The UK Space Agency is gearing up to celebrate the 50th anniversary of Britain in space: the launch of a scientific satellite called Ariel-1 in April 1962. Today the country has a thriving space sector covering science, communications, Earth observation and other applications.
But it is 40 years since a far less happy event for UK space enthusiasts: the official decision to abandon Britain’s capability to develop and build satellite launchers, whether independently or in partnership with others.
Even so, some UK rocket engineers have long believed they have something original to offer. With little government funding, they have been working for 30 years on a reusable spaceplane that could take satellites (and eventually people) into orbit after taking off horizontally like an airliner.
During the 1980s the UK’s two biggest aerospace manufacturers, BAE and Rolls-Royce, supported the project originally known as Hotol (for “horizontal take-off and landing”). But it collapsed because neither the companies nor the government were prepared to make the investment required.
Then a group of Hotol engineers regrouped and set up a new company, Reaction Engines, to pursue the project with low-key private funding that has amounted to just £22m over 20 years. Now the renamed Skylon spaceplane is on the brink of a series of key technology tests that will determine whether it can attract the £220m investment required for the next development stage.
Skylon will fly or fail on the strength or weakness of its Sabre engine, an innovative hydrogen-burning hybrid that sucks oxygen out of the air as it soars through the atmosphere at five times the speed of sound (Mach 5) – and then switches to onboard liquid oxygen when the air becomes too thin above 30km. “We have stitched the best bits of a jet engine and a rocket engine together,” says Alan Bond, a Hotol veteran who has been managing director of Reaction Engines since the company’s creation.
The testing will focus on the Sabre engine’s “pre-cooler”. At Mach 5, incoming air would be heated to 1,000C – far too hot for the engine to operate. The engineers have developed an intricate cooling device that absorbs the heat into the engine’s liquid hydrogen fuel, so the air enters the combustion chamber at -140C.
The pre-cooler is a marvel of precision engineering. It contains 55km of ultra-thin tubing, 1mm in diameter and with walls just 40 microns thick, made from a special nickel-based alloy. Secret frost-control technology prevents it freezing up when it chills damp air.
The system is not yet ready to test in flight, so Reaction Engines has fitted the pre-cooler in front of a stationary Rolls-Royce Viper jet engine in a test pit close to its headquarters at Culham Science Centre in Oxfordshire. Bond wants to prove that the pre-cooler can work, on the ground at least, in time to present the technology at the Farnborough International Air Show in July. Then the drive to sign up £220m investment will begin.
Though the money must come mainly from the private sector, government support for Reaction Engines through the UK Space Agency is building. “I can’t overemphasise the improvement in our relationship with government over the past five years or so,” Bond says. “The government has helped us gain credibility with the technical community.”
Because Skylon can travel directly into orbit, each launch should be less expensive than other vehicles that have to carry much larger amounts of liquid oxygen and jettison expendable boosters. The current design is optimised for launching large satellites but it could be adapted to carry people if demand for human spaceflight grows.
Of course taking even an unmanned Skylon into commercial production would require huge investment and years of work. The last full cost estimate in 2004 came to $12bn – comparable to Europe’s Ariane 5 rocket or Airbus A380 airliner. It is easy to take the sceptical view that this spaceplane will never fly. But there must be at least a chance that Skylon and its successors will be the centrepiece of celebrations when Britain marks its space centenary.
Rain check: what fossilised drops tell us
In an astonishing piece of geological detective work, researchers at the University of Washington have deduced important clues about the state of the atmosphere 2.7 billion years ago from the fossilised imprint of raindrops.
Their study, published in Nature, was an attempt to solve one of the mysteries of ancient Earth: why temperatures were high enough to maintain liquid water at a time when the young Sun generated much less heat than today.
“Because the Sun was so much fainter back then, if the atmosphere was the same as it is today the Earth should have been frozen,” says lead author Sanjoy Som.
It is unclear whether the ancient atmosphere captured more solar energy because it was much denser than today or because it contained higher concentrations of powerful “greenhouse gases”. To resolve the issue, the researchers analysed impressions of raindrops that fell on volcanic ash 2.7 billion years ago and are now exposed on the surface of sedimentary rocks at Omdraaivlei, South Africa. These were compared with the fresh imprints of measured droplets falling on new volcanic ash of similar composition from Hawaii and Iceland. The comparisons, combined with computer simulations of drops falling through air of varying density and pressure, showed that the ancient atmosphere was no thicker than it is today – and was probably less dense. So it must have been rich in greenhouse gases.
Asteroid one minute, mini-moon the next
The Moon has been Earth’s constant companion for more than 4 billion years. But we also have fleeting liaisons with “mini-moons” – lumps of rock that orbit our planet for a few months and then resume their previous lives as asteroids orbiting the Sun.
Through a combination of asteroid observation and supercomputer modelling, astronomers from the University of Hawaii and Paris Observatory calculated that at any given time at least one mini-moon more than a metre in diameter is in Earth’s orbit.
Mini-moons are small asteroids captured temporarily by Earth’s gravity. They do not have a neat round orbit like the permanent Moon but follow a complicated, twisted path, pulled in different directions by Earth, Sun and Moon, until the Sun tugs them back into its orbit.
A typical mini-moon stays with Earth for nine months but a few may remain in orbit for decades, according to the study which is published in the journal Icarus.
Most mini-moons are too small to be seen with Earth-based telescopes, though a car-sized one was discovered in 2006 by the University of Arizona’s Catalina Sky Survey. It departed less than a year after first detection.
“Mini-moons are scientifically extremely interesting,” says Robert Jedicke of Hawaii. “A mini-moon could some day be brought back to Earth, giving us a low-cost way to examine a sample of material that has not changed much since the beginning of our solar system over 4.6 billion years ago.”