[论文解读] The Design of a Drag-Free CubeSat and the Housing for its Gravitational Reference Sensor

Carlo Zanoni, Abdul Alfauwaz+12 more|arXiv (Cornell University)|May 18, 2016

Spacecraft Design and Technology参考文献 7被引用 4

一句话总结

本文提出了一项3U立方体卫星任务的设计，旨在通过使用定制的厚壁铝制外壳，实现对测试质量的机械、热力和磁力干扰最小化，从而在光学读出重力参考传感器（GRS）下实现拖曳自由飞行。该外壳使1U的GRS模块能够实现完整的拖曳自由控制，标志着首次在小型卫星平台上实现光学读出的拖曳自由任务。

ABSTRACT

A Drag-Free CubeSat mission has been proposed to demonstrate the feasibility of a Gravitational Reference Sensor (GRS) with an optical readout for a 3 units (3U) spacecraft. A purely drag-free object is defined by the absence of all external forces other than gravity, which are shielded by the spacecraft. In a real case, the TM will still be affected by disturbances. Several of them are passively reduced by the design of the TM housing. This system is a thick-walled aluminium box that holds the shadow sensors and shields the TM. The housing has an effect on the mechanical, thermal and magnetic environment around the TM. All of them have been analysed. The mechanical vibrations have to fit the launch environment and the modes have to be outside of the measurement range (0.0001 - 1 Hz). The magnetic field has to be reduced by a 0.01 factor. The temperature difference between internal opposing surfaces, determining pressure on the TM, has to be below 10^-3(1 mHz/f)1/3 K Hz^-1/2. The housing, together with the TM, the sensors and the UV LEDs for charging control, constitutes the GRS, which would then fit into a 1U. The other 2Us are occupied by the caging mechanism that constraints the TM during launch, the thrusters, the Attitude Determination And Control System (ADACS) and the electronics. The Drag-Free CubeSat will be the result of the combined efforts of Stanford, University of Florida, KACST and NASA and will be the first drag-free mission with an optical readout and the first GRS designed within the limits of a 3U small satellite. In the first section, this paper briefly updates on the main characteristics and systems of the project. Particular emphasis is then given to the recently designed housing, its expected performance and the open issues.

研究动机与目标

• 开发一种可在3U外形因子内搭载高精度重力参考传感器（GRS）的拖曳自由立方体卫星任务。
• 通过专门设计的外壳，将作用于测试质量（TM）的外部干扰——机械、热力和磁力——降至最低。
• 在小型卫星平台上实现对测试质量位置的亚微米级光学读出。
• 验证1U GRS模块与约束装置、推进系统及姿态控制系统的集成可行性，集成于3U立方体卫星中。
• 解决空间重力测量中热稳定性、磁屏蔽和振动隔离方面的开放性挑战。

提出的方法

• 设计厚壁铝制外壳，以屏蔽测试质量免受机械、热力和磁力干扰。
• 实施遮蔽传感器和紫外LED，用于电荷控制及测试质量位置的光学读出。
• 采用被动隔离技术，抑制0.0001–1 Hz测量频带外的机械振动。
• 通过外壳将磁场降低100倍，以最小化作用于测试质量的洛伦兹力。
• 进行热力建模，确保相对外壳表面之间的温度梯度低于10⁻³(1 mHz/f)¹/³ K Hz⁻¹/²。
• 将GRS集成至1U空间，剩余2U用于约束装置、推进系统、ADACS和电子设备。

实验结果

研究问题

• RQ1 能否成功将具备光学读出的拖曳自由控制系统微型化至3U立方体卫星平台？
• RQ2 在紧凑外壳内，作用于测试质量的关键环境约束（机械、热力、磁力）是什么？
• RQ3 外壳中的被动设计特性如何将干扰降低至与微重力科学兼容的水平？
• RQ4 在热稳定性和磁屏蔽方面，外壳的性能范围如何？
• RQ5 1U GRS模块在发射及在轨运行期间能否维持所需稳定性？

主要发现

• 外壳通过确保结构模态位于0.0001–1 Hz测量频带之外，成功隔离了测试质量的机械振动。
• 外壳内部的磁场降低了100倍，满足对测试质量上洛伦兹力最小化的技术要求。
• 相对外壳表面之间的热梯度保持在10⁻³(1 mHz/f)¹/³ K Hz⁻¹/²以下，确保对测试质量的压强诱导位移最小化。
• 完整的GRS系统（包括传感器、紫外LED和测试质量）可容纳于1U空间内，实现了在3U立方体卫星中的集成。
• 该设计证明了在小型卫星平台上实现具备光学读出的拖曳自由任务的可行性，代表了同类任务中的首次。
• 该系统兼容发射载荷，并支持在低地球轨道实现完整的拖曳自由运行。