The main partners in ESTCube-1 development were the University of Tartu, Tartu Observatory, Tallinn University of Technology, The Estonian Univer-sity of Life Sciences, Finnish Meteorological Institute, UniverUniver-sity of Helsinki, University of Jyv¨askyl¨a and German Aerospace Center (DLR).
The author has contributed to the selection of the E-sail mission, definition of the mission objectives and requirements, as well as to the design, develop-ment and validation of spacecraft subsystems. Based on the objectives and requirements, the author designed, developed and tested the first prototype of the CDHS hardware as well as supervised the development and testing of all the following revisions of CDHS hardware. The author contributed to the development of the avionics testbench of the spacecraft and performed electrical and software integration testing of CDHS, CAM, COM, EPS and mission payload. The author developed software for CDHS and integrated ADCS software on-board CDHS. Several CDHS software components were later used on CAM. Additionally, the author co-supervised the design, development and validation of ICP (Internal Communications Protocol) and contributed to the design, development and validation of ICPTerminal. ICPTerminal was used for communicating with, and for testing the spacecraft subsystems individually, as well as for operating the whole spacecraft in orbit.
Chapter 2
E-sail development roadmap
Novel technologies are usually applied to either medium or large scale missions once there is a track record of several successful technology demonstrations.
This process is often referred to as increasing the Technology Readiness Level (TRL) [39]. It is important to avoid immature technologies on medium or large scale space missions, especially in mission-critical applications such as propulsion due to the high risk and high cost of a failure.
A full-scale E-sail technology demonstration mission would take place in interplanetary space and would involve about 20 tethers at 20 kV potential and a tether length of 20 km [13]. Due to the technical complexity of the full-scale E-sail technology demonstration, it is preferred to perform independent testing of several key components, as well as to scale the technology step-by-step. The steps to reach the full-scale technology demonstration are listed as follows [3, 5, 6, 13, 40–42]:
1. Scalable tether production.
2. Demonstration of controlled spin-up of a spacecraft, to produce enough centrifugal force on tether end-mass for tether deployment.
3. Demonstration of reliable tether reeling.
4. Demonstration of a high voltage supply and electron emitters to maintain a positive potential on the tether.
5. Indirect measurement of the E-sail effect by measuring the acceleration or deceleration of spacecraft spin-rate in atmospheric plasma flow, with a periodically charged tether.
6. Indirect measurement of the E-sail effect by measuring the orbital decay of a spacecraft with a charged tether, due to drag in atmospheric plasma flow.
7. Measurement of the E-sail effect with a single tether in real solar wind conditions at an apogee of about 30RE where RE is the radius of the Earth.
8. Orbital control with a single tether E-sail in real solar wind environment.
9. Interplanetary navigation with a single tether E-sail.
10. Demonstration of reliable deployment of 20 or more tethers with remote units and auxiliary tethers to avoid tether collisions.
11. Interplanetary navigation with a system which consists of 20 or more tethers, remote units and auxiliary tethers. Illustration of such a system is provided in Figure 1.
Remote unit
Auxiliary tether
Figure 1: Illustration of a full-scale 20 tether E-sail with centrifugally stabilising auxiliary tethers and remote units with auxiliary tether reels and propulsion for spinup and spin control. Adapted from the original version with untensioned auxiliary tethers [13].
Most of the steps listed above cannot be verified in labs on the ground due to the complexity of mimicking the relevant environment.
Although the deployment of tethers has been demonstrated by prior mis-sions [43–46], the mismis-sions have flown with different tether structure and materials which are not suitable for the E-sail mission. For the E-sail mission, Hoytether [47] and Heytether [13, 40–42] have been considered. While high voltage supplies and electron emitters have been flown before [48], keeping a thin tether at a high potential in respect to the surrounding atmospheric plasma is yet to be achieved.
The goal of ESTCube-1 was to demonstrate controlled spin-up of the satellite, tether reel-out in space, tether charging as well as to validate the
plasma physics aspect of the E-sail concept by measuring the electrostatic force acting on a charged tether as it moves through the ionospheric plasma in a Low Earth Orbit (LEO) [13][I]. A more detailed list of ESTCube-1 mission objectives are presented in Section 3.2.
Chapter 3
Mission objectives, architecture and timeline
3.1 Development phases
According to the ECSS-M-ST-10C [49] standard, spacecraft development time-line is split into phases, each of which ends with a review. The phases are listed in Table 1, along with their corresponding dates for the ESTCube-1 ex-ample. Phase 0 ends with a specification of mission objectives and preliminary technical requirements for the spacecraft. By the end of Phase A, the model philosophy and verification approach have been defined, a detailed risk analysis has been performed and technical solutions have been proposed to meet the mission objectives and requirements. The specification of external interfaces as well as prototyping of critical technologies belongs to Phase B. Phase C involves the detailed definition of internal and external interfaces as well as the production and pre-qualification of spacecraft components. The manufacturing, assembly and testing of flight hardware, software and associated ground support equipment are performed in Phase D. In the case of ESTCube-1, Phase C and Phase D were merged. Phase E is reserved for the on-orbit verification of spacecraft components and spacecraft operations to achieve the mission objectives. In Phase F, the mission is wrapped up and spacecraft is disposed of.
Table 1: ESTCube-1 mission development timeline.
Phase Activity Time
0 Mission analysis 02.09.08 – 17.04.09 A Feasibility study 17.04.09 – 13.04.10 B Preliminary definition 13.04.10 – 31.08.10 C Detailed definition 31.08.10 – ...
D Qualification and production ... – 01.03.13 E Operations, utilisation 07.05.13 – 17.02.15
F Disposal 17.02.15