New Horizons is an old spacecraft – but it will transform our knowledge of Pluto

After travelling for nearly 10 years, NASA’s New Horizons spacecraft is finally set to fly past Pluto in humankind’s first close encounter with the dwarf planet.

But the spacecraft is at least a decade old (arguably more like two decades, as spacecraft need to use tried-and-tested components). If it had been built with today’s technology, New Horizons could have been able to send back a lot more data a lot faster. So how do space scientists cope with using old technology to make new discoveries and how will it affect the science they can do?

The search for Pluto began in 1906 when Percival Lowell started a project to find a ninth planet. Unfortunately, he died just ten years later, but the search was eventually continued by Clyde Tombaugh who found the first indications of the planet on 18 February 1930, when he noticed a tiny speck of light moving between two pictures taken in January that year.

New Horizons is actually carrying Tombaug’s ashes aboard, on his request.

Some 60 years after this discovery, a group of scientists started to work getting a spacecraft to Pluto and its moon Charon. This was being done at a time when we didn’t know about its four additional companions, the moons Nix and Hydra (discovered in 2005), and Kerberos and Styx (discovered in 2011 and 2012 respectively). We also didn’t know that Pluto had an atmosphere.

Various ideas were developed, from Pluto 350, which was a small spacecraft with only four instruments, to a large and highly capable spacecraft similar to Cassini, which is exploring Saturn and its surroundings. Ultimately these ideas didn’t get beyond the design phase.

But the race was on. By the late 1990s astronomers knew about Pluto’s atmosphere and believed it would freeze onto the surface before 2020 as Pluto moved away from the Sun. So in order to be able to study Pluto’s atmosphere it was important to get something launched quickly. Pressure from the public and the scientific community led to the selection of the New Horizons project in November 2001, which launched in January 2006.

Old technology, new horizons?

New Horizons, like any space mission, has different parts: the spacecraft, its scientific instruments and the equipment back at the mission base on Earth – such as the radio telescopes used to communicate with deep space missions.

Obviously we can continually improve the part on the ground as technology advances. This was done to support NASA’s Galileo mission to Jupiter and the Voyager mission to the giant planets. But we obviously can’t go and change anything on a spacecraft to Pluto which has been in space since 2006.

Technicians working on the New Horizons spacecraft in 2005.NASA/wikimedia

Spacecraft communicate with Earth by transmitting microwave signals to radio telescopes on Earth. The speed that we can receive images and other data gets slower the further away a spacecraft gets, just like being far from the telephone exchange can mean you get slower broadband at home. If a spacecraft took two minutes to transmit an image from Mars to Earth then it would take more than 10 minutes at Jupiter, 20 minutes at Saturn, and an hour at Pluto! This was a difficult problem that the designers of New Horizons had to overcome.

Generally speaking, higher-frequency microwaves allow us to reduce those times. If you want to map the entire surface of Pluto this is very important. At the birth of the space age, missions such as Mariner 4 which flew past Mars in 1964 used “S-band”, which is a frequency between 2 and 4 GHz (FM radio is about 100 MHz).

More than a decade later Voyager used the higher frequency “X-band”, between 8 and 12 GHz, allowing Voyager to return much more data than Mariner. Most spacecraft still use X-band (including New Horizons) but there is a move to use higher frequencies and NASA launched its first mission using “Ka-band”, 27-40 GHz, in 2009, just two years after New Horizons was launched.

If New Horizons had been able to use Ka-band it would have potentially been able to return much more data (by a factor of three-to-four times), or return a similar amount of data more quickly than the year it will take to send back all the measurements made at Pluto (to around three to four months). But this might not have led to such large improvements. The design of spacecraft is not straightforward. One small change in a particular area can affect the entire spacecraft design and mission plan.

NASA’s 70m diameter Deep Space Network antenna in Goldstone, California, is communicating with New HorizonsNASA

As for the actual instruments it is harder to know how things could have been different. The Cassini spacecraft carries a camera known as the wide-angle camera which used a telescope that was built as a spare part for Voyager. This is a camera designed in the early 1970s, put on a spacecraft designed in the 1990s, and is still returning amazing scientific images 40 years later that continue to enable us to understand Saturn’s secrets.

In a similar vein, Galileo was launched in 1989 and carried an instrument to measure charged particles around Jupiter that was based on an updated instrument from Voyager, also designed in the early 1970s. So having instrumentation that is 10-15 years old doesn’t appear to be a problem.

Space missions are mainly restricted by costs and are designed for what they are to study. If they are overly restricted by the available technology then they usually don’t get selected for launch. NASA could have spent more money on New Horizons to include more instruments, or more power to have allowed it to send back more data more quickly, but this could have resulted in a mission that was never sent in the first place or one that got there much later and missed something exciting.

The main thing is that we are continuing our exploration of the solar system. Humankind is continuing a journey that started 115 years ago in an astronomical observatory in Arizona.

Chris Arridge receives funding from the the Royal Society and Science and Technology Facilities Council. He also chairs the Solar System Advisory Panel which provides advice to the Science and Technology Facilities Council on Solar System research carried out in the UK.