Space Systems Engineering & Operations (SSEO/SMAD), Appunti di Ingegneria Aerospaziale

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Dipartimento di Scienze e Tecnologie Aerospaziali Politecnico di Milano

SSEO

Space Systems Engineering

& Operations

Michèle Lavagna

2 .1. | M A R C H I O E LO G OT I P O

Notes by Valerio Santolini, spring 2021

Arguments

The course will go through:

• space system engineering: process, life cycle, standards; whole system of system design strategies;
• space environment: Sun, vacuum, radiations, atmospheres, magnetic field, micro-gravity, debris, their effects on space hardware, countermeasures and open points
• mission categories: mission categories, clients and users; payload class and working principles according to the mission classes
• Payloads: overview of the possible different on board payloads: solutions; existing hardware, trends both for remote sensing and in situ analysis
• Trajectory design: advanced mission analysis for preliminary mission design: constellations and formation flying, entry descent and landing, low thrust trajectories sizing, non keplerian orbits design, B-plane, tisserand’s planes, universal variable
• Launchers: availability, principle for selection; performance
• GNC (Guidance, Navigation & Control): navigation principles, autonomous and ground based, relative and absolute navigation: sensors and architectures, basic solving chain; guidance and control concepts: station keeping, trajectory control maneuvers
• Propulsion subsystem: chemical, electric, advanced propulsion solutions: principles, propellants, technological solution, available technology, performance and limitation, testing process, on going research; feeding solutions, architectures, sizing process
• Telecom and Telemetry subsystem & Operations: signal manipulation, encoding and modulation, transmission principles, international regulation, technological solution, available technology, performance and limitation, testing process, on going research; ground stations availability, signals management and whole mission TMTC typical architectures, sizing process.Effects on on and dependencies from the whole system design. Ground seg- ments sizing and selection; Operations definition and management
• Electrical Power Subsystem: power generation and storage principles; main space domain solutions sizing, technological solutions, availability, performance and limitation, testing process, on going research; electrical subsystem possible architectures, benefits and drawbacks. power budget generation and sizing process;effects on on and dependencies from the whole system design
• Thermal control Subsystem: thermal exchange in space: environment and criticality, passive and active con- trol approaches, principles for thermal flux control, available technology, performance and limitation, testing process. Sizing process, mid-complexity thermal network solving, numerical approach and available standardized utilities; effects on on and dependencies from the whole system design
• Attitude determination and Control subsystem: recall of the attitude dynamics determination and control prin- ciples: available architectures for space vehicles; available equipment for determination and control ( sensors and actuators):performance and limitations. Pointing budget generation;sizing process according to require- ments, effects on the whole system design
• On board data handling subsystem: possible architectures in terms of buses, processors, memories; available technologies and trends; performance and limitation, preliminary sizing process.Effects on and dependencies from the whole system design
• Structural and configuration subsystems: approach to settle the space vehicles configuration; possible solutions and driving factors; dependence on the whole system design. structural loads; materials and shape selection;

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Contents

1. Introduction

1.1 Course introduction

The natural evolution of this course is the optional course given the next fall semester, the Applied Space Mission Design (ASMD), in which you basically put in practice what you are going to learn in this course; you will mimic, if you will attend that course, a complete complex mission design. That course is up to you, and for this I would like you to experience that process also in this course, even if in a lighter way though a preliminary design. I think it is an opportunity for you as it is a business card for the future. That is why you are going to have lessons but also practice along this month. Who is going to lead you in this adventure? At the top of this chart you see the answer.

M. Lavagna Aerospace Science & Technologies Dept.

o Leonardo Company SpA o TAS-I o OHB o ELECNOR-Deimos o DLR o SITAEL

Who

Advanced Space Technologies 4 Robotics &Astrodynamics

TEACHER

• Prof. Michèle Lavagna  PoliMi [email protected]  ASTRA Team: P.Lunghi, A.Colagrossi, S.Silvestrini, A.Capannolo, J.Prinetto, G.Zanotti, M.Piccinin, M.Quirino, A.Brandonisio, M.Bechini ( Assistant Professor, PhD candidates, PostDoc, Assistant Researchers)

Experts from Academy\ Industries/Agencies: o PoliMi DEIB o INAF-IAPS o ESA - ESOC\ESTEC o ASI o International Universities

Figure 1.1: Slide 3, "course introduction" pack

I did not introduce myself, I am Michelle Lavagna, full professor in flight dynamics at the DAER since more than 20 years, and I used to chair the former course of this for 20 years almost. I have a group that is called Astra, some members are reported here: they will be available during the project you are required to develop to answer your questions and to support you with it. And then, as you know, this year you will have some lessons shared with former Space Mission Analysis and Design course. I would like you both to benefit from external seminars that I use to organize every year, given by different entities that have a role in space, so from agencies as the European Space Agency, the Italian Space Agency, other universities around the world; now, having the virtual lessons we also have the opportunity to have more speakers also from far away, and to have fundamental intervention and speeches from companies: companies give you the idea of the state of the art of the technologies, the challenges, the issues; this also allows you to have a window on the real life in terms of work and possible enrollment in the near future. The kind of seminars will depend on the missions that I give to the other course so that they are focused on specific disciplines, for example technology for the entry descent and landing, technology for robotics, for exploration. Each of those companies has an expert in one field and the personnel that will come will focus on a specific area of discussion to enlarge your knowledge in that field. So how will the course be organized? The main part through classes of course, so through the lessons as you are well used to; almost all of them will be given through presentations: it is a matter of learning how to design and to size, and learning about technology for each of the disciplines, and managing a process of designing and producing a system; there will be very few of the analytical formulations you are well used to, but more practical applications and discussions. I already mentioned the external lectures and, as said, as I want you to do some proactive work, I expect you to build up very small teams, up to 4 or 5 people no more, to focus on the very first step of the design life-cycle that we will see in the next lessons, so to formalize a preliminary mission that shall be performed by small sats... so when I say "to formalize the mission" it means that I will give you the environment, so I will tell you whether the mission shall be an Earth mission for Earth Observation, an Earth mission for communication or problem solving, a Martian mission for exploration; I will give you the large environment limited to a domain and then what I expect you to do is to identify an interesting goal for the mission and understanding how far this is feasible; I do not want you to design the mission nor to size spacecraft the whole, because this will become possibly the topic for the full future course, but to define the borders for a very high level goal of the mission to make it feasible: some sizing at a system level, but very limited and just for small platforms that are easier to be designed. We will check this work with reviews along the month, with teams and all together just to check what you propose, if it is reliable and feasible from the technology point of view. If it is feasible, depending on the COVID, there will also be the opportunity to visit the companies’ labs. as We did and I used to do up to the 2019. I think this is relevant, to have you conscious of the environment that is going to be used in the future; and then there will be of course, as always, individual examination through different kind of tests, to check if you learnt the logic for sizing a space system and the available technology... So, as I mentioned you before, the course is focused in preparing you as system engineers, not subsystem engineers; so you will not become expert of a single discipline, so you will not become an expert in thermal control subsystem design or in electrical power subsystem design, but the scope is to have you prepared to face the sizing of any of those subsystems and to harmonize this sizing in a feasible mission design as a whole, compliant with the requirements and the goal. As I mentioned you before, what I expect you with the practical work is to define the goals, so to think out of the box which could be nice mission to do with a small class satellites, and to identify and justify the requirements for that mission. To do this you will be asked to size the mission at a very high level, so it means with a mass budget as a whole, as a power budget as a whole, not getting through the whole subsystem design. The aim of using a small satellite is the availability of every technology, so that you will not have to size them but only to choose them, assessing the feasibility of your mission and doing simple calculations. Every choice should be compliant with the goals and justified.

40For all the team members there is a plus from 0 to 2 for the "harmony" of the final project. Test arguments: first part: questions to check the process used and the drivers for the design of each subsystem. Second part: sizing exercise, using every possible means one has available, e.g. books, sites.

1.3 Contents introduction

A space mission is made up of two main blocks: one is the space segment, the other is the ground segment. During a design both are required to be accounted for. System engineering is getting through the design, implementation, the actuation, namely the in-flight operations, and the end of life of a satellite mission.

M. Lavagna Aerospace Science & Technologies Dept.

Space Missions and System Engineering

Service Module Payload

Space System breakdown

Space Segment

Control Center Ground Station Ground Segment

Operations

Figure 1.3: Slide 7, "course introduction" pack

• Space segment: everything that flies (e.g. orbiter, rover, sat in a constellation). Breaking it up more, there are two sub-boxes: payload and platform, also known as service module. - Payload: object motivating the mission, object used to answer a specific goal (scientific, commercial, military, civil-based, exploration based). High level goals, so only the baseline of the mission aim. This is the goal type to start from in the project. In real life this goal determines the instrument required for it, even a suit of multiple instruments: e.g. thermal band or optical band for an imager? A spectrometer in case of particles analyzer? These payloads requirements are passed to industries, building the payload.

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• Platform: I must build something that feeds the payload in terms of energy, that stores data, that protects it thermally and sustains it structurally. The course is focused on systems, for the payload but mainly for the service module.
• Ground segment: this is made up of two components, ground stations and control centers. Telemetry, commercial, scientific data are transferred through ground stations to control centers.
• Ground stations: it is the hardware that receives data and physically sends orders back to satellites: places with receivers, namely antennas; each of these ground station works with fixed gains and frequencies e.g. radio frequencies or optical bands.
• Operation centers: centers that elaborate received data. Mission operation centers for the service module and science operation centers for the payload.

During the space system design the space and ground segments with their sub-segments are to be carefully considered at the same time, e.g. control centers availability, personnel availability to be verified in order tackle a mission aim without spending too much money and time and possibly making the mission non realizable. Looking at the timeline of a mission, there are three main blocks, managed by space mission system engineer- ing: the mission design (the design of the ground and space segments), mission implementation (the realization of the two segments) and system management (the management of the two segments) during the in-flight operations. During the mission design,implementation and management need to be correctly considered, docu- mented and assessed, as a correct planning prevents from money and time losses. Considering implementation and management we can analyse how these reflect into the design phase of each block.

M. Lavagna Aerospace Science & Technologies Dept.

Sys Implementation

Sys Design

Sys Management

Mission Engineering

Space Missions and System Engineering - phases

Figure 1.4: Slide 8, "course introduction" pack

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trajectory design is accounted, from the launcher detachment to the disposal. Communication with Earth, Sun pointing for power production, manoeuvres are accounted for; the control-history of the satellite is in this phase planned. After launch, the real operations and the real trajectory are accounted for: the control of the satellite switches from the nominal planned to the analysis of the real one; from mission analysis we pass indeed to Flight Dynamics. Indeed, during the mission design a possible error is accounted for; this modelling error appears during the real mission; the maximum real error allowed for in the operational phase is indeed chosen and corrective manoeuvres are performed accordingly. The Management/Operation phase naturally follows the implementation choices: the architecture for the ground control ("Major Tom to ground control") is usually based on a ground antenna (e.g. Malindi-White Sands Complex); more rarely an in-flight satellite is chosen for data relaying, if for example the memory to stare data on board is not sufficient. It is this satellite that afterwards sends data to ground station. The transferred data is afterwards transmitted to the payload owner, and sometimes different science centers are sent data to, as payloads could be more than one. How is a mission typically planned? I start from a goal, from the mission objective. This aim is to be translated into possible constraints: e.g. from Earth to Mars what is the C3 I need? The minimum value needs to be respected and provided by the system I am designing. Other examples include the robustness required, and consequently technology must be chosen, or the mass budget I can consider. Some alternatives are proposed to fulfil the final aim. There is no point in going deep in each of these alternatives, as the best one must be trade-off, using a multi-objective approach after a proper comparison between each alternative. The baseline chosen, that must be properly justified in each of its shallow features, as the final baseline must be possibly defended during discussions. The baseline is afterwards developed in detail.

2. Tech and subsystems intro

2.1 Example of a space segment breakdown (Rosetta Service module,

used to study a comet)

Objective: Become able in reading a spacecraft, looking very carefully inside its design; everything is there with a motivation and a trade-off between different optimal solutions. Engineering solutions are never optimal (ideal) but come from compromises. Here the explanation of some of the components of the Rosetta s/c.

M.Lavagna, Aerospace Science & Tech Dept.

11 Instruments:

• OSIRIS- UV, IR camera
• ALICE –UV spectrometer
• VIRTIS- IR& UV spectrometer
• MIRO – Microwaves and gas detector
• ROSINA- Ion spectrometer
• GIADA- impacting particles sensor
• RSI- nuclei density and gravimetry sensor

On board scientific Payload

• Launch mass: 3000 kg
• Fuel mass: 1680 kg
• Solar panel: 32 m^2 each
• Lander mass: 100 kg
• p\l mass: 165 kg
• Power: 850 W @ 3.4AU

Example of a space segment breakdown

Rosetta Service Module

Figure 2.1: Slide 2, "L2 Tech and subsystems intro" pack

• Central cylinder: one of the typical configurations consists in the cylinder s/c. Its function is to withstand structural loads and keep mechanical parts "safe" (far from radiation or general external environment).

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