Fly Me to the Moon

An Insider's Guide to the New Science of Space Travel

Edward Belbruno

• Publisher: Princeton University Press
• Year: 2013
• ISBN:
  9781400849192
• Topic: Ciencias físicas
• Subtopic: Astronomía y astrofísica

When a leaf falls on a windy day, it drifts and tumbles, tossed every which way on the breeze. This is chaos in action. In Fly Me to the Moon, Edward Belbruno shows how to harness the same principle for low-fuel space travel--or, as he puts it, "surfing the gravitational field."
Belbruno devised one of the most exciting concepts now being used in space flight, that of swinging through the cosmos on the subtle fluctuations of the planets' gravitational pulls. His idea was met with skepticism until 1991, when he used it to get a stray Japanese satellite back on course to the Moon. The successful rescue represented the first application of chaos to space travel and ushered in an emerging new field.
Part memoir, part scientific adventure story, Fly Me to the Moon gives a gripping insider's account of that mission and of Belbruno's personal struggles with the science establishment. Along the way, Belbruno introduces readers to recent breathtaking advances in American space exploration. He discusses ways to capture and redirect asteroids; presents new research on the origin of the Moon; weighs in on discoveries like 2003 UB313 (now named Eris), a dwarf planet detected in the far outer reaches of our solar system--and much more.
Grounded in Belbruno's own rigorous theoretical research but written for a general audience, Fly Me to the Moon is for anybody who has ever felt moved by the spirit of discovery.

Chapter One

A Moment of Discovery

“Houston, we have a problem.” That plea for help got Tom Hanks and his crew out of a jam on Apollo 13. But, who do you call when you don’t work for NASA? … NASA!

At my door was a person I had never seen before. He introduced himself as James Miller. He had a problem.

The Japanese had launched a space probe to the Moon about three months earlier, in late January 1990. The main purpose of the mission was to demonstrate Japan’s technical prowess in spaceflight. They had been gradually developing their technical abilities in space travel since the 1970s with less ambitious Earth orbiting missions. By 1990 they had built a considerable infrastructure to handle missions beyond Earth orbit including the Kagoshima Space Center. Now they wanted to become the first country to reach our neighbor after the Americans and Soviets. For Japan, this was an important mission, supported with national pride and a great deal of publicity.

But the mission had failed. Miller wanted to know: Could I save it? He had tried all the other obvious solutions and I was the last resort.

The Japanese had launched two robotic spacecraft MUSES-A & B into Earth orbit. These two spacecraft were attached to each other as they orbited the Earth. The smaller one, MUSES-B (renamed Hagoromo), the size of a grapefruit, detached on March 19 and went off to the Moon on a standard route, called a Hohmann transfer. But the Japanese lost contact with it, and it wasn’t known if it ever made it to lunar orbit. It was last observed approaching the Moon, and preparing to go into orbit by firing its rocket engines, when communication was lost.

I was familiar with the mission, since it was widely broadcast in the press. One headline read, “Japan’s Lunar Probe Lost.” I didn’t know much beyond what I heard through informal gossip from engineers in the hallways—that Japan was desperate to somehow get things back on track. The other spacecraft, MUSES-A, was renamed Hiten, meaning “A Buddhist angel that dances in heaven.” Hoping to salvage the mission, Japan wanted to get Hiten to the Moon since Hagoromo appeared to be lost.

The Buddhist angel was the size of a desk, and was never designed to go to the Moon, but rather to remain in Earth orbit and be a communications relay for the now lost Hagoromo.

Miller was an aerospace engineer at NASA’s Jet Propulsion Laboratory (JPL). He explained that he was trying to find ways for Japan to get Hiten to the Moon and into lunar orbit. But there were major problems—Hiten had very little fuel; it was not built to go to the Moon; and it would be impossible for it to reach the Moon by normal methods.

He asked if my theory of low fuel routes to the Moon could do it. He had heard that I had figured out a way to go to the Moon with much less fuel than conventional methods. He knew it was controversial, but was “willing to try anything.”

I hadn’t quite figured it out, but as soon as he asked me this question, it was like a light was turned on. As if the answer just jumped into my mind! I suggested that he do a computer simulation, and assume that Hiten was already at the Moon at the desired distance from it, and traveling with the right speed as specified from my theory. This was the first time I had ever applied my work to a real spacecraft, and there was no way to know if my suggested approach would be successful. The problem presented to me by Miller triggered the missing piece in my research that was needed to make my method work. It was one of those rare moments of scientific discovery that happen in the blink of an eye.

Miller was a bit skeptical that it would work. I gave him some initial critical parameters he would need to use in the computer simulation, and he left to try it out. I knew it was going to work.

He came by my office the next day, looking both excited and stunned—with computer output in hand, saying, “It worked!” I was excited as well. Our results looked promising, but it would take some work to come up with a fully completed solution. So we started to determine a polished usable path to the Moon within the required margins. Not only would this path salvage the Japanese lunar mission, it would represent a new and revolutionary route to the Moon.

Chapter Two

An Uncertain Start

Big ideas start small. Some, as I’ve said, are aha! moments, others develop through years of research, and some, such as the Hiten mission, are a combination of the two. To see how we rescued the Hiten mission, we have to start at the beginning.

I arrived in Pasadena, California, in January 1985 to work at JPL. It was great to get out of the cold rainy climate of Boston, and the sunny, warm weather in Pasadena could not have been more welcoming. I was starting a new adventure in my life, but had no idea of the roller-coaster ride I was about to take.

I had just given up my position as an assistant professor of mathematics at Boston University. My research was not going as planned, and I was in need of some new ideas, often not easy in an academic setting in which one has to pay attention to what is acceptable or trendy at the time. So I felt JPL would be a perfect place to work. It sits in a small valley at the base of the imposing San Gabriel mountains, near Mt. Wilson.

JPL is responsible for exploring our solar system with robotic spacecraft. The list of their successes is many, notably in the mid-1960s the famous Surveyor landings on the Moon, and in the 1970s, the Mariner missions to Mercury and Venus, and the launch of the legendary Voyager spacecraft to Jupiter, Saturn, Uranus, Neptune, and beyond. Who could forget the historic landings of the two Viking spacecraft on Mars in the late 1970s. JPL’s accomplishments are in the news today with the two Mars rovers, Spirit and Opportunity, rolling around on the red planet, and with the Cassini spacecraft arriving at Saturn with absolutely stunning views of Saturn’s rings with its many moons—most notably the moon Titan. Titan’s surface had been hidden from view by dense clouds. As this book is being written, Cassini, together with its Huygens probe, which landed on Titan, unveiled a bizarre world with possible oceans and rivers of liquid methane.

My new position was as trajectory mission analyst, and I was assigned to the Galileo mission to Jupiter. The Galileo spacecraft completed a successful mission on September 21, 2003, by plunging into Jupiter’s atmosphere.

It was an eye-opening job. I had come from the very theoretical mathematical world of celestial mechanics where planets are regarded just as simple points. At JPL planets are naturally regarded as real objects. I had to get used to the fact that Jupiter was not a mere point anymore—that it has such things as a radius, a chemical composition, many satellites, magnetic fields, and radiation belts. Spacecraft were not just theoretical points either—they were real operational machines, with propulsion systems, guidance systems, communications antennae, computer operating systems, and so forth. My training was more concerned with the theoretical ways objects can move in space, and not focused on applications. The goal at JPL, on the other hand, was purely applied. They were interested in getting a spacecraft to a specific planet.

To make matters more challenging, I was used to the environment of academia where my colleagues were mainly mathematicians. Here at JPL, I was in a more company-structured environment, where most of my colleagues were aerospace engineers. They were less interested in the theory of how objects can move in space than in ensuring that a spacecraft successfully complete its mission.

This is a serious business—for several reasons. First, these missions are high profile and represent national aspirations and goals voted upon at the congressional level. They are also expensive—from hundreds of millions to billions of dollars apiece. For example, the cost of the Cassini mission was about $3 billion. So the bottom line here is that you don’t want to make a mistake or take chances with these missions. Space travel and launching rockets into space is a risky business. Thus, the attitude at JPL is to be conservative in mission planning and to use tried and tested methods. This does not mean that engineers cannot be creative—but the creativity has to be carefully tested and monitored. My mathematical training at New York University’s Courant Institute, under the direction of Juergen Moser, was more concerned with theoretical types of motion. When we talked, we used phrases like, “In general, it can be proven that,” or “It is possible that the following motion will occur.”

To a mathematician, the point is to show that a particular motion exists without paying too close attention to its precise explicit motion. The main issue is the general type of motion. Mission-design engineers are interested only in the explicit motion and not in hypothetical situations. They want to see it, measure it, and plot it. Thus, I encountered a sharp difference of cultures.

I felt like a fish out of water. As part of my job, I ran countless computer simulations of trajectories for the Galileo spacecraft from the Earth to Jupiter and compiled unending columns of numbers. It was tedious work. But it was bearable, since it supported the human race’s quest to explore our solar system and get off of this planet. I was, however, beginning to question whether I had made the right decision in moving to California and giving up my academic career as a mathematician. The magnitude of the risk I had taken in switching careers was becoming more apparent.

Chapter Three

Conventional Way to the Moon

I wanted to keep theoretical research active, and I had a gut feeling that I would find some promising new ideas at JPL from the way trajectories were designed for missions. One thing stood out and caught my interest. Spacecraft were launched to the Moon and other places of our solar system on Hohmann transfers. A transfer, in general, is a trajectory in space from one location to another.

The person who first formulated a precise way to determine special paths from the Earth to the Moon, or more generally from a given planet to another location in space, was the German Walter Hohmann in 1916. Hohmann transfers minimize the energy (fuel) required to go from one point to another in space under certain restrictive assumptions. Hohmann’s theory for computing them is relatively simple, but effective in many situations.

Although it is applicable in a general setting, the best place to start is to describe a Hohmann transfer from the Earth to the Moon. Because there are many references on this, I’ll just give a brief description of how it works. Let’s start at the very beginning—on the ground.

Figure 3.1 Rocket with payload going into Earth orbit

A rocket lifts off from a launching pad on the Earth. It has several stages, each filled with the necessary fuel to reach orbit around the Earth. The uppermost stage contains a small payload—the cargo being carried into space. When this stage reaches Earth orbit, at a typical altitude of 124 miles (200 kilometers), the payload is released into circular orbit. It takes the rocket only a few minutes to reach this altitude, and all of the stages it used to reach this distance have fallen away as planned. Let’s assume the payload is a small satellite planned to orbit the Moon, and it is now in a circular orbit 124 miles above the Earth. At the desired time, the satellite uses its own engines to give it the necessary kick to put it onto a path to the Moon (see figure 3.1). The moment these engines are started, the Hohmann transfer begins. The path to the Moon is fairly fast, taking about three days, and when the satellite approaches the Moon at the desired altitude of, say 62 miles, (100 kilometers) from the lunar surface, it has to slow down by firing its rocket engines, otherwise it will just fly past the Moon (see figure 3.2). By the time the satellite, or spacecraft, reaches the Moon it is going about .62 miles per second (2,232 miles per hour) with respect to the Moon. If you want to slow down enough to place the satellite into a circular orbit around the Moon at 62 miles above the surface, you have to lose most of this high approach speed. You have to s...