Miguel Aguirre was the Technical Officer during the so-called Definition Phase when the concept for the GOCE mission was being developed. It was Miguel who came up with the novel idea of mounting the gradiometer’s six accelerometers in a special three-axis diamond configuration – for which he won an ESA award for outstanding achievement in 2001.
Prior to GOCE being selected for implementation at the end of 1999, Miguel Aguirre was the Technical Officer for the Definition Phase of the mission (1997-1999) providing the mission concept, a set of mission requirements, costs and risk assessment. Miguel had also been involved in several attempts to realise a space mission to map the Earth’s gravity field since 1990.
Miguel Aguirre, a Spanish national, is currently a Senior Mission Engineer for ESA’s Earth Observation Future Missions Division where he continues to design concepts for new space missions for Earth science and related applications. He was the Technical Officer during the Definition Phase of the recently approved Sentinel-3 mission.
ESA: Can you explain what was involved in formulating the concept for the GOCE mission?
We faced a completely new set of challenges when we were working on the concept for GOCE. Trying to sense the Earth’s gravity field from space means that the signal is very weak, so we had to design a satellite that was capable of orbiting the Earth at an unusually low altitude where the edges of the Earth’s atmosphere remain. This aspect of the mission forced us to come up with not only advanced orbit and attitude control techniques, but also the unusual shape of the satellite. Furthermore, we had to design a satellite that was exceptionally stable and quiet so that the measurements of gravity wouldn’t be affected by any movement of the spacecraft.
ESA: How long did it take to come up with a well-defined concept for GOCE?
There were several studies carried out at ESA for a number of different gravity-measuring mission concepts between the mid-1980s and 1996 that went under various concept names, such as the Solid Earth Mission, Aristoteles and the Gravity Explorer Mission. Subsequently, the concept for GOCE became a reality in a matter of just four years. Innovative missions such as GOCE, where new technology is being developed, naturally take time to mature.
ESA: GOCE is different from most satellites in that the instrumentation actually forms part of the satellite, does this mean that the definition phase was particularly complicated?
The nature of GOCE is such that the gravity-sensing instrument, the gradiometer, is also a tool to determine the satellite’s attitude and derives the angular and lineal accelerations. This results in a situation where the satellite is the instrument and the instrument is the satellite. The definition phase required a special perspective where the scientists and engineers involved had to have continuous interactions and a common understanding of the challenges involved. In a way the engineers had to become scientists and the scientists had to become engineers!
ESA: During the definition phase, how difficult was it to balance the scientific requirements with what is feasible from an engineering perspective?
It was clear that the cost of the mission had to fall within the strict budget set out for Earth Explorers. It was therefore necessary to play with various parameters such as orbit altitude, mission duration, satellite shape and size, instrument sensitivity and external and internal disturbances. The availability of an ‘End-to-End’ mission simulation tool and the close cooperation between science and engineering helped balance these two aspects of the mission.
ESA: Why did you win your award?
I won the award after I had proposed the idea of mounting the gradiometer arms in a three-axis special configuration. The configuration allows independent high-accuracy determination of the satellite angular acceleration and the recovery of a supplementary component of the gravity field. The result is a sizable increase in the scientific output at almost zero extra cost.
ESA: What makes GOCE different from other gravity missions such as GRACE and CHAMP?
The CHAMP mission employs similar techniques as GRACE and GOCE, but at a much lower level of accuracy. GRACE is specialised in recovering the variable component of gravity field with moderate resolution. GOCE, on the other hand, is specialised in recovering a highly accurate and very high resolution snapshot of the Earth’s gravity field that can be used as an absolute reference. GOCE will also be the first mission flying a gradiometer in space – ensuring perfect isotropic recovery of all gravity effects (without being influenced by the direction the satellite is travelling).
ESA: Where will you be for launch?
I will be at ESA’s establishment in Villafranca in Spain to take part in a media event covering the launch of GOCE.
This is one in a series of interviews with a few of the key people that are involved in the GOCE mission. Please check back as the list will be added to over the coming weeks.