Mangalyaan: ISRO's Mars Orbiter Mission

negi · Post by **negi** » 08 Nov 2013 09:53

^ OT here but it's not inefficient burning of fuel as such (not that it cannot happen but in rocketry that is caught long before in development cycle) because these are rockets not air breathing vehicles; I think what you are looking for is primarily propellant mass fraction and propellant burn rate.

juvva · Post by **juvva** » 08 Nov 2013 10:13

^^OT: Declared range of DRDO missiles is to be taken with more than a pinch of salt.

juvva · Post by **juvva** » 08 Nov 2013 10:34

Sridhar wrote:Vinod,

......
The short answer is that ISRO chose a low-risk, high return strategy, progressively building on its solid capabilities developed since the early sounding rocket days, and crucially for the SLV-3.....

Plus, I suspect, for obvious stategic reasons it was deemed advangtageous to master the solids first.

Arunkumar · Post by **Arunkumar** » 08 Nov 2013 10:38

Regarding orbit raising, At which stage of the elleptical orbit is the firing done?. Is it immediately after crossing perigee.

disha · Post by **disha** » 08 Nov 2013 10:59

At perigee, it is at max velocity. So any delta v imparted at perigee boosts the apogee.

Has anybody tried the desi kind of slingshot? Circle it over your head and then send the stone to make the birds fly away? Well you get the concept.

negi · Post by **negi** » 08 Nov 2013 11:07

^ Boss I have a question the kind of orbital transfers which Mangalyaan will undergo are bi elliptical right ? I mean will it at any time need to undergo a Hohmann transfer as such ? I ask because I don't see Mangalyaan being put into a circular orbit during any point in it's journey to Mars (? ).

Arunkumar · Post by **Arunkumar** » 08 Nov 2013 11:44

Thanks disha.

vinod · Post by **vinod** » 08 Nov 2013 14:07

Thanks to all the gurus! The mars mission has certainly piqued my interest to know some more details of the rockets. I'm sure its not just me only.

partha · Post by **partha** » 08 Nov 2013 14:11

negi wrote:^ Boss I have a question the kind of orbital transfers which Mangalyaan will undergo are bi elliptical right ? I mean will it at any time need to undergo a Hohmann transfer as such ? I ask because I don't see Mangalyaan being put into a circular orbit during any point in it's journey to Mars (? ).

Correct me if I am wrong but it is the elliptical orbit that enables Mangalyaan to gather speed and leave the earth's sphere of influence ultimately, right? It won't be possible to gather speed in a circular orbit without burning fuel.

Sridhar · Post by **Sridhar** » 08 Nov 2013 14:31

juvva wrote:
Sridhar wrote:Vinod,

......
The short answer is that ISRO chose a low-risk, high return strategy, progressively building on its solid capabilities developed since the early sounding rocket days, and crucially for the SLV-3.....
Plus, I suspect, for obvious stategic reasons it was deemed advangtageous to master the solids first.

Perhaps at some level, but DRDL ironically mastered liquids before solids.

Sridhar · Post by **Sridhar** » 08 Nov 2013 14:39

disha wrote: Sridharji, I would not call ISRO' choice as "low risk", it was given the budgetary and industrial constraints a prudent choice. And ISRO is not behind liq. tech either - PSLV is a very well designed stack of solid and liq. stages!!

Also with GSLV, barring manufacturing defects, the liq. tech. is good - it is the cryo stage where ISRO is working things out.

Once again, I would suggest reading Reach for the Stars.

The investment in solids was indeed prudent precisely because it was low risk high return!

ISRO mastered solids well before it mastered liquids - the Viking/Vikas development/acquisition was meant to address this gap, but indirectly ended up delaying capability building in liquids, including cryogenic (and semi cryo) engines. That said, the capabilities are being systematically built up now.

negi · Post by **negi** » 08 Nov 2013 16:55

^ Well actually liquid and solid fuel propulsion efforts kind of ran independent , I think everyone knew that liquid fuel motors were more complex and would take time so when Vikas happened it made it to the PSLV. Actually it was DRDL which mastered the liquid motors even before ISRO in form of project Devil . ISRO had a jump start on solid propulsion because of our access to sounding rockets like nike-apache of US make and then graduating to our own Rohini series , SLV , SLV-3 and ASLV. The liquid propulsion front was not such a smooth ride for obvious reasons that is why we got on board with the French on the Viking. In hindsight it was an excellent decision on part of ISRO to jump on to the Viking project. The Vikas today is our work-horse engine and forms the backbone of the GSLV and will continue to be so until the semi cryogenic engine materializes. The ability to throttle a liquid fueled engine and high Isp makes it a very good choice for civilian applications in space. That is why even Americans use the RD-180 onboard the Atlas-V.

Klaus · Post by **Klaus** » 08 Nov 2013 17:18

After Mars, it should be Saturn's moon Titan on the list. I would guess the real significance of the methane detector, to be used for studying prospective space colonies either on Saturnian moon system or Jovian moons (specially Europa). Even Ganymede with a magnetosphere could be a surprise candidate for future colonies.

harbans · Post by **harbans** » 08 Nov 2013 18:15

At which stage of the elleptical orbit is the firing done?. Is it immediately after crossing perigee.

Not checked but hazarding a guess here. Should be done in the longer arm of the elliptic post perigee crossing. At the perigee it's speed will be the fastest and as it turns around under gravity and begins it's journey towards the apogee, it slows down. In that (Almost straight) passage a bit of engine being fired up will help calculate better it's post firing apogee and perigee congfigurations.

Edited once: Initally thought it would be better firing post Apogee, but i guess if i use a sling shot i'd release bit more post perigee.

symontk · Post by **symontk** » 08 Nov 2013 18:51

[quote="ramana"]yes vinod, when solid propellants burn a lot of smoke is generated. Need all those metal particles to add mass to the exhaust gases. The ISRO launchers have solid boosters and main stage made with solid propellants. Its soon to change once the semi-cryogenic stage SC 200 comes into play.
quote]

I am not sure this will happen, as per the current figures ISRO has release the SC200 does not generate enough thrust (difference of 400KN with L110) to lift an entire launch vehicle efficiently. It would still need solid rocket boosters

GSLV Mk3 - L110 (From Wiki)

Engines 2 Vikas
Thrust 1,600 kN
Specific impulse 300 sec
Burn time 240 sec
Fuel UDMH + N2O

ISRO annual report: Semi Cryogenic Engine Development (SCED)
Semi-Cryogenic Engine development envisages the development of a high thrust engine producing 2000 kN (Vacuum) thrust with Liquid Oxygen and kerosene propellant combination for the Common Liquid Core in Unified Launch Vehicle (ULV). As part of semi-cryo engine development pre-project activities, five designs of single element pre-burner injector were realized and tested. Semi-cryo Project Report was prepared and clearance obtained. Conceptual design of the semi cryo engine has been completed

Most importantly 2000KN is at vacuum, and so the engine is efficient more at vacuum. That is, it needs some other mechanism to make it reach vacuum

Rahul M · Post by **Rahul M** » 08 Nov 2013 18:55

my guesstimate w/o any calculations would be that engine is fired at its lowest speed point, where least absolute increase in speed would translate into maximum gains in speed and radius.

sivab · Post by **sivab** » 08 Nov 2013 19:09

Rahul M wrote:my guesstimate w/o any calculations would be that engine is fired at its lowest speed point, where least absolute increase in speed would translate into maximum gains in speed and radius.

Congratulations, you just flunked basic science test

Speed does not change in orbit unless acted upon by external force ...

negi · Post by **negi** » 08 Nov 2013 19:12

http://my.execpc.com/~culp/space/orbit.html

Check the transfer orbit section.

I think motor will be fired at Perigee at the point where satellite is fastest. Also since in this case we are going from earth to mars Oberth effect will come into play (? I am just guessing) i.e. " where the application of an impulse, typically from a rocket engine, close to a gravitational body (where the gravity potential is low, and the speed is high) can result in a higher change in kinetic energy and final speed (i.e. higher specific energy) than the same impulse applied farther from the body for the same initial orbit." (quoted part from wiki).

Oh ho tukka lag gaya .

http://en.wikipedia.org/wiki/Delta-v_budget

"Another effect is the Oberth effect - this can be used to greatly decrease the delta-v needed, as using propellant at low potential energy/high speed multiplies the effect of a burn. Thus for example the delta-v for a Hohmann transfer from Earth's orbital radius to Mars' orbital radius (to overcome the Sun's gravity) is many kilometres per second, but the incremental burn from LEO over and above the burn to overcome the Earth's gravity is far less if the burn is done close to the Earth than if the burn to reach a Mars transfer orbit is performed at Earth's orbit, but far away from Earth."

Rahul M · Post by **Rahul M** » 08 Nov 2013 19:14

sivab wrote:
Rahul M wrote:my guesstimate w/o any calculations would be that engine is fired at its lowest speed point, where least absolute increase in speed would translate into maximum gains in speed and radius.
Congratulations, you just flunked basic science test

Speed does not change in orbit unless acted upon by external force ...

I wonder what external jinn force acts on sats/probes other than engine thrust.
(so congrats on flunking basic comprehension test)

edit : negi, thx. so, firing at apogee for circular orbit, firing at perigee for more elliptical orbit.

Bade · Post by **Bade** » 08 Nov 2013 20:10

Rahul_M, basically yes. It was pointed out earlier in links on Hohmann transfer. Here it is. delta-v and delta-v' for at perigee and at apogee. (though this one is a change to orbit parameters imparted from an initial circular orbit, the principle is the same.)

http://en.wikipedia.org/wiki/File:Hohma ... _orbit.svg

ramana · Post by **ramana** » 08 Nov 2013 20:10

sivab, A mark of a gnani is that they impart gnan/knowledge without ahankar even in jest.

NRao · Post by **NRao** » 08 Nov 2013 20:18

Rahul M wrote: I wonder what external jinn force acts on sats/probes other than engine thrust.

Just two days ago I was talking with a ComSat specialist and one of the things she stated was how they take advantage of solar flares to elevate a sat whoes orbit has degraded over time. This is normally achieved using fuel, she said, but, engineers take every opportunity to save a billion dollar investment. So, in this case they are preparing the sat - as I post - to point their solar panels to take advantage of an impending solar flare to elevate all their sats.

I will ask her what else influences sats.

Bade · Post by **Bade** » 08 Nov 2013 20:19

Title is misleading a bit.
Isro could have taken more time, done homework for Mars mission: PM's scientific adviser

Flaying the highly critical comments about the MOM by former Isro chairman Madhavan Nair, who is sceptical about the mission, Rao said, "It is unbecoming of Nair to make such comments. I'm critical of an Indian who makes such statement.

The reasons for the choice of a final elliptical orbit after Mars capture has not been made. A good guess is the usual suspect of fuel limitation. The standard bus to carry the payload was the same as that used for Chandrayaan, if I am not wrong and so is the fuel tank that goes with it. The other reason could be that they wanted to avoid the same issues encountered when they lowered the orbit with that mission, resulting in early termination. Instrument payloads are also fairly similar. Does anyone here know for sure.

Rahul M · Post by **Rahul M** » 08 Nov 2013 20:32

thx Bade mian. the reason for CY-1 failure was heat wasn't it ? would that matter so far away from the sun ?

NRao ji, interesting. IIRC NASA had a plan for a program that had a huge umbrella shaped membrane pointed towards the sun that would use radiation pressure to accelerate away from the sun.
p.s. my question about other factors was not a serious one though, if you get the context.

ramana · Post by **ramana** » 08 Nov 2013 20:42

Bade orbiting Mars with that instrument payload is not worth the payback. Ajey Lele of IDSA writes the highly elliptic orbit brings both Mars and two of its moons in field of view. He wrote a whole book on this in June 2013 and even said the flight would be inn November.
Its a Springer Verlag book and not any pavement publisher.

At work I always say Best is enemy of good enough.

Anyway use OT thread for dhak.

Lilo · Post by **Lilo** » 08 Nov 2013 20:56

Bade wrote:Title is misleading a bit.
Isro could have taken more time, done homework for Mars mission: PM's scientific adviser
Flaying the highly critical comments about the MOM by former Isro chairman Madhavan Nair, who is sceptical about the mission, Rao said, "It is unbecoming of Nair to make such comments. I'm critical of an Indian who makes such statement.
The reasons for the choice of a final elliptical orbit after Mars capture has not been made. A good guess is the usual suspect of fuel limitation. The standard bus to carry the payload was the same as that used for Chandrayaan, if I am not wrong and so is the fuel tank that goes with it. The other reason could be that they wanted to avoid the same issues encountered when they lowered the orbit with that mission, resulting in early termination. Instrument payloads are also fairly similar. Does anyone here know for sure.

Yes if i understand clearly, due to the launcher limitation (week ass pslv) isro had to place it in a relatively lesser elliptical orbit(correspondingly nearer to earth and with less total energy) post the final boost stage has separated from the probe and through the series of not sustained but very short firings of the weak ass thrusters of the probe at the perigee onlee - to efficiently use the piddly propellant tank and gain maximum proportion of energy from those firings as KE near perigee rather than PE with respect to earth's gravity field .
So a time involving series of revolutions around earth with short bursts are required near perigee - to gain sufficient velocity when slingshot is released from earths orbit - so that the probe travels to Mars in 300 days rather than 3000 days or some thing.

Is the above phyjicks explanation correct or mistakes onlee?

Neela · Post by **Neela** » 08 Nov 2013 20:58

Rahul M wrote:thx Bade mian. the reason for CY-1 failure was heat wasn't it ? would that matter so far away from the sun ?

Based on news reports, yes. CY-1 carried 11(?) instruments. IIRC They had to shutdown some as enough heat wasn"t dissipating out.

Bade · Post by **Bade** » 08 Nov 2013 21:01

Rahul_m, distance from the sun alone does not determine what the orbiting satellite sees reflected from the surface of the planetary body.

Enceladus, a moon of Saturn, has one of the highest known albedos of any body in the Solar system, with 99% of EM radiation reflected. Another notable high-albedo body is Eris, with an albedo of 0.96.[14] Many small objects in the outer solar system[15] and asteroid belt have low albedos down to about 0.05.[16] A typical comet nucleus has an albedo of 0.04.[17] Such a dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds.

The overall albedo of the Moon is around 0.12, but it is strongly directional and non-Lambertian, displaying also a strong opposition effect.[18] While such reflectance properties are different from those of any terrestrial terrains, they are typical of the regolith surfaces of airless solar system bodies.

http://en.wikipedia.org/wiki/Albedo

Radius of Mars is ~ 0.533 Earth radius
Radius of Moon is ~ 0.273 Earth radius

So the ratio of effective surface Area that captures Sun's radiation is ~ R^2 ~ 4

Sun-Mars distance is 1.66 AU, so the ratio of distances for moon and mars are like 1.66, moon is 0.0024 AU from earth, small correction to be neglected for now. Since radiation drops as inverse distance squared, so the final ratio is like 4/(1.66)^2 > 1.

So comparable to what was seen near the moon. Mars albedo must be like a desert sand on earth so like 0.4 or so, whreas moon's 0.10. So factor of 4 more there too.

It is as significant for this mission too, IMO.

Rahul M · Post by **Rahul M** » 08 Nov 2013 21:17

bade saar, albedo is basically reflectivity. so while mars might have a high value, the solar energy density at those distances would be much less than at our moon. at least that's how it seems to me.

Neela ji, I was inquiring about effects on MoM, not CY-1.

Neela · Post by **Neela** » 08 Nov 2013 21:21

BTW, why should we meet Mars when it is 300 million km away? Why not when it is "just" 54 million km away?

Bade · Post by **Bade** » 08 Nov 2013 21:24

rahul, check above..made some additions.

Rahul M · Post by **Rahul M** » 08 Nov 2013 21:38

thanks, so still significant. now amitabha ghosh's comment about 'ISRO needs to first figure out why CY-1 had problems' make some sense.

btw, this says http://www.asterism.org/tutorials/tut26-1.htm mars has albedo of 0.15 against 0.12 of moon. so this factor will certainly be significant.

Bade · Post by **Bade** » 08 Nov 2013 21:47

^^ True if they have not redesigned the bus, then internal heat dissipation profile is likely the same from a naive perspective without knowing the details. So they may have to limit how low an orbit they can go for. Add the fuel constraint bit due to same tank size with more firings for orbital corrections, leaves little juice left for more corrections required for a lower orbit. Like for all missions it will be a compromise on something or the other, one cannot complain.

It was a two-in-one mission. CY-1 was the first, now similar payloads we get Mars too hopefully, and learn a thing or two in the process. Not bad at all, still.

SaiK · Post by **SaiK** » 08 Nov 2013 21:50

so, how are the instruments playing here for the orbital needs? say they can only get to some orbit? will it be possible for all the mission critical measurements still be taken at that final higher orbit scenario?

NRao · Post by **NRao** » 08 Nov 2013 21:59

I think the way this game plays out is that they have a duplicate of the spacecraft on earth. They program and test what ever they want the spacecraft to do on earth and then upload the instruction set (either prior to liftoff or during flight). "Details" have a different meaning when applied to spacecrafts.

SaiK · Post by **SaiK** » 08 Nov 2013 22:12

learning a thing or two is not a bad process, but there would be nothing to learn (or non-directed learning) if the predicted path is not on the expected line of learning path.

Arunkumar · Post by **Arunkumar** » 08 Nov 2013 22:57

Neela wrote:BTW, why should we meet Mars when it is 300 million km away? Why not when it is "just" 54 million km away?

hazarding a guess , maybe something to do with acceleration required to approach a planet so as not to overshoot it or crash into it.

NRao · Post by **NRao** » 08 Nov 2013 23:24

arvin wrote:
Neela wrote:BTW, why should we meet Mars when it is 300 million km away? Why not when it is "just" 54 million km away?
hazarding a guess , maybe something to do with acceleration required to approach a planet so as not to overshoot it or crash into it.

I would think it is an issue related to efficiency.

A "direct" (short) trip would require more energy than a sling shot propelled longer trip.

Arunkumar · Post by **Arunkumar** » 09 Nov 2013 00:02

http://lasp.colorado.edu/home/maven/fil ... eline1.jpg

maven's flight path is a longish one riding on more powerfull atlas-v without a slingshot. Another thing in the equation is the effect of suns gravity. Maybe that has some role in the trajectory.

NRao · Post by **NRao** » 09 Nov 2013 00:10

arvin wrote:http://lasp.colorado.edu/home/maven/fil ... eline1.jpg

maven's flight path is a longish one riding on more powerfull atlas-v without a slingshot. Another thing in the equation is the effect of suns gravity. Maybe that has some role in the trajectory.

So, the "more powerfull" still used up more energy than the ISRO solution. Even within the "longish" variety there is a more efficient solution - it seems to me.

I am sure that ISRO would have used the same mechanism to tackle the 53 million shorter route. They did that to reach the moon too. Just more efficient (or less fuel consumption).