Bharat Rakshak

Rahul M wrote: >> But nobody has answered my question. Space gurus please share some gyan.
not a space guru by any means but I guess the reason is tidal forces.

No.

In the first 3 orbits, I don't think lunar and solar gravitational forces vis-a-vis earth's attraction are significant enough. Even if it were, the force exerted by the sun would be greater than the moon. So I would rather have the sun's gravitational forces and the earth's gravitational forces in the opposite direction at the perigee, while increasing the velocity of the craft. Therefore, it would have been better to do it during the day. Instead they chose do it at night. So, either I am missing something fundamental or this is not the case.

My only guess was that they wait for the situation when the Indian landmass is towards the perihelion while the spacecraft is nearing the perigee, to insure uninterrupted communication link.

actually, highly eccentric orbits are affected by tides. as this NASA article on chandra

Why Launch Chandra Late at Night?

To avoid most of the belts, Chandra would have to be placed in a highly elliptical orbit. That makes tidal forces a bigger concern than they would be for a satellite in low Earth orbit, explained Dr. Jonathan McDowell, a scientist with the Chandra Science Center in Cambridge, Mass.

"It was not picked for any astronomical reason. It was picked for orbital lifetime as determined by lunar and solar perturbations," he said. Highly eccentric orbits will have their perigee (point closest to the Earth) shifted up and down by tidal forces from the Sun and Moon. "The trick is to choose an orbital plane where you ensure a long orbit."

http://science1.nasa.gov/science-news/s ... 23jul99_1/

In the first 3 orbits, I don't think lunar and solar gravitational forces vis-a-vis earth's attraction are significant enough.

even 2nd or 3rd order perturbations would be significant enough for project scientists.

Assuming I understood the question by Indranil I will guess an answer.

The choice of perigee location on the the dark side of the earth (away from the sun and earth) is decided by the fact that it is the only way one can impart the right kick to enter/intersect mars orbit with the least amount of energy expended. The direction of revolution of the satellite is fixed by the earth's rotation, as it was leveraged during launch for optimal choice and energy budget. Also, Mars and Earth are revolving along same direction around the sun. How would a choice of perigee in between the Earth and Sun, help to inject to Mars orbit ? To me it looks like there is no choice at all.

The exact date and time of the firing is done to coincide with when earth stations in India is facing the perigee point, which happens to be night time by the above.

Gurus,
Please help me understand - the NY20 site shows the latitude as being constant for Mangalyaan suggesting the orbital plane for MOM around the earth is not the same as the earth's orbital plane (Earth's axis being tilted from its orbital plane around the sun). Yet the other pictures showing Mangalyaan's proposed Mars orbit insertion show it orbiting Earth in the same plane containing Earth, Sun and Mars).

Which is true?

^^^

The PSLV rocket successfully lifted off at 09:08 UTC (2:38 p.m. IST), and placed into Earth orbit at 09:50 UTC,[26] with a perigee of 264.1 km, an apogee of 23,903.6 km, and inclination of 19.20 degrees,[27] with both the antenna and all three sections of the solar panel arrays being deployed.[28]

From wiki, http://en.wikipedia.org/wiki/Mars_Orbiter_Mission

What you are seeing in N2YO is the projected nadir point on earth's surface, and the track crosses the equator. Latitude is changing and not a constant due to the tilt of the earth.

Aren't satellites with an eccentric orbit moving fastest at the perigee and they gradually slow down as the approach the apogee and gravity pulls them back to earth. They accelerate as they approach perigee. That is why the best time to "kick" them into an even faster velocity is at perigee - so that they are flying faster as they go towards apogee and thereby make the apogee orbit higher. At one stage the kick provided at perigee will be enough to escape the earth's gravity at which point they fly off at a tangent to the orbit. Hopefully that tangent will intersect Mars' orbit after 300 days.

Check this animation. Make the orbit very eccentric by sliding the bar and the animation will show how the satellite is fastest at perigee. The animation can be speeded up as well.
http://www.windows2universe.org/physica ... ctive.html

Bade wrote:Assuming I understood the question by Indranil I will guess an answer.

The choice of perigee location on the the dark side of the earth (away from the sun and earth) is decided by the fact that it is the only way one can impart the right kick to enter/intersect mars orbit with the least amount of energy expended. The direction of revolution of the satellite is fixed by the earth's rotation, as it was leveraged during launch for optimal choice and energy budget. Also, Mars and Earth are revolving along same direction around the sun. How would a choice of perigee in between the Earth and Sun, help to inject to Mars orbit ? To me it looks like there is no choice at all.

The exact date and time of the firing is done to coincide with when earth stations in India is facing the perigee point, which happens to be night time by the above.

Then you and me are saying the same thing.

Take for eg., an elliptic orbit of 200 KM perigee & 20000 KM Apogee. As mentioned earlier, The satellite will be slowest at apogee and fastest at perigee ( Keplers Law). Another way to explain this elliptical orbit is that, at 20000 KM, the satellite is too slow to remain in a circular orbit of 20000 KM, therefore it starts falling back to earth. So, if you fire the rocket motor and impart enough additional velocity, its orbit will change to a circular orbit of 20000 KM. On the other end of the elliptic orbit (perigee), the velocity is too much for it to remain in a circular orbit of 200 KM, So it shoots away from earth after reaching perigee. If you impart additional velocity at perigee, the satellite will shoot away faster, elongating the ellipse by increasing the Apogee. That is what is beinng done with Mangalyaan.

Indranil, then I misunderstood your initial question, and interpreted it as why the perigee point does not happen during daytime.

Perigee point for the satellite's orbit is always located on the night side of the earth. The only choice left is whether to issue thrust firing commands for orbital manoeuvrings from an Indian station or any other station that is visible for each perigee point during the initial orbits.

In summary for orbital changes, you fire at perigee to increase the semi-major axis, and fire at apogee to circularize your orbit if you want to. If you fire at apogee, the orbit does not close around the initial perigee point in its follow through.

There are perturbations as mentioned before, as well as how exactly you timed your firing duration and location of firing, which determines how close or far from the initial perigee your orbit follows through after a firing...like what MY-1 is doing now.

Even for MAVEN, they are using an Hohmann transfer. It is just that they are doing it in one shot, rather than successively like ISRO has to, due to our limitations (PSLV) as well as the quantum of thrust available on the orbiter engines perhaps. I have not looked into that aspect to make a comparison with NASA.

http://www2.jpl.nasa.gov/basics/bsf4-1.php

Bade wrote:The choice of perigee location on the the dark side of the earth (away from the sun and earth) is decided by the fact that it is the only way one can impart the right kick to enter/intersect mars orbit with the least amount of energy expended. The direction of revolution of the satellite is fixed by the earth's rotation, as it was leveraged during launch for optimal choice and energy budget. Also, Mars and Earth are revolving along same direction around the sun. How would a choice of perigee in between the Earth and Sun, help to inject to Mars orbit ? To me it looks like there is no choice at all.

Agree. This also explains (to me) a question I had about the orientation of the (semi) major axis of the mangalyaan orbit. In an ISRO picture inlined by Indranil on the previous page, the major axis of the ellipse is at an angle w.r.t the sun (Was originally expecting it to be aligned with earth-sun axis). I think the orientation of the axis of mangalyaan orbit is such that the perigee 'point' (= max. velocity of satellite) lines up with the exit trajectory from earth orbit which is determined solely by the trajectory to Mars (and is a unique value).

As an aside, theoretically anyway, one could approach Mars by meeting it 'head on' instead of chasing it 'from behind' as is being done now. There are probably good reasons why this is not done but if Mars were closer 'behind' the earth, then it just might be a faster path to hurl the satellite 'backward' in relation to direction of earth's revolution. Then one would expect the perigee to come on the sunny side (of course, relative velocity between the satellite and Mars would be too high for an intercept).

On a different note, mangalyaan will hit perigee sometime today (in a few hours). http://www.n2yo.com/?s=39370 One could check out the velocity and altitude at that time.
No orbit change today.

'head on' trajectory would require a retrograde trajectory for the orbiter and increase the fuel requirements, as you are working against the direction of revolution of the earth around the sun, i.e. your initial velocity at leaving earth orbit has to be overcome and does not help you. Not an optimal solution.

For inner orbits as targets (like Venus) you still have to fire your engines at perigee again but in the opposite direction to fall inward, once you leave earth centric orbit to a sun centric orbit.

Bade wrote:Indranil, then I misunderstood your initial question, and interpreted it as why the perigee point does not happen during daytime.

Perigee point for the satellite's orbit is always located on the night side of the earth. The only choice left is whether to issue thrust firing commands for orbital manoeuvrings from an Indian station or any other station that is visible for each perigee point during the initial orbits.

No, this is not the case. In the first and second parking orbit, the satellite orbited the earth thrice and twice everyday. So it was certainly at the perigee at some point when it was daytime in India. But the orbit was not raised during those times.

Actually, it is easy to find how many times the space craft was designed to orbit in each parking orbit by knowing the time of revolution in each orbit and the time it spent in that orbit.


By just doing the above, we can know that the spacecraft was designed to be:
in the first parking orbit for 3 revolutions,
in the second parking orbit for 2 revolutions,
in the third parking orbit for 2 revolutions,
in the fourth parking orbit for 2 revolutions, and
in the fifth parking orbit for 4 revolutions.

So, I repeat my question again. Why were we waiting for the spacecraft to be at the perigee while it was nighttime in India to lifts its orbit?

P.S. I will keep a record of the times spent by the spacecraft in each orbit and time of revolution in each orbit. This will make a nice example to teach unitary method to children. The accompanying story will go a long way in making them remember what is taught and piquing their interest in science.

I still think it was answered already The orbital periods does not tell you anything to contradict what was said. Take the first one ~ 8hrs. So in a 24 hr period there are almost 3 crossings of the perigee while the earth rotates and all three perigee locations are on the far side away from the earth and sun. The only time the earth stations on the Indian continent are closest to the perigee is at night. Of course they could have used the earth stations on the side of the planet in CA to do orbit raising when it was daytime in India, but they chose not to do it very likely. Need someone from ISTRAC to answer why.

indranilroy wrote: So it was certainly at the perigee at some point when it was daytime in India. But the orbit was not raised during those times.

....because there is no direct line of sight to mangalyaan from tracking stations in India during the time when India has daylight and the MOM is in perigree.

Can it be done from other stations on the other side of earth from India...sure. It will be night time for them and daylight in India when they have a line of sight. That's all management and logistics on how many command/control centers to set up. (Bade already responded and did not want to jump in but well...).

Bade Sahab, SriKumar ji,

I had specified that reason in first post itself.

indranilroy wrote:For the first 3 orbits, the kicks (raising of orbit) were not done every time the SC was at its apogee perigee. They did it only when it was at the perigee and it was nighttime in India. The only explanation I have for this is better communication and tracking. Is there any other reason?

They are raising the orbit in stages probably to measure the gravitational field between earth and mars as they did for Chandrayaan. Unlike NASA, they don't have prior data.

Okay. ISRO has answered my question. And we were right. It is because of visibility from ISTRAC ground stations.

Mars Orbiter Mission's big night tonight, spacecraft will be hurled to an apogee of nearly one lakh kilometres

"Firing has to happen near the perigee and in the visibility from ISTRAC ground stations. All these orbits have argument of perigee of ~285 degress. When all these constraints are put together, firings time will almost always fall in to midnights of Indian sub continent," Isro explained about the reasons for the midnight manoeuvres.

Meanwhile fourth orbit raising maneuver is now on going.

For those of you who want to track the satellite live, go here.
1. Click on the 4th icon (satellite).
2. It will give you a drop down box to "select a satellite".
3. In the drop down menu of "satellite group", chose Last 30 Days' launches, and in the "Select satellite", choose "MARS ORBITER MISSION".
4. Enjoy celestial bliss.

^^^ that is a good link. Was not aware of it. thanks.

geeth wrote:They are raising the orbit in stages probably to measure the gravitational field between earth and mars as they did for Chandrayaan. Unlike NASA, they don't have prior data.

No that is not the reason. They are still in earth centered orbit in these initial parking orbits.

indranilroy wrote:Okay. ISRO has answered my question. And we were right. It is because of visibility from ISTRAC ground stations.

Mars Orbiter Mission's big night tonight, spacecraft will be hurled to an apogee of nearly one lakh kilometres

"Firing has to happen near the perigee and in the visibility from ISTRAC ground stations. All these orbits have argument of perigee of ~285 degress. When all these constraints are put together, firings time will almost always fall in to midnights of Indian sub continent," Isro explained about the reasons for the midnight manoeuvres.

Meanwhile fourth orbit raising maneuver is now on going.

For those of you who want to track the satellite live, go here.
1. Click on the 4th icon (satellite).
2. It will give you a drop down box to "select a satellite".
3. In the drop down menu of "satellite group", chose Last 30 Days' launches, and in the "Select satellite", choose "MARS ORBITER MISSION".
4. Enjoy celestial bliss.

amazing, thanks for sharing !!!

I am worried, there might have been slight problems with raising the satellite to its 4th orbit. From the MOM FB page, they could impart 35 m/s incremental velocity to the craft. With 440 N thrust and weight of the craft around 1320 kg (would be much less now), the acceleration would be at least 0.33 m/s. So 35 m/s increase in speed is surely the burn time was less than a 105 second. They said they will get back after calculating the orbit.

Hoping for the best.

Mars Mission is Rs 11per km , based on actual distance traveled and Rs 20 per km based on shortest possible distance it could have traveled. In Ahmedabad, autorikshaw charged Rs 9 per km, and ac taxis on long distance is Rs 20 per km. So mars-mission is quite competitive by even Indian rates. Only train fare will be cheaper than mars mission.

==

some numbers

distance between mars and India = 22,79,00,000 km = 23 crore km approx

cost of mission = Rs 450 crore

actual distance satellite will travel = 43 crore km approx

Ahmadabad auto fare = Rs 13 for first 1.2 km, and Rs 9.50/km thereafter

ahmedabad ac taxi fare = Rs 20 /km

train fare , 2nd ac = Rs 3 per km, most places

train fare , general class , unreserved, non-ac = Rs 0.50 per km, if you can survive

air india flight = Rs 10 per km, in general

indranilroy wrote:Okay. ISRO has answered my question. And we were right. It is because of visibility from ISTRAC ground stations.

Mars Orbiter Mission's big night tonight, spacecraft will be hurled to an apogee of nearly one lakh kilometres

"Firing has to happen near the perigee and in the visibility from ISTRAC ground stations. All these orbits have argument of perigee of ~285 degress. When all these constraints are put together, firings time will almost always fall in to midnights of Indian sub continent," Isro explained about the reasons for the midnight manoeuvres.

Meanwhile fourth orbit raising maneuver is now on going.

For those of you who want to track the satellite live, go here.
1. Click on the 4th icon (satellite).
2. It will give you a drop down box to "select a satellite".
3. In the drop down menu of "satellite group", chose Last 30 Days' launches, and in the "Select satellite", choose "MARS ORBITER MISSION".
4. Enjoy celestial bliss.

MOM-11102013-09-47EST

I just twisted the view so that we can see desh!!

Hopefully MOM is carrying extra fuel for events like an under-burn and can do a reboost in a couple of days if the new orbit is less than planned.

The previous one was below what was the target I think, 77k (target) vs 71k (achieved).

well it is been more than an hour i captured those data.. MOM has gone on the elliptical a bit more now:

Satellite ID
39370
Velocity (km/s)
1.428
Velocity (mi/s)
0.887
Latitude (°)
19.211
Longitude(°)
111.374
Height (km)
62932.590
Height (mi)
39104.486

Bade wrote:The previous one was below what was the target I think, 77k (target) vs 71k (achieved).

I dont think that is quite right. The inlined image above on altitudes (by indranilroy) suggests a 78,000 km apogee for 3rd boosted orbit, but per an ISRO conference on Oct. 30, i.e. prior to launch, quoted a number of 70,656 km. I think the 78,000 km number is suspect (or old number). 3rd boosted orbit looks good. Here is the exact quote:

“.... Dr. Annadurai said. ISRO Chairman K. Radhakrishnan told a press conference at Sriharikota on October 30 that after the Mars orbiter’s apogee is raised first on November 7 to 28,793 km, the second firing of the engine will take place on November 8 early morning. This second firing will take the orbiter’s apogee to about 40,000 km from the earth. The third orbit-raising operation will take place on November 9 when the apogee will be boosted to about 70,656 km.

And the link:
http://www.thehindu.com/sci-tech/scienc ... epage=true

Added later: The inlined graphic is from Frontline (also a Hindu publication!!), dated Nov.15th (i.e. a few days from today). It was written prior to launch though exact date is not claer.

mom-11112013-12-34est

nearing 70k

According to Emily Lakdawalla there has been an hiccup in today's MOM orbit raising. More info at http://www.planetary.org/blogs/emily-la ... ssion.html

The Mars Orbiter Mission completed its first, second, and third of six planned maneuvers in Earth orbit successfully last week. However, the fourth maneuver, conducted on Sunday at 12:36 PST / 20:36 UTC / Monday 02:06 IST, failed to lift the apogee of the orbit as high as planned. The rocket firing should have lofted the Mars Orbiter Mission to an apogee of 100,000 kilometers, but the burn imparted only 35 meters per second of velocity to the spacecraft, less than a third of what was needed to achieve the desired orbit. As of this moment ISRO has not yet provided an update on the status of the orbit.

Here is the only information I have regarding the cause of the apaprent underburn, from an Indian space blogger (Pradeep Mohandas) who has been a reliable source of information in the past, and who says he had it from someone at ISRO:

So the 440-Newton main rocket motor (the LAM, or Liquid Apogee Motor) didn't run as long as it should have. There's no information yet on why it didn't, but if they're planning to perform another maneuver tonight (i.e. Monday morning California time), it can't be a serious problem. Assuming there is nothing seriously wrong with the spacecraft, it should be straightforward to correct an underburn during this phase of the mission, and the underburn and subsequent correction shouldn't have cost the mission any significant amount of precious fuel.

I realize this post doesn't contain much information, but I wanted to have something in the blog before I went to bed. I will keep you informed of further developments as I find them out!

Bade wrote:The previous one was below what was the target I think, 77k (target) vs 71k (achieved).

Bade, is that a cause for concern? Can this shortfall be overcome in the next 2 or 3 burns?

Added later:
Looks like ms. Lakdawala answered the question - at least partially. Hoping here for positive news by tomorrow.

Still Bade's view would be appreciated.

Based on my calculation the apogee would be around 86155 KM for the 4th burn, which is a short fall of 13844 km.

Praveen, your post does not have the quote from Pradeep Mohandas, maybe some issues in copying from the main site. Am updating it below in bold

Praveen wrote:According to Emily Lakdawalla there has been an hiccup in today's MOM orbit raising. More info at http://www.planetary.org/blogs/emily-la ... ssion.html

The Mars Orbiter Mission completed its first, second, and third of six planned maneuvers in Earth orbit successfully last week. However, the fourth maneuver, conducted on Sunday at 12:36 PST / 20:36 UTC / Monday 02:06 IST, failed to lift the apogee of the orbit as high as planned. The rocket firing should have lofted the Mars Orbiter Mission to an apogee of 100,000 kilometers, but the burn imparted only 35 meters per second of velocity to the spacecraft, less than a third of what was needed to achieve the desired orbit. As of this moment ISRO has not yet provided an update on the status of the orbit.

Here is the only information I have regarding the cause of the apaprent underburn, from an Indian space blogger (Pradeep Mohandas) who has been a reliable source of information in the past, and who says he had it from someone at ISRO:

Underburn because of some issue with the [Liquid Apogee Motor]. Issue expected to be corrected today and another burn expected tonight or early tmrw morning.

— Pradeep (@pradx) November 11, 2013

So the 440-Newton main rocket motor (the LAM, or Liquid Apogee Motor) didn't run as long as it should have. There's no information yet on why it didn't, but if they're planning to perform another maneuver tonight (i.e. Monday morning California time), it can't be a serious problem. Assuming there is nothing seriously wrong with the spacecraft, it should be straightforward to correct an underburn during this phase of the mission, and the underburn and subsequent correction shouldn't have cost the mission any significant amount of precious fuel.

I realize this post doesn't contain much information, but I wanted to have something in the blog before I went to bed. I will keep you informed of further developments as I find them out!

Update on FB.

The health of ISRO's Mars Orbiter Mission Spacecraft is normal.

In the fourth orbit raising operation conducted this morning (02:06 Hrs IST) the apogee of MOM spacecraft was raised to 78,276 km against the targeted apogee of about one lakh km.

This is because the incremental velocity imparted to the spacecraft was 35 m/s against the targeted 130 m/s.

A supplementary orbit raising operation is planned at 05:00 hrs IST on November 12 to raise the apogee to nearly one lakh km.

A detailed press note is appearing shortly on ISRO website.

Oh, those extra revolutions come in handy. But it becomes very interesting now. Because of this unintended shorter orbit, the craft will reach its perigee a few hours earlier. If everything goes according to plan, then the injection into heliocentric orbit will also be a few hours earlier. Unless they make the 4th and/or 5th parking orbit slightly larger than what they had initially planned.

EDIT: *snip* duplicate stuff

BTW, I don't see Mars Orbiter liste in the nasa site under 30 days launches tab.

Folks,

What Ms Lkadawalla is saying is confirmed on MOM FB site (haraam from my place of work...)....Let me quote it as I read it from my mobile phone.

The health of ISRO's MOM Spacecraft is normal. In the fourth orbit raising operation conducted this morning, the apogee of MOM spacecraft was raised to about 78276 km against targeted apogee of about one lakh km. This is because the incremental velocity imparted to the spacecraft was 35 m/s against the targeted 130 m/s. A supplimentary orbit raising operation is planned at 05:00 hrs IST on November 12 to raise the apogee to nearly one lakh km. A detailed press note is appearing shortly on ISRO website.

indranilroy wrote:Update on FB.

The health of ISRO's Mars Orbiter Mission Spacecraft is normal.

In the fourth orbit raising operation conducted this morning (02:06 Hrs IST) the apogee of MOM spacecraft was raised to 78,276 km against the targeted apogee of about one lakh km.

This is because the incremental velocity imparted to the spacecraft was 35 m/s against the targeted 130 m/s.

A supplementary orbit raising operation is planned at 05:00 hrs IST on November 12 to raise the apogee to nearly one lakh km.

A detailed press note is appearing shortly on ISRO website.

Oh, those extra revolutions come in handy. But it becomes very interesting now. Because of this unintended shorter orbit, the craft will reach its perigee a few hours earlier. If everything goes according to plan, then the injection into heliocentric orbit will also be a few hours earlier. Unless they make the 4th and/or 5th parking orbit slightly larger than what they had initially planned.

Cant the arrival time at Mars be adjusted by slightly changing the direction of the route from earth to mars in the final firing (so that MOM path intersects the Mars orbit a bit early or later based on its direction adjusted)

ToI says

A supplementary orbit-raising operation is planned at 05:00 hrs IST on November 12 to raise the apogee to nearly one lakh km.

kvraghavaiah wrote:
Cant the arrival time at Mars be adjusted by slightly changing the direction of the route from earth to mars in the final firing (so that MOM path intersects the Mars orbit a bit early or later based on its direction adjusted)

Of course. There are other options too. Same predesignated path and slowing down earlier before rendezvous with Mars. Question is, which of these requires least amount of energy, so that the craft has maximum fuel left when it reaches Mars.

Actually I am not sure about my guess here too.
1. Having slightly larger 4th and 5th orbits will require cumulatively 10-15 secs of additional fuel burn at most.
2. On the other hand they must have incorporated a tolerance of a few hours of reaching Mars orbit earlier or late than intended. So it is not worth breaking a sweat.

But for an aam abdul like me, it is very interesting to watch the decisions they take.