Landing on Pluto may just be a hop, skip and jump away

There are plenty of crazy ideas for missions in the space exploration community. Some are simply better funded than others. One of the first ways to fund the crazy ideas is NASA’s Institute for Advanced Concepts. In 2017 and again in 2021, it funded a mission investigation into what most space enthusiasts would consider only a modestly ambitious goal, but what those outside the community might consider bizarre: a landing on Pluto.

Two key questions stand out in the mission’s design: How would a probe arriving at Pluto slow down, and what kind of lander would be useful on Pluto itself? The answer to the first is one that is becoming increasingly common in planetary exploration missions: aerobraking.

Pluto has an atmosphere, albeit sparse, as confirmed by the New Horizons mission that zoomed past in 2015. One advantage of the small planet’s relatively weak gravity is that its low-density atmosphere is almost eight times larger than Earth’s, making for a much bigger target. for a fast incoming aerobraking craft to target.

Much of NIAC’s Phase I project focused on the details of that aerobraking system, called the Enveloping Aerodynamic Decelerator (EAD). Combined with a lander, that system forms the ‘Entrycraft’ around which the mission is designed. Ostensibly it could alternatively contain an orbiter, and there are plenty of other missions discussing how to place an orbiter around Pluto. Therefore, the main thrust of this article is to focus on a lander.

After aerobraking and slowing down to several tens of meters per second, from 14 km/s during the interplanetary cruise phase, the mission would drop the payload from the lander, then rest on the surface, and then take off again under its own power. The answer to the second question, what kind of lander would be useful on Pluto, is: a hopper.

Hoppers have become increasingly popular as an exploration tool everywhere from the moon to asteroids. Some obvious benefits include visiting a wide range of interesting scientific sites and not having to navigate tricky obstacles on land. Ingenuity, the helicopter that accompanied Perseverance, paved the way for the idea, but in other words, the atmosphere is not compact enough to support a helicopter. So why not use the current favorite method of almost all spacecraft: rockets?

A hopper would fire its onboard thrusters to reach the area on Pluto’s surface and then land elsewhere. It could then do some research in its new location before taking off and do that again somewhere else.

NIAC’s Phase I final report describes five key scientific objectives of the mission, including understanding surface geomorphology and conducting a number of in-situ chemical analyses. A hopper structure would enable these goals much better than a traditional rover at a relatively low weight cost, because Pluto’s gravity is so weak.

Other objectives of the report include mathematical calculations of the trajectory, including the aerobraking itself and the stress and strain it would place on the materials used in the system. The authors, who work primarily for Global Aerospace Corporation and ILC Dover, two private companies, also updated Pluto’s atmospheric models with new New Horizons data, which they then fed into the aerobraking model they used. Designing the lander/hopper, integrating all scientific and navigation components and estimating their weights were also part of Phase I.

The original launch window for the mission was planned for 2029 in 2018, but now, despite receiving a Phase II NIAC grant in 2021, that launch window seems wildly optimistic.

Because the mission would require gravity support from Jupiter, the next potential launch window would be 2042, with a lander eventually reaching Pluto’s surface in the 2050s. That later launch window is likely the only feasible one for the mission, so we may have to wait almost 30 years to see if it will become a reality.