The Space Race used to be a 100-metre sprint. Now it’s more like a three-legged event. Things move slower and cooperation is vital.
The manned space missions of previous decades captured the public’s imagination like nothing else. Since then dwindling budgets and weaker political will means NASA has been taking some time to explore its own space.
That doesn't mean there isn't cutting-edge research going on. The Johnson Space Centre in Houston, Texas houses thousands of employees working in numerous disciplines relating to human space flight. And there's an awful lot of talk about Mars these days.
"We've been discussing it ever since we landed on the moon," says Kerry T Lee, physicist with the NASA Space Radiation Analysis Group (SRAG). "If Congress told us to go tomorrow, and could provide a budget that matched the ability to meet that task, we could make it happen."
Congress is unlikely to do anything of the sort. Besides, a successful mission to Mars would require a global effort, of which NASA would be but one part.
Future manned missions
So for the last two decades research has focused on the
International Space Station
(ISS). Astronauts can be transported to and from the station in a matter of hours, almost to the point that travelling has become a routine matter. Still there are some key research areas on board which have major implications for future manned missions into deep space, one of which is the impact of space radiation.
The SRAG’s raison d’etre is to understand how to protect astronauts, and sensitive on-board equipment, from the effects of prolonged exposure to space radiation.
The control room comprises of numerous computer screens with multi-coloured illustrations of radiation levels both inside and outside the ISS. They are in direct communication with the Flight Control Team and advise them of what actions the astronauts should take.
“We have a number of instruments on board to help monitor and measure radiation of all kinds,” says Lee. “The Tissue Equivalent Proportional Counter (TEPC) calculates the dose that is being received and simulates a depth of two microns in human tissue. It is telling us what kind of exposure the astronauts are receiving on their skin.”
They also have an Extra Vehicular Charged Particle Directional Spectrometer (EV-CPDS), which measures the “charge, energy, and direction of any particle” that passes through the instrument. Until recently, they had an Intra Vehicular CPDS too. “The IV-CPDS was a single detector that failed back in 2007,” says Lee. “We have recently finished designing a replacement, known as the ISS Radiation Assessment Detector [ISS-RAD)], which is planned to go up on the next Space-X mission. However, given the outcome of the last mission, it may be delayed further.”
Lee is referring to Elon Musk’s SpaceX commercial space flight company, which holds a $1.6 billion (€1.4 billion) NASA contract to send up to 12 unmanned supply rockets to the ISS. In June, its seventh mission, which was carrying food, supplies and scientific experiments, malfunctioned and never made it. The previous six missions, however, were successful.
Galactic cosmic rays Harmful cosmic radiation takes various forms. The two most common originate from subatomic particles given off by the sun and galactic cosmic rays (GCR) which come from outside our solar system.
Both affect human cells at different levels, the former being less frequent but more concentrated, the latter at a lower level but ever-present.
“We track radiation effects through what’s known as a human phantom,” explains Lee. “This is a computer modelling system which simulates what happens as radiation passes through the human body. We have learnt that various organs in the body have varying levels of sensitivity to radiation exposure. That’s what we care about: the risk.
“That risk is weighted based on the sensitivity of each organ to come up with a total risk of developing cancer based on a given exposure.”
Certain organs, such as the reproductive, are more susceptible to cosmic radiation than others. Likewise, blood-forming organs are also higher risk.
“That’s because they are producing new cells all the time and making copies of DNA. The DNA is being damaged from the exposure but continues to replicate itself.”
In addition, scientists at the University of California, Irvine, recently conducted research which exposed mice to high-energy particles – akin to those found in GCRs. The mice suffered nervous system damage. They exhibited reduced performance ability, loss of memory, awareness and focus: all side effects that could prove fatal during a deep space mission.
Physical properties
Female astronauts are at a higher risk than their male counterparts. Interestingly, heavier people would be better protected against harmful GCRs as extra body fat could serve as a shield.
Has NASA ever considered instructing their astronauts to gain weight before travelling? “Someone with additional weight may be more prone to certain cancers, heart failure and other weight-related illnesses anyway,” says Lee.
“We are protecting against very particular risk levels,” he adds. “Current NASA requirements state we cannot allow crew members to be at risk of developing cancer by 3 per cent more than the rest of normal society. And that 3 per cent has to be measurable at a 95 per cent confidence level.”
How much is too much? One study suggests astronauts on the ISS would exceed lifetime exposure limits after 18 months for women and 24 months for men. Any mission to Mars would take at least this long, not to mention result in even harsher exposure in deep space.
The cosmic trade-off
There are ways around this, though. During certain periods in the solar cycle, GCRs are reduced.
“GCRs are low-level but constant,” says Lee. “That low level adds up after hundreds of days in space. But their intensity levels change depending on where we are in the solar cycle. The more active the sun is, the more it pushes back on the incoming GCRs and decreases their impact. But the closer we are to solar max, the more likely the sun is going to produce a solar particle event, which would increase the short-term intensity of harmful radiation to much higher levels. Bar something with very energetic particles, however, solar particle events can be protected against.
“It’s a trade-off. If we go to Mars, do we roll the dice by going during a solar max and hope there is no large solar particle event, or go during solar min, when you’ve got those constant GCR particles coming at a higher level? It’s one of those things still being debated. We model these things and know it’s easier to protect astronauts from solar particle events, as they’re lower energy. So I’d probably gamble and send a mission during a solar max period.”
They don’t make ‘em like they used to
The dangers of exposure to radiation have been known for as long as people have been going into space.
The dawn of the ISS age, however, has made understanding the impacts of long-term cosmic radiation exposure more pertinent, as astronauts spend longer periods of time on board.
One wouldn’t think space engineering is an industry where the cliche “they don’t make ‘em like they used to” could ring true. In some cases, however, it does.
“Ironically, the electronics on older spaceships were less prone to damage from cosmic radiation interference,” says Lee.
“The transistors used were larger and much tougher, so a single particle affecting them was unlikely. Modern transistors are down to nanometres in size and it only takes low levels to affect them.”
