Difference between revisions of "Navigation Sensors"
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Revision as of 11:14, 6 May 2007
Radar
To detect large objects such as space debris and asteroids, the habitat uses a continuous wave radar(CWR) system similar to that used on advanced air-to-air missiles. Each continuous wave radar system of the habitat consists of two radar dishes. One dish sends out a continuous radar signal and the other dish is devoted to receiving the signal emitted by its counterpart. This enables the radar system to calculate the velocity of the target by measuring the frequency shift due to the Doppler effect.
A continuous radar wave emmited at a certain frequency is incapable of calculating distance. To make up for this deficiency, the amplitude of the radar waves is moved up and down. When a reflection is received, the amplitudes is measured, and by knowing when in the past that particular amplitude was sent out, a range calculation can be performed to determine the distance between the radar and the object.
LIDAR
There are several disadvantages to the CWR system on the habitat. It is easily disrupted by radiation and pulsars, and it cannot detect gas clouds. To compensate for these deficiencies, a light based system is also mounted to complement the CWR. LIDAR, or Light Detection and Ranging, uses a reflected light beam to detect objects. It does this by emitting a light beam at a known frequency (usually in the infrared or ultraviolet ranges). This light is reflected by various objects and picked up by a receiver. In addition to being able to detect gases, the LIDAR can determine the types of gases present, as different gases react in different ways to ultraviolet and infrared light. These changes can be picked up by the LIDAR and can help determin the chemical makeup of the gas cloud.
Also, since it can detect clouds and gases, LIDAR can be used to gather meteorological data about planets.
The main disadvantage of LIDAR is that it used a fairly concentrated beam; and thus the sweep area of a LIDAR detector is extremely small compared to that of the radar. By combining the two, we can use the radar to scan broad areas for navigational hazard, whereas the LIDAR is used only for specific areas of interest and to study gaseous phenomena such as planetary rings and gas clouds
The habitat is capable of computing its position within the solar system based on the theoretical speed and direction that the habitat has traveled since it left earth. This, combined with the radar and LIDAR, is accurate enough to ensure that the habitat does not run into any planets or moons. However, the habitat does not travel in an ideal world, and risks such as solar wind and calculation errors are real.
To allow the detection of any errors, the Habitat navigational software also compares the observed positions of astronomical bodies (such as planets) with their predicted positions. Because the positions of planets can be predicted with a very high degree of accuracy, even a small discrepancy will be detected. Once the discrepancy is known, the Habitat's true position can be determined, and the 'dead reckoning' sensors take over again.
