We Like Big Rockets and We Cannot Lie: Saturn V vs. SLS

On this day 50 years ago, human beings embarked on a journey to set foot on another world for the very first time


At 9:32 a.m. EDT, millions watched as Apollo astronauts Neil Armstrong, Buzz Aldrin and Michael Collins lifted off from Launch Pad 39A at the Kennedy Space Center in Cape Canaveral, Florida, flying high on the most powerful rocket ever built: the mighty Saturn V.


As we prepare to return humans to the lunar surface with our Artemis program, we’re planning to make history again with a similarly unprecedented rocket, the Space Launch System (SLS). The SLS will be our first exploration-class vehicle since the Saturn V took American astronauts to the Moon a decade ago. With its superior lift capability, the SLS will expand our reach into the solar system, allowing astronauts aboard our Orion spacecraft to explore multiple, deep-space destinations including near-Earth asteroids, the Moon and ultimately Mars.


So, how does the Saturn V measure up half a century later? Let’s take a look.

Mission Profiles: From Apollo to Artemis 

Saturn V


Every human who has ever stepped foot on the Moon made it there on a Saturn V rocket. The Saturn rockets were the driving force behind our Apollo program that was designed to land humans on the Moon and return them safely back to Earth.


Developed at our Marshall Space Flight Center in the 1960s, the Saturn V rocket (V for the Roman numeral “5”)  launched for the first time uncrewed during the Apollo 4 mission on November 9, 1967. One year later, it lifted off for its first crewed mission during Apollo 8. On this mission, astronauts orbited the Moon but did not land. Then, on July 16, 1969, the Apollo 11 mission was the first Saturn V flight to land astronauts on the Moon. In total, this powerful rocket completed 13 successful missions, landing humans on the lunar surface six times before lifting off for the last time in 1973.

Space Launch System (SLS) 


Just as the Saturn V was the rocket of the Apollo generation, the Space Launch System will be the driving force behind a new era of spaceflight: the Artemis generation.


During our Artemis missions, SLS will take humanity farther than ever before. It is the vehicle that will return our astronauts to the Moon by 2024, transporting the first woman and the next man to a destination never before explored – the lunar South Pole. Over time, the rocket will evolve into increasingly more powerful configurations to provide the foundation for human exploration beyond Earth’s orbit to deep space destinations, including Mars.

SLS will take flight for the first time during Artemis 1 where it will travel 280,000 miles from Earth – farther into deep space than any spacecraft built for humans has ever ventured.

Size: From Big to BIGGER 

Saturn V


The Saturn V was big. 

In fact, the Vehicle Assembly Building at Kennedy Space Center is one of the largest buildings in the world by volume and was built specifically for assembling the massive rocket. At a height of 363 feet, the Saturn V rocket was about the size of a 36-story building and 60 feet taller than the Statue of Liberty!

Space Launch System (SLS)


Measured at just 41 feet shy of the Saturn V, the initial SLS rocket will stand at a height of 322 feet. Because this rocket will evolve into heavier lift capacities to facilitate crew and cargo missions beyond Earth’s orbit, its size will evolve as well. When the SLS reaches its maximum lift capability, it will stand at a height of 384 feet, making it the tallest rocket in the world.

Power: Turning Up the Heat 

Saturn V

For the 1960s, the Saturn V rocket was a beast – to say the least.

Fully fueled for liftoff, the Saturn V weighed 6.2 million pounds and generated 7.6 million pounds of thrust at launch. That is more power than 85 Hoover Dams! This thrust came from five F-1 engines that made up the rocket’s first stage. With this lift capability, the Saturn V had the ability to send 130 tons (about 10 school buses) into low-Earth orbit and about 50 tons (about 4 school buses) to the Moon.

Space Launch System (SLS)


Photo of SLS rocket booster test

Unlike the Saturn V, our SLS rocket will evolve over time into increasingly more powerful versions of itself to accommodate missions to the Moon and then beyond to Mars.


The first SLS vehicle, called Block 1, will weigh 5.75 million pounds and produce 8.8 million pounds of thrust at time of launch. That’s 15 percent more than the Saturn V produced during liftoff! It will also send more than 26 tons  beyond the Moon. Powered by a pair of five-segment boosters and four RS-25 engines, the rocket will reach the period of greatest atmospheric force within 90 seconds!


Following Block 1, the SLS will evolve five more times to reach its final stage, Block 2 Cargo. At this stage, the rocket will provide 11.9 million pounds of thrust and will be the workhorse vehicle for sending cargo to the Moon, Mars and other deep space destinations. SLS Block 2 will be designed to lift more than 45 tons to deep space. With its unprecedented power and capabilities, SLS is the only rocket that can send our Orion spacecraft, astronauts and large cargo to the Moon on a single mission.

Build: How the Rockets Stack Up

Saturn V


The Saturn V was designed as a multi-stage system rocket, with three core stages. When one system ran out of fuel, it separated from the spacecraft and the next stage took over. The first stage, which was the most powerful, lifted the rocket off of Earth’s surface to an altitude of 68 kilometers (42 miles). This took only 2 minutes and 47 seconds! The first stage separated, allowing the second stage to fire and carry the rest of the stack almost into orbit. The third stage placed the Apollo spacecraft and service module into Earth orbit and pushed it toward the Moon. After the first two stages separated, they fell into the ocean for recovery. The third stage either stayed in space or crashed into the Moon.

Space Launch System (SLS)

Much like the Saturn V, our Space Launch System is also a multi-stage rocket. Its three stages (the solid rocket boosters, core stage and upper stage) will each take turns thrusting the spacecraft on its trajectory and separating after each individual stage has exhausted its fuel. In later, more powerful versions of the SLS, the third stage will carry both the Orion crew module and a deep space habitat module.

A New Era of Space Exploration 

Just as the Saturn V and Apollo era signified a new age of exploration and technological advancements, the Space Launch System and Artemis missions will bring the United States into a new age of space travel and scientific discovery.

Join us in celebrating the 50th anniversary of the Apollo 11 Moon landing and hear about our future plans to go forward to the Moon and on to Mars by tuning in to a special two-hour live NASA Television broadcast at 1 p.m. ET on Friday, July 19. Watch the program at www.nasa.gov/live.

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New Hubble Constant Measurement Adds to Mystery of Universe’s Expansion Rate

Galaxies Used to Refine the Hubble Constant

Credit: NASA, ESA, W. Freedman (University of Chicago), ESO, and the Digitized Sky Survey

Astronomers have made a new measurement of how fast the universe is expanding, using an entirely different kind of star than previous endeavors. The revised measurement, which comes from NASA’s Hubble Space Telescope, falls in the center of a hotly debated question in astrophysics that may lead to a new interpretation of the universe’s fundamental properties.
Scientists have known for almost a century that the universe is expanding, meaning the distance between galaxies across the universe is becoming ever more vast every second. But exactly how fast space is stretching, a value known as the Hubble constant, has remained stubbornly elusive.
Now, University of Chicago professor Wendy Freedman and colleagues have a new measurement for the rate of expansion in the modern universe, suggesting the space between galaxies is stretching faster than scientists would expect. Freedman’s is one of several recent studies that point to a nagging discrepancy between modern expansion measurements and predictions based on the universe as it was more than 13 billion years ago, as measured by the European Space Agency’s Planck satellite.
As more research points to a discrepancy between predictions and observations, scientists are considering whether they may need to come up with a new model for the underlying physics of the universe in order to explain it. 
«The Hubble constant is the cosmological parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves,» said Freedman. «The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an immediate and compelling reason to believe that there is something fundamentally flawed in our current model of the universe.”
In a new paper accepted for publication in The Astrophysical Journal, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their new observations, made using Hubble, indicate that the expansion rate for the nearby universe is just under 70 kilometers per second per megaparsec (km/sec/Mpc). One parsec is equivalent to 3.26 light-years distance.
This measurement is slightly smaller than the value of 74 km/sec/Mpc recently reported by the Hubble SH0ES (Supernovae H0 for the Equation of State) team using Cepheid variables, which are stars that pulse at regular intervals that correspond to their peak brightness. This team, led by Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Baltimore, Maryland, recently reported refining their observations to the highest precision to date for their Cepheid distance measurement technique.

How to Measure Expansion

A central challenge in measuring the universe’s expansion rate is that it is very difficult to accurately calculate distances to distant objects.
In 2001, Freedman led a team that used distant stars to make a landmark measurement of the Hubble constant. The Hubble Space Telescope Key Project team measured the value using Cepheid variables as distance markers. Their program concluded that the value of the Hubble constant for our universe was 72 km/sec/Mpc.
But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the big bang, which is called the Cosmic Microwave Background. The Planck measurements allow scientists to predict how the early universe would likely have evolved into the expansion rate astronomers can measure today. Scientists calculated a value of 67.4 km/sec/Mpc, in significant disagreement with the rate of 74.0 km/sec/Mpc measured with Cepheid stars.
Astronomers have looked for anything that might be causing the mismatch. «Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don’t yet understand about the stars we’re measuring, or whether our cosmological model of the universe is still incomplete,» Freedman said. «Or maybe both need to be improved upon.»
Freedman’s team sought to check their results by establishing a new and entirely independent path to the Hubble constant using an entirely different kind of star.
Certain stars end their lives as a very luminous kind of star called a red giant, a stage of evolution that our own Sun will experience billions of years from now. At a certain point, the star undergoes a catastrophic event called a helium flash, in which the temperature rises to about 100 million degrees and the structure of the star is rearranged, which ultimately dramatically decreases its luminosity. 
Astronomers can measure the apparent brightness of the red giant stars at this stage in different galaxies, and they can use this as a way to tell their distance.
The Hubble constant is calculated by comparing distance values to the apparent recessional velocity of the target galaxies — that is, how fast galaxies seem to be moving away. The team’s calculations give a Hubble constant of 69.8 km/sec/Mpc — straddling the values derived by the Planck and Riess teams.
«Our initial thought was that if there’s a problem to be resolved between the Cepheids and the Cosmic Microwave Background, then the red giant method can be the tie-breaker,» said Freedman.
But the results do not appear to strongly favor one answer over the other say the researchers, although they align more closely with the Planck results.
NASA’s upcoming mission, the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s, will enable astronomers to better explore the value of the Hubble constant across cosmic time. WFIRST, with its Hubble-like resolution and 100 times greater view of the sky, will provide a wealth of new Type Ia supernovae, Cepheid variables, and red giant stars to fundamentally improve distance measurements to galaxies near and far.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.


Ray Villard
Space Telescope Science Institute, Baltimore, Maryland


Louise Lerner
University of Chicago, Chicago, Illinois


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Remember the Women Who Made #Apollo50th Possible

As the world celebrates the 50th anniversary of the historic Moon landing, we remember some of the women whose hard work and ingenuity made it possible. The women featured here represent just a small fraction of the enormous contributions made by women during the Apollo era. 

Margaret Hamilton, Computer Programmer


Margaret Hamilton led the team that developed the building blocks of software engineering — a term that she coined herself. Her systems approach to the Apollo software development and insistence on rigorous testing was critical to the success of Apollo. In fact, the Apollo guidance software was so robust that no software bugs were found on any crewed Apollo missions, and it was adapted for use in Skylab, the Space Shuttle and the first digital fly-by-wire systems in aircraft.

In this photo, Hamilton stands next to a stack of Apollo Guidance Computer source code. As she noted, “There was no second chance. We all knew that.”

Katherine Johnson, Aerospace Technologist


As a very young girl, Katherine Johnson loved to count things. She counted everything, from the number of steps she took to get to the road to the number of forks and plates she washed when doing the dishes.

As an adult, Johnson became a “human computer” for the National Advisory Committee for Aeronautics, which in 1958, became NASA. Her calculations were crucial to syncing Apollo’s Lunar Lander with the Moon-orbiting Command and Service Module. “I went to work every day for 33 years happy. Never did I get up and say I don’t want to go to work.“

Judy Sullivan, Biomedical Engineer


This fabulous flip belongs to biomedical engineer Judy Sullivan, who monitored the vital signs of the Apollo 11 astronauts throughout their spaceflight training via small sensors attached to their bodies. On July 16, 1969, she was the only woman in the suit lab as the team helped Neil Armstrong suit up for launch.

Sullivan appeared on the game show “To Tell the Truth,” in which a celebrity panel had to guess which of the female contestants was a biomedical engineer. Her choice to wear a short, ruffled skirt stumped everyone and won her a $500 prize. In this photo, Sullivan monitors a console during a training exercise for the first lunar landing mission.

Billie Robertson, Mathematician


Billie Robertson, pictured here in 1972 running a real-time go-no-go simulation for the Apollo 17 mission, originally intended to become a math teacher. Instead, she worked with the Army Ballistic Missile Agency, which later became rolled into NASA. She created the manual for running computer models that were used to simulate launches for the Apollo, Skylab and Apollo Soyuz Test Project programs. 

Robertson regularly visited local schools over the course of her career, empowering young women to pursue careers in STEM and aerospace.

Mary Jackson, Aeronautical Engineer


In 1958, Mary Jackson became NASA’s first African-American female engineer. Her engineering specialty was the extremely complex field of boundary layer effects on aerospace vehicles at supersonic speeds.

In the 1970s, Jackson helped the students at Hampton’s King Street Community center build their own wind tunnel and use it to conduct experiments. “We have to do something like this to get them interested in science,” she said for the local newspaper. “Sometimes they are not aware of the number of black scientists, and don’t even know of the career opportunities until it is too late.”

Ethel Heinecke Bauer, Aerospace Engineer


After watching the launch of Sputnik in October 1957, Ethel Heinecke Bauer changed her major to mathematics. Over her 32 years at NASA, she worked at two different centers in mathematics, aerospace engineering, development and more. 

Bauer planned the lunar trajectories for the Apollo program including the ‘free return’ trajectory which allowed for a safe return in the event of a systems failure  — a trajectory used on Apollo 13, as well as the first three Apollo flights to the Moon. In the above photo, Bauer works on trajectories with the help of an orbital model.

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