Like the International Space
Station, the Gateway will be a permanent and changeable human
outpost. Instead of circling our planet however, it will orbit the Moon, acting
as a base for astronauts and robots exploring the lunar surface.
The
Gateway concept
Like a mountain refuge, it will also provide shelter and a place to stock
up on supplies for astronauts en route to more distant destinations, as well as
providing a place to relay communications and a laboratory for scientific
research.
Mission analysis teams at ESOC are continuing to work closely with
international partners to understand how this choice of orbit affects vital
aspects of the mission – including landing, rendezvous with future spacecraft
and contingency scenarios needed to keep people and infrastructure safe.
The angelic halo orbit
The Gateway, it has recently been decided, will follow a ‘near-rectilinear
halo orbit’, or NRHO. Instead of orbiting around the Moon in a low lunar orbit
like Apollo, the Gateway will follow a highly ‘eccentric’ path. At is closest,
it will pass 3000 km from the lunar surface and at its furthest, 70 000 km. The
orbit will actually rotate together with the moon, and as seen from the Earth
will appear a little like a lunar halo.
Orbits like this are possible because of the interplay between the Earth
and Moon’s gravitational forces. As the two large bodies dance through space, a
smaller object can be ‘caught’ in a variety of stable or near-stable positions
in relation to the orbiting masses, also known as libration or Lagrange points.
Such locations are perfect for planning long-term missions, and to some
extent dictate the design of the spacecraft, what it can carry to and from
orbit, and how much energy it needs to get – and stay – there.
Travelling on the NRHO path, one revolution of the Gateway in its orbit
about the Moon would take approximately seven days. This period was chosen to
limit the number of eclipses, when the gateway would be shrouded by the Earth
or Moon’s shadow.
“Finding a lunar orbit for the gateway is no trivial thing.” says Markus
Landgraf, Architecture Analyst working with ESA’s Human and Robotic Exploration
activities.
“If you want to stay there for several years, the near rectilinear halo
orbit is slightly unstable and objects in this orbit do have a tendency of
drifting away”.
To keep the Gateway in position, regular small station-keeping manoeuvres
will be required.
Full article: https://www.esa.int/Our_Activities/Operations/Angelic_halo_orbit_chosen_for_humankind_s_first_lunar_outpost
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