In recent years, as APL has shift from a dependency on naval research contracts, the lab has sought to carve out a new role as a growing rival to NASA's Jet Propulsion Laboratory for the design and management of Solar System exploration missions. Most notable among the Lab's recent success was the NEAR asteroid mission to Eros which was by all accounts a stunning success.

Moreover, in these early days as the story of what went wrong from with Contour begins to take shape there are several reasons why APL will face tough questioning as its seeks to recover from the loss of Contour and go on to manage more missions to deep space - not least of which includes a possible mission to Pluto in 2006. Among the many issues facing the investigation panel are three critical points:

• Firstly, is the fact that the probe was out of range of Earth tracking stations when it ignited its STAR-30BP solid motor to boost itself out of Earth orbit making it extremely hard to diagnose the cause of the failure.

• The possibility that the unknown cause of the failure might have been connected with negligence or poor design management and testing by APL.

• And thirdly, the fact that the failure occurred just as APL's "New Horizons" Pluto spacecraft - whose avionics are largely based on Contour - is confronting the key moment of its struggle for last-minute Congressional approval against the wishes of both NASA headquarters and the White House.

Sources connected with APL report that, while the probe's telemetry wasn't monitored during the unsuccessful burn, it was observed by various instruments of the U.S. military (orbiting and/or ground-based). According to these sources the motor's burn appeared normal until 2 or 3 seconds before its scheduled end, at which point a sudden "flare" appeared almost 10 times brighter in the infrared. This meshes well with telescopic observations of Contour's three visible fragments, which appear to be in the solar orbit that would have resulted from a burn cut 3 seconds short.

There seem to be only two possible sources in the craft for such an explosion: a rupture in the STAR motor itself, or an explosion in Contour's own supply of hydrazine fuel for its maneuvering and attitude control thrusters.

The thrusters, however, had been used repeatedly for a long series of maneuvers during the three weeks the craft spent in elongated Earth orbit before the escape burn, and (like Contour's other systems) had worked perfectly.

Moreover, they were not fired during the burn itself - although they would have been used afterward to despin the craft so that it could switch back from spin stabilization to active 3-axis stabilization.

In Contour's design the STAR motor is nestled inside the craft's structure, raising suggestions that - if Contour's thermal design and testing had been seriously flawed - heat generated by the solid motor might have raised the temperature of the main hydrazine tank enough to trigger its ignition or vaporization.

APL sources, have however told SpaceDaily that this possibility had indeed been considered from the very start of design work on the craft - and that tests had shown that the heat pulse from the STAR burn would have taken an hour to spread fully into the craft, and would never have raised the temperature of any part of it by more than 20 degrees Centigrade - not nearly enough to destabilize its hydrazine.

This would seem to indicate that the explosion did indeed occur inside the STAR motor itself. There are, however, two odd features of this.

First, Thiokol's series of STAR motor models, manufactured for decades, are very reliable - the STAR-30BP motor has been used routinely since 1984, with only two failures in 86 missions. Nor do STAR solid motors seem to deteriorate from prolonged exposure to the space environment; one STAR-48 motor worked perfectly after 15 months in space to brake the Magellan spacecraft into orbit around Venus.

Second, it would seem odd that the explosion occurred at the very end of the burn, just when the intense pressure inside the motor was tapering off. However, yhe latter makes more sense on closer examination.

Solid motors have exploded near the end of their burn on several previous space missions - including Syncom 1 (the very first attempt at a geosynchronous comsat) back in February 1963, and the Surveyor 4 lunar soft lander in July 1967 (which lost contact with Earth at just the moment when its accelerometers indicated that the STAR-37 motor, that had served as its main retrorocket, was starting to drop off in thrust less than 2 seconds before the scheduled end of its burn).

The reason is that a solid motor's thrust starts to drop at the time when its solid fuel has been completely consumed back to the motor's chamber wall in many places, leaving many isolated patches of fuel which are supposed to remain bonded firmly to the wall until they are done burning.

But if one breaks loose, it can instantly be blasted into the motor nozzle, plugging it long enough to create an explosive pressure buildup inside the motor.

Given this danger. solid motors are carefully radiographed during assembly to remove the possibility that flaws exist in the glue bonding the solid fuel to the motor wall, but occasionally flaws can slip through.

Another commentator has suggested that, since Contour spent three weeks in Earth orbit, it might have passed several times through Earth's shadow, leading to major changes in the craft's temperature that might have produced repeated tiny contractions and expansions in the STAR motor's metal wall, thus loosening the glue bonding the fuel to it.

However, APL sources have told SpaceDaily that the spacecraft's elongated Earth orbits were deliberately designed from the start so that it would never fly through Earth's shadow at all, since such periods of cold and dark might have harmed the craft's systems in other ways.

If so, then - while the cause of the failure is still far from certain and will obviously require a detailed inquiry - it would seem likely that it was indeed due to sheer bad luck: a slight flaw in that particular STAR motor that slipped past inspection, rather than negligence in the Contour craft's design and testing by APL.

Exploration Horizons Beyond Contour
If so, this would be very good news indeed for New Horizons, whose approval would be seriously endangered by any evidence of APL negligence - especially since, unlike Contour, it would carry 7 kg of highly radioactive plutonium-238 for power.

Complicating matter is that it's unlikely that the official inquiry into the Contour failure can be completed before the House votes on whether to approve the Pluto probe; but there would be nothing to keep Congress from approving initial funds for New Horizons - that could be withdrawn later if the inquiry did actually give cause to doubt the probe's reliability.

It should also be noted that New Horizons differs very significantly in design from Contour. While its avionics are substantially based on Contour; its body shape, and mechanical and thermal structures are radically different in design, and the engineering team that designed it is more closely associated with APL's highly successful NEAR asteroid rendezvous craft.

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