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NASA is very interested in developing a propulsion method that will allow spacecraft to move faster. We’ve reported several times on various ideas in support of this goal, and most of the more successful ones have made good use of the sun’s gravity, usually by slinging around it, as is commonly done with Jupiter right now.

But there are still significant obstacles to this, not the least of which is the energy emitted by the sun, simply vaporizing anything that gets close enough to use a gravitational assist. That’s the problem a project supported by NASA’s Institute for Advanced Concepts (NIAC) and led by Jason Benkoski, now of Lawrence Livermore National Laboratory, is trying to solve.

The project received a NIAC Phase I grant in 2022 focused on combining two separate systems – a heat shield and a thermal fuel system. According to the project’s final report, combining these two technologies could allow a spacecraft to perform what is known as an Oberth maneuver around the sun.

In this trick of orbital mechanics, a spacecraft makes good use of the sun’s gravity to slingshot itself at high speeds in the direction it’s headed. It is similar to the sundiver technology discussed in other articles.

So what makes this project unique? One thing is the heat shield – Dr. Benkoski and his team have developed a material that is able to withstand up to 2,700 K. While that’s still nowhere near the temperature of the Sun’s surface, which can reach 5,800 K, it’s enough to get pretty close, too. way to unlock the spaceship’s ability to use an Oberth maneuver in the first place.

Samples of the material with these thermal properties have already been produced. However, further research is needed to understand whether they are suitable for spaceflight. And the heat shield alone is not enough to perform the maneuver – the spacecraft must also have a propulsion system that can withstand these temperatures.

A solar thermal propulsion system could potentially do this. These systems use the sun’s energy to pressurize their own propellant and then expel those propellants to obtain thrust, a necessary component of the Oberth maneuver. There are several different types of fuels that could work for such a system, and much of the research in the Phase I project looked at the different costs/benefits of each.

Hydrogen is one of the most common fuels considered for solar thermal propulsion. Although it is light, it requires a bulky cryogenic system to store the hydrogen as it is heated to the point where it is used as thrust. Ultimately, its trade-offs made it the least effective of the propellants considered during the project.

Lithium hydride was the surprise winner for the fuel that allowed the fastest escape velocity. Calculations show that this could result in a velocity of over 12 AU/year. However, there are limitations to fuel storage and handling.

Dr Benkoski settled on a more common fuel as the overall winner in the modeling he did – methane. Although it usually results in a lower terminal velocity than lithium hydride, its terminal velocity is still respectable at over 10 AU/year. It also eliminates many storage problems for other fuels, such as the cryogenic cells needed to store hydrogen.

However, there are some drawbacks – the calculated top speed is only about 1.7 times faster than what can already be done with gravitational assistance from Jupiter, which wouldn’t require all the fancy thermal shielding.

However, there are other drawbacks to this, such as the direction in which the spacecraft can travel is limited by where Jupiter is in relation to other objects of interest. Orbiting the sun, on the other hand, it’s possible to reach almost anywhere in the solar system and beyond with the right controlled burn.

As Dr. Benkoski notes in the final report, he made many assumptions when he did his modeling calculations, including that the system would only be able to use technologies already developed, not speculative ones that could dramatically affect the results.

So far, it does not appear that NASA has selected this project to move to Phase II, and it is unclear what future work is planned for further development. If nothing else, it’s a step toward understanding what it would take to actually send a spacecraft past the sun and into deep space at a speed far greater than anything else seen before. Given NASA’s ongoing attention to this topic, one of the missions will undoubtedly be able to do so someday.