SMALL SATELLITES — A TOOL FOR EARTH OBSERVATION? 
Gottfried Konecny 
Institute of Photogrammetry and Geolnformation, University of Hannover, Nienburger Str. 1, D-30167 Hannover, 
Germany, phone: +49-511-762-2487; fax: +49-511-762-2482; konecny@ipi.uni-hannover.de 
Invited Paper: Commission IV 
KEY WORDS: Satellites, remote sensing, mapping 
ABSTRACT: 
Small satellites with a mass between 10 to 500 kg have become a competitor to large satellites with a mass of over 1000 kg. This 
development has come about through the technological advances in micro-electronics. Small satellites are obviously less costly for 
launch. However, limitations for uses of small satellites exist through special requirements imposed in particular for remote sensing 
missions such as orbital and attitude control, sensor design and data readout. About 500 small satellites have been launched sofar, 
but only a small percentage of these for earth observation. Nevertheless sensing with 8 m ground pixels has been achieved. The 
International Academy of Aeronautics and its biannual symposia on small satellites in Berlin promote the future uses of small 
satellites as a cost-saving measure. 
1. INTRODUCTION - WHAT ARE SMALL 
SATELLITES? 
The first satellite, Sputnik-1, launched on October 4, 1957 was 
a small satellite. The success of launching a manmade object 
into earth orbit was a phenomenal achievement, even though its 
user performance of sending a few radio signals was minimal. 
It took an equivalent large effort to develop a usable platform 
for lunar, planetary and earth observation with components 
assuring orbital performance, attitude control, sensor operation, 
telecommunication of signals and ground reception and ground 
processing of these. 
While the U.S. lunar missions succeeded in building the Lunar 
Orbiter missions 1 to 5 to achieve this goal in preparation for 
the lunar landing in the years 1966 and 1967, it took until 1972 
to launch a general earth observing platform in the Landsat 
program of the U.S. 
Earth observation is a relatively minor application branch of 
satellite technology, and the use of satellites is primarily 
important for telecommunications, and to a lesser extent to 
scientific missions. 
Large satellites have always been built by governments and 
large consortia, which had sufficient funding to assure reliable 
long range operation without severe mass and power 
restrictions. E.g. the communication satellite Intelsat 6 was 
built for 10 to 14 year operation with a mass of 6 x 4 x 12 
meters dimension and 4600 kg producing 2600 W power by 
solar panels. A medium size small satellite of today has a mass 
of 50 kg, accommodating a space of 0.6 x 0.4 x 0.3 m 
producing only 30 W of power by batteries. 
Nevertheless it can perform well for specific purposes as small 
satellites integrated by Surrey University in the UK have 
proven (UoSAT 2 launched 1984). Surrey’s marketing claims 
that 95 % of performance of large satellites can be reached with 
small satellites at 5 % of the cost or 70 % performance at 1 % 
of the cost (Wei Sun, IAA Symposium on Small Satellites for 
Earth Observation, Berlin, April 2-6, 2001). 
The classification of satellites according to mass is usually as 
follows: 
- large satellites: mass > 1000 kg 
- medium satellites: mass 500 to 1000 kg 
- mini satellites: mass 100 to 500 kg 
- micro satellites: mass 10 to 100 kg 
- mano satellites: mass 1 to 10 kg 
- . pico satellites: mas 0.1 — 1 kg 
- . fenito satellites: mass « 100 g. 
It is obvious that the performance of the satellites will depend 
on the necessary auxiliary devices, which lead to' additional 
mass requirements. The usability of small satellites is therefore 
generally restricted to micro, mini, and medium satellites. 
2. SATELLITE USES 
The website http://centaur.sstl.co.uk lists the uses of small 
satellite customers in the 1980's and 1990's as 
commercial 37.1 % 
military 35.1% 
government 17.3 % 
University 5,4 % 
amateur 5.1%. 
The application of these satellites in that period is: 
communications 69.2 % 
science 14.4 % 
technology demonstration 11.0 % 
military —— 2.3% 
education 1.7 96 
earth observation 1.4 95. 
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