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CaSSIS - Colour and Stereo Surface Imaging System

Welcome to the web site of the Colour and Stereo Surface Imaging System (CaSSIS). We are currently preparing a new web site that will go online soon. So do come back soon. In the meantime you will find quite some information, news, and pictures about CaSSIS on this site.

 

CaSSIS is in the fairing!!

Pictures from ESA's web site.

..... and encapsulated ......

 

 

 

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Introduction

In January 2010, NASA issued an Announcement of Opportunity which described the setting-up of a joint ESA-NASA programme for the investigation of Mars. Initial discussions between the agencies focussed on mission concept studies for the 2016 and 2018 Mars launch opportunities.  The University of Arizona and the University of Bern answered this call with a proposal for an imaging system called HiSCI. However, ESA and NASA ultimately failed to reach agreement on hardware provision and the programme changed into a joint ESA-Roskosmos venture with Russia providing some of the experiments. The University of Arizona had to withdraw and the University of Bern has now taken up the lead with a revised concept called CaSSIS – the Colour and Stereo Surface Imaging System. 

Mission Overview

The 2016 mission is ESA-led and launched by Roskosmos. ESA will provide a Mars orbiter and an Entry, Descent and Landing (EDL) demonstrator. The ExoMars Trace Gas Orbiter (EMTGO) will accommodate scientific instruments to address three main objectives

• Detection of a broad suite of atmospheric trace gases

• Characterization of their spatial and temporal variation

• Localization of the sources of key trace gases

Additionally, the 2016 orbiter will provide surface telecommunications support for the 2018 mission and for other landed assets.

ESA will design, build and integrate a large spacecraft composite consisting of an ESA Orbiter (EMTGO) which will carry the scientific trace gas payload instrumentation and an ESA EDL demonstrator. The spacecraft composite will be launched in January 2016 by a Roskosmos provided launcher and will arrive at Mars in the last quarter of 2016. After Mars orbit insertion, the spacecraft will begin a series of manoeuvres to change the orbit inclination to 74 degrees and reduce the apoapsis, down to a 1 sol (1 Mars day) orbit. Further reductions of the apoapsis will be performed using aerobraking techniques over a period of about 6 to 9 months followed by a final circularization manoeuvre to arrive at the science and communications orbit with an altitude in the range of 350 km to 420 km.

 

The science operations phase is expected to begin at the earliest in May of 2017 (depending on the actual duration of the aerobraking phase) and last for a period of one Martian year. The science instruments on-board will determine the presence, quantity and potential sources and sinks of atmospheric methane, its precursor and product trace gases in the Martian atmosphere. Near the end of the science operations phase, the rover of the 2018 mission should arrive at Mars (January 2019) so that the emphasis on EMTGO operations may shift to provide a data relay function for the rovers, should other communications assets not be available in orbit around Mars. EMTGO will be designed for consumables that will allow further data relay support and science operations until the end of 2022. 

Whilst the goals and objectives of EMTGO are rather straightforward, the spacecraft design proposed by ESA does present some difficulties for remote-sensing. The spacecraft is generally nadir-pointing but it rotates about the nadir-pointing axis in order to maintain the solar panels orthogonal to the Sun while keeping the Sun away from spectrometer radiators. This has no implications for point spectrometers (such as the microwave spectrometer in the strawman payload) but is a serious issue for line-scan imaging systems. This motion can be stopped for short durations to allow imaging but the orientation in which the lines of a line scanner are orthogonal to the direction of motion over the surface varies depending upon orbital position. In addition, the volume available for experiments is restricted by the design of the nadir-pointing platform which limits the overall size of an instrument. 

Experiment Overview

CaSSIS (Colour and Stereo Surface Imaging System), as its name suggests, is a high resolution imaging system designed to complement the data acquired by the other payload on EMTGO while also enhancing our knowledge of the surface of Mars by extending the observations of the High Resolution Imaging Science Experiment (HiRISE) which is currently orbiting Mars onboard NASA’s Mars Reconnaissance Orbiter (MRO).

The instrument comprises a number of sub-elements.

Telescope

The CaSSIS telescope was originally conceived as a three-mirror anastigmat system (off-axis) with a fold mirror. The absence of a central obscuration reduces the straylight by allowing simplified baffling. However, the continuing delays with implementation have forced us to choose a solution with an already-existing mirror for the M1 component. The mother for this mirror has already been manufactured and a section of it identified for the CaSSIS M1. (It should be noted that otherwise manufacturing time for this mirror would normally be 14 months alone). The absence of development has also forced consideration of a non-lightweighted solution for M1 – which has the negative effect of forcing the instrument mass up.

A solution has been found using the pre-existing mirror for M1. This is not trivial because there is a need to force the detector behind M3 for integration purposes. The resulting optical design has power on all four reflecting surfaces. 

The primary mirror is around 13.5 cm in diameter. The mirrors are held in a carbon fiber reinforced polymer (CFRP) structure. The focal plane will comprise a single silicon hybrid detector with 4 colour filters mounted on it following the push-frame technique to be used by the SIMBIOSYS experiment onboard ESA’s BepiColombo.

The Focal Plane System

The system is based on re-use of the focal plane assembly of the SIMBIOSYS instrument for ESA’s BepiColombo mission. The system is based upon a Raytheon Osprey 2k hybrid CMOS detector. The detector can be read-out extremely quickly with 14 bit digital resolution. However, it remains a framing device meaning that acquiring an un-smeared image along a rapidly moving ground-track requires short exposures and a rapid imaging sequence. The along-track dimension of the image is then built up and put together on ground (see above).

To avoid mechanisms the detector is covered with a single monolithic rad-hard fused silica substrate with filters deposited on it. Different coatings with different transmission properties cover the substrate to produce the CaSSIS Filter Strip Assembly (FSA). The transmissions are relatively broad because of signal to noise considerations. Between the filters are small dark bands needed to reduce spectral cross-talk. 

Rotation Mechanism

The telescope and focal plane are mounted on a rotation mechanism. This allows us to solve two key problems. Firstly, the rotation of the spacecraft about the nadir direction can be compensated for. Prior to image acquisition, the imager can be rotated. so that the lines are orthogonal to the direction of motion. (In case of rotation mechanism failure, the system would be able to acquire data but at reduced resolution and lower signal to noise.) Secondly, the rotation mechanism can be swiveled by ~180° to acquire a stereo image. Hence, the imager has been designed to look 10° ahead of the spacecraft for the first image and 10° behind to acquire the stereo pair. The time necessary to complete the rotation drives the design of the rotation mechanism. 

The instrument rotates to build up a stereo image.

The rotation mechanism consists of a hollow shaft supported by two ceramic bearings and driven by a worm gear, whereby the worm wheel is integral part of the hollow shaft. The reduction ratio is ca. 200:1 (exact value depends on final design).

High-strength titanium alloys are used for the gear component, which are hard coated to provide durability. The housing is made of AlBeMet. A stepper motor (modified Port Escap P430) is connected to the worm shaft via a bellow coupling. End switches are used for zeroing; backlash is compensated by S/W and is calibrated in-flight.

A cable management system (the twist capsule) has been implemented to support cables which go from the rotating part of the instrument to fixed electronics box.

Electronics Unit

The ELU is the main command and telemetry interface between the instrument and spacecraft bus, supporting all instrument functions including imaging, rotation control, and instrument thermal control. The following image shows the ELU or E-Box from the side where all the connectors from the Spacecraft are connected.

The electronics unit comprises 3 modules which are assembled with board to board connectors to generate a complete box. The modules are:

Power Converter Modules (PCM) 

Digital Processing Module (DPM) 

Rotation Control Module (RCM)

CAD/CAM of the current CaSSIS design

CaSSIS Pictures

You can see some pictures from the CaSSIS by following this link.

Basic Mars and TGO Orbit Parameters and CaSSIS Expected Design and Performance

Quantity

Value

Orbit type

Circular

Orbit altitude

400 km

Orbit inclination

72 deg

Orbit period

1.966 h

Mars radius

3394 km

Mars eccentricity

0.0934

Perihelion dist.

1.387 AU

Aphelion dist.

1.666 AU

Mars density

3.94 g/cm3

Solar flux at periapsis

718.9 W m-2

Solar flux at apoapsis

498.2 W m-2

Maximum ground track speed

3.012 km/s

Maximum change in true anomaly

0.0509 deg/s

Focal length

880 mm

Aperture diameter

135 mm

Nominal F#

6.52

Pixel size (square)

10 um

Angular scale

11.36 urad /px

Scale at periapsis

4.54 m/px

Scale at apoapsis

4.54 m/px

Rotation axis-boresight angle

10.0 +/- 0.2 deg

Stereo angle from 400 km altitude

22.39 deg

Nominal slant distance to surface

406.92 km

Scale at slant angle

4.62 m/px

Time between stereo points along track

46.91 s

Bits per pixel

14 (returned as 2 byte integers)

Maximum dwell time (1 px of smear)

1.51 ms

Detector size

2048 x 2048 px

Image size

2048 x 256 px

Number of images returned per exposure

4

Detector area used

2048 x 1350

FOV of used area

1.33 deg x 0.88 deg

Nominal image overlap

10%

Pixel read rate

5 MHz

Time between exposures

367 ms

Read-time of sub-images (all)

419 ms

Filters  (central wavelength/bandwidth)

Pan

675 nm / 250 nm

Blue-Green

485 nm / 165 nm

Red

840 nm / 100 nm

IR

985 nm / 220 nm

 

 

Science Team

Name

Organisation

Country

Team
Function

Email

Nicolas Thomas

Uni Bern

CH

PI

Nicolas.thomas (at) space.unibe.ch

Gabriele Cremonese

INAF

I

Co-PI

gabriele.cremonese (at) oapd.inaf.it

Marek Banaszkiewicz

SRC

PL

Co-I

marekb (at) cbk.waw.pl

John Bridges

Uni Leicester

UK

Co-I

jcb36 (at) leicester.ac.uk

Shane Byrne

Uni Arizona

US

Co-I

shane (at) lpl.arizona.edu

Vania da Deppo

Uni Padova

I

Co-I

dadeppo (at) dei.unipd.it

Stefano Debei

CISAS, Padova

I

Co-I

stefano.debei (at) unipd.it

M. (Ramy) El-Maarry

Uni Bern

CH

Co-I

mohamed.elmaarry (at) space.unibe.ch

Ernst Hauber

DLR-PF

D

Co-I

Ernst.Hauber (at) dlr.de

Candice Hansen

PSI

US

Co-I

cjhansen (at) psi.edu

Anton Ivanov

EPFL

CH

Co-I

Anton.ivanov (at) epfl.ch

Lazslo Kestay

USGS

US

Co-I

laz (at) usgs.gov

Randy Kirk

USGS

US

Co-I

rkirk (at) usgs.gov

Ruslan Kuzmin

Vernadsky Inst.

RUS

Co-I

rok (at) geokhi.ru

Nicolas Mangold

Uni Nantes

F

Co-I

nicolas.mangold (at) univ-nantes.fr

Lucia Marinangeli

Univ. Chieti-Pescara

I

Co-I

luciam (at) irsps.unich.it

Wojceich Markiewicz

MPS

D

Co-I

marko (at) mps.mpg.de

Matteo Massironi

Uni Padova

I

Co-I

matteo.massironi (at) unipd.it

Alfred McEwen

Uni Arizona

US

Co-I

mcewen (at) lpl.arizona.edu

Chris Okubo

USGS

US

Co-I

cokubo (at) usgs.gov

Piotr Orleanski

SRC

PL

Co-I

porlean (at) cbk.waw.pl

Antoine Pommerol

Uni Bern

CH

Co-I

antoine.pommerol (at) space.unibe.ch

Livio Tornabene

Western Uni

CAN

Co-I

ltornabe (at) uwo.ca

Pawel Wajer

SRC

PL

Co-I

 

James Wray

Georgia Tech.

US

Co-I

jwray (at) eas.gatech.edu

Hardware Development Team:

 

Name

Affiliation

Country

Role

Ruth Ziethe

Uni Bern

CH

Project Manager (PM)

Daniele Piazza

Uni Bern

CH

Senior System Engineer

Michael Gerber

Uni Bern

CH

System Engineer

Tawon Uthaicharoenpong

Uni Bern

CH

Mech./Therm Engineer

Matthias Brändli

Uni Bern

CH

Mech. Engineer

Marc Erismann

Uni Bern

CH

Mech. Engineer

Martin Rieder

Uni Bern

CH

FEM Analysis

Lisa Gambicorti

Uni Bern

CH

Optical Eng.

Claudio Zimmermann

Uni Bern

CH

Elec. Engineer

Werner Trottmann

Uni Bern

CH

PCB-Layout

Jürg Jost

Uni Bern

CH

Elec. Engineering Supervision

Thomas Gerber

Contractor

(Wavelab)

CH

Electronics

Kaustav Ghose

Uni Bern

CH

PA/QA

Mario Gruber

Uni Bern

CH

Low Level S/W

Pascal Gübler

Uni Bern

CH

Low Level S/W

Vicky Roloff

Uni Bern

CH

Student/Cal.

Irene Bütler

Uni Bern

CH

Administration

Dervis Vernani

RUAG

CH

Telescope PM

Michael Johnson

RUAG

CH

Telescope SE

Elena Pelò

RUAG

CH

Telescope PA/QA

Thomas Weigel

RUAG

CH

Tel. Optical Design

Jacques Viertl

RUAG

CH

Mirrors Procurement

Nicolas De Roux

RUAG

CH

Tel. MAIT

Patrick Lochmatter

RUAG

CH

Tel. Thermo-Mech

Guido Sutter

RUAG

CH

Tel. Mech. Design

Antonio Casciello

RUAG

CH

Tel. Mech. Expert

Thomas Hausner

RUAG

CH

Tel. Technology

Iacopo Ficai Veltroni

SES

I

Focal Plane System PM

Vania Da Deppo

Padova

I

Alignment

Piotr Orleanski

SRC

PL

PCM Manager

Witold Nowosielski

SRC

PL

PCM Engineer

Tomasz Zawistowski

SRC

PL

PCM Engineer

Sandor Szalai

SGF

H

FSW Manager

Balint Sodor

SGF

H

FSW Eng.

Gabor Troznai

SGF

H

FSW Eng.

Hardware Industrial Partners

Switzerland

RUAG Space, Zurich

Italy

SELEX-ES, Campi Bisenzio

Hungary

SGF, Budapest

Poland

CreoTech, Warsaw

Other experiments

EMTGO has three other main experiments onboard. They are

ACS (PI: O. Korablev)

NOMAD (PI: A.-C. Vandaele)

FREND (PI: I. Mitrofanov)

Planetary Imaging Group Web Site

Space Research & Planetary Sciences Division Web Site