How to build a spacecraft: The beginning
Building a spacecraft can be surprisingly simple. You can buy a kit off the Internet for about the cost of a used car and make something that will function in orbit around the Earth for a few weeks or months.
Building a NASA flight-quality spacecraft that can fly millions of miles across the void of space to another planet is much more difficult, and the process is far different than building anything else most people are familiar with.
Arizona State University’s team leading a 2018 moon mission kicked off their first group meeting this month, but it will be years before you can see parts on a table in a lab.
The mission is unique: Build and fly a cutting-edge nanosatellite smaller than a piece of carry-on luggage to the moon, orbit around the poles 141 times during 60 days while sniffing for hydrogen, transmit what it finds back to Earth, and then, having done its job, crash (be “disposed” of, in NASA parlance) into the south pole.
Its job is part of NASA’s hunt for water on the moon. And the reason for the search is simple: If ice is discovered on the moon, water wouldn’t have to be hauled from Earth. And ice can be used for rocket fuel or to support a human push out into the solar system.
The Lunar polar Hydrogen Mapper, or LunaH-Map, will be a CubeSat, a miniature satellite built to a standardized size and volume. One unit is about the size of a large Rubik’s cube. LunaH-Map will be the size of six of those put together — a 6u, in space-systems terminology.
“It’s a little mini spacecraft,” said Craig Hardgrove, principal investigator of the mission. Hardgrove is a postdoctoral research associate in the School of Earth and Space Exploration in the College of Liberal Arts and Sciences.
While a CubeSat is tiny and designed to do one simple mission, it’s also complex. Building a huge interplanetary spacecraft with tons of money is in many ways simpler than what Hardgrove and his team are doing. In a big beast, you have space to put in components and systems, for one, and you can build in lots of redundancy if something fails. And a ton of money means a ton of personnel experienced in aerospace and space-systems engineering.
For LunaH-Map, there’s not very much of either space or money.
“This project with LunaH-Map is unprecedented in its scale — on the tiny end of the scale,” said co-investigator Jim Bell, an astronomer, planetary scientist, professor in the School of Earth and Space Exploration and veteran of nine NASA missions.
“You start building a small spacecraft the way you begin building a large spacecraft: you look at what’s been done in the past and figure how to leverage what’s already there,” Hardgrove said. “It’s a bit like saying we know how to build a car. Now we want to build a tiny car. Or a car to drive around the moon.”
Off the shelf?
CubeSat references almost always include the phrase “off-the-shelf commercial components.” While you won’t find everything you need for a CubeSat at Radio Shack, there are manufacturers offering every part from solar panels to power systems. The problem is, they just aren’t built for deep space.
There are four main problems an off-the-shelf CubeSat can’t handle that the LunaH-Map must overcome:
• The usual CubeSat lifetime is days or weeks. LunaH-Map has to survive for months.
• The Earth’s magnetic field shields low-Earth-orbiting craft from electronics-damaging radiation. Interplanetary spacecraft have to be built with tougher electronics.
• Earth-orbiting CubeSats just float around where they were delivered. The LunaH-Map has to propel itself across the void of space and make course corrections.
• Communication with Earth-orbiting CubeSats is pretty simple. Interplanetary CubeSats need to communicate across a much larger distance.
The team doesn’t have to start completely from scratch, however. CubeSats, which began as teaching exercises in engineering classes, have been around for 10 years now. Propulsion, control boards, antennae, radiation-hardened parts, everything you’d see on a normal spacecraft has been miniaturized down through engineering designs done over the past decade in education.
Smartphone tech has been a huge contributor to the field, too. One commercial space company is using the processors found on iPhones in its CubeSats. One of the things that come out of smartphones is reliability.
“They need to make millions and millions of them, and they need to make sure they don’t fail,” Hardgrove said. “A by-product of making things that don’t fail is that you make them radiation-tolerant. They weren’t doing that at all, but that’s a by-product of doing that. ...
“So you can use some components that are off a shelf like that because they’ve been developed in such a way that they are mass-manufactured and mass-marketed. By no means can you buy your spacecraft at Radio Shack, but certain things.”
Scientists are discovering that some cameras can be radiation-tolerant for months in space. Another factor in designing spacecraft is where they’re going and what they’re doing.
“It depends on the length of your mission and where you’re going,” Hardgrove said. “Are you going to the Van Allen belts? Is it going to be a yearlong mission to the moon, where you’re exposed to galactic cosmic rays for a long time? There are nuances to it.”
The concept of 'heritage'
A layman browsing web pages of private space companies ranging from propulsion manufacturers to launch brokers will often come across the word “heritage” in their copy. The concept of heritage in space-systems engineering bears some explanation. Bell explains it well in his book “Postcards From Mars.” There’s a NASA saying, “It doesn’t fly unless it’s already flown.” What that means is using tried and true engineering, materials and systems.
It’s a lot like planning a serious wilderness expedition. You don’t want to buy the latest gadgets from the outfitters because they might fail in the middle of nowhere, leaving you in serious trouble. You want your grandfather’s hunting knife, those old German binoculars and the stove that’s maybe a little heavy but never, ever fails.
“We have gone for components and subsystems that have a track record, most importantly,” said Jekan Thanga, mission co-investigator and chief engineer. Thanga,Thanga is also an assistant professor in the School of Earth and Space Exploration. a space-systems engineer, heads the Space and Terrestrial Robotic Exploration Laboratory at ASU. “That’s how we get evaluated. You get really dinged if you go for brand-new technology that’s developed in-house and unproven. ... You want something ideally with heritage that’s already flown.”
Even though some of the LunaH-Map will be new, the team will pull heritage where they can in designing the spacecraft.
“Absolutely,” Bell said. “That’s how you lower risk.”
“You can’t call this a heritage mission because it’s unique and very different,” Hardgrove said. “But I think we want to build on as much experience in terms of people as we can.”
The spacecraft’s propulsion system may be a pulse plasma thruster or an ammonia-based system widely used on satellites in the 1960s. The high-performance propulsion systems aren’t ready for CubeSats, according to Thanga.
“These are past-their-prime technologies,” he said. “More refined technologies took over ... these are now in the history books. ... That’s one of our internal philosophies we’ve been using: to not go for sci-fi stuff. It’s stuff that’s fundamentally proven, that’s already been used in space, but has passed its prime so to speak in the mainstream world of space.”
MarCO and the test run
Thanga likes to describe building the LunaH-Map as “a different problem domain.”
“It’s relearning stuff,” he said. “In some ways it is like doing this for the first time. What’s going to set the big precedent is MarCO.”
MarCO (an abbreviation of Mars Cube One) is a technology demonstration of two CubeSats flying on the next Mars mission in 2016. They will be pioneering CubeSats, both the first to leave Earth orbit and the smallest objects ever to fly across deep space to another planet.
The Insight mission will consist of two CubeSats and a lander. They’ll be launched on an Atlas V rocket, be deployed into space and then, like three siblings walking to the bus stop, fly separately to Mars.
The CubeSats will relay radio signals from the stationary lander deployed to the Red Planet’s surface, confirming a successful landing. Chief engineer on the mission is Jet Propulsion Laboratory engineer Andy Klesh, an adjunct professor at the School of Earth and Space Exploration and a member of the LunaH Map team.
“In the CubeSat world, heritage right now means mostly lower-Earth orbit,” Thanga said. “There’s maybe one or two CubeSat missions that have gone to geostationary orbit. That’s all. Nothing beyond, except what will come out of MarCO, and that’s going to be one of those ‘Hold still and see what happens’ moments. It’s going to give us some lessons learned. We may be in for a surprise.”
LunaH-Map’s proposed radio is going to Mars on the MarCO mission. That fact illustrates the key word to describe the entire building process: fluidity.
“It’s a test of our radio, but it’s on a different CubeSat,” Hardgrove said. “We’ll be able to see what worked, what didn’t work, what do we need to change next year. So there’s this idea of future heritage. ... We’ll be able to change course. Some element of our system is going to fly.”
Everyone is rolling the dice on MarCO to see what happens.
“What I would say is the MarCO mission has a lot riding on it to set the stage,” Thanga said.
On a problem this constrained, any solution is viable, Bell said.
“We’ll look at anything,” he said. “If it fits in that space, we’ll consider all options. It’s kind of a fun problem that way.”
Building a team
Assembling the right mission team is critical. The LunaH-Map team consists of people from ASU, quasi-governmental organizations like JPL, and private-sector businesses. Hardgrove wants to be subjected with as much criticism as possible.
“You don’t want to be bombarded with it, but at the same time it helps to have people who are used to a typical model of how to build a spacecraft and they’re going to say, ‘Don’t do this; don’t do that,’” he said. “I absolutely welcome that. I want people to say, ‘This isn’t going to work for this reason.’ ”
The total mission budget is about 10 percent of the cost of one instrument for a big NASA spacecraft. It’s about 1 percent of the cost of a NASA mission, according to Jim Bell.
“What you want to do to put together a team is to find the most experienced people, people who have built spaceflight hardware before, who understand NASA flight procedures and flight requirements and risk assessments and budgeting and flight hardware handling, paperwork, and experience,” Bell said. “That’s what you’d like to do. But for 1 percent of the budget we can’t afford any of those people. So what we try to do instead is cobble together a group of people who have the relevant experience but don’t need to be fully funded off this project.”
Faculty members fall into that description. They’re paid to teach by the university and to do a little research, and LunaH-Map falls into that category. About a dozen students will be involved on the mission in various ways, too.
“We can’t afford an aerospace workforce, but the next best thing we can do are students because, bless their souls, they’re cheap,” Bell said. “They’re also really good. One of the great things about having an 80,000-plus student body at ASU is that that is a big Gaussian bell curve of capabilities.”
Some of the private-sector team members are paid consultants. Others are colleagues interested in the educational component, for possible future hires. The small businesses working on LunaH-Map know how to build things like sensing monitors or propulsion systems. They just might not have thought of how to build a little version.
“We are closely tied with a lot of small businesses,” Thanga said. “Many of these entities will be critical to success. It could not have been done alone and at ASU. … KinetX and their crack team were critical in coming up with trajectory.”
KinetX Aerospace is an engineering, technology, software-development and business-consulting firm providing systems, hardware and software engineering, and satellite and space-vehicle navigation.
That’s part of the mission as well. The mission poster states: “By partnering with small businesses, LunaH-Map will demonstrate the potential of low-cost planetary exploration for scientific discovery, scouting and resource utilization.”
“My mentality going into this is to leverage as much as has been done before,” Hardgrove said.
Although every other aspect of the process will be fluid, spacecraft development follows a pre-defined plan. NASA will review LunaH-Map periodically. A mission can end at a review.
“It’s go/no-go at each of these steps,” Thanga said.
“It’s no-go unless you address this (issue), not necessarily the cancellation of the project,” Bell explained.
Or go, and accept risk.
“For 1 percent of the cost of a NASA mission, we have to accept a lot of risk,” Bell said. “We have no choice. That’s just fundamentally built into the architecture of these missions.”
First there will be an internal mission concept review. Following that will be a requirements review, which will have NASA in on it. A preliminary design review (PDR) will be held around June 2016. (“PDR is getting there,” Thanga said.)
A critical design review (CDR) held around December 2016 will kick off construction. That’s when you will start seeing parts on a table.
“You formally start building after CDR, then it’s build, build, build,” Thanga said.
It’s also test, test, test. There are two ways of writing code. Write your code first and compile it, then debug it — or, as you add every new line of code, test it. “Chances are we’ll be doing a mix of those methods,” Thanga said.
That is not done with hardware because it’s too risky and expensive. Space systems don’t come cheap. There are suppliers, but Home Depot is not one of them.
“In our case we will build up slowly,” Thanga said. “You operate as you should and then suddenly one of the capacitors blows and that’s it. You’re done. ... It’s not as easy to go back to the manufacturer and say, ‘Hey, your board blew up. Can we get another one?’ It’s a big-ticket item. It gets a little hairy that way.”
An integration review is followed by a final readiness review, then a delivery review. After that, LunaH-Map will go into space.
Ideally, LunaH-Map will discover ice on the moon. If it fails in some way, it will still be a success, Bell said.
“Part of what we’re doing is entirely educational,” he said. “Part of what we’re doing is training this generation of students, giving them hands-on experience building things, designing things, testing them, launching them, operating them in space. If our scientific mission is not successful, but we’ve been successful in that educational mission, that’s a partial win.”