Author Archives: Mason Peck

A Hacker’s Mars-Ascent Vehicle

DIY_Mars_Rocket Mars One is a project that hopes to send the first colonists to Mars. It will be a one-way trip, which vastly simplifies the technology compared to what’s required for a round trip (and makes it cheaper). Cynics assert that the thousands of people who have volunteered to be colonists must be out of their minds, that the trip is some sort of suicide mission. I disagree. And in the spirit of full disclosure, let me explain that I’m on the Board of Advisors for Mars One. So, I would be expected to disagree with that view.

There are many motivations for becoming one of the first settlers on Mars, none of them insane, in my opinion. They include a noble sense of self-sacrifice, if you believe that extending human presence into the solar system will help ensure the survival of the species; a desire for the immortality that comes with fame, despite the risk to life and limb—in some sense, putting yourself at risk helps ensure your influence on the history of humanity will outlive your physical being; a desire for personal accomplishment, or overcoming a challenge, the same sort of thing that drives people to join expeditions to the summit of Mount Everest; self-interest, including the prospect of making money as a Mars entrepreneur, or helping your family and friends back on Earth do the same.

Here’s the thing. I reject on its face that this trip is a Kobayashi Maru scenario. One of the first things I would do upon landing is to begin building the tools, the equipment, and even the economic structures to one day construct an Earth-return vehicle. Such a hope would not be irrational. In fact, it’s easier to lift off from Mars and enter Mars orbit than to do the same on Earth. I’m confident that the right group of engineers could pull this off over the course of a couple of decades, at least returning to cislunar space. And remember—they’ll likely have Internet access, probably with the help of lasercomm. So, the folks back home can send them schematics, analyses, even test results, to help make that effort a success.

Let’s take a look at what a space-hardware hacker might build to enable his or her return journey. But not just one hacker. Let’s say three people will plan to make the return trip in a single vehicle.

In coming up with a design, we’ll have to keep in mind that exquisite, custom components will be unavailable or in short supply. The hacker is unlikely to find spools of carbon filament for high-tech composites, an unlimited supply of cryogenic valves, electric motors, circuit boards, or other high-precision special-purpose parts. Maybe a few items can be sent from Earth, on demand. I wouldn’t count on it.

What we can count on is a ready supply of water. As much as the hacker wants. NASA has documented the abundance of water on Mars many times over. It’s just beneath the surface. Meteor impacts expose it in the form of an ice-strewn field fairly often. So, hydrogen and oxygen are no problem. They’re available by electrolysis, which any kid can achieve on a small scale. So can graduate research assistants at Cornell University.

We’ll start by keeping it simple, with a single-stage-to-orbit design. The hacker’s goal is to return to Earth in a human-habitation module sized for three people. NASA’s Mars Design Reference Architecture 5.0 mission (circa 2009) sizes a two-stage system for six astronauts. We’ll cut that mass exactly in half: the structure, solar panels, the food, everything. We’ll take the added penalty of carrying the mass that DRM 5.0 associates with the first stage all the way to orbit. So, the vehicle we anticipate that our hacker will build is conservatively heavy at 26,025 kg (without propellant). After all, it’s to be expected that the Mars hacker isn’t able to build something as weight-optimal as NASA contractors can. Also, our design doesn’t need methane and liquid-oxygen cryocooling hardware required by DRM 5.0, which our hacker probably couldn’t build anyway, saving considerable mass, and adding even more margin for error.

It doesn’t need that cryogenic hardware because the hacker uses gaseous hydrogen and oxygen as propellant. That gaseous mixture results from electrolyzing 89,000 kg of water, which fills four spherical aluminum tanks (each about 3 m in radius). The image at the top of this post shows the vehicle, including its tanks, sized about right. These tanks are just over 2 cm thick, holding H2 and O2 gas at 10 Earth atmospheres of pressure (over 1,000 N/m2, for those of you on Mars right now taking careful notes). At that pressure, material in a spherical tank experiences about 50 MPa (megaPascals) of stress, which represents a factor of safety of 2.5 times what the welds in the aluminum can withstand (1.5 margin). Let me emphasize that this concept is not a critique of DRM 5.0. It’s what you or I might do if you didn’t have expectations of that level of sophistication and, frankly, safety.

Where would the hacker get these tanks? All four total just over 20,000 kg. I would suggest sand-casting many identical equilateral triangles and welding them together to form a geodesic approximation of a sphere. We’ll still need to ensure that enough aluminum is available. It would have to come from recycling bits of the lander, or other equipment. Alternatively, combining available aluminum powder with water produces H2 gas and alumina (aluminum oxide, or Al2O3). That’s a ceramic that has very nice properties, and it’s strong enough for this application. Its main advantage is that because Al2O3 is half aluminum (by weight), using alumina stretches the aluminum available to the hacker. A downside is that the tanks must be assembled by sintering, a kind of 3D printing technique, and that’s more time-consuming that melting down, casting, and welding aluminum triangles.

Yet another solution would be to create watertight inflatable sacks. Cotton fiber has a very high strength-to-weight ratio. So, worn-out t-shirts, lint from the clothes dryer in the Mars hab, and some sort of rubberized liner might also do the trick. The result might even be lighter than metal tanks.

But for this exercise, we’ll stick with these aluminum geodesic spheres. In any case, testing will be essential. The test campaign includes launching smaller tanks of water into Mars orbit. You’ll see why in a moment.

Fueled up, with three passengers and 1,325 kg of food, the hacker’s Mars ascent vehicle weighs 133,000 kg. The water-electrolysis propulsion system in development at Cornell is simple, requiring no solenoid valves, cryogenic plumbing, or other subtleties. Its specific impulse approaches 371 sec. That efficiency is lower than cryogenic H2/O2, but the simplicity can’t be beat. Furthermore, the gaseous mixture is stoichiometrically ideal (i.e. there’s just enough of each molecule to burn completely). As a gas, the combination is extremely well mixed, which eliminates the need for the combustion chamber to include an injector (which is complicated and expensive to fabricate).

The propulsion subsystem provides about 4,000 m/s delta-V. That’s enough to reach a 300 km altitude Mars orbit. The vehicle won’t stay there long. It needs to refuel, and then it heads to Earth. It refuels by docking with tanks of water that have been launched to orbit over the past two years. Those tanks refill the now-empty aluminum tanks on the ascent vehicle. The water is much denser than the gaseous H2/O2 mixture. About 493,000 kg of water can fit in those tanks. So, the resulting vehicle’s delta-V capability is far greater. The electrolyzers that the hacker has been using on the surface of Mars are installed in each tank before liftoff. After the water is on board, these same electrolyzers slowly bubble the water into combustible fuel.

Water propellant can impart over 10,000 m/s delta-V to this spacecraft. It does so much more slowly than the gaseous mixture did at liftoff, but that’s OK. Unlike lifting off from the surface, the return trip does not require a lot of thrust at once. Low thrust delivered over many months would do it. According to Bobby Braun and his colleagues, that 10,000 m/s is well above what’s necessary to return to Earth, more than twice what’s needed (depending on the timing). So, this design forgives a little imprecision in hacker navigation, and a little underperformance in other areas.

The spacecraft spins. The resulting centripetal acceleration separates the water from the gas. The plumbing pulls the H2/O2 gas from the inboard-most point on each spherical tank, leaving the water to electrolyze. The spin need not be fast, and indeed too fast a spin speed would have bad results. These large water tanks offer a final benefit: they shield the astronauts from radiation. Water is among the best substances to keep humans safe from the space environment. And if the drinking water, even the oxygen, runs out in the habitat, our three hackers know where to find more.

It will be essential for all involved in a one-way trip to Mars to proceed with a clear understanding of the risks: that is, the probability of success (or failure) and the consequences. To me, that’s the key ethical concern: transparency. If people choose to undertake this risky activity with full knowledge of the risks, I see no ethical issues. In fact, I think we may be morally obligated to permit people the freedom to do so, and not impede their desire to realize their dreams by imposing our own fears or superstitions based on uninformed perspectives. But the real key to success in living on Mars will be the hacker ethos: make due with what you have. Be creative. Your instinct for innovation may even be enough to bring you home again.

Beachcombing Technology on the Shores of the Cosmic Ocean

antarctica_meteorites

Here’s why I’d like to take a trip to Antarctica.

The Kepler spacecraft has changed the world. It has discovered 974 planets we’re sure of (as of June 2014), and there are 3,601 candidate planets awaiting confirmation. They’re exoplanets, orbiting other stars in our galaxy. A few are Earth-like—well, not far from our planet’s size and in the habitable zone of their respective stars. At their distance from their star, they wouldn’t be too hot or too cold for life that we understand. These results have led us to conclude that there may be 17 billion Earths in our own galaxy.

In 1950, well before Kepler’s findings, Enrico Fermi and some colleagues were discussing the possibility of life elsewhere in the galaxy. He offered what’s now known as the Fermi Paradox: if the universe is as old as we think it is, with its vast number of stars, odds are that extraterrestrial life is common. And we can even expect some technologically advanced species. Kepler’s many planets make Fermi’s case even stronger. So, why haven’t we heard from them? Why haven’t we at least found evidence of that life? Years later, John von Neumann’s interest in self-replicating machines inspired his answer: maybe so-called von Neumann probes are already here. Self-replicating devices may have made their way across the galaxy and now lie dormant and undetectable, only infrequently transmitting information about Earth to their planets of origin.

I submit that a probe like this, something tiny enough and transmitting in a way we would not detect, might go unnoticed. Something small enough might appear to us as a dust mote, or a micrometeorite. Thousands of tons of interplanetary and interstellar debris land on Earth every year. In fact, whether or not a working von Neumann probe has ever made it to Earth, bits of failed probes would be continually circling gravitational drains throughout the galaxy. They would collect on planetary surfaces like the little shattered bodies of diatoms, whose calcium-rich remains litter the ocean floor. Such tiny interstellar probes might be ground up over the course of thousands, maybe billions, of years as they tumble through space and end up as particles on the interstellar wind.

And if so, we might find some in Antarctica. That’s where you can pick up micrometeorites off the ground—bits of black jetsam on a beach of snow and ice. So, here’s a Spacecraft-a-Week idea turned on its head. Rather than designing a spacecraft, let’s see if we can discover someone else’s. Let’s try to identify space-technology debris from a long time ago, maybe a galaxy far, far away. What we learn from very careful analysis of the dust that has been falling on Earth for eons may lead us in unexpected directions. It may teach us how to build spacecraft we cannot conceive of now.

This idea has been in the back of my mind for about 40 years. When I was six, I visited a beach in Italy, a town known as Anzio, where Nero once had a villa. At some point the coastline had eroded, and the sea claimed the villa. But wading through the water near where this villa once lay, I found ellipsoidal bricks, rounded-off bits of tile, even pieces of mosaics. The surf had ground them down, but what I saw was unmistakably building material: cement in a matrix holding stones (concrete!). Right-angle shapes (corners of bricks!). A smooth piece of marble with one unaccountably flat face (tile!). A chamfered glass square that was certainly not an igneous rock. Even a kid can tell the difference between what’s natural and what’s man-made.

Craig Ventner did something related a decade ago. His research team scooped up a sample of the Sargasso Sea to understand the genetic diversity of the oceans. Sequencing the genes of this large sample revealed enormous diversity—far more species than we knew. His is a similar approach because he exploited the power of computation to address a problem that is simply intractable on the scale of what humans can accomplish. And he was interested in a statistical result. So am I. How much interplanetary dust is the result of someone’s handiwork? I expect that the fraction approaches zero, but I also speculate that it is not zero.

What we’ll need is a very large sample of micrometeorites, a microscope that captures digital images, a spectrometer, some fast computers, and a smart algorithm (that’s the hard part) that can identify what’s natural and what’s not. This project would be a mechanical version of what SETI has attempted. Rather than looking for intelligent radio-frequency signals among the many natural emissions from the stars, we would seek out unnatural dust particles. Craig Ventner’s expedition and later analyses were funded by grants totaling well over $25M. I think we could do it for that amount.

The next step would take a little more money, but not unreasonably more. The particles that survive the fall to the surface of the Earth represent a very specific subset of all the stuff that’s circling our gravitational drain right now. Only the particles with a low-enough ballistic coefficient land intact, and we would find only those portions of larger bodies that can survive the heat of reentry. The rest vaporizes. But we may discover artificial materials that have been designed to survive the heat of entering a planet’s atmosphere, solutions we have not yet come up with. Whether those materials are artificial or natural, those solutions are important. They may improve our ability to send mass back from the International Space Station or, in the longer term, land people on Mars. And that’s just the beginning.

if this Antarctic micrometeorite survey is at all successful—and we would already have changed the world at that point—we should launch a spacecraft to follow up. I suggest we send it to the Moon. Consider one or more small rovers, maybe CubeSat size, equipped with a microscope and that same algorithm, beachcombing the lunar surface, picking out those unexpected shapes and materials: polymers, alloys, and composites that are one in a million and have no business being there, like Andy Dufresne’s piece of black volcanic glass. The rover transmits that one-in-a-billion image to Earth, along with its spectral data, for us to analyze. Those candidate particles, like the SETI signals or Kepler’s uncertain stellar-wobble data, don’t all pan out. But I’ll be satisfied with just the one.

Stochastic Exploration

sprite_evanescence

There’s strength in numbers.  Many hands make light work. The whole is greater than the sum of its parts. It takes a village to explore the solar system. These aphorisms are so familiar—well, three of the four, anyway—that we rarely recognize their potential to change how we think.

So, let’s recognize it. What would it mean to explore space the way that cottonwood seeds and maple samaras drift across the landscape, blown randomly and yet ensuring that some small number of new saplings take root? What if we could use sheer numbers of spacecraft to design a mission that reaches its target—not focusing on high-precision trajectory control but seeking a statistical guarantee that some fraction of the many spacecraft arrives at the intended destination? Let’s take this idea further. What if the destination were a region of space? The entire solar system? What space-system architecture would guarantee good odds that one of our many spacecraft would encounter a celestial body?

What makes this idea even remotely credible is the possibility that someday soon we’ll see some very small spacecraft. Launch costs are what they are, and the U.S. Congress is willing to budget relatively little for new ideas in space. So, for the foreseeable future, the only way to put more spacecraft into orbit is to make them smaller. Sprites are a start. They’re one way to do more with less. The current Sprite technology demonstrator weighs about 5g. I’m confident we can knock that down to 500mg if we could find the resources to support that technology development. (The fact that there is so little funding—public or private—for this kind of research is one reason for the blog. So, I might as well put these ideas out there for free).

Let’s posit that the SpaceX Falcon Heavy will be able to launch 10,000 kg on our desired Earth-escape trajectory. SpaceX expects that it will carry 13,200 kg to Mars. So, a lighter, 10,000 kg payload would go even farther. And let’s say that 30% of this payload has to be dedicated to spacecraft infrastructure, such as something to tie the Sprites together and later deploy them, as well as communicate with the ground at the time of this event, which takes power, and thermal control, etc. The remaining 7000 kg worth of 500mg Sprites would comprise 14 million individual explorers.

Some of us have been thinking about this idea for a while: Cornell graduate students Lorraine Weis and Zac Manchester, for example. Zac wrote a paper about some of the mathematics.  Lorraine is working on ways for a large number of such spacecraft to exploit solar pressure and other subtle physics.

Here’s how it might work.

A mothership launches on a Falcon Heavy. It’s a 10,000 kg spacecraft that includes 100 kg worth of solar panels to power a 10 kg communications subsystem, a 50 kg traditional propulsion subsystem, another few hundred kg of other structural and electrical bits and hardware for guidance and navigation. Those spacecraft-design details are straightforward. Here’s what isn’t. About 2500 kg of material is an ultraviolet-degradable binder (if you’re an applied chemist), or mortar (if you’re a mason), or matrix (if you’re a geologist). This mortar is shot through with Sprites. They are frozen in temporary amber, which keeps them safe during launch and enables them to travel together after the launch vehicle upper stage separates from the mothership. Or maybe they’re like pineapple chunks in Jell-o. You get the picture.

Operators on the ground design a trajectory-correction maneuver of some kind, upload it to the mothership, and initiate it. Now the mothership’s job is done, and the Sprites are en route to somewhere. They should head for the nearest on ramp to the Interplanetary Transport Network. The ITN is a chaotic, multidimensional set of gravitational pathways through the solar system. Gravity from the Sun and planets is partly responsible for its existence. So is the rotational churn of the planets as they orbit the Sun. These pathways are hard to predict exactly, and no spacecraft has ever tried hitching a ride.

Until this Sprite mission. Arguably some of NASA’s interplanetary spacecraft, like Cassini, leverage parts of the ITN to cut down on propellant and enable them to travel to the outer planets affordably. However, it’s risky to depend on the ITN exclusively because of its mathematical subtlety and its chimerical behavior—risky for a single, exquisite, expensive spacecraft anyway.

For our 14 million Sprites, it’s another story. As the Sun’s ultraviolet radiation washes over the block of Sprites, the UV binder evanesces. The Sprites begin to flake off, and the individual Sprites fan out. The process resembles how the Sun’s heat and pressure burns off ice from comets, producing that characteristic tail. And like a comet’s tail, these Sprites roughly follow their siblings for a while. As time passes, their paths diverge. Differences among the individual Sprites’ flight dynamics separate them. The first Sprites to flake off end up at the statistical extremes. So do the last ones.

The “average” trajectory here is a slippery concept: the mean or median of this statistical distribution involves a cloud of Sprites, and we need to describe its motion with at least six coordinates (Kepler’s orbital elements, for example) or through even subtler mathematics like statistical moments. The goal is to put the average close enough to the trajectory we want that the number of Sprites on slightly different trajectories compensates for unexpected disturbances. Those disturbances would prevent a typical, single spacecraft from reaching its goal. In stochastic exploration, they’re part of a blurred reality in which we design the odds. And thanks to the number of chances, the number of spacecraft, the mission architecture confidently meets those odds.

Assuming we’ve licked the problem of how to plan the trajectory of a cloud of particles, we now have a cloud headed somewhere interesting. How about Jupiter? It’s well known that the combined gravity of Jupiter and the Sun trap asteroids—the so-called Trojans. Their orbits reside in a permanently stable tidepool in the planetary ocean. We call it a “Lagrange point.” Maybe some Sprites end up there. Others may slip past and begin to orbit Jupiter, where they slow down thanks to electrodynamic drag and collisions with gases found among Jupiter’s many orbiting moons. Over time they encounter those moons and the spaces between. Some likely end up entering Jupiter’s atmosphere.

Another aphorism: if a tree falls in a forest and no one is there to hear it, does it make a sound? We could ask, “if a Sprite encounters a planetary body but transmits nothing back to Earth, have humans explored?” A few of us think the answer is “yes.” But, you know, some scientists are all “me, me, me.” For these solipsistic types, let’s consider a couple of ways for these interplanetary Sprites to tell us what they’ve found.

Taking a page from the Kicksat mission, we could use a matched filter to detect special gold code pseudorandom sequences, each a unique signature emitted by one of the 14 million Sprites. The Sprite ground station’s special brand of signal processing helps it pick out a Sprite’s faint transmissions from all the other noise. The longer the code, the better—that is, the greater—the signal-processing gain. And there’s another reason for a long code: each Sprite should have a unique signature, and creating 14 million unique codes demands that they be long. In fact, if it’s to be like the Kicksat Sprites, we’ll need 28 million codes—a 1 and a 0 for each spacecraft. Each would be about 10 gigabits long.

Solar power might be sufficient for spacecraft on ITN pathways among the inner planets. Near Jupiter a more likely choice would be a nuclear power source, a betavoltaic battery. Widetronix, a start-up in Ithaca, NY, is developing this technology, and they’re already able to power integrated circuits with a microchip-scale nuclear source. Some of their batteries have half-lives of a century. So, a nuclear Sprite is well within the realm of possibility. What’s more, it could last far longer than most of the engineers who designed and launched it.

But let’s say that nuclear power is off the table. How about scavenging the energy of impact? When a Sprite strikes an asteroid, for example, a piezoelectric layer in its structure deflects and produces high power for a brief instant. In that instant, current flows through an analog circuit designed to emit a short, high-power pulse at a specific frequency. The Sprite’s swan song is a transmission that confirms an impact (in this case something very short, nothing like the 10 gigabit sequence of that nuclear design). That information could be useful in figuring out the statistics of the Trojan asteroid population—how many, how big, and where they are. How about we design this analog circuit to include a device whose inductance varies with matter that happens to adhere to the Sprite during its voyage? Maybe electrostatic charge makes it stick. That variation would alter the frequency of this swan song. When we detect it, such a transmission might reveal something scientifically novel about interplanetary gases or particulates.

How we ask the question can determine the answer. Rather than asking “how can we build a spacecraft to take high-resolution images of Trojan asteroids,” we might ask “what science can you do with tiny sensors that offer a statistical guarantee of asteroid collisions?” The latter is a question that demands more from our imaginations. It’s the kind of question we need to ask more often.

Spaceflight with a Sharpie

cusat

CUSat launched on September 29, 2013. It is Cornell University’s first formation-flight technology-demonstration mission. The name is pronounced “see you sat,” as in “I see you.” The spelling references Cornell University’s initials, of course, but it also refers to a key mission objective: demonstrating how one satellite can inspect another in orbit—for repair, servicing, and so on.

It went up on a SpaceX Falcon 9 rocket and shared the ride with several other customers, including another student-designed and -built satellite, Dande, from the University of Colorado (the CU of the Southwest). Dande is working great, as far as I know. CUSat’s mission-operations team flew the spacecraft for about a month before its flight computer overheated and invited in the grim reaper. Its early demise meant that CUSat never was able to demonstrate its capabilities fully.

With success only a hair’s breadth away, CUSat deserves another chance. As the Principal Investigator for this project, I’ll take the heat for what went wrong, but I also have the benefit of hindsight and have learned invaluable lessons. Here’s what I’ll do next time, if we ever find a sponsor willing to help us try again. In the spirit of Spacecraft a Week, I’ll offer a new design.

First of all, let me explain why this mission is important and boast a little about the great work that the Cornell students did in designing and building this experiment. CUSat’s architecture comprises two 25 kg satellites that fly in close proximity. They use GPS to detect the satellites’ position in orbit. That’s a fine thing, but it’s nothing new.

What’s new is that each of the two CUSat spacecraft has three GPS receivers, not just the one that your smartphone has. CUSat’s GPS antennas are spaced as widely as possible. Knowing the distance and direction (i.e. the vector) among these three antennas on a single satellite can tell us the orientation of that satellite relative to the Earth. Knowing the vectors among these antennas from spacecraft to spacecraft can tell us the orientation and position of one spacecraft relative to the other. That’s new.

And we know those vectors really well. Thanks to research by Dr. Shan Mohiuddin, formerly a graduate research assistant for my colleague Dr. Mark Psiaki, we know them to within about 3mm, likely about 1mm. That’s really new.

CUSat’s incredible precision and accuracy comes from tracking not just the GPS data you’re familiar with, which yields position accurate to about 1m, but also the so-called carrier phase. That is, we track the oscillations in the GPS radio transmissions themselves, measuring where the radio-frequency wave is at any time (i.e. the phase). As that radio wave passes one antenna, and then another, we mash together the phase difference, the speed of light, and the GPS transmissions’ frequency into an estimate of that relative position—again, good to a few millimeters or better.

The GPS receivers on CUSat are homemade, the result of research by the late Dr. Paul Kintner at Cornell. They cost about $1k. So, for about $6k and some software, we can navigate one spacecraft relative to another more precisely than you can write with a Sharpie. That’s why CUSat is worth doing, and that’s why I want to try again.

Cornell students designed, built, and tested CUSat. They did so under my leadership and with the guidance and support of the University Nanosatellite Program at the Air Force Research Lab. In addition to a well-conceived and implemented structural and electronic design, there are some unusual innovations that deserve special acknowledgment.

  • One is that the entire two-spacecraft system is single-fault tolerant. No single failure can prevent mission success. The fact that there are two spacecraft in the formation is part of the reason. On top of that redundancy, each spacecraft has three GPS subsystems where two would do, two radios where one would do, eight pulsed-plasma thrusters where seven would be sufficient (and four would do nearly everything we want), two cameras, multiple solar panels, and a few other backups. Even if the spacecraft computer fails (the infamous Viper, to which I’ll return), the mission control center can send and receive commands to cycle the power through separate electronics. Furthermore, all the flight software, as well as some of the microcontroller code, can be reprogrammed from the ground.
  • Another is that the flight electronics are protected by being nestled together, each board in its own aluminum box (to prevent electromagnetic interference among the boards). The most critical items are near the inside of this stack, with the flight computer at the center. It’s a little like organs in the human body, with the heart or brain protected by surrounding tissue that’s not quite as important. Radiation in the space environment has a hard time reaching these interior boards. High-energy particles need to pass through about 1 cm of aluminum to reach the flight processor. All this metal also helps wick away thermal energy, which of course we can’t remove in space with a fan, the way it’s done in a laptop.

In my opinion these are very successful design decisions, and the students who put it all together are to be commended. Somehow they managed to pack all this hardware, as well as the electrical harness to tie it all together, into a volume the size of a salad bowl. The Air Force tells us that CUSat is the densest spacecraft they’ve ever seen. In fact the students did it twice—two spacecraft, remember—and finished all this hardware in about two years.

So why didn’t it work when it finally launched five years later? The proximate cause is that the Viper overheated. Maybe that’s because it was packed in with other electronics, all of which generated heat, but I don’t think so. Despite the technical specifications reported by the manufacturer and our thermal analysis, the temperature rose to about 95°C over the course of a month’s orbiting in full sun (not expected when the students designed the mission). And that was the last telemetry we received. There were other problems, notably that the battery-charging software was incorrectly designed and implemented, merely counting up current in and out of the batteries and fundamentally misreporting the state of charge. However, that could have been fixed with a simple software patch if we had had the time.

But looking a little deeper, I now understand that we should not have let the spacecraft out of our sight until we had a firm commitment to launch. As it was, we delivered the spacecraft to the Air Force in 2008, five years before it actually launched. After 2008 our team gradually lost hardware expertise as generations of students came and went. CUSat went through four launch campaigns, each one a big hurry, during which I made bad decisions. For example, the most recent launch campaign but one led us not to repair some electronics that had failed during some previous pre-launch testing. And for one reason or another, we ended up launching one of the CUSat halves as a non-functioning mass that stayed with the launch vehicle while the other went on its way.

So, here’s what I’d do differently.

  1. Let’s launch CUSat via the International Space Station. Leave one of the two spacecraft on the ISS and send the other on its way, demonstrating formation flight with its highly accurate GPS navigation.
  2. I would not let the spacecraft leave the lab until it is ready to launch.
  3. And a few little technical tweaks:
  • Use commercial electronics. Instead of the myriad “interface boards” that our students enjoy building from scratch, I would permit only off-the-shelf microcontrollers, such as an Arduino, to interface with hardware. No building boards.
  • Get rid of the Viper flight computer, which was buggy, inexplicably crashing so that students wrote software patches and epoxied a USB drive to the board to accommodate them. The Viper board itself had integrated circuits mounted atop others, soldered to the traces on the board, with some other traces cut, making its overall quality very questionable. Unfortunately, we were committed to this flight computer. But with no response from the manufacturer, one of the Cornell students ultimately found a reseller online from which we continually bought more as generations of Vipers gradually died off.
  • Use only commercially available wiring harness that comes with connectors; no making custom cables. Nearly every test failure on CUSat can be traced to an issue with harness workmanship or design.
  • Build our own reaction wheels from commercial brushless DC pancake motors. No rotor (i.e. no flywheel), just the motors. Easiest thing in the world. We’ve done it twice since.

You heard right. For about $6k and some software, we can navigate one spacecraft relative to another more precisely than you can write with a Sharpie. Every spacecraft should have this capability. Imagine if any satellite could pinpoint its location relative to, say, the International Space Station within a few millimeters. The right combination of receivers and transmitters would make this possible. In this new world, a spacecraft could navigate to ISS and dock without radar, joysticking, or optical navigation. Spacecraft could sidle up to propellant depots and refill their water tanks, knowing their precise trajectory at any time. Spacecraft orbits would be known with astonishing precision, maybe avoiding collisions that lead to orbital debris. A CUSat reboot could show the way.

Mooncraft

shoers_microroverSpace exploration and space science are serious undertakings. Steely-eyed missile men with furrowed brows insisting that failure is not an option. Suits and skinny black ties. Short haircuts. Special safety regulations. Lots of jargon and three-letter acronyms (TLAs). We rarely hear the word “adventure” in the context of professional spacecraft engineering, let alone “fun.” And I never heard it on Capitol Hill during my two years working in Washington, D.C. But here’s the thing. Isn’t all this at least a little exciting? Even enjoyable? Honestly, if you’re an aerospace engineer and you don’t get some kind of kick out of what you’re doing, just go back to school, get an MBA, and make a lot more money doing something soulless that involves straightforward arithmetic and nothing more death-defying than Earnings Before Interest, Taxes, Depreciation, and Amortization (EBITDA).

That’s why it’s great to see Astronaut Chris Hadfield playing Space Oddity. He’s confirming for us that space and popular culture can be one and the same. Maybe even better, NASA flew some Legos recently. What would you build in orbit if you had something like Legos?

Connecting people to space in this way has some immediate benefits, sure—motivating the public to advocate for space-program budgets, moving Congress to appropriate money for NASA, and all that. But I think there’s a much more long-term benefit to embracing our natural curiosity, sense of adventure, and desire for play. What if we could create a killer app—a game, say, that people want to play desperately enough that they’ll invest in space hardware the way they invest in video games? What if a killer app for space showed us what’s possible if we all pull together and do what humans do best: build, create, and seek adventure?  What if you could play Minecraft on the Moon? For real? Would you and thousands of your friends pay enough to kick start a gamer’s space age?

Let’s call the game Mooncraft. Here’s how it might work.

A tactical objective is to survive the lunar night—about 14 Earth days long. There are no zombies or other lunar miscreants that skulk about (as far as I know), but nighttime is bad enough without creepers. Your avatar is a very small rover. Let’s say 100g in mass, for reasons I’ll explain. It captures a 176×144 grayscale imagery at a few frames per second.  These small frames and data compression would enable communications at less than 12Kbps, less than an old dial-up modem. The rover transmits its data to a larger, shared communications node to downlink to Earth. Servers on Earth distribute the video to gamers. So, you’re looking at the gray, black, and white lunar surface in grayscale. Makes sense to me.

There’s the question of light-travel time, which delays the signals to the rovers, and the video back to Earth.  It’s a few seconds. That’s too slow for joysticking a fast vehicle, but these little things travel slowly—a few millimeters a second. Commands to the rovers consist of “move forward x distance,” or “turn y amount,” delivered by a special type of game-controller interface that interprets typical Xbox controller or Wii controller motions as macroscopic commands that are executed on the scale of seconds. It will take some training, but I am confident that we’ll get used to it.

To survive, and in fact to thrive, on the Moon, players mine the regolith and build structures. Rather than whacking at the material with a pickaxe, as in Minecraft, some rovers dig up and nudge the powdery, sandy regolith forward with a snowplow-like attachment. Others pick up and place small rocks with a simple robotic arm. Still others can sinter igneous rocks together, tack-welding them in place. Yet another type of rover can provide bursty power to rovers that request it. Dr. Joe Shoer designed the microrover shown at the head of this post. Future posts will go into the technical designs of some of these microrovers.

Game designer and author Erin Hoffman clued me into the gaming value of creating different characters for these rovers, establishing an essential story line. We would start with a few of these characters but (and here’s the part I really like) we would let people design their own. The Mooncraft company, if it were ever to exist, would launch its own rovers for the use of the gaming community and would also launch rovers designed by its players (for an appropriate fee, of course).

The business case depends on utilization. Say that a gamer is willing to spend $5 per hour operating a rover. That’s over $44,000 per year, if a user wants a rover all to himself or herself. Those economics don’t make sense for most of us. My daughter assures me that the people who play Minecraft for hundreds of hours straight are also not the people with that kind of money to spend.

Instead, a time-share arrangement probably makes more sense, in which the rover is available to a gamer for a session and then autonomously leaves the site that a gamer has been working and goes to another gamer’s site to serve as his/her avatar for a while. And that shuttling back and forth continues. There’s likely an optimal algorithm for sending the rovers where they’re desired, a sort of traveling salesman problem to be solved for this kind of lunar gaming.

Let’s consider a business case. If a rover survives for three years, at 50% utilization, it provides about $22,000 in income. The cost of launching a 3U CubeSat to the Moon is alleged to be $1M. Say half the mass of this 4 kg 3U combines landing systems (airbags, in my opinion, and/or crushable foam) and requisite software, radios, solar panels, and structure. That leaves room for 20 tiny rovers.  I would suggest a sign-up fee for users, like buying a gaming system.  Say it’s $500 and that 1,000 people per rover sign up.  The total income over that three-year lifetime would be over $1.8M. Assuming the launch cost stays at $1M, and accounting for the cost of money, taxes, operations, building the rovers, and other things, we would conclude that this enterprise is on the ragged edge of profitability. Now, where’s that guy with the MBA that I insulted earlier?

A little more profitability might come from special users—people who level up or even choose to create a private population of these rovers to fabricate their own lunar outpost. Maybe NASA or other organizations would like to operate a fleet of these rovers for the sake of science and human exploration.

Remember, we’re playing with the actual surface of the Moon here. An accidental (?) outcome of playing the game Mooncraft may be the creation of a supply of lunar bricks (and Mooncraft could share the profits of selling these bricks to other users, with the gamers who created them). Another outcome may be a very large radar or optical reflector on the surface of the Moon, and who knows what else? An intentional outcome of these leveled-up players’ work may be the creation of a lunar base, or a space hotel. Or a lunar runway.

In any case, a game like this would provide an economic incentive for private launches to the lunar surface and, maybe, eventually, human habitation of the Moon. As awesome as Minecraft is, I might prefer the real version, the one in which I could go live in the structures that my avatar builds.

Let me summarize. There are three reasons for Mooncraft. First, maybe someone can make a buck from the entertainment aspects of this idea. The second and third objectives here go beyond mere entertainment. We’ll get some lunar structures built. And the gamers can share in the rights to license them for use. But most of all, Mooncraft is one of several ways in which to increase consumer demand for space. Increasing the demand for hardware in space will lower launch costs by making rockets a commodity. Launches could become such a common occurrence that they begin to resemble the mail. Think about how much it would cost to send a package across the country if we had no postal service, in fact no roads. You would need an expedition, outfitted for survival during a weeks- to months-long trek. Starts to sound like space travel, doesn’t it? So, let’s create the demand for sending hardware across the cosmos and motivate a business case for the 21st century version of the Pony Express: frequent, commercial access to space. Games maybe the way to start.

I’ve spent some time with a few startups in the Bay Area recently. Some will probably be successful. But I’ve seen what that success requires. Money, yes. Also a realistic business plan. But most of all you’ll need passionate employees willing to work for a fraction of their value in the hope of building something that will change the world. Well, I think a real-world version of an already compelling game might generate such passion.

Massless Exploration

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NASA’s various technology programs are investing in a wide range of additive-manufacturing technologies. Some focus on the terrestrial problem of how to manufacture aerospace parts. Others focus on the NASA-unique problem of how to fabricate hardware in space. It’s not just NASA-unique. It’s also revolutionary. If done right, these technologies may revolutionize space science and human exploration.

timthumbThe image above is from Deep Space Industries. It’s a concept in which a sort of 3D printer sucks mass out of an asteroid and prints it into a deep-space habitat. That would be revolutionary, no doubt about it.

There’s a larger point to be made here, one beyond designing a single spacecraft a week (which is this blog’s charter, remember). So, let me start with this bigger picture, something a little polemical, which I think will motivate the spacecraft I have in mind.

A little recent history, first. In 2012 the National Research Council identified the top technology-development priority for NASA: improving access to space. So, late last year Air Force Space Command, the Air Force Research Laboratory, and NASA partnered to sponsor a study at the NRC with the following goals:

      1. Lower the cost of space research and exploration in the long term through targeted, sustained investments that start immediately.
      2. Identify new space-system architectures that can be realized only if in-situ manufacturing is possible.

For this first goal, even with a new generation of lower-priced launch vehicles, e.g. from SpaceX, the economics of space will continue to deter most commercial and government organizations from using space for the nation’s scientific and economic benefit. Unless someone creates a killer app to kickstart commercial use of space, we will need a paradigm shift.

That new paradigm is what some of us call Massless Exploration: change the ratio of mass launched from earth to mass used in space. In the limit, the mass we use in space would all come from space. So, we would be exploring space without mass from Earth, i.e., masslessly—at least from the launch perspective. But you see that this perspective gets around the access-to-space barrier, if it could be made real.

As for the second goal, imagine if we could fabricate in space all the spacecraft components, structures and instruments for human exploration, and expendables (such as propellant, food, and oxygen) to support those efforts. In such a future, what would space-system architectures look like? What would we be fabricating if we had the means to do so? Spacecraft, habitats, even human-specific operations would likely look very different and be composed of unfamiliar materials. And for the U.S. to realize such architectures, what are the advanced-manufacturing technologies we must develop now? That’s the real question, in my opinion.

Massless Exploration provides a purpose, a direction for what are at best uncoordinated technology-development activities in additive manufacturing across various space agencies. At worst, some of them are duplicative or poorly motivated. We need a substantive roadmap that takes us from where we are now—3D printed plastic—to space-systems architectures conceived in a way that exploits what’s novel in an in-orbit manufacturing capability.

So, let me try to state it again succinctly. Massless Exploration is the working title for the paradigm that answers this unique question:

“What science and exploration architectures are made possible by in-situ fabrication and assembly of space systems, whether from new raw material brought from earth, unused components already in orbit, or in-situ material, and what advances in additive-manufacturing technologies must be achieved in order to lower the ratio of mass launched from Earth to mass used in space?”

As we learn to reuse and extract resources from the space environment, we may be able to increase this ratio to the point where access to space is no longer the driver for the size, weight, and power of spacecraft. At that point, we may be launching only people and the particularly hard-to-manufacture components, such as integrated circuits and exquisite components for scientific instruments. I joked about this idea in a Reddit AMA I did a few months ago, and the humor associated with manufacturing humans got taken seriously. It would be an interesting and familiar science-fiction story, though, printing up humans. Or maybe it’s too real to be funny. But I digress.

NASA’s current portfolio has a coordinated vision for an agency-wide path to the future. Additive manufacturing needs connectivity to other activities at the agency and elsewhere at a strategic level. If the NRC points the way, it is my hope that NASA and the Air Force will take on the much harder problem of developing science- and exploration-unique capabilities that will end NASA’s, and the nation’s, dependence on high-cost space launch. In doing so, I expect that transformational new technologies will spin off to the benefit of sectors of the economy beyond aerospace.

In this time of declining budgets for technology research, NASA has to focus and synergize its technology investment dollars on high-priority areas that produce fundamental and required capabilities that NASA cannot acquire through other means. NASA cannot justify investing resources in capabilities already being advanced by others. That need for focus motivates this NRC study.

What_Is_What_Could_Be_Massless

Image Courtesy of NASA

This image shows just a few of the ingredients of Massless Exploration that are already being brought together. Whether it’s painting lunar habitats into existence with a sort of toothpaste-like lunar-regolith cement or simply fabricating CubeSat components with the goal of doing so in orbit, there is a wide range of applications and solutions. I’m not alone in thinking about this problem.

I believe that the Maker Community has a big role to play here. We’ve reached a point in history where an individual can hope to build and launch his or her own spacecraft. The impulse to make space, or make space work for us, informs Massless Exploration as well, whether through business-development incentives as well as simply the desire for adventure. The role of government is to establish and nurture these grand visions for the sake of the nation’s citizens and businesses. If the right policies are in place, if we can consider space more of a national park (a “land of many uses”) than a sacred shrine, an object of mere detached scientific study, or the military high ground, we’ll see Massless Exploration all the sooner.

So, that’s the big picture. Now here’s an idea for a spacecraft I don’t think you’ve seen before.

Let’s agree that it’s hard to gather mass from the moon, say, even though it’s relatively nearby. You would need enough energy to change the velocity of a spacecraft by thousands of meters per second to go to the moon, secure regolith, and bring it back to low Earth orbit (LEO). It’s probably about as hard as gathering it from asteroids, although for different reasons. So, let’s pull it out of Earth’s atmosphere instead.  How about a spacecraft that slowly collects ions hovering in low Earth orbit until there’s enough mass to feed into a 3D printer?  Or a greenhouse?

Here’s roughly what a spacecraft rams into at 300 km altitude, just below the International Space Station’s orbit, if the sun activity is low.  If the sun is acting up, there’s about ten times more:

  • 1×1014 oxygen atoms (O) per cubic meter
  • 5.6×1012 hydrogen molecules (H2) per cubic meter
  • 3×1012 helium atoms (He) per cubic meter
  • 1.8 x1012 nitrogen molecules (N2) per cubic meter
  • 5.6×1010 oxygen molecules (O2) per cubic meter
  • A little argon, too, but I don’t really care about argon.  Do you?

The ratio is about right for making ammonia (NH3), e.g. by the Haber process. Then we would have fertilizer. And there’s more than enough oxygen to collect and use as an oxidizer, with the goal of nitrification. So, our spacecraft would provide water, which may be the key to everything. The image at the beginning of this post shows a satellite (adapted from IBEX, in this case, courtesy of NASA, just to show something modest in size). It extends a boom that collects ions sort of like dipping a candle in molten wax, or maybe making rock candy. Electrostatic charge attracts some ions. A chemical catalyst might help, too.

As this wick—this ion collector—orbits the Earth, a combination of ram effects and electrostatic attraction pulls in particles from the ionosphere. There’s a lot to this. Let’s not worry about the details of the plasma dynamics right now. For simplicity, let’s say that this collector sweeps out 10 square meters’ worth of area as it goes. A year’s collecting mass in this orbit yields mass that corresponds to between 80 and 800 grams of ammonia, depending on solar activity. That’s enough nitrogen for a large garden.

For this design to be worth the effort, it needs to produce enough fixed nitrogen to justify launching the satellite in the first place. If you can simply launch the nitrogen fertilizer to your orbiting colony, don’t bother with the satellite to collect it from Earth’s atmosphere, right?  If a 3U CubeSat (traditionally 4 kg) with a 10m long, electrically charged tether can accomplish this task, the spacecraft would justify its launch cost in about 9 years. If there’s a market for helium in space, and/or a way to use that extra oxygen, the break-even point arrives sooner.

And we’ll have to come up with a way to make this satellite stay in orbit, not drag down into and burn up in the very atmosphere it is trying to collect. But that’s a post for another day.

The larger point here is that we should be exercising our imaginations to come up with new ways to explore sustainably. All the mass we need to establish permanent human colonies throughout the solar system is already in orbit. It’s just in the wrong shape.

Corona Light

corona_light_cafe

Spacecraft extend human consciousness into space. We see galaxies through their optics, touch other planets with their robotic arms, and dance virtually through the solar system as they propel themselves ever farther from Earth. Communications technology connects us to these spacecraft. Images of Earth, Mars, what have you, reach us by radio, usually encrypted. Without this flow of data between Earth and our distant robotic avatars, the spacecraft might as well not be there. At least, that’s the principle that governs the design of most contemporary spacecraft.

There is another approach. In the early 1960s, three decades before President Clinton declassified the existence of the National Reconnaissance Office, the United States operated the Corona series of earth-imaging satellites. The spacecraft would fly overhead, take pictures on Eastman Kodak film, and release a canister of this film–called a “bucket”–to reenter the Earth’s atmosphere. As it fell, an aircraft captured it. The film was developed and images printed in basically the same way that it had been done since the 19th century. Not only was this Corona architecture an elegant adaptation of the photographic technology of the time, it was also quite secure. No one could intercept Corona’s images simply by listening in.

Let’s consider a spacecraft that communicates its discoveries Corona style. And not just any spacecraft. Let’s look at a spacecraft that does science at an exoplanet. Cornell astronomy professor Jamie Lloyd and I have been thinking about this idea lately.

Our version of the Corona architecture begins with a spacecraft-on-a-chip: like a Sprite but a single application-specific integrated circuit (ASIC). Really. A single silicon or gallium arsenide chip that weighs only milligrams. Most of a Sprite’s electronic guts reside in a single IC already: the wonderful CC430 chip by Texas Instruments. So, it’s not asking too much for the rest of the circuitry to be collapsed into a single semiconductor device. If an ASIC proves to be too hard, maybe we would use a Field Programmable Gate Array (FPGA), which is a sort of all-purpose reconfigurable IC that can be naturally radiation tolerant. Tiny solar cells, nanowire antennas, and a CMOS camera round out the key subsystems.

Traditional radio communication from such a tiny device is hopeless on the scale of solar system distances, let alone interstellar distances. There just isn’t enough power available through solar cells or within an on-board energy-storage technology to transmit a signal powerful enough to be received back on Earth. For example, the current Sprite can manage roughly 1 bit per second from low Earth orbit for very low power, thanks to a subtle trick known as matched filtering. Even if continuous communications at this rate were possible from much farther away, downlinking every bit of this SD card’s data would take 31 millennia. Hence the Corona architecture. Let the golden light radiating from its angelic countenance illuminate our imaginations.We’ll save the data on a memory device and retrieve it physically.

Thanks to 21st century technology, our Corona Light can carry a few milligrams of silicon to house terabytes of information. Back in 2010 SanDisk offered a 2 terabyte SD card, a version of which serves as Corona Light’s bucket. We’ll count on this SD card, or something like it, to retain the spacecraft’s discoveries.

We would speed Corona Light on its way out of the solar system. How? Well, that’s another post. No more than one miracle per week, I think. But to fix ideas, let’s say we’ll accelerate it out of an orbiting railgun. The U.S. Navy apparently can launch 3.2 kg to 2.6 km/sec from its experimental railgun. They continue to make progress. So, let’s say they’ll exceed 700 megaJoules some day. Although the dynamics of launching something tiny differ, that energy would propel a 30mg spacecraft-on-a-chip to 7,000 km/sec, i.e. 2.3% of the speed of light. The spacecraft will need that sort of speed if it is to make it to Alpha Centauri, about 4.3 light years away, on a human time scale. The simplest version of the celestial mechanics involved says that the spacecraft reaches the exoplanet NASA has found there in 184 years. Maybe we can do better, but (again) that’s for a future post.

The trick is to get this spacecraft-on-a-chip back to Earth, or at least within the solar system, where we can pop the cap on this tiny satellite and drink in its knowledge. It will need a beacon, and I’ll propose that we simply replicate what we know we can do on Sprite today: a specific pseudorandom noise sequence that we would be looking for (accounting for all that Doppler shift, of course) when the spacecraft completes its ring around our spiral arm of the Milky Way and returns home.

Sometime in year 184, Corona Light performs a fly-by of Alpha Centauri. As it approaches this star, the power available to the spacecraft through its tiny solar cells increases, enabling some very minimal science: capturing a few photons from the environment and recording a time stamp in the form of counts of radioactive decay of a small on-board sample of an isotope. It would be carbon-dating itself, in some sense. A realtime on-board clock would be asking a lot—power that requires mass, slowing it down. But if possible, that would be great; these days an atomic clock on the scale of a microchip is mainstream technology. But the isotope-decay trick trades precision for even lower mass, which I think we want.

This fly-by puts the spacecraft on a trajectory that uses the pull from the galactic center to redirect the spacecraft back into our solar system. Make no mistake: this maneuver is not easy. Missing the Earth is likely. Fortunately, Corona Light is cheap, a few pesos each. We’ll fabricate thousands, maybe millions of them (they would fit in a suitcase) and fire them toward Alpha Centauri as a halo of tiny exploration vehicles. If one makes it back, we will have visited the nearest star. The SD card with a couple of centuries of data will represent our most distant physical interaction with the cosmos. Let’s toast to the original Corona mission and raise our bottles of Mexican beer to the possibility of interstellar discovery.