29 April

2001: On 29 April 2001, ESA's Maxus-4 microgravity mission was successfully launched from Esrange, just north of the Arctic Circle near Kiruna in northern Sweden.

The rocket, an 11.5-tonne solid-fuelled Castor 4B, carried a 489 kilogram payload of seven scientific experiments with their associated telemetry and video links. These were arranged in five independent modules and the whole package included 14 video cameras and one infra red camera.

Countdown and launch took place in near-perfect conditions. Maxus hurtled upwards to reach a maximum speed of about 3600 metres per second and a maximum height of 704 kilometres. From booster burn-out 70 kilometres up until atmospheric re-entry 740 seconds later, the payload was in excellent microgravity conditions. All seven science packages, housed in five independent modules, functioned perfectly, as did the mission telemetry. Scientists were able to operate their experiments interactively - in one case from as far away as Naples.

However, the parachute recovery system did not deploy properly and the payload package was badly damaged on impact with the ground.

Scientists were relieved to find that much of their experimental work was salvageable. The science modules were robust and although most of the equipment was too damaged for re-use, much data stored on board was recoverable. Many of the valuable samples produced in microgravity - silicon and zeolite crystals, for example - had survived the crash unscathed.

1997: On 29 April 1997, ESA announced that its Infrared Space Observatory (ISO) mission had found water in a wide variety of sources in the cosmos where it was previously unknown. Astronomers found water vapour in dark clouds lying towards the centre of the Milky Way. They calculated that water is abundant in our Galaxy.

Equally striking was ISO's discovery of water vapour in the outer planets, Saturn, Uranus and Neptune. As those chilly planets cannot release water from within, they probably have a supply of water coming from elsewhere in the Solar System. Since ISO went into orbit at the end of 1995, it used its unique power of analysing infrared rays coming from the Universe to identify water vapour and water ice near dying stars and newborn stars. It has also measured the water vapour steaming from Comet Hale-Bopp.

Observations from aircraft and balloons gave early hints of cosmic water, but thorough investigations had to wait for ISO's unhampered view from space. Three of the satellite's instruments, the Short Wavelength Spectrometer (SWS), the Long Wavelength Spectrometer (LWS) and the photometer ISOPHOT operating in spectroscopic mode, took part in the hunt for water.

1854: On 29 April 1854, (Jules) Henri Poincaré was born. He was a French mathematician, physicist and astronomer, who influenced cosmology, relativity and topology and was a gifted interpreter of science to a wide public. In applied mathematics he studied optics, electricity, telegraphy, elasticity, thermodynamics, quantum theory, the theory of relativity and cosmology. In the field of celestial mechanics he studied the theories of light and electromagnetic waves.