NASA is studying a variant of its planned Ares 5 heavy-lift rocket that would enable an Apollo 8-like trip around the Moon in the 2015 time frame, a top U.S. space agency official told reporters Jan. 25.

Scott Horowitz, NASA's associate administrator for exploration systems, said he asked engineers at the agency's Marshall Space Flight Center in Huntsville, Ala., to study a rocket design that would combine the Ares 5 main stage with the Ares 1 upper stage to permit an around-the-Moon-and-back shakeout flight of the Orion Crew Exploration Vehicle [image] several years ahead of the first lunar landings.

"You could do an Apollo 8 kind of mission," he said during a roundtable discussion with reporters. "You could test out the capsule and the service module all the way around the lunar environment as a build up to the actual landing ... and you could have the capsule re-enter at lunar velocities."

One key objective of such a mission, Horowitz said, would be to conduct a full-scale test of a skip-entry technique that would give NASA greater control over where the Orion capsule lands when it comes back to the Moon.

Astronaut-carrying spacecraft to date, including the Apollo capsules, have used direct-entry trajectories for their returns home, Horowitz said.

"Normally when you come back to Earth you hit the atmosphere and you just, whoosh, go in," he said. "You can get a lot more flexibility in picking your landing site if you can hit the [Earth's atmosphere], skip out a little bit, and then re-hit the Earth."

Horowitz said the direct-entry technique used on Apollo required NASA to carefully select the date of return in order to have some control over the stretch of ocean where the capsule would splash down.

NASA wants Orion to routinely land on terra firma inside the United States, preferably within the same landing zone it uses for trips back from the international space station or other low-Earth orbit destinations.

Skip entry would give mission planners more flexibility and control for lunar returns, he said.

"Depending on when you leave the Moon and where you leave the Moon from, the Earth is not always pointed in the right direction for you to target the landing site you want," he said. "So you almost have to pick the day you depart from the Moon, if we did it like Apollo, before you take off. It's like a launch window from the Moon. With skip entry you get a lot more variability on that launch window. You get it to the point where you can basically go home any day you want."

Horowitz said there are a number of arguments for testing Orion at lunar-return velocities prior to the first Moon landing, not the least of which has to do with sound program management. "Having the people who are designing and building the rockets and operating the rockets doing one every so often in itself is value added to the program just because you keep all the skills you need sharp."

And while skip entry promises "tremendous operational capabilities," he said, it "creates interesting technical challenges for to the thermal protection system as well as control and guidance."

NASA is designing an ablative heat shield for Orion that will be scrapped and replaced after each flight. Skimming the atmosphere before plunging in creates unique thermal stresses that NASA does not fully understand, and that could drive the agency to build more robustness than necessary into the heat shield.

"There is some risk associated with how well the thermal protection system will work," Horowitz said. "If you can put some of that risk to bed early with a high-velocity test and proper instrumentation on board and you can look at it after you get it back, before you go into production you may be able to knock a couple hundred pounds off because you say, 'hey, my unknowns are smaller, therefore I can shave of an inch of thermal protection system because I don't have to protect for unknowns because its not unknown any more.'"

Horowitz said the Ares 5 variant, referred to by some people as Ares 4, is just one option for enabling early high-velocity tests of Orion. NASA also is looking at whether Ares 1 could be tweaked to enable Orion to demonstrate a skip-entry landing without having to circle the Moon, he said.

"I'm asking the program to look at all kinds of ideas ... for how to do this," he said.

Skip Hatfield, NASA's Orion project manager, told Space News that a crewed skip-entry flight would be preceded by unmanned tests involving subscale spacecraft in the 2011 timeframe. He said a Delta 2-class rocket, for example, could kick a subscale Orion out far enough from Earth to achieve lunar return velocities without having to go as far as the Moon.