Mangalyaan: ISRO's Mars Orbiter Mission

juvva · Post by **juvva** » 15 Sep 2014 08:51

Regarding verification of uploaded commands: I think the MOM will read back to earth station all the commands it received and stored in its memory. The ground station will then verify the received read back with the uploaded commands. ( just guessing of course ! )

This would be in addition to the normal transmission protocols involving automatic error correction, parity checks, repeat requests from the receiving station etc.

The above may explain the longish time taken for transmission and verification of commands.

shiv · Post by **shiv** » 15 Sep 2014 09:30

matrimc wrote:shiv: On mars sun side is not that hot - it is quite cold but shade side (and in deep craters) it is really cold. So the temperature range is quite wide.

No I was referring to Mangalyaan in transit in space. Would one side be constantly exposed to sunlight?

symontk · Post by **symontk** » 15 Sep 2014 09:43

shiv wrote:
matrimc wrote:shiv: On mars sun side is not that hot - it is quite cold but shade side (and in deep craters) it is really cold. So the temperature range is quite wide.
No I was referring to Mangalyaan in transit in space. Would one side be constantly exposed to sunlight?

Yes, since it is orbiting Sun, it will be. That is the design complexity, not sure how they resolved. I had a chance to go to Shriharikota 13 years ago and had a chance to see the PSLV, IRS and 2 other country satellites. I talked to a scientist who was testing the IRS solar panels about the temperature control. He told that since it revolves around earth, both sides will get heated up in different time frames and so they will manage it

But not sure on this MOM how they planned it

srin · Post by **srin** » 15 Sep 2014 09:43

shiv wrote:
matrimc wrote:shiv: On mars sun side is not that hot - it is quite cold but shade side (and in deep craters) it is really cold. So the temperature range is quite wide.
No I was referring to Mangalyaan in transit in space. Would one side be constantly exposed to sunlight?

+1 to that question. I'm also interested to know how they can keep something cool. Because it is in vacuum, there is nowhere to dump the heat, except as radiation.

Amber G. · Post by **Amber G.** » 15 Sep 2014 09:49

Shivji - As said before, while MOM is in orbit of Mars (Time period of highly elliptical orbit, IIRC is about 3 days as it is quite high) it does not (or extremely little) get any heat from Mars.. just radiation from Sun.. it does NOT remain out of Sunlight for very long .. The temperature inside can be controlled and should not be a a problem.(I know Chandrayaan had some heating problems but I am sure we have learned a lot.. and Mars is further from Sun then earth/moon)

Amber G. · Post by **Amber G.** » 15 Sep 2014 09:59

srin wrote:
+1 to that question. I'm also interested to know how they can keep something cool. Because it is in vacuum, there is nowhere to dump the heat, except as radiation.

Dumping heat is always there.. (by radiation)..and that depends on surface area and temperature.
(In fact, it is a fairly easy Physics exercise (to help design to control space-craft's internal temperature)
as heat radiated is (Area)x(Emissivity)x(T^4))

As you get radiated energy from Sun which is absorbed by the craft the temperature increases.. so radiated heat increases and you reach a steady state of temperature..

Neshant · Post by **Neshant** » 15 Sep 2014 10:38

I still don't understand how its done (the temp control).

Are they varying the pitch angle of the solar panels so that if it gets too hot they turn away from the sun and if it gets too cold they turn the panels towards the sun. i.e. actively controlling the heat gain and loss? Is it something like that ? The only way it can cool down is to radiate heat and likewise to heat up is that correct?

member_28108 · Post by **member_28108** » 15 Sep 2014 13:50

SwamyG wrote:So why is MAVEN so expensive than MANGALYAAN?

Multiple reasons fire eg weight, complexity ,orbital height,lower labor cost and many more. MOM is a technical feat no doubt but MAVEN Pis more complex in construction, scope and goals.

vdutta · Post by **vdutta** » 15 Sep 2014 13:54

This may be a naive question to everyone here but why does MOM require a new software at this stage. Couldnt have they uploaded it before they put it out on journey.

first thing comes in mind is storage issue where most of the software would be for transit but with size of memory coming down to nothing that should be an non issue.

member_28108 · Post by **member_28108** » 15 Sep 2014 14:39

The uploaded instruction sets are not small. Also current data will need to be factored in to send the final commands.

negi · Post by **negi** » 15 Sep 2014 15:14

srin wrote:
+1 to that question. I'm also interested to know how they can keep something cool. Because it is in vacuum, there is nowhere to dump the heat, except as radiation.

By reflecting as much incident radiation as possible , most of the satellites are wrapped in Gold foils including Mangalyan.

vina · Post by **vina** » 15 Sep 2014 15:27

Amber G. wrote:One has space heaters (if needed near equipment), thermostats, heat pumps (or simple radiators) to control (individual equipments - different parts have different temperature and can be insulated etc) but by adjusting the orientation etc the keeping the temperature inside the probe is not that difficult.

Ah, but you forgot to mention the most extensively used and most reliable one of all, the heat pipe!

member_28108 · Post by **member_28108** » 15 Sep 2014 17:58

Most interplanetary probes require heating system as batteries etc will not function and electronics call boards have to be maintained at particular temperatures. The albedo of a celestial body can heat a sattelite if significant.
The gold looking sheet is Mylar foil used to protect against solar radiation causing heating. The most striking use was when they had to pin one down on Skylab if my memory is right as a cooling system failed so they had to create and put a Mylar umbrella/blanket to decrease radiant heating of the craft

member_28108 · Post by **member_28108** » 15 Sep 2014 20:04

http://www.grc.nasa.gov/WWW/epbranch/Lo ... lecAbs.htm

nikhil_p · Post by **nikhil_p** » 15 Sep 2014 21:52

There was a program on Rajya Sabha TV (by the name of Eureka) today evening. I accidentally put it on - and it had the ISRO bigshot speaking about Mangalyaan. 450 cr project 1/10 the price and so on.

He said everything till date has [limbu+mirchi] NOT gone according to plan [/limbu+mirchi].

All is [limbu+mirchi] NOT well [/limbu+mirchi]

The presenter did close by saying we will meet more often till the 24th when it is [limbu+mirchi] doomed to fail [/limbu+mirchi]

Dilbu · Post by **Dilbu** » 15 Sep 2014 22:02

MOM will fail onlee.

member_28108 · Post by **member_28108** » 15 Sep 2014 22:28

http://www.isro.gov.in/mars/pdf/press%2 ... %20MOI.pdf

Gives accurate timelines etc of the uploading and also Mars orbital insertion

shravanp · Post by **shravanp** » 15 Sep 2014 22:35

The step where the thrusters were to be tested for a few seconds, is that done?

member_28108 · Post by **member_28108** » 15 Sep 2014 22:43

skekatpuray wrote:The step where the thrusters were to be tested for a few seconds, is that done?

that is on the 22nd when MOM enters the sphere of influence of Mars check out slide 9 (4th TCM) details in the PDF link in my previous post.

member_28108 · Post by **member_28108** » 15 Sep 2014 22:44

Fourth Trajectory correction manoeuver
and test-firing of Main Liquid Engine
• Duration : 3.968 seconds
• Fuel consumption: 0.567 kg
• ∆V : 2.142 m/s
22-09-14
@1430 Hrs (IST)

member_28108 · Post by **member_28108** » 15 Sep 2014 22:45

The D Day - 24th September,2014
When? IST What?
1 T-3 hours 04:17:32 Change over to Medium Gain Antenna
2 T-21 minutes 06:56:32 Forward rotation starts
3 T-5 minutes 13 seconds 07:12:19 Eclipse starts
4 T-3 minutes 07:14:32 Attitude control with thrusters
5 T 07:17:32 Liquid Engine Burn starts
6 T+4.3 minutes 07:21:50 Mars occult starts
7 T+5 minutes 07:22:32 Telemetry OFF
8 T+ 12.5 minutes 07:30:02 Confirmation of Burn start
9 T+19.48 minutes 07:37:01 Eclipse endsMars Orbiter Mission
When? IST What?
10 T+ 24.23 minutes 07:41:46 Liquid engine Burn Ends
11 T+ 25.73 to
T+ 47 minutes
07:42:46 to
08:04:32
Reverse Manoeuver starts
12 T+ 27.78 minutes 07:45:10 Occult ends
The D Day-24th September, 2014
11
12 T+ 27.78 minutes 07:45:10 Occult ends
13 T+ 30.43 minutes 07:47:46 Telemetry resumes and Doppler
measurement to provide first
information about total burn
performance
14 T+ 35.23 minutes 07:52:46 Reverse Manoeuver ends

shravanp · Post by **shravanp** » 15 Sep 2014 22:51

prasannasimha wrote:
skekatpuray wrote:The step where the thrusters were to be tested for a few seconds, is that done?
that is on the 22nd when MOM enters the sphere of influence of Mars check out slide 9 (4th TCM) details in the PDF link in my previous post.

thank you saar

member_28108 · Post by **member_28108** » 15 Sep 2014 22:51

We get to know if the burn starts at 7.30.02 12.5 minutes after the burn starts. at 7.47.46 we will know first information and at 7.52 46 the insertion will be complete so we probably will know at 8.08 AM approx if the insertion parameters are successful or not .

chetak · Post by **chetak** » 15 Sep 2014 23:04

Sri wrote:I hope when PM Modi meets POTUS, he carries a high def pic of one of the rovers taken from Mangalyaan, with a tag "Howdy Partner!!!'. Timing is just perfect...

wouldn't that be namaste, partner??

Amber G. · Post by **Amber G.** » 15 Sep 2014 23:13

Few comments -

- The gold foil covering's most important use is to prevent the electronics from cosmic rays.. (Sun is still causing lot of x-rays and cosmic rays and there is no ozone layer there to protect it). When cost is is calculated differently (for earth based things where lead is most popular) gold is preferred (It has a similarly high atomic number of 79 but almost twice the density of lead. 19.28 vs 11.3 g/cm3)

- Another reason for gold covering (but other coverings can be used too - google/wiki for MLI) is actually to reduce heat loss, and keep the things warm. Simple calculation can show, say at 20C, with e(emmisity)=1, each square meter (space-craft part in the shade) will radiate about 400 Watt, a simple layer will reduce it by a factor of 2.

- Engineering part of thermal control is complex but fundamentals are easy. The primary heat input (apart from heaters, fuel, nuclear thermal batteries inside the space-craft) is Sun (and if you are near Mars, the IR radiation from Mars). You get about 600 Watt per square meter (Mars is about 1.5 times as far as earth, and at that distance, MOM is receiving that much energy = 1400/(1.5)^2). How much MOM absorbs depends on the area exposed to sun and nature of the surface(it's e, black color will absorb more than a shiny mirror).
This heats up the space craft.

The amount of radiated heat depends on the area (total outside area, including MLI etc) and the temperature. and it is proportional to T^4.. and you reach state temperature. (This is outside temperature - or average in the long run - individual objects may be insulated/heated etc so it can vary a little inside).

When you are closer to Mars, you will get IR (radiated from Mars), which has to be taken into account.

(Most of the calculations are fairly easy to reach values which are fairly close to actual values)

Amber G. · Post by **Amber G.** » 16 Sep 2014 01:50

Seeing this (see picture below) brought two thoughts..

1. The sign is little more positive than usual ("muh Kala") and IMO more apt.

2. The charge this auto-riksha charges is about the same (just a little higher) than MOM is spending..
(about 11 Rs/Km - Not bad if you ask me- for about 680Km - journey)

picture

***

From prasannasimha links given before, nice to watch:
MOI Simulation Video

Amber G. · Post by **Amber G.** » 16 Sep 2014 03:35

Few comments..

srin wrote: b) Bandwidth: In signal theory, there is this principle (i forgot the name) that the bandwidth is dependent upon the frequency of the carrier signal. For long range communications, lower frequency is used and hence less data can be sent in unit time.

Just guessing ...

Yes bandwidth does depend on frequency but here the main reason is S/N ratio as the signals are weak (very far - inverse square law). For perspective, one frequency used for MOM is in S-band (of the order of 3 GHz -(limit placed on bandwidth due to that principle is very high - in Gigahertz.. ).. similar to cell-phone carriers (or Wi-Fi modems) ... but just like data speed is much lower when signal is week (mainly due to retries etc).. (Not too different - in a noisy room, one speaks loudly and slowly (if enough loudness is not possible) to be understood..(Again for perspective, the signal is so week that receiving antennas are many meters in diameters...)

SriKumar · Post by **SriKumar** » 16 Sep 2014 04:58

A question about how/where the craft fires its rocket to slow it down to get captured by Martian gravity in a manner that it ends up in the right orbit. Is this determined by the gravity sensors on the craft.....or is it dependent on measuring the distance of the craft from the martian surface. I would tend to think it is the former. If so, do the scientists have to know the strength of Martian gravity with high accuracy? Or does that not matter, they just calibrate the rocket force to the gravity sensor reading and let equilibrium do the rest?

member_22733 · Post by **member_22733** » 16 Sep 2014 04:59

^^^ I think it could be perturbations in the orbit. Gyroscopes and accelerometers can provide and accurate idea.

disha · Post by **disha** » 16 Sep 2014 06:07

shiv wrote:
matrimc wrote:shiv: On mars sun side is not that hot - it is quite cold but shade side (and in deep craters) it is really cold. So the temperature range is quite wide.
No I was referring to Mangalyaan in transit in space. Would one side be constantly exposed to sunlight?

Mangalyaan does not have spin, even though it has a roll axis. The roll axis will come into play during MOM insertion., where the sat will be re-oriented.

What Mangalyaan has is "passive radiation management" system., where the components are rated to work under a particular level of radiation under 22 AWG Aluminium. On top of it there is Gold foil.

Note even if one-side is constantly exposed to Sun., the size is not large enough to cause runaway radiation (and the other side is not exposed to sun) so there will be radiation losses from the unexposed side.

In case of Moon, there was additional reflection from the surface which was unaccounted for and that caused "heat up".

----

The commands are uploaded and "compiled" by the sat., and once it is compiled - it is read out back (like a log) - since this is transmitted in space, there *will* be interference and that may lead to "lost packets" which of course needs to be corrected. Further each command transmission takes 13 minutes (average., otherwise 3 mins minimum and 22 minutes max) to be received by sat. Either the DDM made an error of recording the 13 mins as 13 hours *or* the entire upload and verification process takes 13 hours.

Simulators are local, so for testing they feed the commands to the simulator and execute to see the behaviour. All the kinks are ironed out locally first and once validated is uploaded to Sat. Hence the reverification is crucial.

---

Guidance - Gyros provide the "initial" reference and star sensors provide accurate reference. Prior to injection (actually during the entire course) telemetry is sent back to Earth + triangulation of communication provide information on the position of Sat which is fed back into sat as commands on how to fire the rockets.

Amber G. · Post by **Amber G.** » 16 Sep 2014 06:27

SriKumar - Best "gravity sensors", as you may have guessed it, are the space-crafts. You measure (position etc can be VERY accurately measured) your position and how it changes ( as Newton will say) and you have a very accurate value of gravitational force.

This is why even 100 years ago mass of Mars (or Jupiter) was accurately known while we did not know mass (gravity) of closer planet like Venus. Mars has natural satellite(s), Venus does not. We have to wait till we sent space probes near Venus to measure its gravitational field accurately. Small perturbations in satellites enabled us to map the gravitational field of earth much more accurately.

Internal "gravity sensors" (nothing but very precise accelerometers/gyroscopes etc) are no doubt very helpful (for say adjusting orientation of space craft) etc but the position of the space-craft (and speed etc), and where and when the rockets should be fired are primarily done by its location, measured precisely by (radar bounces from surface if needed) normal but very accurate navigational means)

HTH

Sri · Post by **Sri** » 16 Sep 2014 06:40

Noob question... I saw the trajectory in slide no. 5 here .

is it that mangalyaan is currently following Mars and is catching up? or is it that Mangalyaan is moving slow on a parallel trajectory and waiting for Mars?

SriKumar · Post by **SriKumar** » 16 Sep 2014 06:50

Amber G. wrote:SriKumar - Best "gravity sensors", as you may have guessed it, are the space-crafts. You measure (position etc can be VERY accurately measured) your position and how it changes ( as Newton will say) and you have a very accurate value of gravitational force.

This is why even 100 years ago mass of Mars (or Jupiter) was accurately known while we did not know mass (gravity) of closer planet like Venus. Mars has natural satellite(s), Venus does not. We have to wait till we sent space probes near Venus to measure its gravitational field accurately. Small perturbations in satellites enabled us to map the gravitational field of earth much more accurately.

Internal "gravity sensors" (nothing but very precise accelerometers/gyroscopes etc) are no doubt very helpful (for say adjusting orientation of space craft) etc but the position of the space-craft (and speed etc), and where and when the rockets should be fired are primarily done by its location, measured precisely by (radar bounces from surface if needed) normal but very accurate navigational means)

appreciate it. Using radar to determine distance from the Martian surface to determine firing was not what I was expecting

though I did flag it as an option. Seeing that its orbit (of any satellite) is a function of solely of the gravitational force it experiences + the force from the thrusters, I would have assumed primacy would be given to the on-board accelerometer readings. To use radar, one would have to know a priori (and very accurately) the gravity field around Mars in 3D (how would ISRO know this without sending anything prior) and also, what if the on-board accelerometer shows a gravity reading at variance with what was calculated/assumed to be at that pre-determined spot. Which one would be over-ridden? Thanks.

Amber G. · Post by **Amber G.** » 16 Sep 2014 07:08

Sri wrote:Noob question... I saw the trajectory in slide no. 5 here .

is it that mangalyaan is currently following Mars and is catching up? or is it that Mangalyaan is moving slow on a parallel trajectory and waiting for Mars?

Please see This which is a nice simulation, it also answers your question. (Which btw is fairly easy to think, if one assumes the MOM's orbit (before it is captured by Mars) is nothing but a ellipse going around Sun (as one of it's focus) and , whose one end is at a distance of 1AU (earth-sun distance) and the other end is 1.5AU (Mars-sun distance).. and think of conservation of angular momentum).. ..IOW Mangalyaan is moving "faster" on the parallel trajectory and needs to be slowed down)

juvva · Post by **juvva** » 16 Sep 2014 08:56

Will MOM be spun up (spin stabilization) before firing the LAM?

member_28108 · Post by **member_28108** » 16 Sep 2014 14:38

What uis the difference between a Mars eclipse and a Mars occult ?

juvva · Post by **juvva** » 16 Sep 2014 15:46

prasannasimha wrote:What uis the difference between a Mars eclipse and a Mars occult ?

I understand it this way:

eclipse: Mars is between the Sun and the spacecraft. The space craft is in the shadow of Mars, Sunlight does not reach it and has to depend on batteries for power.

occult: Mars is between Earth and the spacecraft. Radio communication with the probe is not possible to and from the Earth stations.

rsingh · Post by **rsingh** » 16 Sep 2014 19:19

Two questions
- How come Americans (playing golf on moon) and Russian (with Lunakhods) could not find water on moon but an Indian jugad found it on very first flyby?
- Americans and European have rovers on Mars for long time. How come they have not detected traces of Methane in atmosphere ? MOM's main objective it to look for methane.
Either rest of the world not sharing complete data with us or we baniyas are very chalak. If MOM finds Methane…….then it is big tight slap on Ameurussians who spend billion of dollars polluting martian surface and found nothing.

member_20067 · Post by **member_20067** » 16 Sep 2014 19:42

rsingh wrote:Two questions
- How come Americans (playing golf on moon) and Russian (with Lunakhods) could not find water on moon but an Indian jugad found it on very first flyby?
- Americans and European have rovers on Mars for long time. How come they have not detected traces of Methane in atmosphere ? MOM's main objective it to look for methane.
Either rest of the world not sharing complete data with us or we baniyas are very chalak. If MOM finds Methane…….then it is big tight slap on Ameurussians who spend billion of dollars polluting martian surface and found nothing.

It is not so straight forward---- there had been continuous search for Methane in Mars.....

http://io9.com/heres-why-everybody-is-f ... 1355589246

if American, Ruskies or Europeans have found it and kept it secret going by the same logic we should also do the same... so it is not exactly a reflection of capabilities of technology --- IMHO the whole mars mission is a validation exercise for interplanetary missions technologies and less of finding anything radical in Mars----

Amber G. · Post by **Amber G.** » 16 Sep 2014 23:23

SriKumar wrote:
....
Seeing that its orbit (of any satellite) is a function of solely of the gravitational force it experiences + the force from the thrusters, I would have assumed primacy would be given to the on-board accelerometer readings. To use radar, one would have to know a priori (and very accurately) the gravity field around Mars in 3D (how would ISRO know this without sending anything prior) and also, what if the on-board accelerometer shows a gravity reading at variance with what was calculated/assumed to be at that pre-determined spot. Which one would be over-ridden? Thanks.

I am sure you know, if you think it carefully, that "on board accelerometer readings" will be absolutely useless for MOI - for any measurements of gravity field, or to find exact timing/duration of the burn etc.. (apart from orienting, if needed, or verifying the thrusts after or during the firing of rockets - on board accelerometer will play no part, so to speak).

Actually, as you know for most of MOM's journey - while no rockets are fired - the space craft is in "free fall" - zero gravity. Zero weight means zero acceleration (as measured by internal devices) .. and unless you look out, you can not even tell which direction Mars is.

, let alone how strong the gravitational field is)

Martian gravity is very accurately mapped, by all the spacecraft's sent before. Actually Phobos and Deimos have given all the mapping we need to calculate when/where and how much delta-V one would need.

To be clear - for most efficient fuel burn (to save fuel).. one would need..

- Firing of rockets near the point MOM is closest to Mars. (accurate knowledge about the orbit - measured by navigational systems). (This also makes it necessary that MOM is eclipsed from Sun)
- Firing in the direction of motion. (Orient the rockets accurately)
- Delta V has to be precise . (within very close range)

If delta V is not precise MOM will not be captured by Mars. (If MOM is not slowed down sufficiently it will fly-by Mars and return back to a point in Earths orbit and will keep this elliptic orbit ... if it is slowed down too much, it will crash on Mars)