Quote from: cave_dweller on 10/01/2014 12:49 am1) Being able to Launch -- Success2) Escape Earth Gravity -- Success3) Enter into Helio-Centric Orbit towards Mars -- Success4) Arrive at Mars -- Success5) Enter into an elliptical Mars Orbit in full autonomous operating mode -- Success (the signal propagation delay between Mars and Earth is an average of 12 mins)6) Observe Mars -- Ongoing7) Crash on to Mars -- 6 to 9 months from nowCrash on to Mars?? Are you really sure that is an objective? Never mind the question of whether any scientific knowledge can be gained out of doing it, but did the spacecraft undergo the level of microbial decontamination that is required of a Mars landing? If not, with the tenuous atmosphere of Mars, isn't it probable that parts of the spacecraft will survive re-entry and bring earth's microbes to its surface? This is not Moon we are speaking about, as the question of Mars's capability to sustain microbial life isn't resolved yet. The worst nightmare that can happen to our efforts to find answers for Mars would be to find earth's microbes colonizing it.
1) Being able to Launch -- Success2) Escape Earth Gravity -- Success3) Enter into Helio-Centric Orbit towards Mars -- Success4) Arrive at Mars -- Success5) Enter into an elliptical Mars Orbit in full autonomous operating mode -- Success (the signal propagation delay between Mars and Earth is an average of 12 mins)6) Observe Mars -- Ongoing7) Crash on to Mars -- 6 to 9 months from now
MOM is going to crash on Mars sometime in the future anyway (unless it is recovered, which is probably unlikely). By doing it at the end of the mission, its in a controlled fashion into a known location. It also removes any possibility of creating future orbital debris around Mars.
Is it just me or do the low res. pictures look like paintings and not pictures. Can't they get better resolution from their pictures.
7) Crash on to Mars -- 6 to 9 months from now
1. I remember reading that one disadvantage of using GSLV-II for a Mars mission was that it cannot make the coasting that PSLV did during MOM launch to adjust its Argument of Perigee (AOP), probably because PSLV has a separate 3rd and 4th stages while GSLV-II has a single non-restartable 3rd stage. I guess the mentioned payload capability take this into account?
In order to utilise the GSLV and GSLV Mark III, the cryogenic engines on those rockets will need ‘multi-start’ capability so that they can be shut down after one burn, undergo a period of coasting and restart, noted Dr. Adimurthy.Starting, shutting down and restarting a cryogenic engine in space is complicated, noted S. Ramakrishnan, who retired recently as director of the Vikram Sarabhai Space Centre, ISRO’s lead centre for launch vehicle development, and earlier headed the Liquid Propulsion Systems Centre that develops liquid propellant engines needed for the space programme.Restart capability has not yet been demonstrated with the GSLV’s cryogenic engine. As for the cryogenic engine being developed for the Mark III, “once we do the initial engine-level tests, we can look at introducing the restart capability,” he remarked
(EDIT: Would bundling an additional hypergolic upper stage with the spacecraft be of some use here, something in the lines of PAM-G? Spacecraft+Upper Stage does the coasting, then US fire multiple times for any necessary orbital adjustments and then do TMI and separate.. Not sure how much of sense it makes considering we are talking of bundling a less efficient hypergol on top of a more efficient cryo, just a thought that came to my mind..)
ISRO has designed and ground-tested a ‘Payload Assist Module’ using a liquid-propellant engine that powers the PSLV’s fourth stage. This module had originally been developed so that the GSLV could launch Russia's Global Navigation Satellite System (GLONASS) satellites, a proposal that ultimately did not materialise.The module could go atop the GSLV or GSLV Mark III and enhance their capabilities to send probes to Mars, said Mr. Ramakrishnan.
EDIT: As per news reports, former ISRO chairman U.R.Rao had mentioned recently that ISRO might target the 2018 launch window for the next Mars mission as 2016 is too close to plan a good science oriented mission. So we may have to wait for the 2018 then.
For future missions, ISRO will have to turn to the Geosynchronous Satellite Launch Vehicle (GSLV) and GSLV Mark III that can lift much heavier spacecraft than the PSLV.ISRO needed to carry out a system study of how the GSLV and GSLV Mark III launchers could be used to carry probes for Mars, observed its chairman, K. Radhakrishnan “Certainly for the next mission we have to go for [a spacecraft with] higher mass.”The space agency would not be in a position to send a spacecraft to that planet during the 2016 launch opportunity, he told this correspondent. The launch window that opened in 2018 would be the earliest that the next mission to Mars could go. It was also necessary to be clear what science such a mission could carry out, he added.
Quote7) Crash on to Mars -- 6 to 9 months from nowIs there a source for this? I don't recall seeing this in any of the ISRO materials, but could easily have missed it. They do mention a possible extended mission after the nominal 6 months.It seems odd to me: AFAIK no NASA Mars orbiters have been intentionally de-orbited, and MOM has relatively little propellant to spare. The MOM orbit seems like it shouldn't decay for a long time, though perturbations might be an issue.
Once that mission is complete, the spacecraft will not be allowed to crash onto Mars but manoeuvered away.
The Indian Mars craft Mangalyaan would crash on Martian surface following exhaustion of fuel.
The idea of SC + upper stage coasting together has already been attempted, so to speak, by RKA for Phobos-Grunt with a modified Fregat attached to the craft.
But the problem for GSLV as mentioned earlier would be the payload loss due to bundling of an additional hypergol upper stage. The ideal solution would have been to make CE-7.5 restartable. But as S.Ramakrishnan says in the link, its complicated to add such a capability for cryo-engines and will take time to develop.
Quote from: sultanofhyd on 10/02/2014 02:02 pmThe idea of SC + upper stage coasting together has already been attempted, so to speak, by RKA for Phobos-Grunt with a modified Fregat attached to the craft.But the problem for GSLV as mentioned earlier would be the payload loss due to bundling of an additional hypergol upper stage.
Meanwhile, the committee under former Isro chairman UR Rao met earlier this week to work out the possibilities of MOM studying Comet Siding Spring, which is expected to go past Mars on October 19. "Now that MOM has completed one revolution around Mars, we know its position vis-a-vis the comet," Rao told TOI.Scientists are calibrating the various payloads. Rao said the final decision on what type of study should be conducted will be taken in October."The important payload to study the comet will be the methane sensor. But we'll have to work out the plan and what results we may expect with different options," another scientist said, adding, "A final decision will be taken around October 15 depending on MOM's position."
There was a discussion about PAM-G, cryogenic engine restart capability and how Centaur upper stage does it, in one of the GSLV discussion threads. You may find it interesting:http://forum.nasaspaceflight.com/index.php?topic=33622.msg1148624#msg1148624
Even if we use PAM-G, payload and mission life would be much more than what can be achieved using PSLV.
The final burn duration was only 23.08 seconds, a difference of nearly a minute from the planned duration. This duration is actually determined by the on-board accelerometer itself, which shuts off the engine automatically once the required change in velocity—actually a braking velocity to slow down the spacecraft to enable its capture into the Martian orbit—is realised. As against the targeted 1,098.7 m/s, the operation achieved a velocity change of 1,099 m/s. That is indeed an amazing precision. A difference of one minute in the burn time also means a significant gain in terms of the on-board fuel saved.
Before the MOI, the quantity of effectively available on-board fuel was 281 kg, of which about 250 kg was expected to be consumed during the LAM firing. But that difference of one minute has meant a fuel saving of about 10 kg and this can, in principle, increase the spacecraft life beyond the targeted six months. “We achieved a completely unexpected efficiency of 99.6 per cent in the LAM performance during the test firing,” Radhakrishnan said. “Normally, one does expect a performance degradation of about 2 per cent when you restart after leaving it idle for as long a duration as 300 days. Even our simulations had indicated that. But to our surprise, we got such high efficiency that we decided to reduce the burn time during the MOI,” he said. And even the final firing seems to have gone off with equal efficiency.
The idea of the September 22 test firing itself was quite innovative. It was actually a two-in-one operation: one to carry out a trajectory correction manoeuvre (TCM) of bringing the altitude of the final orbit down to the designated value of around 500 km from the 720-odd km that the spacecraft would have achieved if this firing had not succeeded and the spacecraft had gone along in its trajectory; two, to test the performance of the main engine for the crucial D-day operation. This TCM, which was otherwise scheduled to be carried out on September 14, was not done with this two-birds-with-one-stone operation in mind. You could argue that that there was a risk of not getting the correct altitude if the LAM had failed in the test. But, if the LAM had failed, in any case an optimum orbit with thrusters alone would not have been possible. So why not this? So went the scientists’ logic and it was indeed remarkable thinking.
Latest Frontline article about how ISRO planned the LAM test-firing and MOI in detailhttp://www.frontline.in/science-and-technology/giant-leap/article6460749.ece?homepage=true
Ok.. So the Mars payloads you quoted in one of your earlier posts (1000kg for elliptical and 550kg for circular orbits), are they applicable when using PAM-G? What are the other solutions ISRO can consider for Mars missions using GSLV-II (barring, of course, the restartable cryo-stage) ?
The author of that article uses a pretty strange method of representing time... 24.14 minutes is an acceptable fraction, 23.08 seconds is a completely different thing altogether.
Quote from: sultanofhyd on 10/03/2014 07:16 amThe author of that article uses a pretty strange method of representing time... 24.14 minutes is an acceptable fraction, 23.08 seconds is a completely different thing altogether. I guess he meant to say 23.08 minutes - perhaps onboard accelerometer sensed that the MOI delta-v was achieved after 23 minutes of firing of LAM and shut it off (instead of predicted 24 minutes) and saved some fuel in the process.
here is a picture of mars taken by the 70's era viking mission...compare and contrast
Quote from: abhishek on 09/30/2014 02:38 amhere is a picture of mars taken by the 70's era viking mission...compare and contrastWhich one is closer to what Mars actually looks like to naked eye? Seems there's a big difference in hue and lightness.