In May 1995, my wife, Usha and I --our daughter, Rimanika was not born--landed at Los Angeles airport and were waiting for a bus to take us to our hotel at Sunset Boulvard. While waiting, I spotted a board which stated ``buses to JPL.'' When I saw it I got excited and felt really tempted to just board a bus and visit the lab about which I have read and heard so much about being a spacebuff. But I could not make it, and during our few days in Los Angelos, on account of our tight tour sked we were unable to go to that mecca for spacebuffs--JPL. While travelling around Los Angeles, I felt a sense of disappointment when I came acoss signages indicating ``Way To JPL.'' with an arrow mark. Why could not have I just followed that road? (!)
But, I do hope I visit it someday. I did land at Los Angeles two or three years ago. But I was part of a media party, and on arrival we were directly transferred to the terminal from where we boarded a flight to Seattle.
However on Thursday evening my dream of visiting JPL was I would say partially fulfilled. Yes, I repeat partially fulfilled. You would wonder what I mean by ``partially fulfilled?'' This means I witnessed the Epoxi encounter of Comet Hartley 2 live at the mission control room in JPL thanks to Nasa TV. It was thrilling and I felt I was a part of the unfolding drama sitting in our room at Breach Candy.
In this mission, the Epoxi spacecraft which is nothing but the same one which impacted on Comet Tempel 1 on July 4,2005, flew very close to Comet Hartley 2, its closest point was 435 miles. This much-awaited encounter took place at about 7.30 p.m. (IST). At its nearest approach, its velocity was 12,3 kms per second. Comet Hartley 2, also known as 103P/Hartley 2 is a relatively small, but very active periodic comet which orbits the sun once every 6.5 years.
The spacecraft has two telescopes with digital colour cameras and an infrared spectrometer to examine the comet in detail during the fly by Epoxi is an acronym bindging two science investigations, These are the Extrasolar Planet Observation and Characterisation and Deep Impact Extended Navigation. The name of the spacecraft is called Deep Impact, while the mission has been christened Epoxi.
According to Nasa, the science objectives of this mission include:-
* Observe multiple transits of giant planets in orbit around the stars.
* Find additional planets.
* Search for rings and moons associated with giant planets.
* Understand the structure, composition and formation history of cometry nuclei.
* Understand the early formation of the solar system.
Project manager, Tim Larson, said that the mission ``will help to study the beginnings of the solar system. We are going to get some fantastic science.'' Director of JPL/s Solar System Exploration, Rick Grammier, observed: ``We already have a lot of fantastic science.''
Flying at 27,000 mph, the science observations were kicked off on September 5. The hours surrounding the encounter were challenging for the mission team since they were commanding a spacecraft which was really not meant for this comet flyby. This spacecraft was designed and employed successfully for Nasa's Deep Impact encounter of Comet Tempel 1 in July 2005. By recycling Deep Impact, the Epoxy mission provided a nearly 90 per cent saving to Nasa.
The comet was discovered in 1986 by a British-born Scottish-educated Malcolm Hartley, while working at observatory in New South Wales, Australia.
Said Mumbai-born Shyam Bhaskaran who is the mission navigator: ``I've worked the Stardust flyby of Comet Wild 2 and the Deep Impact encounter with Comet Tempel 1 and I have never seen a comet flit around the sky like this one.'' According to him part of the reason Hartley 2 is hard to pin down is because the small comet is very active.
Encounter sequence: * The encounter phase was first initiated on Wednesday when the spacecraft was about eight hours away for executing the flyby. When this started all images were stored initially in its two computers.
* About 496,000 miles and 18 hours from the comet, the spacecraft locked its instruments on the comet and began the encounter phase data collection.
* Fifty miles before the closest approach, the spacecraft's onboard autopilot, the Auto Nav mode went active. In this mode the spacecraft receives attitude (pointing) instructions from its computer to help keep the comet's nucleus centered in spacecraft's images.
* The Auto Nav mode is used because the JPL's mission control room is 23 million miles away from the spacecraft. This means that commands flashed from the control room will take 75 seconds to reach the spacecraft which is stated to be quite long.
As the spacecraft was nearing the comet, a sense of nervous apprehension filled the mission control room. There was silence and the scientists were hoping that the encounter would be executed flawlessly. The much-awaited moment arrived at 7.30 p.m.(IST) when the spacecraft started clicking images once in every four seconds,
After the encounter there was five minutes of loss of signal. and contact was reestablished at 7.45 p.m (IST). This moment triggered instant applause among the team members leading to exchange of handshakes and embraces.
The commentator declared: ``The riskiest moment is behind us. Everything looks green.''
The images then started coming in,
The mission was a success.
Congratulations Nasa. Shyam you have good reasons now to enjoy a great divali!
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