ROOM
20
Special Report
which makes communication distances very
manageable. Near Earth Asteroids (between 0.98
and 1.3 astronomical units (AU) distant from
the Sun) are another rich target set, with their
number estimated at over 14,000, and ~1000
of them larger than a kilometre in diameter.
By the end of this century, we will probably
only visit a handful with larger spacecraft like
NEAR Shoemaker, or Japan’s Hayabusa. But
nanosats could be sent in large numbers to
examine hundreds of asteroids close up within
a generation, at a much lower price tag than the
larger missions.
A launch window for energy-efficient
trajectories to Mars opens up at intervals of about
26 months and, in recent times, most windows
have one or more spacecraft taking advantage of a
fast transit to the red planet. Nanosats could ride
along as ballast to make up the launch mass on
larger Mars missions, or make their way there as
free-flying spacecraft. With a few km/s of Delta-V
(propulsion) capability, free-flying nanosats could
be placed into orbit around Mars, opening up the
potential for science from orbit, and adding to the
communications and navigation infrastructure.
The main asteroid belt, situated 2.2 to 3.2 AU
out from the Sun, contains 0.7-1.7 million objects
with a diameter of greater than 1 km. Thus far,
spacecraft passing through the asteroid belt en
route to the outer planets have given us a closer
glimpse of only a few; and NASA’s Dawn mission
has provided detailed examination of just two
of the largest, Ceres and Vesta. This is definitely
rich hunting ground for nanosat missions – the
asteroid belt is close enough to the Sun that
solar power generation is practical, and close
enough to Earth that communication distances
are manageable. It can take a long time to get
out to the main asteroid belt though – Dawn
arrived at its first target, Vesta, nearly four years
after launch – so reliability and longevity will
need to be demonstrated over several years
before we send nanosat explorers to the Belt.
We know of 5000 comets to date whose
orbits take them close enough to the Sun
that their tail is visible from Earth. Again, our
spacecraft have visited less than a dozen:
Halley’s comet, 21P/Giacobini–Zinner, 26P/
Grigg–Skjellerup, 107P/Wilson–Harrington,
19P/Borrelly, 81P/Wild, 9P/Tempel, 103P/
Hartley, 2P/Encke, and 67P/Churyumov–
Gerasimenko. That leaves plenty of possibilities
for nanosat mission flybys and encounters of
future comets.
We know enough about comet trajectories
to plan and quickly execute flyby missions, but
rendezvous missions where we catch up with
a comet take a little longer and will require a
higher standard of reliability: ESA’s flagship
Rosetta mission took 10 years to rendezvous
with comet 67P/Churyumov–Gerasimenko. Such
long mission durations are not unusual when
we plan missions to chase the so-called ‘short-
period’ comets.
X-Band
Deplyable
Antenna
X-Band
Transmission
UHF
Transmission
The inner Solar System is fairly easy to reach,
being accessible to both free-flying and ‘hitch-
hiker’ cubesats/nanosats
The two MarCO
cubesats will execute a
flyby of Mars and relay
UHF telemetry received
from the InSight lander
directly back to Earth
using an X-band
communications link.
NASA/JPL
NASA/JPL
