As the 40th-anniversary
celebrations of the moon landing end, a human voyage to Mars remains a holy
grail for NASA.
"We're still looking at human
exploration of Mars as one of the goals of the future at the top level,"
said NASA researcher Bret Drake with Lunar and Mars Integration at Johnson
Space Center in Houston. "Having a human actually set foot on another
planet would be one of the greatest adventures possible, one of the greatest
monuments to history."
A crewed mission to the red planet
is a daunting challenge that lies at the edge of current technological
capabilities and possibly beyond. Still, NASA keeps a strategy to go there and constantly
keeps up to date with new ideas.
"Mars is one of those targets
of fascination that has been around a long time," Drake said.
How to get there
A voyage to Mars would take a crew
about 180 days. So far NASA is exploring two options for propulsion there — a nuclear
thermal rocket and a chemical engine.
A nuclear thermal rocket, based
off designs from the '60s and '70s, would use a nuclear reactor to super-heat a
gas and blast it out the nozzle to generate thrust. "It's a very
high-performance vehicle, and we think it's very safe, not radioactive at
launch, but it is a nuclear system," Drake said. "The idea for the
chemical engine is similar to that used on the space shuttle, liquid oxygen and
liquid hydrogen. It's a fairly well-known technology, but it's not as efficient
as nuclear thermal."
To reach the Martian surface, NASA
envisions an aerodynamic lander that flies down with thrusters to help it
descend. The ascent vehicle that takes the crew back into space for the
six-month trip home will likely rely on a combination of methane and liquid
oxygen. "Oxygen is present in the Martian atmosphere in the carbon
dioxide, so you can use resources on Mars to make it," Drake said.
Before the crew even gets to Mars,
the plan is to send as much cargo there ahead of time as possible.
"That way we can know it's
operating right before we ever commit the crew," Drake said. "A Mars
mission is not like a lunar mission where you can come home at any time — once
they're committed, a crew is out there for years."
By current NASA estimates, a
crewed mission to Mars needs to lift about twice the mass of the International
Space Station into space — roughly 1.76 million lbs. (800 metric tons) of
technology. To launch the equipment, NASA plans on using the Ares
V rocket, designed to be the most powerful rocket ever built and capable
of carrying about 414,000 lbs. (188 metric tons) to low Earth orbit at one
time.
"We're going to try to minimize the amount of assembly
needed," Drake said. "The heavy lift capacity we'll have with the
Ares V will allow for simple automatic rendezvous in orbit and docking of
components."
The crew would ride up in one of the upcoming Ares I rockets
before starting the voyage to Mars.
"Having humans in place could
bring a wealth of experience and training and the ability to put into context
what they see and to make real-time decisions, all things difficult to do with
robots," Drake said.
The very habitat the crew stays at
on the Martian surface would be sent ahead of time. "You can also do
things like produce and store oxygen from resources at Mars beforehand for the
crew and the ascent vehicle. You could generate water as well."
Big crew, long stay
NASA envisions a crew of six
astronauts for a Mars mission. "That's about what's required for the
skills needed — a commander, scientist, engineer, medical officer, things like
that, as well as cross-training," Drake said. "They'll need expertise
in a wide range of disciplines."
Currently NASA envisions a long
stay for a crew at Mars, about 500 days.
"Crew autonomy is vital,
because there's an up to 40 minute time delay in communication between Earth
and the crew because of the distance," Drake said. "And the crew
doesn't have a capability for re-supply — they'll just have what they send
ahead or what they bring with them — so when things fail, they'll have to be
able to repair them. They must be self-sufficient."
To survive the voyage, air and
water need to be completely recycled regularly.
"We're learning a lot on the
International Space Station right now on air revitalization and water
recovery," Drake said. "What's nice about Mars is that there's carbon
dioxide in the atmosphere, so that can help get us oxygen and water for the
crew. In terms of food, we're looking at smaller systems, 'salad machines,' to
grow food for the crew. Fresh food is not only good for nutrition, but good for
the mind as well. A fresh tomato can really boost psychology."
Mental and physical challenges
The long hardship of roughly
two-and-a-half years in space with only a few people in a potentially lethal
environment will undoubtedly challenge the psyches of Mars explorers.
"The Russians are conducting
a test right now that hopefully will shed light on the behavioral sciences
aspect of a Mars mission," Drake said. "Looking at other remote
exploration endeavors is helpful as well — Antarctica, or submarines — all that
feeds into the human behavioral aspects of crew selection."
A key concern for astronauts as
well as during the stay on Mars is dangerous radiation in the form of storms of
high-energy particles from the sun as well as cosmic rays from deep space.
"The best radiation protection material is hydrogen, or water, which is
rich in hydrogen," Drake said.
On the surface of Mars, NASA
envisions that cargo deployed ahead of time can produce water before the crew
arrives to use as a shield during the crew's stay there. On the way to and from
Mars, the ship could be configured so that water and food surround areas where
crew spend most of their time, but "a 'storm shelter' aboard the ship will
be an integral part for short events of radiation that can be lethal,"
Drake said.
No firm date has been set for any potential
Mars mission, but it remains of keen interest not just to NASA, but also
others, such
as China.
"It's humanity's next step to
understanding and expanding our presence outward," Drake said. "We
view human exploration of Mars as being an international endeavor, most likely
not limited to just one country, but probably of global scale.
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