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Raumfahrt - Re-Entry von ISRO´s Navigationssatelliten IRNSS-1H in 40-60 Tagen erwartet

5.09.2017

Satellite, heat shield of Indian rocket to re-enter in 40-60 days 

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"At this speed of re-entry, the whole structure is expected to get burnt," Sivan added.  

Simply put, the earth's gravitational pull increases the speed of the object that is falling towards it from the space. This increases the friction and heat, resulting in the object catching fire.  

The impact damage depends on the combination of mass and velocity.  


The Indian navigation satellite IRNSS-1H stuck inside a rocket's heat shield -- together weighing around 2.4-tonnes -- now tumbling in outer space, is expected to re-enter the earth's atmosphere in a couple of months.  

However, there may not be any impact on the ground, said a senior official of the Indian space agency.  
"The satellite tracking stations are getting intermittent signals from IRNSS-1H. The fuel on-board the satellite has been depleted by firing the motors whenever there was a signal.  

"The satellite-heat shield assembly is tumbling in space," K. Sivan, Director, Vikram Sarabhai Space Centre (VSSC) told IANS on Tuesday.  

"The whole thing is expected to re-enter the earth's atmosphere between 40-60 days. But the days could vary as the structure is tumbling, in space," K. Sivan, Director, Vikram Sarabhai Space Centre (VSSC) told IANS on Tuesday.  

"The whole thing is expected to re-enter the earth's atmosphere between 40-60 days. But the days could vary as the structure is tumbling," Sivan added.  
On August 31, the heat shield of Indian Polar Satellite Launch Vehicle's XL variant did not separate three minutes after crossing the atmosphere.  

As a result, India's navigation satellite IRNSS-1H was trapped and not put into orbit.  

Satellites are housed atop the rocket and covered by a heat shield or payload fairing, which protects them from getting burnt when the rocket crosses the atmosphere.  
Queried about the possibility of the whole structure hitting the earth and going on to be a 'mini-Skylab', Sivan said: "As per our current estimates whatever remains of the structure (heat shield, satellite and the rocket's fourth stage) will fall into the sea."  

The Skylab was US' first space station that fell back to earth in 1979. It weighed around 77-ton and it was a major incident.  
According to Sivan, the speed at which the rocket crosses the atmosphere on its way up is much less than the speed at which the heat shield-satellite coming down would be.  

"The rocket crossed the atmosphere at a speed of around one km per second. On the other hand, the heat shield housing the satellite is expected to re-enter the atmosphere at a speed of eight to nine km per second," Sivan said. 
"At this speed of re-entry, the whole structure is expected to get burnt," Sivan added.  

Simply put, the earth's gravitational pull increases the speed of the object that is falling towards it from the space. This increases the friction and heat, resulting in the object catching fire.  

The impact damage depends on the combination of mass and velocity.  

According to a space expert, the perigee (nearest point to the earth) and apogee (farthest point to the earth) of the satellite-heat shield assembly is around 164 km and 6,500 km.  

As per the original flight plan the satellite's perigee and apogee were to be 284 km and 20,650 km respectively.  
A space expert not wanting to be quoted told IANS: "The perigee will come down in course of time. Once the perigee touches 100 km then the rate of PSLV's heat shield-satellite assembly's fall towards the earth will be faster."  

According to him, the ISRO should calculate the ground trace -- the probable point of impact on ground.  
Sivan said the ISRO is tracking the heat shield-satellite assembly through its stations and through its multi-object tracking radar (MOTR) at the rocket port in Sriharikota.  

He also said there are free space debris tracking data which is also being used by the ISRO now.  

"The exact spot where the satellite housed inside the heat shield will fall will be known around 36 hours before the actual impact," the space expert said.  
Quelle: theeconomictimes
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NASA will track satellite, no danger: ISRO

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He said that all satellites in low earth orbits fall back through the atmosphere at one time or the other and burn up during reentry.

Nellore: NASA’s Two Element System, which keeps tabs on all objects in space, might spot the IRNSS-1H satellite before it begins to drift back to earth. 

Isro former director Dr M.Y.S. Prasad said NASA periodically updates data of active and passive satellites as well non-functional satellites apart from debris after due confirmation. 

He said the Vikram Sarabhai Space Centre in Thiruvananthapuram had tracking facilities and it was not difficult to predict the reentry time and trajectory in advance to take necessary precautions.  

He said that all satellites in low earth orbits fall back through the atmosphere at one time or the other and burn up during reentry. He said satellites with orbits with a perigee of more than 180 km perigee were safe.

“It is like any other space debris and it will burn up soon after entering the earth atmosphere because of temperatures running into thousands of degrees. We can identify the place where the debris would fall one week before such an eventuality” Dr K. Sivan, director, Vikram Sarabhai Space Centre, Thiruvanan-thapuram, told this newspaper. 

Replying to a question on the threat posed by the propellant in the satellite, he said, “we have depleted all the propellant through the gap in the heat shield and the fourth stage.”

Quelle: DeccanChronicle

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Down but not out: on the failed PSLV launch attempt

The failed PSLV attempt to launch a navigation satellite is unlikely to affect future missions 

After 39 consecutive successful launches, the Indian Space Research Organisation had almost made it appear that launching satellites was indeed child’s play when it used its workhorse rocket, the Polar Satellite Launch Vehicle. But the PSLV, which has been placing satellites in their respective orbits for the past 24 years, faced a setback on August 31. The PSLV-C39 rocket carrying the eighth satellite of the Indian Regional Navigation Satellite System (IRNSS) had a normal lift-off and flight events but ended in an unsuccessful mission. The heat-shield failed to separate, resulting in the satellite separation occurring within the shield. This is just the second instance when the PSLV has had an unsuccessful mission in all of its 41 launches; the first setback was back in 1993. Over the years, the PSLV has played a pivotal role in ISRO’s programme, and this February it set a world record by launching 104 satellites in one go. With such an enviable track record, the failure of the mission this time almost comes as a surprise. This is especially so as the lift-off and the stage separation of the first and second stages, which are the most challenging parts of the mission, went off smoothly. In comparison, the heat-shield separation is a relatively minor operation which takes place once the rocket crosses an altitude of 100-110 km, and the temperature in the absence of the heat-shield will no longer damage the satellite. The failed mission serves as a reminder that utmost care and scrutiny are required before every single launch. While scientists are working to identify the cause of the anomaly in the heat-shield separation event, the failed mission should have no impact on future launches involving the vehicle.

 
 

The failure of the mission is particularly disheartening as the IRNSS-1H satellite was jointly assembled and tested by ISRO and a Bengaluru-based private company, the first time a single private company, rather than a consortium, was involved in building a satellite. The satellite was in no way to blame for the failure of the mission. The space organisation has thrown open its doors to private companies to build as many as 18 spacecraft a year beginning mid or end-2018. The IRNSS-1H satellite was launched as a replacement for the IRNSS-1A satellite, which became inoperational in terms of surveillance following the failure of all three atomic clocks. As only six of the seven satellites are operational, there are gaps in the navigation data sent by the IRNSS. With the failure of this mission, India will have to wait for some more time before the next mission to send a replacement for the IRNSS-1A satellite is ready. The IRNSS was created so that the country would not need to rely on American-based GPS data — the encrypted, accurate positioning and navigation information provided by the system will make Indian military operations self-reliant.

Quelle: TheHindu

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Update: 6.09.2017

ISRO suspects pyro elements failed to separate rocket’s heat shield

The Indian space agency is strongly suspecting the failure of pyro elements for the non-separation of the heat shield of its rocket Polar Satellite Launch Vehicle’s (PSLV) XL variant on Aug 31, said a senior official.

As a result of the heat shield not separating the 1,425 kg navigation satellite IRNSS-1H got stuck inside it resulting in the failure of the around Rs 250 crore mission.

Normally the heat shield will be separated soon after the rocket crosses the earth’s atmosphere.

According to K. Sivan, Director, Vikram Sarabhai Space Centre (VSSC), all the systems during the rocket’s flight worked well while the only suspect place is the pyro elements.

The VSSC is part of the Indian Space Research Organisation (ISRO).

“Tests are going on to find out the reasons for the failure of heat shield separation. Each test takes around 72 hours,” Sivan told IANS.

One fortunate aspect of the failure is that ISRO has all the flight data as the rocket was not lost during its one way journey.

Sivan said the heat shield would separate after on-board computers give the command to ignite the explosives. The explosives would then ignite and explode to separate the two parts of the heat shield joined by bolts.

Quelle: The Statesman

 

 
 
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