Future Tech: Pluto hopper

A NASA project is working on a new way to slow down planetary spacecraft to enable an ingenious hopping dwarf planet mission


Once the speed had dropped to 50 metres per second GAC’s design would separate from the balloon to make a conventional (but economical) rocket-powered landing. Image credit: Adrian Mann

Planetary exploration missions are always a trade off of technology and cost. The very first ones just flew past or crashed into their targets, then came stationary soft landers and an increase in the use of wheeled rovers. If you’re visiting a planet you want to explore as much of it as possible but, as the Google Lunar XPrize has demonstrated, it remains prohibitively expensive and challenging to place something on the Moon, let alone on a distant planet. The problem becomes more pronounced the further away the target is, and each destination has its own challenges: Venus has a thick atmosphere but a toxic environment, Mars has lower gravity but hardly any atmosphere to aid braking. Pluto is perhaps the ultimate challenge, being so distant the trip requires the most energy of any in the Solar System. It took New Horizons, one of the fastest-ever space probes, over nine years just to get there just to fly past. However, Pluto has an advantageous combination of atmospherics and gravity that a team from the Global Aerospace Corporation (GAC) are hoping to exploit to open up Pluto for exploration.

GAC are an aerospace engineering company based in Irwindale, California. They have experience in the use of inflatable structures in space, which they are using to design an ingenious spacecraft braking system. Although Pluto’s surface pressure is only ten millionths of Earth’s, its low gravity (6.7 per cent of the Earth) means the atmosphere stretches out a long way from the planets surface. It stretches to about 1,600 kilometres (1,000 miles), or 135 per cent of the radius of the planet – Earth’s atmosphere is in the region of 12 or so per cent of its average radius. GAC have engineered Earthly balloons, inflatable space habitats and drag sails for satellites, and plan to efficiently deliver a payload to Pluto’s surface with a balloon decelerator that expands in space to something like the dimensions of a football pitch. Despite a likely approach speed of about 14 kilometres (8.7 miles) per second, the huge, lightweight cross section of the balloon should enable a spacecraft to gently decelerate into the atmosphere, needing less than 3.5 kilograms of propellant for the final soft touchdown.

Exploiting the in situ resource of the atmosphere to land almost for ‘free‘ would free up valuable payload space for a local propulsion system. GAC have a spectacular plan to reuse the rocket propulsion that the craft has to have anyway. After making its initial soft landing and investigating the area, GAC’s design will fire up its engine with the propellant not needed for landing and launch itself off across the landscape in a series of hops. In this way it would be able to collect data from a number of landing sites, at different heights through the atmosphere and take aerial photographs.

Although in its early stages, GAC propose testing sub-scale versions of the system packed into a cubesat that could be deployed from the International Space Station. This way, complete craft could be evaluated in Earth orbit before final launch to Pluto. Such an inflatable drag sail could also be useful in helping spacecraft brake into orbit around any body that has an atmosphere. In the future GAC hope to be able to develop a complete mission in collaboration with a NASA centre like JPL or LaRC, within a timeframe between ten to 15 years.

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