NASA is gearing up to launch a series of exploration missions to the moon that will set the stage for journeys to destinations farther in deep space, such as Mars. The agency is developing its Space Launch System (SLS) rocket and Orion spacecraft to carry humans back to the lunar vicinity for the first time since the Apollo missions ended in 1972.

Exploration Mission-1

Exploration Mission-1 (EM-1) will be the first of these missions, and will consist of an uncrewed flyby around the moon with the Orion spacecraft. The planned launch date for EM-1 is December 2019. SLS will blast off from Launch Complex 39B at Kennedy Space Center in Florida to place Orion in a distant lunar retrograde orbit (DRO) before it returns to Earth.

Artist’s concept of the Space Launch System (SLS) rocket with Orion atop it. Source: NASA

Orion will deploy its solar panels and the SLS upper stage known as the Interim Cryogenic Propulsion Stage (ICPS). The ICPS will provide the thrust necessary to exit Earth orbit on a trajectory to the moon.

After separating from Orion, the ICPS will deploy its payload. According to current plans, the payload consists of a number of tiny CubeSat satellites that will perform deep space experiments and technology demonstrations.

On the several day journey from Earth orbit to the moon, propulsion, power, air and water will be provided by a service module supplied by the European Space Agency.

Arriving at the moon, Orion will pass by just 62 miles above the surface before using the moon’s gravitational force to enter a deep retrograde orbit that takes it 40,000 miles from the moon. Orion will remain in the retrograde orbit for six days, traveling in a direction opposite to the one that the moon takes as it orbits Earth.

Orion will exit moon orbit by firing the service module’s engine and using the moon’s gravity to set it on a path back to Earth. Entering the atmosphere at a speed of 25,000 miles per hour, the spacecraft’s heat shield will be exposed to temperatures around 5,000 degrees Fahrenheit before splashing down in the Pacific Ocean off the San Diego coast.

EM-1 will be Orion’s first trip to the “proving ground,” an area of space around the moon where NASA can practice deep space operations, validate systems and gain experience needed for a mission to Mars.

“This is a mission that truly will do what hasn’t been done and learn what isn’t known,” said Mike Sarafin, EM-1 mission manager at NASA Headquarters in Washington. “It will blaze a trail that people will follow on the next Orion flight, pushing the edges of the envelope to prepare for that mission.”

Exploration Mission-2

The second mission to the proving ground will be Exploration Mission-2 (EM-2). With a planned launch date in 2023, EM-2 will be the first crewed Orion mission, carrying a crew of up to four people on a flyby mission around the moon that will test the systems and capabilities needed for humans to operate in deep space.

“It’s just like the Mercury, Gemini and Apollo programs, which built up and demonstrated their capabilities over a series of missions,” said Bill Hill, deputy associated administrator, Exploration Systems Development, NASA Headquarters in Washington. “During this mission, we have a number of tests designed to demonstrate critical functions, including mission planning, system performance, crew interfaces, and navigation and guidance in deep space.”

Mission profile for Exploration Mission-2 illustrating its multi-translunar injection maneuvers and free return flight. Source: NASA. (Click to enlarge.)

EM-2 will have a flight profile known as multi-translunar injection (MTLI) that uses multiple propulsive maneuvers to put Orion on a path to the moon.

Following launch, Orion will complete one 90 minute circular Earth orbit at an altitude of 100 nautical miles to verify that its systems are functioning properly.

Four RL-10 engines that are part of the SLS’s exploration upper stage (EUS) will then boost Orion into a highly elliptical orbit around Earth in a partial translunar injection maneuver. This elliptical orbit will last 24 hours and range in distance from 500 to 19,000 nautical miles from Earth.

The EUS will then separate from Orion and release any potential payloads mounted in the SLS’s universal stage adapter. A final propulsion maneuver will involve firing the service module’s engine in a translunar injection burn to put Orion on a path toward the moon.

Orion will complete a flyby of the moon before returning to Earth in a free return trajectory that uses the moon’s gravity as a slingshot instead of requiring additional spacecraft propulsion.

The exploration missions to the proving ground are critical for NASA to gain knowledge about deep space environments and test the safety and efficacy of its deep space systems.

“Between the DRO on our first flight, and the MTLI on the second flight, we will demonstrate the full range of capabilities SLS and Orion need to operate in deep space,” said Hill.

EM-1 and EM-2 will be followed by a series of additional planned exploration missions at a rate of about one per year. These missions will deliver components of a space station in lunar orbit that will serve as a gateway to deep space and the lunar surface.