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Indian Space Programme Discussion - Sept 2016

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Re: Indian Space Programme Discussion - Sept 2016

Postby NRao » 19 Feb 2017 14:27


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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 19 Feb 2017 20:59

SSSalvi wrote:A question to vehicle experts:

Earlier PSLV launched sats even at 900 kms orbit @ equator.

This flight was a slow riser ... attained 500 kms @ about -20 deg Lat.

Is it due to vehicle constraint or deliberate?
people have opined that it is intentional, for various reasons, one being the need to inject it into a specific orbit. I was thinking along a different line..that perhaps the 'slow' rising was for a need to conserve energy in the ascent phase (lower velocity = lower aero drag) in order to give it a higher orbital velocity in the satellite insertion phase that is needed at a lower orbit (450 km vs. 900 km) but the difference in orbital velocities between the two does not seem significant (7.6 km/sec vs 7.4 km/sec) so, I guess this is not a reason.

question at large: when the nanosatellite quad packs are being ejected, at one point in the video (4:23) they are ejected directly at earth. One would think that the orbit velocity vector should be tangential to earth at any point in time; (so during ejection one expects to see the horizon) but in this case, at 4:25, the entire frame is all earth, and the satellites are going directly at it, which does not seem intuitive. By the way, my recollection is that this is a circular orbit with an altitude of about 450 km. For the ejection of Cartosat and the next satellite, one sees both space and earth and the cartosat is ejected 'along space', so here there is some visual indication of 'tangentiality'. https://www.youtube.com/watch?v=ACCsMTZ_qKo

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Re: Indian Space Programme Discussion - Sept 2016

Postby prasannasimha » 19 Feb 2017 23:06

A higher orbit has a higher velocity
The height of injection is dependent on the orbital parameters of the satellite
The ejection appearing in various directions is just an artifact depending on the angle of the camera- all of the satellites in orbit are in permanent free fall when orbiting. Some of the satellites are packed on the side and are being ejected so seen at an angle whereas the major 3 satellites were ejected form in line the main axis of the spacecraft (in the cneter) see the figure that SSSalvi postedregarding packing of the satellites

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 19 Feb 2017 23:57

prasannasimha wrote:A higher orbit has a higher velocity

If by 'higher velocity' you mean 'higher orbital velocity' (which is what I cited in my post), the statement is clearly incorrect. For satellite to be in orbit, the centripetal force should equal the gravitational force of attraction. I.e. m*v^2/R = GM*m/R^2 (M= mass of earth, m= mass of satellite, R = radius of orbit = radius of earth + altitude above earth surface). Solving, you get orbital velocity v = sqrt (GM/R).

So orbital velocity is inversely proportional to the radius of orbit, i.e. higher orbit means an orbiting satellite will have a lower velocity. There are several web calculators for this: http://www.calctool.org/CALC/phys/astronomy/earth_orbit

The ejection appearing in various directions is just an artifact depending on the angle of the camera- all of the satellites in orbit are in permanent free fall when orbiting. Some of the satellites are packed on the side and are being ejected so seen at an angle whereas the major 3 satellites were ejected form in line the main axis of the spacecraft (in the cneter) see the figure that SSSalvi postedregarding packing of the satellites
A lot of different things are mentioned above. Of course all satellites are always in freefall, it is not specific to this particular launch. It is irrespective of the launch/insertion angle. Yes, satellites were ejected from different sides of the rocket relative to the camera, but the time of launch that I am talking about (4:25) the satellites do seem go to towards the earth (P- case). At first glance, it does not seem to be an optical illusion, to me anyway. I have not seen SSSalvi's post on packing of satellites...I'll check it out. (added later: I saw the post).

Added later:
Around 5:00 to 5:30, there are plenty of satellites with a velocity vector pointing to earth ....and they clearly move towards earth's surface initially (before 'stabilizing' in some way). It seems like the satellite ejection is happening not along the upper stage's orbit but at an angle to it.This probably corresponds to a case where an orbiting satellite is given a delta 'v' towards earth and not along the orbit of the upper stage. I think I need to go back to Amber.G's exercise in a previous page on the 4 scenarios.

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Re: Indian Space Programme Discussion - Sept 2016

Postby vasu raya » 20 Feb 2017 00:41

if spare capacity for nano sats is going to be available, while their might be a backlog in that segment of the market, maybe there will still be PSLV launches looking to fill some spare capacity, can they add the parachute based recovery systems to the specific stages for reusing them?

if such recovery systems are an option, then the logistics of getting it back to mainland can be worked

maybe we get the amphibian planes, the US-2 from Japan in exchange of LCH, as a tangent they should always have a separate line/partition for exports and not wait to fulfil the domestic orders completely

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 20 Feb 2017 00:52

^^ Check your video you linked around 1:28 - 1:30. After cartosat separation there is rapid attitude changes - after it ejects cartosat - it quickly first veers 'left' and then 'right' ejecting INS 1A/B and then veers hard 'right'.

On top of it think that the PS4 is racing towards geo 'North' while over Antartica (another frame of reference for what follows) and starts ejecting nanosats 'below' and 'above' it (think you are riding the rocket but facing the other way and tossing sats using overarm chucking and underarm chucking).

Earth is vast and covers the entire camera., earth is so vast and the clouds over antartica even if 25 km diameter cover a significant frame. So the entire end-to-end frame of the camera Field-of-view is not covering more than 250 km (IMHO). In that sense, the earth thus appears flat and forms the 'back screen'. Against the back screen of white (particularly on P- side) as the sats are ejected (and remember they are tiny., like 10x10x30 cm (and still they seem big on the screen) - hence when scattered along the orbital path they appear to be either 'down' (as you thought) or they appear to be 'up' (to me it appeared that they were shot up :-D )

Just to note., they are ejected along the orbit of the upper stage.

*The left/right is viewers frame of reference.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Hiten » 20 Feb 2017 11:26

When An Indian Rocket Shot Up Into The Norwegian Sky

Image

http://www.spansen.com/2017/02/when-ind ... -from.html

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 21 Feb 2017 00:51

kit wrote:Out of curiosity sakes 8) .. how different is an MIRV bus from a multi payload injector adapter ???

As I said before (see some of the posts) comparing these makes little sense. The "I" of MIRV stands for independently Targetable. "Bus" (or the post-boost stage) can dispense the warheads against multiple targets across a broad area. There is no such (NOT even close) mechanism here...

Perhaps some people are confused and may not fully understand the concept of "precise orbit" in this context . Here the sats are pushed (with delta-V only a few meter/second - something one strong person can push).. the direction etc have to be in right ball-park but in NO WHERE close to precision needed for MIRV (or TMI of Mangalyaan). IOW the point I want to make is, the sats are in orbit but all one needs is right ball park figure.

disha wrote:
On the issue of MIRV vs. Multi-Sat launch., we can agree to disagree - it is a question & debate of slicing a hair longitudinally first and then latitudinally or slicing it latitudinally first and then longitudinally to get the best 'hair splitting' result. But if you get a chance, do talk to a real 'missile man' like the people who manned minuteman missiles on how targets are acquired and how the missiles are launched. And this we can take it up in missile thread.


Okay. If you think that they are not "too dissimilar" to 108 doing "tandav over Chinese cities" ..Okay. For me, for the reason I gave, I still think it is silly. :)

In the C37 launch., after PS4 cutoff <- note the keyword 'cutoff' - the C37-PS4 stage will be at a higher orbit than the launched satellites and will stay there for 10 or so orbits before being "passivated" and brought back into a degenerate orbit. Hence for that 10 orbits., ISRO has a PS4-C37 satellite


Can you give a reliable source to state what you are stating about C37 flight profile. Specially where do you get "higher" orbit (by how much ?) or staying "10 orbits or so".. (are these 10 or 100, for example).. and what exactly is "passivated" and brought back to "degenerate orbit" (what are the parameter of "degenerate orbit")?? .(I think that some of the above are not clear enough and need additional details)

****

As SriKumar has pointed out, some of the aspects (and understanding of basic physics) are very similar to post I have put in other thread (in response to lot of discussion by Disha ji etc).. (Here: https://forums.bharat-rakshak.com/viewtopic.php?f=3&t=6652&p=2036920&hilit=500+Km+100+m#p2036920...

There are lot of similarities.. 500 Km is in right ball park. I gave delta-V in my exercise as 100 m/s .. in C37 case it is just a few m/s.

I am curious, Dishaji - Do you agree with my analysis given there. (People can read all the discussion there ... my final recap is at:
https://forums.bharat-rakshak.com/viewtopic.php?p=2037787#p2037787...
Last edited by Amber G. on 21 Feb 2017 03:27, edited 2 times in total.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 21 Feb 2017 01:33

SriKumar wrote: I think I need to go back to Amber.G's exercise in a previous page on the 4 scenarios.


You are correct wrt to many of the points you made --

Obviously a few things I did not consider in those "exercises'.
- Push in direction perpendicular to the orbit . (This changes the orientation of the orbit - but calculations can be done similarly).

Also, I assumed that earth is an uniform sphere. For C37, the aspect that earth is bulging at the equator pays part in calculations. The calculations become a little more complicated, and need some perturbation theory. (This is not covered in basic physics UG courses) but basically for any polar type orbit:

- The orbit is not stable but precesses. (This is similar to movement of Lunar orbit and it's nodes with 18.6 year time-period)
- The rate of precession depends on, among other things, the inclination or orbit (wrt to equator)
- One chooses the altitude/inclination etc in such a way that the precession value comes out to be about 1 per year.

So as I said before, this is taken in consideration where the sats are released.

One thing one should also keep in mind that when all is said and done, the sat's orbit (and C37) are not that drastically different from each other. Sure the sats do not collide with each other (but that is easy - space is vast so even if you shoot blindly you will not hit other object) but the delta-V is really or the order of m/s or (less than 0.1 % of 8Km/sec).. In other words the orbital parameters (eg time it takes for the orbit, altitude etc) are very similar.

I think, this is what Prasannasimha was pointing at.. (Which directions one particular sat was pushed is *not* that interesting)
****

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 21 Feb 2017 07:17

^^^. I did go back to the posts :) and finally understood some of JayS's comments.
As I watch the video, it seems to me that different satellites were launched in different directions (and to my limited understanding, this implies different orbits). For example, both Cartosat and INS-1 were launched in a similar orbit i.e. forward, along the flight path of the 4th stage.

One bunch of nanosat packets i.e. quad pack seem to have been launched in a totally different direction IMHO. If you look at the video at around 5:08 and later, couple of things jump out...one, the camera (angle) is a different one from the one that showed Cartosat launch. This camera (5:08) seems to point 'sideways'. You can see the way the ground goes 'sideways' (like looking out of a window in a plane, as opposed to looking out of the front of a plane cockpit). This camera does not point along the direction of motion of the 4th stage. From this camera angle, one sees that satellites are pointed/released along a vector that goes towards earth. Some have argued that is this an artifact due to distortion of camera image (or something along those lines). It seems to me that these satellites were deliberately ejected sideways relative to the path of the rocket to give it a different orbit from cartosat and even some other nanosatsetc. I am thinking that the many nanosats (90+) have several different orbits among them.

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 07:55

SriKumar'ji et al - simplify it. No need to bring PhD thesis here - we will leave that to ISRO :-D

Think of the PS4 going "up" and while going "up" tossing out the nanosats. P+ and P- are directions in which they are tossed off (ejected off using springs., nanosats are just 10x10x30 cm and do not have their own propulsion).

From the reference frame of S'hkota looking straight at the rocket - it is a straight line up and P+ and P- are vectors pointing at you and pointing away. Or visually - just turn this: +|- by 90" towards right.

Here is the ejection sequence:

1. PS4 Cut-off @16min 47.80 sec @alt: 509.536 km
2. 1st pair of nano sats separation @18min 32.80 sec @alt: 511.719 km
3 last pair of nano @28 min 42.80 sec @alt 524.075 km

Here is the brochure (AmberG flight profile details you are looking for are as well in that brochure): http://www.isro.gov.in/pslv-c37-cartosat-2-series-satellite/pslv-c37-brochure-0.

---

AmberG., can you please do some research on "stage passivation" and "degenerate orbits"? This are standard engineering practices of space launches where theory does not come into picture.
---

For others., the final stage always has additional fuel. Also has charged batteries etc. Basically it has enough of energy that if not properly released may cause an explosion (remember PS4 has hypergolic fuel and over period of time the storage valves may leak causing the fuel to mix up and go boom). Uncontrolled explosion will lead to space debris. Yes., even batteries heat up and may explode - more likely in space than in your pockets like the phone batteries.

Hence the goal for all last stage boosters is to remove any stored energy., this venting out the energy (generally fuel and draining the batteries) is called stage passivation. While the stage is passivated., it may also put in a degenerate orbit. That is a highly elliptical orbit that causes the stage to eventually re-enter earth's atmosphere and burn up. This is better than keeping the stage orbiting around for several more years as space junk.

Of course the general practice is to passivate the last stage at the earliest opportunity and put it in a degenerate orbit which will lead to burn up and if there is any debris the fallout can be in pacific ocean. However, the last stage itself can be used to do additional studies. Or sometimes a stage itself is reused as in skylab.

Even the satellites are passivated and moved to a grave yard orbit. In case of GEO sats., the orbit of the satellite is boosted up by some 360 km and the sat is passivated (basically all stored energy is removed). Note that it is easier to boost it up rather than bring it down (energy required is less to boost it up, it is already flying high!)

Now what ISRO plans to do with C37 PS4 stage *may* be found in this recorded (it is not live any more) video: https://www.youtube.com/watch?v=yPtFNJ2SSUw. And there are some further gems
Last edited by disha on 21 Feb 2017 07:58, edited 2 times in total.

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 07:57

SriKumar wrote: Some have argued that is this an artifact due to distortion of camera image (or something along those lines).


No sir., that was only part of the argument - not the whole. Couple that with ejection of sats 'sideways' (as you mention) to get the complete picture of your own query.

Also check out Planet's website itself. The nanosats are like a line scanner of earth. They have very few different orbits among them.

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 08:09

Hiten wrote:When An Indian Rocket Shot Up Into The Norwegian Sky

http://www.spansen.com/2017/02/when-ind ... -from.html


Thx. Also from above: http://www.spansen.com/2017/02/that-chinese-satellite-pslv-c37-launched.html

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 21 Feb 2017 09:00

disha wrote:
Also check out Planet's website itself. The nanosats are like a line scanner of earth. They have very few different orbits among them.

The ISRO brochure clearly mentions the orbits. The Cartosat+ the two INS sats have pretty orbits pretty close to each other, at 510.38 km, 510.59 and 510.6 km respectively. The vertical separation between the three is about 20 meters. By contrast, the first nanosat orbit is about 1 km higher, starting at 511 kms and the last few ones are at 524 kms. The vertical separation between them is 13 kilometers.

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 10:03

SriKumar wrote: By contrast, the first nanosat orbit is about 1 km higher, starting at 511 kms and the last few ones are at 524 kms. The vertical separation between them is 13 kilometers.


Are you suggesting that they will all be in distinct orbits? My understanding is that several of the doves will share an orbit. This nano sats operate in flocks and some flocks are in very similar orbital path.

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 21 Feb 2017 10:17

I never suggested it explicitly nor implied that. My post was a comment about the differences in the ejection of satellites in the beginning of the process (cartosat INS, etc) and the satellites that came later on, especially towards the end (5:10). The camera showed some clear differences. The data on the brochure seems to shed some light on this.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Prem » 21 Feb 2017 11:11

India eying moon as energy source, ISRO professor tells seminar

NEW DELHI: India hopes to meet all its energy requirements from resources from the moon by 2030, according to a professor at the Indian Space Research Organisation (ISRO), which recently launched a record 104 satellites with a single rocket, reports said on Sunday.Elaborating on ISRO’s future plans, Dr Sivathanu Pillai, who was formerly the chief of BrahMos Aerospace, said all of India’s energy requirements could be met through Helium 3 mined from the moon.“By 2030, this process target will be met,” he said while delivering the valedictory address at the three-day ORF-Kalpana Chawla Space Policy Dialogue, organised by Observer Research Foundation here on Saturday.Dr Pillai said that mining lunar dust, which is rich in Helium 3, is a priority programme for his organisation. He added that other countries were also working on this project and that there was enough Helium on the moon to meet the energy requirements of the entire world.
He said that ISRO was planning the whole process of mining and transporting helium back to Earth.Lt Gen P.M. Bali, director general of Perspective Planning, Indian Army, said that India now acknowledged the growing requirements of space technology for its national security and was beginning to put in place relevant policy and institutional frameworks.He pointed out that at present India possessed one of the largest constellations of communication and remote-sensing satellites covering the Asia Pacific. The launch of GSAT-7 in 2013, India’s first dedicated military satellite, was testimony to its outlook towards utilisation and exploitation of outer space for national security.Lt Gen Bali also said that though India continued with a civilian orientation to its space programme, the changing regional and global realities required it to also develop military assets in space and on the ground, as an emerging regional and global power.He added that there was a need for a dedicated military space programme with adequate resources at its disposal because of “the changing realities in our eighbourhood”.Delivering a special address on “Outer space and strategic stability”, retired Lt Gen B.S. Nagal said that maintaining space stability was “very difficult” with changing warfare and space being no taboo unlike nuclear weapons.Speakers saw clutter in space and greater challenges in the form of space debris, conflicts over demands for spectrum allocation and radio frequency interference. The question of cyber vulnerabilities, the increasing trend towards weaponisation of cyberspace itself — all of these pose serious challenges for the governance of outer space, the seminar was told.

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Re: Indian Space Programme Discussion - Sept 2016

Postby SSSalvi » 21 Feb 2017 11:23

Current orbit ellipse shape ( Perigee * Apogee in Kms ) of identified objects:

Carto 2D : 506*521
INS 1A and 1B : 497*508
Flock 3P - 30 : 496*504
41951 : 497*507
41953 : 495*504
42052 : 476*496

Last item could be the 4th stage/launcher .. yet to be officially confirmed.

BTW: The onboard camera video by ISRO seems to be memory dump at high speed. You run the on-board camera video @ 1/4 th speed ( Browser / Youtube player gives option in settings ) and see the turning of launcher .. Earth disc moving in the background ...

There seem to be 4 cameras : Tail ( 3rd stage release ). Just below INS 1A ( shows Carto, INS 1A and 1B release ), P+ '' pointing to cold / dark sky showing the bright stars being released , and P- camera showing sats on Earth background.

DOVE sats ( with a protruding rod ) are released with a spin ( to ensure that the antenna is pointed to Earth ????? ).. while the last 4 sats ( rectangular box shaped ) are not spinning.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 21 Feb 2017 12:33

disha wrote:Here is the brochure (AmberG flight profile details you are looking for are as well in that brochure): http://www.isro.gov.in/pslv-c37-cartosat-2-series-satellite/pslv-c37-brochure-0.

---

AmberG., can you please do some research on "stage passivation" and "degenerate orbits"? This are standard engineering practices of space launches where theory does not come into picture.


Disha - I have seen the link you have posted, and also actually familiar with "stage passivation" degenerate orbits"... my post there was to give some perspective and challenge you on the numbers like "10 or so orbits" (Is it 10 or so, or 100 or 1000"s)..Think about for a sec, and you may be able to guess why I asked.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 21 Feb 2017 13:08

SriKumar wrote:I never suggested it explicitly nor implied that. My post was a comment about the differences in the ejection of satellites in the beginning of the process (cartosat INS, etc) and the satellites that came later on, especially towards the end (5:10). The camera showed some clear differences. The data on the brochure seems to shed some light on this.


Hi SriKumar - One thing to keep in mind also is the "ejection speed" and "change in orbit" in many cases (as you may have seen from my exercise before) could be quite counter intuitive. For example two sats one ejected with a small delta V in p+ , and other p- (one towards earth, other away from earth) from a (let us suppose a circular orbit) of C37 both sats will have identical elliptical shaped orbits.

Another thing - which generally baffles non-scientists - if you wants to, say "catch up" another sat in the same orbit but a little ahead of you -- the intuitive way of firing a control thruster "backwards" (so that you get forward push) may/will not work.

For example, suppose you are in the same orbit as a space station but a little behind of that station and want to catchup to that station. Unless the distance is only a few tens of meters, the efficient way is actually firing thruster so that you move "backwards".. drop in the orbit (thus increasing speed and angular velocity too) and thus catch up and then come back up.... (Yes, many space movies forget that :) )

(All of this is quite counter-intuitive and earlier astronauts have to be trained (for say docking to space stations) and it was not intuitive for them because many of then were test pilots and these things work differently)

All I am saying here is one has to be careful in drawing inferences watching videos and employing intuitive reasoning.

Hope this helps.

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Re: Indian Space Programme Discussion - Sept 2016

Postby prasannasimha » 21 Feb 2017 16:23

The firing backwards to catch up was Buzz Aldrin's PhD thesis.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 21 Feb 2017 18:16

prasannasimha wrote:The firing backwards to catch up was Buzz Aldrin's PhD thesis.

Indeed!

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Re: Indian Space Programme Discussion - Sept 2016

Postby srinebula » 21 Feb 2017 18:58

Amber G. wrote:
prasannasimha wrote:The firing backwards to catch up was Buzz Aldrin's PhD thesis.

Indeed!


I understood dropping the orbit to increase angular velocity part; but what is the need to move backwards?

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Re: Indian Space Programme Discussion - Sept 2016

Postby prasannasimha » 21 Feb 2017 19:49

Acceleration forward makes you go into a higher orbit which pushes you back!! It is coutnerintuitive. Please see V bar R bar and Z bar approaches of space rendezvous

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 23:39

Amber G. wrote:
Disha - I have seen the link you have posted, and also actually familiar with "stage passivation" degenerate orbits"... my post there was to give some perspective and challenge you on the numbers like "10 or so orbits" (Is it 10 or so, or 100 or 1000"s)..Think about for a sec, and you may be able to guess why I asked.


Amber., I do not think this pages should be your PhD thesis thread. If you want to make a PhD thesis out of this., there is the physics thread. And the math thread. Please feel free to make/post puzzles there.

Further if you have already thought on why the upper stage is orbited for 10 orbits., then it will help if you can post it. Till that point it can be safely assumed that you yourself did not have the information (you asked for twice where did I find that information!) until it was presented on platter & neither you have an answer to the above qstn that you post above for us.
Last edited by disha on 21 Feb 2017 23:54, edited 1 time in total.

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Re: Indian Space Programme Discussion - Sept 2016

Postby disha » 21 Feb 2017 23:53

SriKumar wrote:I never suggested it explicitly nor implied that. My post was a comment about the differences in the ejection of satellites in the beginning of the process (cartosat INS, etc) and the satellites that came later on, especially towards the end (5:10). The camera showed some clear differences. The data on the brochure seems to shed some light on this.


Fair., At the same time see SSS'jis post. There is definitely a change vector done by PS4. I had pointed out earlier in my post which you might have discounted - where I was trying to indicate that there is indeed differences in the ejection of sats :-)

At the same time I do not personally think that ISRO will disclose all data on how the sats are packed and how precisely they were released. It will leave us to infer from previous launches (C34 for eg) to show how the sats were packed etc. and show us videos on how they were released and also give a release schedule to infer based on this information.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 22 Feb 2017 00:14

disha wrote:...., then it will help if you can post it. ,,

Disha - First there is no reason to get upset, and really this is NOT phD thesis, more like high-school physics.

But since you asked, and others may be curious, I will post the answer, and put my comments in next post so that it does not get cluttered with needless tangential discussion. Let us keep this thread technical.. add/correct the discussion if you can and learn if there is something new.

As you see in my comments in the next post that: I was some what surprised to hear about all that talk (authoritative type) about "degenerate orbits" and "10 or so orbits" which I think is quite inaccurate in C37 case. From what I know (or guess) the orbit of the fourth stage is *not* going to "de-orbit" anytime soon. Not in 10 or so orbits... perhaps not even in 100 or even 1000 next orbits.. (BTW I wasn't the one who brought "10 orbits or so" part ... you did, I was just curious where you got that value) (I can not locate your post at present but you know the post)

Of course I can be wrong but in that case, I will be really surprised and impressed with ISRO, if they planned something which you claim they have planned. Hence the query. If you (or anyone else) has additional information which makes me know something new, please do post it. .. Because if what you say that C37's profile is to "de-orbit" in near future, that is something new and must be publicized..

Anyway *all* please see my next post. Comment/corrections etc are welcome.
Last edited by Amber G. on 22 Feb 2017 00:47, edited 1 time in total.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 22 Feb 2017 00:38

Rishi Verma wrote:SSSJi, can you roughly tell where the empty C37 piece starts de-orbiting, by which mechanism does it fall back and burn up? Does it take less than a full orbit or several orbits to enter back into "atmosphere"? Thanks.


There has been some discussion about this.. let me add. (If there is additional info, feel free to add/comment/correct)

First stage - Falls into ocean.
Second stage - Burns down in atmosphere.

...
Last stage, as common to most such cases, is now at present in a near circular orbit ( difference between perigee and apogee may be about 20 Km or so that is negligible when you take radius of orbit which is about 7000 Km) is what many call (sorry for using politically incorrect term) "space junk" and it's going to remain there for quite some time. (measured in years)

I am not aware (but I can be wrong so if some one knows the details please post) of any planned event to "de-orbit"..Though I guess if some fuel is left, delta-V of a few hundred m/sec can make the perigee small enough and the orbit can decay in few years. (Since it is present making about 15 orbits per day it is not going to enter atmosphere in "less than one" or even a few orbits.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 22 Feb 2017 01:22

srinebula wrote:
Amber G. wrote:Indeed!


I understood dropping the orbit to increase angular velocity part; but what is the need to move backwards?

To add to prasannasimha -- Any good text book (or wiki :) could further explain. Perhaps google the term for "orbit phasing" or "Space rendezvous" or something like that.
(I just did "orbit phasing" and I get fairly good account and drawing from wiki :) )
Image
If spacecraft is behind the final position on the same orbit, the spacecraft must slow down to enter a smaller, faster phasing orbit to catch up to final position

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 22 Feb 2017 05:34

disha wrote:Fair., At the same time see SSS'jis post. There is definitely a change vector done by PS4. I had pointed out earlier in my post which you might have discounted - where I was trying to indicate that there is indeed differences in the ejection of sats :-)
Not only did I not discount it, I myself had noticed it in the video and mentioned it briefly in a post 2-3 pages behind viewtopic.php?p=2117038#p2117038

At the same time I do not personally think that ISRO will disclose all data on how the sats are packed and how precisely they were released. It will leave us to infer from previous launches (C34 for eg) to show how the sats were packed etc. and show us videos on how they were released and also give a release schedule to infer based on this information.
I agree ISRO will not disclose the data, and I was not expecting it to. Sometimes a post on BRF generates some insights/ideas etc. and that was the purpose of my post. I think this one has come to the end of that line.

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Re: Indian Space Programme Discussion - Sept 2016

Postby SSSalvi » 22 Feb 2017 10:33

Here is what I feel is the orientation changes of Launch Capsule during release of satellites based on the real-time video.

Below, On left is reproduced an image posted earlier showing the photograph of Launch Capsule ( 4th stage ) captured from the PSLV C37 assembly video.
It is superimposed with the symbol that we will use in this post.
Little Red square is the location of camera that shows the release of Cartosat 2D and INS 1A and INS 1B.
Blue and Yellow represent P+ and P- cameras respectively.

Image

The symbol is superimposed on the launch geometry posted earlier showing the orientation of Launch Assembly in 3 orientations along the PSLV C37 launch path.

Image

Only the Launch Capsule is shown below.
Vehicle started from SHAR and brought the capsule in the position shown on top .. the Orange cylinder is the 4th stage engine pointed backwards. Within about 40 seconds after the PS4 shutdown the capsule is rotated so that the satellites which are attached to this assembly are facing backwards. alsothe capsule is rolled 1/4 th turn so that the Red square camera is now on 'left' of the path.

Image

Cartosat and INS satellites are released in this position but in the video it appears that the satellites are released while the camera is on the 'TOP' surface of satellite. It is not so. The arc of Earth in the background is actually the Eastern edge illuminated with morning Sunlight.

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 22 Feb 2017 12:40

Saw news reports and some may have heard that Google will/has entered into a multi-year contract to purchase Earth-imaging data from those sats from Planet Labs.

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Re: Indian Space Programme Discussion - Sept 2016

Postby arun » 23 Feb 2017 06:21

Gopal N Raj in the Indian Express.

GSLV launch in March to send up "Satellite for South Asia".
GSLV Mk III (LVM3) Launch in second half of April.

Reaching for the stars

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Re: Indian Space Programme Discussion - Sept 2016

Postby SriKumar » 23 Feb 2017 06:35

SSSalvi wrote:Here is what I feel is the orientation changes of Launch Capsule during release of satellites based on the real-time video.

Below, On left is reproduced an image posted earlier showing the photograph of Launch Capsule ( 4th stage ) captured from the PSLV C37 assembly video.
It is superimposed with the symbol that we will use in this post.
Little Red square is the location of camera that shows the release of Cartosat 2D and INS 1A and INS 1B.
Blue and Yellow represent P+ and P- cameras respectively.
Thanks for taking the trouble to create the graphics. I did think that the 4th stage did a 180 turn given that some satellites seemed to be launched 'backwards', one can see the earth move 'away' from the rocket.

By the way, you posted the orbits of the various satellites in a previous post. Is that actual orbit data? Where is it avaible from?

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Re: Indian Space Programme Discussion - Sept 2016

Postby Gagan » 23 Feb 2017 07:05

Very nice graphics sssalvi ji
Are the sats released ahead of the 4th stage or behind it?
If behind, does the 4th stage do a 180 degree maneuver?

The nano sats seem to have been ejected to the side of the 4th stage weather p+ or p-

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Re: Indian Space Programme Discussion - Sept 2016

Postby Gagan » 23 Feb 2017 07:08

How do those nano sats stabilize themselves? Reaction wheels? Ion thrusters?
They can't be of much use of they are rotating around in all three axes I imagine

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Re: Indian Space Programme Discussion - Sept 2016

Postby SSSalvi » 23 Feb 2017 10:50

The 4th stage did point backwards in PSLV C37 release sequence. It can be seen in video - play it at 1/4 speed to observe - just before Carto is released observe the sunlight falling on Carto as well as the Earth rising slowly behind Carto ( seen through small gaps ).
4th stage was at 514 kms during this sequence and the sats had to be released in 505 kms orbit. So they were thrown backwards so that the speed reduces and sats sink lower.
Sats released earlier were thrown with a higher push and subsequent sats were released with reducing steps of speeds so that the distance between sats was maintained to avoid collision.

An official representation of Launch methodology is available in PSLV C20 Launch brochure.
The Orbit data is a computed value based on status values given at a given instant ( Technically called TLE ) which is available at ' Last 30 days launch data ' in Celestrak.com

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Re: Indian Space Programme Discussion - Sept 2016

Postby Varoon Shekhar » 23 Feb 2017 21:17

http://www.isro.gov.in/annual-report-2016-2017-english

New annual report of ISRO, covering 2016, is out surprisingly early. In recent years, the annual report has been coming out as late as April and May.

Many gems as usual!

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Re: Indian Space Programme Discussion - Sept 2016

Postby prasannasimha » 23 Feb 2017 22:03

^ Budget was preponed for a reason !!

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Re: Indian Space Programme Discussion - Sept 2016

Postby Amber G. » 23 Feb 2017 23:38

Gagan wrote:How do those nano sats stabilize themselves? Reaction wheels? Ion thrusters?
They can't be of much use of they are rotating around in all three axes I imagine

Believe it or not brf had discussed it before :) .. many years ago in physics dahaga - to answer/explain a strange utube video of strange behavior of a "spinning" top - I discussed this, and remarked that in early space flights to stabilize camera (so that they point in right direction) without gyro/thrusters.. Engineers learned again what Newton/Euler did about Moment of Inertial tensor. (See Note ** If you are interested in Physics part).

Basically this stabilization is achievable "passively" (that is without servo, reaction wheels or gas jets) by using earth's gravity gradient, (or some times even magnetic field gradient if parts are made of metal). The theory and practice is known and there are quite a few good sources for interested people.

For example: this 1964 article: http://techdigest.jhuapl.edu/views/pdfs/V03_N5_1964/V3_N5_1964_Fischell.pdf

Gyro-effect (that is providing some spin when nano's are released) is used, here too one has to not forget some graduate level physics choosing the right eigen vector of moment of Inertia tensor as one of early satellite with camera did. (see note ** below)

Note ** - I can not find physics dhaga where this was discussed nicely.. If you are interested in this check out "Dzhanibekov Effect" (Named after an soviet gaganaut who was first-one to bring it to popular press) or something like "Tennis racket theorem" in a physics book/wiki.

https://www.youtube.com/watch?v=4dqCQqI-Gis
Added later: Know what? Wiki has an entry, pretty good imo - https://en.wikipedia.org/wiki/Tennis_racket_theorem


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