Parachute Satellites For Earth Observation
- Paper number
IAC-07-D1.4.05
- Author
Dr. Didier Massonnet, Centre National d'Etudes Spatiales (CNES), France
- Year
2007
- Abstract
The parachute concept presented here is a generic definition for Earth observation systems essentially made of a reflector under which a detector associated with a telemetry antenna is suspended. The concept can be applied to any wavelength (radar, visible and infrared) in passive or active mode (for the latter the suspended part also includes a transmitter). The concept is characterized by its simplicity and performances. We illustrate it in the optical domain by describing a constellation composed of 10-15 kg nano satellites without propulsion and an attitude control passively obtained by gravity gradient. The elementary satellite does not include a computer or any storage for energy or data. All satellites transmit their data using the same frequency band, gathered on the ground by stations within the visibility circle. The system works by saturation : with 100 satellites (total constellation mass of 1500 kg) each with 20-km swath width and capable of a resolution on the order of the metre, the probability to reach any point on the equator in less than 24 hour is 0.53. At the latitude of Paris the probability reaches 0.68. With 200 similar satellites, these probabilities are 0.78 and 0.90 respectively. Without propulsion and taking into account the possible roll of the suspended part, the position of the acquired imagery is precisely known only after reception. This leads to new architectures for the ground segment: orders are placed within an archive very frequently updated. In addition, several satellites may be simultaneously visible from a given station, which should ideally have several antennae. Among other features, the system is extremely robust (very simple satellites in great number) and in practice invulnerable. The uplink is drastically reduced: the satellites turn on as soon as they are sufficiently illuminated by the Sun; the reflector is easily made wide enough to achieve metre-resolution from low altitude whereas the length of the suspending rods allows a large focal length which in turn forgives length errors. Without propulsion the choice of orbital altitude is limited to less than 600 km or more than 2000 km in order to observe space debris regulations. In folded position, the satellite is essentially no more bulky than its reflector which has the solar array fixed on the non reflecting side. Even a small launcher is capable of injecting a few tens of these satellites into orbit.
- Abstract document
- Manuscript document
IAC-07-D1.4.05.pdf (🔒 authorized access only).
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