# Orbital Mechanics Questions and Answers – Types & Locations of Sensors

This set of Orbital Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Types & Locations of Sensors”.

1. How many categories of radar sensors are present?
a) 1
b) 2
c) 3
d) 4

Explanation: Radar sensors are classified into two broad categories-detection fan and trackers. The detection radars make around 12,000 observations per day with a range of 2,500-3,500 miles.

2. What is the specification of the detection fan in terms of width and elevation?
a) 2 deg width, 4 deg apart elevation
b) 1 deg width, 3 $$\frac{1}{2}$$ deg apart elevation
c) 4 deg width, 8 deg apart elevation
d) 2 deg width, 3 $$\frac{1}{2}$$ deg apart elevation

Explanation: The detection fan which is a part of BMEWS system consists of two horizontal fan shaped beams that are 1 deg in width and 3 $$\frac{1}{2}$$ deg apart elevation. This makes sure to detect the missile or satellite as it has a fast sweep rate.

3. Which of these developments in tracking radars help in tracking multiple targets?
a) Thinned array
b) Antenna array
c) Smart antenna
d) Phased array

Explanation: Phased array antenna makes use of beam of radio waves which is launched in different direction without moving the antenna. This helps in tracking multiple targets.

4. Which of these radars operate by identifying signature od a booster by disturbance in ionosphere?

Explanation: OTH radar operates on the principle of detecting launches and identifying the signature of a particular booster by the disturbance it causes in the ionosphere.

5. Which of these devices is used to observe objects by having two or more antennas with high aperture?
b) Telescope
c) Hyper telescope
d) Optical Interferometer

Explanation: Radio interferometers are sensors which accurately measure the directional information of a satellite using radio interferometry. It makes use of 2 or more antennas of high aperture and waves interferes on the same receiver. This is similar to the double- slit experiment phenomenon.

6. What are the disadvantages of the optical sensors?
a) They are not accurate
b) Satellite must be in darkness
c) They are not efficient
d) Weather must be favorable

Explanation: The optical sensors are very accurate in determining the satellite. For taking a good photo, there are some conditions that have to be followed- good weather conditions, correct lighting and the satellite must be in the sunlight.

7. What is the position uncertainty for detection radar?
a) 1000 m
b) 5000 m
c) 1000 km
d) 5000 km

Explanation: For detection radars, satellite position uncertainties can be as high as 5 ,000 meters, while for tracking radars the uncertainty can vary from 1 00 to 500 meters.

8. What is the position uncertainty for tracking radar?
a) 100m – 500 m
b) 500m – 1km
c) 100 – 500 km
d) > 500 km

Explanation: For tracking radar the position uncertainty for the satellite target varies from 100-500m whereas for the detection radar it can be as high as 5,000 m.

9. How accurate is the directional information provided by the radio interferometer?
a) 10-20 sec
b) 20-40 sec
c) 40-50 sec
d) 1-4 min

Explanation: The radio interferometer technique yields directional information accurate to 20-40 seconds of arc and time of passage through the radio fence accurate to 2-4 milliseconds.

10. Which of these reasons does not result in persistent residue level?
a) Non- uniform gravitational field
b) Oblateness
c) Wind pressure

Explanation: The persistent residue levels are due to departures from two-body orbital motion caused by the earth’s equatorial bulge, nonuniform gravitational fields, lunar attraction, solar radiation pressure and atmospheric drag.

Sanfoundry Global Education & Learning Series – Orbital Mechanics.

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