Trips to Mars in 39 Days

Using traditional chemical rockets, a trip to Mars – at quickest — lasts 6 months. But a new rocket tested successfully last week could potentially cut down travel time to the Red Planet to just 39 days. The Ad Astra Rocket Company tested a plasma rocket called the VASIMR VX-200 engine, which ran at 201 kilowatts in a vacuum chamber, passing the 200-kilowatt mark for the first time. “It’s the most powerful plasma rocket in the world right now,” says Franklin Chang-Diaz, former NASA astronaut and CEO of Ad Astra. The company has also signed an agreement with NASA to test a 200-kilowatt VASIMR engine on the International Space Station in 2013.

The tests on the ISS would provide periodic boosts to the space station, which gradually drops in altitude due to atmospheric drag. ISS boosts are currently provided by spacecraft with conventional thrusters, which consume about 7.5 tons of propellant per year. By cutting this amount down to 0.3 tons, Chang-Diaz estimates that VASIMR could save NASA millions of dollars per year.

The test last week was the first time that a small-scale prototype of the company’s VASIMR (Variable Specific Impulse Magnetoplasma Rocket) rocket engine has been demonstrated at full power.

Plasma, or ion engines uses radio waves to heat gases such as hydrogen, argon, and neon, creating hot plasma. Magnetic fields force the charged plasma out the back of the engine, producing thrust in the opposite direction.

They provide much less thrust at a given moment than do chemical rockets, which means they can’t break free of the Earth’s gravity on their own. Plus, ion engines only work in a vacuum. But once in space, they can give a continuous push for years, like wind pushing a sailboat, accelerating gradually until the vehicle is moving faster than chemical rockets. They only produce a pound of thrust, but in space that’s enough to move 2 tons of cargo.

Due to the high velocity that is possible, less fuel is required than in conventional engines.

Currently, the Dawn spacecraft, on its way to the asteroids Ceres and Vesta, uses ion propulsion, which will enable it to orbit Vesta, then leave and head to Ceres. This isn’t possible with conventional rockets. Additionally, in space ion engines have a velocity ten times that of chemical rockets.

Specfic impulse and thrust graph. Credit: NASA
Specfic impulse and thrust graph. Credit: NASA

Rocket thrust is measured in Newtons (1 Newton is about 1/4 pound). Specific impulse is a way to describe the efficiency of rocket engines, and is measured in time (seconds). It represents the impulse (change in momentum) per unit of propellant. The higher the specific impulse, the less propellant is needed to gain a given amount of momentum.

Dawn’s engines have a specific impulse of 3100 seconds and a thrust of 90 mNewtons. A chemical rocket on a spacecraft might have a thrust of up to 500 Newtons, and a specific impulse of less than 1000 seconds.

The VASIMR has 4 Newtons of thrust (0.9 pounds) with a specific impulse of about 6,000 seconds.

The VASIMR has two additional important features that distinguish it from other plasma propulsion systems. It has the ability to vary the exhaust parameters (thrust and specific impulse) in order to optimally match mission requirements. This results in the lowest trip time with the highest payload for a given fuel load.

In addition, VASIMR has no physical electrodes in contact with the plasma, prolonging the engine’s lifetime and enabling a higher power density than in other designs.

To make a trip to Mars in 39 days, a 10- to 20-megawatt VASIMR engine ion engine would need to be coupled with nuclear power to dramatically shorten human transit times between planets. The shorter the trip, the less time astronauts would be exposed to space radiation, and a microgravity environment, both of which are significant hurdles for Mars missions.

VASIMR. Credit: Ad Astra
VASIMR. Credit: Ad Astra

The engine would work by firing continuously during the first half of the flight to accelerate, then turning to deaccelerate the spacecraft for the second half. In addition, VASIMR could permit an abort to Earth if problems developed during the early phases of the mission, a capability not available to conventional engines.

VASIMR could also be adapted to handle the high payloads of robotic missions, and propel cargo missions with a very large payload mass fraction. Trip times and payload mass are major limitations of conventional and nuclear thermal rockets because of their inherently low specific impulse.

Chang-Diaz has been working on the development of the VASIMR concept since 1979, before founding Ad Astra in 2005 to further develop the project.

Source: PhysOrg

South Korea Launches Rocket; Satellite Fails to Reach Its Orbit

South Korea successfully launched its first rocket on Tuesday, but the satellite payload failed to reach its designated orbit, officials said. The rocket, a two-stage rocket, called the Naro lifted off on schedule at 5:00 pm local time, (0800 GMT). The first stage separated successfully less than five minutes after lift-off and the South Korean-built 100-kilogram (220-pound) scientific research satellite was placed into Earth orbit. But science and technology minister Ahn Byong-Man said it was not following the designated orbit, hampering communications with mission control. “All aspects of the launch were normal, but the satellite exceeded its planned orbit and reached an altitude of 360 kilometres (225 miles),” Ahn said.
Continue reading “South Korea Launches Rocket; Satellite Fails to Reach Its Orbit”

NASA Tests Inflatable Heat Shield

NASA conducted a successful test Monday morning of a new type of heat shield that could make it possible to land larger payloads on Mars. The Inflatable Re-entry Vehicle Experiment (IRVE) demonstrated an inflatable heat shield which could slow and protect spacecraft entering atmospheres at hypersonic speeds. “This was a small-scale demonstrator,” said Mary Beth Wusk, IRVE project manager, based at Langley Research Center. “Now that we’ve proven the concept, we’d like to build more advanced aeroshells capable of handling higher heat rates.”

IRVE launch from Wallops Island, Virginia.  Credit: NASA
IRVE launch from Wallops Island, Virginia. Credit: NASA

IRVE was vacuum-packed into a 38 cm (15-inch) diameter payload shroud and launched with a Black Brant 9 sounding rocket from NASA’s Wallops Flight Facility on Wallops Island, Va., at 8:52 a.m. EDT. The 3 meter (10-foot) diameter heat shield, made of several layers of silicone-coated industrial fabric, inflated with nitrogen to a mushroom shape in space several minutes after liftoff.

At four minutes into the flight, the rocket reached 210 km (131 miles), and deployed the heat shield, which took less than 90 seconds to inflate. According to the cameras and sensors on board, which relayed real-time data back to engineers on the ground, the heat shield expanded to its full size and went into a high-speed free fall. The key focus of the research came about six and a half minutes into the flight, at an altitude of about 50 miles, when the aeroshell re-entered Earth’s atmosphere and experienced its peak heating and pressure measurements for a period of about 30 seconds.

“Our inflation system, which is essentially a glorified scuba tank, worked flawlessly and so did the flexible aeroshell,” said Neil Cheatwood, IRVE principal investigator and chief scientist for the Hypersonics Project at NASA’s Langley Research Center in Hampton, Va. “We’re really excited today because this is the first time anyone has successfully flown an inflatable reentry vehicle.”

NASA engineers check out the Inflatable Re-entry Vehicle Experiment (IRVE) in the lab. Credit: NASA/Sean Smith
NASA engineers check out the Inflatable Re-entry Vehicle Experiment (IRVE) in the lab. Credit: NASA/Sean Smith

Inflatable heat shields hold promise for future planetary missions, according to researchers. To land more mass on Mars at higher surface elevations, for instance, mission planners need to maximize the drag area of the entry system. The larger the diameter of the aeroshell, the bigger the payload can be.

For more information on the problems of landing on Mars, and other inflatable heat shields and supersonic decelerators that are being developed, check out our previous article with Rob Manning of JPL and Glen Brown of Vertigo, Inc.

Fact Sheet on IRVE (pdf)

Sources: NASA, NASA