86 September 2014 sky & telescopeFocal Point Paul Contursi
It ’s no secr e t that CubeSats are chang-
ing the face of space exploration in a dra-
matically aff ordable way (S&T: Nov. 2013,
p. 64). But new technologies could turn
slightly larger versions of today’s CubeSat
designs into budget-priced interplanetary
probes by the end of the decade.
The fi rst CubeSats had no active
propulsion. But numerous systems are
maturing that will enable them to per-
form a wide range of maneuvers. Aerojet
Rocketdyne is developing miniaturized
chemical thrusters. BUSEK Space Propul-
sion and Systems is pursuing pulsed
plasma and ion thrusters, producing very
low thrust at very high effi ciencies. One
of the most promising avenues is solar
sailing, which uses the pressure exerted
by sunlight on thin, refl ective membranes.
Since the Japanese IKAROS mission dem-
onstrated the feasibility of interplanetary
solar sailing in 2010, NASA has issued
a requirement that CubeSat solar sails
measure no more than a hundred square
meters. The sails must be stowed and
deployed from tight volumes, which poses
the central challenge facing these systems.
A conventional rocket could deliver an
interplanetary CubeSat into Earth orbit
as a secondary payload. After a solar sail
is deployed, each successive orbit could
boost the CubeSat into an ever-widening
spiral trajectory that would ultimately
achieve escape velocity. A 1997 publica-
tion outlined a series of pathways through
the inner solar system called the Inter-
planetary Transfer Network (ITN). These
trajectories optimize the gravity-assist
technique used so successfully since
NASA’s Voyager missions to vastly reduce
the acceleration needed to reach another
celestial body. ITN missions would take
longer and follow a convoluted path, but,for an uncrewed vehicle with limited pro-
pulsion, they would be ideal.
Interplanetary CubeSats would have to
transmit large data volumes over hun-
dreds of millions of miles. In the wake
of NASA’s recent LADEE mission, which
demonstrated the feasibility of laser trans-
mission from lunar distances at data rates
high enough to stream movies, NASA is
working with the Aerospace Corporation
to test a CubeSat version of a similar sys-
tem by early 2015. Instead of using radio,
interplanetary CubeSats will communi-
cate by transmitting optical laser signals
to large telescopes.
CubeSats will suff er radiation dam-
age to electronics and subsystems. These
concerns are magnifi ed for CubeSats
spending months or years in interplan-
etary space, where they’re not protected
by Earth’s magnetic fi eld. As devices are
miniaturized, they become even more
vulnerable. Researchers are developing
techniques to harden these systems by pro-
viding multiple data paths and processors.Interplanetary CubeSats will never
replace larger planetary probes such as
the Mars rovers. After all, some missions
will require large telescopes or bigger
probes that carry more instrumentation.
But when only one or two instruments are
required that can be suffi ciently minia-
turized, the range of potential missions
is wide. JPL researchers are planning
several interplanetary CubeSat missions:
an asteroid mineral prospector, a space-
weather-monitoring platform, and even a
sample return from one of Mars’s moons.
At about $30 million each, these missions
could be fl own for a fraction of the cost of
conventional planetary probes. Since the
fi rst Interplanetary CubeSat Workshop in
2012, the gathering has become an annual
event that off ers a unique opportunity for
collaboration among the growing list of
players in this promising new fi eld. ✦Paul Contursi is a space advocate, consul-
tant, and entrepreneur focusing on CubeSat
launch services.CubeSats to the Planets
Miniaturized spacecraft might soon be exploring the solar system.
UNIVERSITY OF MICHIGANFP layout.indd 86 6/23/14 12:17 PM