Future Mars outposts or colonies may seem more distant
than ever with NASA's exploration plans in flux, but the rocket technology that
could someday propel a human mission to the red planet in as little as 40 days may
already exist.
A company founded by former NASA astronaut Franklin
Chang-Diaz has been developing a new rocket engine that draws upon electric
power and magnetic fields to channel superheated plasma out the back. That
stream of plasma generates steady, efficient thrust that uses low amounts of
propellant and builds up speed over time.
"People have known for a long time, even back in the
'50s, that electric
propulsion would be needed for serious exploration of Mars," said Tim
Glover, director of development at the Ad Astra Rocket Company.
The rocket technology could drastically cut down the
amount of time a spacecraft needs to send astronauts on Mars
missions. Instead of half a year, a spacecraft could make the trip in just
over a month using the engine and a large enough power source, according to an
Ad Astra mission study.
NASA's recent
course change has freed up some funding for new propulsion
technologies. And the U.S. space agency has not lost sight of the red planet,
NASA administrator Charles Bolden told Congress as he presented a new budget last
month.
"While we cannot provide a date certain for the
first human visit, with Mars as a key long-term destination we can identify
missing capabilities needed for such a mission and use this to help define many
of the goals for our emerging technology development," Bolden said.
Familiar chemical rockets that burn solid or liquid
chemical propellants won't get humans to Mars fast because they would require
too much propellant. They can create a huge boost for several minutes at the
cost of huge inefficiency — not unlike a speed demon with poor gas mileage.
Slow but steady push
Some satellites and spacecraft already rely upon electric
propulsion in their ion engines that create thrust based on energized
gas. Similarly, Ad Astra's Variable Specific Impulse Magnetoplasma Rocket
(VASIMR) ionizes gases such as xenon or hydrogen to create superheated plasma
stream for thrust.
But VASIMR also has the advantage of relying upon
electromagnetic waves to create and energize the plasma, rather than physical
electrodes that get worn down due to contact with the superheated plasma. That
translates into greater reliability over time and allows for a very dense
plasma stream to create more thrust.
VASIMR can also adjust its thrust to speed up or slow
down, and even has an "afterburner" mode that provides a temporary
high-speed boost at the cost of efficiency.
"Our technology is different," Glover told SPACE.com.
"It's one possibility. We certainly think it has the most potential at
high power levels."
Yet even the most efficient rocket engine needs a power
source. VASIMR may use gas as the propellant, but it also requires an electric
power source that can ionize the gas to create its plasma.
I need more power!
A mission trajectory study estimated that a VASIMR-powered
spacecraft could reach the red planet within 40 days if it had a
200 megawatt power source. That's 1,000 times more power than what the current
VASIMR prototype will use, although Ad Astra says that VASIMR can scale up to
higher power sources.
The real problem rests with current limitations in space
power sources. Glover estimates that the Mars mission scenario would need a
power source that can produce one kilowatt (kW) of power per kilogram (kg) of
mass, or else the spacecraft could never reach the speeds required for a quick
trip.
Existing power sources fall woefully short of that ideal.
Solar panels have a mass to power ratio of 20 kg/kW. The Pentagon's DARPA
science lab hopes to develop solar panels that can achieve 7 kg/KW, and stretched
lens arrays might reach 3 kg/KW, Glover said. That's good enough for VASIMR to
transport cargo around low-Earth orbit and to the moon, but not to fly humans
to Mars.
Ad Astra sees nuclear power as the likeliest power source
for a VASIMR-powered Mars mission, but the nuclear reactor that could do the
job remains just a concept on paper. The U.S. only ever launched one nuclear
reactor into space back in 1965, and it achieved just 50 kg/kW.
A way forward
VASIMR and the necessary power sources could get a boost
in the coming years. NASA's new five-year budget includes more than $3 billion
for developing heavy-lift and propulsion technologies, as well as a Game
Changing Innovation program that similarly targets next-gen propulsion and
power sources.
The U.S. space agency's new chief
tech guru has also emphasized propulsion as a critical area, under
NASA's new Space Technology program.
"The budget's emphasis on developing advanced
technologies to make space exploration easier and cheaper is very encouraging
to us," Glover noted.
VASIMR reached a milestone late last year by achieving
200 kilowatts of power with the VX-200 prototype. Since then, Ad Astra has worked
on the flight-capable VF-200 version that could undergo testing at the
International Space Station (ISS) within the next several years.
As for getting VASIMR into space, Ad Astra has discussed
possible launch options with commercial spaceflight providers.
"Anybody who wants to send anything to ISS after the
shuttle retires is talking
with SpaceX, and Orbital Sciences," Glover said.
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