UConn professor says trip to Mars is possible, if risks are accepted
By Steve Smith - Staff Writer
Tolland - posted Fri., Mar. 15, 2013
Brice Cassenti, a professor in residence at the University of Connecticut mechanical engineering department, said that if he were allowed to go to Mars, even if it was a one-way trip, he would do it.
About 25 curious local residents listened as Cassenti presented a light-hearted, but serious, lecture at the Tolland Public Library on March 13 about the logistics of a manned mission to Mars, and compared several models for the venture.
Cassenti said putting humans on the red planet would get a lot more done than robots. Simply put, humans can make quicker decisions about where and what to study next, as opposed to communications across millions of miles, which take about 25 minutes, telling rovers like Opportunity what to do.
“They [rovers] move about 6 feet a day,” Cassenti said. “It's worth it to send people if you have the money. You get more science per mile.”
Cassenti compared the types of fuel, including chemical rockets (which are currently used), gas-core nuclear rockets (theoretical), ion power (possible, but relatively weak), and nuclear fusion power (experimental, but potentially highly effective). One of the important factors is the ratio between the mass of fuel needed compared with the mass of the craft that ultimately returns to earth. The most common model, known as the Van Braun model, uses a highly inefficient 225-to-1 ratio.
Also compared were four main models of the type of trip from Earth to Mars, including the number of stages a spacecraft would have, and how much fuel it would need to carry. The Zubrin model, which has a fuel-to-mass ratio of 6-1, necessitates the creation of fuel on Mars for the return trip, but the creation of a fuel factory on a foreign planet is not exactly the safest proposition.
“It saves money,” he said. “You don't have to push the propellant that's going to get you back to Earth, because you pick it up over there [on Mars]. But, it's risky. What if the factory fails? The crew is dead.”
Some of the models have a risky rendezvous between lander and orbiter spacecraft, or a more direct landing approach, but the balance of that equation is that they also cost less.
Cassenti said the type of mission that was used to put men on the moon used a lunar orbit rendezvous, which was the most risky option of three available. While much is made of the launch of the Apollo missions, as well as the first steps on the moon after the lunar landing, the riskiest part of the mission was docking the lander with the orbiter after leaving the lunar surface.
“Once they come up again, they've got to rendezvous with that craft or they're not coming back home,” he said. “That one is the risky one.”
Of the 12 Apollo missions, two failed – or one in six. Of the 135 Space Shuttle missions, two failed – one in 60. “The space shuttle is a lot better,” Cassenti said. “It's also a lot more expensive. You have to make a decision of how much risk you are willing to take to get the cost down.”
Cassenti said the same approach must be used when considering a manned Mars mission. With costs in the billions and trillions, the difference in price can often be the difference in deciding what will happen or not, as it did with Apollo. “In order to get the cost down, you have to increase the risk,” he said. “People could die, so you have to make this judgment about which way you want to go. You have this trade-off you have to do.”
Cassenti said that if it were up to him, the best way for earthlings to get to Mars would be a mission that begins with a bi-modal, nuclear-thermal rocket engine to escape from Earth. It would then use a manned lander with aero assist (slamming into the atmosphere of Mars, with a heat shield), and then produce propellant on the surface for return.
“Using humans increases the cost, but you also get more science and technology returned from them,” Cassenti said. “I want them to find life. If they can find life on the surface of Mars that is different from here, it will not only revolutionize science and biology, but medicine. It gives you a whole new insight. It would more than pay for everything else.”
Cassenti said the problem is he doesn't believe NASA will make the decision to go to Mars, because they won't accept the risk factor. “They want really good reliability,” he said, “and that's increasing the cost so much that it's too expensive to go… and then you just don't go. They're just going to have to accept the increased risk.”