NASA’s AstroPix gamma-ray sensor will reach orbit as a bonus payload on the agency’s Fly Foundational Robots mission, set to launch in late 2027. The mission was built to test a commercial robotic arm that picks up and repositions a modular unit in low Earth orbit. AstroPix will collect data on the universe’s highest-energy light once the robotic demonstration is complete.
The pairing turns a single-purpose robotics test into a dual-technology demonstration, and it gives the gamma-ray team a ride that is rarely available. Gamma-ray bursts, the brightest emissions from distant black-hole-powered galaxies, and many other high-energy sources all fall inside the energy band AstroPix is designed to image. The sensor itself borrows from the same kind of CMOS architecture used in cellphone cameras, scaled up to handle photons tens of thousands of times more energetic than visible light. NASA will integrate the chips into the mission’s Orbital Replacement Unit, an 11.8-inch (30-centimeter) modular cube that the robotic arm will move. If the data come back clean, the orbital test will feed into the design of a future flagship gamma-ray telescope.
A Bonus Payload Built Into a Robotic Test
The Fly Foundational Robots (FFR) spacecraft was designed around a single goal: prove that a commercial robotic arm could pick up and reposition a modular payload unit in orbit the FFR mission’s planned orbital operations. The arm, supplied by Rocket Lab Robotics, was always meant to grasp an 11.8-inch cube called the Orbital Replacement Unit, move it across the spacecraft, and demonstrate a servicing-style swap. As the mission matured, engineers realized the unit had spare volume, power, and data capacity that a second technology demonstration could use. The team began looking for a partner whose hardware could fit.
“The unit already had the volume, power, and data needed to support the AstroPix team’s design,” said Bo Naasz, senior technical lead, In-space Servicing, Assembly, and Manufacturing in the Space Technology Mission Directorate at NASA Headquarters in Washington. “One of our major goals with Fly Foundational Robots is to demonstrate robotic changeout of payloads in orbit, enabling upgrades or improvements to satellites and space instruments at a fraction of the cost of a full mission. Allowing AstroPix to complete its own technology demonstration in orbit is a bonus.”
AstroPix was developed at NASA’s Goddard Space Flight Center under the agency’s Astrophysics Division, with funding from the Astrophysics Research and Analysis Program and the Nancy Grace Roman Technology Fellowship. The shared ride cuts the cost for both teams, and it gives the gamma-ray payload months of orbital exposure that a sounding rocket or balloon cannot match.
The MeV Gap That AstroPix Aims to Close
Gamma rays are the highest-energy form of light, with each photon carrying tens of thousands to billions of times the energy of a visible-light photon. NASA’s current gamma-ray missions, the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory, image these photons at energies higher than the MeV band. Between 500,000 to 1,000,000 electron volts, however, existing detectors are less sensitive. That range, where many gamma-ray bursts and the brightest emissions from the most distant, black-hole-powered active galaxies are expected to peak, is what astronomers call the MeV gap.
| Instrument | Energy range observed |
|---|---|
| AstroPix (planned) | 20,000 to 700,000 electron volts |
| Fermi Gamma-ray Space Telescope | Energies above the MeV gap, into the GeV range |
| Neil Gehrels Swift Observatory | Higher-energy gamma rays, including bursts |
AstroPix targets the range just below that band, with chips designed to register photons from the lower edge of the soft gamma-ray regime upward. Stacking chips in a future telescope could extend the effective collecting area, allowing a follow-on mission to image the gamma-ray sky in finer detail across the gap. For the FFR mission, the goal is narrower: confirm that the silicon pixels hold their low-noise performance through long stretches in orbit.
A Silicon Sensor Modeled on a Phone Camera
AstroPix is built on monolithic active pixel sensor technology, the same kind of CMOS architecture used in the image sensors of cellphone cameras, scaled up to handle high-energy photons. Each chip carries four silicon pixel detectors, and each detector holds 1,225 pixels.
The pixel architecture sets AstroPix apart from older space-based gamma-ray instruments. Conventional detectors use stacks of high-purity germanium or cryogenically cooled crystals, both of which are heavy, power-hungry, and expensive to scale. AstroPix uses a high-voltage CMOS design, which lets each pixel collect charge directly from incoming gamma rays and run on far less power. The result is a small, low-power detector that can be manufactured in standard semiconductor fabs, an approach that would be impractical with traditional gamma-ray instrumentation. The combination of small pixels and low-power readout makes a larger, stacked array possible without a flagship-sized budget.
For an orbital test, the chip design also simplifies the supporting electronics. The Orbital Replacement Unit can host the AstroPix payload, including the chips, power conditioning, and the data system that transmits observations back to the ground, in a single compact package. Each chip can be tested independently, so the team can compare in-orbit performance against ground measurements made before launch. The chips also have a degree of redundancy, since a single chip failure does not end the test, a quality visible in the A-STEP detector hardware prepared for flight.
The design is intentionally scalable. Multiple chips can be stacked to build a larger effective detector for a future telescope, with each layer reading the same incoming photons in parallel. That layered approach would let a future mission build up collecting area without the high cost and mass of a single, very large crystal. For now, the FFR mission will fly a small representative stack, sized for the unit’s spare capacity.
Why a Ride to Orbit Is Hard to Find
Orbital test opportunities for small gamma-ray payloads are scarce, and that scarcity is the reason AstroPix is flying on FFR at all. Sounding rockets and high-altitude balloons can carry a sensor briefly to the edge of space, but they return after minutes and leave most of the data uncollected. A satellite, by contrast, offers months to years of observation, which matters for a sensor that needs to track faint, slowly varying sources such as distant active galaxies.
“We’ve flown comparable technologies on a scientific balloon mission, and the current prototype eventually will be part of a sounding rocket payload,” said Dan Violette, an AstroPix team member and post-doctoral fellow at NASA Goddard. “Many of those flight opportunities only reach near space, though. It’s not often that technology demonstrations like ours can find a ride into orbit.”
An orbital run gives the team long-duration data on noise, drift, and radiation damage that no short flight can produce, as detailed in the primary announcement of the FFR and AstroPix mission. The Fly Foundational Robots mission is funded through the Space Technology Mission Directorate’s In-space Servicing, Assembly, and Manufacturing portfolio and managed at NASA Goddard. Rocket Lab Robotics, which acquired Motiv Space Systems, supplies the robotic arm under a NASA Small Business Innovation Research Phase III award. Astro Digital of Littleton, Colorado, provides the host spacecraft through NASA’s Flight Opportunities program, which is managed at NASA’s Armstrong Flight Research Center in Edwards, California.
The robotic demonstration runs first. The arm will pick up the Orbital Replacement Unit, reposition it, and execute a sequence of in-orbit operations. Once the unit is in its new position, the AstroPix payload will power up and begin collecting gamma-ray data. The sequence ensures that the technology demonstration the mission was originally funded to perform is not interrupted, and that the bonus science is layered on after the servicing test is complete.
Integration Timeline and What Comes After
The AstroPix team is working through a sequenced integration of its hardware into the Fly Foundational Robots mission, with delivery planned for September of this year. After delivery, the chips and their supporting power and data electronics will be installed into the Orbital Replacement Unit, and the unit will be integrated onto the Astro Digital spacecraft for launch. The Fly Foundational Robots mission is scheduled to lift off in late 2027, with the robotic arm demonstration running first. The AstroPix payload will power up and begin collecting data after the arm has repositioned the unit. The launch date and the integration sequence are both subject to standard mission-development adjustments, with a final manifest to be confirmed closer to flight.
If the test goes well, the data will feed into decisions about a future flagship astrophysics mission that could carry a larger, stacked AstroPix array into orbit and fill the MeV sensitivity gap. The demonstration would mark the first time this generation of silicon pixel sensor has operated long enough in space to characterize its behavior as a flight-ready instrument. NASA’s astrophysics and space technology directorates would then share a starting point for designing the follow-on mission, a payoff that piggybacks on a single robotic arm test.
Frequently Asked Questions
What is AstroPix?
AstroPix is a silicon pixel gamma-ray sensor developed at NASA’s Goddard Space Flight Center. Each chip carries four detectors with 1,225 pixels apiece, all built on a monolithic CMOS architecture similar to the image sensors in cellphone cameras. The sensors are tuned to image high-energy photons in the 20,000 to 700,000 electron volt range, a band that current gamma-ray telescopes handle less well.
When will AstroPix reach orbit?
The A-STEP AstroPix payload is scheduled to launch in late 2027 aboard the Fly Foundational Robots mission. The hardware is to be delivered by the AstroPix team in September, then installed into the mission’s Orbital Replacement Unit before final integration onto the host spacecraft.
What is the MeV gap?
The MeV gap is a sensitivity blind spot in current gamma-ray astronomy between 500,000 and 1,000,000 electron volts. Many gamma-ray bursts and the brightest emissions from the most distant, black-hole-powered active galaxies are expected to peak in this energy range, and existing instruments cannot resolve them clearly. AstroPix is designed to start closing that gap from below.
Who is building the robotic arm for the FFR mission?
Rocket Lab Robotics, which acquired Motiv Space Systems, supplies the mission’s robotic arm under a NASA Small Business Innovation Research Phase III award. Astro Digital of Littleton, Colorado, provides the host spacecraft through NASA’s Flight Opportunities program, with the mission overall managed at NASA Goddard.
