Another wave is coming! The "black technology" that changes human exploration of space

On January 10, 2023, NASA’s official website released the funding list for the annual Innovative Advanced Concepts Program. A total of 20 projects were shortlisted, and the project contents were later gradually updated and announced.

These projects mainly include: jet telescope, photophoretic propulsion, nuclear-powered heating detectors, bending forming of large electrostatically driven space structures, oxygen pipelines at the lunar South Pole, particle beam propulsion, new bimodal nuclear thermal/nuclear electric propulsion, bio-mineral self-generated building blocks for Martian habitats, large long-wave observatory, advanced liquid collection technology, nuclear fusion energy flashlight, diffraction interferometer coronagraph exoplanet analyzer, radioisotope thermal radiation battery generator, aerogel nuclear fission fragment rocket engine, quantum radar, planetary defense system, radioisotope electric propulsion system, advanced air vehicle silent solid-state propulsion device, long-range observatory, and space pharmaceutical factory.

We have selected 9 innovative solutions that are closely related to the aerospace field, involving innovative propulsion, asteroid defense, life support, etc., to see how these "black technologies" work and how they may change the "rules of the game" for human exploration of space.

Photophoretic propulsion: Exploring Earth's atmosphere and looking to Mars

The mesosphere is part of the Earth's atmosphere, with an altitude of approximately 50 to 80 kilometers. Obviously, this range is too high for balloons and airplanes, and too low for spacecraft such as satellites. So far, humans have not yet achieved stable long-term exploration of this area, and the only knowledge they have comes mainly from the few minutes of stay when rockets pass by.

Schematic diagram of photophoresis propulsion scheme

In order to achieve the detection of the mesosphere, the research team of the University of Pennsylvania proposed a new propulsion system concept. It does not require any propulsion energy, and can make the aircraft float in the atmosphere for a long time just by irradiating the device with light.

The research is based on a phenomenon called "photophoretic levitation," whereby when a solid is heated by illumination relative to the surrounding gas, a so-called "photophoretic force" is generated, causing momentum exchange between the solid and the gas. This force can generate lift for the sensing platform while absorbing light at the bottom, generating heat, but keeping it cool at the top.

The design of the University of Pennsylvania uses a plate with two different sides. The top is made of polyester film for insulation, and the bottom polyester film is coated with a "fluffy blanket" composed of tiny rod-shaped carbon filaments of carbon nanotubes. The technical team demonstrated the plate under various air pressures in the laboratory, proving the feasibility of centimeter-scale detectors floating in the air "indefinitely". Although the flat plate is only a few centimeters long and wide, it can also be equipped with a large number of micro sensors. Scientists believe that with a slight improvement in this technology, the sensing platform can obtain horizontal thrust and reach anywhere in the mesosphere using only light as a propulsion source.

In addition, since the air pressure of the Martian atmosphere is similar to that of the Earth's mesosphere, the technical team is also exploring the potential application of this technology in Mars exploration.

Lattice confinement fusion: helping to explore the oceans of alien planets

In order to study the possibility of life on other planets, scientists have been looking for water resources on other planets. As we all know, many other planets are covered with thick ice, such as Ceres, Enceladus, Pluto and Europa. The thickness of the ice sheet is estimated to be tens of kilometers, and there is a huge liquid ocean underneath. These oceans on other planets may be formed by the tidal heating of their planets or by residual radioactive decay.

There are many challenges in exploring these alien oceans. NASA is studying the possibility of using heated or drilled probes to penetrate the ice and enter the interior oceans of alien planets, and has suggested using nuclear-powered probes to generate heat through radioactive decay to melt the ice on the surface of alien planets. However, nuclear-powered probes are limited by safety and price.

Imaginary picture of ocean probe under the ice layer of alien planet

Glenn Research Center has proposed a new method called "lattice confinement fusion", which mainly provides power through the fusion of fuel in the metal lattice. Simply put, if the conductive metal has a high electron density, the possibility of two light atomic nuclei repelling each other when they are close will decrease, and the lattice confinement can stimulate the fusion of positively charged atoms.

Currently, engineers at the Glenn Research Center are studying whether this method can provide power for small unmanned probes on the surface of Mars. Since lattice confinement fusion does not require high-cost, difficult to safely handle fissile materials (such as enriched uranium), its use will be more extensive when the technology matures in the future. It can not only meet the needs of space missions, but also serve the public, such as providing electricity for individual buildings, thereby reducing dependence on fossil fuels and improving the resilience of the power grid.

New bimodal nuclear thermal/nuclear electric propulsion: Hope for rapid arrival on Mars

Nuclear thermal propulsion is recognized as the "propulsion technology of choice for manned space missions in the solar system." During the Cold War, the United States and the Soviet Union spent decades researching nuclear thermal propulsion, but unfortunately, the results of its practical application were limited. In 2023, NASA funded a nuclear propulsion project to develop bimodal nuclear propulsion, which is a combination of nuclear thermal propulsion and nuclear electric propulsion. The system plans to use the so-called "wave rotor top cycle," which can theoretically reduce the time it takes for a spacecraft to travel to Mars to just 45 days.

According to the concept, nuclear thermal propulsion heats liquid hydrogen propellant through a nuclear reactor, converting it into ionized hydrogen, which then generates thrust through the nozzle. Nuclear electric propulsion relies on nuclear reactors to provide electricity for Hall effect thrusters. Hall effect thrusters hope to use magnetic fields to restrict the axial motion of electrons, ionize propellants, accelerate ions, generate thrust, and neutralize ions in the plume to improve safety.

Imaginary picture of ocean probe under the ice layer of alien planet

According to public information, the most advanced nuclear thermal propulsion solution is solid core rocket nuclear engine technology, which is expected to provide 900 seconds of specific impulse, twice that of chemical energy rocket engines. However, behind the high specific impulse of nuclear thermal rocket engines are some potential defects, especially when performing high orbital speed missions, it is difficult for them to meet the mission requirements throughout the entire process. In contrast, nuclear electric propulsion can provide an ultra-high specific impulse of about 1 million seconds, but the thrust is low and the mass-power ratio is limited. In particular, the demand for power worsens the heat dissipation problem. Under ideal conditions, the thermal energy conversion rate can reach up to 30% to 40%.

In response to such problems, this project proposes a new wave rotor top cycle method. The propulsion system is expected to obtain thrust equivalent to nuclear thermal propulsion, and the specific impulse can reach 1400-2000 seconds. If it is equipped with nuclear power propulsion, the specific impulse can be further increased to 1800-4000 seconds by only increasing the minimum structural mass. This design is expected to make it possible to carry out a rapid manned space mission to Mars in 45 days, thereby greatly reducing the health risks caused by cosmic radiation, microgravity, etc., and even completely change the journey of human exploration of the solar system.

Radioisotope thermal radiation battery: CubeSats are even more powerful

Currently, most spacecraft are powered by solar panels, but in deep space beyond the orbit of Mars or in harsh environments such as Martian dust storms and the long nights of the moon, sunlight cannot provide the necessary energy. As an alternative, many spacecraft carry multi-purpose radioisotope devices that use temperature gradients to generate electricity, but this device is bulky and restricts the performance of the spacecraft to a certain extent.

To solve this problem, the Rochester Institute of Technology proposed a power source that is said to be "revolutionary" - a thermal radiation battery. Compared with traditional multi-task radioisotope devices, its volume is reduced by three orders of magnitude.

In essence, it is a "reverse working" solar panel. When a solar panel absorbs light, part of the light energy is converted into electrical energy, and most of it is converted into heat energy. The operation of thermal radiation cells follows the principle of thermal radiation elements. The cell panel is composed of elements such as indium, arsenic, antimony, and phosphorus. The heat released in the form of infrared photons hits the panel, which will produce a potential difference with the opposite polarity to the solar panel. In other words, thermal radiation cells use heat to generate electricity and release the consumed energy in the form of infrared photons. It can be said that it works in the "reverse direction" of solar panels and is more efficient.

If this new technology is practical, then missions to explore Jupiter and even beyond, or to the permanently shadowed craters at the moon's poles, could allow probes to abandon large and bulky designs and use cubic satellites carrying small energy systems.

Nuclear fission fragment rocket engine: Searching for habitable planets outside our solar system

To meet the urgent need for advanced propulsion solutions, Positron Dynamics has developed a nuclear fission-fragment rocket engine that is theoretically far more efficient than currently used rocket engines and can achieve high specific impulses of more than 100 kiloseconds at high power density.

In fact, nuclear fission fragment rocket engines are not a new concept. Their operating principles are basically the same as those of current nuclear power plant reactors. However, previously proposed nuclear fission fragment rocket engine designs are too large and have too great thermal limitations. Their practical application requires overcoming technical obstacles, such as particle plasma suspension.

An image of a nuclear-powered rocket transporting a deep space probe

To address this problem, Positron Power is trying to solve it in two ways: first, by loading the nuclear fission material into ultra-light aerogel to ensure that the fuel particles involved in the nuclear fission reaction are fixed together, while controlling the overall structural mass so that they can be sent into orbit; second, by using superconducting magnets to confine the plasma produced by the reaction, guiding the nuclear fission fragments in the same direction, and then effectively converting them into thrust to prevent the fragments from damaging the engine.

The ultimate goal of this power system is to drive the spacecraft to reach the solar gravitational lens position 500 astronomical units from the Earth after about 15 years of flight, and to decelerate and maneuver in time to conduct direct imaging and high-resolution spectral analysis of exoplanets 100 light-years away. In the future, the space telescope deployed there will enable the detection range to cross the Einstein Ring region and photograph the surface characteristics and signs of habitability of exoplanets.

Schematic diagram of a nuclear powered rocket

Particle beam propulsion: Accelerating the exploration of nearby stars

According to simulations, a spacecraft using traditional thrusters would need to fly for 19,000 to 81,000 years to reach Proxima Centauri, the nearest star outside the solar system, which is about 4.25 light-years away from Earth. To this end, engineers have been studying new probe solutions, hoping to use directed energy beams (such as lasers) to accelerate the light sails that drive the probes to a fraction of the speed of light, accelerating the exploration of nearby stars.

Researchers at the University of California, Los Angeles, have gone a step further and proposed a particle beam solution. If this solution is realized, it will be possible to deliver about 1 ton of payload to a distance of 500 astronomical units in less than 20 years.

In fact, the beam that propels the light sail is composed of tiny particles, each of which is accelerated to incredibly high speeds by laser ablation, and then uses momentum to drive the spacecraft. Unlike laser beams, these particles do not diverge as quickly, making it possible to accelerate heavier spacecraft. After all, these particles are much heavier than photons, carry more momentum, and can transmit greater force to the spacecraft.

Currently, space exploration is limited by rocket equations, and only two probes have passed through the heliosphere and entered interstellar space. Among them, the Voyager 1 probe flew for 35 years at a speed of 3.6 astronomical units per year before reaching the top of the heliosphere. The particle beam propulsion scheme proposed by the University of California, Los Angeles may greatly shorten this long period of time for spacecraft: it is expected to reach an exoplanet in less than 1 year; it will take about 3 years to fly out of 100 astronomical units; it will take 15 years to fly to the position of the solar gravitational lens 500 astronomical units away. More importantly, particle beam propulsion can drive a spacecraft weighing about 1 ton, greatly expanding the mission adaptability.

Schematic diagram of particle beam propulsion scheme

As the first phase of work, researchers will demonstrate the feasibility of particle beam propulsion through detailed modeling of different subsystems and concept verification experiments, focusing on exploring the role of particle beam propulsion systems in interstellar missions.

Asteroid Defense: Planning the War to Defend Earth

Traditional asteroid defense methods mainly involve launching spacecraft to collide with threatening asteroids, changing the asteroid's orbit through momentum transfer and causing it to deviate from the Earth.

In 2022, Philip Rubin, a researcher at the University of California, proposed an asteroid defense plan based on existing technology, emphasizing the role of energy transfer. It mainly deploys a series of small hypervelocity kinetic impactors in space to crush and decompose asteroids or comets, and then uses the Earth's atmosphere as a "shield" to reduce the threat of debris. This method is suitable for both interception modes with long warning times and can be used in time a few minutes before an asteroid hits the Earth.

Schematic diagram of asteroid defense plan

The research project aims to understand the physical characteristics of an impactor colliding with an incoming celestial body at high speed, and how to more effectively impact an incoming celestial body into small enough fragments. The research team worked with NASA's Supercomputer Center to use fluid dynamics software to simulate and test the effects of different incoming celestial bodies being hit. Preliminary simulation results show that asteroids can be easily fragmented using a smaller impactor, and the cloud of debris spreads radially outward. If intercepted in a short warning time mode, the cloud of debris will enter the atmosphere, but the volume of these fragments is very small, so they will not fall to the ground and will burn up in the air. Preliminary simulations show that the resulting sound waves and flashes will be below the threshold of significant damage.

The second phase of the project includes further expansion of the above simulation work to explore key parts of the asteroid defense system roadmap, including ground testing of impactors and simulated targets, studying atmospheric chemical effects, and conducting high-frequency sky surveys.

Advanced air mobility: low-noise transport with electric-propulsion drones

The so-called "advanced air traffic" is to use small electric unmanned aerial vehicles to carry out passenger, freight and private business within and between cities. In addition to technical challenges, residents' aversion to noise is probably the biggest obstacle to the plan.

Related research shows that unmanned vertical take-off and landing aircraft using electric propulsion devices can theoretically perform air-to-air missions. This electric propulsion device mainly generates thrust by accelerating ions through an electric field and is almost silent, so future aircraft are expected to meet residents' demand for low noise.

Schematic diagram of an electrically propulsion low-noise drone

So far, the research work has mainly focused on conceptual aircraft design and propulsion modeling. Next, the research work will focus on the detailed design and manufacturing of the aircraft, and accumulate flight tests as soon as possible. The research team will manufacture a verification aircraft with vertical take-off and landing functions, which has the same structure as the target aircraft, and verify the target aircraft design model through flight tests and wind tunnel tests, especially the propulsion performance and noise control effect, and further improve the performance of electronic components.

Space pharmaceuticals: long-term care for the health of "astronauts"

Disease prevention, diagnosis and treatment are crucial for human space exploration missions. Currently, astronauts mainly rely on drugs developed on the ground to treat or prevent diseases, but these drugs may not be reliable in the space environment, especially small proteins (peptides), which have a shelf life of only a few months even if they are carefully refrigerated. With the advent of a new era of space exploration, humans will carry out long-term exploration missions beyond Earth orbit, and may continue to fly in orbit for several years in the future. Therefore, solving the problem of human space medicine has become a focus of widespread attention, and "on-demand production" in space is undoubtedly the fundamental solution.

An imaginary picture of the space pharmaceutical laboratory cabin in operation

NASA's Ames Research Center has proposed a plan to use bacteria to make drugs during long-term space missions. In the first phase of the project, researchers modified Bacillus subtilis to try to produce drugs to treat radiation damage and protect human bone health, and used a small and lightweight system to purify it, achieving good results. However, it is still unknown whether drugs can be produced in sufficient quantity and purity to meet the needs of astronauts in reality, which has become a key issue to be solved in the second phase of the project.

In the future, researchers will study other drugs on the astronauts' medication list to further expand the scope of use of the system. They will also build a prototype of a microfluidics-based lightweight production/purification system for space drug production.

If the relevant technology can be put into practical use, space pharmaceuticals will achieve a major breakthrough and are expected to support the medical needs of long-term manned deep space missions. In fact, space biopharmaceuticals not only have unique advantages in scientific research, but also contain huge economic value, and have become a frontier field in the development of global space science and technology.

NASA's Innovative Advanced Concepts Program aims to fund early research, cultivate innovative aerospace concepts, collect breakthrough solutions that may change future mission modes, and expand the breadth and depth of human space exploration. Since 2011, the program has funded many "sounds like science fiction" programs and preliminarily proved their feasibility. Therefore, science fiction is not a wild and unrealistic fantasy, but a reasonable imagination based on modern scientific theories, which is likely to have a profound impact on scientific development and provide inspiration to researchers. With the continuous advancement of aerospace technology, I believe that "science fiction entering reality" will not always be out of reach, and space exploration will present unprecedented new prospects.