When astronauts are on their first test flight aboard NASA’s Orion spacecraft, which will take them farther into the solar system than humanity has ever traveled before, their mission will be to confirm all of the spacecraft’s systems operate as designed in the actual environment of deep space. After an Orion test campaign that includes ground tests, systems demonstrations on the International Space Station, and uncrewed space test flights, this first crewed test flight will mark a significant step forward on NASA’s Journey to Mars.
This will be NASA’s first mission with crew in a series of missions in the proving ground, an area of space around the moon where crew can build and test systems needed to prepare for the challenge of missions to Mars. The mission will launch from NASA’s Kennedy Space Center in Florida as early as August 2021. Crew size will be determined closer to launch, but NASA plans to fly up to four astronauts in Orion for each human mission.
“Like every test flight, we will have test objectives for this mission both before and after we commit to going to the moon,” said Bill Hill, deputy associated administrator, Exploration Systems Development, NASA Headquarters in Washington. “It’s just like the Mercury, Gemini, and Apollo programs, which built up and demonstrated their capabilities over a series of missions. 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.”
The mission plan for the flight is built around a profile called a multi-translunar injection (MTLI), or multiple departure burns, and includes a free return trajectory from the moon. Basically, the spacecraft will circle our planet twice while periodically firing its engines to build up enough speed to push it toward the moon before looping back to Earth.
After launch, the spacecraft and upper stage of the rocket will first orbit Earth twice to ensure its systems are working normally. Orion will reach a circular orbit at an altitude of 100 nautical miles and last 90 minutes. The move or burn to get the spacecraft into a specific orbit around a planet or other body in space is called orbital insertion.
Following the first orbit, the rocket’s powerful exploration upper stage (EUS) and four RL-10 engines will perform an orbital raise, which will place Orion into a highly elliptical orbit around our planet. This is called the partial translunar injection. This second, larger orbit will take approximately 24 hours with Orion flying in an ellipse between 500 and 19,000 nautical miles above Earth. For perspective, the International Space Station orbits Earth from about 250 miles above.
Once the integrated vehicle completes these two orbits, the EUS will separate from Orion and any payloads selected and mounted inside the rocket’s universal stage adapter will be released. The payloads will then fly on their own to conduct their unique missions.
After the EUS separation, the crew will do a unique test of Orion’s critical systems. They will gather and evaluate engineering data from their day-long orbit before using Orion’s service module to complete a second and final propulsion move called the translunar injection (TLI) burn. This second burn will put Orion on a path toward the moon, and will conclude the “multi-translunar injection” portion of the mission.
“Free” ride home
The TLI will send crew around the backside of the moon where they will ultimately create a figure eight before Orion returns to Earth. Instead of requiring propulsion on the return, the spacecraft will use the moon’s gravitational pull like a slingshot to bring Orion home, which is the free return portion of the trajectory. Crew will fly thousands of miles beyond the moon, which is an average of 230,000 miles beyond the Earth.
A flexible mission length will allow NASA to gather valuable imagery data during daylight for the launch, landing and recovery phases. It will take a minimum of eight days to complete the mission, and pending additional analysis, it may be extended up to 21 days to complete additional flight test objectives.
Two missions, two different trajectories
The agency is scheduled to test SLS and Orion together for the first time without crew over the course of about three weeks in late 2018. The MTLI will build upon testing that will be done in a distant lunar retrograde orbit, or DRO, for that first mission. The DRO will put Orion in a more challenging trajectory, and will be an opportunity to test the kind of maneuvers and environments the spacecraft will see on future exploration missions. The DRO will require additional propulsion moves throughout the trip, including a moon flyby and return trajectory burns.
“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.
Once these first two test flights are completed, Hill added that NASA hopes to begin launching missions every year with crew, depending on budget and program performance.
NASA recently outlined its exploration objectives in deep space and grouped them into three categories: transportation, working in space, and staying healthy. The early missions in the proving ground are a critical step on the journey to learn more about the deep space environment and test the technologies the agency needs to eventually take humans to Mars.