NASA’s Space Launch System, or SLS, is a super heavy-lift rocket designed to send the Orion spacecraft, astronauts, and cargo beyond low Earth orbit. It is the launch vehicle for the Artemis lunar missions, which aim to return humans to the Moon and prepare for later missions to Mars. SLS matters because deep-space missions require much more energy than launches to nearby Earth orbit.
Its design combines powerful rocket engines, large propellant tanks, and solid rocket boosters to produce enormous thrust at liftoff.
The SLS Block 1 rocket uses a core stage with liquid hydrogen and liquid oxygen propellants feeding four RS-25 engines. Two five-segment solid rocket boosters provide most of the thrust during the first two minutes of flight, then separate after their fuel is used. Above the core stage, the upper stage completes the push toward the Moon by performing a trans-lunar injection burn.
The Orion spacecraft rides at the top, protected during launch by a launch abort system that can pull the crew capsule away in an emergency.
Key Facts
- SLS Block 1 liftoff thrust is about 39 MN, which is about 8.8 million pounds of force.
- Newton’s second law for launch is Fnet = ma, where Fnet must exceed the rocket’s weight to accelerate upward.
- Rocket weight near Earth is W = mg, where g = 9.8 m/s^2.
- Ideal rocket performance is estimated by the rocket equation: Δv = ve ln(m0/mf).
- The core stage burns liquid hydrogen fuel with liquid oxygen oxidizer in four RS-25 engines.
- The Orion spacecraft is sent toward the Moon after the upper stage performs a trans-lunar injection burn.
Vocabulary
- Space Launch System
- The Space Launch System is NASA’s super heavy-lift rocket built to launch Orion and large payloads on deep-space missions.
- Core stage
- The core stage is the main liquid-fueled body of the SLS that stores propellant and powers the RS-25 engines.
- Solid rocket booster
- A solid rocket booster is a side-mounted rocket that burns solid propellant to provide very high thrust early in launch.
- Orion spacecraft
- Orion is NASA’s crew spacecraft designed to carry astronauts beyond low Earth orbit and return them safely to Earth.
- Trans-lunar injection
- Trans-lunar injection is the engine burn that places a spacecraft on a trajectory from Earth toward the Moon.
Common Mistakes to Avoid
- Confusing thrust with speed is wrong because thrust is a force, while speed describes how fast the rocket is moving.
- Ignoring the rocket’s changing mass is wrong because burning propellant makes the rocket lighter, so the same thrust can produce greater acceleration later in flight.
- Assuming the boosters work all the way to space is wrong because the SLS solid rocket boosters burn for only about the first two minutes before separation.
- Treating the Orion capsule as the rocket is wrong because Orion is the spacecraft on top, while SLS is the launch vehicle that lifts it into space.
Practice Questions
- 1 An SLS launch has a liftoff thrust of 39,000,000 N and a liftoff mass of 2,600,000 kg. Using g = 9.8 m/s^2, calculate the rocket’s weight and its initial net upward force.
- 2 If a rocket stage changes velocity by 3,200 m/s while burning for 480 s, what is its average acceleration in m/s^2?
- 3 Explain why the SLS uses both liquid-fueled RS-25 engines and solid rocket boosters instead of only one type of propulsion.