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The International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beiiing 2008 
2. SMALL SATELLITE MISSIONS: FACTS AND 
TRENDS 
From figure 1 we can learn that, roughly, the smaller the satel 
lite the less the cost and the response time. This is a strong 
motivation to try to go for small satellite missions. The IAA 
study (Sandau, 2006) presented the state of the art of small 
satellite missions and examined more factors that enable one to 
produce a cost-effective small satellite mission for Earth obser 
vation. It seems, while there are several examples of such mis 
sions flying today, the lessons that must be learned in order to 
produce cost-effective small sat missions have neither been 
universally accepted nor understood by all in the space commu 
nity. One of the intentions of that study was to point out how a 
potential user can produce a cost effective mission. One of the 
key enablers of designing a cost-effective mission is having the 
key expertise available. As the number of successfully space- 
faring nations grows, the pool of expertise available to meet the 
challenges of small mission grows. 
2.1 General Facts 
Small satellite missions can be achieved by using different 
approaches and methods. 
Since the advent of modem technologies, small satellites have 
also been perceived to offer an opportunity for countries with a 
modest research budget and little or no experience in space 
technology, to enter the field of space-borne Earth observation 
and its applications. 
One of the possible approaches is taking full advantage of the 
ongoing technology developments leading to further miniaturi 
zation of engineering components, development of micro 
technologies for sensors and instruments which allow to design 
dedicated, well-focused Earth observation missions. At the 
extreme end of the miniaturization, the integration of micro 
electromechanical systems (MEMS) with microelectronics for 
data processing, signal conditioning, power conditioning, and 
communications leads to the concept of application specific 
integrated micro-instruments (ASIM). These micro- and nano 
technologies have led to the concepts of nano- and pico- 
satellites, constructed by stacking wafer-scale ASIMs together 
with solar cells and antennas on the exterior surface, enabling 
the concept of space sensor webs. 
The advantages of small satellite missions are: 
• more frequent mission opportunities and therefore faster 
return of science and for application data 
• larger variety of missions and therefore also greater diversi 
fication of potential users 
• more rapid expansion of the technical and/or scientific 
knowledge base 
• greater involvement of local and small industry. 
After some years of global experience in developing low cost or 
cost-effective Earth observation missions, one may break down 
the missions into categories like: 
Commercial - Requiring a profit to be made from satellite data 
or services 
• Scientific/Military - Requiring new scientific/military data 
to be obtained 
• New technology - Developing or demonstrating a new level 
of technology 
• Competency demonstration - Developing and demonstrat 
ing a space systems competency 
• Space technology transfer/training - Space conversion of 
already competent engineering teams 
• Engineering competency growth - Developing engineering 
competence using space as a motivation 
• Education - Personal growth of students via course projects 
or team project participation 
Large satellite missions and small satellite missions are consid 
ered to be complementary rather than competitive. The large 
satellite missions are sometimes even a precondition for cost- 
effective approaches. 
2.2 Trends 
Small satellite missions are supported by several contemporary 
trends: 
• Advances in electronic miniaturization and associated per 
formance capability; 
• The recent appearance on the market of new small launchers 
(e.g. through the use of modified military missiles to launch 
small satellites); 
• The possibility of ‘independence’ in space (small satellites 
can provide an affordable way for many countries to 
achieve Earth Observation and/or defense capability, with 
out relying on inputs from the major space-faring nations); 
• Ongoing reduction in mission complexity as well as in those 
costs associated with management; with meeting safety 
regulations etc.; 
• The development of small ground station networks con 
nected with rapid and cost-effective data distribution meth 
ods. 
3. APPLICATIONS 
3.1 Remote sensing requests 
Different remote sensing applications need different approaches 
for cost-effective missions. Figures 2 and 3 show the very di 
vers requirement coming from the different remote sensing 
application fields. 
The range of GSD covers centimetres to several hundred meters. 
The revisit time ranges from less than one hour to 10 years. The 
range of spectral requirements starts with panchromatic only for 
topographic mapping and ends with hyperspectral resolution, 
for instance in the field of hydrology. Even within the different 
application fields, the related subtasks may cover huge areas 
again. Figure 4 shows the requirement range for different 
coastal applications. In fig. 4 the GSD ranges from meters to 
kilometres with revisit times from half an hour to several years. 
It is obvious, a satellite system for remote sensing needs to 
focus on one of the application fields and within that application 
field on a specific task or group of tasks where feasible.