Quote:
Originally Posted by RS_DEL There has been work done on turbine powered alternators/battery chargers for Hybrid EVs'. Let us wait and see shall we? |
Well, I am not going to talk about Turbines, rather about Rocket powered engines
time for some ka-boom not for some woosh woosh whining!
Next part:
Different Orbits
Let me give you a small intro into different orbits that are used:
Although the image shows circular orbits, they are not circular in most cases, rather they are mostly elliptical, that is why there is always a farthest point(apogee) and the nearest point(perigee) - same like in elliptical geometry, which many of us learned to forget during our school days. The "gee" in the words means "Earth" in greek, from which the latin is derived. we will talk more on this in the coming days.
This link gives a detailed view on various altitudes and compared with the moon. (image is too big, hence not posting here!) please follow the following link:
http://upload.wikimedia.org/wikipedi...laltitudes.jpg 1. Low Earth Orbit(LEO):
Any where above 100kms(there is actually no fixed boundary where the atmosphere ends and actual space starts! a topic with never ending discussion) so, lets assume 100kms is where atmosphere ends and space starts. So, the low earth orbit, as name suggests means the zone near the earth's upper atmosphere between 100 kms and 2000 kms. The main advantage of this orbit is that the orbital time(time taken to go around the earth once) is between 90 -120 minutes (1.5 hrs to 2 hrs @ ~7.7 km/s - 27,743.8 km/h).
Advantages of this orbit:
1. Easy to reach with normal ICBM(Inter-Continental Ballistic Missiles) which became the rockets(launch vehicles)!.
2. World-wide coverage, able to see any point on earth.(when and how is a different topic, will discuss it when we see about satellites and orbit determination!)
3. Useful for telephonic, navigation, remote-sensing, spy and gravity measurement and atmospheric analysis missions.
Some notable satellites using this orbit:
International space station(s), many RADAR and remote sensing satellites, almost all early manned space missions (SPACELAB, MIR, Gemini, early Apollo and Soyuz programs), most of the Indian Remote sensing and RISAT-1,2, Iridium satellites, Hubble space telescope, chandra X-ray observatory.
Disadvantages:
1. Too low, suffers from drag (thermal and atmosphere).
2. Too low view time over a point on earth
3. make a mistake, and plunge into a suicidal dive into the earth and end result burn up in the atmopshere.
4. needs constant attitude control and orbital corrections
5. Less contact times with the ground station - needs many ground stations spread all over the earth.
2. Medium Earth Orbit(MEO):
The orbit above the Low earth and between the High earth or the Geo-stationary orbit is the medium earth orbit. Though the orbital time period is longer than LEO, but one gets more time over a particular place due to the high altitude.
Advantages:
1. Larger area coverage over the face of the earth visible to the satellite.
2. Longer orbital periods - the object at earth sees the satellite stationary over its position for longer durations - good for navigation receivers.
Most prominent satellites: GPS, GLONASS, Galileo and Telstar 1.
Disadvantage:
1. Needs larger rockets(larger than ones used for LEO)
2. Space debri - blocks access to GEO orbit
3. When the satellite is dead(end of life), the issue of de-orbiting (either to make a suicidal plunge into earth or raise the orbit into graveyard orbit!) problem while coming down: Might have no control and might damage satellites in LEO orbit.
Problem going up into graveyard: blocks GEO transfer and needs fuel and some amount control to reach there in the first place.
3. Geostationary-transfer Orbit(GTO):
Used by satellites intended to be stationed in the Geostationary orbit. This is a sort of intermediate path towards its final destination. Quite often, even recently during the GSAT-10 launch we heard that its on its way and needs couple of days to reach its final orbit. So this is that "on-its way" orbit. This is otherwise also known as a "
Hohmann transfer orbit" (click on it to read more on Hohmann transfer! -again saving space and not to bore you with too much text, avoiding the explanation.)
4. Geo-stationary Orbit(GEO):
The final and the highest point any earth-observation satellite could reach.(so far!!) The orbit altitude is around 35000kms above earth's surface(add 6384 kms -earth radius to it!). So this is where one satellite or when a human placed, keeps revolving around the earth, basically, at the same time-period as the earth. What that means? One is stationary above a fixed point. Mostly used by television/telephone/internet transpoding satellites. Its like the object is let afloat over a place, tied by a string, its always there.
Advantages:
1. Ability to cover huge land area(sometimes whole country)
2. Satellite visibility is 24x7(both ways!)
3. Satellite never has eclipse or lack of sunlight (except for some time in summer) due to the inclination of the earth (11°). Hence, satellite has access to solar power 24x7.
4. No complex orbit maneuvers required - read saving costly on-board fuel and there by saving weight(important for launch).
5. Only one ground station is enough to communicate with the satellite.
Disadvantage:
1. reaching the orbit needs a huge rocket or an extra stage(4th or sometimes 5th stage).
2. The transmission needs high power antennas and receivers, due to the distance.
3. The satellite needs to be radiation hardened as it is easily exposed to cosmic radiation and harmful sun's rays. (on the way it crosses Van-Allen belts!)
4. Decomissioning the satellite needs a orbit-raising maneouvre! To be put into the Graveyard orbit, above the normal GEO orbit.
I hope I have covered all the basic aspects of orbits, coming up next, we will read more into how rockets are designed, staging, fuels, shapes and some physics of reaching the space.
The orbits I left are:
1.
Molniya
2.
Tundra
(Image courtesy: Wikipedia)
Questions??
Edit: Mods, sorry about the huge images. These images explain the concept to the best and are simple, hence used them!