The thinnest, most delicate thing in space

The line between the success and failure on a space mission can be a very fine one. Very fine.

We’ve had an illustration of that in recent days with the contrasting fortunes of two European Space Agency (Esa) missions - Goce and Cryosat.

The Goce satellite is in orbit and about to start its quest this week to make the most detailed global map ever obtained of Earth’s gravity field.

Cryosat - or at least the second version of it - is heading back to the launch pad for another attempt to get its ice science off the ground following a disastrous rocket failure four years ago.

Launches are always high anxiety events.

I remember in March chatting with a member of the Goce team just 20 minutes prior to what would eventually prove to be a successful climb to orbit - and it was clear at the time that his stomach was doing some Olympic somersaults.

You could tell because he was ever so slightly struggling for breath as he spoke. We’ve all been there; we all know and sympathise with that experience.

Some of the stress comes from knowing all of the things that could possibly go wrong. One in particular on Goce caught my attention, and this concerned some spectacularly thin wires.

Goce will make its gravity map using an instrument called a gradiometer. Put very simply, it’s a box that houses three pairs of platinum blocks.

These metal blocks, or test masses as they call them, sit across the three axes of the spacecraft; and as Goce bumps and grinds through the Earth’s gravity field, the blocks sense the disturbance.

Of course that disturbance is fantastically small. It is so tiny in fact that if an electrical potential were to build up in the mechanism, the attraction between the blocks and their housing would totally swamp the measurements.

So to get over this problem, the engineers attached gold wires to the blocks to, in essence, "ground" them so that potential could not develop. But then the weight of the wire might also have introduced a bias to the measurements, so the engineers were forced to make the wires ridiculously slim and light.

The wires are just five microns (millionths of a metre) thick.

Problem solved? Yes, perhaps. But how would these astonishingly slender wires survive the violent shaking experienced on launch? If the vibration snapped them then Goce would arrive in orbit as a worthless hunk of junk.

This single puzzle kept Goce engineers engaged for 18 months while they carried out the tests needed to prove the wires were sufficiently robust.

Their confidence was well placed. All the wires did the business and Goce is now "go for science".

Cryosat, sadly, fell victim to a "circumstances beyond our control" event - the failure of its Russian Rockot launcher.

The Rockot is a converted intercontinental missile, a former war machine pressed into the civil service of space.

It had an excellent record at the time; there was nothing to suggest Cryosat might be at risk - but fail, it did.

Richard Francis, the Esa project manager on the mission, re-lives the gory detail (you can listen below).

It gives a remarkable insight into the emotions that exist in a control room when a shiny new satellite goes missing, and all the procedures to deal with an emergency that were practised in the pre-launch simulations fail to recover the situation.

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To summarise: The Rockot is a three-stage vehicle. The first stage worked perfectly.

It was in the second-stage that something went amiss. An onboard command was executed out of sequence which meant the second-stage engine, instead of shutting down at the correct moment to allow for separation with the third-stage, continued to burn.

The whole assembly - second and upper-stages, and the precious Cryosat on top - went tumbling out of control and fell back to Earth.

The descending mass was moving at about 5km per second and eventually exploded over the Arctic some 120km from the pole. It’s said a Russian meteorological station saw the fireball come in.

A fireball that had taken in the region of 75m euros and 6,000 man-hours to build.

Richard Francis recalls:

"The flight operations director, who had normally been very careful at the end of each simulation as to how we should shut down our various computers, basically said, ’turn them off anyway you want, and go’. And at that point a large number of the operations team were in tears."

Events have turned for Cryosat. The European Space Agency ordered a replacement.

We filmed the new spacecraft in Ottobrunn, Germany, last week. It was about to be packed up ready for despatch to the launch complex at Baikonur.

At the end of filming, as we turned to head out of the cleanroom door, the mission’s chief scientist Professor Duncan Wingham mused: "That’s probably the last time I’ll see it."

Let’s hope he’s wrong. Let’s hope he’ll see Cryosat-2 again soon as a fast-moving dot in the night sky, heading pole-to-pole to acquire some of the best data yet on the state of the Earth’s ice sheets.

http://www.bbc.co.uk/blogs/thereporters/jonathanamos/2009/09/thin-line.shtml