The PhoneSats are similar to the Spheres free-flyer experiment already conducted in the International Space Station's Destiny lab, except the PhoneSats were deposited into orbit on the inaugural Orbital Sciences Corp. Antares launch. They will last only a few weeks in space because their orbit was 240 X 260 km (150 X 160 mi.). But in small packet bursts, they have communicated through a worldwide Ham Radio network and transmitted Earth images using smartphone technology, says Project Manager Jim Cockrell. Two PhoneSat 1s, which cost just $3,500 each, relied on Android HTC Nexus One smartphones and one $8,000 PhoneSat 2 used the more advanced Samsung Nexus S model.
The PhoneSat 1 used the phone's accelerometer and magnetometer but left its lithium-ion batteries at home because they are not suitable for the thermal shifts of working in space. Instead, the phones were snuggled diagonally into the cubesat surrounded by nickel-cadmium batteries that will barely last the length of the mission.
Although it is only a beta test model, PhoneSat 2 has greater capabilities. The Nexus uses gyroscopes so users can flip screens vertically or horizontally. Combined with a set of magna torque wheels little bigger than a man's thumb, they gave PhoneSat 2 three-axis stability, which the simpler PhoneSat 1 lacks. The Ames team simplified making mounts for the wheels with 3-D printing.
Solar cells for PhoneSat 2 came from edges discarded in Boeing Spectrolab's manufacturing process. Ames connected 20 of them on each side of the 10-cm cubesat and on the flip side built copper wire magna torque coils directly onto their PC board to save weight and space.
The point, says Korsmeyer, is to drive tailored original equipment manufacturing out of satellite-making as much as possible by adapting existing hardware. In the future, this will mean that programming the spacecraft is the biggest hurdle. “You have transformed a hardware problem into a software problem,” he says.
Because cubesats operate in low Earth orbits (nominally 425-450 km/265-2,800 mi.), they are protected by the planet's magnetic field and do not face major radiation hardening issues. “We buy rad-hard commercial parts rather than space parts,” Korsmeyer says, saving millions. He compares having to operate with occasional interference from radiation to having to reboot a PC. “Is that really a problem?” he asks.
Manufacturing for organizations that must tolerate problems or be priced out of existence is part of the smallsat culture, just as managing missions with part-time teams is. But there are payoffs to working in a Class D culture, NASA's minimum qualification standard. Bruce Yost, NASA's small technology mission director, says a “six-pack” of 3U nanosats can be built with only a third of their configuration reserved for spacecraft operations, leaving two-thirds for payload. The normal ratio is just the opposite.
Development work for very small satellites is flowing from companies such as San Francisco's Pumpkin Inc., which has an online catalog for a nanosat starter kit, although founder Andrew Kalman says International Traffic in Arms Regulations prevent fill-the-shopping cart ordering.
Started in 2004, Pumpkin is on its fifth generation of electronics. But its staff of fewer than 10 relies on specialty suppliers, such as San Francisco Bay Area machine shops that hold tolerances to 0.004 in. It used to spend 2 hr. per cell making solar panels but has cut that to just 12 min. by adapting Spectrolab cells. “Our focus has always been on how to crank out [satellites] quickly,” Kalman says. He can deliver in as little as 90 days.