Monday, January 17, 2011

Indian Astronauts Must Wait For A Better Rocket

The 2010 Christmas Day failure of India's Geosynchronous Satellite Launch Vehicle was a sad blow to India's space program. ISRO, India's space agency, lost a rocket and a major satellite. There's an obvious need to plan a replacement for the lost bird, and debug the problems that caused the failure. Beyond this, there could be further implications. The loss of this rocket will have an influence on India's fledgling human spaceflight program.

India announced plans for a space capsule in 2008, and planning has gone on without much comment ever since. The capsule is a blunt, conical spacecraft with a cylindrical service module. It's designed to carry up to three astronauts. The generically dubbed "orbital vehicle" is designed to be launched by a modified version of the Geosynchronous Satellite Launch Vehicle, the same rocket that recently failed.

Sadly, this is not the first time that GLSV has failed. Out of a total of seven launches, only two are judged to be complete successes. Four were unquestionable failures (including both of the launch attempts in 2010). One 2007 flight is judged to be a partial failure, placing a satellite in the wrong orbit.

Clearly, ISRO does not plan to simply bolt a spacecraft atop the GLSV as we currently know it and blast an astronaut into space. There will be modifications to the vehicle and testing. But the appalling performance record of the GSLV will complicate attempts to use it for human missions.

The process of certifying a rocket as fit for carrying astronauts is known (with some lingering sexism) as "man rating". Much of this process involves building up a high expectation of reliability, demonstrated in test flights.

Man rating also involves the addition of extra safety systems, such as escape rockets for the crew capsule. There will also be modifications to some regular components to ensure a higher chance of success. Issues such as acceleration levels and the acoustic and vibrational environment also play a part. Clearly, getting a launch vehicle man rated is far more complex than certifying a launch of a satellite.

Man rating is also a subjective process. Reliable figures for the projected failure rates of certain launch vehicles can be difficult to estimate. Sure, there can be test missions and calculations, but these can still be off the mark. The safety levels and risks that managers are prepared to accept are also matters of personal judgment.

India has marked 2016 as a possible target date for its first manned space mission. If ISRO hopes to launch in roughly five years, it will need to produce some miracles of engineering. Building the spacecraft is one thing. This will be complex, but it's probable achievable in the time frame. The greatest challenge of all will be taming the rocket to launch it.

Apart from the rather poor track record of GSLV launches, another problem is at play. The GLSV has gradually evolved over the course of its launches. The most recent GSLV is substantially different from the first.

These changes have been good in principle, and have focused on improving the rocket and phasing in indigenous technology. In practice, the numerous changes make it hard to generate a reliable statistical base for the overall launch campaign. Can earlier launches truly be used to evaluate the reliability of a new model of the rocket?

In some ways, this "apples and oranges" problem makes things look good. Some of the earlier failures can be written off as teething troubles with a new and unevolved prototype. In other ways, it looks even worse.

The failure rate of more advanced versions of the rocket remains high, and the overall statistical base is even smaller. Furthermore, failures seem to happen for different reasons on different launches. This could suggest problems with multiple sub-systems, which further complicates the debugging process.

Man rating the GSLV will require ISRO to settle on a design and test it extensively, demonstrating a good performance record. This will require a lot of work to make the rocket more reliable, and a high flight rate in the years ahead.

At the present, it's not exactly clear how ISRO is planning to deploy the GSLV in the years ahead, but it seems that 2011 will be free of any launches while the recent failures are digested.

Many payloads are earmarked for GSLV launches in 2012 and beyond, with a rough average of four launches per year expected. Any more than three failures in the next five years will seriously compromise faith in this launch system.

Beyond showing that GSLV can be trusted as a satellite launcher, ISRO will need to test the capsule and the modified GSLV that will launch it on several uncrewed test flights. How will these be integrated into the overall launch manifest for the decade ahead? How many flights will be needed? These are unresolved issues.

Ultimately, India may find itself placing the cart before the horse. An Indian space capsule may be ready for action, but the GSLV could still be unfit to launch it.

In such a case, ISRO may wish to compromise by launching its indigenous orbital vehicle atop a foreign rocket. If this path is not taken, and if the GSLV does not prove its worth in the years ahead, then India's astronauts will be waiting for their flights for a very long time.

No comments:

Post a Comment