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.
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