space-based astronomy instruments

CERN Summer School May 2009CERN Summer School May 2009 11

Space-based Astronomy Space-based Astronomy InstrumentsInstruments

David Lumb David Lumb

Science & Robotic ExplorationScience & Robotic Exploration

European Space AgencyEuropean Space Agency


Momentous Week for Momentous Week for Space AstronomySpace Astronomy


Why Space ?Why Space ?


The atmosphereThe atmosphere AbsorptionAbsorptionMost radiation incident on the Earth’s upper atmosphere does not Most radiation incident on the Earth’s upper atmosphere does not

reach the ground. The atmosphere opaque to all but some radio reach the ground. The atmosphere opaque to all but some radio wavebands and light in the wavebands and light in the optical windowoptical window. (390 nm – 780 nm) . (390 nm – 780 nm) plus the near UV, near IR and some far-IR wavebands. Much of plus the near UV, near IR and some far-IR wavebands. Much of the infrared (21 mm to 1 mm) suffers absorption from Hthe infrared (21 mm to 1 mm) suffers absorption from H22O and O and COCO22 whilst UV absorbed by O whilst UV absorbed by O33. Gas atoms and molecules absorb . Gas atoms and molecules absorb X-rays and γ-rays .X-rays and γ-rays .

ScatteringScatteringScattering of light is strongest when the Scattering of light is strongest when the λλ of the light is ~ of the light is ~

diameter of the scattering particles. Visible light more readily diameter of the scattering particles. Visible light more readily scattered by dust and mist than IR. ( car headlights in fog ) scattered by dust and mist than IR. ( car headlights in fog ) Try Try experimenting with IR TV remote control with water bag or experimenting with IR TV remote control with water bag or chalk cloudschalk clouds

SeeingSeeingVariations in density of the atmosphere in a line of sight with an Variations in density of the atmosphere in a line of sight with an

object cause intensity fluctuations. The variations in the object cause intensity fluctuations. The variations in the refractive index of a cell of air above a telescope will alter the refractive index of a cell of air above a telescope will alter the apparent position of an object, normally over a range of a few apparent position of an object, normally over a range of a few arcseconds. (distinguish between a star and a planet merely by arcseconds. (distinguish between a star and a planet merely by observing Stars “twinkle” more than the bright planets)observing Stars “twinkle” more than the bright planets)


HST HistoryHST History Lyman Spitzer developed the Lyman Spitzer developed the

concept of a telescope in space. In concept of a telescope in space. In 1946 — more than a decade 1946 — more than a decade before the launch of the first before the launch of the first satellite satellite

In 1962, the USA's National In 1962, the USA's National Academy of Sciences recommends Academy of Sciences recommends building a large space telescope. building a large space telescope.

In 1977, Congress votes to fund In 1977, Congress votes to fund the project and construction of the project and construction of Hubble Space Telescope begins. Hubble Space Telescope begins.

Launch in 1990 – discovery of the Launch in 1990 – discovery of the spherical aberrationspherical aberration

1993 – first Servicing Mission1993 – first Servicing Mission 1995 – first Hubble Deep Field data1995 – first Hubble Deep Field data


Early Instrument Early Instrument ConceptsConcepts

Earliest Earliest concepts concepts considered considered astronauts astronauts periodically periodically retrieving retrieving film! film!

CCDs eventually prevailed over vidicons after CCDs eventually prevailed over vidicons after a period of “a period of “invention push & market pull”invention push & market pull” driven by NASA and CCD manufacturers driven by NASA and CCD manufacturers


Space Radiation Space Radiation EnvironmentEnvironment


CCDs and Cosmic RaysCCDs and Cosmic Rays Ground based – muons with rate varying with Ground based – muons with rate varying with

altitudealtitude In orbit – order magnitude higher in LEO, several In orbit – order magnitude higher in LEO, several

times more again in interplanetary spacetimes more again in interplanetary space


CCDs and Radiation CCDs and Radiation DamageDamage

Early tests of ~krads Co60 showed no Early tests of ~krads Co60 showed no major ionising damage problemsmajor ionising damage problems

Environment specific tests for neutrons Environment specific tests for neutrons and protons then showed that bulk and protons then showed that bulk damage very important for dark spikes damage very important for dark spikes and charge transfer efficiency at low and charge transfer efficiency at low signal levelssignal levels

Shielding and mitigation methods Shielding and mitigation methods critical, and still remains the Achilles critical, and still remains the Achilles heel for space-borne use of CCDsheel for space-borne use of CCDs


HST OperationsHST OperationsThe HST is in a low earth orbit (LEO) with an orbital The HST is in a low earth orbit (LEO) with an orbital

period of approximately period of approximately 96.5 minutes96.5 minutes. This introduces . This introduces a variety of observing constraints a variety of observing constraints

Depending on target declination, viewing times range Depending on target declination, viewing times range from approximately from approximately 52 —96.5 minutes52 —96.5 minutes per orbit. per orbit.

Reflected and scattered light also restrict the science Reflected and scattered light also restrict the science instruments, and the pointing control system (PCS), instruments, and the pointing control system (PCS), from observing targets within from observing targets within 20 degrees of the bright 20 degrees of the bright earth limbearth limb and 7.6 degrees of the dark earth limb. and 7.6 degrees of the dark earth limb.


HST Operations #2HST Operations #2The poles of the HST orbit lie 28.5 degrees from Earth's The poles of the HST orbit lie 28.5 degrees from Earth's

equatorial pole and combine with the HST earth limb equatorial pole and combine with the HST earth limb avoidance to define a variable circle of roughly 4 — 16 degrees avoidance to define a variable circle of roughly 4 — 16 degrees in radius centered on the orbit pole near declination. in radius centered on the orbit pole near declination.

Orbital precession causes these northern and southern Orbital precession causes these northern and southern continuous viewing zones (CVZ)continuous viewing zones (CVZ) to sweep completely around to sweep completely around the equatorial pole in right ascensionthe equatorial pole in right ascension

A A 50-degree cone of avoidance around the sun50-degree cone of avoidance around the sun and a 9-degree and a 9-degree cone around the moon define limits within which observations cone around the moon define limits within which observations are not normally planned or executed. This prevents stray light are not normally planned or executed. This prevents stray light contamination and damage to the inside of the telescope from contamination and damage to the inside of the telescope from those bright sources. those bright sources.

Spacecraft Roll RestrictionsSpacecraft Roll RestrictionsHST's solar panels rotate around only one axis. The resulting HST's solar panels rotate around only one axis. The resulting

single degree of freedom translates into roll limits of the single degree of freedom translates into roll limits of the spacecraft about the target-telescope line of sight. spacecraft about the target-telescope line of sight.


HST Operations#3HST Operations#3Guide Star AvailabilityGuide Star AvailabilityObservations require one or two guide stars to enable HST to maintain Observations require one or two guide stars to enable HST to maintain

stable pointing during long exposures. The use of one guide star only stable pointing during long exposures. The use of one guide star only provides X and Y axis control and allows the telescope to drift in roll provides X and Y axis control and allows the telescope to drift in roll about the guide star position at a rate of about one milliarcsecond about the guide star position at a rate of about one milliarcsecond per second of time. The magnitude of the target's motion in the per second of time. The magnitude of the target's motion in the science aperture increases with the exposure time and the length of science aperture increases with the exposure time and the length of the moment arm between the guide star and target position. the moment arm between the guide star and target position.

Therefore, most observations require two guide stars. Three Fine Therefore, most observations require two guide stars. Three Fine Guidance Sensors (FGS) use areas lying at the outer edge of the Guidance Sensors (FGS) use areas lying at the outer edge of the primary field of view to locate and lock onto the necessary guide primary field of view to locate and lock onto the necessary guide stars. guide stars move in and out of the FGS fields of view over time stars. guide stars move in and out of the FGS fields of view over time and may not be available at all times for a given target. and may not be available at all times for a given target.

South Atlantic Anomaly (SAA):South Atlantic Anomaly (SAA): Earth's offset magnetic dipole allows Earth's offset magnetic dipole allows solar and extrasolar particle radiation to penetrate closer to its solar and extrasolar particle radiation to penetrate closer to its surface in the region and produces a many orders of magnitude surface in the region and produces a many orders of magnitude increase in the ionizing radiation density at HST'S altitude. Data increase in the ionizing radiation density at HST'S altitude. Data contamination increases for all detectors and presents safety contamination increases for all detectors and presents safety concerns for some instruments. HST passes through some part of the concerns for some instruments. HST passes through some part of the SAA inabout 60% of the physical orbits each day, SAA inabout 60% of the physical orbits each day,

Unplanned eventsUnplanned events, instrument safing sub-system failures (gyros , instrument safing sub-system failures (gyros computers)computers)


Space vs GroundSpace vs Ground Resolution advantage of HST over ground-Resolution advantage of HST over ground-

based telescopes will decrease as based telescopes will decrease as adaptive opticsadaptive optics systems become more systems become more widespread. One advantage of the larger widespread. One advantage of the larger ground-based telescopes is their ground-based telescopes is their sensitivitysensitivity as their primary mirrors are much larger. as their primary mirrors are much larger.

Space-based telescopes essential for most Space-based telescopes essential for most IR, UV, X-ray and γ-ray observations. IR, UV, X-ray and γ-ray observations. Developments over decades have seen Developments over decades have seen improvements in resolution, sensitivity and improvements in resolution, sensitivity and operational life spans. But …operational life spans. But …


Space vs GroundSpace vs Ground CostCost. More expensive to design, build, launch and operate a . More expensive to design, build, launch and operate a

telescope in space. HST cost about US$2 billion to build & launch. telescope in space. HST cost about US$2 billion to build & launch. (&>$700M/service) The Gemini project of two 8m telescopes cost (&>$700M/service) The Gemini project of two 8m telescopes cost US$184m. The VLT in Chile cost $600m for 4 x 8.2m telescopes US$184m. The VLT in Chile cost $600m for 4 x 8.2m telescopes

LifespanLifespan.. The lifetime of most space telescopes is limited by the The lifetime of most space telescopes is limited by the amount of onboard fuel they can carry for corrections and orbital amount of onboard fuel they can carry for corrections and orbital adjustment. Also rely on gyroscopes for control and pointing. adjustment. Also rely on gyroscopes for control and pointing. Difficult or impossible to control the telescope if fail. Difficult or impossible to control the telescope if fail.

RiskRisk.. Some space astronomy missions have failed to Some space astronomy missions have failed to catastrophic failure of the launch vehicle. Others, such as catastrophic failure of the launch vehicle. Others, such as HipparcosHipparcos have had to be curtailed or modified due to incorrect have had to be curtailed or modified due to incorrect orbit insertion. orbit insertion.

SizeSize. For an ESA mission to L2 . For an ESA mission to L2 €€200,000 per kilogram. Also 200,000 per kilogram. Also restrictions on the size of satellites. The primary mirror for the restrictions on the size of satellites. The primary mirror for the HST was limited to fit into the cargo bay of a Shuttle. HST was limited to fit into the cargo bay of a Shuttle. James Webb Space TelescopeJames Webb Space Telescope will use a 6.5m segmented mirror will use a 6.5m segmented mirror made of beryllium that will be folded up for launch on an made of beryllium that will be folded up for launch on an ArianeAriane 5 5 launch vehicle. launch vehicle.

Upgrades and MaintenanceUpgrades and Maintenance Ground-based telescopes can be Ground-based telescopes can be upgraded relatively easily. Telescopes such as the AAT, Gemini upgraded relatively easily. Telescopes such as the AAT, Gemini and the VLT are improved throughout their lives by the addition and the VLT are improved throughout their lives by the addition of new instruments and sometimes improved optics. Mechanical of new instruments and sometimes improved optics. Mechanical and software problems can be fixed by engineers and scientists. and software problems can be fixed by engineers and scientists.


Herschel InstrumentsHerschel Instruments PACS is a camera and low to medium resolution PACS is a camera and low to medium resolution

spectrometerspectrometer in range 55-210 µm. Four detector arrays, two in range 55-210 µm. Four detector arrays, two bolometer arrays and two Ge:Ga photoconductor arrays. The bolometer arrays and two Ge:Ga photoconductor arrays. The bolometer arrays are dedicated for wideband photometry, bolometer arrays are dedicated for wideband photometry, photoconductor arrays are exclusively for spectroscopy. PACS photoconductor arrays are exclusively for spectroscopy. PACS can be operated either as an imaging photometer, or as an can be operated either as an imaging photometer, or as an integral field line spectrometer. integral field line spectrometer.

SPIRE is a camera and low to SPIRE is a camera and low to medium resolution medium resolution spectrometerspectrometer Wavelengths in the Wavelengths in the range 194-672 µm. An imaging range 194-672 µm. An imaging photometer and a Fourier Transform photometer and a Fourier Transform Spectrometer (FTS), use bolometer Spectrometer (FTS), use bolometer detector arrays.detector arrays. HIFI is a very high resolution HIFI is a very high resolution heterodyne spectrometerheterodyne spectrometer covering the 490-1250 GHz and covering the 490-1250 GHz and 1410-1910 GHz bands. It utilises low 1410-1910 GHz bands. It utilises low noise detection using noise detection using superconductor-insulator-superconductor-insulator-superconductor (SIS) and hot superconductor (SIS) and hot electron bolometer (HEB) mixers, electron bolometer (HEB) mixers, together with acousto-optical and together with acousto-optical and autocorrelation spectrometers. HIFI autocorrelation spectrometers. HIFI is not an imaging instrument, it is not an imaging instrument, it observes a single pixel on the sky at observes a single pixel on the sky at a time. a time.

Biggest space telescope ever !


PACSPACS

Ge:Ga photoconductorGe:Ga photoconductor - - application of stress shifts application of stress shifts the cut-off wavelength to the cut-off wavelength to higher values by breaking the higher values by breaking the degenerate valence band degenerate valence band forcing the heavy hole band forcing the heavy hole band closer to the acceptor state closer to the acceptor state thus allowing less energetic thus allowing less energetic photons to excite free charge photons to excite free charge carrierscarriers

Responsivity changes to Responsivity changes to irradiation!irradiation!

TopScanning electron microscope (SEM) micrograph of part of one

PACS 16 × 16 bolometer matrix. Bottom

The detail, marked by the red rectangle, shows the structure of one pixel: a (coarser) grid in the front acts as a resonant

absorber while the (finer) grid in the back acts as a λ/4 back-reflector.


SPIRESPIRE SPIRE Photometer Detector AssemblySPIRE Photometer Detector Assembly

The SPIRE photometer has three arrays of bolometer The SPIRE photometer has three arrays of bolometer detectors each dedicated to one of the instrument's detectors each dedicated to one of the instrument's three wavelength bands centred on approximately three wavelength bands centred on approximately 250, 350 and 500 μm. This image shows the whole 250, 350 and 500 μm. This image shows the whole detector assembly for the 500 μm band. The 43 holes detector assembly for the 500 μm band. The 43 holes in this front view of the assembly are the entrances to in this front view of the assembly are the entrances to feedhorns that direct the light onto the actual feedhorns that direct the light onto the actual detectors: 43 bolometers lying behind the feedhorns detectors: 43 bolometers lying behind the feedhorns in the assembly.in the assembly.


SPIRESPIRE

Close-up of a single bolometer, hexagonal in Close-up of a single bolometer, hexagonal in shape, with parts of surrounding bolometers shape, with parts of surrounding bolometers also visible. also visible.

The tiny crystal (towards the bottom of the The tiny crystal (towards the bottom of the bolometer), reacts to changes in bolometer), reacts to changes in temperature. When a source on the sky is temperature. When a source on the sky is observed, the green circular area of the observed, the green circular area of the bolometer absorbs the energy from the light bolometer absorbs the energy from the light that falls on it and heats up by a small that falls on it and heats up by a small amount. amount.

Measurement of brightness is carried out by Measurement of brightness is carried out by measuring crystal the change in resistancemeasuring crystal the change in resistance


Herschel CryostatHerschel Cryostat A large cryostat surrounds the A large cryostat surrounds the

instruments maintaining an operational instruments maintaining an operational temperature of 1.7 K for a nominal temperature of 1.7 K for a nominal mission lifetime of 4 years. Helium-II mission lifetime of 4 years. Helium-II conditions arranged by the use of vacuum conditions arranged by the use of vacuum pumping for several days to below the pumping for several days to below the Lambda point at about 2.17 Kelvin then Lambda point at about 2.17 Kelvin then lowered even further by continued lowered even further by continued vacuum pumping to about 1.7 Kelvin. vacuum pumping to about 1.7 Kelvin.

Continually refilled with additional He & Continually refilled with additional He & pumping until four days before the launchpumping until four days before the launch

Helium gas keeps the cryostat cold Helium gas keeps the cryostat cold After the launcher fairing placed over the After the launcher fairing placed over the

Herschel and Planck spacecraft access Herschel and Planck spacecraft access points used to ensure the cryostat tank points used to ensure the cryostat tank itself is kept as cold as possible for the itself is kept as cold as possible for the following days by flushing helium gas following days by flushing helium gas

The helium is used to cool the three The helium is used to cool the three science instruments' focal plane units science instruments' focal plane units (FPU) and the shields. (FPU) and the shields.

A porous plug allows the separation of the A porous plug allows the separation of the gas from the boiling liquid helium such gas from the boiling liquid helium such that only gas leaves the tank. It slowly that only gas leaves the tank. It slowly flows from the tank into pipes around the flows from the tank into pipes around the payload (highlightedpayload (highlighted in blue) to cool it to in blue) to cool it to between 1.7 K, 4 K and about 10 K.between 1.7 K, 4 K and about 10 K.


PlanckPlanckPlanck has the ability to:Planck has the ability to: Detect much smaller temperature Detect much smaller temperature

variations in the CMB than previous variations in the CMB than previous missions missions

Perform CMB measurements with a higher Perform CMB measurements with a higher angular resolution than ever before angular resolution than ever before

Measure over a wider band of frequencies Measure over a wider band of frequencies to enhance the separation of the CMB to enhance the separation of the CMB from interfering foreground signalsfrom interfering foreground signals

Possibly see first anisotropies in Possibly see first anisotropies in Universe and undermine Copernican Universe and undermine Copernican Principle?Principle?


Planck InstrumentsPlanck Instruments Planck’s Low Frequency Planck’s Low Frequency

Instrument (LFI), and the Instrument (LFI), and the High Frequency Instrument High Frequency Instrument (HFI), are equipped with a (HFI), are equipped with a total of 74 detectors covering total of 74 detectors covering nine frequency channels. nine frequency channels. These detectors cooled to These detectors cooled to temperatures < 20 K. temperatures < 20 K.

3-stage refrigeration chain 3-stage refrigeration chain which takes over after the which takes over after the passive cooling system ~ 50 passive cooling system ~ 50 K. Dilution refrigerator 0.1KK. Dilution refrigerator 0.1K

The bolometric detectors, The bolometric detectors, located behind the horns, located behind the horns, absorb the light and heat up absorb the light and heat up slightly. A thermometer slightly. A thermometer reads the temperature rise reads the temperature rise and converts it to an and converts it to an electrical signal which travels electrical signal which travels down wires connecting the down wires connecting the low- and high-temperature low- and high-temperature ends of the instruments.ends of the instruments.


Sensors and CoolingSensors and Cooling Cryogenic photon detectors offer advantages in Cryogenic photon detectors offer advantages in

terms of terms of

1.1. Higher sensitivity in terms of NEPHigher sensitivity in terms of NEP

2.2. Better energy resolution E / Better energy resolution E / ΔΔE = E = λλ / / ΔλΔλ


System Design IssuesSystem Design Issues

Decision to adopt cryogenic design will be Decision to adopt cryogenic design will be based on trade-off analysis considering based on trade-off analysis considering among others the mass savings, power among others the mass savings, power consumption and reliabilityconsumption and reliability

Total energy balance depends critically on Total energy balance depends critically on the efficiency of the system:the efficiency of the system:

Passively cooled subsystem has positive Passively cooled subsystem has positive energy balance, while actively cooled (eg energy balance, while actively cooled (eg Stirling cooler) has a critical energy Stirling cooler) has a critical energy balancebalance

Choice between passively and actively Choice between passively and actively cooled design depends on operating cooled design depends on operating temperature and even the type of orbit of temperature and even the type of orbit of the satellitethe satellite


System Design IssuesSystem Design Issues Cooler must have heat lift compatible Cooler must have heat lift compatible

with satellite size and power resourceswith satellite size and power resources Low temperature equipment must be Low temperature equipment must be

properly supported, insulated from the properly supported, insulated from the room temperature satellite bus & room temperature satellite bus & protected from solar/earth radiationprotected from solar/earth radiation

Cold parts have to be accessed for Cold parts have to be accessed for wiring and for the optical inputwiring and for the optical input

Ancillary equipment has also to be Ancillary equipment has also to be cooled (heat links, heat switches, filters cooled (heat links, heat switches, filters thermometers)thermometers)

Testability of the system (instrument Testability of the system (instrument performance, environment qualification performance, environment qualification tests) has to be ensuredtests) has to be ensured


System Design IssuesSystem Design Issues

Cooling system must survive vibrations of Cooling system must survive vibrations of launch (compromise between cross-section launch (compromise between cross-section for support and for thermal isolation)for support and for thermal isolation)

Cooler must operate in zero gravity for Cooler must operate in zero gravity for period time ~yearsperiod time ~years

Payload needs to be built from materials Payload needs to be built from materials compatible for both space and cryogenic compatible for both space and cryogenic environmentenvironment

No vibrations or pick-up sensitive elements No vibrations or pick-up sensitive elements Lifetime (MTBF) of equipment should be Lifetime (MTBF) of equipment should be

compatible with and exceed nominal compatible with and exceed nominal mission duration and operational cyclesmission duration and operational cycles


Types of coolersTypes of coolers Passive radiator to deep space 2.73K (~Passive radiator to deep space 2.73K (~σεσεAreaTAreaT44 ) efficient to ) efficient to

100K until parasitic inulation loads100K until parasitic inulation loads Open cycle stored cryogens (Open cycle stored cryogens (work done by liquefier on-groundwork done by liquefier on-ground) )

No energy to radiate but gas to be released – limited lifeNo energy to radiate but gas to be released – limited life Closed cycle mechanical cooler, work done continuously . For Closed cycle mechanical cooler, work done continuously . For

lowest temperatures require multiple stageslowest temperatures require multiple stages


Bolometers for High Bolometers for High EnergiesEnergies Not immediately apparent this Not immediately apparent this

technology would be applicable:technology would be applicable: The total energy deposited by X-The total energy deposited by X-

rays from the sky via focussing rays from the sky via focussing telescopes over 30-40 years of telescopes over 30-40 years of observatories would heat a observatories would heat a teaspoon of water ~1 microKelvinteaspoon of water ~1 microKelvin


X-Ray OpticsX-Ray Optics


X-ray CalorimeterX-ray Calorimeter

Absorber

Thermometer

Cold BathThermal

link

VI(t)

SQUID

Single Single pixel pixel calorimetecalorimeterr


Microcalorimeter ArraysMicrocalorimeter Arrays Development issues:Development issues: Each pixel Each pixel the samethe same thermal link thermal link

to the cold bathto the cold bath(independent of the amount of (independent of the amount of

pixels)pixels) Pixels closely packed together Pixels closely packed together

(efficiency) =>(efficiency) =>(limited space for wiring and (limited space for wiring and

thermal link)thermal link) Small electrical and thermal cross Small electrical and thermal cross

talktalk(do not degrade the energy (do not degrade the energy

resolution)resolution) Fabrication feasibility, Fabrication feasibility,

ruggednessruggedness(thermal cycling)(thermal cycling)

Response to charged particlesResponse to charged particles(need for anti coincidence, dead (need for anti coincidence, dead

times)times)


X-ray CCDX-ray CCD

Essentially the same operation as for Essentially the same operation as for visible band, except read out fast visible band, except read out fast enough to guarantee single photon enough to guarantee single photon countingcounting

Energy absorbed and photoelectron Energy absorbed and photoelectron cascade liberates 1 e/h pair per 3.65eVcascade liberates 1 e/h pair per 3.65eV

ΔΔE E (fwhm)(fwhm) = 2.35 * √(r = 2.35 * √(r²² + +FEFE//3.653.65) ~100eV) ~100eV


XMM-Newton CCDsXMM-Newton CCDs XMM EPIC imager used two XMM EPIC imager used two

different sorts of CCD- different sorts of CCD- conventional CMOS and a pn conventional CMOS and a pn structure with heritage from drift structure with heritage from drift detectorsdetectors

Also CCDs used to readout Also CCDs used to readout dispersed spectrum from grating dispersed spectrum from grating instrument instrument


Simultaneous Imaging and Simultaneous Imaging and SpectroscopySpectroscopy

Tycho Tycho Supernova Supernova remnantremnant


Radiation Radiation DamageDamage

Very low individual photon count Very low individual photon count raterate

Most frames empty and trap sites Most frames empty and trap sites from damage remove charge from damage remove charge during transferduring transfer


Data selection and Data selection and artefactsartefacts

Data rate limited Data rate limited to ~16kbit/secto ~16kbit/sec

Need to select Need to select valid X-ray valid X-ray events, reject events, reject CR events and CR events and ensure correct ensure correct background background local zero local zero estimation estimation


Data selection and Data selection and artefactsartefacts


Light FilterLight Filter

For X-ray CCDs and For X-ray CCDs and bolometers need to ensure bolometers need to ensure that X-rays detected that X-rays detected without the effect of light without the effect of light and IR loading that and IR loading that increases noiseincreases noise

Visible:X-ray ratio for stars Visible:X-ray ratio for stars typically 10typically 1077. .

Aluminised plastic window Aluminised plastic window (<100nm A) must not (<100nm A) must not prevent soft X-ray prevent soft X-ray absorption yet robust to absorption yet robust to launch!launch!

Transmission Aluminised Plastic

0.00E+00

2.00E-01

4.00E-01

6.00E-01

8.00E-01

1.00E+00

0 200 400 600 800 1000 1200

Photon Energy (eV)

Tran

smiss

ion


Gamma Ray detectorsGamma Ray detectors

Historically needed large , thick Historically needed large , thick proportional counters. proportional counters.

Compton effect and pair Compton effect and pair production energy regime?production energy regime?

Compound semiconductors and Compound semiconductors and scintillators – but as yet immature scintillators – but as yet immature technology cf. silicontechnology cf. silicon


Integral SPIIntegral SPI


Integral Imager (IBIS)Integral Imager (IBIS)


Alternate Imaging MethodAlternate Imaging Method IBIS can reconstruct images IBIS can reconstruct images

of powerful events like of powerful events like gamma-ray bursts (GRBs) gamma-ray bursts (GRBs) using the radiation that using the radiation that passes through the side of passes through the side of INTEGRAL's imaging INTEGRAL's imaging telescope. telescope.

IBIS uses two detector layers, IBIS uses two detector layers, the higher energy gamma the higher energy gamma rays can Compton scatter in rays can Compton scatter in first detector layer (called first detector layer (called ISGRI), losing energy, but not ISGRI), losing energy, but not being completely absorbed.being completely absorbed.

The deflected and now less The deflected and now less energetic rays then pass energetic rays then pass through to the layer below through to the layer below where they can be captured where they can be captured and absorbed The blue-and absorbed The blue-shaded part of the image shaded part of the image describes the fully coded describes the fully coded field of view of the field of view of the instrument. instrument.


Gamma Ray focusingGamma Ray focusing Coded mask Coded mask

telescopes have telescopes have only 50% open only 50% open factor, and factor, and detectors must detectors must have frontal area have frontal area equivalent to equivalent to collecting areacollecting area

Large background Large background could be decoupled could be decoupled by focussing by focussing advantage – but advantage – but gamma ray gamma ray focussing is not focussing is not easy.easy.

Bragg-relation2 d sin θB = n λ


Laue LensLaue Lens

Energy bandpasses Energy bandpasses 460 – 522 keV 460 – 522 keV 825 – 910 keV825 – 910 keV

Effective area in Effective area in ~ 1 m~ 1 m22

bandpassesbandpassesField of view Field of view > 30 arc seconds> 30 arc secondsAngular resolution Angular resolution ~ 10 arc seconds~ 10 arc secondsFocal Length Focal Length 400m400m

Rings of Cu and Si crystals for energy bandpass Rings of Cu and Si crystals for energy bandpass around nuclear emission lines ~ tonnes payloadaround nuclear emission lines ~ tonnes payload

Separated telescope and detector spacecraftSeparated telescope and detector spacecraft But detector size only <10cm – much lower But detector size only <10cm – much lower

backgroundbackground


TestingTesting Space-bound scientific instruments are subjected to Space-bound scientific instruments are subjected to

extensive ground testing before launch to ensure successful extensive ground testing before launch to ensure successful launch and on-orbit operation. launch and on-orbit operation.

This is a radical departure from testing terrestrial laboratory This is a radical departure from testing terrestrial laboratory instruments since these instruments typically operate in a instruments since these instruments typically operate in a more benign environment, and are generally accessible for more benign environment, and are generally accessible for repair during their useful life. Among the various tests repair during their useful life. Among the various tests conducted for space environmental testing are thermal, conducted for space environmental testing are thermal, structural (including vibration and acoustic) and structural (including vibration and acoustic) and electromagnetic interference (EMI). electromagnetic interference (EMI).

The test series is intended to validate design, assembly, The test series is intended to validate design, assembly, performance and reliability of flight qualified units. performance and reliability of flight qualified units.

The qualification tests will demonstrate performance The qualification tests will demonstrate performance margins over and above requirements under operating margins over and above requirements under operating environmental conditions. environmental conditions.

Random vibration tests and mechanical shock tests will be Random vibration tests and mechanical shock tests will be performed at 1.5 times the load level specified for performed at 1.5 times the load level specified for acceptance requirements. acceptance requirements.

The random vibration tests simulate launch conditions and The random vibration tests simulate launch conditions and will induce stresses to uncover any potential structural will induce stresses to uncover any potential structural deficiencies that might exist. The mechanical shock tests deficiencies that might exist. The mechanical shock tests will simulate potential impacts incurred as a result of will simulate potential impacts incurred as a result of handling or transport.handling or transport.


Major Design Issues Major Design Issues for Space-Borne for Space-Borne AstronomyAstronomy Mass Mass (= M(= M€)€) Power Power (= large solar arrays = mass)(= large solar arrays = mass) VolumeVolume (= support structure and mass)(= support structure and mass) RadiationRadiation (require shielding = mass)(require shielding = mass) Cosmic ray removalCosmic ray removal (processing = mass)(processing = mass) CalibrationCalibration (on-ground time and in-orbit (on-ground time and in-orbit

efficiency)efficiency) VacuumVacuum (materials, testing time, design effort)(materials, testing time, design effort) ThermalThermal (testing, design, power, )(testing, design, power, ) FiltersFilters (single point failure)(single point failure) EmcEmc (test on-ground with spacecraft ?)(test on-ground with spacecraft ?) Stray lightStray light (Baffles, operations = mass / time)(Baffles, operations = mass / time) PointingPointing (Mechanisms, stability, lifetime)(Mechanisms, stability, lifetime) CompressionCompression (processing=mass, robustness)(processing=mass, robustness) DownlinkDownlink (Bandwidth = power= mass)(Bandwidth = power= mass)


Future Missions – ESA Future Missions – ESA Cosmic Visions Programme Cosmic Visions Programme 2015-20252015-2025 Following proposals from the science Following proposals from the science

community, 6 missions are being community, 6 missions are being studied for a down-selection at the end studied for a down-selection at the end 20092009

2 medium-class missions (2 medium-class missions (€300-€300-400M) 400M) and 1 large mission (and 1 large mission (€600M) will be €600M) will be defined furtherdefined further

Covers range of solar-system, Covers range of solar-system, planetary and astronomy missionsplanetary and astronomy missions


CV M-Class AstronomyCV M-Class Astronomy PLATO – planet finder (transits and PLATO – planet finder (transits and

asteroseismology)asteroseismology) Stable conditions in space for accurate photometryStable conditions in space for accurate photometry Long duration (2yr) high duty cycle (95%) at one field Long duration (2yr) high duty cycle (95%) at one field Low backgroundLow background Euclid Dark Energy/MatterEuclid Dark Energy/Matter Weak lensing signal not subject to systematics of Weak lensing signal not subject to systematics of

atmosphere stable PSFatmosphere stable PSF Wide waveband for Vis/near-IR to cover redshift rangeWide waveband for Vis/near-IR to cover redshift range Simultaneous field spectroscopy to calibrate redshift Simultaneous field spectroscopy to calibrate redshift

samplesample Baryon Acoustic Oscillations in correct redshift range Baryon Acoustic Oscillations in correct redshift range

to measure standard ruler (spectroscopy with low to measure standard ruler (spectroscopy with low background) background)


The instrumental concept of PLATO(model payload)

- ensemble of 28 telescopes with 10cm pupil- each equipped with 4 CCD 3584 x 3584 x 18- all telescopes observe the same field - field of view: 557 deg2

- 26 identical: cadence 30 sec, white light dynamical range mV = 8 - 14

- 2 specific: 1 sec, frame transfer, 2 broadband filtersdynamical range mV = 4 - 8

injection into large Lissajous L2 orbitcontinuous observation, field rotation every 3 months

wide Field-of-view + large collecting area


EuclidEuclid WL survey cover 20,000

deg2 and provide 40 galaxies per amin2 usable for WL with a median redshift z>0.8.

shear systematics variance σsys

2 <10-7

100M galaxies spectroscopic redshift measurement shall be σz < 0.001

space-based astronomy instruments

Documents

use of ccdscern summer

large space telescope

hst orbit

hst operationsthe hst

scattered light

scatteringscattering

visible light

low earth orbit leo