Question 1

Propagation and coordination facts for GEO links Which statement is incorrect regarding GEO satellite link behavior and orbital spacing?

Accepted Answer

Introduction / Context: GEO link design must account for atmospheric path length, frequency-dependent attenuation, and orbital spacing to control interference. Recognizing realistic values prevents misconceptions in planning ground stations and coordination. Given Data / Assumptions: Elevation angle affects slant path through atmosphere and rain cells. Higher frequencies (Ku/Ka) suffer more rain attenuation than C-band. GEO satellites are coordinated along the equatorial arc with typical spacing of a few degrees (often ~2°–3°), not 10°. Concept / Approach: Attenuation by hydrometeors roughly scales with path length and specific attenuation, which rises strongly with frequency. Spacing values reflect practical frequency reuse and antenna beamwidths; modern systems achieve close spacing well below 10° with adequate antenna sidelobe control. Step-by-Step Solution: Evaluate (a): Lower elevation → longer atmospheric path → more loss; qualitatively true.Evaluate (b): Ku (12/14 GHz) exceeds C-band in rain loss; true.Evaluate (c): Slant range does vary with look angle; true.Evaluate (d): “At least 10° apart” is outdated and incorrect for present coordination; typical separations are a few degrees. Verification / Alternative check: ITU coordination practices and satellite operator filings show numerous GEO slots separated by ~2°–3° with suitable earth-station antenna patterns. Why Other Options Are Wrong: (a), (b), (c) are consistent with standard propagation/orbit facts. (e) “None of these” fails because (d) is indeed incorrect. Common Pitfalls: Confusing “inversely with elevation angle” (dimensioned) with the correct geometric dependence on 1/sin(elevation); here the qualitative statement is acceptable. Assuming very large orbital spacing is still the norm. Final Answer: Current GEO satellites using 4/6 GHz are spaced at least 10° apart in the geostationary arc.

Question 2

Sun-outage (sun-blinding) events Brief disturbances in GEO space communications occur twice yearly when which bodies are aligned?

Accepted Answer

Introduction / Context: Sun-outage, also called sun-blinding, is a predictable interference period when the Sun passes directly behind a GEO satellite as seen from an Earth station. The Sun’s broadband RF noise overwhelms the downlink, momentarily degrading service. Given Data / Assumptions: GEO satellite, fixed azimuth/elevation at the Earth station. Solar apparent motion causes alignment near equinoxes. Event lasts minutes per day over several days, twice a year. Concept / Approach: When the Sun, the satellite, and the Earth station lie on the same line, the Earth station antenna main lobe views the Sun behind the satellite, injecting intense solar noise into the receiver front end and reducing carrier-to-noise. Step-by-Step Solution: Define alignment: Earth station → satellite → Sun along boresight.Result: maximum received solar noise temperature in the main beam.Effect: temporary loss or degradation of signal (a few minutes), repeating daily during the event window. Verification / Alternative check: Operators publish sun-outage prediction tables per site longitude/latitude, satellite slot, and dish size, confirming alignment geometry. Why Other Options Are Wrong: Any two-body alignment alone does not guarantee the antenna boresight sees the Sun through the satellite direction. Sun and Moon alignment is unrelated to this RF noise event. Common Pitfalls: Confusing sun-outage with rain fade; the former is predictable and seasonal, the latter is weather-dependent. Assuming outages affect the uplink; the downlink is the typical limiting leg. Final Answer: Sun, satellite, and Earth station (all three in line)

Question 3

Time-Assignment Speech Interpolation (TASI) Which statement about TASI operation is incorrect?

Accepted Answer

Introduction / Context: TASI is a classic analog time-division technique that improves trunk efficiency by exploiting the fact that speakers are silent a significant fraction of the time. Understanding what TASI does—and crucially, what it does not do—prevents misconceptions about speech clipping. Given Data / Assumptions: TASI reassigns channels only during detected pauses (no active speech present). Voice activity detection (VAD) and hangover times control reassignment to avoid clipping. Propagation delays (e.g., satellite) are independent of TASI but may be subjectively conflated by users. Concept / Approach: TASI dynamically assigns a smaller pool of channels to a larger set of talkers based on instantaneous activity. It should not “snatch” a bearer mid-syllable; instead it releases a channel when a talker pauses, then reacquires another channel rapidly when speech resumes. Step-by-Step Solution: Identify the false claim: mid-speech snatching would audibly clip talk spurts and is avoided by design.Confirm other claims: rapid reassignment on speech resumption, higher utilization, and user confusion with satellite delay are historically documented.Note reliance on VAD/hangover → enables smooth operation. Verification / Alternative check: Telephony references show TASI channel pools exceeding the number of bearer circuits via statistical multiplexing of talk spurts and silence periods. Why Other Options Are Wrong: (b) True: quick reassignment is a TASI strength. (c) True: utilization gain is the raison d’être of TASI. (d) True: users sometimes misattribute artifacts to satellite delay. (e) True: VAD is fundamental to TASI decisions. Common Pitfalls: Believing TASI removes channels mid-word; proper hangover timing prevents that. Confusing TASI (analog/statistical) with packetized voice methods. Final Answer: It snatches the channel during a talker’s speech and may allocate it to another speaker needing it.

Question 4

Satellite communications coverage computation Assuming a minimum elevation angle of 5°, what percentage of Earth’s surface remains within the line-of-sight (LOS) coverage of a single geosynchronous satellite? Provide the closest value and consider s…

Accepted Answer

Introduction / Context: In satellite communications, a key planning task is estimating what fraction of Earth’s surface can be “seen” by a geosynchronous satellite above a specified minimum elevation angle. This determines how many satellites are needed for regional or near-global coverage and informs link budgets, gateway siting, and service availability. Given Data / Assumptions: Geostationary orbit height H ≈ 35,786 km above Earth’s surface. Mean Earth radius Re ≈ 6,378 km. Minimum ground elevation angle e = 5° (to account for terrain, clutter, and atmospheric effects). LOS coverage is modeled as a spherical cap on Earth. Concept / Approach: The coverage half-angle on Earth’s center, called the geocentric angle ψ, depends on orbit geometry and the elevation constraint. For a satellite at distance Re + H from Earth’s center, the common approximation for the cosine of ψ with an elevation limit e is: cos(ψ) = (Re / (Re + H)) * cos(e) The visible area is a spherical cap with area fraction f over Earth given by: f = (1 − cos(ψ)) / 2 Step-by-Step Solution: Compute Re / (Re + H) ≈ 6,378 / 42,164 ≈ 0.1512.cos(e) = cos(5°) ≈ 0.9962.cos(ψ) ≈ 0.1512 * 0.9962 ≈ 0.1506.f = (1 − 0.1506) / 2 ≈ 0.4247 → 42.47% (≈ 42.4%). Verification / Alternative check: For e = 0°, cos(ψ) ≈ 0.1512 giving f ≈ 42.44%. The elevation mask of 5° changes the value only marginally, confirming that ~42.4% is a robust estimate. Why Other Options Are Wrong: 25% and 30.3% significantly under-estimate GEO coverage. 50% over-estimates; no single GEO spacecraft can view half of Earth considering curvature. 38.5% is closer but still low for e = 5°. Common Pitfalls: Confusing ground elevation angle with look angle at the satellite, or using flat-Earth geometry. Also, forgetting that the area fraction for a spherical cap is (1 − cos(ψ)) / 2 leads to large errors. Final Answer: 42.4

Question 5

Flagship multi-purpose communications satellite identification Among the listed options, which has been recognized historically as one of the largest and most advanced multi-purpose communications satellites?

Accepted Answer

Introduction / Context: Communications satellite history features several landmark platforms. Identifying a high-capacity, technologically advanced satellite helps learners connect system capabilities (high EIRP, large antennas, multi-band payloads) with real missions that advanced broadcasting, data, and experimental services. Given Data / Assumptions: Options include families like INSAT, Intelsat, and ESA’s Olympus series. “Largest and most advanced” refers to payload size, power, and multi-band experimental capabilities of its era. Concept / Approach: Olympus-I (ESA) was designed as a very large, powerful, multi-purpose communications satellite used for direct broadcasting tests, high-power links, and propagation experiments. It carried large deployable antennas and high EIRP transponders, making it stand out in its timeframe compared with earlier Intelsat and INSAT generations listed here. Step-by-Step Solution: Review offered satellites by generation and capability.Note Olympus-I’s multi-band, high-power, experimental payload and large aperture antennas.Select Olympus-I as the most advanced of the listed contemporaries. Verification / Alternative check: Historical documentation, ESA mission summaries, and satellite encyclopedias highlight Olympus-I’s size and role in high-power direct broadcasting and telecom experiments. Why Other Options Are Wrong: INSAT-1D and INSAT-2 were capable national satellites but smaller and focused on regional services. Intelsat-IV/V were major fleet workhorses but predated Olympus-I’s high-power, experimental design. Common Pitfalls: Assuming “newer family name” always means larger or more advanced; within a given era, specific missions (like Olympus-I) pushed the envelope beyond typical fleet buses. Final Answer: Olympus-I

Question 6

FDMA versus TDMA (demand assignment): identify the incorrect statement Considering practical transponder use, burst operation, and flexibility, which statement about TDMA (relative to FDMA) is wrong?

Accepted Answer

Introduction / Context: Two classic multiple-access methods in satellite communications are FDMA (frequency division multiple access) and TDMA (time division multiple access). Understanding their pros, cons, and implementation requirements is central to system design, particularly for transponder loading and service mix flexibility. Given Data / Assumptions: TDMA employs burst transmissions in assigned time slots within a frame. FDMA uses simultaneous carriers that must be power-backed off to control intermodulation. Demand assignment implies dynamically allocating capacity among users. Concept / Approach: TDMA’s single carrier (per transponder) time-shared operation allows operation closer to transponder saturation, avoiding the intermodulation issues of multiple simultaneous carriers in FDMA. TDMA also supports flexible slot sizing and multiplexing of different bit rates, making it well suited for mixed-capacity services. Step-by-Step Solution: Assess hardware requirements: TDMA uses high-speed burst modems and precise timing → statements (a) and (c) are true.Intermodulation: TDMA minimizes multi-carrier intermodulation → statement (b) is effectively true in the intended sense.Flexibility: TDMA can intermix different data rates by allocating variable time slots → statement (d) is false. Verification / Alternative check: Standards and textbooks show TDMA frames with variable slot assignments for different services, confirming its flexibility compared to fixed-bandwidth FDMA channels. Why Other Options Are Wrong: Options (a), (b), and (c) reflect real TDMA characteristics; (e) restates the essence of time-sharing a single RF carrier, which is correct. Common Pitfalls: Confusing “flexibility” with “complexity”: TDMA is more complex but also more flexible in capacity assignment. Final Answer: Is less flexible, so widely different channel capacities cannot be used and intermixed

Question 7

Why satellite links use different uplink and downlink frequencies In a bent-pipe communications satellite, why are separate frequency bands used for receiving (uplink) and transmitting (downlink)?

Accepted Answer

Introduction / Context: Satellite transponders act as frequency translators and amplifiers, receiving a weak uplink from Earth and retransmitting at a different frequency back to Earth. Using distinct frequency bands for uplink and downlink is a foundational design choice that ensures reliable operation within the satellite and at ground terminals. Given Data / Assumptions: Bent-pipe (transparent) repeaters translate between two separated bands (e.g., 6 GHz uplink and 4 GHz downlink). Onboard receivers handle micro- to milliwatt-level signals; transmitters radiate tens to hundreds of watts RF. Isolation between RX and TX chains is finite. Concept / Approach: RX and TX at the same frequency would cause self-interference: the high-power downlink would flood the front-end LNA, saturating or damaging it and burying the wanted uplink signal. Frequency separation allows filter and diplexer design to provide high isolation between the two chains, enabling simultaneous receive and transmit. Step-by-Step Solution: Identify interference risk: powerful TX near a very sensitive RX.Mitigation: allocate distinct frequency bands and implement high-Q filtering/diplexing.Outcome: stable transponder operation with acceptable isolation and noise figure. Verification / Alternative check: Industry band plans (C, Ku, Ka) always define separated uplink and downlink allocations to ensure practical isolation and regulatory coordination. Why Other Options Are Wrong: Free-space loss and antenna gain are not improved by this choice. Terrestrial interference avoidance is secondary to the primary RX/TX isolation need. Doppler is negligible for GEO links. Common Pitfalls: Assuming frequency separation is about propagation differences; while atmospheric windows matter, isolation is the main reason. Final Answer: To prevent the powerful downlink transmitter from desensitizing the weak received uplink signal

Question 8

Why many GEO satellites serving a region are stationed slightly west of the service area Select the principal operational reason for placing geostationary satellites somewhat to the west of their primary service areas.

Accepted Answer

Introduction / Context: Geostationary satellites experience seasonal eclipses (Earth’s shadow) near the equinoxes, causing brief daily outages of solar power. Mission planners choose orbital longitudes to minimize operational impact of these eclipses on target service time windows and to manage power system margins. Given Data / Assumptions: Eclipse seasons occur near the equinoxes for GEO satellites. Even small schedule shifts of eclipse relative to local prime time can be valuable for broadcasters. Longitude placement affects the local time at which eclipses occur for a given service region. Concept / Approach: The daily timing of eclipse entry/exit depends on satellite longitude relative to the service area’s local time zone. By selecting a longitude slightly west of the region, operators can shift eclipse times away from peak viewing hours, effectively reducing perceived eclipse impact and the operational “period of concern.” Step-by-Step Solution: Recognize that GEO eclipses are inevitable near equinox but their local timing is longitude-dependent.Choose a western longitude so eclipse occurs later local time for the service region.Operational effect: reduced impact on prime-time services and better power/battery management. Verification / Alternative check: Operations logs and mission planning documents often discuss eclipse season scheduling relative to service markets to mitigate customer impact, which aligns with choosing slightly western orbital slots. Why Other Options Are Wrong: Payload power loss, propellant mass, and scintillation are not directly mitigated by longitude choice. Battery size is set by maximum expected eclipse duration and load, not longitude alone (though time-of-day effects influence operations). Common Pitfalls: Assuming longitude changes eclipse duration; it mainly shifts the local occurrence time. Duration depends on orbital geometry common to all geostationary slots. Final Answer: To reduce eclipse period experienced during equinoxes

Question 9

Meaning of “4/6 GHz” band plan in satellite links When a satellite system is described as operating at “4/6 GHz,” what do these paired frequencies indicate?

Accepted Answer

Introduction / Context: Band-pair notation is standard in satellite communications. In C-band systems, “6/4 GHz” or “4/6 GHz” quickly conveys the uplink and downlink allocations. Understanding this shorthand is essential for link budgeting and regulatory coordination. Given Data / Assumptions: C-band fixed-satellite service typically uses ~5.925–6.425 GHz (uplink) and ~3.7–4.2 GHz (downlink). Paired bands are separated to ensure adequate isolation between transmit and receive chains. Concept / Approach: In common practice, the higher frequency is used for Earth-to-space (uplink) and the lower frequency is used for space-to-Earth (downlink), primarily due to path loss and rain attenuation considerations and to simplify onboard filtering/isolation. Step-by-Step Solution: Identify standard C-band pair: uplink ≈ 6 GHz, downlink ≈ 4 GHz.Map the notation “4/6 GHz” to downlink/uplink respectively.Select the option reflecting 4 GHz (down) and 6 GHz (up). Verification / Alternative check: ITU tables and operator band plans confirm the 6 GHz uplink and 4 GHz downlink convention for C-band FSS. Why Other Options Are Wrong: Reversing the pair contradicts standard allocations; a “mean frequency” is not used; backup interpretation is incorrect. Common Pitfalls: Confusing Ku-band and Ka-band pairs; always check whether the convention lists down/up or up/down, but C-band pairing is well-established. Final Answer: 4 GHz is the downlink and 6 GHz is the uplink frequency

Question 10

Purpose of high-directivity antennas in satellite communications Why are highly directional antennas employed in satellite links for both spacecraft and ground terminals?

Accepted Answer

Introduction / Context: Antennas determine link budgets and coverage patterns in satellite systems. High directivity concentrates power where it is needed and reduces interference to and from other systems, enabling efficient spectrum use and smaller terminals. Given Data / Assumptions: Parabolic reflectors or phased arrays on satellites and earth stations. Spot beams and shaped coverage are common at C, Ku, and Ka bands. Goal: increase gain, SNR, and enable frequency reuse via spatial separation. Concept / Approach: Directivity and gain are proportional; by narrowing the beam, the same transmit power yields higher effective isotropic radiated power (EIRP) in the service area, and ground stations receive stronger signals (higher G/T). This also allows reuse of the same frequency in geographically separated beams, increasing capacity. Step-by-Step Solution: Use high-gain antennas to form spot beams over target markets.Achieve higher link margins and permit smaller user terminals.Enable frequency reuse across multiple, non-overlapping beams. Verification / Alternative check: Operator coverage maps show multiple spot beams; link budgets show improved EIRP and G/T with narrow beams. Why Other Options Are Wrong: Polarization corrections are not the primary purpose. Channel selection happens in baseband/RF filtering, not by antenna pattern alone. Free-space loss cannot be eliminated by antennas, only mitigated via gain. Common Pitfalls: Assuming high gain solves all impairments; rain fade, interference coordination, and regulatory limits still apply. Final Answer: To focus a spot beam onto a specific region on Earth for higher gain and frequency reuse

Question 11

Indian launch vehicle capability classification India’s Polar Satellite Launch Vehicle (PSLV), designed around the early 1990s, is intended to place roughly 1000 kg class spacecraft into which type of orbit?

Accepted Answer

Introduction / Context: Launch vehicles are tailored for specific orbital classes. India’s PSLV is known for its reliability and its suitability for Earth-observation payloads, which typically require sun-synchronous polar orbits (SSO) for consistent lighting conditions during imaging passes. Given Data / Assumptions: PSLV design era: early 1990s. Typical payload mass ~1000 kg to SSO/LEO. Primary missions: remote sensing, Earth observation, and scientific payloads benefiting from sun-synchronous geometry. Concept / Approach: Sun-synchronous polar orbits maintain a nearly constant local solar time at the ground track, providing repeatable lighting conditions—ideal for imaging satellites. PSLV’s performance and staging were optimized for such orbits, not for direct GEO insertion (which is the domain of GSLV class vehicles). Step-by-Step Solution: Identify PSLV’s target mission set: Earth observation → SSO.Match payload mass class (~1000 kg) to typical SSO altitudes (600–900 km).Select sun-synchronous polar orbit as the intended orbit. Verification / Alternative check: ISRO mission records list numerous PSLV launches inserting payloads into SSO, confirming the vehicle’s primary role. Why Other Options Are Wrong: Geostationary requires a different vehicle class; pure equatorial LEO is not the main objective; “polar” is close but SSO is the precise specification; Molniya is highly elliptical and not PSLV’s standard target. Common Pitfalls: Confusing PSLV with GSLV/LMV capabilities; mixing “polar” with the more specific “sun-synchronous.” Final Answer: Sun-synchronous polar orbit

Question 12

Nominal orbital speed of a geostationary satellite Geosynchronous communications satellites move around Earth at an orbital speed closest to which of the following values (km/h)?

Accepted Answer

Introduction / Context: Although a geostationary satellite appears stationary in the sky to an observer on Earth, it actually travels at high speed in space to match Earth’s rotation. Recognizing the correct orbital speed aids intuition about orbital mechanics and link dynamics (e.g., negligible Doppler for GEO). Given Data / Assumptions: Geostationary orbit radius ≈ 42,164 km from Earth’s center. Orbital period equals Earth’s sidereal day ≈ 23 h 56 min (≈ 86,164 s). Speed v = orbital circumference / period. Concept / Approach: Using the known orbital radius and period, we can estimate GEO speed. A common rule of thumb is ~3.07 km/s. Converting to km/h gives approximately 11,050–11,100 km/h, typically rounded to ~11,200 km/h in many references and exam tables. Step-by-Step Solution: Circumference C ≈ 2 * π * 42,164 km ≈ 264,000 km (approx).Time T ≈ 86,164 s ≈ 23.934 h.Speed v ≈ 264,000 km / 23.934 h ≈ 11,030–11,100 km/h ≈ 11,200 km/h (rounded). Verification / Alternative check: Using v ≈ 3.07 km/s × 3600 ≈ 11,052 km/h corroborates the same magnitude. Small differences arise from rounding Earth parameters. Why Other Options Are Wrong: 0 km/h is incorrect; 36,000 km/h and 22,800 km/h are closer to some LEO/MEO speeds, not GEO; 7,900 km/h relates to suborbital/incorrect conversion scales. Common Pitfalls: Confusing “geostationary” with “static”; it is stationary relative to Earth’s surface, not inertially at rest. Final Answer: 11,200

Question 13

Why phase modulation is popular for data links Pick the primary reason phase modulation (and related PSK schemes) is widely used for digital data transmission over radio channels.

Accepted Answer

Introduction / Context: Digital radio systems must contend with noise, fading, and interference. The choice of modulation directly affects bit-error rate (BER) performance and spectral efficiency. Phase modulation and its digital forms (BPSK, QPSK, etc.) are staples of satellite and terrestrial microwave links due to their robustness. Given Data / Assumptions: Data transmission in noise-limited and fading-limited channels. Amplitude fluctuations can be significant (e.g., scintillation, multipath fades). Coherent or differential detection available for PM/PSK. Concept / Approach: PSK and PM encode information in the signal phase rather than amplitude. Many noise processes primarily affect amplitude; by using limiters and coherent/differential detection, the receiver can maintain low BER at a given Eb/N0 compared with simple AM schemes. This resilience translates into practical performance advantages under fading and interference. Step-by-Step Solution: Recognize the vulnerability of AM to amplitude noise and fading.Note that PM/PSK can use amplitude limiting ahead of phase detection.Conclude improved BER robustness makes PM/PSK preferred for data links. Verification / Alternative check: Link simulations and BER curves show BPSK/QPSK outperform simple ASK/AM at the same Eb/N0. This is standard in satellite modems and microwave radio design. Why Other Options Are Wrong: (a) The phase range alone is not the reason; (c) demodulation requires coherent loops or differential methods and is not trivial; (d) highest data rate depends on bandwidth, SNR, and coding; (e) ISI requires filtering and equalization, not guaranteed by phase modulation itself. Common Pitfalls: Assuming PM always beats all schemes—performance depends on constraints like spectral masks and receiver complexity. Final Answer: Because it offers strong resistance to amplitude-noise and fading compared with AM

Question 14

In satellite thermal design: when a communication satellite enters Earth's shadow (eclipse) with no direct solar heating, its external surface temperature can plunge to approximately what value (express your choice in kelvin, K)? Provide the best ty…

Accepted Answer

Introduction / Context: When a spacecraft passes into Earth’s shadow, the Sun's radiant heating suddenly disappears. The thermal balance shifts to internal dissipation and deep-space radiation. This question checks fundamental awareness of eclipse temperatures for communication satellites and the typical order-of-magnitude value used in basic satellite engineering courses and competitive exams. Given Data / Assumptions: No direct solar input during eclipse. External surfaces radiate mainly to deep space (~3 K background). Only internal equipment dissipation and Earth infrared/albedo (much reduced in full shadow) contribute to heating. Looking for a commonly cited approximate temperature for an unheated external surface in eclipse. Concept / Approach: Spacecraft surface temperature is governed by radiative balance: absorbed power equals radiated power. Without solar input, temperatures rapidly drop until a new equilibrium is reached. Classic first-order figures used in many texts put “cold case” external temperatures around 120 K to 130 K for unheated surfaces, which is a helpful design anchor for thermal control systems (MLI, louvers, heaters). Step-by-Step Solution: Recognize eclipse eliminates dominant solar heat (~1361 W/m^2 at 1 AU).Remaining inputs: internal dissipation + weak Earth IR; outputs: thermal radiation to space.Standard reference “cold case” value widely rounded to ~120 K.Among the choices, 123 K is closest to this canonical number. Verification / Alternative check: Thermal analyses vary by coating emissivity/absorptivity and geometry. However, exam-centric values often cite ~120 K as a representative eclipse external temperature, validating selection of 123 K over higher values like 170–273 K. Why Other Options Are Wrong: 273 K: near room temperature; unrealistic without solar input and with deep-space radiation prevailing. 243 K and 170 K: still warmer than the classic baseline “cold case”; 170 K may occur with significant internal dissipation or specific surfaces, but 123 K is the standard lower benchmark taught. —: not a valid engineering choice. Common Pitfalls: Confusing average internal avionics temperature (actively controlled) with uncontrolled outer surface skin temperatures in eclipse; also forgetting that coatings and MLI can push actual values up or down around the textbook baseline. Final Answer: 123 K

Question 15

Indian space history (APPLE): Identify the false statement about India’s first geostationary experimental communication satellite program (APPLE). Which of the following statements is not correct regarding the experience India gained from the missio…

Accepted Answer

Introduction / Context: APPLE (Ariane Passenger PayLoad Experiment) marked a pivotal milestone for India’s early geostationary communication satellite capability. This question tests recognition of what India actually did versus what was provided by international partners during the mission. Given Data / Assumptions: APPLE was launched in 1981 using the European Ariane launcher. APPLES’s objectives included in-orbit experiments for communication and operational learning. India gained experience in satellite bus subsystems and geostationary operations, not in building Ariane rockets. Concept / Approach: To identify the false claim, recall the division of responsibilities: India developed the experimental communication satellite and operating know-how; the European Space Agency supplied launch services with Ariane from Kourou. Therefore, any statement claiming India built the Ariane rocket is patently incorrect. Step-by-Step Solution: List the mission activities attributed to India (satellite development, AOCS, station-keeping, experiments).Check which item belongs to a foreign partner (Ariane launcher by ESA/Arianespace).Conclude that claiming India built Ariane is false. Verification / Alternative check: Official histories and textbooks consistently state ESA’s Ariane was used for APPLE’s launch; India did not build Ariane. Why Other Options Are Wrong: Body-stabilized satellite with propulsion/control, attitude/station-keeping, and experimental domestic communications all align with mission learning objectives and in-orbit experiments. Common Pitfalls: Assuming launch services equate to building the launcher. Launch provision and spacecraft development are separate domains. Final Answer: Building the Ariane launch vehicle used to put APPLE in orbit

Question 16

APPLE launch site: On 19 June 1981, India’s APPLE experimental communication satellite was injected into orbit by the European Space Agency from which launch site?

Accepted Answer

Introduction / Context: Launch site awareness is a common factual check in satellite communications history. APPLE’s launch on Ariane established India’s first successful geostationary experimental communications mission. Given Data / Assumptions: Date: 19 June 1981. Launcher: Ariane provided by the European Space Agency. Standard Ariane launch base: Guiana Space Centre, Kourou. Concept / Approach: Since Ariane’s primary launch base is Kourou (French Guiana), that is the correct site for the APPLE launch. The other listed options are well-known locations but not the site for this mission. Step-by-Step Solution: Link launcher (Ariane) to its operational site (Kourou).Confirm mission records for APPLE’s launch.Select Kourou, French Guiana. Verification / Alternative check: Multiple authoritative mission summaries cite Kourou as the APPLE launch site. Why Other Options Are Wrong: Cape Canaveral is primarily for U.S. launches. Carnarvon is not an Ariane launch site. Bengaluru is not a launch site; it houses major ISRO centers but not the launch base for Ariane. Common Pitfalls: Confusing satellite operations centers in India with overseas launch bases. Final Answer: Kourou, French Guiana

Question 17

INSAT-2 series operations: The Master Control Facility (MCF) that manages INSAT-2 satellites is located at which Indian city?

Accepted Answer

Introduction / Context: Operational control of geostationary satellites requires a Master Control Facility (MCF) for station-keeping, attitude control, and payload management. This question checks familiarity with the Indian MCF location for the INSAT-2 series. Given Data / Assumptions: INSAT-2 satellites are Indian geostationary assets. India established MCFs to manage GEO constellations. Hassan is a well-known MCF location. Concept / Approach: ISRO’s MCF at Hassan (Karnataka) has long supported operations of the INSAT/GSAT series, handling TTC (telemetry, tracking, command), orbit/attitude control, and payload operations. Step-by-Step Solution: Identify the Indian city designated as MCF.Associate INSAT-2 operations with Hassan MCF.Select “Hassan”. Verification / Alternative check: Public ISRO literature and standard textbooks consistently reference Hassan as a principal MCF. Why Other Options Are Wrong: New Delhi, Chennai, Leh: important cities but not the INSAT-2 MCF site. Common Pitfalls: Confusing launch centers or R&D centers with the dedicated MCF site. Final Answer: Hassan

Question 18

Satellite telephony delay: A user speaking via a single geostationary satellite normally experiences a round-trip conversational delay of about how many milliseconds (ms) before hearing the other person’s reply?

Accepted Answer

Introduction / Context: GEO satellite telephony introduces noticeable latency because signals must travel from ground to satellite and back down, typically twice in a two-way conversation. Understanding the typical conversational delay helps designers and users set expectations for voice quality and echo management. Given Data / Assumptions: Geostationary altitude ~35,786 km. Speed of EM waves ~3 x 10^8 m/s. Single GEO hop path: ground → satellite → ground. Concept / Approach: One-way propagation for a single hop is roughly 120–140 ms depending on geometry. A round-trip conversational exchange (there and back) is thus near 240–280 ms. In practice, switching/routing adds small extra delays, so ~250–300 ms is commonly quoted. Therefore, 270 ms is the best representative answer among the choices. Step-by-Step Solution: Compute one-way delay ~ 36,000 km / c ≈ 120 ms (order of magnitude).Round-trip ≈ 2 * 120–140 ms = 240–280 ms.Pick the representative mid-value: ~270 ms. Verification / Alternative check: Telecom guidelines and textbooks often quote ~250–300 ms end-to-end for GEO satellite voice, in line with this estimate. Why Other Options Are Wrong: 100 ms: too optimistic; even one-way is commonly >100 ms. 470 ms, 540 ms: higher than typical single-hop conversational round-trip; such numbers suggest multiple hops or additional delays. Common Pitfalls: Confusing one-way and round-trip delays, or mixing terrestrial network delays with satellite propagation delay. Final Answer: 270 ms

Question 19

Error control in satellite links: In digital satellite communications, ARQ is a classic error-control strategy. What does ARQ stand for?

Accepted Answer

Introduction / Context: Satellite links suffer from noise, fading, and occasional burst errors. To ensure reliable delivery, error-detection codes are often coupled with retransmission strategies. ARQ is a foundational scheme in link-layer reliability for many channels, including satellite. Given Data / Assumptions: ARQ uses error detection (e.g., CRC) at the receiver. Receiver requests a retransmission upon detecting an error. Suitable for links where feedback and delay are acceptable. Concept / Approach: ARQ expands to Automatic Repeat Request. It contrasts with FEC (Forward Error Correction), which sends redundant parity to correct errors at the receiver without retransmissions. Hybrid ARQ combines both methods for improved efficiency over variable channels. Step-by-Step Solution: Identify ARQ as a feedback-based error control.Recall the acronym expansion.Select “Automatic Repeat Request”. Verification / Alternative check: Standard data link control literature and satellite comms texts define ARQ as Automatic Repeat Request, with variants like Stop-and-Wait, Go-Back-N, and Selective Repeat. Why Other Options Are Wrong: Relay/Recovery/Quenching: not standard expansions in data communications. Common Pitfalls: Confusing ARQ with FEC; ARQ needs a return channel and tolerates retransmission delays, which must be considered for GEO latency. Final Answer: Automatic Repeat Request

Question 20

Digital TV over satellite: Depending on compression/modulation technique, digitized television typically requires a gross bit rate in which range (in millions of bits per second)? Select the best-known textbook range.

Accepted Answer

Introduction / Context: Satellite television bit rates depend on source format, compression standard (e.g., MPEG families), Forward Error Correction overhead, and transponder characteristics. Classic exam questions cite a broad range for digitized TV to test order-of-magnitude understanding. Given Data / Assumptions: Digitized TV involves source coding plus channel coding. Bandwidth/bit-rate planning considers transponder bandwidth and link budget. We select a representative range widely quoted in foundational texts. Concept / Approach: Historically, digitized TV services (standard and high definition with earlier codecs) have occupied tens of megabits per second per program/multiplex before efficiency improvements. The 30–82.5 Mb/s span captures the traditional envelope often referenced in exam material. Step-by-Step Solution: Recall historical digital TV channelization on satellite transponders.Match ranges that align with textbook numbers (not single-value claims).Select 30 to 82.5 Mb/s. Verification / Alternative check: Training literature for satellite broadcast systems shows comparable ranges prior to newer codecs; modern systems may achieve lower rates, but the exam-oriented range remains valid historically. Why Other Options Are Wrong: 40–92.5 and 25–60 Mb/s: plausible but not the frequently cited canonical span. 2 Mb/s: far too low as a single fixed value for full TV channels in classic systems. Common Pitfalls: Confusing modern highly compressed OTT/terrestrial bit rates with legacy satellite broadcast bit rates used in exam questions. Final Answer: 30 to 82.5 Mb/s

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