This feature was originally published on May 3, 2016.
In the News
What do "Star Wars," NASA's Dawn spacecraft and Newton's Laws of Motion have in common? An educational lesson that turns science fiction into science fact using spreadsheets – a powerful tool for developing the scientific models addressed in the Next Generation Science Standards.
The TIE (Twin Ion Engine) fighter is a staple of the "Star Wars" universe. Darth Vader flew one in "A New Hope." Poe Dameron piloted one in "The Force Awakens." And many, many Imperial pilots met their fates in them. While the fictional TIE fighters in "Star Wars" flew a long time ago in a galaxy far, far away, ion engines are a reality in this galaxy today – and have a unique connection to NASA’s Jet Propulsion Laboratory.
Launched in 1998, the first spacecraft to use an ion engine was Deep Space 1, which flew by asteroid 9969 Braille and comet Borrelly. Fueled by the success of Deep Space 1, engineers at JPL set forth to develop the next spacecraft that would use ion propulsion. This mission, called Dawn, would take ion-powered spacecraft to the next level by allowing Dawn to go into orbit twice – around the two largest objects in the asteroid belt: Vesta and Ceres.
How Does It Work?
Ion engines rely on two principles that Isaac Newton first described in 1687. First, a positively charged atom (ion) is pushed out of the engine at a high velocity. Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction, so then a small force pushes back on the spacecraft in the opposite direction – forward! According to Newton’s Second Law of Motion, there is a relationship between the force (F) exerted on an object, its mass (m) and its acceleration (a). The equation F=ma describes that relationship, and tells us that the small force applied to the spacecraft by the exiting atom provides a small amount of acceleration to the spacecraft. Push enough atoms out, and you'll get enough acceleration to really speed things up.
Why is It Important?
Compared with traditional chemical rockets, ion propulsion is faster, cheaper and safer:
- Faster: Spacecraft powered by ion engines can reach speeds of up to 90,000 meters per second (more than 201,000 mph!)
- Cheaper: When it comes to fuel efficiency, ion engines can reach more than 90 percent fuel efficiency, while chemical rockets are only about 35 percent efficient.
- Safer: Ion thrusters are fueled by inert gases. Most of them use xenon, which is a non-toxic, chemically inert (no risk of exploding), odorless, tasteless and colorless gas.
These properties make ion propulsion a very attractive solution when engineers are designing spacecraft. While not every spacecraft can use ion propulsion – some need greater rates of acceleration than ion propulsion can provide – the number and types of missions using these efficient engines is growing. In addition to being used on the Dawn spacecraft and communication satellites orbiting Earth, ion propulsion could be used to boost the International Space Station into higher orbits and will likely be a part of many future missions exploring our own solar system.
Newton’s Laws of Motion are an important part of middle and high school physical science and are addressed specifically by the Next Generation Science Standards as well as Common Core Math standards. The lesson "Ion Propulsion: Using Spreadsheets to Model Additive Velocity" lets students study the relationship between force, mass and acceleration as described by Newton's Second Law as they develop spreadsheet models that apply those principles to real-world situations.› See the lesson!
This lesson meets the following Next Generation Science and Common Core Math Standards:
- MS-PS2-2: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object.
- HS-PS2-1: Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
- HS-PS2-1: Use mathematical representations to support the claim that the total momentum of a system of objects is conserved when there is no net force on the system.
Common Core Math Standards:
Grade 8: Expressions and Equations A.4: Perform operations with numbers expressed in scientific notation, including problems where both decimal and scientific notation are used. Use scientific notation and choose units of appropriate size for measurements of very large or very small quantities (e.g., use millimeters per year for seafloor spreading). Interpret scientific notation that has been generated by technology.
High School: Algebra CED.A.4: Rearrange formulas to highlight a quantity of interest, using the same reasoning as in solving equations.
High School: Functions LE.A: Construct and compare linear, quadratic, and exponential models and solve problems.
High School: Functions BF.A.1: Write a function that describes a relationship between two quantities.
High School: Statistics and Probability ID.C: Interpret linear Models
High School: Number and Quantity Q.A.1: Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays."
- Website: Dawn Mission
- Blog: Dawn Journal
- Video: Crazy Engineering - Ion Propulsion
- Ion propulsion interactives
- Eyes on the Solar System: Dawn Mission Tour (scroll to "Solar System Tours" and click the "Dawn" link)
It started as a technology test mission, but NASA's Deep Space 1 had become much more. In 1999, having already made a historic up-close encounter with asteroid 9669 Braille, the "spacecraft that could" was being pushed ever further with an extended mission to encounter two comets in a single year.
But in November of that year, something went wrong. The star tracker, a device that acts as a sort of spacecraft compass, failed, rendering the craft blind in the stellar abyss with no way of relaying its valuable reserve of science data back to Earth.
For Michela Muñoz Fernández, it was a chance to do something big.
In February 2000, Muñoz Fernández, then a master's student at France's International Space University, arrived at NASA's Jet Propulsion Laboratory in Pasadena, Calif., for the start of her three-month internship. Her task was to help analyze communications between Deep Space 1 and the ground stations that make up NASA's Deep Space Network (DSN) -- a global system of powerful antennas for spacecraft communication and navigation.
As the NASA lab that had pioneered deep space communication and managed the DSN, JPL was a mecca for aspiring telecommunications engineers like Muñoz Fernández.
"My dream was always to work on telecom, doing telecom analysis for a deep space mission," said Muñoz Fernández, who before starting her master's program had worked for the company that manages the DSN complex in her native Madrid. "So for me, it was like a dream to work on Deep Space 1."
Her dream quickly evolved into a career's worth of real-world experience when, soon after starting her internship, she was thrust into a team tasked with wrenching the science data from the wayward Deep Space 1 and potentially rescuing the mission altogether.
Working with her mentor, Jim Taylor, and the flight team, Muñoz Fernández and the group quickly devised a strategy. If mission controllers could temporarily point the spacecraft close enough toward Earth, the telecom team could send commands through the spacecraft's high-gain antenna. The strategy required that Muñoz Fernández and Taylor analyze the signals coming from the spacecraft and send commands during the small window when the antenna was pointed toward Earth. If all went according to plan, a new software package would be radioed to the spacecraft instructing it to use its onboard camera as a de facto navigation tool.
"Initially, the probability of getting the high-gain antenna pointed on Earth and keeping it there for a typical communications pass was significantly below 50 percent," said Marc Rayman, who at the time was Deep Space 1's Mission Manager. "But there were two mottos I tried to get the team to adopt: 'If it isn't impossible, it isn't worth doing,' and, 'Never give up. Never surrender.' I took the second one from the movie 'Galaxy Quest.'"
The plan worked. In 2001, Deep Space 1 made a successful flyby of comet Borrelly, snapping hundreds of up-close photos of the comet. And the operation to save the mission went down as one of the most successful robotic spacecraft rescues in history.
"I got so much done in three months. It's unbelievable what we got accomplished," said Muñoz Fernández.
Having been accepted to a doctoral program at Caltech just before the start of her JPL internship, Muñoz Fernández carried the momentum from her experience into earning her doctorate in optical communications. When she came back to JPL in 2006, she was hired as a flight and project systems engineer for the Space Interferometry Mission.
These days, she divides her time between a busy schedule of research in deep space communications, techniques for model-based systems engineering for NASA missions, and task managing information architecture standards for space systems. And she says the lessons from her internship still play an essential role in her work - as does the mentoring she received from Taylor and Kar-Ming Cheung.
"I had the best mentors, that's for sure," said Muñoz Fernández. "You work with many different people, and I realize how fortunate I was that the first time I came here, I got to work with these amazing people - not just nice people, but so knowledgeable technically."
This summer Muñoz Fernández is preparing to mentor her own students, and she says she has plenty of advice from her experience to pass along to the next generation.
"It's exciting to be able to teach new generations the knowledge that you have," she said. "And it's not only that the student learns from the mentor, but the mentor can also learn from the student. They can think of something that someone who was working here for a long time didn't think about because they come with a new perspective."
Dr. Michela Muñoz Fernández is a principal investigator at JPL. She has also worked as a systems engineer and science payload engineer on instruments and operations for the Juno mission. She currently directs research for model-based systems engineering for NASA space missions, is a task manager for information and architecture standards, conducts research on optical communications in deep space, and studies the complexity of DSN links.