Small but useful

A detector onboard a CubeSat made a successfully detection of the X-ray polarization from the Crab nebula and also saw something new. What else can we do with these miniature spacecrafts for space astronomy?

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Space astronomy is never easy. It usually costs a tremendous amount of time, money, and manpower for instrument development, in order to make sure that everything is going to work as expected after launch. In recent years, the rapid growth of the CubeSat market seems to suggest that launching a satellite has become commonplace. Many astronomers are thinking about how to use nano-satellites for space-borne explorations. The number of papers (Fig. 1) about CubeSats in astronomy keeps growing and shows a tight correlation with the number of CubeSat launches (Fig. 2).

Figure 1
Fig. 1. Number of papers with CubeSat in the title or abstract listed in NASA ADS.
Figure 2
Fig. 2. CubeSat launches per year (credit: Erik Kulu, Nanosats Database, www.nanosats.eu).

It is obvious to use CubeSats for technical demonstration in the space, as long as the instrument can fit in the mass and power budgets. Luckily for X-ray polarimetry, the detector that was initially developed by the INFN-Pisa group weighs roughly 500 grams and consumes a power of about 2 watts, suitable for a CubeSat payload. However, how to perform cutting-edge sciences with limited resources is always a challenge. In particular, it sounds contradictory to the trend that astronomical facilities are getting larger and larger nowadays.

Large observatories are usually a collaboration of multiple institutes or even countries, and their observing times will be shared by a large community. As a result, it is impractical for these large facilities to focus on one particular science objective. For example, how can you imagine that one uses the Hubble Space Telescope to monitor one or a few objects over a year or two? Sometimes, however, this could be interesting too. Astronomy is full of surprises. Staring at the well-known Crab nebula still brings us something unexpected, of course, with some sort of new eyes

I want to clarify that PolarLight does not refer to the whole CubeSat, but a payload on it. It shares the spacecraft with other payloads. This means that we just need to pay for a seat instead of the whole bus. Of course, it is important to make sure with the satellite vendor that other payloads have no conflict in attitude control. In other words, please try to buy the seat behind the wheel.

Whenever possible, I am always trying to emphasize the role of student training with these kinds of tiny space projects, which is often overlooked. Why is this so important? Because most of the students are in universities, while most of the space programs are developed and operated by research institutes, who need students from universities. Direct participation in space programs is perhaps the best way to attract and train today’s students to be tomorrow's leaders. Small space missions, with an overall duration of 3-5 years from development to operation, is ideal for serving such a purpose. A student can go all the way from hardware development, laboratory tests, in-orbit operation, data analysis, result interpretation, to paper publication. This kind of training involves all-around knowledge and skills and is perhaps difficult to be fulfilled by participating in a large mission.

The full article Re-detection and a Possible Time Variation of Soft X-ray Polarisation from the Crab by H. Feng et al. is available at https://www.nature.com/articles/s41550-020-1088-1

 Header image credit: Zhu Xiong (Spacety).

Go to the profile of Hua Feng

Hua Feng

Professor, Tsinghua University

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