Andres Almeida (Host): Wouldn’t it be nice if your spacecraft could simply unfurl a sail like a sailboat and let nature do the rest? No expensive fuel, no risk of engine problems. Well, NASA is demonstrating a technology that could work on this principle. 

It’s called a solar sail, and instead of using wind to push the sail (you know, because it’s in space), the spacecraft takes advantage of the steady stream of light particles from the Sun. 

NASA’s Advanced Composite Solar Sail System, or ACS3, is a demonstration mission to test large, lightweight materials that roll out from a small spacecraft to deploy a propulsion technology designed to operate without a drop of fuel. The sail itself gets packaged into a small satellite called a CubeSat, in this case, about the size of a microwave oven. 

In space, it deploys using carbon-fiber composite booms, each side of the sail measuring 9 meters, or about 30 feet long. The concept sounds straightforward. The engineering is anything but. 

Let’s get into it in this episode of Small Steps, Giant Leaps, the final episode of 2025.

Welcome to Small Steps, Giant Leaps, the podcast from NASA’s Academy of Program/Project & Engineering Leadership. I’m your host Andres Almeida.

Today, we’re talking with Philip Shih of Ames Research Center in California’s Silicon Valley. He’s the project manager for ACS3 and he’ll tell us about the potential benefits of solar sail technology, as well as the engineering challenges of unfurling it flawlessly in space. 

Host: Hey, Philip, welcome to the podcast. 

Philip Shih: Hi, how are you?

Host: I’m well, thank you. Can you tell us more about what the Advanced Composites Solar Sail System is? What is it? And why is NASA investing in this technology? 

Shih: It is a NASA technology demonstration mission that’s designed to test the next generation solar sail of a large area. 

So, it’s about 80 square meters and using, yeah, using lightweight composite materials. And also, one of the special things is we also use a composite booms deployer in a very small package that can fit in a 12U CubeSat. 

So, in the past, I think, they have thought about using a bigger spacecraft and also a small or smaller solar sail. So, this time is the first time that [we] put a large solar sail in a small spacecraft. 

And NASA is investing this technology because it offers a revolutionary way to propel the spacecraft using sunlight instead of fuel, so that we don’t need propellant to travel to deep space.  

Host: The idea is to use solar energy? 

Shih: Yes, actually, with a more technical term, is use of photons from the Sun. And a lot of people thought that it’s the solar wind, but no, it is actually the photon particle[s] from the Sun that will hit the solar sail, that will transfer momentum to the solar sail. That propels the solar sail forward. 

Host: How did the composite booms in Solar Sail – and we’ll link to images of it – how does it differ from previous designs, and why are they so advanced? 

Shih: So, previously, solar sail missions mostly using metallic booms. So, aluminum. 

This particular mission, we use the carbon fiber reinforced polymer boom. So, it is a kind of a composite material. So, the key advantages of this kind of boom, this kind of material is very lightweight and also high strength-to-weight ratio. Another good characteristic is it has a good thermal stability. 

It can be coil or folded into very compact volumes. So, if you use a metal to build a boom, then you probably will be more difficult to, to coil it off put it in as compact volumes. 

And finally, this kind of composite materials is more resistant to corrosion and metallic fatigue. And so, in the composite booms used in ACS3 were 75% lighter than the comparable metal metallic booms and 100 times more thermal stable.

Host: Wow, that’s a lot. So, when it’s, because of that, there have to be some challenges in making sure that it all unfurls correctly and that it operates correctly. Can you name any challenges during development? 

Shih: Yeah, I think the first one, the first challenge is, as I mentioned before, we we file and we put it in a small package. So, the packaging and storage is one of the biggest challenges because the sail must be folded or actually rolled into very compact volumes for CubeSats. But then it leads to another challenge: It’s the reliability of the deployment mechanism. 

So, because the booms and sail must deploy using motors and springs, and now often, once it starts, you will run autonomously. So, we are once it starts, we cannot – we can stop it, but it cannot be rolled back. 

Host: Oh, yeah.

Shih: So, that’s a risk of mechanical failure. It may, also may jam right in the middle. The boom can, does not complete the extension. And in addition, we use, also use a device called “pin puller” to start the unfurling. So, if that device fails, then the sail will not be deployed at all. So, the reliability of this, all these other components (deployment mechanism components) need to be very great. 

And also, the extreme temperatures experienced by the spacecraft. 

So, once it is in space, the extreme materials may warp, strain, or expand. I mean, because we don’t have an atmosphere through to kind of protect, protect the spacecraft or mechanism from this extreme temperature, so you will affect the deployment, and also the sail tension. 

And control is another challenge we need to deal with, because during unfurling, the sail must remain flat and taut so that you will generate consistent thrust to extend. So, any wrinkle or slack can cause instabilities. 

And one of another issues we will need to deal with this if any small forces can cause the spacecraft to tumble or oxidize during the, when the sale unfurls. 

So, during the unfurling, the spacecraft needs to be very stable at that time. We cannot intervene once the process starts. Most of the deployments are autonomous and we cannot be manually corrected, so any failure during deployment may, may be the end of mission. 

Host: A lot is at stake, and your teams certainly have worked hard. So, I wonder what unique opportunities could this open up?

Shih: Yeah, I mean this, this could enable deep space CubeSat missions, and also any missions that need a very large solar sail. 

But one of the open opportunities [it] will open up is fuel-free long duration, long duration missions. For example, we have a mission, want to go to other planets in the solar system, solar sail is a very good alternative. And then we don’t need to worry about propellant runs out in the propulsion [system]. 

Host: And it’s also a lot of weight, mass, correct? 

Shih: Yes, because solar sail, even a large solar sail, because, because it’s lightweight, so you can save weight on the fuel, yeah. 

And large solar sail can be used to shorten the travel time, so the larger, the faster. 

Host: What are some key lessons learned during development and deployments? 

Shih: I think one of the key lessons learned is during development, the mechanical systems and the control system are developed into two different locations. The mechanical systems is developed in Langley and electrical control systems being in Ames. 

So, I think we think back that it is better to put these two teams in the same location. This will reduce a lot of interface headache, particularly, I mean, this is true particularly for very complicated electro-mechanical systems like [with] this mission. And also, this can simplify the logistics when we do the integration and tests. 

And another one is we should build more buffer in the schedule to accommodate the late delivery of a critical part. 

Also, in the design of the spacecraft, we should have more [room] for mechanical parts and wiring. This time, because we packaged the solar sail and the deployment system in a very small volume. So, during development, we find there’s a pinched [wire] in the spacecraft because of the tight space in the bus. So, so we have to, we have to take everything apart and just replace the wire.

Host: Philip, what was your giant leap? 

Shih: Before I joined the ACS3 project, most of the projects I was involved before consist of teams from either from just one company or from one NASA center. 

So even, even the team from one company or one location, there were already a lot of challenges to bring people together. So,I was asked to join the ACS3 project right before the COVID shutdown. So, and then we already have a try to figure out, okay, how to communicate team members in different locations. 

Last year, I, actually end of last year, I was asked to be the project manager of this project, because the previous project manager moved on to another project. So, even though the mission objective was pretty simple – well, because it was just to demonstrate the deployment of the solar sail. So, to ensure the mission to be successful, actually a smooth collaboration of multiple organizations is very essential. 

We have teams from three NASA centers, Ames, Langley and Marshall. And we also have one university to help us, Santa Clara University in California. So, how to bring all the teams to work together toward the same goal is a very big challenge, because each center and locations have different cultures and different ways of doing things.

So, in addition to the technical challenge we have, how to communicate well, with all the teams in different location, is something that no technology can really help. Communicate, well, communication between people is, is an art, not just a technology. 

Host: Oh, that’s for sure! 

Shih: Yeah, so I’ve really appreciated the efforts the team members in this small mission so far. So, stepping into managing a project consists of teams from multiple organizations would definitely be one of my giant leaps. 

Host: Well, we’re glad you’re part of it. Thank you, Phillip, for everything. Thanks for your time. 

Shih: Okay, thank you. 

[Music] 

Host: You know, when we look back on this year of Small Steps, Giant Leaps, it’s amazing how many topics we covered. We heard from scientists, project managers, subject matter experts, and every conversation reminded us why capturing and sharing knowledge matters. 

Our guests let us behind the scenes of NASA’s most challenging work. We learned about how living in space affects the human body, improvements to air traffic management, and how scientists discover worlds in other solar systems. We also celebrated our many incredible engineers in episode 148 with NASA Chief Engineer Joe Pellicciotti, and Deputy Chief Engineer Katherine Van Hooser. 

And what really stood out was everybody’s honesty. About the risks, the surprises, the moments where somebody learned a new process to make a mission more efficient. 

Engineers are always learning and looking toward the future. And we’re looking ahead next year with Artemis II, the mission that will send four humans around the Moon for the first time since the Apollo Program. We’re also looking at the Nancy Grace Roman Space Telescope, set to launch in 2026 on a mission to unravel the mystery of dark matter and dark energy.

It’s been a year of curiosity and discovery, and we’re grateful to everyone who came along for the ride. We’re excited to learn with you in the new year. 

In the meantime, you can listen to past episodes on nasa.gov/podcasts. While you’re there, check out our other podcasts like Houston, We Have a Podcast, Curious Universe, and Universo curioso de la NASA. 

Before we sign off for 2025, one question for you: What was your giant leap? 

From all of us at NASA APPEL, Happy Holidays and see you in January. 

Outro: This is an official NASA podcast.