Ever skip stones across a pond? Imagine doing it with a spacecraft.
When NASA’s Orion returns to Earth on Dec. 11 at the end of the Artemis I mission, it will attempt a guidance and control maneuver called a skip-entry – the first time a skip entry maneuver will be attempted for a human spacecraft.
While it’s not a perfect analogy, Orion will mimic a stone skipping across a pond by dipping into the Earth’s atmosphere, skipping out, then re-entering. Performed by the crew module, this maneuver gives Orion more space to travel before splashing down, allowing it to be more precise with where it lands.
“Skip entry gives us a consistent landing site that supports astronaut safety because it allows teams on the ground to better and faster coordinate recovery efforts,” said Joe Bomba, Lockheed Martin’s Orion Aerosciences Aerothermal Lead.
Where in the World?: Achieving A Consistent Landing Site
To understand why skip entry is so important on Artemis, you need to look back at Apollo.
“If you mapped the Apollo lunar mission landings, you’d see that upon return to Earth, each craft landed at around the same longitude, but were spread out in terms of latitude,” said Bomba.
The latitude of a spacecraft’s entry for lunar returns is determined by the day of the return and the Earth and Moon’s positions. That variability, plus the fact that with direct landings, Apollo could only travel up to 1,725 miles beyond where it entered the atmosphere before it splashed down, meant that back in the day, NASA had to station recovery crews at various potential landing sites across the Pacific Ocean.
“Skip entry can correct for the variability Apollo saw with its direct landings by allowing us to ‘skip’ shorter or longer distances to bring us closer to the pre-determined landing site,” said Bomba.
With skip entry, Orion can travel up to 5,524 miles before splashing down – almost 4,000 miles more than Apollo.
Skip entry allows for next-level precision. “To put it in perspective, if Orion was actually a rock skipping off a pond, it could hit a one-foot diameter target from a distance of one and a half football fields away,” said Bomba.
By dividing the heat and force of re-entry into two events, skip entry also offers benefits like lessening the g-forces astronauts are subject to while traveling 25,000 mph during re-entry and lowering the instantaneous heat flux the vehicle and its heatshield experience.
This Isn’t Apollo
Orion will be the first human-rated spacecraft to test the skip entry maneuver – but it’s an engineering feat that’s a long time coming.
“The Apollo missions had skip capability in their design but didn’t use it because engineers couldn’t build enough confidence in the accuracy of the maneuver through the kind of testing available at the time,” said Chris Salerno, Orion Mission Analysis, Lockheed Martin.
Today’s ground computational capability that allowed Lockheed Martin and NASA engineers to run thousands of Orion entry simulations (giving them the confidence Apollo engineers couldn’t attain), the advanced integration between Orion’s hardware and software and better general knowledge of the Earth’s upper atmosphere are game changers.
“The advancements in engineering, testing and space knowledge in the past 50 years are what make this maneuver possible,” said Salerno.