September 25, 2022

Artemis 1 flight to moon depends on precision rocket firings to pull off a complex trajectory


This graphic from NASA illustrates the major events of the Artemis 1 launch sequence. Credit: NASA

Even using the most powerful rocket NASA’s ever built, getting the agency’s unpiloted Orion spacecraft to the moon for the Artemis 1 test flight won’t be easy. It will hinge on a complex series of precisely orchestrated deep space maneuvers.

Mission planners had to take into account the constantly changing positions of Earth and moon to ensure the Space Launch System rocket accurately delivers Orion to a moving point in low-Earth orbit for the critical “trans-lunar injection” — TLI — rocket firing that will begin the trip to the moon.

They had to design a trajectory sending Orion within a scant 60 miles of the moon’s surface for a flyby that will bend its path out toward the planned “distant retrograde orbit” — one that will carry the capsule farther from Earth than any other human-rated spacecraft.

The trajectory must minimize the amount of time the solar-powered Orion is in the shadow of the moon while setting up a final lunar flyby to precisely target the capsule’s splashdown in the Pacific Ocean during daylight hours as Earth moves through space and rotates on its axis.

All of those factors played into defining a two-hour launch window that opens at 8:33 a.m. EDT Monday when, if all goes well, the 322-foot-tall Space Launch System rocket will blast off from pad 39B at the Kennedy Space Center.

Generating 8.8 million pounds of thrust at liftoff, the SLS rocket will propel Orion, its service module and the booster’s upper stage into an initial orbit, one with a high point, or apogee, of about 1,100 miles and a low point, or perigee, of just 18 miles.

Ten minutes after separation from the SLS core stage but still attached to the Interim Cryogenic Propulsion Stage, or ICPS, the Orion capsule’s service module, provided by the European Space Agency, will deploy four steerable solar panels to begin recharging on-board batteries.

The ICPS’s single Aerojet Rocketdyne RL10B engine will fire for the first time when the spacecraft nears to high point of the orbit about 51 minutes after launch. The result of the “burn” will raise the low point of the orbit from 18 to about 115 miles.

The SLS’s two-hour lunar launch window is defined by a requirement for the ICPS to reach a point in space on the opposite side of Earth from the moon known as the antipode, where it can fire its engine to break out of Earth orbit and head for the moon.

That point is constantly moving as Earth rotates and moves along its orbit around the sun while the moon moves in its orbit around Earth. The Artemis 1 trajectory is designed so the rocket’s perigee syncs up as required with the antipode so an engine firing can send Orion to a point in space where the moon will be five days later.

At that moment, one hour and 36 minutes after launch, the ICPS’s RL10B engine will fire for 18 minutes, the longest burn ever attempted by that family of engines, increasing the spacecraft’s velocity to some 22,600 mph and effectively raising the high point of the orbit to the vicinity of the moon.

A half hour after the TLI engine firing, the Orion capsule will separate from the ICPS to fly on its own. From that point, the ICPS will continue toward the moon — deploying a dozen small scientific research satellites, called CubeSats, along the way — before thruster firings to head out into a “disposal” orbit around the sun.

The Artemis 1 mission profile will carry the Orion spacecraft into a distant retrograde orbit around the moon, flying at an average 43,000 miles (70,000 kilometers) from the lunar surface. The Orion spacecraft will return to Earth for splashdown in the Pacific Ocean at the end of the mission. Credit: NASA

Orion flight controllers, meanwhile, will test the orbital maneuvering system engine powering the capsule’s service module, carrying out four trajectory correction maneuvers. Those will set up a critical “outbound powered flyby” engine firing.

“That’s the big burn that will actually move Orion and send it toward the planned distant retrograde orbit (around the moon),” said lead Flight Director Rick LaBrode. “So when we do that burn and we go by the moon, we’re going to be about 60 miles off the surface. It’s going to be spectacular.”

The outbound powered flyby will occur over the back side of the moon when Orion is out of contact with mission control.

“So we’ll be praying and I’ll hold my breath,” LaBrode joked. “But (we’re) confident that all will go well.”

After a slingshot-like loop around the moon, another burn will put the craft in the planned distant retrograde orbit.

Cameras inside and out

Throughout the flight, cameras inside and outside Orion will document the view, beaming back selfies and shots of the spacecraft, moon and Earth, including planned views of Earthrise over the limb of the moon reminiscent of a famous shot from the Apollo 8 mission that came to symbolize the environmental movement.

All the while, flight controllers will be testing Orion’s systems and collecting a steady stream of engineering telemetry to document the spacecraft’s performance in the deep space environment. The service module will be closely monitored given the Artemis 1 mission will last twice as long as the module’s 21-day design certification.

Artist’s concept of the Orion spacecraft’s crew module and service module near the moon. Credit: Lockheed Martin
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