Destination Pluto: new horizons in engineering

Diversity is key in a team operating a mission as challenging as New Horizons, said Alice Bowman, the Mission Operations Manager of the first spacecraft to travel to Pluto.

At her talk at the Institute of Technology of the University of Lisbon, on October 7th, Bowman told the story of an exciting journey to the far reaches of our solar system, but also described the difficulties of aiming at a planetary body that is unlike any of the other worlds explored so far.

Alice Bowman

Alice Bowman, New Horizons Mission Operations Manager.
Credits: NASA/Joel-Kowsky

Approved in 2000, the New Horizons programme had its spacecraft launched six years later. It took almost a decade to travel nearly five billion kilometres across the solar system before reaching Pluto. To remain focused on its goal for such a long time, Alice Bowman’s team had to demonstrate high levels of commitment and patience, she said. But the success of a mission posing so many novel challenges also depended on the diversity of thought within the team, Bowman added.

When New Horizons was launched, back in 2006, the best picture we had of Pluto was a bunch of pixels taken by the Hubble Space Telescope. Pluto lost its place as a planet when the spacecraft was already on its way. In the meantime, two new moons were discovered orbiting Pluto, and Bowman’s team feared that other smaller and unanticipated objects could damage the spacecraft as it approached the Pluto system.

To tackle the large unknown surrounding Pluto and its moons, the team Alice Bowman managed had to think outside the box and come up with alternative ways to solve problems. Bowman herself has a diverse background. In her early career she researched on drug-delivery systems, computer simulations and infrared detectors for astronomy.

When New Horizons was launched, back in 2006, the best picture we had of Pluto was a bunch of pixels taken by the Hubble Space Telescope

At the Mission Operations Center, located in the Applied Physics Laboratory of Johns Hopkins University, Bowman managed a team whose tasks included responding to abnormal conditions detected in the spacecraft, calling experts when needed, accepting input from scientists and engineers for calibrations, and running computer simulations of the spacecraft behaviour (including faulty situations). These were critical to test commands before actually sending them through radio waves to be run by the spacecraft software.

During the journey, the team had about eight hours per day of contact with the spacecraft, but when it got closer to Pluto, the team became 24 hours on call. The challenges were manifold and started to pop up long before the launch in 2006. The distance of Pluto from Earth was at the root of most of them.

That distance is not constant. On its very eccentric orbit around the Sun, which the dwarf planet completes every 248 Earth years, Pluto was at its closest distance from our star (and the Earth) in 1989. After that it started its more than a century-long journey into the winter, when it is believed its atmosphere will freeze. Scientists wanted to reach Pluto in time to study its atmosphere and within a relatively short period. This is the reason why this mission was undertaken now.

New Horizons trajectory
New Horizons trajectory across the solar system
Source: Press kits available at http://pluto.jhuapl.edu

In order to arrive at Pluto as fast as possible, the New Horizons spacecraft had to be lightweight enough to benefit from the thrust given by the rocket that launched it. The use of solar panels, commonly employed as power source in other spacecrafts, was out of question. At the orbit of Pluto, the light from the Sun is one thousand times fainter than on Earth and solar panels would have to be huge, Bowman said. The mission engineers opted for a battery that produces electricity from the radioactive decay of plutonium dioxide. When the spacecraft reached Pluto, the battery was supplying 202 watts of power. It was a true challenge to the engineers to design a spacecraft that could run with the same energy consumed by two 100-watt light bulbs.

New Horizons spacecraft
The New Horizons spacecraft
Source: Press kits available at http://pluto.jhuapl.edu

Due to its only 478 kilograms and the mighty Atlas V rocket that launched it, New Horizons became the fastest object to leave the Earth orbit, reaching a speed of about 58,000 km/h, nearly 47 times faster than the speed of sound. It crossed the orbit of the Moon just nine hours later and in February 2007 was passing near Jupiter, where scientific instruments were tested and calibrated.

As the years passed by and the spacecraft got further away from Earth, the delay in the communication between the operations centre and the spacial observatory increased. Even at the speed of light, radio waves have to travel 4 hours and 25 minutes to cross the distance that separates Earth from Pluto. Whatever happened at the spacecraft position, you could only know four and half hours later.

Due to its only 478 kilograms and the mighty Atlas V rocket that launched it, New Horizons became the fastest object to leave the Earth orbit

“Nothing happens quickly,” said Bowman. Once you had a command that was thoroughly tested in the simulation environment and ready to be sent, you would have to wait an equal amount of time before it would actually be performed by the New Horizons systems. Within that time the spacecraft was travelling 231,000 km from the initial position. Radio antennas that transmitted the messages had to point to the place where the New Horizons would be 4 hours and 25 minutes later.

The data collected during the closest approach to Pluto is yet being downloaded at a rate of 2,000 bits per second, about one thousand times slower than traditional cable modems on Earth. This rate is due to the distance and the relatively small antenna on the spacecraft. It is estimated that the whole of the information stored in the spatial observatory will have reached the Earth by late 2016.

Trajectory beyond Pluto

New Horizons trajectory beyond Pluto
Source: Press kits available at http://pluto.jhuapl.edu

But the story isn’t over. Scientists will have plenty of material to study for at least 10 years, said Bowman. Moreover, New Horizons is now beyond Pluto and headed to meet, by early 2019, one of the objects of the Kuiper Belt, the cloud where comets come from. Scientists expect to be working on data from the New Horizons spacecraft well into the third decade of this century.

Have your say