Sunday, November 17, 2013

Mars mission: Isro performs last orbit-raising

The Indian Space Research Organization (Isro) on Saturday performed the last of the five orbit-raising manoeuvre on its Mars Orbiter in the early hours, raising the apogee (farthest point from Earth) of the spacecraft to over 1.92 lakh km.
"The fifth orbit-raising manoeuvre of Mars Orbiter Spacecraft, starting at 01:27am (IST).. with a burn time of 243.5 seconds has been successfully completed. The observed change in apogee is from 1,18,642 km to 1,92,874 km," Isro said.

Current status

On 19 October 2013, ISRO Chairman K. Radhakrishnan announced that the launch had to be postponed by a week as a result of a delay of a crucial telemetry ship reaching Fiji Islands. The launch was rescheduled for 5 November 2013. The PSLV rocket successfully lifted off at 09:08 UTC (2:38 p.m. IST), and placed the satellite into Earth orbit at 09:50 UTC, with a perigee of 264.1 km, an apogee of 23,903.6 km, and inclination of 19.20 degrees, with both the antenna and all three sections of the solar panel arrays being deployed.

During the first three orbit raising operations, ISRO has progressively tested the autonomy functions of the spacecraft that are essential for trans-Mars injection and Mars orbit insertion. The systems tested satisfactorily are:
  • The prime and redundant chains of gyros and accelerometers.
  • Liquid motor attitude control thrusters.
  • Attitude, orbit control electronics and associated logics for their fault detection isolation, and reconfiguration.
  • Functioning of the prime and redundant star sensors.

Orbit raising manoeuvres

Orbit-raising burns
Date Burn time Resulting
apogee (Km)
5 November
15:35 min in 5 stages                                          23,9033                                  
6 November 416 s 28,825 
7 November 570.6 s 40,186 
8 November 707 s 71,636 
10 November Incomplete 78,276 
12 November
303.8 s 118,642    
16 November 243.5 s 192,874 
Six orbit raising operations were planned to be conducted from the Spacecraft Control Centre (SCC) at ISRO Telemetry, Tracking and Command Network (ISTRAC) at Peenya, Bangalore on 6, 7, 8, 10, 11, 16 November and on 1 December by using the craft's on-board propulsion system and Earth flybys for gravity assist. The aim is to gradually build up the necessary escape velocity (11.2 km/s) to break free from Earth's gravitational pull while using a minimum of fuel. The first three orbit raising manoeuvres were successfully completed, while the fourth was only partially successful. However, the subsequent supplementary manoeuvre raised the orbit to the intended altitude aimed for in the original fourth manoeuvre.
First orbit raising
The first orbit-raising manoeuvre was performed in 6 November 2013 at 19:47 UTC when the 440 Newton liquid engine of the spacecraft was fired for 416 seconds. With this engine firing, the spacecraft's apogee was raised to 28,825 km, while its perigee is at 252 km.
Second orbit raising
The second orbit raising manoeuvre, starting at 20:48:51 UTC on 7 November 2013, with a burn time of 570.6 seconds has been successfully completed. The resulting apogee was 40,186 km.
Third orbit raising
The third orbit raising manoeuvre, starting at 20:40:43 UTC on 8 November 2013, with a burn time of 707 seconds was successfully completed. The apogee was increased to 71,636 km.
Fourth orbit raising
The fourth orbit raising manoeuvre, starting at 20:36 UTC on 10 November 2013, only imparted an incremental velocity of 35 m/s to the spacecraft instead of the planned 135 m/s as a result of underburn by the liquid apogee motor.Because of this, the apogee was boosted to 78,276 km instead of the planned 100,000 km. When testing the redundancies built-in for the propulsion system, the flow to the liquid engine stopped, with consequent reduction in incremental velocity. During the fourth orbit burn, the primary and redundant coils of the solenoid flow control valve of 440 Newton liquid engine and logic for thrust augmentation by the attitude control thrusters were being tested. When both primary and redundant coils were energised together during the planned modes, the flow to the liquid engine stopped. Operating both the coils simultaneously is not possible for future operations, however they could be operated independently of each other, in sequence.
Supplemental burn
An unscheduled supplemental burn was performed on 12 November 2013 that successfully increased the apogee to 118,642 km, the apogee originally intended to be obtained in the fourth manoeuvre.
Fifth orbit raising
The apogee was raised in 16 November to 192,874 km in this final orbit raising manoeuvre.

by-sanjay kv



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