Correct Answer : Ground tracks
Explanation : The projection of a satellite’s orbit onto the earth’s surface is called its ground track. At a given instant, one can imagine a radial line drawn outward from the center of the earth to the satellite. The point at which this line pierces the earth’s surface is called ground track.
Correct Answer : Sine curve
Explanation : During each satellite’s orbit, it reaches the maximum and minimum latitude while passing the equator twice. Thus, the ground track of the satellite in low earth orbit resembles a sine curve.
Correct Answer : 180 deg rotational symmetry
Explanation : When the perigee and apogee lie in the same equatorial plane, the argument of perigee is zero. In that case, the ground track of the satellite in the orbit appears to have a 180-degree rotational symmetry about the orbital nodes i.e. it appears both same above and below the equator of the Earth.
Correct Answer : Single point
Explanation : Geostationary orbit is a type of geosynchronous orbit which has the orbital period same at the time period of the earth’s rotation. This means that the satellite always appears to be at the same point overhead the earth at all times. Thus, its ground track is a single stationary point.
Correct Answer : Sun- Synchronous orbit
Explanation : The unique property of the low altitude circular sun-synchronous orbits is that the satellite’s ground track has one local time on its ascending half and another local time (12 h away) on its descending half. The two local times remain the same for the entire mission.
Correct Answer : Frame of reference of ground observer
Explanation : The satellite’s imaginary path as traced on the earth’s surface is called ground track. This is measured in reference to the ground’s observer. The observer will see the point at which satellite passes directly overhead (zenith).
Correct Answer : Zig-zag
Explanation : In a geosynchronous orbit, the orbit period of the satellite is equal to the Earth’s rotation time period. This leads to the ground track having a figure eight shape over the fixed location of the earth which crosses the equator twice.
Correct Answer : Aerospace Force of Aerospace Defense Command
Explanation : There are millions of objects orbiting the Earth and the task to keep track of the growing space population is given to Aerospace Force of Aerospace Defense Command. They maintain a catalogue of all the objects orbiting.
Correct Answer : Northern hemisphere
Explanation : Surveillance is nothing but the outgrowth of ballistic trajectory monitoring. For this reason, all the radars are located in the northern hemisphere. Satellite tracking cameras which are present all around the world provide with the data from the southern hemisphere.
Correct Answer : Explode the unwanted debris
Explanation : Spacetrack deployed for space surveillance does various task apart from cataloguing the space debris. It helps in recovering reconnaissance satellite payload, antisatellite targeting, spacecraft collision avoidance and interception of midcourse ICBM.
Correct Answer : Space object recognition system
Explanation : Spacetrack was started to maintain observation of the catalogue of objects in space. They use input from various sources such as Ballistic Missile Early Warning System, Navy Space Surveillance System, over the horizon radars, radio and visual.
Correct Answer : Over the horizon radar
Explanation : Over the horizon radar (OTH) or beyond the horizon (BTH) is a type of radar which is used to detect targets at a longer range. This range can vary from hundreds to thousands of kilometers. They were often used for early warning and now have come into use for long- range tracking.
Correct Answer : To keep track of space debris to avoid collision
Explanation : Since there are several thousands of space debris in the outer space, posing threat to the current launches or threat of collision of the satellites orbiting, space surveillance is required. This helps in tracking the space debris and whenever there is threat of collision, it issues alert.
Correct Answer : 100-200
Explanation : In order to obtain a degree of precision for space surveillance for a new object that has been launched and orbits in space, 100-200 observations per day have to be taken for few initial days.
Correct Answer : 20-50
Explanation : To obtain a higher degree of precision for space surveillance, once the object is launched in the orbit, more observations have to be taken later to update the precise established orbit. For this purpose, 20-50 observations need to be taken.
Correct Answer : Apparent solar day
Explanation : The time between two successive upper transits of the sun across our local meridian is called an apparent solar day. It differs according to the observer’s location i.e. local longitude. Sidereal time is with reference to the stars. Universal time is the mean solar time at Greenwich meridian.
Correct Answer : The main purpose of time is to define with precession, the exact moment of a phenomenon
Explanation : The correct sentence is that ‘the main purpose of time is to define with precession, the exact moment of a phenomenon’ because Time is a fundamental dimension in science, it cannot be calculated by the same method throughout the universe and the epoch designates a particular instant described as a date.
Correct Answer : 24 hours
Explanation : A solar day is the time required for the sun to return to the same position overhead. As observed from earth, the duration amounts to 24 hours.
Correct Answer : The Stars
Explanation : The Stars is the reference for the sidereal time because their relative location doesn’t change much even after a year owing to its large distance from the Earth.
Correct Answer : Polar time
Explanation : Out of the options, Polar time is incorrect. Others are different types of time systems. The Julian day is the number of days since noon UT on January 1, 4713 BC. Atomic time defines one second as the time it takes a Cesium-133 atom at the ground state to oscillate exactly 9,192,631,770 times. Universal time is determined by the sun’s passage across the Greenwich meridian, which is 0° terrestrial longitude.
Correct Answer : Julian day is more useful for people resident on the Earth
Explanation : The Julian day is mainly used by the astronauts and astronomers dealing with outer space to keep track of time. In these cases, the universal time is taken as a reference. People living on the surface of the earth prefer other time systems like the Universal time or the Local time.
Correct Answer : January 1, 4713 BC
Explanation : The Julian day number is the number of days since the noon on January 1, 4713 BC as per Universal Time. It counts the days elapsed since the mentioned date & finds use in astronomy and software purposes. Julian Day Number (JDN) is an integer value denoting each solar day passed.
Correct Answer : 2
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.
Correct Answer : 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.
Correct Answer : 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.
Correct Answer : 20-40 sec
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.
Correct Answer : 5000 m
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.
Correct Answer : Over- the- horizon radar
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.
Correct Answer : Radio 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.
Correct Answer : 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.
