Lancio di GSLV-F02 - Scoperte le cause del fallimento

La commissione di inchiesta stabilitasi dopo lo sfortunato lancio del vettore indiano GSLV-F02, finito con la distruzione del lanciatore e del carico pagante, ha stabilito che la sostanziale mancata accensione di uno dei quattro booster a combustibile liquido fin dai primi momenti dopo il lancio è la causa dell’incidente.

Indian Space Research Organisation Bangalore, India

September 6, 2006

GSLV-F02 Failure Analysis Committee Report

The Failure Analysis Committee (FAC), constituted for investigating the
failure of ISRO’s Geosynchronous Satellite Launch Vehicle, GSLV-F02 mission
from Satish Dhawan Space Centre (SDSC SHAR) Sriharikota, on July 10, 2006
has submitted its report.

The 49 metre tall and 414 tonne GSLV comprises three stages. The first stage
consists of a solid propellant motor and four liquid propellant strap-ons.
The second stage is also a liquid propellant stage and the third is a
cryogenic stage.

GSLV-F02 launch was the fourth in the series. All the three earlier missions
(GSLV-D1, D2 and F01) were completely successful. The mission objective of
GSLV-F02 was to place INSAT-4C, an operational satellite into
Geo-synchronous Transfer Orbit (GTO). About 55 sec into the flight, GSLV-F02
started deviating significantly from its nominal flight path resulting in
the vehicle breaking up at 62 sec after lift-off. The debris fell into Bay
of Bengal.

The 15 member FAC chaired by Mr K Narayana, former Director of SDSC SHAR,
with the participation of experts from academic and research institutions
besides ISRO, has reviewed the performance of GSLV-F02 from lift-off to the
end of flight. FAC had detailed deliberations for over 100 hours in several
sittings and was assisted by eight specialist sub-committees examining the
flight data of vehicle subsystems, manufacturing documents, inspection,
calibration and test results, etc. Especially, the details related to the
realisation of liquid propulsion stage of GSLV were closely scrutinized.
Several tests simulating possible failure modes were also conducted to
identify the exact cause.

FAC has concluded that the performance of all vehicle subsystems, except one
strap-on stage was normal until 56.4 sec. The primary cause for the failure
was the sudden loss of thrust in one out of the four liquid propellant
strap-on stages (S4) immediately after lift-off at 0.2 sec. With only three
strap-on stages working, there was significant reduction in the control
capability. However the vehicle attitude could be controlled till about 50
sec. At the same time the vehicle reached the transonic regime of flight and
the vehicle attitude errors built up to large values, resulting in
aerodynamic loads exceeding the design limits thus leading to break up of
the vehicle.

The thrust of the liquid engines used in the strap-on stages is precisely
controlled by a set of regulators. Detailed analyses have indicated that in
S4 engine the thrust control was not effective. Instead of stabilizing at
5.85 MPa (Mega Pascal) chamber pressure, it reached 7.11 MPa at 2.8 sec.
This was much beyond the design limits and the engine failed at 0.2 sec
after lift-off, that is 5 sec after its ignition.

Simulations and analyses of flight data and verification through calibration
tests have led to the conclusion that the propellant regulator in the failed
engine had much higher discharge coefficient in its closed condition. The
reason for this could be an inadvertent error in manufacturing, which
escaped the subsequent inspection, and acceptance test procedures. This
regulator has functioned satisfactorily in all the previous 50 engines
manufactured and tested so far.

The larger flow of propellant led to higher operating pressure in the gas
generator (4.7 MPa against design specification of 3.6 MPa). Due to this
higher operating pressure of the gas generator, the water flow rate into it
got reduced. The combined effect of larger flow of propellants and reduced
flow of water led to a very high gas temperature of 1823 K against design
specification of 900 K and pressure of 4.7 MPa against the design
specification of 3.6 MPa. The very high operating pressure and temperature
resulted in the structural failure of the gas generator. The consequent
abrupt stopping of the turbo pumps that feed propellants at very high
pressures to the engines led to loss of thrust of S4 engine. The water
calibration tests conducted simulating the malfunction of the propellant
regulator hardware could closely reproduce the flight phenomenon thereby
confirming the larger flow area.

FAC has concluded that the design of GSLV is robust and recommended
implementation of strict control on fabrication, inspection and acceptance
procedures. Among others, FAC has recommended fabrication processes to be
critically reviewed and updated. It has recommended for independent
inspection of all critical dimensions of components and subassemblies by
in-house agencies. Further, long duration hot test on one out of every 20
engines fabricated has been recommended to ensure that production process is
under control. In addition, FAC has recommended strengthening the process of
clearance of launch during Automatic Launch Sequence (ALS) phase.

FAC conclusions and recommendations have been accepted and necessary action
has been initiated to implement all of them.

IMAGE CAPTIONS:

[Image 1:
http://www.isro.org/pressrelease/images/gslvf2-01.jpg (285KB)]
Sequence of Events

[Image 2:
http://www.isro.org/pressrelease/images/gslvf2-02.jpg (245KB)]
Flight Parameters

Questo è il lanciatore con cui (si spera) verrà lanciato Agile? Qualcuno ne è a conoscenza?

No, mi risulta che sarà lanciato da un vettore PSLV, secondo quanto riportato qui: http://agile.iasf-roma.inaf.it/a-status.html

Il vettore saltato è diverso.
Riporto da wikipedia

Il Polar Satellite Launch Vehicle (PSLV) è un lanciatore a cinque stadi a combustibile liquido e solido. Il primo stadio è uno dei più grandi razzi a combustibile solido del mondo. Il PLSV può trasportare 1200 kg in orbita polare sincrona con il sole.

Il Geosynchronous Satellite Launch Vehicle (GSLV) è un quattro stadi a carburante solido e liquido. Il GSLV può trasportare 200 gk di carico utile in orbita geostazionaria.

Speriamo bene!

P.S.
Per i più curiosi o novizi, avevamo parlato di AGILE qui http://www.forumastronautico.it/index.php?msg=10891#10891