Flock of 104 Spacecraft Set for Launch

Illustration: Ben Bishop

(Update, 16 May: After a successful launch in mid-April, KickSat suffered a fault a few weeks later that reset its master clock. The spacecraft reentered Earth's atmosphere on 13 May before it had a chance to deploy the Sprites.)

(Update, 14 March: The launch of the SpaceX rocket that will carry KickSat to space has been postponed until 30 March at the earliest.)

In a few weeks time, a fleet of 104 spacecraft the size of small cheese crackers should be released into space.

This will be the first free-flying test of what could be a new approach to space exploration, one that aims to use bare integrated circuits as spacecraft. Since chips are small and easy to mass produce, it might be possible to launch them by the thousands for use as distributed sensors to monitor space weather, measure the ionosphere, or explore other planets. As Cornell University professor and former NASA Chief Technology Officer Mason Peck described in a 2011 feature for IEEE Spectrum, tiny chip-based spacecraft might ultimately be able to fall gently onto Martian plains without a parachute or coast around for weeks in Titan’s thick atmosphere.

For this mission, each spacecraft in the small armada has a mass of just 5 grams and fits its solar panels, logic, communications gear, and sensors on a single square circuit board measuring 3.5 cm on each side. “They’re way smaller than anything else that’s flown in space—on purpose at least,” says organizer Zac Manchester of Cornell University.

The ensemble of spacecraft, which the team calls Sprites, will to be carried into space on 16 March on a SpaceX rocket. They’ll all be released from a specialized satellite called KickSat, which will jettison them in a matter of seconds after about two weeks in orbit. You can see an idealized vision of what this deployment would look like in the video below.

These aren't the first “chips in space”. Three earlier-generation Sprites launched in 2011 and are currently in orbit. They are attached to the exterior of the International Space Station as part of a materials science experiment called MISSE-8, for Materials on International Space Station Experiment 8, which is designed to see how different materials fare in the harsh space environment.

Those first Sprites were equipped with solar panels and radio transmitters, and Peck’s team had hoped they might be able to transmit some sort of signal to Earth. But, Manchester says, the chips were a last-minute addition after a space opened up on the experiment. “Basically we got a phone call three days before it had to be shipped off for launch," asking if they might have something that could be placed on the MISSE-8 pallet, he said. The team sent their chips along, but in the end, the experiment was placed on the far side of the space station with no clear transmission path to Earth ground stations.

But “even though we’re not getting signals from them, it’s not a lost cause,” Manchester says. MISSE-8 is set to return to Earth later this year, and that will give the team a chance to dissect the chips and see how they fared after more than three years of radiation exposure and big temperature swings.

For their next mission the team wanted to send up free-flying satellites. They applied for a free berth on NASA’s ELaNA CubeSat program and started a Kickstarter campaign to raise funds to build the hardware. They offered sponsors who contributed enough a chance to program their own chipsat and ended up raising nearly $75 000, more than double their goal.

The mission will ride in the upper stage of a SpaceX rocket, behind a Dragon capsule carrying cargo destined for the International Space Station. Once the Dragon is away, KickSat will be deployed and will turn on its radios about an hour layer. Some 16 days after that, once a Soyuz mission has made it to the station and the coast is clear, the Sprites themselves will be released from the KickSat.

Unlike their stationary predecessors, each of these Sprites comes equipped with a 3-axis magnetometer and a 3-axis MEMS gyro. They are also equipped with higher efficiency solar panels than the previous version, which will be used to power the spacecraft systems directly— no energy will be stored in batteries or capacitors. The spacecraft will send their sensor data, along with call signs and initials submitted by Kickstarter donors. One Sprite will run a program designed by the British Interplanetary Society. It will turn the spacecraft’s RAM into a makeshift radiation detector by populating it with pseudorandom data and watching for flipped bits caused by incoming charged particles.

The spacecraft won't receive messages from Earth, but they will be able to send data down by sharing a single radio frequency (437.24 MHz, in the amateur radio band). To prevent interference, they’ll use code-division multiple access (CDMA), the same kind of protocol used for frequency sharing by cell phones and GPS systems. As an added interference prevention measure, the Sprites have been programmed to wake up at random times—every 10 seconds or so—send a data packet, and then go back to sleep. So only 5 or 6 Sprites are on at any given time. When a Sprite has power, it should be able to send data that can be picked up and processed on the ground at a rate of 50 bits per second.

The Cornell team will listen in from a ground station in Ithaca, New York. Using a small Yagi antenna, a low-noise amplifier, and some other gear, HAM radio aficionados should be able to pick up Sprite signals as well. But on their own, the signals won’t sound like much more than noise. Each Sprite’s transmission power is just 10 mW and will require a few digital signal processing tricks to decode.

Ultimately, Manchester says, the team hopes to make Sprites into a “general purpose sensor platform” that could be used for a range of missions where small, distributed sensors might be useful. He says one near-term application could be measuring Earth’s ionosphere. NASA is currently preparing a four-satellite mission called the Magnetospheric Multiscale mission to study Earth’s magnetosphere, which helps protect our atmosphere from the solar wind. Manchester says a swarm of dozens or hundreds of Sprites could potentially complement such a mission by providing better spatial resolution, even if the individual measurements would not be as precise.

The Sprites won't have the ability to maneuver. They should stay aloft on their own for between two days and a week before reentering and burning up in Earth's atmosphere.  

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