One of the great things about CubeSat designs is that they constrain the engineers who design them. Constraints are a great way to develop novel solutions to problems that might otherwise be ignored without them. As CubeSats become increasingly popular, more and more researchers are looking at how to get them to do more with less. A paper from 2020 contributes to that by designing a 3U CubeSat mission that weighs less than 4 kilograms to perform a fly-by of a Near Earth Asteroid (NEA) using entirely off-the-shelf parts.
The research, carried out by a team based at the Delft University of Technology, had several mission requirements they were trying to meet. Some were standard like it had to have a propulsion system and a way to get data back to Earth. However, some were more challenging – it had to weigh less than 4 kg, it had to fit into a 3U CubeSat body (which measures (100mm x 100mm x 340.5mm), it had to perform its mission in less than 650 days, and, perhaps the most technically challenging goal – it has to “exploit a fully-autonomous navigation strategy.”
First, let’s look at the mission design. Since there are around 35,000 known NEAs, mission designers would be spoiled for choice. However, getting to one with a relatively limited propulsion budget (since propellant increases the weight – one of the design constraint limits) and finding the right one would require extensive searching of the JPL Small-Body Database.
Once an NEA has been selected, the mission designers could plan the optimal trajectory. However, to meet the requirement of an autonomous navigation strategy, the CubeSat itself will have to find its way to the asteroid and enact any course corrections along the way. This could be extremely difficult, given the low brightness of many of the target asteroids and how that brightness might change based on what side of it is facing the Sun and what angle the CubeSat is approaching it from. The scientific payload, including a visible light and IR camera, would have to work in tandem with a micro star tracker to ensure the trajectory is optimal for scientific data collection.
That data collection might only last a few minutes, as the limited propellant for the mission would require it to be a fly-by rather than an orbit. The resulting image might be as small as a 6 x 6 pixel image for a 300m diameter asteroid. This would provide orders of magnitude with more resolution than ground-based observations for most. Still, it would not be enough to get into the details of mass and composition that planetary protectors and asteroid mining enthusiasts alike would most desire.
Any new information is better than no information, though, and the simplicity of the design for this mission’s hardware makes it relatively inexpensive and, therefore, mass-producible. It consists of six major sub-systems – the “payload,” which is essentially a visible light and infrared camera; the propulsion system, which is a microjet ion propulsion engine; the attitude determination and control system (ADCS), which helps navigate; a communication system that uses an X-band antenna to communicate back to the Deep Space Network infrastructure, and a power system that would involve deployable solar panels.
Credit – NASA Jet Propulsion Laboratory YouTube Channel
Overall, the mission met the goal of fitting entirely into a 3U package and came in at 3.8kg using off-the-shelf components. However, thermal management systems and radiation shielding were not considered in the design. Other challenges, like getting time on the already overstretched Deep Space Network ground antennas, are left for another paper.
But if nothing else, this paper proves that it is possible, on paper at least, to design an inexpensive mission to collect data on an asteroid and that that mission can be replicated hundreds or even thousands of times at relatively low cost. As CubeSats gain more and more capabilities and more and more traction, and as launch costs get lower and lower, it’s becoming increasingly plausible that someday, a system like this might very well make its way past an asteroid and send data back that we otherwise wouldn’t have gotten.
Learn More:
Casini et al – Novel 3U Stand-Alone CubeSat Architecture for Autonomous Near Earth Asteroid Fly-By
UT – A Pair of CubeSats Using Ground Penetrating Radar Could Map The Interior of Near Earth Asteroids
UT – A Mission To Find 10 Million Near Earth Asteroids Every Year
UT – Swarms of Orbiting Sensors Could Map An Asteroid’s Surface
Lead Image:
ESA’s Hera Mission is joined by two triple-unit CubeSats to observe the impact of the NASA-led Demonstration of Autonomous Rendezvous Technology (DART) probe with the secondary Didymos asteroid, planned for late 2022.
Credit: ESA