No Comments on that. I was Op Dir for that sat. Got it??Prem Kumar wrote:S^3 - thanks for the clarification.
On a related note, is it true that the CartoSat 2's performance has not been satisfactory, as mentioned in some news reports? Or is it plain old-fashioned DDM?
ARTOSAT-2 is an advanced remote sensing satellite capable of providing scene-specific spot imagery. The data from the satellite will be used for detailed mapping and other cartographic applications at cadastral level, urban and rural infrastructure development and management, as well as applications in Land Information System (LIS) and Geographical Information System (GIS).
The first imagery, received on January 12, 2007, covered a length of 240 km from Paonta Sahib in Shivalik region to Delhi. Another set of imagery of about 50 km length covered Radha Nagari to Sagoan in Goa. Analysis of the first imagery received at National Remote Sensing Agency's data reception station at Shadnagar, near Hyderabad, confirmed excellent performance of the on-board camera.
The Science article is here: http://m3.jpl.nasa.gov/Science_April-10-09.pdfVipul wrote:It's strike II for Chandrayaan.
Tanaji-saarTanaji wrote:Sorry for a really dumb question, but I really dont know:
Why is a satellite orbit as shown by SSSalvi on the earlier page always "sinusoidal"? Or, how do I interpret the diagram shown ? Are the various "sine waveforms" "phase-shifted" from each other the various tracks of the satellite? Also, isn't it true that the sat can only image a swathe of the area at a time, which is usually like a long rectangular piece? What governs the size of the swathe?
Apologies for dumb questions again...
That indicates its a simple collection of individual antennas mounted on a hemispherical dome and only one of them is used at a time. I was hoping they will use immediate neighboring elements for tighter beam shaping. Is each element Circularly Polarized or linear?SSSalvi wrote:It has a narrow beam which is pointed continuously to the intended station only.Arun_S wrote:
Incidentally IIRC that is a very interesting shaped (spiked) antenna. I would suspect not only wide angle/coverage but also programmable beam forming/nulling to ensure data radiated to 'pavitram' bearings onleeee.
See what happens. The projection of the "still" orbit on the moving earth will make those sinusoidal looking maps for the orbit projection on the earth/globe.Actually, ISRO says the X-band antenna was a phased array!Arun_S wrote:That indicates its a simple collection of individual antennas mounted on a hemispherical dome and only one of them is used at a time. I was hoping they will use immediate neighboring elements for tighter beam shaping. Is each element Circularly Polarized or linear?SSSalvi wrote: ...
It has a narrow beam which is pointed continuously to the intended station only.
Well all is well that works well.
A simpler way of thinking about it is as follows. Imagine a dot on the wheel of a car. Initially let the dot be at the top. Now let the car move forward. What will the path taken by the dot ? The dot is moving forward (because the car is moving forward) at the same time it is moving down (because the wheel is turning). Then it reaches the lowest position and then rises all the way up (all the while moving forward). The shape it traces out will be a sinusoid.Tanaji wrote:Sorry for a really dumb question, but I really dont know:
Why is a satellite orbit as shown by SSSalvi on the earlier page always "sinusoidal"? Or, how do I interpret the diagram shown ? Are the various "sine waveforms" "phase-shifted" from each other the various tracks of the satellite? Also, isn't it true that the sat can only image a swathe of the area at a time, which is usually like a long rectangular piece? What governs the size of the swathe?
Apologies for dumb questions again...
The same thing on a spherical earth is indicated here.Tanaji wrote:Sorry for a really dumb question, but I really dont know:
Why is a satellite orbit as shown by SSSalvi on the earlier page always "sinusoidal"? Or, how do I interpret the diagram shown ? Are the various "sine waveforms" "phase-shifted" from each other the various tracks of the satellite? Also, isn't it true that the sat can only image a swathe of the area at a time, which is usually like a long rectangular piece? What governs the size of the swathe?
Apologies for dumb questions again...
There are several ( I don't know if the actual number is a secret ... so I will say more than 60 ) elements and by controlling the phase and power fed to each element the a narrow beam is formed which can be steered +/- several degrees in the 'pavitram' direction where 'our' station is located. Eventhough 'a-pavitram' stations point their antenna to the satellite they may at most see a very feeble 'presence' of signal but not sufficient signal. The radius where good signal can be received is less than 100 kms.Arun_S wrote:That indicates its a simple collection of individual antennas mounted on a hemispherical dome and only one of them is used at a time. I was hoping they will use immediate neighboring elements for tighter beam shaping. Is each element Circularly Polarized or linear?It has a narrow beam which is pointed continuously to the intended station only.
Well all is well that works well.
Thanks for confirming the hypothesis I lived with since TES was launched. Some times we have on this forum the person who was receiving the 'pavitram' 6 degree beam.SSSalvi wrote:There are several ( I don't know if the actual number is a secret ... so I will say more than 60 ) elements and by controlling the phase and power fed to each element the a narrow beam is formed which can be steered +/- several degrees in the 'pavitram' direction where 'our' station is located. Eventhough 'a-pavitram' stations point their antenna to the satellite they may at most see a very feeble 'presence' of signal but not sufficient signal. The radius where good signal can be received is less than 100 kms.
Can anyone shed light on why these are being used in this day and age. source: AGI spam mail."Tracking data indicate Kosmos 2450 is in an orbit with a high point of about 208 miles [335 km] and a low point of about 105 miles [169 km]. The orbital inclination was reported as 67.1 degrees.
"Analysts believe Kosmos 2450 is a Kobalt-class satellite with retrievable film canistersthat can return imagery to Earth through a mission lasting at least several months.
"Earlier Kobalt spy satellites were operated in similar orbits."
Bade-saarBade wrote: Can anyone shed light on why these are being used in this day and age. source: AGI spam mail.
background info: this was a recent russian launch from this week. The source they link to is below.
http://www.spaceflightnow.com/news/n0904/29soyuz/
Infinite resolution dear, infinite resolution.Bade wrote:Can anyone shed light on why these are being used in this day and age. source: AGI spam mail."Tracking data indicate Kosmos 2450 is in an orbit with a high point of about 208 miles [335 km] and a low point of about 105 miles [169 km]. The orbital inclination was reported as 67.1 degrees.
"Analysts believe Kosmos 2450 is a Kobalt-class satellite with retrievable film canisters
"Earlier Kobalt spy satellites were operated in similar orbits."
background info: this was a recent russian launch from this week. The source they link to is below.
http://www.spaceflightnow.com/news/n0904/29soyuz/
but finally got it.See Mercator projection in http://en.wikipedia.org/wiki/Map_projection for Technical infojamwal wrote:Anujan, Bade, SSalvi saar
Dhanyawaad for very nice explanation about "sinusoidal" orbit. I had to use pen and paper
SSSalvi wrote:
Infinite resolution dear, infinite resolution.
Since ages russia is using the same tech.
Remember Rakesh Sharma holding suitcase size camera?
"The RISAT has begun taking images since two days ago," ISRO chairman G Madhavan Nair . . . He said that the RISAT would take about a month to stabilise.
Yes, in simple termswould not the resolution be a function of the resolving capacity of the optics???
CHENNAI: India’s manned mission to space has taken a small step forward with the fabrication of the ergonomic model of the crew module that will take two Indian astronauts into space in seven years from now.
...
In its first set of biological experiments, the Indian Space Research Organisation (ISRO) will send bacteria cells into space — and bring them back — in the second Space Capsule Recovery Experiment (SRE-2) scheduled for launch this year-end.
However, for some reason, ISRO has been reluctant until now to develop a liquid-booster stage that could replace the solid booster and achieve a higher payload capability, notwithstanding the fact that it has mastered the solid-motor technology, which is completely indigenous. As recounted by N. Gopal Raj, the science correspondent of The Hindu in his 2000 book Reach for the Stars on ISRO's rocket development, similar efforts at developing indigenous capability in liquid propellants have been lacking all these years. Nearly all the effort on this front was directed at indigenising the imported Viking engine technology into Vikas and consolidating this capability, including creating industrial capacity to produce Vikas engines to meet the needs of PSLV and GSLV launches.
One of the chief architects of ISRO's solid propellants programme was Dr. Vasant Gowariker, a chemical engineer-scientist who later became the Secretary of the Department of Science and Technology (DST) and is currently ISRO's Satish Dhawan Professor in Pune. It was Gowariker who pioneered the work on cryogenic engine development in ISRO. In 1971, under Sarabhai's suggestion, he set up the Cryogenic Techniques Project (CTP) with six people and initiated the conceptualisation and design of a semi-cryogenic engine.
"The project was more like a software kind of work as a step towards fully cryogenic technology," Gowariker says. "It was Sarabhai's idea to use this as a basis to get familiarised with cryogenic technology because while making liquid hydrogen is risky business, liquid oxygen was easily available from the industry. The idea was to make do with whatever systems that were available at that time, get experience with liquid oxygen in its handling and the filling process and develop systems to utilise its full oxidation capacity," Gowariker said.
"I feel that wisdom has finally dawned on them," says P.R. Sadashiva, an important member and the first recruit in the six-member team under Gowariker, who took voluntary retirement from ISRO in 1992. "After the testing of one small-scale semi-cryo engine, the whole project - costing Rs.3.48 crore then - was shelved and the setting up of a dedicated liquid oxygen plant costing just Rs.16 lakh was stopped," he recalled. In fact, this was the last thing that Sarabhai approved a day before his death in December 1971. According to Dr. Sadashiva, after listening to a presentation on solid propellants for the Defence Research and Development Laboratory that went on well into the night, Sarabhai retired to Kovalam Hotel in Thiruvananthapuram when Gowariker rushed in with the papers on the proposal for a 10-tonne LOX plant. Sarabhai promptly signed it.
"People connected with Vikas and the proponents of solid propellants pulled it down, in particular one man who was interested in pushing the imported Vikas," adds Sadashiva. Although he refrained from naming the person, it is amply clear that he was referring to Dr. A.E. Muthunayagam, who led the Vikas programme at ISRO's Liquid Propellants Systems Centre (LPSC).
"Although the Vikas project definitely gave us the liquid propellant technology, semi-cryo [technology] is the cheapest option as compared with earth-storable liquids," he pointed out. He said ATF was available at nominal cost and liquid oxygen was about 20-25 times cheaper than UDMH or N2O4 at that time.
"The proposal was to develop a 75-tonne thrust semi-cryo engine, similar to the 68.5-tonne Saturn V engine, and we could have easily achieved that. And by clustering four of these, we would have had an extremely powerful booster by now, equivalent to the most advanced rockets, which could have formed the basis for our main version of the PSLV. And in parallel a 7.5-tonne thrust LOX-LH cryogenic engine could have been developed. We have lost valuable time," he observed.
Sadashiva recounted how they would transport LOX by jeep from Fertilizers and Chemicals Travancore Ltd. in Kochi, where it was obtained as a by-product and was largely wasted, in containers that were so bad that half the content would have evaporated by the time they reached the testing facility near Thiruvananthapuram.
"The man to blame is [Satish] Dhawan," says Prof. H.S. Mukunda of the Indian Institute of Science (IISc), Bangalore, who headed the committee that prepared the report on the semi-cryogenic engine. "He, for some reason, went along with the arguments of people involved with the Vikas engine project and did not even give us a hearing. Even U.R. Rao [former Chairman of ISRO] was extremely unhappy with our proposal."
"Of course, there was no requirement, or even any ambition, for a payload greater than INSAT-II at that time to say that there was a shortfall [in Vikas's capability] and we lacked an engine with a greater thrust. But our idea was to get hands-on experience with cryogenic systems over three years so that we could be in a position to develop full cryogenic engines on our own, on the basis of this experience," Mukunda adds.
The curious thing is that ISRO wants to develop the semi-cryo engine now after developing the full cryogenic engine, instead of having done it the other way around. "I don't really know for what kind of payload is the present semi-cryo engine being developed. But the environment now is completely different after the handling of the Russian cryogenic engines and systems. Moreover, much better hardware is available today. So developing the semi-cryo engine should not take more than three years," Prof. Mukunda says.
Gowariker does try to rationalise Dhawan's decision in retrospect. "The functional requirements of mission [of the time] are important and from that perspective the Viking-Vikas liquid engine route was a good idea. Given limited financial and human resource, the overall performance of a system becomes important and decisions on where and how we direct the development effort become extremely difficult. So, instead of letting too many things go on simultaneously, it must have been felt that a semi-cryo project was less important then," says Gowariker.
The Vikram Sarabhai Space Center in Thiruvananthapuram is finalizing the design of a spacecraft propelled by a semi-cryogenic engine, which represents a completely new development, "according to the Director of ISRO G. Madhavan Nair . "The technology for return to Earth requires powerful launchers. To do this, we develop a system to process semi-cryogenic rocket engines that will power future missions. The goal is to develop this vehicle in the next 6 years, with a budget 250 million euros. "The design phase is almost completed. We expect a project proposal soon. Then, a series of ground tests will be made, "says Nair, who is also Secretary of the Department of Space.
"If you just want to reach the moon, you need a certain capacity. For the return to Earth, that ability should be doubled. MkI The GSLV-II (which will be tested by 2010) for example, has a capacity of 10 tons for a relatively close orbit of the Earth. We have to incorporate an additional capacity of 20 tons to bring our ship. The launcher semi-cryogenic boosters provide bigger, more powerful and less consumers, which could be used to larger missions. " The semi-cryogenic system works best with kerosene or paraffin refined (RP1), considered a clean fuel. It also has an operating cost 30% lower if it replaces the liquid hydrogen expansive. India will be the second nation after the former Soviet Union to adopt this technology, according to PS Sastry, Director of Program Launch.
Does that include the full cryo LH2/LOX engine for the GSLV MK2?All other engines we have done have <80 atm chamber pressure.
