Day 313: How We'll Live on Mars

Recently, after one of his rockets exploded just above its launch pad, Elon Musk wryly tweeted: “Rockets are tricky.” He’s right: close to two-thirds of all the attempts to get probes to Mars have failed.

A casual observer might well wonder why humans have had so much trouble getting to Mars when getting to the moon more than fifty years ago seemed relatively easy. Mostly, it’s a matter of distances. The scale changes are phenomenal. The moon floats between 225,000 and 250,000 miles from Earth, depending on the lunar cycle. Mars can be up to a thousand times farther away. In 2003, Mars and Earth were closer than they had been in almost sixty thousand years—only about 34 million miles apart. But because Earth’s orbit around the sun takes 365 days and Mars’s takes 687 Earth days, the two planets can get out of sync and wind up very far apart, with each on a different side of the sun. When they are far apart, they are really far apart—about 250 million miles. Mars thus varies between being 140 and 1,000 times farther away from Earth than the moon.

Put another way, humans can make a round-trip to the moon and back in six days. (We could have gotten there in one day with the boost the Saturn V rocket offered, but we would have been going so fast when we arrived that we would simply have shot by instead of being captured by the moon’s weak gravity.) Using the Hohmann transfer orbits suggested by von Braun in Das Marsprojekt, even if we went much faster than the speed at which the Apollo astronauts went to the moon, we would still have to fly about a thousand times farther than the distance to the moon to end up at Mars. That’s because we simply can’t carry enough fuel to blast ahead in a straight line. Without unlimited cheap energy, we will always be in orbit around something in this solar system, so all our trajectories will be curved. There are no foreseeable shortcuts in the next twenty years that could get us to Mars in much less than 250 days each way, although SpaceX is designing more powerful and more efficient rocket engines that could shorten the trip substantially.

Even the early, more straightforward missions to Mars—missions that merely attempted to fly by the planet—regularly met with disaster. The far more difficult Mars orbiter missions, and especially the lander missions, made something of a mockery of our grasp on space technology.

The Soviets seemed to get the worst of the early Martian calamities. The first Earth object ever to reach the surface of Mars was a Soviet lander called Mars 2. It crash-landed in November of 1971, and was a follow-up project to Kosmos 419, which never got out of orbit around the Earth, much less headed to Mars. The next month, Mars 3 actually made a successful landing but stopped sending signals after twenty seconds. Mars 4’s guidance system failed, and it whizzed by the planet completely. Mars 5 was the most successful Soviet probe. It was inserted into an elliptical orbit in February 1974, and returned about sixty photos during twenty-two orbits, then failed. Mars 6 reached the planet in March of 1974 and launched a lander that crashed on the surface. It transmitted atmospheric data for about four minutes before it went silent, but the data was largely incomprehensible because of a computer chip failure. Mars 7 also entered orbit in March 1974 but launched its lander four hours too early and missed the planet. There were a handful of other earlier Mars missions launched by the Soviets that failed, as well as later failed missions. In 1996 the Russian Space Agency launched an orbiter/lander called Mars 96 that didn’t escape Earth’s gravity and broke up over the Pacific Ocean. Since then, the Russians have seemed less than eager to challenge their jinx.

A huge hindrance to successfully landing a probe on Mars is that it takes communications a long time to arrive from Earth. When Earth and Mars are farthest apart, it takes a radio signal twenty-one minutes to get from Earth to Mars, and then another twenty-one minutes for a return signal to get back to Earth. Unmanned spacecraft must therefore use artificial intelligence software to make decisions in emergencies, because there’s no time to call home for help.

But all the bad history of early lander mission failure slipped into the darker reaches of our consciousness after NASA scored big by successfully landing the Spirit and Opportunity rovers on Mars. More recently, the success of the Curiosity rover has stolen our attention. Opportunity is still actively exploring Mars after more than a decade. Curiosity finished a Martian year’s (just under two Earth years) worth of exploration in 2014, and is just getting started on its longer mission. Nevertheless, the distances these rovers have covered is not impressive. Opportunity has traveled only about twenty-six miles since 2004, and Curiosity has gone a bit more than six miles in nearly three years.

Despite the failures of the past, NASA’s success with Curiosity proves that relatively large payloads can be delivered to the surface of Mars, making not only manned flights more realistic but also the idea of cargo and resupply flights. Changing the equation from large payloads like Curiosity to human cargo is mostly just a step up in scale, frequency of cargo launches, and oxygen. SpaceX is refining a Dragon spacecraft with the ability to carry seven astronauts that it expects to fly to the International Space Station as early as 2016, although Musk recently said that “2017 is probably a realistic expectation of when we’ll send a human into space for the first time.” He has joked that a stowaway astronaut on its current Dragon vehicle that resupplied the International Space Station would survive the flight because part of the craft is pressurized; it was designed from the start to be converted to carry astronauts instead of cargo.

Currently, the Russian Soyuz spacecraft is the only vehicle that can get astronauts to the space station and back in the absence of the space shuttle. It dates to 1966 and, along with the Soyuz rocket that carries it into space, has proven to be the most reliable space vehicle in history. As made famous in the movie Gravity, at least one Soyuz spacecraft is attached to the International Space Station at all times for use as an emergency escape vehicle. The Russians charge more than $50 million to fly an astronaut to the space station. SpaceX wants that business.

~~How We'll Live on Mars -by- Stephen L. Petranek

Day 46 : Book Excerpt : Making Starships and Stargates

Ernst Mach, an Austrian physicist of the late nineteenth and early twentieth centuries, is now chiefly known for Mach “numbers” (think Mustang Mach One, or the Mach 3, SR71 Blackbird). But during his lifetime, Mach was best known for penetrating critiques of the foundations of physics. In the 1880s he published a book – The Science of Mechanics – where he took Newton to task for a number of things that had come to be casually accepted about the foundations of mechanics – in particular, Newton’s notions of absolute space and time, and the nature of inertia, that property of real objects that causes them to resist changes in their states of motion.

Einstein, as a youngster, had read Mach’s works, and it is widely believed that Mach’s critiques of “classical,” that is, pre-quantum mechanical, physics deeply influenced him in his construction of his theories of relativity. Indeed, Einstein, before he became famous, had visited Mach in Vienna, intent on trying to convince Mach that atoms were real. (The work Einstein had done on Brownian motion, a random microscopic motion of very small particles, to get his doctoral degree had demonstrated the fact that matter was atomic). Mach had been cordial, but the young Einstein had not changed Mach’s mind.

Nonetheless, it was Mach’s critiques of space, time, and matter that had the most profound effect on Einstein. And shortly after the publication of his earliest papers on General Relativity Theory (GRT) in late 1915 and early 1916, Einstein argued that, in his words, Mach’s principle should be an explicit property of GRT. Einstein defined Mach’s principle as the “relativity of inertia,” that is, the inertial properties of material objects should depend on the presence and action of other material objects in the surrounding spacetime, and ultimately, the entire universe. Framing the principle this way, Einstein found it impossible to show that Mach’s principle was a fundamental feature of GRT. But Einstein’s insight started arguments about the “origin of inertia” that continue to this day. Those arguments can only be understood in the context of Einstein’s theories of relativity, as inertia is an implicit feature of those theories (and indeed of any theory of mechanics). Since the issue of the origin of inertia is not the customary focus of examinations of the theories of relativity, we now turn briefly to those theories with the origin of inertia as our chief concern.

Einstein had two key insights that led to his theories of relativity. The first was that if there really is no preferred reference frame – as is suggested by electrodynamics – it must be the case that when you measure the speed of light in vacuum, you always get the same number, no matter how you are moving with respect to the source of the light. When the implications of this fact for our understanding of time are appreciated, this leads to Special Relativity Theory (SRT), in turn, leads to a connection between energy and inertia that was hitherto unappreciated. The curious behavior of light in SRT is normally referred to as the speed of light being a “constant.” That is, whenever anyone measures the speed of light, no matter who, where, or when they are, they always get the same number – in centimeter-gram-second (cgs) units, 3 10 10 cm/s. Although this works for SRT, when we get to General Relativity Theory (GRT) we will find this isn’t quite right. But first we should explore some of the elementary features of SRT, as we will need them later. We leave detailed consideration of Einstein’s second key insight – the Equivalence Principle – to the following section, where we examine some of the features of general relativity theory.

Mention relativity, and the name that immediately jumps to mind is Einstein. And in your mental timescape, the turn of the twentieth century suffuses the imagery of your mind’s eye. The principle of relativity, however, is much older than Einstein. In fact, it was first articulated and argued for by Galileo Galilei in the early seventeenth century. A dedicated advocate of Copernican heliocentric astronomy, Galileo was determined to replace Aristotelian physics, which undergirded the prevailing Ptolemaic geocentric astronomy of his day, with new notions about mechanics. Galileo hoped, by showing that Aristotelian ideas on mechanics were wrong, to undercut the substructure of geocentric astronomy. Did Galileo change any of his contemporaries’ minds? Probably not. Once people think they’ve got something figured out, it’s almost impossible to get them to change their minds. As Max Planck remarked when asked if his contemporaries had adopted his ideas on quantum theory (of which Planck was the founder), people don’t change their minds – they die. But Galileo did succeed in influencing the younger generation of his day.


~~Making Starships and Stargates- The Science of Interstellar Transport and Absurdly Benign Wormholes -by- James F. Woodward