By the time you read this, flight engineers controlling the SMART-1 Moon mission will know whether last week's ion engine burn was a success. Completion of the critical burn process will ensure the satellite smoothly enters lunar orbit next month.
The ion engine burn is just one of the complex challenges regularly overcome by spacecraft controllers based at the European Space Operations Centre (ESOC) in Darmstadt, Germany.
The main purpose of SMART-1 is to let space engineers evaluate a new way of propelling spacecraft on long-range missions using a Sun-powered electric propulsion system known as an ion drive. In addition, the mission will gather valuable scientific data from the Moon, including surface mineral analysis, when it enters lunar orbit on 15 November.
However getting there is part of the challenge and the craft has had to follow a spiral-up trajectory taking it on a long, looping path to the Moon. The craft has also relied on gravity assistance from the Moon itself as it orbited ever farther from Earth.
Ion drive: slow but steady
This unusual course has been dictated by the craft's ion-drive technology, which generates only weak thrust precluding a more direct path to the Moon. The advantage, however, is that the drive requires very little fuel and over time builds up a great deal of momentum.
"We have had two gravity assists from the Moon and numerous engine burns," said Octavio Camino-Ramos, Spacecraft Operations Manager for SMART-1, speaking last week in the mission's dedicated control room at ESOC during the ion drive burn.
Camino-Ramos explained that the third burn, underway for most of last week, would bring the craft within capture distance of the Moon. "The burn will last for almost 100 hours and we'll finish in the evening on 14 October," he said. "It's the last long burn, and the most critical."
Camino-Ramos gestures to a chart projected on the wall showing what could happen if, for any reason, the engine underperforms by as little as five percent.
Were this to happen, the craft and its payload could be left on a direct collision course towards either of the two nearest celestial objects: the Earth or the Moon. Otherwise, the craft could be tipped into a trajectory that would take it out into the solar system, far away from the Earth-Moon system. Any of these outcomes would be a significant challenge from which to recover.
To monitor the critical, 100-hour burn, the seven-person SMART-1 control team at ESOC is working in shifts 24 hours per day; team members watch the craft, perform data analysis, and carry out minor troubleshooting while sitting their over-night shifts.
Additional support teams at ESOC, including scientists from the Flight Dynamics team and software support engineers, as well as teams from ESTEC (the European Space Research and Technology Centre, in Noordwijk, the Netherlands) and industry specialists, are on call for quick response for unexpected events or should a new trajectory profile be required.
"Within four or five hours after the burn ends, we'll know whether we can take a little break," says Camino-Ramos, adding, with confidence, "For now, we're planning to relax a little on 15 November, after the vessel is safely captured by the Moon."
On 14 October 2004, at 18:50 CET, SMART-1 Spacecraft Operations Manager Octavio Camino-Ramos sent a message announcing: "The last long burn before Moon capture was successfully completed today. SMART-1 is now on course for Moon capture."