Measuring the halo of the Milky Way with a CubeSat
I remember the exact moment in the office of professor Philip Kaaret when I decided to enroll in graduate school at the University of Iowa and help build the HaloSat science instrument destined for space.
Just over two years later, I would be sitting at the launch that would carry HaloSat to the International Space Station, and only a few months after that I would take charge of science operations scheduling for the HaloSat instrument on-orbit.
Our aim was to measure the mass and geometry of the million-degree halo of the Milky Way by probing its soft X-ray emission features in all directions. To accomplish our goals, we needed to build an altogether new X-ray observatory that could fulfil a niche role. Such an observatory would be difficult to justify at the cost of a larger mission but was well-suited to the CubeSat platform. CubeSats, or standard sized small satellites, are intended to decrease cost and increase access to space, and they have done just that.
Smaller missions can have smaller budgets, shorter turnaround times, and result in a wider spread of institutional knowledge by providing invaluable hands-on experience. The increased risk tolerance afforded to the CubeSat platform allows for students and early career scientists to play a significant role in the mission. A primary driving force behind the design and construction of the HaloSat science instrument consisted of a postdoctoral scholar, a graduate student, and a handful of focused and dedicated undergraduate students. To accomplish the various tasks required to build the instrument, we were each able to work under the guidance and advice of individuals with a long legacy of launching successful instruments into space, and we each gained invaluable experience that we have since carried with us to the next endeavors in our careers.
The success of HaloSat has helped to pave the way for other upcoming astrophysical CubeSats such as BurstCube, CUTE, SPARCS, and BlackCAT. Each will innovate, perform meaningful science, and spread institutional knowledge to students and early career scientists. With the increase in launch opportunities and the availability of reliable and inexpensive spacecraft, access to space becomes less exclusive. Although there is a tendency to focus our attention on the large missions, a wide breadth of smaller missions with higher risk tolerance and rapid timescales is vital to drive technology and innovation. Astronomy should be on the verge of a small satellite revolution, where astrophysical instruments are built and qualified before easily hitching a ride to space. The halo of the Milky Way may be clumpy, but how we do astronomy does not need to be.