Historically, planetary exploration has been performed using
large, complex, and costly spacecraft that have attempted
to bring a laboratory of instruments with them. Only in the
early days of the American and Russian space programs were
the missions less complex and more focused. The Canadian
Robotic Asteroid Flyby and Tentatively Impact (CRAFTI)
mission proposes to return to some of the philosophies of
that era, and to bring modern microsatellite design philosophies
into planetary exploration.
The CRAFTI mission is a concept study completed by the University of Toronto Institute of Aerospace Studies Space Flight Laboratory (UTIAS-SFL) and the Canadian Space Society, with funding from the Canadian Space Agency. The study is aimed at proving that microsatellite technology can, and should, be applied to planetary exploration. The principal investigator is Dr. Kimmo Innanen of York University, and the lead engineer is Henry Spencer of UTIAS-SFL. The target of this project is a Near Earth Asteroid suitable for a relatively slow flyby, tentatively chosen to be Toutatis during its closest approach with the Earth. Asteroids present the best target for such a mission, as they offer the greatest possible science return for relatively simple instruments and relatively low mission cost. In addition, a flyby during closest approach turns out to be a surprisingly easy mission.
CRAFTI mission presents an opportunity to prove that microsatellite
technology has come of age, not only in Earth orbiting spacecraft,
but also in the realm of planetary exploration. The key to
success is a careful tradeoff between available spacecraft
resources and mission design, and having on board only what
is absolutely necessary for the mission to succeed.
planetary exploration missions cost hundreds of millions,
or even billions, of dollars. For instance, the Cassini spacecraft
now on its way to Saturn has an estimated total program cost
of US$3.3 billion. Even NASA's Discovery program, which emphasizes
lower costs, typically costs $100M or more per mission. Lunar
Prospector, the first Discovery mission, was considered an
outstanding bargain at approximately $63M. More recent Discovery
missions have all been more expensive. The Canadian Space
Agency could afford expenditures even at the comparatively
modest Discovery level only as part of a major policy initiative,
which seems politically unlikely. At first glance, the cost
alone would seem to preclude independent Canadian planetary
exploration missions. Upon closer examination, however, this
is not the case. The Microvariability and Oscillations of
Stars (MOST) microsatellite, with a budget of approximately
CDN$6M, could almost operate in deep space. It would need
small adjustments to engineering details, plus:
- An attitude control system (ACS) less dependent on Earth's
magnetic field (star sensors and thrusters instead of magnetometers
- Longer communications range (high-gain antennas and greater
would complicate the design, but the cost increase would be
modest. This suggests that deep space spacecraft need not
being able to operate in deep space is not sufficient to conduct
a planetary mission. Also required are:
- A launch and subsequent maneuvers sufficient to reach
- Trajectory corrections to encounter the target in the
- Instruments capable of returning useful science data from
issues present somewhat more substantial problems, but not
so severe that they are beyond low-cost solutions, provided
the mission is chosen with care and restraint. Small spacecraft
cannot do every planetary mission. But with careful balance,
planetary exploration is not beyond the reach of the microsatellite
approach, and at microsatellite price tags. There are some
constraints. Planetary exploration on a microsatellite budget
appears possible if:
- Spacecraft design is optimized for low-cost, available
- Small-scale propulsion is developed to flight readiness.
- Targets and missions are chosen with cost in mind.
- Restraint is exercised in choice and development of science
- Microsatellite philosophy is applied throughout and existing
design heritage is maximized.
- An experienced team performs the required work.
- Project work is completed at a fast pace to avoid the
extra overheads of lengthy programs.
the Canadian Robotic Asteroid Flyby and (Tentatively) Impact
(CRAFTI) concept. CRAFTI is a Canadian Space Agency (CSA)-sponsored
concept study for an all-Canadian planetary mission on a microsatellite
budget. The target cost is under CDN$20M (approximately US$13M)
including launch and operations. The mission involves a flyby of
a near-Earth asteroid as the asteroid passes near Earth,
and is implemented using two secondary launches. To enhance
mission reliability, CRAFTI proposes to revive a venerable
NASA custom: launching two identical spacecraft for each mission.
Building and launching a second identical spacecraft is relatively
inexpensive, and it provides excellent insurance against mission
loss due to component failure, operations error, or launch
question that arises, then, is given two spacecraft, what
extra science can be performed if both spacecraft succeed
in arriving at the target? If this occurs, one spacecraft
will be tasked with the primary mission flyby, while the other
spacecraft will attempt an impact. The impacting spacecraft
can perform science, including imaging, at very close range,
and the observations of the impact from the flyby spacecraft
will yield information about the structure of the outer layers
of the asteroid.
MOST project is currently demonstrating that a small astronomy
satellite can be built and flown for a total cost (excluding
launch) of ~CDN$6M (US $4M). Much of the design heritage for
CRAFTI comes from the MOST hardware. Many components on the
MOST system can be reused, with modification, in a spacecraft
such as CRAFTI. While new subsystems are needed, and some
need to be largely redesigned (for instance, the radio subsystem),
the reuse of this hardware will help make CRAFTI inexpensive.
Additionally, the experience gained by the UTIAS-SFL team
in building and operating MOST and other planned microsatellite
projects provides an excellent experience base for building
and flying CRAFTI.