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Dawn's engines have a specific impulse of 3100 seconds and a thrust of 90 mNewtons. A chemical rocket on a spacecraft might have a thrust of up to 500 Newtons, and a specific impulse of less than 1000 seconds.

The VASIMR has 4 Newtons of thrust (0.9 pounds) with a specific impulse of about 6,000 seconds.

The VASIMR has two additional important features that distinguish it from other plasma propulsion systems. It has the ability to vary the exhaust parameters (thrust and specific impulse) in order to optimally match mission requirements. This results in the lowest trip time with the highest payload for a given fuel load.

In addition, VASIMR has no physical electrodes in contact with the plasma, prolonging the engine's lifetime and enabling a higher power density than in other designs.

To make a trip to Mars in 39 days, a 10- to 20-megawatt VASIMR engine ion engine would need to be coupled with nuclear power to dramatically shorten human transit times between planets. The shorter the trip, the less time astronauts would be exposed to space radiation, and a microgravity environment, both of which are significant hurdles for Mars missions.

VASIMR could also be adapted to handle the high payloads of robotic missions, and propel cargo missions with a very large payload mass fraction. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse.

Chang-Diaz has been working on the development of the VASIMR concept since 1979, before founding Ad Astra in 2005 to further develop the project.

 

Source: PhysOrg

India's Jurassic nest dug up in Tamil Nadu

Geologists in Tamil Nadu discover Dinosaur eggs. (TOI Photo)

 

Researchers from the Salem-based Periyar University found clusters of Dinosaur eggs. (TOI Photo)

 

Geologists exhibit the dinosaur eggs on Wednesday. (TOI Photo)

 

 

COIMBATORE: Geologists in Tamil Nadu have stumbled upon a Jurassic treasure trove buried in the sands of a river bed. Sheer luck led them to Geologists exhibit the dinosaur eggs on Wednesday.

Hundreds of fossilized dinosaur eggs, perhaps 65 million years old, underneath a stream in a tiny village in Ariyalur district.

Researchers from the Salem-based Periyar University found clusters of eggs of what they believe to be the most aggressive Carnosaur and the docile, leaf-eating Sauropod at Sendurai village.

While Carnosaurs were large predatory dinasaurs, Sauropods were long-necked, herbivores which grew to enormous heights and sizes.

That dinosaurs once roamed the area was known from the fossils found there on earlier expeditions. But this is the first time that hundreds of nests embedded with hundreds of clusters of dinosaur eggs have been unearthed in the district.

Located on the highway between Chennai and Tiruchi, the Ariyalur and the neighbouring Perambalur geological sites nestle in the northern plains of the Cauvery river. The place is a veritable museum of ancient organisms, dating back to 140 million years. Ever since a British couple -- the Wines -- collected 32 boxes of "strange stone objects" in 1843, the Ariyalur region has drawn geologists from across the world for its rich fossil presence and diversity.

Scientists have found the tiniest marine algae or the nano fossils besides the rare shell-like bivalve, gastropoda, telecypoda and brachiopoda in the geological sites spread across 950sqkm in Ariyalur and Perambalur districts.

"We found clusters and clusters of spherical eggs of dinosaurs. And each cluster contained eight eggs," says Dr M U Ramkumar, geology lecturer of the Periyar University. Each egg was about 13 to 20 cm in diameter and they were lying in sandy nests which were of the size of 1.25 metres.

In the 1860s, a British geologist first recorded the presence of bone remains of dinosaurs in Ariyalur. Over a century and a half later, the egg of a dinosaur was found in a cement factory of the state-owned Tamil Nadu Cements Ltd in 1990s. But officials realized that it was a dinosaur egg only 10 years later.

On a sultry afternoon on September 12 this year, Ramkumar and his research students went to Ariyalur to scour the rocks and sediments as part of a study funded by Indian and German scientific institutions. As they paused by a stream on a grazing land at Sendurai, they found spherical-shaped fossils peeping out of the sand beds. "We got really excited. As I have seen a dinosaur egg, I was sure these were dinosaur eggs," said Ramkumar.

A quick digging revealed clusters of eggs beneath seven layers of sand spread over two sqkm. The eggs may not have hatched due to the Deccan volcanic eruptions or seasonal flooding, surmise the team. "We suspect the extinction of dinosaurs was triggered by the Deccan volcano. Volcanic ashes cap the eggs," said one researcher.

"This is a very significant finding as never before have we found so many dinosaur eggs in the country. Besides the spherical size of the eggs covered with sand and volcanic ash provide significant insight into the possible reasons for extinction of the species," says Dr Jyotsana Rai, senior scientist, Birbal Sahni Institute of Paleobotany in Lucknow. Her team will collect samples of these eggs to determine its exact age.

Because a similar discovery in Jabalpur led to a plunder of the fossilized treasure, the researchers have requested the Ariyalur district administration to cordon off the site. Samples of the eggs will travel to Germany for further research. The vicinity of Jabalpur in Madhya Pradesh is considered the richest dinosaur field in the country.