An interstellar journey for CubeSats

In Greek mythology, Icarus was the impulsive son who ignored his father's warning about flying too close to the sun but the students in the Drexel University chapter of Icarus Interstellar are much too dedicated to do anything that careless. Besides, they're aiming for a star located even farther away.

Those students went above and beyond to create the first chapter at any university of Icarus Interstellar, an international nonprofit foundation dedicated to achieving interstellar flight—travel to star systems beyond our own solar system—by the year 2100.

The research-oriented organization's mandate is to train the next generation of interstellar engineers, so the idea of a Drexel chapter organization wasn't very far-fetched.

Icarus is attempting to build the first-ever mission to Alpha Centauri, the star system located the closest to our solar system.

The timing of the project is especially important because no other similar missions are planned and the only mission that could reach a neighboring solar system—the Voyager spacecraft launched into space in 1977—will take tens of thousands of years.

Icarus' Project Tin Tin aims to reach the nearest star in about one-third of the Voyager's time, even though the Voyager will have received a 40-year head start.

Through Project Tin Tin, Icarus plans to create cost-effective technology and prototype CubeSats, or tiny cube-shaped research spacecraft nanosatellites, to test before sending to Alpha Centauri.

The Drexel students will contribute to the mission by designing, analyzing and building their own interstellar CubeSat.

"The idea is that this CubeSat will push the boundaries of what is possible with our current technology and will serve as a stepping-stone for future [faster] missions," said Damien Turchi, a pre-junior mechanical engineering and mechanics major and the president and founder of Drexel's Icarus chapter.

The group plans to send Icarus a project proposal by March 2014 to earn approval and start funding for the Drexel CubeSat, which will potentially be launched as early as 2016.

"By promoting specifically student involvement in interstellar research, the breakthroughs required for this endeavor may very well happen in our generation, because innovation tends to lie in the naïve," Turchi said.

Other activities planned for the Drexel chapter include discussions about Icarus' projects and the implications of long-term interstellar flight on human health and psychology.

The group is also planning a possible trip to the Icarus Interstellar Starship Congress in Texas and is looking into ways to aid other universities to create student chapters.

Researchers calculate radiation exposure associated with journey to Mars

The RAD instrument measures radiation dose using silicon detector and plastic scintillator technology.

The latter has a composition somewhat similar to tissue and is more sensitive to neutrons than are the silicon detectors.

This illustration of RAD shows the silicon detectors (A, B & C) that measure charged particles and the plastic detectors (D, E & F) that measure both charged and neutral particles.

Credit: Hassler et al., 2012. Space Science Reviews, 170, 503.

On November 26, 2011, the Mars Science Laboratory began a 253-day, 560-million-kilometer journey to deliver the Curiosity rover to the Red Planet.

Radiation Assessment Detector

En route, the Southwest Research Institute (SwRI) Radiation Assessment Detector (RAD) made detailed measurements of the energetic particle radiation environment inside the spacecraft, providing important insights for future human missions to Mars.

Cary Zeitlin

"In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Dr. Cary Zeitlin, a principal scientist in SwRI's Space Science and Engineering Division and lead author of Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory, scheduled for publication in the journal Science on May 31.

"Understanding the radiation environment inside a spacecraft carrying humans to Mars or other deep space destinations is critical for planning future crewed missions," Zeitlin said.

"Based on RAD measurements, unless propulsion systems advance rapidly, a large share of mission radiation exposure will be during outbound and return travel, when the spacecraft and its inhabitants will be exposed to the radiation environment in interplanetary space, shielded only by the spacecraft itself."

Two forms of radiation pose potential health risks to astronauts in deep space: a chronic low dose of galactic cosmic rays (GCRs) and the possibility of short-term exposures to the solar energetic particles (SEPs) associated with solar flares and coronal mass ejections.

Radiation dose is measured in units of Sievert (Sv) or milliSievert (1/1000 Sv). Long-term population studies have shown that exposure to radiation increases a person's lifetime cancer risk; exposure to a dose of 1 Sv is associated with a 5 percent increase in fatal cancer risk.

GCRs tend to be highly energetic, highly penetrating particles that are not stopped by the modest shielding provided by a typical spacecraft.

These high-energy particles include a small percentage of so-called heavy ions, which are atomic nuclei without their usual complement of electrons.

Heavy ions are known to cause more biological damage than other types of particles.

Energetic protons constitute about 85 percent of the primary galactic cosmic ray flux and easily traverse even the most shielded paths (reds) inside the MSL spacecraft.

Heavy ions tend to break up into lighter ions in thick shielding, but can survive traversal of thin shielding (blues) intact.

The solar particles of concern for astronaut safety are typically protons with kinetic energies up to a few hundred MeV (one MeV is a million electron volts).

Solar events typically produce very large fluxes of these particles, as well as helium and heavier ions, but rarely produce higher-energy fluxes similar to GCRs.

The comparatively low energy of typical SEPs means that spacecraft shielding is much more effective against SEPs than GCRs.

"A vehicle carrying humans into deep space would likely have a 'storm shelter' to protect against solar particles. But the GCRs are harder to stop and, even an aluminum hull a foot thick wouldn't change the dose very much," said Zeitlin.

"The RAD data show an average GCR dose equivalent rate of 1.8 milliSieverts per day in cruise. The total during just the transit phases of a Mars mission would be approximately .66 Sv for a round trip with current propulsion systems," said Zeitlin.

Time spent on the surface of Mars might add considerably to the total dose equivalent, depending on shielding conditions and the duration of the stay.

Exposure values that ensure crews will not exceed the various space agencies standards are less than 1 Sv.

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