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Humanity’s quest to explore the unknown has led us to reach for the stars. With advancements in space technology, we have embarked on ambitious missions to explore deep space using smaller spacecraft known as microsatellites and CubeSats. These miniature wonders are revolutionizing space exploration, offering cost-effective alternatives to traditional satellites while presenting unique challenges and opportunities. In this article, we will delve into the challenges faced and the exciting technologies embraced in the realm of deep-space microsatellites and CubeSats.
Microsatellites, Cubesats and Nanosatellite Technology: Advancements, Applications and Market Trends
Since the introduction of the CubeSat standard in the early 2000s, there has been a proliferation of nano-/small microsatellites in low Earth orbit, with 100–300 or more launched annually and at
a growing rate (according to reports from SpaceWorks and Euroconsult). CubeSats have reduced entry-level costs for space missions in low Earth orbit (LEO) by more than an order of magnitude.
With more piggyback opportunities, platform capabilities and small payloads have rapidly advanced to a level that are suitable for real operational missions. Niche commercial applications are emerging based on operating multiple CubeSats together in distributed systems, e.g. constellations and swarms.
In recent years, micro- and nano- satellites have also started venturing into deep-space, beyond low Earth orbit, taking advantage of ride-share opportunities. Now microsatelites and cubesats are being developed beyond LEO out to GEO and cis-lunar and deep space. Piggyback opportunities for CubeSats to lunar orbit and interplanetary space are already becoming available, and innovative miniaturized technologies are being developed to overcome the severe technical challenges of deep-space missions.
Scientific and Commercial Applications: Expanding Possibilities
Deep-space microsatellites and CubeSats are not only paving the way for scientific exploration but also opening doors for commercial endeavors. These miniature spacecraft are being utilized for a wide range of applications, including asteroid mining, space tourism, and even interplanetary internet connectivity. The lower costs associated with these small satellites are democratizing access to space, empowering researchers, entrepreneurs, and educators to engage in space-based activities like never before.
Deep Space Missions
PROCYON (Proximate Object Close flyby with Optical Navigation), the first micro-sat deep-space mission (67 kg launch mass), and the first deep-space mission by a University, was launched in 2014 as piggyback of Hayabusa. It escaped the Earth gravity and returned one year later for a distant flyby. PROCYON validated a fully capable bus, with low, middle and HG antennas, reaction wheels and cold gas jets, electric propulsion systems, telescope and cameras. PROCYON was proposed, developed, and launched in just about 14 months, and most of the mission team consisted of students of the University of Tokyo.
EQUULEUS and OMOTENASHI are both 6U CubeSats that were launched on the Artemis 1 mission on November 16, 2022. EQUULEUS is a scientific mission that will study the plasma environment around the Earth-Moon Lagrangian point L2. OMOTENASHI is a technology demonstration mission that will test the feasibility of using a small spacecraft to land on the Moon.
EQUULEUS is a 6U CubeSat that weighs approximately 10 kilograms. It is powered by solar panels and has a communications system that can transmit data to Earth. The spacecraft will use its propulsion system to reach L2, where it will orbit for at least one year. During its mission, EQUULEUS will study the plasma environment around L2 using its two instruments: a Langmuir probe and a plasma wave experiment.
OMOTENASHI is also a 6U CubeSat that weighs approximately 10 kilograms. It is powered by solar panels and has a communications system that can transmit data to Earth. The spacecraft will use its propulsion system to reach the Moon, where it will attempt to land on the surface. If successful, OMOTENASHI will be the smallest spacecraft to ever land on the Moon. The spacecraft will carry a number of instruments that will measure the radiation environment around the Moon and on the lunar surface.
The EQUULEUS and OMOTENASHI missions are important milestones in the development of CubeSats for deep-space exploration. These missions demonstrate the ability of small spacecraft to conduct important scientific research and to test new technologies. As technology continues to improve, CubeSats are likely to play an increasingly important role in the exploration of deep space.
One of the most successful deep-space missions using a microsatellite was the NASA Deep Impact mission. Deep Impact was a spacecraft that collided with a comet in 2005. The mission was designed to study the composition and structure of comets, and it was a major success.
Another successful deep-space mission using a CubeSat was the Planetary Society’s LightSail 2 mission. LightSail 2 is a spacecraft that is powered by sunlight. The mission was designed to test the feasibility of using solar sails for deep-space propulsion. The mission is still ongoing, and it has already made significant progress.
The success of these missions and others has helped to pave the way for future deep-space missions using microsatellites and CubeSats. These small spacecraft offer a number of advantages over their larger counterparts, and they are becoming increasingly capable of conducting complex scientific missions. As technology continues to improve, microsatellites and CubeSats are likely to play an increasingly important role in the exploration of deep space.
Recent Challenge
NASA has decided to terminate the Lunar Flashlight mission due to propulsion system issues that prevented the probe from entering a stable orbit around the moon. The mission aimed to search for ice deposits in the lunar southern polar region using an infrared ice-detecting laser reflectometer. Unfortunately, the propulsion system’s weak and inconsistent thrust hindered the spacecraft’s orbital operations. NASA suspects that debris might have accumulated in the fuel lines, potentially caused by metal fragments or shavings from the 3D-printed structure.
Although the mission did not achieve its primary objectives, it served as a technology demonstration and did provide some positive outcomes. The Lunar Flashlight mission utilized the Advanced Spacecraft Energetic Non-Toxic (ASCENT) monopropellant, which aims to replace the highly toxic hydrazine propellant. However, the “green” propellant system did not perform well in this instance.
Despite the setbacks, certain components of the Lunar Flashlight exceeded expectations. The mission successfully tested the Sphinx flight computer, a low-power computer designed by NASA’s Jet Propulsion Laboratory to withstand deep space radiation. The radio module called Iris was also demonstrated, enabling precision navigation and tracking for landing on celestial bodies within the solar system.
The Lunar Flashlight was launched as a rideshare payload on a SpaceX Falcon 9 rocket, which also carried the ill-fated HAKUTO-R lander from Japan’s Ispace. Although the Lunar Flashlight mission did not achieve its intended goals, it benefited from the cost-effective opportunity to hitch a ride to space with another mission.
Currently, the satellite is beyond the moon’s orbit but will pass within 40,000 miles (65,000 kilometers) of Earth on May 17 before entering a solar orbit. NASA maintains communication with the probe and is assessing potential future uses for the mission despite its inability to achieve a stable lunar orbit.
Mission Design
Mission design for small deep-space spacecraft, such as CubeSats, presents unique challenges due to their limited orbit control capabilities. Despite their small size, these spacecraft need to reach similar destinations as larger satellites. Mission design activities for small satellites are complex and critical, relying on expert manpower and advanced tools. Currently, mission design for small satellites is mostly carried out by space agencies, which can be costly and limit participation by new stakeholders. To reduce costs and enable broader participation, the development of open-source and ITAR-free mission design tools is essential. These tools would facilitate access to mission design expertise, promote collaboration, and democratize deep-space exploration by allowing more organizations and individuals to contribute to the design and planning of small spacecraft missions.
Operations:
Like mission design, operations for a small satellite can be as complex and expensive as for a large mission. Operations of deep-space missions are mostly carried out with a man-in-the-loop approach. Autonomy would reduce mission costs, but it is currently not implemented to its full potential on expensive missions because of the associated risk. Deep space missions will benefit from automation efforts in the near-Earth environment currently being developed for swarms and formations. Deep-space nanosats, however, must rely on an even higher degree of autonomy because of the limited ground station availability.
Support towards the development of autonomous operation and navigation technologies would enable deep-space exploration by small satellites, and eventually reduce the cost of large-class missions as well. Furthermore, advancements in navigation systems, including precise star trackers and deep-space GPS, are enhancing the accuracy and reliability of these small explorers as they traverse the cosmic landscape.
Architecture
The European Space Agency’s (ESA) General Studies Programme includes investigations into lunar and interplanetary CubeSat mission concepts. These missions have been designed with two different architectures: the mother-daughter system and the stand-alone system.
In the mother-daughter architecture, CubeSats are deployed from a larger spacecraft, typically referred to as the “mothercraft,” once it reaches its target destination, such as lunar orbit or a near-Earth object (NEO). This architecture offers certain advantages. Since the CubeSats are carried by the mothercraft during the cruise phase, they can benefit from the resources and accommodation provided by the larger spacecraft. This includes power, thermal control, and other resources required for operation. Additionally, the mothercraft handles the long-range communication with Earth ground stations, allowing the CubeSats to transmit data via inter-satellite links. The mother-daughter architecture simplifies the technical challenges associated with propulsion, long-range communication, and surviving the deep-space environment.
On the other hand, the stand-alone system involves CubeSats that operate independently without a mothercraft. In this scenario, the CubeSat must address the technical challenges associated with propulsion, long-range communication, and surviving the deep-space environment on its own. These challenges require the identification and/or development of suitable technology solutions. For example, the stand-alone CubeSat needs to have its own propulsion system to maneuver in space, employ robust communication systems for long-range communication with Earth, and incorporate suitable designs and materials to withstand the rigors of the deep-space environment.
Both architectures have their own merits and challenges. The mother-daughter architecture offers the advantage of leveraging the resources and infrastructure of a larger spacecraft, making it less demanding for the CubeSats themselves. However, it requires coordination and integration between the mothercraft and the CubeSats. On the other hand, the stand-alone system provides more autonomy and flexibility to the CubeSat but necessitates developing or adapting technologies specifically tailored for deep-space missions.
Technology Challenges
Miniaturization: Opening New Frontiers
The miniaturization of satellites has been a game-changer in the space industry. Traditional satellites can be enormous and costly, but microsatellites and CubeSats are significantly smaller, often measuring less than a cubic foot. This reduction in size enables rapid deployment, lowers launch costs, and provides flexibility in mission design. However, it also poses challenges such as limited power availability, payload capacity, and reduced communication capabilities.
CubeSats require compact and lightweight sensors to perform scientific measurements. Advancements in sensor miniaturization are required to enable a wide range of scientific experiments and data collection.
Long-Duration Operations: Surviving in the Void
Deep-space missions come with their own set of challenges. Unlike satellites in Earth’s orbit, deep-space microsatellites and CubeSats must withstand harsh radiation, extreme temperature fluctuations, and prolonged periods of isolation. This can affect their electronics and performance, hence Radiation tolerance is a critical factor for deep-space missions. The development of radiation-tolerant parts and components can enhance the durability and longevity of CubeSats in harsh space environments.
Engineers are developing innovative solutions, including radiation-hardened components, advanced thermal management systems, and robust communication protocols, to ensure the survival and functionality of these small explorers in the unforgiving depths of space.
Communication: Bridging the Gap
CubeSats operate in remote and challenging environments, making reliable communication a significant concern. Maintaining reliable communication with deep-space microsatellites and CubeSats is critical for mission success. However, the vast distances involved pose significant challenges.
The democratization of deep-space exploration may necessitate the support of numerous nanosatellites, particularly during the launch and early operation phase. For instance, the upcoming EM-1 mission will deploy 13 CubeSats, and most of them will need to perform a critical maneuver within two days of deployment. This maneuver requires downlink and uplink capabilities for operations and precise orbit determination using two-way Doppler and Delta-Differential One-Way Ranging (DDOR) techniques.
There is a need for high-bandwidth communication systems and efficient power management to facilitate data transmission over long distances. Deep-space missions require high-gain antennas, and advanced modulation techniques to transmit data across millions of miles. Deep-space missions require X-band or Ka-band on-ground antennas for communication, relying on the support of large space agencies with their ground station networks. However, recent developments in optical link equipment and X-band transceivers present new possibilities for telecommunications solutions.
Ground stations strategically positioned around the globe play a vital role in establishing and maintaining communication links with these tiny pioneers as they venture into the vastness of the cosmos. The emergence of distributed, smaller ground stations around the world holds promise for providing continuous coverage in the future, akin to the UHF ground station networks supported by the radio amateur community in the CubeSat community.
Propulsion and Navigation: Charting New Courses
Navigating through the vast expanse of space is a complex task for microsatellites and CubeSats. At significant distances from the sun, energy generation requires large solar arrays (as for ROSETTA) or use of alternative energy sources.
Traditional propulsion systems are often too bulky for these small spacecraft. Nuclear generators (as for Cassini, or Galileo) have flown on interplanetary spacecraft but are currently not available for CubeSats.
CubeSats typically have limited propulsion capabilities, which restricts their ability to maneuver in space. Thus, only the very limited storage resources of batteries can be used, demanding very careful operations in order to not waste those scarce resources. There is a need for advances in propulsion technologies to enable precise trajectory adjustments and extended missions for CubeSats.
Engineers are developing innovative propulsion methods, such as ion thrusters and solar sails, to enable precise trajectory adjustments and efficient propulsion over long durations.
In LEO, one CubeSat mission, AeroCube 8 has already demonstrated miniature electric propulsion system capabilities. For deep space missions, (total impulse/volume) must be increased, complemented by larger fuel storage capacities. Innovative technologies like solar sailing are being considered and may provide solutions.
Launch Opportunities:
Increasing access to space is crucial for expanding the frequency of scientific missions. While launch opportunities for near-Earth missions have significantly improved, the availability of rideshares for deep space missions is more limited. Small satellite launchers currently under development offer promising prospects for expanding the range of orbits accessible to CubeSats, without being constrained by the trajectory of the primary spacecraft.
The ability to regularly utilize excess launch capacity on lunar, Lagrange point, and interplanetary missions would be a game changer for deep space CubeSats. This would enhance their access to distant destinations and enable a greater number of small spacecraft to be deployed on deep space missions. As a result, the scientific exploration of deep space using CubeSats could see significant advancements and discoveries.
Technology Innovations
Current technology innovation trends addressing some of the limitations of small satellites in low earth orbit include:
- Noise reduction in miniaturized components: Software-based filter technologies are being employed to reduce susceptibility to noise in miniaturized components. This is important for small satellites because they often have limited power and computing resources, so they cannot afford to lose data due to noise. This helps improve the overall performance and reliability of small satellite systems.
- Attitude and orbit control capabilities: Electric propulsion systems are also being utilized for orbit control. Recent miniature reaction wheel developments improve attitude control at low power consumption and electric propulsion systems provide orbit control. This is important for small satellites because they often have limited mass and volume, so they cannot carry large, powerful attitude control systems or propulsion systems. Magnetic attitude control subsystems are also being explored as a potential solution.
- Communication link capacity: New developments on optical links promise capacities beyond 100 MB/s at clear sky. This is important for small satellites because they often have limited data storage capacity, so they need to be able to transmit data back to Earth as quickly as possible. Additionally, miniaturized X-band transceivers are becoming available, offering alternative communication options for small satellite missions.
- Extending the lifetime: Advanced fault detection, identification, and recovery (FDIR) methods, along with redundancy concepts, are being implemented to ensure a reasonable lifetime in orbit. Even with the use of commercial off-the-shelf components, small satellites have demonstrated prolonged operational lifetimes despite encountering single-event upsets (SEUs) and latch-ups.
- Ground segment: University ground station networks such as GENSO and UNISEC have been established to facilitate the frequent transmission of data from small satellites. These networks help alleviate the storage and processing requirements onboard the satellites. Additionally, commercial networks like KSAT lite are providing global coverage for small satellite missions. This is important for small satellites because they often have limited data storage capacity and computing resources.
Air Force Taps Blue Canyon to Develop, Test Micro-Satellite for Deep Space Missions
In November 2021, Blue Canyon Technologies, a subsidiary of Raytheon Technologies, secured a $14.6 million contract from the U.S. Air Force to develop and demonstrate a small satellite bus for operations beyond geosynchronous Earth orbit (GEO). The satellite bus is still under development and is expected to be completed by February 28, 2023. Once the bus is complete, it will be tested to make sure that it meets the Air Force’s requirements. If the tests are successful, the bus will be launched into space.
The contractor will build a satellite capable of operating and maneuvering for up to three years in orbits beyond GEO under the Air Force Research Laboratory’s Space Situational Awareness Micro-Satellite Bus program. The development of this satellite bus is a significant milestone in the Air Force’s efforts to develop small satellites for deep-space missions. The bus will allow the Air Force to launch smaller, more affordable satellites into space. This will enable the Air Force to conduct more missions and to collect more data about space.
Conclusion:
Deep-space microsatellites and CubeSats are pushing the boundaries of space exploration by overcoming challenges and embracing innovative technologies. These small but mighty spacecraft are reshaping our understanding of the universe while fostering scientific advancements and commercial opportunities. As we continue to unlock the potential of these miniature explorers, the final frontier is becoming more accessible and inviting for humanity to reach for the stars.
References and Resources also include:
https://www.esa.int/gsp/ACT/doc/MAD/pub/ACT-RPR-MAD-2018-MARGO.pdf
https://www.sciencedirect.com/science/article/pii/S0273117719305411
