Space Imaging for SSA

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When satellite imaging is mentioned, we usually think of satellites taking pictures of the weather, floods or downtown New York. This is one of the primary uses of satellites and one which has brought great benefits to many people. Within space surveillance, satellite imaging refers to taking pictures of satellites on orbit. But why would we want to do that?

One reason is when things don’t go as planned. Satellite operators cannot always see what is happening on the satellite directly, but rely on specific sensors to tell them if something has – or hasn’t – worked. This could be a signal to say that the solar panels have been set correctly. If this signal hasn’t been received, it could mean one of two things. Either the solar panel hasn’t been set correctly or the sensor has malfunctioned. But which one of the two is it? Sometimes this specific situation can be verified because there is no power being generated by the solar panel or the satellite’s attitude moves in such a way that indicates the solar panel is not sticking out of the side of the satellite body. In either case, an independant way to verify this would be useful.

Another reason is during re-entry. The way a space object is oriented can effect large changes in the re-entry profile. It can determine if the satellite will break up high in the atmosphere and these small pieces vapourise without touching the Earth’s surface or if the orientation will cause some drag or lift as it comes through the atmopshere and hence change the impact point. Being able to image an object as it comes close to re-entry and begins to be affected by the atmosphere can really help reduce the uncertainty in both these areas.

A final reason why satellite imaging is important is – as can be guessed – military. Having intelligence regarding the capabilities of satellites in orbit is very useful to military commanders. Using satellite imaging could be a good way to do this.

Of course any specific military requirments are out of the scope of the ESA SSA programme. It can be predicted that the resolution required to perform the first two functions of anomaly resolution and re-entry prediction is much less than that required for the third one.

Survillance and Tracking for SSA

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The ESA OGS (image credit: Emmet Fletcher)

There are sometimes confusing statements made regarding the different sensors used within a Space Situational Awareness (SSA) system. Even if we are discussing radar or optical, there are – in essence – three types of sensor: surveillance, tracking and imaging. Since imaging sensors are a very special type – and do not figure in the development of the ESA SSA system, we will ignore them for this specific discussion. What we will discuss here is the difference between surveillance and tracking sensors – a difference that is often overlooked or ignored or just not understood, but is of prime concern when discussing the development of an effective space surveillance system.

Tracking Sensors

It is probably easier to start any discussion of the differences between tracking and surveillance sensors by focussing (no pun intended) on the major characteristics of a tracking sensor.

Tracking sensors usually have a very small field of view – rather like when you use a domestic telescope and you can see a very small area of the sky. Given a fixed detector performance, the smaller the field of view, the more precise the locations of the objects detected within this field of view (when comparing like-for-like). This is fantastic when you want to increase the precision of an object for when you already have some orbital data of, such as a piece of debris for which you have a rough orbit and may collide with an operational spacecraft. You just take this rough orbit and set your tracking sensor to point along this orbit at the position you think the debris should be. When you see the debris, you can then create a more precise orbit – since your detector is looking at a very small region of space and so has a high precision.

The problem is – of course – that since you only see a small area of the sky, if the error on your rough orbit is too high, you might not see the debris at all (it might slip by outside your field of view). It also makes these sensors very inefficient (read: almost useless) for the build-up a catalogue of objects. Since the view is small, it is difficult to trap new objects, unless you are very lucky. Even then, given the small view, you only have a very short reading as the debris passes across the sensor. This results in an initial orbit guess (orbit determination) which can have very high errors. For the development and maintainence of a catalogue, we need a surveillance sensor.

Examples of European tracking sensors: TIRA (Germany), BEM Monge (France), OGS (ESA), CAMRA (UK)

Surveillance Sensors

The TFRM (image credits: Emmet Fletcher)

A surveillance sensor is the workhorse of a surveillance system. It provides the data for both the initial catalogue development (the so-called ‘cold start’) as well as the day-to-day maintenence of the catalogue.

The main difference between the tracking and surveillance sensor is that the surveillance sensor sees a very large area of the sky at the same time. It is also not actively looking for objects, but rather passively (which counterintuitveilly can be active) waiting for debris – any debris – to pass over it. Once it detects something passing over it, the data related to this pass is processed and passed to the catalogue maintainence system.

In this way, the surveillance sensor creates a ‘fence’ which is triggered by any object passing through it. No prior information is needed by the sensor to generate new data regarding a specific debris object and the system therefore does not need to be ‘tasked’ to look out for an object. In reality, the fence can also be generated using an active sensor scanning the sky with a frequency that ensures nothing will be missed. This is the case for radar systems which quickly scan across a path. It doesn’t look in all directions at all times, but still forms an effective fence.

Through the use of surveillance sensors, a catalogue can be built up. The precision of this catalogue will not be very high initially, although the design of the surveillance network should be such that the eventual precision using just the surveillance assets will be enough to give a reliable warning of potential collisions with operational satellites. When the warning is triggered, then comes the turn of the tracking sensors to refine the orbit of this debris and provide the precise information that satellite operators need to plan their maneouvres.

Examples of European surveillance sensors: GRAVES (France), RAF Fylingdales (UK/US), TFRM (Spain)

If you have any comments, clarifications, corrections or suggestions – please comment!

Phobos-Grunt re-entry position uncertainty

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Phobos-Grunt re-entry (image: Michael Carroll)

There’s a nice article with a portion of an interview with me on space.com here: http://www.space.com/14312-russia-mars-probe-phobos-grunt-conspiracy-theories.html.

Working together to be able to get the maximum amount of data spread over as much area as possible is critical to ensuring we can locate where re-entry objects could have landed. It’s a long road towards complete harmony, but the IADC is doing a lot of work towards that aim.

It could be quite a while before we know where exactly the probe landed – there may be a lot of data to sift through before a true picture emerges, but at the moment, I still think the probe landed in the empty areas of the Pacific ocean (just where we wanted it to go!). I hope that the prediction stays that way.

A Safer Space for a Safer World

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I’m now getting ready for the 5th International Association for the Advancement of Space Safety (IAASS) conference which will be held in the beautiful French town of Versailles from the 17th to the 19th October.

As the conference outline says:

The fifth IAASS Conference “A Safer Space for a Safer World” is an invitation to reflect and exchange information on a number of topics in space safety and sustainability of national and international interest. The conference is also a forum to promote mutual understanding, trust, and the widest possible international cooperation in such matters. The once exclusive “club” of nations with autonomous sub-orbital and orbital space access capabilities is becoming crowded with fresh, and ambitious new entrants.

All of which means that ever more cooperation is needed in the fields of debris abatement, space surveillance and cooperation among space-faring entities. Indeed, this has been recognised in this year’s conference where there will be special sessions on debris remediation and space traffic control.

I’m really looking forward to this year’s event – the only problem is that there are four parallel sessions and I’d like to be able to divide my time between most of them!

If you are going to be there, please say “hello!”

Everything you ever wanted to know about SSA (and were afraid to ask)

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A nice overview of why SSA is so important to protect our daily lives. Created by Astrium and very closely in line with what we have stated in the ESA SSA precursor programme….

European experts gather at space hazards seminar – Space Ref (press release)

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Space Ref (press release)
European experts gather at space hazards seminar
Space Ref (press release)
Strong agreement was voiced on the need for Space Situational Awareness (SSA) by delegates representing a wide range of European-level and national stakeholders at an SSA seminar in Warsaw while exchanging views and ideas on the future direction of …

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700.000 fragmentos de basura espacial catalogados

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Article relating to the news article broadcast on Antena 3 TV on the 12 June 2011:

Link to video

La Agencia Espacial Europea (ESA) está diseñando un sistema para clasificar y catalogar los más de 700.000 fragmentos de basura que los científicos estiman hay en el espacio, un sistema que pretende evitar colisiones y mejorar la seguridad de los satélites y otros instrumentos actualmente en uso.

Esta es una de las iniciativas de las que se ha hablado en la Conferencia Europea sobre Vigilancia Espacial celebrada esta semana en Madrid, a la que han acudido 180 expertos de varios países. Los investigadores creen que los satélites están amenazados por más de 700.000 fragmentos de basura espacial y para evitar una colisión es necesario conocer y monitorizar su trayectoria con ayuda de radares y telescopios, de ahí que la ESA esté trabajando en un sistema para detectar los objetos espaciales “peligrosos”.

Según ha relatado Emmet Fletcher, responsable del segmento de vigilancia espacial del programa europeo de “Conocimiento del Medio Espacial” (SSA en sus siglas en inglés) de la ESA, actualmente hay en órbita unos mil satélites activos. Lo que ahora trata de hacer la ESA, ha continuado, es generar un catálogo de todos los objetos peligrosos que orbitan la tierra (EEUU tiene clasificados unos 22.000 de estos fragmentos).

Entre los 700.000 trozos que se cree que hay en el espacio, existen desde pedazos de un centímetro hasta satélites enteros ya en desuso y bastaría la menor de estas piezas para estropear un satélite, chatarra que se triplicará en los próximos 20 años. Catalogar es, entre otros parámetros, conocer la posición y velocidad del objeto, con lo que los investigadores saben hacia dónde va y comparan así la órbita de éstos con la de un satélite.

“Podemos calcular si coinciden y si lo hacen podemos dar avisos a los operadores de los satélites para que maniobren con seguridad y con el menor uso de combustible, y evitar el choque”, según Fletcher. Fletcher, quien ha declarado que siempre se intenta avisar al operador lo antes posible -no más tarde de 72 horas antes de la supuesta coincidencia de un pedazo de basura con el satélite-, ha manifestado que la ESA ya está trabajando en el citado catálogo, aunque será en 2012 cuando los países, en una reunión ministerial, den su visto bueno definitivo y se establezca un presupuesto.

Prueba de este trabajo es que recientemente se ha completado el desarrollo de un software de última generación capaz de alertar a los satélites cuando exista el riesgo de impacto con un fragmento de basura espacial. “De momento estamos probando el sistema utilizando datos de fragmentos de basura espacial ya conocidos. Es el primer paso hacia el software que se utilizará cuando Europa disponga de su propia capacidad de vigilancia del medio espacial”, ha afirmado Fletcher.

Este catálogo es una de las tres patas del programa de Conocimiento del Medio Espacial (SSA), cuyo objetivo es desarrollar e implementar un sistema de alerta temprana, pero no sólo respecto a colisiones espaciales, sino también en cuanto a impactos de objetos naturales contra la Tierra y en relación a la meteorología espacial. Desde 2009 se trabaja para definir la estructura técnica del sistema, para lo que primero se está evaluando la capacidad de la infraestructura ya existente en Europa, como radares de investigación científica y telescopios, que podrían incorporarse al futuro sistema SSA.

El programa SSA ha sido otro de los temas debatidos en la conferencia de Madrid, de cuyos resultados Fletcher ha asegurado sentirse satisfecho. “El espacio es un bien común y nos hemos puesto al día”, ha concluido este experto.

Radar Tracking Campaigns for ESA CO-VI

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Jordi Fontdecaba i Baig, Francis Martinerie, Moise Sutter, Vincent Martinot, Emmet Fletcher
European Space Surveillance Conference, 7-9 June 2011, Madrid, Spain. 

Following the decision at the Ministerial Council 2008 to initiate a Preparatory Programme on Space Situational Awareness, the European Space Agency has started a series of activities with the industry, implementing both classical design approaches: bottom-up and top-down. For Space Surveillance and Tracking, the bottom-up approach translates in particular into an activity in CO-VI consisting of an assessment of the existing European assets that can be used for tracking campaigns, both in low and high altitude regions. It addresses non only the technical performances of the assets but also the identification of their current operational constraints that could be in fine parts of a Service Level Agreement for their contribution in the future European SSA System.

In that context, this paper presents both aspects, addressing only the radar tracking campaigns i.e. the LEO region (a similar article is written on the high altitude region). During the campaigns, the following existing European radars – EISCAT and CAMRa – were used to track several satellites selected to cover a wide range of altitude and inclination in the LEO region. Two different campaigns were done to track the satellites. Orbit restitution was performed in order to characterise the role of the different observation parameters and to point out the best way to improve the orbit estimation performance with a single assets or with a combination of the different assets.

This paper describes the preparation of the campaigns as well as the results obtained, with particular focus on the first campaign. The campaigns were mainly driven by the availability of radar assets and the visibilities of the satellites. The precise orbit determination enabled the comparison of the different assets performance.

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Scanning the skies for debris hazards

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Today, orbiting satellites are threatened by some 700,000 pieces of debris. Assessing related risks requires surveillance, tracking and statistical observations with radars and telescopes. ESA is designing a system to catalogue debris and warn satellite operators when to take evasive action.

This week, over 150 global experts will meet at an ESA-organised conference to share the latest research findings on space debris, surveillance technology, orbital hazard detection and satellite safety. The first European Space Surveillance Conference (ESS2011) will be held 7–9 June in Madrid, Spain.
The conference spotlights ESA’s Space Situational Awareness (SSA) programme, now in the preliminary phase, which aims to put in place a ‘three-legged’ system to warn of hazards posed by orbital debris, space weather and natural objects like asteroids that may strike Earth.

Extensive reuse of existing resources

Since 2009, the Agency’s SSA team have been working to define the system’s overall technical structure, while actively evaluating existing European assets, such as scientific research radars and telescopes, which could contribute to SSA.

The development strategy is based on an extensive use of national and European assets, as well as the procurement of the missing components of the future SSA System.

2011 is a busy year for SSA surveillance development activities, perhaps the most urgent leg of the programme.

Complex engineering and scientific challenge

A new generation of software was recently implemented to warn when satellites could be hit by orbiting debris.

“At the moment, it is undergoing extensive testing using known debris orbits, but it’s a first step toward the software we’ll use when Europe has its own surveillance capability,” says ESA’s Emmet Fletcher, Head of the Space Surveillance and Tracking Segment at the SSA programme office.

Hosting an international conference like ESS2011 is crucial for staying up to date with global best practises and meeting scientific experts who work with current-generation radars and telescopes.

Debris surveillance is a complex engineering and scientific challenge in part due to the fact that even a tiny piece of debris – just 1 centimetre across – can seriously damage or even destroy a functioning satellite if it impacts at orbital velocities.\

“We are now finalising a pan-European survey and test of existing tracking facilities, such as radars and telescopes located in France, Germany, Italy, Norway, UK, Switzerland and Spain,” says Emmet.

“Knowing how precise these are is fundamental to designing ESA’s new SSA system, which may make use of their data in combination with debris readings obtained by new, highly accurate radars and telescopes in the future.

“We know there is a huge amount of knowledge across Europe and globally. Having a single forum where experts from around the world can meet and present new information is vital and helps move our collective know-how forward.

“New techniques, new approaches and sharing past experience helps all space-faring nations work more safely in orbit.”

Conference brings together global experts

At the conference, over 150 experts from more than 20 nations will take in over 50 presentations. There are also dedicated information sessions on policy, optical and radar observations, and engineering design as well as presentations from the future customers of the SSA system.

Today, Europe cannot scan as much of space as necessary to provide comprehensive debris warning services to private and public spacecraft operators, like those flying telecommunication, climate and weather satellites.

“But we have to ensure that the design for the next-generation debris surveillance and tracking systems that SSA will propose at the end of the current preliminary phase in 2012 will perform as needed at a cost that is realistic,” says Emmet.

“This is a challenging task, and achieving it means that conferences like ESS2011, involving a large number of experts, are crucial for knowing the best way forward.”

Link: http://www.esa.int/SPECIALS/SSA/SEM61NJ4LOG_0.html

Status and progress of ESA’s Space Situational Awareness Programme

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Advanced Maui Optical and Space Surveillance Technologies Conference, 14-17 September 2010

In November 2008, the European Space Agency (ESA) Council at Ministerial level approved the start of ESA’s Space Situational Awareness programme. Between 2009 and 2012 a preparatory phase will run that will develop the architectural design of the system, the governance and data policy and the provision of precursor services in the areas of: Space Surveillance and Tracking, Space Weather and Near Earth Objects.

This paper will concentrate on the first of these segments: Space Surveillance and Tracking. It will develop the following main topics: Customer requirements and their integration, the initiation of an integrated catalogue, extension of correlated data to service provision and international cooperation and data fusion The development of the services resulting from these points will be a key driver in the final architecture. This architecture will be proposed at the next Ministerial Council to further develop a full SSA system from 2012 onwards.

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