Satellites used for telecommunication relay are kept in a geostationary orbit. A satellite is said to be in such an orbit when: 1. The orbit is geosynchronous. 2. The orbit is circular. 3. The orbit lies in the plane of the Earth's equator. 4. The orbit is at an altitude of 22,236 km. Select the correct answer using the codes given below:
Contents16
- A1, 2 and 3 only
- B1, 3 and 4 only
- C2 and 4 only
- D1, 2, 3 and 4
Show answer
Answer: (A) 1, 2 and 3 only
A geostationary satellite must meet THREE conditions (Statements 1, 2, and 3):
(1) Geosynchronous (✓): Its orbital period must equal Earth's rotation period (23 hours, 56 minutes) — so it completes one orbit in exactly one day.
(2) Circular orbit (✓): If the orbit were elliptical, the satellite would speed up and slow down, appearing to drift east-west from a ground observer's perspective.
(3) Equatorial plane (✓): The orbit must be directly above the equator. If tilted, the satellite would appear to move north-south daily — not stationary.
Statement 4 is WRONG: The correct altitude for geostationary orbit is approximately 35,786 km (about 36,000 km), NOT 22,236 km. The number 22,236 MILES ≈ 35,786 km — so the question used miles instead of km to create confusion!
Memory aid: Geostationary = 36,000 km above equator, circular orbit, same speed as Earth's rotation.
Geostationary satellites enable direct TV broadcasting, GPS navigation, and weather monitoring by appearing stationary above one point on Earth's surface.
The altitude trap uses 22,236 miles converted incorrectly to kilometers - the actual geostationary altitude is approximately 36,000 km above Earth.
UPSC is testing whether students understand that truly stationary positioning requires all three orbital conditions working together, not just matching Earth's rotation speed.
Geostationary Satellites
Science And Technology geostationary orbit telecommunication relay
Geostationary Satellites: Complete Requirements & UPSC Traps
Geostationary satellites require three conditions: geosynchronous + circular + equatorial plane
Altitude is ~36,000 km (35,786 km precisely), not 22,236 km
Used for telecommunication relay because they appear stationary from Earth
Orbital period matches Earth's rotation (23 hours 56 minutes)
What Makes It 'Stationary'
A geostationary satellite appears fixed in the sky from any point on Earth's surface. This makes it ideal for telecommunication relay — ground antennas can point at one spot without tracking movement.
For this to work, the satellite must meet three strict orbital requirements:
Three Geostationary Conditions
Condition | Requirement | Why Essential |
|---|---|---|
Geosynchronous | Orbital period = 23h 56min | Must rotate with Earth's spin |
Circular orbit | Constant orbital speed | Prevents east-west drift from ground view |
Equatorial plane | Orbit directly above equator | Prevents north-south movement |
Key Technical Facts
Altitude: 35,786 km above Earth's surface (approximately 36,000 km)
All geostationary satellites orbit at the same altitude — this is the only distance where orbital period matches Earth's rotation
Ground track: satellite remains above one point on the equator
Coverage: one satellite covers about 1/3 of Earth's surface
Question Analysis
This question tested all three geostationary conditions plus a units trap. Statement 4 gave 22,236 km as the altitude — but the correct altitude is 35,786 km. The trap: 22,236 miles converts to approximately 35,786 km, so UPSC used the wrong unit to confuse students.
Units trap: 22,236 km vs 35,786 km — the question used miles (22,236) instead of kilometers
Missing condition: Students often forget the circular orbit requirement — elliptical orbits cause apparent movement
Equatorial confusion: Satellites can be geosynchronous but not geostationary if they're tilted from equatorial plane
All conditions needed: Geostationary requires all three conditions — geosynchronous alone is insufficient
Satellite Orbits Classification
Science And Technology orbit
Satellite Orbits: LEO, MEO & GEO Classification
LEO (Low Earth Orbit): 160-2000 km, fast-moving, ISS and spy satellites
MEO (Medium Earth Orbit): 2000-35,786 km, GPS satellites at ~20,200 km
GEO (Geostationary): exactly 35,786 km, communication satellites
Orbital Classifications
Orbit Type | Altitude Range | Orbital Period | Main Uses | Examples |
|---|---|---|---|---|
LEO | 160-2000 km | 90 minutes - 2 hours | Earth observation, spy satellites | ISS, Hubble |
MEO | 2000-35,786 km | 2-12 hours | Navigation systems | GPS, GLONASS |
GEO | 35,786 km | 24 hours | Communication, weather | INSAT, TV broadcast |
Key Distinctions
LEO satellites move fast across sky — need satellite constellations for continuous coverage
GPS satellites orbit at ~20,200 km in MEO — need 4 satellites visible for positioning
Geostationary orbit is a special case of GEO — all geostationary satellites are at exactly the same altitude
Polar orbits can be LEO or MEO but cross both poles — used for Earth observation
Geosynchronous vs Geostationary: All geostationary are geosynchronous, but not vice versa
GPS altitude: Remember ~20,200 km for GPS satellites, not geostationary altitude
ISS orbit: ~400 km altitude, completes orbit in ~90 minutes
Telecommunications Satellites
Science And Technology telecommunication relay
Telecommunications Satellites: Technology & Applications
Use geostationary orbit for fixed ground antenna pointing
INSAT series provides India's satellite communication services
Work via transponders — receive uplink signal, amplify, retransmit on downlink
Why Geostationary for Telecom
Telecommunications satellites must maintain constant contact with ground stations. Geostationary orbit allows ground antennas to point at a fixed direction without tracking satellite movement. This enables continuous relay services for TV broadcasting, internet, and phone communications.
Satellite Communication Applications
Service Type | Technology | Coverage | Example |
|---|---|---|---|
TV Broadcasting | Direct-to-Home (DTH) | Regional/National | Tata Sky, Dish TV |
Internet | VSAT terminals | Remote areas | Rural broadband |
Mobile backhaul | Cellular tower connectivity | Islands, remote regions | BSNL satellite phones |
Weather data | Meteorological sensors | Continental | IMD weather forecasting |
India's Satellite Communication
INSAT series — India's multipurpose geostationary satellites for communication + meteorology
GSAT series — dedicated communication satellites replacing older INSAT models
ISRO launches communication satellites to 36,000 km orbit using heavy-lift rockets
Three satellites provide complete India coverage — positioned over different longitudes
Orbital Mechanics Basics
Science And Technology
Orbital Mechanics: Period, Velocity & Altitude Relationship
Higher altitude = longer orbital period and slower orbital speed
Orbital period depends only on altitude, not satellite mass
Circular orbits maintain constant speed; elliptical orbits speed up/slow down
Altitude-Period Relationship
Orbital mechanics follows Kepler's Third Law — satellites farther from Earth take longer to orbit. The gravitational force weakens with distance, so satellites move slower in higher orbits.
Geostationary orbit exists at the unique altitude where orbital period exactly matches Earth's rotation (24 hours).
How Orbital Period Changes
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Satellite at low altitude**
Strong gravity pulls satellite → high orbital speed needed`"]
s2["`**Higher altitude = weaker gravity**
Less gravitational force → slower orbital speed required`"]
s3["`**Orbital period increases**
Slower speed + longer orbit path = more time per orbit`"]
s4["`**At 35,786 km altitude**
Orbital period = exactly 24 hours (geostationary)`"]
s1 --> s2
s2 --> s3
s3 --> s4Key Orbital Principles
Centripetal force = gravitational force for stable circular orbits
Elliptical orbits: satellite speeds up at perigee (closest point), slows at apogee (farthest)
Escape velocity from Earth's surface: 11.2 km/s — needed to break free from gravity
Orbital velocity decreases with altitude — LEO satellites move much faster than GEO