earlier in the week that
suggested the population of
objects in low-Earth orbits (LEO) -
the important altitudes used by
imaging spacecraft to health-check
the planet - would likely rise
steadily over the next 200 years
even under the most optimistic of
scenarios.
The research highlighted the need
for better adherence to best-
practice guidelines.
DEOS is a demonstration mission
being pursued by the German
space agency
These "rules" call on space
operators in LEO to make sure
their equipment naturally falls out
of the sky within 25 years of the
end of a mission.
But compliance with the
guidelines is far from perfect, and
the panel said active removal was
now the urgent topic on the
agenda.
Quite how much time there was to
act before conditions became
intolerable was not yet clear, said
Christophe Bonnal from the
French space agency (Cnes).
"We say we want to 'stabilise' the
environment. Does that mean we
are satisfied with today's
situation? Could we live with a
situation that is two times worse
than today, or do we need to
decrease [the debris population]?
These are questions which are
ongoing at international level," he
told BBC News.
Active removal would see new
spacecraft launched specifically to
take other, redundant satellites
out of orbit. And the Darmstadt
meeting was presented with an
array of concepts that included
the use of nets, harpoons,
tentacles, ion thrusters and lasers.
The conference summary panel
told the media it was vital that
pilot programmes were
implemented to advance these
technologies.
Commercial barrier
A few have been approved. The
German Space Agency (DLR) is
developing a project called DEOS
that would demonstrate the
robotic capture of a tumbling
object in space.
"In this mission, what we want to
show is that it is technically
possible to safely approach a
satellite, which we launch together
with our main satellite, to capture
it by means of a robotic arm and
to perform a number of services
like repairing or maintenance
operations," explained DLR's Dr
Manuel Metz.
"Many of the technologies which
are currently being developed for
DEOS would be useful for potential
future international active debris-
removal missions."
The experts also stated that the
international community needed
to sort through the myriad legal
issues that would currently
frustrate attempts to clean up
space.
At the moment, international law
permits only the launching nation
or agency to touch an object in
orbit, something that would
prevent, for example, commercial
debris removal activities.
"My dream is that a new agency
like the International
Telecommunications Union will be
proposed at UN level to
coordinate all this activity," said
Dr Claudio Portelli from the
Italian space agency (Asi).
Costly mission
Esa was hosting this week's
meeting. It has two old satellites
in orbit that are likely to become
targets for a future de-orbiting
exercise.
ERS-1 and Envisat both suffered
major failures that left them
drifting uncontrolled through LEO.
At over eight tonnes, Envisat is
considered a high priority for
active removal
The duo can be tracked but
nothing can be done to move
them off a potential collision
course, should one arise.
Envisat in particular is considered
a high priority for removal
because of its great size - over
eight tonnes.
However, de-orbiting this dead
satellite would probably be very
expensive. And the robotic
spacecraft sent up to bring Envisat
down would itself be very large.
Prof Klinkrad explained: "If you
want to have a controlled de-orbit
- and this is what you should have
for Envisat because large portions
are going to survive to ground
impact - then you should have a
highly energetic chemical
propulsion system, and to reliably
de-orbit Envisat from its altitude
you'd need, I'd say, about 6% of
its mass in terms of fuel.
"With everything included, you are
talking about a two-tonne-type
spacecraft [to do the de-
orbiting]," he told BBC News.
To date, there have only been a
handful of major collisions in
orbit involving the largest objects.
Perhaps the best known was the
2009 impact between the defunct
Russian Cosmos 2251 spacecraft
and the American Iridium 33
satellite. The collision produced
over 1,500 trackable fragments,
many of which continue to pose a
threat to operational missions.
