by Gurbir Singh
N.C. Bhat. ISRO Scientist. Bangalore 8/2/2014. Telephone interview in Bangalore on N.C. Bhat’s recollections as one of the two ISRO astronauts selected to fly aboard the Space Shuttle.
Ravish Malhotra. Former Indian Air Force. Test Pilot and Astronaut. Bangalore 10/09/2013.Telephone interview in Bangalore on Ravish Malhotra’s experiences during the astronaut selection and the Indo-Soviet flight training for flight aboard the Soyuz to the USSR Salyut space station.
Rakesh Sharma. Former Indian Air Force. Test Pilot and Astronaut. Coonoor, Tamil Nadu 12/08/2014. Interview in Coonoor on Rakesh Sharma’s experiences during the astronaut selection, training, flight aboard the Soyuz and eight-day on-board the USSR Salyut space station in 1984.
Professor Roddam Narasimha. Aerospace Scientist. Bangalore 6/2/2015. Telephone interview in Bangalore on Professor Narasimha’s recollections of Satish Dhawan and his role as a member of the Space Commission in the Department of Space.
Gloria Morris and Lucy Morris. London 5/7/2016. Stephen Smith’s granddaughter and great granddaughter. They provided personal details of Stephen Smith’s life via email and telephone.
V.S. Hegde. Director at Antrix. Bangalore. Interview in Bangalore on ISRO’s commercial operations.
Mrinalini Sarabhai. Vikram Sarabhai’s widow. Ahmedabad 3/11/2012. Telephone interview to discuss Vikram Sarabhai’s legacy.
Monica Sarabhai. Vikram Sarabhai’s daughter. Ahmedabad 26/6/2015. Monica Sarabhai provided consent to use one of the family pictures. Contact via Facebook.
Professor Praful Bhavsar. Former Director of Space Applications Centre. Ahmedabad 18/12/2012. Professor Bhavsar held several roles, including that of the project scientist for the first rocket launch from Thumba. He shared via telephone and email personal recollections and some images of the first launch event on 21 November 1963.
Professor Jacques Blamont. Astrophysicist and pioneer of the French space programme. Paris. 19/04/2013. Telephone interview in Paris, France, on Professor Blamont’s recollections of the sodium payload of the first rocket launch from India on 21 November 1963, his personal recollections of Vikram Sarabhai and the wider collaboration between the Indian and French space programmes.
Professor Rajesh Kochhar. London. 23/06/2016. Meeting with Professor Kochhar during his trip to London, UK. He provided assistance that led to establishing contact with Stephen Smith's family in London.
Dr Rajinder Singh. Historian and Physicist. Oldenburg, Germany 31/08/2015. Correspondence by email from University of Oldenburg, Germany. Dr Singh has written extensively on the scientific contributions of Indian scientists, especially in the pre-independence period.
Melvyn Brown. Kolkata. 2/4/2014. Interview in Kolkata, India, on Melvyn Brown’s research on Stephen Smith, his meeting with Stephen Smith’s son Hector and the wider experiences of the Anglo-Indian community in India.
Indian Currency
The Indian rupee, managed by the Reserve Bank of India, is the currency used across India’s 29 states and 7 union territories. It is usually abbreviated to Rs. The International Organization for Standardisation’s currency code for the Indian rupee is INR. The rupee is made up of 100 paise. The name rupee is derived from the rupiya, a silver coin first issued by Sultan Sher Shah Suri in the 16th century. The nomenclature used to express large currency (and large numbers in general) uses the Hindi words, lakh and crore. The location of the comma in a series of zeros is also unique.
Hindi
International
Scientific Notation
Comma
Placement
USD ($)
2015 Rate
1 lakh
100 thousand (105)
1,00,000
1,576
1 crore
10 million (107)
1,00,00,000
157,600
As a British colony, the value of the Indian rupee was pegged to British pounds. From 1927 to 1966, it was 13 rupees to the British pound. In 1966, the rupee was devalued and pegged to the US dollar at a rate of 7.5 rupees to the US dollar. This value lasted until the US dollar devalued in 1971. Since then, the value of the Indian rupee has fluctuated along with all other international currencies.
The Exchange Rate of the US Dollar and Indian Rupee between 1971 and 2015
Through the 1980s, the value remained less than ten rupees to the US dollar and saw a sharp increase in 1991 following the relaxation of financial controls and increase in foreign investment. By the end of 1993, the exchange rate was around 30 rupees to the US dollar.
I have attempted to present all monetary values in both Indian rupee and the US dollar. The approximate value of the alternate currency, either Indian rupee or the US dollar, is given in brackets. The values presented throughout should be considered approximate given the rounding errors and fluctuating exchange rates. In addition, there are inconsistencies in the values documented in publically available sources.
Types of Orbits
Orbits are classified on their altitude (height from the Earth's surface), inclination (offset from the equator) and eccentricity (extent of deviation from a circular orbit). There are three primary classifications of orbits. Low Earth Orbit (LEO) between 160 to 2,000 km, Medium Earth Orbit (MEO) between 2,000 to 35,786 km and Geostationary Earth Orbit (GEO), almost circular orbit 35,786 km above the Earth's equator (or 42,164 km from the centre of the Earth). An orbit of 35,768 km but not over the equator is a Geosynchronous Orbit (GSO). All GEO and GSO orbits have a period of almost 24 hours (or specifically sidereal day (23.934461223 hours). With increasing altitude, the spacecraft's speed reduces and the time taken to go around the Earth once (also known as the period) increases. Almost all satellites in GEO orbit the Earth in the same direction as the Earth's rotation, that is, anti-clockwise if looked down upon from the North Pole.
Altitude above Sea Level (km)
Speed km/s
Period (minutes)
Period (Hours)
Re-entry after*
100
7.84
86
1.4
87 days
200
7.78
88
1.5
130 days
300
7.73
90
1.5
139 days
400
7.67
92
1.5
174 days
500
7.62
94
1.6
218 days
1,000
7.35
104
1.7
1.2 years
2,000 (Start of MEO)
3.89
127
2.1
24 years
35,786 (GEO)
3.07
1435
23.9
43 years
50,000
2.66
2219
37.0
60.5 years
200,000
1.39
15550
259.2
242 years
The values in the re-entry column are approximate. These are periods by when atmospheric drag would naturally cause a satellite orbit to decay and re-enter.
In practice, these periods are influenced by several factors in addition to drag including mass and surface area (1000 kg/1 m2 is assumed for the table above). Further, the Earth’s magnetic field and solar radiation contribute to orbital decay, and both are subject to variation. The re-entry figures assume the that the spacecraft’s orbit is not actively managed by the satellite operators. There are many orbital configurations. Five of the most common are:
Low Earth Orbit: This is a circular or elliptical orbit parallel or inclined to the equator with a wide altitude range.
Polar Orbit: An orbit that takes the spacecraft over the North and South Poles and is thus tilted around 90° to the equator. Typically, they have a period shorter than two hours. An Earth observ
ation satellite in a polar orbit can cover the entire surface in one day.
Sun-synchronous Polar Orbit (SSPO): An orbit where the altitude and inclination are uniquely tuned so that a spacecraft crosses the equator at a same time of the day on every orbit. This is a very useful feature for EO satellites that require consistent illumination.
GSO and GEO: Both orbit the Earth at an altitude of 35,786 km and have a period of 24 hours, that is, they circle the Earth once every day. A GEO orbit is parallel to the Earth’s equator, while GSO is not. A spacecraft in GEO orbit appears to be stationary in the sky. This orbit is ideal for satellite TV. Once the receiving dish is set up to point to a specific satellite, it does not need to be adjusted. A spacecraft in GSO also takes 24 hours to orbit the Earth, but it will appear to move up and down in the sky every day.
Highly Elliptical Orbit: Communication satellites in GEO cannot be accessed by users living in higher latitudes on Earth. More than about 55° above or below the equator, a satellite in GEO orbit is close to or below the local horizon. A satellite in HEO (instead of GEO) is a solution for such users. A Molniya orbits is a specific HEO of 63.4°.
Typical Orbital Configurations
Low Earth Orbit
There is no well-defined point at which the Earth's atmosphere ends, and space begins. Like a twilight sky where day fades into night, the Earth's atmosphere gradually fades into space. Internationally, 100 km above sea level is regarded as the official boundary, where space begins. This boundary is known as the Karman Line, named after Theodore von Karman, a Hungarian-American scientist. At that altitude and speed, a spacecraft would orbit the Earth once in 86 minutes.
An altitude of 160 km is the lowest with sufficient vacuum for a spacecraft travelling at 7.8 km/s to sustain an orbit to fulfil a function. However, the orbit is not stable, atmospheric drag will cause the orbit to decay in a matter of days. At higher altitudes, there is less drag, speed of the spacecraft in orbit is lower, the period longer and the decay of orbit slower. LEO is used mostly by spacecraft for EO, photo reconnaissance and science and sometimes by communication satellites. The Hubble Space Telescope, Astrosat and the ISS are in LEO.
Polar Orbit
A polar orbit is one where a satellite's orbit is inclined at around 90° to the equator (pole to pole). The Sun Synchronous Polar Orbit SSPO is a special type of polar orbit that combines the altitude and inclination, such that a satellite in SSPO crosses the equator at the same time each day. For example, ISRO’s Cartosat-2 orbits the Earth at 635 km with an inclination 97.87° and has a period of 94.7 minutes crossing the equator at 09:30 hours every day. Most EO satellites are in Polar Orbit.
Medium Earth Orbit
A spacecraft in orbit between 2,000 km and 37,786 km is said to be in MEO with an orbital period between 2 and up to 15 hours. Most global positioning constellations use MEO, including those of the US, China, Europe and Russia, but not India (Glonass 11 h 15 m, GPS 11 h 58 m, Beidou 12 h 35 m and Galileo 14 h and 7 m). This configuration ensures that there are at least four satellites overhead at any one time. India’s NavIC constellation is not global but regional. It uses GSO and GEO.
Geosynchronous and Geosynchronous Equatorial Orbit
GSO and GEO orbit the Earth once every 24 hours and are predominantly used for communication satellites. Because of their unique properties, GEO orbits have limited availability. Their allocation is determined by the UN’s International Telecommunications Union. India has 11 GEO slots. India’s current occupancy in GEO/GSO consists of
32.6E IRNSS-1F
47.9E INSAT 4CR
55.0E IRNSS-1A and IRNSS-1B (both inclined at 29°)
55.0E GSAT-8, GSAT-16
74.0E Kalpana-1, GSAT-7, GSAT-14, GSAT-18, INSAT-3DR
83.0E GSAT-6, GSAT-10, GSAT-12, GSAT-19E, IRNSS-R1C, INSAT 4A, INSAT 3D at 82. °1 in reserve
93.5E INSAT 4B, GSAT-15, GSAT-17
97.2E SOUTH ASIA SAT
111.8E IRNSS-1D, IRNSS-1E (both inclined at 29°)
129.5E IRNSS-1G
GEO slots are typically divided into 2° longitude slots, which at 35,786 km amounts to an arc about 1,500 km long. When operational, each satellite must be confined to a box of a minimum 0.1° (about 70 km). By high precision control, satellite operators can co-locate multiple satellites in a single slot provided the radio frequencies do not interfere. From GEO, satellites have the whole Earth in their field of view and thus are used for planet-wide meteorological and communication services.
Satellite Communication
Satellite communication makes use of the Electromagnetic Spectrum between 3 GHz to 30 GHz. However, this is not exclusive. While some satellite communication takes place outside this range, the 3–30 GHz range is also used by some terrestrial applications. The table below indicates the typical use of a particular band of the spectrum.
Band
Very Low Freq.
(VLF)
Low Freq.
(LF)
Medium Freq.
(MF)
High Freq.
(HF)
Very High Freq.
(VHF)
Ultra-High Freq.
(UHF)
Super High Freq.
(SHF)
Extremely High Freq.
(EHF)
Wave
100km
10 km
1 km
100 m
10 m
1 m
10 cm
1 cm
Freq.
3
KHz
30 KHz
300 KHz
3 MHz
30 MHz
300 MHz
3 GHz
30 GHz
Typical Use
Maritime radio and navigation beacons
AM Radio
Maritime and aviation radio communication
Shortwave radio communication and Satellite-based Search and Rescue
Terrestrial FM radio, TV and navigation aids
Cell phone, GPS and TV
3 to 30 GHz band for satellite communication
Radio Astronomy
Ground stations with a large dish for high-speed communication are required for most satellite services. An uplink station sends a signal from the ground to the satellite, and a downlink station receives a signal from the satellite. The uplink and downlink stations are typically located within a single installation. To prevent interference, up and downlink channels operate at different frequencies.
Band and Frequency Range (GHz)
Description
L-Band
1 – 2
Used for GPS signals and satellite mobile phones by Iridium and Inmarsat for remote users on land, air and sea. The impact of weather on this frequency is minimal. Hardware is not expensive. The Safety-of-Life signal used by civilian aviation Satellite-Based Augmentation Systems, such as GAGAN, is in a nearby L5 band.
S-Band
2 – 4
Used terrestrially for weather, navigation radar and maritime communication. It was also used for in-space communication between Space Shuttle and ISS. Terrestrial use includes home broadband and cordless telephones in some parts of the world.
C-Band
4 – 8
Used by satellite networks (uplink 5.925-6.425 and downlink 3.625-4.200) data, communication, TV and amateur satellite radio. Typically, it requires a large dish (3 m or larger). These frequencies are not sensitive to “rain fade”, that is, the quality of the signal is not affected by rain or moisture. It is commonly used in areas where tropical rain is common. The first transatlantic TV signal in 1962 by Telstar used C-band. ISRO’s Synthetic Aperture Radar (RISAT) satellites use the 5.35 GHz frequency to produce radar images. Terrestrial use includes home broadband. The newer multiband routers operate at 5 GHz.
X-Band
8 – 12
Primarily used by the military for communication, air defence, weather monitoring, maritime and air traffic control. It is also used by spacecraft t
o transmit data by spacecraft beyond Earth orbit, on the surface of Mars, in orbit around Saturn and on the edge of the solar system. NASA’s Deep Space Network operates in this band. A slice of this frequency is dedicated for use by Amateur Radio Satellite AMSAT.
Ku Band
12 – 18
Used for satellite communication and DTH satellite TV transmissions (uplink 14.00-14.50 and downlink 10.95-12.75). It is also used by NASA's Tracking Data Relay Satellite (TDRS). TDRS was first used in 1975 during the Apollo-Soyuz mission for communication between two crewed spacecraft in space. Since then, it has been used by the space shuttle. Today, it is used by the ISS for routine communications. Two-way Internet connection, including VSATs, use Ku band. These frequencies are almost exclusively used for satellite communication. Ku-band offers higher signal strength and higher data throughput. Although a smaller dish suffices, this frequency band is susceptible to signal deterioration from rain and snow.
Ka-Band (26 – 40 GHz)
Used for higher bandwidth satellite communication. Currently, used by Inmarsat and planned for the Iridium Next satellite series using an uplink frequency of 27.5 GHz and 31 GHz. This band will also be used by the James Webb Space Telescope to be launched in 2018. The Ka band is more susceptible to rain attenuation than the Ku and the C bands. Terrestrially, this band is used by military aircraft for high resolution targeting radar.
Common Frequency bands used by satellites
The device on a satellite that receives signals at one frequency and retransmits at another is called a transponder. Typically, satellites have around two dozen transponders. For example, INSAT-3A is equipped with 12 C–band, 6 upper extended C-band, 6 Ku-band and 1 Satellite Aided Search & Rescue transponders. Some satellites can have over a hundred transponders. A communication satellite is predominantly a vehicle for a collection of transponders. Typical transponders perform the following functions: