Successful guiding of Europe's first Venus spacecraft into planetary orbit

Citation

(2006), "Successful guiding of Europe's first Venus spacecraft into planetary orbit", Aircraft Engineering and Aerospace Technology, Vol. 78 No. 5. https://doi.org/10.1108/aeat.2006.12778eaf.007

Successful guiding of Europe's first Venus spacecraft into planetary orbit

Successful guiding of Europe's first Venus spacecraft into planetary orbit

Keywords: Space technology, Aerospace technology

A new and incredibly accurate, measurement system known as Delta- DOR (Plate 1) has been used by European Space Agency (ESA) for the very first time to successfully guide the Venus Express Spacecraft into orbit insertion.

Plate 1 Delta-Dor

The Delta-DOR technique was developed by the engineers at BAE Systems in Great Baddow, Essex, The University of Rome (La Sapienza) and ESA. The BAE Systems Intermediate Frequency Modem System (IFMS) equipment proved crucially important in the orbit insertion phase, the point where the spacecraft is slowed down by just the right amount so that it correctly enters Venus orbit.

The spacecraft will now take 5 days to manoeuvre into its operational 24h elliptical orbit which will see it travel as close as 250km above Venus.

“This is the very first time that ESA used our equipment with its newly developed and especially accurate Delta-DOR technique,” said BAE Systems Programme Manager Andy Baslington. “This works by measuring the difference in the time it takes signals from the spacecraft to reach two different receiving stations and how this varies over a 30min period. We can do this to an accuracy of better than a billionth of a second.”

The BAE Systems equipment is installed under the 35m deep space ground receiving antennas at Cebreros near Madrid in Spain and at New Norcia near Perth in Australia. The IFMS equipment has been specifically designed for the ESA's Earth station communication, ranging and Doppler signal processing requirements for deep space missions such as Venus Express.

The first part of the Delta-DOR ranging process is to synchronise the clocks at the two ground stations. This is done by getting them to look at the signal received from an astronomical object called a quasar (Figure 1). Quasars are compact, distant radio objects which have very well known positions in the sky. The noisy “thermal” radio signal they emit cannot normally be detected by the ESA ground stations since it is much smaller (less than 1/100) of the thermal noise generated by the stations themselves. But, when you have two ground stations whose clocks are correctly synchronised and you have taken into account the Earth's rotation, and its motion around the Sun, the signal from the quasar will be the same in the two stations but the noise from the stations usually different.

Figure 1 Delta-Dor

So, by capturing the received signal using the IFMS equipment, and seeing what time difference between the two stations is needed to maximise the similarity of the signals received, their clocks can be correctly synchronised. Once this has been done the time difference between the spacecraft signals being received at the two ground stations can be used to accurately position it, in a way similar to the normal triangulation.

Venus Express is the ESA's first space mission to Venus and was launched on a Russian rocket from Baikonur Cosmodrome in Kazakhstan last year on 9 November.

The Venus Express mission is expected to last 2 years and during its orbit the spacecraft will study the atmosphere, plasma environment and surface of the planet in detail and hopes to shed further light on the mechanisms of climate change on our own world. The main body of the spacecraft is 1.65 x 1.7 and 1.4m high onto which all the payload instruments are integrated. The solar arrays, with a collecting area of 5.7m², will provide 1,100W of power once the spacecraft is in orbit around Venus.

BAE Systems has more than 40 years of experience of European and American space projects. Currently, the twin Mars exploration rovers, Spirit and Opportunity, outfitted with BAE Systems radiation hardened RAD6000 computer brains, continue to collect important data from the surface of Mars more than 2 years after they landed and eight times beyond their design life expectancy of about 3 months.

These Mars rovers are studying minerals in rocks on the Red Planet and helping NASA search for evidence about ancient water on Mars. Having landed in January 2004, they continue to travel up to 132 feet each day and operate at temperatures as low as 21008C at night. The radiation hardened RAD6000 is a high- performance 32-bit Reduced Instruction Set Computer which operates in the heavily radiated space environment and is based on the IBM PowerPC architecture. These computers are one of a family of radiation-hardened protected computers developed and produced by BAE Systems with the support of NASA's JPL and the US Air Force Research Laboratory.