[Paper Review] Discovering the Sky at the Longest Wavelengths with Small Satellite Constellations

Xuelei Chen, Jack O. Burns+30 more|arXiv (Cornell University)|Jul 25, 2019

Radio Astronomy Observations and Technology63 references18 citations

TL;DR

This paper proposes using a constellation of small satellites to observe the universe at decameter-long radio wavelengths—previously inaccessible from Earth due to ionospheric absorption and terrestrial interference. By deploying a lunar-orbiting linear array (DSL mission), the study enables all-sky surveys and global spectrum measurements, unlocking discoveries in cosmic dawn, heliophysics, and extragalactic sources.

ABSTRACT

Due to ionosphere absorption and the interference by natural and artificial radio emissions, ground observation of the sky at the decameter or longer is very difficult. This unexplored part of electromagnetic spectrum has the potential of great discoveries, notably in the study of cosmic dark ages and dawn, but also in heliophysics and space weather, planets, cosmic ray and neutrinos, pulsar and interstellar medium, extragalactic radio sources, and even SETI. At a forum organized by the International Space Science Institute-Beijing (ISSI-BJ), we discussed the prospect of opening up this window for astronomical observations by using a constellation of small or micro-satellites. We discussed the past experiments and the current ones such as the low frequency payload on Chang'e-4 mission lander, relay satellite and the Longjiang satellite, and also the future DSL mission, which is a linear array on lunar orbit which can make synthesized map of the whole sky as well as measure the global spectrum. We also discuss the synergy with other experiments, including ground global experiments such as EDGES, SARAS, SCI-HI and High-z, PRIZM/Albatros, ground imaging facillities such as LOFAR and MWA, and space experiments such as SUNRISE, DARE/DAPPER and PRATUSH. We also discussed some technical aspects of the DSL concept.

Motivation & Objective

• Overcome the limitations of ground-based observations at decameter wavelengths due to ionospheric absorption and human-made radio interference.
• Enable exploration of the cosmic dark ages and dawn, key epochs in the universe's early evolution.
• Develop a space-based solution using small satellites to access the unexplored long-wavelength radio window.
• Facilitate synergy with existing ground and space-based experiments to enhance sensitivity and dynamic range.
• Advance instrumentation and mission design for future low-frequency radio astronomy missions in cislunar space.

Proposed method

• Propose a constellation of small satellites, particularly a linear array on lunar orbit (DSL mission), to achieve synthetic aperture mapping of the entire sky.
• Utilize the Moon's far side as a radio-quiet location to minimize terrestrial interference and enable sensitive measurements.
• Implement interferometric techniques using baseline arrays to produce high-dynamic-range sky maps at wavelengths >10 m.
• Integrate global spectrum measurements to probe the redshifted 21 cm line from the cosmic dawn and dark ages.
• Leverage existing missions like Chang'e-4 and Longjiang-2 as technology and operational precursors.
• Design mission architecture for scalability, cost-efficiency, and compatibility with future deep-space science platforms.

Experimental results

Research questions

• RQ1 Can a small satellite constellation effectively map the entire sky at decameter wavelengths despite ionospheric and terrestrial interference?
• RQ2 To what extent can a lunar-orbiting linear array achieve high-sensitivity, all-sky surveys of the long-wavelength radio sky?
• RQ3 How can synergy with ground-based experiments (e.g., LOFAR, MWA, EDGES) and space missions (e.g., DARE, SUNRISE) improve dynamic range and calibration?
• RQ4 What are the technical and operational challenges in deploying a long-wavelength radio interferometer in cislunar space?
• RQ5 Can such a mission detect the global 21 cm signal from the cosmic dawn with sufficient spectral resolution and sensitivity?

Key findings

• The DSL mission concept enables all-sky mapping and global spectrum measurement at wavelengths >10 m, inaccessible from Earth.
• The lunar far side provides a radio-quiet environment essential for detecting faint cosmic signals like the redshifted 21 cm line.
• Existing missions such as Chang'e-4 and Longjiang-2 demonstrate the feasibility of low-frequency radio experiments in cislunar space.
• Synergy with ground-based arrays (e.g., LOFAR, MWA) and experiments (e.g., EDGES, SARAS) can significantly enhance calibration and sensitivity.
• The proposed constellation architecture supports scalable, cost-effective deployment of long-wavelength radio observatories.
• The mission concept is technically viable and aligns with future science goals in cosmology, heliophysics, and planetary science.