Outer casing on Rosetta orbiter that reached comet in 2014 was replaced with bullet-proof ‘vest’
The Rosetta spacecraft, which made history when it orbited a comet, was sent into space wearing a bullet-proof vest after engineers had to cut away its outer casing to save weight, it has come to light.
On the 20th anniversary of the launch, Ian Walters, who was the engineering manager for Rosetta at Airbus in Stevenage, disclosed that the orbiter was too heavy to fly and needed a haircut before setting off.
Rosetta was launched on March 2 2004 and took 10 years to reach comet 67P/Churyumov-Gerasimenko, where it released a probe which landed on the surface. Scientists compared the task with a fly trying to land on a speeding bullet.
The spacecraft needed to carry a huge amount of fuel to carry out the burn required to achieve orbit around the comet, meaning Rosetta and its scientific equipment had to be extremely light.
Mr Walters said: “Mass was really, really critical and when we counted up everything, even the nuts, bolts and washers, we realised, ‘This is going to be too heavy.’ We wouldn’t have even got to Mars, never mind the comet.
“So we had to do some crazy mass-reduction exercises and we proposed 35 to the European Space Agency and one of the ones they let us do was to cut a hole in the top floor of the spacecraft.
“It left a propellant tank sticking out, like cutting the skull off a patient and leaving the brain sticking out. The propellant tanks are very thin, only a millimetre thick, which is OK amongst most things but not against particles travelling at high speeds.”
‘State of continuous panic’
The team realised that if a high-speed micrometeorite hit the exposed tank, it could cause an explosion in space, or a catastrophic puncture that would cause all the fuel to leak out, so they came up with the idea to cover the hole with a Kevlar-like material.
“We thought all we needed was a bullet-proof vest, so we had to design a skull-cap to go over the top, and we launched it like that,” he added.
“We got used to being in a state of continuous panic, thinking that was not going to work, but in the end it did.”
The comet was moving far faster than speeds which could ever be achieved by a spaceship leaving Earth.
Rosetta needed to use the gravitational pull of Earth and Mars to act as a slingshot and allow it to pick up acceleration.
When it reached the crucial speed in July 2011, the spacecraft was put into deep-space hibernation for the coldest, most distant leg of the journey as it travelled some 497 million miles from the Sun, close to the orbit of Jupiter as the comet headed into the outer solar system.
Bounced three times
In January 2014, the spacecraft was woken up by an internal alarm clock when it was within 214 million miles of the Sun. It finally reached the comet on Aug 6 2014. The lander Philae was set down on Nov 12 2014.
However, Philae’s harpoons did not fire on landing to keep the probe anchored to the surface.
It bounced three times before settling under the shadow of a cliff, where its solar panels could not pick up enough energy.
Although the probe managed to send back some data, including images of its landing site, it ran out of power on Nov 14 and stopped communicating with Rosetta.
