Delta II firework display

On 10 January 1997 a Delta II was to have carried the first batch of satellites for the Iridium constellation, but for four consecutive days the countdown was scrubbed before finally being postponed to 19 January.7V6 In the meantime, a Delta II was lost seconds after lifting off from Canaveral on 17 January. This was the first catastrophic failure of a Delta II in 55 launches, and it caused the vehicle to be grounded for an investigation.77^8 Only 200,000 of the 782,000 pounds of thrust for launch was provided by the RS-27A core engine, the remainder being from six of the

The launch of a Delta II on 20 March 2004 with the 11th Block-IIR NAVSTAR satellite.

The explosion of the Delta II on 17 January 1997 carrying the 1st Block-IIR NAVSTAR satellite.

nine strap-ons.79 At T+13 seconds, at a height of 1,600 feet, the vehicle exploded. "Barely had the crackling noise of the solids reached the press site when onlookers saw, to their bewilderment, the rising rocket suddenly erupt into a massive fireball," as one eye-witness put it.80 For the next 10 minutes, 250 tonnes of hardware and propellant rained over a radius of 3,000 feet around Pad 17A, extending about half way to the press site, near the old 'Mercury Control' building.81 The damage to the umbilical structure was minimal, but since the second stage had been loaded with aerozine and nitrogen tetroxide, which are both toxic, the 73-member launch team in the pad blockhouse donned respirators in case fumes penetrated the building. This proved to be a wise precaution as a piece of debris struck a cable track and provided a route for smoke to seep into the building. Worse off, however, were the 20 cars parked adjacent to the blockhouse. Owing to the trend towards larger, more

An artist's impression NAVSTAR satellite.

Block-IIR

powerful strap-ons for the Delta II, it was decided to abandon the blockhouse in favour of McDonnell Douglas's Delta Launch Control Center located in the 1st Space Launch Squadron's Operations Building, which was already under construction some 4 kilometres off. The equivalent facility for SLC-2 at Vandenberg was 13 kilometres from the pad, and the blockhouse was occupied only for non-hazardous activities. In April 1993 the Air Force had awarded the company the contract to launch the NAVSTAR Block-IIR series. As it happened, this Delta II had been carrying the first of these satellites.82 However, its loss did not impair the GPS service because the satellite was to have replaced an older one that was still functioning.

A series of photographs by Carleton Bailie for Aviation Week & Space Technology showed black smoke venting from the side of one of the solid strap-ons about six

_ seconds after it ignited, implying a flaw in its casing.83,84 The Air Force investigation, led by Colonel Ronald J. Haeckel, found from the telemetry that the self-destruct system had intervened at T+13 seconds, when it detected a vehicle distortion a fraction of a second after what seemed to be the explosion of a strap-on.85 In view of the fact that more than 300 such strap-ons had flown successfully, this failure was unexpected.86 Although the investigation did not identify the definitive cause, it found damage to fibres in the outer five composite layers of the motor in question, and concluded that a fracture had indeed developed in its casing six seconds after lift-off.87 In an effort to preclude a recurrence, it was decided to conduct ultrasonic inspections of the new motors and to revise their handling procedures. The 14-tonne motor had been transported in a horizontal configuration on a 'travelling trunnion' system on which one of the supports was close to that part of the casing that had failed. This was considered significant as it was only the second time that this device had been used. The procedure was revised to ensure that the casings of the 36-foot-long, 3.3-foot-diameter graphite-epoxy structures were not subjected to anomalous stresses.8^89

An artist's impression NAVSTAR satellite.

Block-IIR

A close run thing

With the Delta II reinstated on 5 May 1997, a vehicle from Vandenberg put the first five Iridium satellites into low polar orbit.90 In fact, this deployment was threatened by a fault in the attitude control system of the second stage.91 About an hour into the mission - having maintained its attitude to release the first three satellites one at a time - the pressure in its gaseous nitrogen tank started to decrease markedly, and was nearly depleted by the time the fourth satellite was released. Although the vehicle was no longer under positive control and was slowly tumbling, the final satellite was successfully deployed. The Delta II returned to service at Canaveral on 20 May with Thor 2 for Norway.92*93 It was hoped to make one launch per month for the next 24 months to re-establish the schedule drawn up prior to the grounding.

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