Continuing a “drama-free” test flight, NASA’s unpiloted Orion spacecraft is set to fire its main engine Thursday to leave a distant orbit around the moon, heading for a flyby close to the lunar surface next week to swing onto a trajectory bringing it back to Earth for splashdown in the Pacific Ocean on Dec. 11.
The burn with the Orion spacecraft’s orbital maneuvering system engine occurred at 4:53 p.m. EST (2153 GMT). The 6,000-pound-thrust, hydrazine-fueled engine fired for 1 minute and 45 seconds, enough to nudge the spacecraft out of its distant retrograde orbit around the moon, where it’s been flying since Nov. 25. The maneuver was expected to change Orion’s velocity by roughly 310 mph (454 feet per second; 498 kilometers per hour).
The orbit departure burn was the fourth of five main engine firings the Orion spacecraft will execute on on NASA’s Artemis 1 mission, a test flight of the agency’s new deep space capsule and heavy-lift rocket before astronauts strap in for a trip around the moon on Artemis 2, scheduled for late 2024. NASA plans to land astronauts on the moon beginning with Artemis 3, debuting a commercial moon lander derived from SpaceX’s Starship rocket program.
With only a few unexpected events, or “funnies,” so far in the mission, managers have added 11 bonus flight test objectives to further wring out the Orion spacecraft before astronauts fly it in two years. These are on top of the 124 test objectives NASA engineers identified going into the mission.
“Rather than having to work anomalies we’re able to push the boundaries,” said Zeb Scoville, NASA’s deputy chief flight director at the Johnson Space Center in Houston.
The additional tests involve longer-duration firings of the auxiliary engines on the Orion spacecraft’s service module, supplied by the European Space Agency and Airbus. The spacecraft completed a 95-second firing of the auxiliary engines Wednesday, far exceeding the 17-second duration of the mission’s previous longest burn of the smaller thrusters that surround the main engine.
Chris Edelen, deputy manager for NASA’s Orion integration office, said one of the goals of the longer-duration thruster firing was to verify thermal models and observe how the plume and heat from the thruster exhaust affects the four solar array wings on the service module.
The Orion spacecraft is designed to normally fly with its tail pointed toward the sun. That’s the best orientation, or attitude, to keep the spacecraft thermally balanced and maximize power generation from its solar arrays. The spacecraft can veer as far 20 degrees from its tail-to-sun attitude, but for Artemis 1, mission managers planned more conservative limits to keep it within a 2-by-4 degree box.
Edelen said mission controllers in Houston commanded the Orion spacecraft to change its attitude to different parts of the broader 20-degree box to measure changes in the temperatures of various components on the vehicle.
“It’s probably not the most glamorous part of spaceflight, but heaters and analyzing your thermal performance of your spacecraft is very important because, as you can imagine, you don’t want any valves to seize up in the cold of space, or have propellant lines or water lines freeze and potentially burst,” Edelen said. “So it’s very important that we get good data on the thermal environment in these different attitudes, or orientations, of the spacecraft.”
If the spacecraft doesn’t need to power on heaters, engineers could redirect some electricity to support other mission functions.
“The heaters tend to be big power hogs,” Edelen said. “They are one of the biggest impacts to our power usage. So by flying different attitudes, we’re better able to analyze what our power usage is, and hopefully free up some power for future missions.”
NASA says the Orion spacecraft completed a “nominal” burn to leave a distant orbit around the moon & begin the trip back to Earth.
— Spaceflight Now (@SpaceflightNow) December 1, 2022
Other bonus objectives for the return trip to Earth include testing to see how the opening and closing a valve affects a slow, and expected, leak rate in a pressure control assembly in the Orion propulsion system. Another extra test will demonstrate the Orion spacecraft’s ability to change its orientation at a faster rate of up to 4 degrees per second, which it will need to do on the Artemis 2 mission with astronauts on-board.
“All that is telling us about the performance of the thermal systems, about the camera systems, about the navigation systems, so we can know how is this going to work,” Scoville said in a press conference Wednesday.
Another added task will be a test of a so-called three degree of freedom attitude control mode that may allow the spacecraft to conserve more propellant.
The Orion spacecraft is designed to accommodate a crew of four astronauts in deep space for up to 21 days, and can fly longer missions when docked to Gateway mini-space station NASA and its international partners plan to build in orbit around the moon. The Orion crew module, where astronauts will live during lunar expeditions, was built by Lockheed Martin.
NASA awarded Lockheed Martin the contract to develop the Orion spacecraft in 2006 under the umbrella of the agency’s Constellation moon program, which was canceled in 2010.
NASA kept the Orion program alive through two major restructurings of the agency’s deep space exploration efforts, first during the Obama administration, when Congress and the White House agreed to pivot NASA’s focus to a human mission to Mars, with an interim crewed expedition to an asteroid.
The Trump administration shifted NASA’s exploration program back to the moon. NASA dubbed the moon program Artemis, naming it for the twin sister of Apollo in Greek mythology.
Through it all, the Orion program survived. NASA committed $14.2 billion to develop the Orion spacecraft from 2012 through the end of this fiscal year Sept. 30, plus an additional $6.3 billion spent on the program in the prior decade under the Constellation program. That comes to $20.5 billion over the course of a decade-and-a-half of work.
The only minor issues engineers have discovered since Artemis 1’s launch include “funnies” with the spacecraft’s star trackers, which are used to determine the capsule’s position in space. That turned out not to be a problem. “In the case of the star tracker … we’ve learned that this is actually how the system was going to function in the flight environment,” Edelen said.
Engineers have also seen fluctuations in coolant flow in a thermal control system loop, and determined that is likely caused by a gas bubble in the system. A computer also reset when it was hit by space radiation, an expected occurrence on a deep space mission.
Edelen said the mission, so far, has been “drama-free.”
“I would call it over achieving,” said Mike Sarafin, NASA’s Artemis 1 mission manager.
“We’re not finding any huge surprises,” Sarafin said. “The surprises that we we are having are pleasant surprises … We continue to build that confidence that this is our deep space human transportation system, and it is meeting or exceeding expectations across the board.”
While there are no humans on-board Artemis 1, there are three instrumented mannequins inside the Orion spacecraft’s pressurized cabin to gather data on accelerations, vibrations, and radiation on the flight to the moon and back. There’s also a biological experiment inside the cockpit to help scientists study how the deep space environment, including elevated levels of ionizing radiation, affects organisms like plant seeds, fungi, yeast, and algae.
The crew cabin in the Artemis 1 capsule is kept pressurized at a temperature in the mid-50s Fahrenheit, Edelen said. The Orion spacecraft’s full life support system will fly for the first time on Artemis 2.
Engineers on Earth have also been uplinking messages and commands to a voice-activated crew interface technology demonstration payload named Callisto inside the pressurized crew module. A stuffed Snoopy toy is also on-board.
NASA has flown a stripped down Orion crew capsule in space once before in 2014, when the spacecraft launched into a high-altitude orbit around Earth for a four-hour test flight. Artemis 1 is the first time an Orion spacecraft has flown with its European-built service module.
“We are very proud that our system is functioning perfectly,” said Philippe Deloo, ESA’s service module program manager. “It’s even better than we ever expected.”
“The propellant margins have kept increasing throughout the mission through the excellent performance of the system,” he said. “We are rich in power. The solar arrays produce more power, about 15% more power than planned, and the consumption is less. The consumption is less because basically the thermal environment is much more benign in terms of the spacecraft than we had foreseen.
“The regulation of the propulsion system has been our troubled child throughout the development, and it has just worked beautifully,” Deloo said Wednesday. “No problem whatsoever with this propulsion system, and we hope that’s going to continue like this for the big burns and all the trajectory correction burns that will happen up to the return of the vehicle.”
Artemis 1 launched Nov. 16 from NASA’s Kennedy Space Center in Florida on the inaugural flight of the Space Launch System moon rocket, a 322-foot-tall (98-meter) behemoth that took a decade and more than $22 billion to develop.
Another $5.4 billion in the same period went toward readying Kennedy Space Center’s ground infrastructure for SLS and Orion missions.
The SLS moon rocket performed flawlessly, NASA officials said, sending the Orion capsule on a five-day track toward the moon, where it zoomed about 80 miles (130 kilometers) from the surface Nov. 21. The close flyby used lunar gravity to swing the Orion spacecraft into a distant retrograde orbit, or DRO, some 50,000 miles (80,000 kilometers) from the moon.
Another main engine burn Nov. 25 placed the Orion spacecraft into the DRO, so named because it is not a low-altitude orbit like the Apollo capsules of the 1960s and 1970s flew in, and because Orion is moving around the moon in the opposite direction the moon travels around Earth.
Mission planners chose the orbit for the Artemis 1 mission for several reasons. First, the Orion spacecraft’s propulsion system does not have the capability to steer the capsule into a low-altitude orbit around the moon as the Apollo missions did. And the DRO is stable because it is near the balance point between the pull of gravity from Earth and the moon, reducing the fuel Orion needs to burn to maintain its orbit.
The Orion spacecraft spent about six days in the distant retrograde orbit performing tests and checkouts, long enough to complete one-half of a lap around the moon. On Saturday, the capsule broke the distance record for a spacecraft designed to carry humans into space and return them to Earth, according to NASA.
The record was previously set on NASA’s Apollo 13 mission, which reached a distance of 248,655 miles (400,171 kilometers) from Earth when it looped around the far side of the moon with a three-man crew in 1970. Apollo 13’s moon landing was aborted when one of its oxygen tanks exploded on outbound journey from Earth, and the spacecraft steered onto a “free return” trajectory that took it farther from Earth than any of the other Apollo missions.
The Orion spacecraft reached its greatest distance from Earth on Monday, Nov. 28, at more than 268,500 miles (432,000 kilometers).
After Thursday’s 105-second main engine burn to leave the distant retrograde orbit, the moon’s gravity will pull the Orion spacecraft toward a high-speed flyby just 79 miles (127 kilometers) from the surface on Monday, Dec. 5. The Orion main engine will fire again at 11:43 a.m. EST (1643 GMT) for 3 minutes and 27 seconds, the spacecraft’s longest burn on the Artemis 1 mission.
The return powered flyby maneuver will aim Orion toward its splashdown point in the Pacific Ocean. The spacecraft will jettison its European service module just before re-entry, then perform two dips into the atmosphere to bleed off speed before deploying parachutes for splashdown off the coast of San Diego on Dec. 11.
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