Small satellites, once the realm of one-off low-budget science missions and undergraduate engineering classes, have come full circle with the growing realization among hard-pressed, high-end users that the little birds can do the big jobs, too.

The smallest of them—cubesats—are rapidly evolving into an operational commercial, scientific and military technology. Higher up the payload-weight scale, the high cost per pound of launching payloads and the growing skill of spacecraft miniaturizers are making satellites that are small enough to ride as secondary payloads attractive to a variety of customers, particularly if they can be mass-produced or produced rapidly in single units.

The launch-cost consideration may change, as the growing interest in small spacecraft attracts a new generation of small launchers designed to carry them. And the spacecraft themselves are increasingly capable, with government money flowing into the arena in search of a way to do more with less.

“From where we have been 10 years ago to where we are now is a complete 180,” says Roland Coelho, a member of the research staff at California Polytechnic State University's engineering school, one of the main U.S. centers for cubesat development. “In the past it's been primarily educational. . . . As we have kind of grown—the entire community worldwide over the past decade—we really have started to see some niche markets where cubesats can play a vital role. It's clearly the most evident in the government cubesat programs that we have today. The government, and particularly the U.S. government, has been the driving force in this technology because that's where all the funding is.”

Government interest in small satellites is not limited to cubesats, or even to spacecraft. The U.S. Defense Advanced Research Projects Agency (Darpa) is spending $46 million to find ways to launch satellites weighing up to 100 lb. on 24-hr. notice for less than $1 million (see p. 44). And the Air Force and National Reconnaissance Office consider small satellites a way to lower risk in national security spacecraft by adding redundancy in orbit.

“Even if 20% of them failed, you'd still do your mission, so there's sort of a natural resiliency in using constellations of smaller satellites,” says John Roth, whose company—Sierra Nevada Space Systems—makes small satellites for the military and others. “One of the advantages that the military recognizes also is, if we're worrying about countries taking offensive action against our satellites . . . the more satellites you have up doing the same mission, the harder it is for them to do anything to our satellites.”

Building more, smaller satellites also lowers the cost of each bird through mass-production economies of scale. This fall, SpaceX is set to launch the first of 18 second-generation low-Earth-orbit narrowband satellites that Sierra Nevada is building for Orbcomm.

“They contracted with us $117 million for 18 satellites, so that's a unit cost of about $6.5 million a satellite,” says Roth. “And if you look at what a typical NASA or [Defense Department] mission costs, you can't come anywhere close to that.”

Compared to cubesats, however, even that is a high pricetag. With a standardized “1U form factor” measuring 10 cm (4 in.) on a side and weighing no more than 1.33 kg (3 lb.), cubesats typically cost well below $100,000 to build and launch. Coelho has seen changes in the technology first-hand, beginning in 2000 as a Cal Poly undergraduate working with cubesat pioneer Jordi Puig-Suari, and later joining the staff. Among the school's accomplishments is development of the standard cubesat deployment system—the Poly-PicoSatellite Orbital Deployer (P-POD)—and helping to advance the state of the art in cubesats to the point that they are being used to tackle serious science missions (see p. 41).

“It was a training tool for students to build a satellite within their academic career, from design to manufacturing and then to launch and then to on-orbit operations,” says Coelho of the early days. “And it was a good way for small commercial companies to do technology demonstrations for certain components.”

Now, with growing acceptance from users and from the launch-service providers who must weigh the value of carrying secondary payloads against the risk they pose to their primary missions, the ideas for using small satellites, and particularly cubesats, are piling up. One early area of U.S. Air Force interest is multi-source weather data.

“Because the cubesats are small, you can launch them in bunches and disperse them out [with] variable drag capability,” says David Hinkley, a senior project leader at The Aerospace Corp. “Now you've suddenly got 10 useful satellites flying around in different positions that can take temporal data, data that changes with time. In the past they would fly one big satellite, and they would not able to be in multiple places at once.”

Aerospace is experimenting with using the variable drag in low Earth orbit that cubesats get from deploying and retracting different combinations of cruciform solar arrays. NASA's Office of the Chief Technologist (OCT) plans to launch a constellation of eight 1.5U cubesats next summer in a project called the Edison Demonstration of Smallsat Networks. Its goal is to begin developing inter-satellite communications that could be applied to a number of different applications, including monitoring weather, ice cover in the polar regions and other Earth-surface conditions.

With its mission to push technology hard, Darpa is also working on a mission dubbed Phoenix that is aimed at recycling usable hardware from non-functioning satellites in geostationary (GEO) orbits by reactivating them with tiny modular “satlets” designed to perform various spacecraft functions. On July 12, the agency awarded Canada's MacDonald Dettwiler a contract worth as much as $2.1 million to begin developing systems that can revive a usable antenna on an out-of-service GEO satellite.

At the other end of the satellite service life, NASA's Marshall Space Flight Center is building on its work with NanoSail-D—a 100-sq.-meter (1,075-sq.-ft.) solar sail demonstration that deployed on Jan. 21, 2011, from a 3U cubesat—to develop deployable drag sails to pull obsolete smallsats out of orbit instead of adding to the space-debris problem.

Overall, Darpa plans to spend $36 million on the Phoenix project, which is peanuts by U.S. military standards. But it is big money in the smallsat world, where mass production and standard forms continue to cut hardware costs dramatically. A San Francisco-based company—Pumpkin Inc.—is selling cubesat kits starting at $7,500 that can be customized depending on the capabilities needed. To date, more than a dozen have been launched, according to Andrew Kalman, the company's president and chief technology officer, who says Pumpkin is following the Apple Inc. model.

“We want to make sure that cubesats really are one of the foremost places where you can leverage the continuing advance of technology,” says Kalman. “To do that you need to recognize that you are not in the driver's seat when it comes to the technology you want to put up there. Rather, you need to be leveraging other markets which are in the driver's seat, which in this case is essentially the consumer electronics field, and take advantage of those technologies.”

When Orbital Sciences Corp. launches its first Antares rocket from Wallops Island, Va., later this summer, it will be carrying three 1U cubesats that take the consumer-electronics approach to spacecraft to new heights. Wedged into one of them will be a standard Android smartphone, with a bunch of extra batteries, in a test of whether the open-architecture electronics and commercial hardware can survive in space.

“If the platform is open, if the operating system is open, well then, almost anybody could write an app that could do something that may be beneficial to spaceflight, so you can tap into that larger community of app writers,” says Bruce Yost a project manager at Ames Research Center, where NASA's smallsat work is headquartered. “It kind of changes a lot of things that you do in aerospace.”

Another “Phonesat” version carries the innards but not the case of the Android. The work, spearheaded at Ames with funding from OCT, is not limited to smartphone software, but includes such hardware possibilities as removing the weights from the phones' “vibrate” mode and using the motors as tiny reaction wheels, says Yost.

Despite the possibilities, some areas of smallsat technology still need work, particularly in the cubesat arena, where communications is a particular problem. The Phonesats set to fly on the first Antares mission will test the smartphone computing for spaceflight apps, but the radio will be switched off because it would not work in space. Instead, cubesats rely on ham-radio frequencies for links with the ground, and that limits both contact time and bandwidth.

To tackle those problems, experts at the European Space Agency are developing an international ground-station network called the Global Educational Network for Satellite Operations (Genso), which is basically a set of software and protocols that will give cubesat operators a worldwide network of ground stations (see map).

At Ames and California's San Jose State University, preparations are underway to begin operating the Technical and Educational Satellite (TechEdSat), which was launched July 20 on Japan's third H-II Transfer Vehicle. Based on a Pumpkin cubesat-kit structure, the 1U cubesat will become the first U.S. spacecraft to be deployed from the International Space Station (see p. 44)..

Inside are three radios—a Stensat Radio Beacon transmitting with 1 watt of power at 437 MHz, and modems designed for Orbcomm and Iridium low-Earth-orbit communications satellites. Because of licensing issues, only the beacon will be operating during flight, but San Jose State students have already demonstrated that the Iridium and Orbcomm hardware can be integrated into a 1U cubesat, and powered with batteries approved for safety by NASA's ISS program office at Johnson Space Center.

Communications is one of three areas in smallsat technology that will be flight-tested with new funding from NASA. The agency's chief technologist received a heavy response to its request for proposals in communications, proximity operations and propulsion, and expects to make selections for the 2-3-year effort before the end of August.

Sensors, software and thrusters for proximity operations could enable tiny inspectors to fly safely around larger spacecraft—including the ISS—to routinely document their physical condition and pinpoint debris damage or mechanical problems soon after they occur. Some of the software work is already underway inside the station with the Synchronized Position Hold, Engage & Reorient Experimental Satellites (Spheres) control-software testbeds: three volleyball-sized balls designed to give programmers a quick check of their algorithms in microgravity (AW&ST June 25, p. 44).

Because of the size and safety limitations that launch-service providers impose on secondary payloads, propulsion has been a particularly difficult problem for small-spacecraft designers, with the difficulty increasing as the size decreases. The Swedish Space Corp.'s NanoSpace unit has used micro-electromechanical systems (MEMS) fabrication technology to develop miniature thrusters that have been tested in orbit on the Prisma satellite testbeds (AW&ST May 7, p. 21).

At least one proposal in the OCT competition involves an update on the colloid thrusters tested in the 1960s and '70s and dropped in favor of ion propulsion because they just did not work as well. But now, says Paulo Lozano, an associate professor of aeronautics and astronautics at the Massachusetts Institute of Technology, advances in propellant chemistry and MEMS production is enabling development of “electrospray thrusters” that emit ions when subjected to an electric charge, instead of the heavier droplets emitted in the older technology. Using coulomb liquids—electrically conductive liquid salts composed of molecular ions—wicked by capillary action through a plate of tiny emitters produced with proprietary MEMS techniques—the thrusters produce a spray of ions when an electric charge is passed across them. The approach eliminates the need for pumps, valves and other moving parts, and generates specific impulses of 1,500-5,000 sec., depending on the propellant.

“It basically works like a candle,” Lozano says, noting that the thrusters operated with 80% efficiency. “The 'wax' of the candle is the propellant, and the 'wick' is just the transport medium, and the 'flame' is the thrusting mechanism. So it's very similar, except that we evaporate ions, and in the process of evaporating the ions we also accelerate them to very high speeds.”

In the longer term, engineers are studying ways to combine spacecraft so a small satellite can disperse cubesats after launch and then serve as a “mother-ship” communications hub. NASA's Nanosail-D flew to orbit in a P-POD inside the agency's Fast, Affordable, Science and Technology Satellite (Fastsat) developed by Dynetics as a way to get payloads to orbit on a freeflier in fewer than two years after authority to proceed. With the solar-sail demonstration, it also showed that a larger spacecraft can safely jettison a smaller one.

Now the Huntsville, Ala.-based company is looking for new uses for the Fastsat capability.

“The Communications Relay for the Arctic Domain is the next generation of that concept, where we would actually be a mother ship and deploy multiple cubesats to fly in formation with Fastsat and provide a larger coverage ring,” says Mike Graves, manager of the Space Vehicles Department at Dynetics. “So you have the host mother ship in the middle and then you've got in formation flight maybe four 3U cubesats, each one of those having its own localized communications capability and sensors, and then you send it back to the mother ship for the large data bandwidth to the ground.”