Space interferometers could, in principle, exploit the relatively stable space environment and ease of baseline reconfiguration to collect measurements beyond the limitations of ground-based interferometers. In particular, a two-element interferometer could provide excellent uv-plane coverage over a few tens of low Earth orbits. One of the challenges for free-flying interferometers is controlling the optical path distance with subwavelength accuracies despite the collectors flying up to hundreds of meters apart. We consider two approaches: an artificial in-orbit laser guide star (LGS) that provides a phase reference for the space interferometer and fringe tracking on the science target itself. The two approaches (LGS versus no LGS) would require different image processing techniques. In this work, we explore image processing with LGS phase residuals due to global positioning system (GPS) uncertainties. We use GPS uncertainties from the Gravity Recovery and Climate Experiment Follow-On mission to simulate image retrieval with a 300-m baseline laser-guided space interferometer. This is done by fitting the slowly varying phase errors of complex visibility measurements. We also consider a 40-m baseline interferometer with visibility(-modulus)-only measurements. In this case, we simulate the bias in visibility due to fringe tracking in the presence of parasitic forces acting on the spacecraft. We then use a modified version of the hybrid input–output phase retrieval algorithm for image reconstruction. We conclude that under our optimistic assumptions, both approaches could enable general imaging of a few large stars even with CubeSats, although an LGS would significantly improve the best resolution obtainable.

中文翻译：

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由于全球定位系统的不确定性和近地轨道的寄生力，空间干涉仪成像受到限制

原则上，空间干涉仪可以利用相对稳定的空间环境和基线重新配置的便利性来收集超出地面干涉仪限制的测量结果。特别是，二元干涉仪可以在数十个近地轨道上提供出色的紫外线平面覆盖。自由飞行干涉仪面临的挑战之一是，尽管收集器飞行距离长达数百米，但仍以亚波长精度控制光路距离。我们考虑两种方法：人造在轨激光导星（LGS），为空间干涉仪提供相位参考，以及科学目标本身的条纹跟踪。这两种方法（LGS 与无 LGS）需要不同的图像处理技术。在这项工作中，我们探索了由于全球定位系统 (GPS) 不确定性而导致的 LGS 相位残差的图像处理。我们利用重力恢复和气候实验后续任务中的 GPS 不确定性，通过 300 米基线激光制导空间干涉仪来模拟图像检索。这是通过拟合复杂的能见度测量的缓慢变化的相位误差来完成的。我们还考虑使用仅进行可见度（-模量）测量的 40 米基线干涉仪。在这种情况下，我们模拟了在存在作用于航天器的寄生力的情况下由于条纹跟踪而导致的可见度偏差。然后，我们使用混合输入输出相位检索算法的修改版本进行图像重建。我们的结论是，在我们乐观的假设下，即使使用立方体卫星，这两种方法都可以对一些大恒星进行一般成像，尽管 LGS 将显着提高可获得的最佳分辨率。