Have Humans Visited Mercury?

The MESSENGER spacecraft at Mercury (NASA)

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Have astronauts from Earth ever stepped foot on Mercury? No, Mercury has been visited by spacecraft from Earth, but no human has ever gone into orbit around Mercury, let alone stepped on the surface. Just what would it take to visit Mercury?

Humans attempting to visit Mercury would find a similar environment to the Moon. Mercury is airless, so they would need a spacesuit to protect themselves from the vacuum of space. However, the temperatures on Mercury are much greater. During the daytime, the surface of Mercury at the equator rises to 700 Kelvin (427 degrees C). Just for comparison, the surface of the Moon only rises to 390 Kelvin (117 degrees C) during the daytime. So you would need some kind of protection from the intense heat.

But then, nighttime on Mercury dips down to only 100 Kelvin (-173 degrees C) – that’s the same low temperatures you get on the Moon at night. So an astronaut’s spacesuit would need to be able to keep an astronaut warm when they’re in the shade.

The travel time to the Moon is only about 3 days. But the travel time to Mercury is much longer. That’s partly because Mercury is much further away – 10s of millions km. But spacecraft also need to take special trajectories so they can get into orbit around Mercury. All of the spacecraft that have visited Mercury have taken longer than a year to reach the planet. That would be a long, hot journey for astronauts.

Maybe some day in the future humans will visit Mercury, but it hasn’t happened yet.

We have written many stories about Mercury here on Universe Today. Here’s an article about a the discovery that Mercury’s core is liquid. And how Mercury is actually less like the Moon than previously believed.

Want more information on Mercury? Here’s a link to NASA’s MESSENGER Misson Page, and here’s NASA’s Solar System Exploration Guide to Mercury.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Reference:
NASA Star Child: Mercury

8 Ridiculous Things Bigger Than NASA’s Budget

Astronaut John Grusnfeld on the recent Hubble servicing mission. Credit: NASA

Why do we explore? In the days of Magellan, Columbus and da Gama, undoubtedly the average person thought it was foolish to risk lives and spend large amounts of money to find out what was beyond the horizon. Those explorers didn’t find what they expected, but their explorations changed the world.

What drives us to explore and discover is what we don’t know, and the spirit of exploration inspires us to create and invent so that we can go explore and possibly change the world. We don’t know yet exactly what we’ll find if humans ever go to Mars, Europa or beyond, but if we stay in our caves we’ll never find out. Similarly, space probes and telescopes like Hubble, as well as ground-based telescopes have helped us explore remotely and have facilitated the discovery of so many things we didn’t know — and didn’t expect — about our universe.

However, exploration takes money.

The most often-used argument against space exploration is that we should use that money to alleviate problems here on Earth. But that argument fails to realize that NASA doesn’t just pack millions of dollar bills into a rocket and blast them into space. The money NASA uses creates jobs, providing an opportunity for some of the world’s brightest minds to use their talents to, yes, actually benefit humanity. NASA’s exploration spurs inventions that we use everyday, many which save lives and improve the quality of life. Plus, we’re expanding our horizons and feeding our curiosity, while learning so, so much and attempting to answer really big questions about ourselves and the cosmos.

NASA’s annual budget for fiscal year 2009 is $17.2 billion. The proposed budget for FY 2010 would raise it to about $18.7 billion. That sounds like a lot of money, and it is, but let’s put it in perspective. The US annual budget is almost $3 trillion and NASA’s cut of the US budget is less than 1%, which isn’t big enough to create even a single line on this pie chart.
US Federal Spending.  Credit: Wikipedia
A few other things to put NASA’s budget in perspective:

Former NASA administrator Mike Griffin mentioned recently that US consumers spend more on pizza ($27 billion) than NASA’s budget. (Head nod to Ian O’Neill)

Miles O’Brien recently brought it to our attention that the amount of money Bernie Maddof scammed with his Ponzi scheme ($50 billion) is way bigger than NASA’s budget.

Americans spend a lot of money on some pretty ridiculous things. Returning to that oft-used phrase about spending the money used in space to solve the problems on Earth, consider this: *

Annually, Americans spend about $88.8 billion on tobacco products and another $97 billion on alcohol. $313 billion is spent each year in America for treatment of tobacco and alcohol related medical problems.

Likewise, people in the US spend about $64 billion on illegal drugs, and $114.2 billion for health-related care of drug use.

Americans also spend $586.5 billion a year on gambling. Italian’s also spend quite a bit – according to Stranieri, in 2011 gamblers in Italy spent more than 100 billion euros on gambling!

It’s possible we could give up some other things to help alleviate the problems in our country without having to give up the spirit of exploration.

*the numbers used here are from various years, depending on what was readily available, but range from the years 2000 and 2008.

Building an Antimatter Spaceship

A spacecraft powered by a positron reactor would resemble this artist's concept of the Mars Reference Mission spacecraft. Credit: NASA

If you’re looking to build a powerful spaceship, nothing’s better than antimatter. It’s lightweight, extremely powerful and could generate tremendous velocity. However, it’s enormously expensive to create, volatile, and releases torrents of destructive gamma rays. NASA’s Institute for Advanced Concepts is funding a team of researchers to try and design an antimatter-powered spacecraft that could avoid some of those problems.

Most self-respecting starships in science fiction stories use anti matter as fuel for a good reason – it’s the most potent fuel known. While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy).

However, in reality this power comes with a price. Some antimatter reactions produce blasts of high energy gamma rays. Gamma rays are like X-rays on steroids. They penetrate matter and break apart molecules in cells, so they are not healthy to be around. High-energy gamma rays can also make the engines radioactive by fragmenting atoms of the engine material.

The NASA Institute for Advanced Concepts (NIAC) is funding a team of researchers working on a new design for an antimatter-powered spaceship that avoids this nasty side effect by producing gamma rays with much lower energy.

Antimatter is sometimes called the mirror image of normal matter because while it looks just like ordinary matter, some properties are reversed. For example, normal electrons, the familiar particles that carry electric current in everything from cell phones to plasma TVs, have a negative electric charge. Anti-electrons have a positive charge, so scientists dubbed them “positrons”.

When antimatter meets matter, both annihilate in a flash of energy. This complete conversion to energy is what makes antimatter so powerful. Even the nuclear reactions that power atomic bombs come in a distant second, with only about three percent of their mass converted to energy.

Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.

The NIAC research is a preliminary study to see if the idea is feasible. If it looks promising, and funds are available to successfully develop the technology, a positron-powered spaceship would have a couple advantages over the existing plans for a human mission to Mars, called the Mars Reference Mission.

“The most significant advantage is more safety,” said Dr. Gerald Smith of Positronics Research, LLC, in Santa Fe, New Mexico. The current Reference Mission calls for a nuclear reactor to propel the spaceship to Mars. This is desirable because nuclear propulsion reduces travel time to Mars, increasing safety for the crew by reducing their exposure to cosmic rays. Also, a chemically-powered spacecraft weighs much more and costs a lot more to launch. The reactor also provides ample power for the three-year mission. But nuclear reactors are complex, so more things could potentially go wrong during the mission. “However, the positron reactor offers the same advantages but is relatively simple,” said Smith, lead researcher for the NIAC study.

Also, nuclear reactors are radioactive even after their fuel is used up. After the ship arrives at Mars, Reference Mission plans are to direct the reactor into an orbit that will not encounter Earth for at least a million years, when the residual radiation will be reduced to safe levels. However, there is no leftover radiation in a positron reactor after the fuel is used up, so there is no safety concern if the spent positron reactor should accidentally re-enter Earth’s atmosphere, according to the team.

It will be safer to launch as well. If a rocket carrying a nuclear reactor explodes, it could release radioactive particles into the atmosphere. “Our positron spacecraft would release a flash of gamma-rays if it exploded, but the gamma rays would be gone in an instant. There would be no radioactive particles to drift on the wind. The flash would also be confined to a relatively small area. The danger zone would be about a kilometer (about a half-mile) around the spacecraft. An ordinary large chemically-powered rocket has a danger zone of about the same size, due to the big fireball that would result from its explosion,” said Smith.

Another significant advantage is speed. The Reference Mission spacecraft would take astronauts to Mars in about 180 days. “Our advanced designs, like the gas core and the ablative engine concepts, could take astronauts to Mars in half that time, and perhaps even in as little as 45 days,” said Kirby Meyer, an engineer with Positronics Research on the study.

Advanced engines do this by running hot, which increases their efficiency or “specific impulse” (Isp). Isp is the “miles per gallon” of rocketry: the higher the Isp, the faster you can go before you use up your fuel supply. The best chemical rockets, like NASA’s Space Shuttle main engine, max out at around 450 seconds, which means a pound of fuel will produce a pound of thrust for 450 seconds. A nuclear or positron reactor can make over 900 seconds. The ablative engine, which slowly vaporizes itself to produce thrust, could go as high as 5,000 seconds.

One technical challenge to making a positron spacecraft a reality is the cost to produce the positrons. Because of its spectacular effect on normal matter, there is not a lot of antimatter sitting around. In space, it is created in collisions of high-speed particles called cosmic rays. On Earth, it has to be created in particle accelerators, immense machines that smash atoms together. The machines are normally used to discover how the universe works on a deep, fundamental level, but they can be harnessed as antimatter factories.

“A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development,” said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. “Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research,” added Smith.

Another challenge is storing enough positrons in a small space. Because they annihilate normal matter, you can’t just stuff them in a bottle. Instead, they have to be contained with electric and magnetic fields. “We feel confident that with a dedicated research and development program, these challenges can be overcome,” said Smith.

If this is so, perhaps the first humans to reach Mars will arrive in spaceships powered by the same source that fired starships across the universes of our science fiction dreams.

Original Source: NASA News Release