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How to build a space computer

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QinetiQ’s Koen Puimège explains the challenges involved in building the computer responsible for guiding the European Space Agency’s IXV ‘Space Taxi’ back to earth.

IXV On board computer

QinetiQ’s modular computer is designed specifically for small autonomous satellites and re-entry vehicles

Guiding a spacecraft through its critical re-entry phase is never a simple task. As it hits the atmosphere at 27,000 kilometres per hour, experiencing temperatures of up to 1,800 degrees Celsius, the craft must maintain the perfect angle and trajectory or risk breaking into pieces.

The parachute and flotation devices must deploy at the right times and valuable data must be collected, communicated and stored.

Many spacecraft have achieved this over the years, but when we were asked to develop an on-board computer to make these things happen for IXV, the brief demanded we overcome a unique set of challenges:

Power efficiency

The mission scenario of re-entry through the atmosphere does not allow solar panels to be used to generate power, so all power for the 100-minute flight is provided by a single pre-charged battery.

To avoid draining the battery, the computer, which is always on throughout the entire mission, must work as efficiently as possible. We designed IXV’s to operate on just seven watts of power.

To put this into context, a home computer typically consumes between 65 and 250 watts and a standard computer for a big satellite around 30W.

QinetiQ’s earlier work in pioneering small autonomous satellites means we have the technology in-house that has the optimal balance between the required high calculating power for unmanned, autonomous missions and very low power consumption.

Low mass, small size

For the Vega rocket to overcome the earth’s gravitational pull and set IXV on its suborbital path, the mass of everything on board must be kept to a minimum.

In addition, the IXV vehicle is designed, for cost efficiency reasons, to be approximately 10 times smaller than the US Space Shuttle, so everything had to be scaled down to meet this objective.

The IXV computer is based on technology we developed for ESA’s tiny Proba-2 satellite, meaning it weighs in at less than seven kilograms.

Processing power

Despite its low energy requirements, low mass and small size, the IXV computer needs to produce enough calculating power to simultaneously co-ordinate its many crucial tasks.

A typical spacecraft computer processes 10 million instructions per second (10 MIPS), while the IXV computer runs at five times that, delivering 50 MIPS. The computer responsible for the early Apollo missions generated around 2 MIPS.

Reliability

A very high level of reliability is required to ensure the computer operates effectively throughout the mission, guaranteeing a safe return flight.

The mission’s short duration means there is no time to reconfigure mid-flight during critical phases, so we developed a computer with a reliability rate of 99.997%.

It is also essential that the backup systems react quickly, so we have ensured a reboot can take place in 9 seconds, compared to the 60 seconds typical for the reboot of a satellite control system.

The future

Though our work on Proba-2 and IXV we have developed an adaptable computer that uses a modular architecture to keep costs down without compromising on performance.

We hope to apply this technology to many more small autonomous satellites and re-entry vehicles in the future.

Read the press release here

Related stories:

Satellite formation flying: why it’s challenging, but important

QinetiQ’s Proba-2 satellite to beam solar eclipse images back to earth

The post How to build a space computer appeared first on QinetiQ Blog.


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