Friday, July 22, 2011

Updates on Chandrayaan-2 and GSLV

In a recent interview to LiveMint, the chairman of ISRO, Dr. K. Radhakrishnan was asked some question regarding the GSLV and the effects of it's two successive failures on the launch of Chandrayaan-2, planned for 2013.

Does it mean all major missions till Chandrayaan-2 will only use indigenous engines? Since the Russian engine has to be examined, will Chandrayaan-2 be delayed?
Yes, it has to be tested on indigenous cryogenic engines, and we’ll only use our engines for future launches, but that is not why there will be a delay. Historically, the Chandrayaan missions are a joint Indo-Soviet mission. The agreement was that the lander [that will descend on the moon] and the (lunar) rover (a robot vehicle) would be provided by the Russians. We wanted to put a smaller rover; it’s something new that we are developing. However, in Russia there was a rethink. They decided they’ll only develop the lander and some instruments related to it. That means India would have to make a bigger rover, a decision taken almost a year ago. There are also preliminary design reviews to be undertaken this year to select which instruments are to be carried onboard the mission. So it’s not only GSLV (engines); there are other reasons for the delay.

On the GSLV,
Next week you’re launching a satellite on the Polar Satellite Launch Vehicle (PSLV). When can we next expect a launch aboard a Geosynchronous Satellite Launch Vehicle (GSLV) with our own cryogenic engine, given that previous attempts have resulted in failure?

Next year this time, we will be conducting flight stage tests (a preliminary to the launch). Flight stage readiness is one thing, but before it is inducted into a launch, we have to ensure that all the ground tests are okay. Also, when we launched the satellite in December, we used a very costly satellite (GSAT-5P)— almost Rs. 150 crore—with lots of features. This time we’ll go for a cheaper satellite (GSAT-14), something that doesn’t require much effort. At best, we’ll be able to put in some transponders in the C-band. If the vehicle underperforms, it won’t be much of a loss. If this one goes well, we will launch the GSAT-6, the “famous” one (that was embroiled in the Isro-Devas row). This, too, will go only on an indigenously developed cryogenic engine. After that it will be Chandrayaan-2 (scheduled for around 2013). There are also changes in the whole GSLV vehicle per se. From 1.5-tonne payloads, we’ve now reached about 2.2-tonne payloads. The biggest change effected is the size of the heat shield [a protective sheath that also determines the size of communication satellites to be put into orbit] and the materials we use for it. We’ve gone from 3.5m heat shields to 4m, and use composites [such as plastic fibre] instead of metal. For GSLV Mark-3, we may have to use 5m shields. 
Why is developing a GSLV so difficult?
We’ve bought seven cryogenic engines from Russia, of which we’ve used six. The results coming out of GSLV have been mixed. Sometimes unforeseen obstacles don’t emerge until it’s actually launched. For instance, when we tried to launch last April using (an) indigenous cryogenic engine, all the preliminary stages were fine and our cryogenic engine ignited—and ignition in vacuum is a difficult thing. But after a few seconds, it stopped. For it to keep going, another device called a two-steering engine (or turbo pumps, which keep the launcher steady) ought to ignite, too. This will ignite only if hydrogen and oxygen are present in exact amounts. When we looked into it, there are several possible explanations as to why the turbo pumps stopped: There are three bearings for these turbo pumps; the bearings must rotate without being (distorted) out of shape by the liquid hydrogen fuel it is submerged into. It could also be that the turbo pumps were blown out of shape. There are several things that can go wrong, and each time we have to test from scratch and develop new solutions. While all these have been looked into, we have to undertake a full ground test, before we can be sure that this will work in flight. Hopefully, this flight stage should be ready for testing in March 2012.
So what about the seventh cryogenic engine from Russia? There were reports that both Isro and Russia disagreed on technical reasons for the failure of the most recent GSLV mission in December.
The last two engines (the sixth and seventh) have greater thrust than previous engines. They was supplied in 2004 and 2005, and stored in specified conditions. So the reason for the failure (in December) was the inadvertent snapping of the connectors, well before time [connectors are critical for controlling the vehicle]. This happened because the shroud gave away (the shroud is a casing that separates the liquid and solid stages of the launch cover). It’s a cover that sits on (the) bottom of the cryogenic stage. Now, why did the shroud go? Was it the 4m heat shield? We then realized that it was the inherent vulnerability of the shroud. The shroud was at the bottom of the cryogenic stage. There were 10 connectors in two stages, and both gave way. Initially, the Russians said it was our 4m shield that was responsible. We put both our analyses, and finally the Russians also came around. We then decided that the seventh engine has to be inspected, too. We did it and found that they weren’t made in the dimensions specified to in the document. There are lots of shortcomings, and the Russians admitted it. Now, the point is that this has to be corrected before it can be used for launch and would require a detailed inspection by them.
The delay in the launch of Chandrayaan-2, at the time thought to be because of the GSLV failures, was well documented  during the weeks and months following the failure of the F06 flight. But, the additional task of having to develop the rover all by themselves is seemingly a bigger challenge for ISRO. For the record, ISRO does not have any prior experience in building rovers of any sort and different aspects like design, testing are going to take a lot of time (and assistance from the Russians). The rover design will supposedly be finalized this year. The mission itself could possibly be delayed upto 2015 and beyond while ISRO is optimistic about launching it in 2014.

Regarding the GSLV, Dr. Radhakrishnan clears the fact that all future flights of GSLV will use the indigenous upper stage (then the final Russian upper-stage will indeed go unused). The additional time and resources that will have to go into overcoming the short-comings of the Russian stage just for a single mission should have deterred ISRO from using it on any future flights.    

The next launch of the GSLV will use a comparatively inexpensive satellite in the GSAT-14. ISRO wants to ensure that if this launch were to fail, then the loss wouldn't be as great as in the case of the previous launch (GSAT-5P). In case of a successful flight (one which we pray for), the GSLV will then launch the GSAT-6 and the GSAT-7.


Sunday, July 17, 2011

PSLV notches up another success

The launch of PSLV-C17 Credit:ISRO

The PSLV has added another success in it's list after than the successful launch of the GSAT-12A on-board the PSLV-C17. This was the PSLV's 19th flight and it's 15th consecutive successful launch. The satellite was launched into a sub geostationary transfer orbit.

The 53 hour countdown started at 11:48 hours (IST) on July 13, 2011. ISRO has been generous enough to provide us with videos of launch vehicle integration which happened during the months and weeks leading upto the launch.

The integration of Solid rocket boosters with first stage.

Integration of the third and fourth stages.

Integration of the satellite and heat shield.

The GSAT-12A itself is a communications satellite of the INSAT-family, a replacement for the INSAT-3B. It was launched to address the ever-growing demand for transponders. This particular satellite carries 12 C-band transponders.

The launch window for this flight opened at 16:48 hours for 20 minutes. The weather was gloomy but there was no rain leading-up to the launch. The mission director gave the go-ahead for the launch at the scheduled launch time (16:48 hours IST). During the last 15 minutes, the onboard mission computer takes over the launch control. It is also important to mention that this particular flight was the first PSLV flight with the indigenous flight computer Vikram (which was previously used on the GSLV-D3 flight).

Due to this being a launch to sub-GTO orbit, the normal flight profile of the PSLV was altered slightly to obtain the large apogee. The configuration used here was the PSLV-XL
with 13.5 meter long strap on solid boosters that each carried nearly 12 tonnes of propellant instead of the standard version were they are 11.3 meters long and carry 9 tonnes of propellant. At liftoff the vehicle stood 44 meters tall and weighed about 320 tonnes.

The altered fight profile meant that
the fourth stage coasted for 2 minutes 25 seconds before ignition and fired for about 9 minutes. After about 20 minutes of the flight, the satellite was inserted into a sub-Geosynchronous Transfer Orbit (sub-GTO) with a perigee of 284 km and an apogee of 21,020 km with an orbital inclination of 17.9 deg. This was almost equal to the planned 284 km perigee and 21,000 km apogee orbit.

The satellite will be placed into Geostationary orbit by firing of it's onboard thrusters during the coming weeks.

Flight Brochure: Link
Image Gallery: Link