Ingegneria Marketing Tecnologia
Laurea Specialistica in Ingegneria Spaziale
2° anno
Corso ‘Stazioni di Terra’
Appendice 9
I piccoli satelliti
Giorgio Perrotta
Anno Accademico 2007
Index
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Definitions
Advantages and drawbacks of small satellites
Industry’s and Institutions’ response
Technologies
Technology vs. costs
Technology trends
Technology vs. system uses
Small satellite Near-term Missions
Small satellite Longer-term Missions
Small satellite Complementary Missions
Small satellite Future Missions
Concluding remarks
Definitions
Minisatellites: have typically a (wet) launch mass comprised in the 100-500 kg
range and an installed DC power in the 200-800 W range. They offer good pointing
performance and payload carrying capabilities and can be used for both near
Earth and Geostationary Missions. The features make them a sort of ‘small
conventional’ satellites and, as such, they suffer (mainly cost-wise) from many
drawbacks of the larger spacecraft, while do not fully benefit from the advantages
of the ‘small size’. Minisatellites are often used for unchallenging missions where a
conventional ‘larger satellite’ would cost too much or have unnecessary features.
Examples of Minisatellites: Clementine scientific satellite
Microsatellites: usually they have a launch mass between 25 and 100 Kg (the upper
mass range applies to the ‘wet mass’ if the microsatellite is equipped with a
propulsion system). The prime DC power is in the 50-250 W range depending on
technology. Microsatellites tend to be designed around the COTS concept and
implement simplified project management and AIT : this allows achieving
important savings in the procurement costs. These satellites can be used alone or in
distributed systems, for remote sensing, telecom and science Missions.
Examples of microsatellite: UOSATs, Orbcomm
Definitions (2)
Nanosatellites: these have a dry launch mass in the 5 to 25 kg range and , in
general, do not carry a propulsion system though they may be quite sophisticated.
The installed DC power is in the 10 to 100 W range; they can be provided with full
attitude control in three axes and offer sophisticated data communication
capabilities. Nanosatellites, better deployed for lifetimes less than 3 years in LEO,
can be used to inexpensively implement scientific, remote sensing, communication,
technology research and educational missions, being characterized by a high
affordability.
Examples of Nanosatellites: Tubsats, Itamsat, Opal
Picosatellites: objects having a dry mass between 0.1 and 5 kg (though most of
them have a mass less than 2 kg) and an installed DC power in the 0.2 to 10 W
(though many stay below 2 W). These spacecraft do not carry a propulsion system
but their design can range from the extreme simplicity to a quite high complexity.
Their low cost also allows to implement innovative distributed systems for a variety
of uses, such as : educational, space research, technology test-beds, comms and
sensing .
Examples of Picosatellites: Munin, Stensat, various Cubesat;
Advantages and Drawbacks of small satellites
Advantages
- lower production cost, implicit in the size reduction , and further enhanced by
simplified project management procedures;
- cost reductions enhanced also by the COTS approach , since an inherent lower
cost is compatible with the acceptance of greater risks;
- accessibility to more modern /compact / less power-hungry electronics
associated to the COTS approach;
- easier implementation of spatially distributed systems ( e.g. : constellations,
storms, formations) due to the lower unit cost;
- the availability of a ‘family’ of object characterized by different mass-DC
power ranges, allows to optimize the costs vs. mission reqirements;
- better adherence to requirements of low-budget users;
Drawbacks
- mass and DC power limits are incompatible with ambitious missions;
- small satellites require new thinking and management procedures;
- still poorly understood and accepted by Industry and Institutions;
Industry’s and Institutions’ response
Small satellites have been differently ‘received’ in the USA and in Europe.
The American push for technology innovation, risk acceptance, free enterprise, the
availability of new defense tools, has favourably pushed (we mean: with
Government financial support) the development of these emerging technologies
(mini, micro, nano and pico sats) mainly through the SME (Small Medium
Enterprises) as opposed to the traditional Large Aerospace Companies;
In Europe the lack of real interest towards free enterprise and the large political
power exerted by the big Aerospace Companies (they earn Governments’ financial
support mainly to conserve jobs) has negatively affected the development of the
‘small sats’ technology. Moreover when the large Aerospace Companies felt that
small sats could have plaid a good role in the European space market, they failed
to see this as an opportunity but rather as a threat and acted accordingly. The
ESA, notwithstanding the success of few smallsats in the upper mass range, have
not yet succeeded in convincing the ESA members of the importance of supporting
the full development of satellites below 100 kg (which is what the USA are currently
pursuing).
Technologies (1)
COTS
 The Commercial Off The Shelf (COTS) approach goes hand-in-hand with the
micro and nanosats and can be also exploited in some minisatellite missions.
The USA are putting a large effort in assessing the use of COTS for space use,
given the decline of military expenses going to the Hi-Rel devices and the push
for a dual-use approach to space systems definition;
 However, efficiently selecting and adapting COTS to space implies a good
understanding of the environment and devices’ physics and of the means to
counteract potential deficiencies or weaknesses. Thus, terrestrial devices
cannot simply be ‘exported’ for space use: rather, they must be ‘protected’
from the most dangerous space environment effects ( e.g.: radiations,
temperature ranges, void..) to perform satisfactorily. These ‘protections’ can
be simple and cheap (e.g. an heavy metal screening box) or complex and costly
(e.g. current limiters, external anti-latchup circuits).
 We estimate that the relative costs of a terrestrial, space-capable COTS, and
Hi-Rel unit or devices are in the 1 :10:100 range, meaning that a ‘spatialized’
COTS unit is ten times less expensive than a full space-rated unit.
Technologies (2)
 Besides COTS, the small satellites are inherently open to other new
technologies, specially when forced by the dimensions of the spacecraft itself
 In general the platform subsystems are based on devices whose mass and DC
power drain is commensurate to the spacecraft size. The mass and DC power
range of the smaller spacecraft ( nano and picosats) pushes the search for very
innovative techniques even at the expense of ultimate performance, while for
micro satellites one looks at a good compromise between performance/risk
and mass/power.
Item
Structure
Thermal contr
Propulsion
Attit. Measur.
Attit. Contr.
On board D.H.
Communic.
Picosat
xxxx
x
xxx
xxx
x
x
Nanosat
xxx
Xx
x
xxx
xxx
xxx
xx
Microsat
xx
xx
xxx
xxx
xxx
xxx
xx
Minisat
x
xxx
xxx
xx
xx
xx
x
Technology vs. costs
 Small satellites can be designed and produced at a significantly lower cost than
the bigger satellites. The reasons for this statement are the following:
 recurring costs are proportional to size. In fact the latter affects directly the
materials, electrical parts number, the number of units or equipments, the
manhours required for assembly and testing;
 the documentation costs (a significant item in conventional large satellites) is
less because of the reduced project complexity (number of units / subsystems to
be traced);
 the project management costs are also reduced because of the smaller working
team and a much reduced (in an optimised programme) subcontractors’
number;
 integration and testing costs are less by implementing clever strategies ( e.g.
dedicated areas and experience-cumulating personnel) and simplified testing
approaches (e.g. full-test one out of M and fast-check the remaining M)
 The cost savings are much more than inversely proportional to the spacecraft’
mass size, specially for the two ‘lower’ categories (nano and picosats) and for
multiple spacecraft systems.
Technology vs. System uses
 Picosats, nanosats and microsats are ideal to implement spatially distributed
systems based on a multiplicity of orbiting spacecraft.
 Such distributed systems are:
- storms: fleets of space objects not necessarily maintaining any mutual position
relationships among them. Storms can be injected in various orbits and, being
not equipped with propulsion systems, evolve freely in space;
- constellations: groups of satellites coarsely maintaining certain relative
positions among them. The spacecraft can be equipped or not with a
propulsion system, depending on the orbit altitude and mission type. The
constellations may include a small (say less than 6) or large (say greater than
20) number of satellites and are prevalently injected in LEO or MEO (e.g.: the
GPS constellation) ;
- formations: constellations keeping very tight mutual geometrical relationships
among them, for the purpose of implementing special Missions ( for scientific,
remote sensing or telecommunication purposes). The spacecraft can be injected
in LEO, MEO or GEO. This emerging technique is still at the study stage and
waiting for highly performant nano or microsats;
Small Satellite Near-term Missions
-
-
-
 Mini, micro and nanosatellites can be deployed to execute:
dedicated missions ( one payload >> one satellite : e.g: a store and forward
communication system; a small multicolour camera for Earth’s observation)
coordinated missions (multiple payloads >> one satellite: e.g. panchromatic
camera and multicolour cameras , or panchro camera with store and forward
comms and direct-to-ground data relay)
spatially-distributed missions (one or multiple payload >> multiple satellites:
e.g. a probe for near-Earth sounding of different physical phenomena and
multiple satellites injected in orbits having different altitudes or inclinations) ;
complementary missions (one smallsat works in support of a larger one: e.g: a
mother-daughter assembly for interpherometry or 3_D Earth’s altimetry );
substitution missions (one or multiple smallsats replacing a larger but older
operational spacecraft: e.g. a GEO communication satellite is replaced by a
small constellation of co-located minisatellites; a remote sensing spacecraft is
replaced by one lighter, more modern and more performant mini or microsat);
 The mission performance is determined by the spacecraft class / type.
The ground resolution feasible
even with a nanosatellite is
remarkable indeed: order of 9
m with a 10 cm aperture and
around 3 m with a 30 cm
aperture in the optical visibile
bands. In the mid-infrared (45 microns) the resolution is
four
times
coarser
(respectively 36 m and 12 m)
but still very attractive for
many applications (e.g. fire
detection
and
forest-fire
monitoring). In the thermal
infrared bands ( 9-12 microns)
a ground resolution of the
order of 30 m is feasible with a
30 cm diameter telescope.
Such performance more than
justify the great interest for
nano and microsatellites for
Earth Observation purposes.
Small Satellite Longer-term Missions
Considering that modern spacecraft can be designed with a payload mass and DC
power fraction between 0.5 and 0.6, it turns out that the four small satellite classes
can offer the following envelopes for payloads’ accommodation
class
Mini
Micro
Nano
Pico
Low
mass
50
25
5
0.1
50%
fract
25
13
2.5
0.05
High
mass
500
100
25
5
50%
fract
250
50
12.5
2.5
Low DC
power
200
80
10
0.2
50%
fract
100
40
5
0.1
High
DC pow
800
250
80
10
50%
fract
400
125
40
5
As can be seen the various spacecraft types can offer to potential Users very
interesting payload accommodation capabilities. The above ‘gross’ performance
are accompanied by attractive stabilization characteristics: three axis stabilization
and highly performant attitude control is feasible with the latter types, while the
smaller picosats can implement a 2 axis control with passive means.
Small Satellite Complementary Missions
 Complementary missions are a reasonable and convenient use for small
satellites, where they can demonstrate a good cost-effectiveness.
For
‘complementarity’ we mean that the parent satellite leaves behind certain
secondary missions or experiments the implementation of which would be very
costly if done by that satellite (due to increased spacecraft resources’ demand).
Implementing these secondary experiments with a smaller ‘companion’
spacecraft will lead to an overall lower system cost. There have been already
examples of ‘complementary missions’ and others will certainly follow.
 Substitution missions are less intuitive. In fact to replace a conventional
satellite with an equivalent less massive and costly one, we must imagine that
the technology has matured to the point of credibly and reliably doing the
‘switchover’, getting similar or better performance. For the time being such
credibility is still lacking behind, therefore the ‘substitution missions’ are
something for the future.
Small Satellite Future Missions
The most likely future market for micro, nano and picosats stays with spatially
distributed systems, by some considered capable of replacing (in the medium –long
term) the single spacecraft used for Earth monitoring and to support wideband
communications.
Without doubt, exploiting the potential of small satellites in terms of cost-savings
will be enhanced by the realization of wide-scale spatially distributed systems for
small-delay information gathering purposes. Typical examples of Services
optimally implemented through spatially distributed systems are:
- disaster relief, terrain observations, resources inventory /management;
- search and rescue, crisis management;
- medical and health information , emergency communications;
- deferred-time e-mail delivery to remote areas not reached by wired or
wireless terrestrial networks;
- near-Earth real-time space-weather monitoring;
- world-wide weather monitoring from space;
Concluding remarks
 Innovative technologies and emerging needs (cost reduction) are going to
drastically change the way Space will be exploited in the near and far-term.
Accordingly, the design of Space systems will migrate towards distributed
systems constituted by multiple light-satellites;
 The use of COTS will progressively and massively enter in the realization of
space assets, but requires to be properly understood and managed;
 The pervasive use of silicon in many fabrication technologies, besides the
electronic ones, will be a key factor in the miniaturization and mass production
of future micro, nano and picosatellites.
 The exploitation of spatially distributed systems will increasingly become
possible thanks to the availability of inexpensive micro,nano and picosatellites,
all featuring very interesting characteristics;
The expanding and maturing micro,nano and picosatellite industry will favour the
small medium enterprises more than the larger ones.