Bharat Rakshak

ravikr wrote:Noob Question. Why L110 shoots it to 205Kms altitude when required is 170 Kms and when C25 kicks in it starts loosing altitude while gaining RV. Please can any Gurus explain.

Becoz with the relatively underpowered cryo stage, the ISP loss due to gravity is minimized by lofting the upper stage higher then targeted perigee, the C25 is angled for imparting more of tangential velocity (that result in greater centrifugal force, thus minimising need for radial lifting force that is responsible for effective ISP Loss due to gravity) while its radial thrust component is less than gravitational force, so the craft slowly sinks back to earth, giving enough time to Cryo stage to sum up needed delta -V to enter orbital velocity (when effective gravity is zero, the falling back to Earth stops). This will happen when rocket has fallen down to 170 km altitude (still away from effect of atmosphere, which typically is around 105km altitude).

This lofted trajectory is similar in purpose to launching aircrafts from an angled deck of aircraft carrier.

prasannasimha wrote:

Singha wrote:Apollo11 got to the moon and back in 8 days.

so why is our chandrayaan only getting to the moon in 48 days in early september.

was it because they used the huge Saturn5 rocket to make a direct beeline for the moon instead of slowly doing orbit raising manouvers ?
48 days would have needed a lot of food and o2 for the astronauts which was not feasible.

Apollo 11 could directly lift 100 tons to GTO ! Moon lander was 13 tons ! Totally different specs.
We can do TLI to moon directly but weight woild be less

Forgot to mention Apollo mission engine size was dictated by having a shorter flight time, so that crews will need less supplies (food, oxygen etc).

Unmanned mission give luxury of economic flight with lighter rocket, whose small satellite thruster are used for orbit lifting, with no / minimal mass fraction penalty.

An acute factor is that the delta-V for orbit lifting is very small because the thrust is small and the duration of firing is small becoz it must be fired at perigee when angular velocity is very high (thus small time window). So many burns need be performed. Contrast this with mission requiring cicular orbit when thrusters need to operate at apogee.

Haridas Sir ji Thank you..

isro site update:

Chandrayaan2 update: First earth bound maneuver

First earth bound orbit raising maneuver for Chandryaan-2 spacecraft has been performed successfully today (July 24, 2019) at 1452 hrs (IST) as planned, using the onboard propulsion system for a firing duration of 57 seconds. The new orbit will be 230 X 45163 km.

The second orbit raising maneuver is scheduled on July 26, 2019, at 0109 hrs (IST).

mission plan listing all the orbit raising burns:

https://www.isro.gov.in/update/24-jul-2 ... spacecraft

^^^
Will post updated orbit images as and when the details are available in public domain to create those.

7 km at 330 m/s takes 21+ seconds, hain? It took about 4 seconds from first ignition before the rocket started lifting but in another 17 seconds the rocket is already zooming way above the horizon. Better **NOT** hear the rocket before then. Interesting. Did ppl say,

Alloo!!! Look yaar, raakit eej rijing silently onlee!

And then get the blast wave?
Although with that level of force exerted on the ground, was there a vibration of the ground?

https://twitter.com/kakarat2001/status/ ... 4603662336

GSLV MKIII M1 in flight as seen from Launch Viewing Gallery at Satish Dhawan Space Centre SHAR, Sriharikota

First orbit-raising maneuver for Chandrayaan-2 successfully performed.

The first earth bound orbit-raising maneuver for Chandryaan-2 spacecraft has been performed successfully on Wednesday, according to the Indian Space Research Organisation (ISRO).

The maneuver was performed at 2:52 pm as planned, using the onboard propulsion system for a firing duration of 57 seconds.

The second orbit raising maneuver is scheduled on July 26 at 1:09 am, the space agency said.

Wish there was a dashboard with real time orbit being displayed and upcoming events. I think there was a site which used to show this for all active spacecrafts during the MOM/Maven timeline.

Mission Plan for Chandrayaan-2
Launch Orbit: 170 x 45475 km
https://www.isro.gov.in/update/24-jul-2 ... spacecraft

https://twitter.com/kakarat2001/status/ ... 5101349888

GSLV MKIII M1 in flight as seen from Launch Viewing Gallery at Satish Dhawan Space Centre SHAR, Sriharikota

A question for the gurus - does the apogee matter more than the perigee in this scheme of things? Seems like the apogee is bang on after the 1st raising while the perigee has a shortfall of 10 km achieved - 230 X 45163 km planned 241.5 x 45162 km.

Did the orbit raising validate the new LAMs?

Haridas wrote:

ravikr wrote:Noob Question. Why L110 shoots it to 205Kms altitude when required is 170 Kms and when C25 kicks in it starts loosing altitude while gaining RV. Please can any Gurus explain.

Becoz with the relatively underpowered cryo stage, the ISP loss due to gravity is minimized by lofting the upper stage higher then targeted perigee, the C25 is angled for imparting more of tangential velocity (that result in greater centrifugal force, thus minimising need for radial lifting force that is responsible for effective ISP Loss due to gravity) while its radial thrust component is less than gravitational force, so the craft slowly sinks back to earth, giving enough time to Cryo stage to sum up needed delta -V to enter orbital velocity (when effective gravity is zero, the falling back to Earth stops). This will happen when rocket has fallen down to 170 km altitude (still away from effect of atmosphere, which typically is around 105mm altitude). This lofted trajectory is similar in purpose to launching aircrafts from an angled deck of aircraft carrier.

That went over my head. In my thinking, the lift against gravity comes by simply speeding up tangentially. The radial flight at the start is strictly to clear the trees and get out of the tropsophere before accelerating. The exchanges between RV and TV are all just passive orbital dynamics, using the available PE and KE? Have to read Haridasji's post a few more times.

Goat herder garu, what you say is for mard e momin cryo stage, but engineering wise the max payload is always for most optimised weight of upper stage using this type of lofted trajectory allowing cryo stage time to deliver it's deltaV. Recall the gslv mk1/2 CUSP has two thrust settings, second lower level thrust is used when raakit has achieved low altitude orbital speed.

May be I am explaining in my rural cow-belti inglis, hence kanfusing.

UlanBatori wrote:

Haridas wrote: Becoz with the relatively underpowered cryo stage, the ISP loss due to gravity is minimized by lofting the upper stage higher then targeted perigee, the C25 is angled for imparting more of tangential velocity (that result in greater centrifugal force, thus minimising need for radial lifting force that is responsible for effective ISP Loss due to gravity) while its radial thrust component is less than gravitational force, so the craft slowly sinks back to earth, giving enough time to Cryo stage to sum up needed delta -V to enter orbital velocity (when effective gravity is zero, the falling back to Earth stops). This will happen when rocket has fallen down to 170 km altitude (still away from effect of atmosphere, which typically is around 105mm altitude). This lofted trajectory is similar in purpose to launching aircrafts from an angled deck of aircraft carrier.

That went over my head. In my thinking, the lift against gravity comes by simply speeding up tangentially. The radial flight at the start is strictly to clear the trees and get out of the tropsophere before accelerating. The exchanges between RV and TV are all just passive orbital dynamics, using the available PE and KE? Have to read Haridasji's post a few more times.

You do not want to go just up. That's not the goal of a rocket- it needs to go up and pitch. Up is against gravity but the pitch direction also determines the ellipse it will set up. You go up to escape the dense atmosphere as fast as possible but then need to pitch.Now if you hit a gilli with the Dandu at peak versus during fall which will make the gilli go farther for a given hit with the Dandu ?

Thanks, HDji. I think the point I was missing is that the cryo stage burn is fairly long and that you want to finish the burn and chuck the engine ASAP, not carry it to great heights. Mental orbital mechanics is not up to figuring out the effect of a burn when it is not completed at perigee. I suppose that the lofting leaves the cryo engine attached to the gizmo longer without paying to accelerate the engine needlessly. So you add PE before perigee and then convert that to KE approaching perigee, instead of just adding KE at perigee. Smart. Now I understand the aircraft carrier ramp analogy, thanks.

Vivek K wrote:A question for the gurus - does the apogee matter more than the perigee in this scheme of things? Seems like the apogee is bang on after the 1st raising while the perigee has a shortfall of 10 km achieved - 230 X 45163 km planned 241.5 x 45162 km.

Did the orbit raising validate the new LAMs?

I think so. Atmospheric drag is a concern if lower than 150Km. There seems to be enough energy to push Chandrayaan 2 past 45,000Km. The gilli-danda analogy is apt here.

The gilli-danda analogy is apt here.

We are desi gurls and boys!

Farak Betwewn genius and Indinius.
Wondering why China wants to cooperate on Moon exploratioin ?

Good explanation Haridasji. The point that they carry the spent last stage only 5 kms beyond perigee height is quite chankiyaan indeed. I am waiting for ISRO to optimize CE20 engine to roughly 275 kN thrust. I hear it is possible.

UlanBatori wrote:This geeessellvee looks positively mota, not sdre at all. Amazing. As I mentioned, strap a couple more S200 boosters, increase the central tank diameter a bit, and one could lift 16T to GEO. Or stack a series of satellites in a longer tube. Is it limited by G now I wonder, from doing that.

UB ji, I had done some maddrassa math before. Adding more S200s doesn't increase payload by much. IIRC with two more S200s, the payload increases payload by around 2 tons.

I am actually waiting for the SC200 stage. With that, the payload of Mk3 will increase to 6 ton. I really wish that they develop a SC100-ish stage as well. Such a stage can act as the first stage of GSLV Mk2 raising its payload capacity to 3.2 tons to GTO. GSLV Mk3 core (with SC200) + 2 SC100 boosters will have a payload to GTO of 4.5 tons and with 4 SC 110 stages will have a payload of 6.5 tons. But all this is maddrassa math.

Kakarat wrote: we have tried our beast to capture it with a 4K camera with a external mic, kindly request all to be a bit patient and we will definitely release a SD version minimum by weekend and a professionally edited HD version with noise removed by next weekend

Jai Ho!

Vivek K wrote:A question for the gurus - does the apogee matter more than the perigee in this scheme of things? Seems like the apogee is bang on after the 1st raising while the perigee has a shortfall of 10 km achieved - 230 X 45163 km planned 241.5 x 45162 km.

Did the orbit raising validate the new LAMs?

True for Chandrayaan. However the perigee cant remain as low as it was at launch (170 km). When increasing apogee there are small effects on the perigee.

In this first burn the aim was to increase the perigee to over 200 km. We are comfortably over it so no worries. This firing does validate the LAM. A prograde burn would have been made at the apogee (furthest point) to raise the perigee.

Th engines are called Liquid Apogee Motors for a reason. Usually this what the LAM does ie fire at apogee to raise perigee. On Geosyncrhonous launches your apogee at launch is more or less your final apogee and perigee is LEO (170-180 km ). Then the LAM fires at apogee to raise the perigee in stages till a circular geosynchronous orbit is achieved.

For Chandryaan-2, this will be the last time the LAM fires at apogee. After this, all the other burns will be made only at perigee and will increase the apogee with very little effect on the perigee itself.

Thanks for the clear explanation.

Prem wrote:Farak Betwewn genius and Indinius.
Wondering why China wants to cooperate on Moon exploratioin ?

Indigenius!!!

Wondering why China wants to cooperate on Moon exploratioin ?

Ah! Effect of that would be same as effect of S400 on Turkey. COTUS (****NOT POTUS!!*****) has imposed a total ban on NASA collaboration with cheen, IIRC, since about 4 years ago, which is why I say that it predates present POTUS. So effect of cheen-India collaboration will be immediate ban on NASA-ISRO collaboration re: Moon. And ESA poodles follow NASA, and Russia is not wasting money on Moon when they need it for Mariupol expedition.

Since we're talking about lifting....

Chandrayaan 2 Raising Schedule:

24 JUL 19: 14:00-15:30 241.5 x 45,162 Km
26 JUL 19: 01:00-02:00 262.9 x 54,848
29 JUL 19: 14:30-15:30 281.6 x 71,341
02 AUG 19: 14:00-15:00 262.1 x 89,743
06 AUG 19: 14:30-15:30 233.2 x 143,953

Translunar Insertion
14 AUG 19: 03:00-04:00 278.4 x 412,505 Km
Lunar orbit by 20 AUG 19

https://www.isro.gov.in/update/24-jul-2 ... spacecraft

UlanBatori wrote:Thanks, HDji. I think the point I was missing is that the cryo stage burn is fairly long and that you want to finish the burn and chuck the engine ASAP, not carry it to great heights. Mental orbital mechanics is not up to figuring out the effect of a burn when it is not completed at perigee. I suppose that the lofting leaves the cryo engine attached to the gizmo longer without paying to accelerate the engine needlessly. So you add PE before perigee and then convert that to KE approaching perigee, instead of just adding KE at perigee. Smart. Now I understand the aircraft carrier ramp analogy, thanks.

glad you appriciate the SDRE chankian technique. Learnt it in fiddling with discrete ballistics simulation ROCKSIM, then I saw the evidence in PSLV/GSLV flight profile where altitude dips in final stage burn..

I think This was missed during live coverage.

https://www.isro.gov.in/chandrayaan2-gallery#image97


Image Gallery
https://www.isro.gov.in/chandrayaan2-gallery

http://www.unoosa.org/oosa/search.html?q=chandrayaan-2

Chandrayaan-2 mission - India's Mission to Moon UNCOPUOS Meeting
Vienna, June 2019

Mr. P Kunhikrishnan
Director, U R Rao Satellite Centre
ISRO, Government of India


http://www.unoosa.org/documents/pdf/cop ... ech35E.pdf

The LAST act decides the Beginning

There have been several theories about the timing of Chandrayaan 2 Launch. From Neil Armstrong anniversary to 15th August celebrations in India.

But the real reason is as follows.

The Lander and the rover have to land at the specified location and .... The Location should be well illuminated and so the whole mission timing is decided with that goal.

First, the Physicist have decided the location ( high plain between craters Manzinus C and Simpelius N, at a latitude of about 70° south ).

Here is an attempt to map the site and its illumination conditions.

Image below shows the Vikram Lander's Planned position on Moon.
Left is the general view and Right side shows the same situation when viewed from the South of Moon.


Next we try to map when this location starts getting sunlight and upto what time.

On 5th Sept 2019 the the Landing site starts getting illuminated as shown in image below.
( Full disc of Moon view on Left and details on Right )


The Locations remains illuminated upto 19th Sept 2019.

SSSalvi pictures did not come through

I can see the pictures.

Ssalvi ji, are there parts of the moon in perpetual darkness?

prasannasimha wrote:SSSalvi pictures did not come through

I can see it. Probably issue with your browser?

Indranil wrote:I can see the pictures.

Ssalvi ji, are there parts of the moon in perpetual darkness?

No ( At least to my knowledge. There could be some very small portion which is not illuminated anytime .. but not sure ).

What is shown as bright area is mostly what is facing Earth..
Other side is not seen because when it is lit we are in Amavasya period .. so the illuminated portion ( i.e. Backside of moon as far as Earth is concerned ) is away from Earth

Let me answer my own question

There are roughly 13 lunar days in a lunar year and there is no place (not even at its poles) which is in perpetual darkness. Much like the earth, at most, there may be places that could be in darkness for 6 earth-months.

As far as I know due to libration and tidal locking there is no portion of the moon that is not lighted at some time ie no part under permanent darkness.

SSSalvi wrote:

Indranil wrote:I can see the pictures.

Ssalvi ji, are there parts of the moon in perpetual darkness?

No ( At least to my knowledge. There could be some very small portion which is not illuminated anytime .. but not sure ).

What is shown as bright area is mostly what is facing Earth..
Other side is not seen because when it is lit we are in Amavasya period .. so the illuminated portion ( i.e. Backside of moon as far as Earth is concerned ) is away from Earth

There are area's on moon which are in perpetual darkness. There are also places which are in perpetual (or almost perpetual light. (PEL -"Peaks of Eternal Light).

This is because:
Moon is tilted only about a degree from it's spin axis. So theoretically higher peaks near a pole may get light all the time. Similarly a valley near a pole may not get a sun-light.

The actual survey of Moon has identified these places. Some south Pole areas iare quite depressed so there are places where there is no light (and therefore, some think may be water). This was known for a long time. (There was a science fiction story which I liked happened near one such place - so I knew it as a child )

There are a few peaks near south pole where there is eternal light (except time of eclipses or so).
Of course these are not "eternal" as sun is going to die in a billion years or so ... To be clear, at these points sunlight can be there for MONTHS at a time - some time earth or other peaks may block sun for some time)

On Shackleton Crater ridge (Very close to South Pole) there are two peaks where there is sunlight for VERY extended periods.
If interested do google on "Peaks of Eternal Lights" or something like that. Such objects are there

(Such points are possible on astronomical bodies where tilt is near zero, and high peaks exists)

prasannasimha wrote:As far as I know due to libration and tidal locking there is no portion of the moon that is not lighted at some time ie no part under permanent darkness.

True, if there were no mountains or valleys - but for Moon there are a few such places - see my post above.

Even there only 94%