An Ultraviolet imager on a CubeSat for astronomical ... · PDF fileAn Ultraviolet imager on a CubeSat for astronomical transient studies Joice Mathew Indian Institute of Astrophysics,

An Ultraviolet imager on a CubeSat for

astronomical transient studies

Joice Mathew

Indian Institute of Astrophysics, Bangalore

iCubeSat 2016, Oxford

Time Domain Astronomy

• In most electromagnetic bands the static sky has been imaged to interesting depths.

• Technology is now enabling efficient monitoring of large swaths of sky.

• Some of the most exciting frontiers, particularly those related to cosmic explosions, require wide-field imaging surveys.

Transient Surveys

• Large Synoptic Survey Telescope (LSST) - Optical

• Square Kilometer Array (SKA) - Radio

• Laser Interferometer Gravitational-Wave Observatory (LIGO) - Gravitational

• Swift, Fremi - High Energy

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Wide Field UV Imager

• There has been little time-domain study and exploration in the ultraviolet (UV: 100-350nm)

• Large brightness variation of the objects with High temperature (~10^4 K) can be studied in UV.

• Several major questions in astronomy can be addressed even by a modest UV time-domain explorer.

• Revolutionize our understanding of the transient UV universe

• Will resolve key questions regarding cosmic explosions and explore the dynamics around super massive black holes

• Rapid alerts and follow up

• Small scale UV payloads can play an important role. (Noah Brosh et al. 2014)


Atmospheric Window


Science Objectives

• Transients and variability (Cao et al. 2011)

- High energy transients emits in UV

- Less sky back ground in NUV domain

• Transient events such as

- SNe, TDE, GRB, AGN variability etc.

• Gravitational waves and high-energy counterparts

- fine spatial localization by observing in UV

• Detection of asteroids and near Earth objects (NEOs)

and studies of their properties

• Studies of variable stars

- UV amplitudes which are larger than their

visible light variations

- Eclipsing Binaries, RR Lyr Stars, Cataclysmic

Variables


Fig: NUV sky map

Fig: Transient events in UV (Sagiv et al. 2014)

Massive Star Death: Super Novae

• Explosion that takes place at the end of a star's life cycle

• Shock break out and shock cooling

• Early UV emissions


Nakar & Sari 2010SNe Explosion

Tidal Disruption Events (TDE)


• When a star on the orbit around a massive black hole makes a close approach

• Peak of energy distribution in UV

TDE Event Gezari et al. 2012

Gamma Ray Burst (GRB)

• The brightest electromagnetic events known to occur in the universe

• Bursts can last from ten milliseconds to several hours


GRB Burst Nakar & Piran 2003

CubeSat and Time Domain

Astronomy

• CubeSat based a payload can play vital role

• More launch opportunities

• Cost effective

• Small aperture and wide field of view

Challenges

• Aperture

• Deployables

• Pointing

• Limited downlink data rates

• Limited power


Instrument Design Considerations

• Observation in NUV wavelength band: 280-340 nm

• Imager: wide field imaging

• Field of view: spatial resolution, Detector size

• CubeSat payload

• Incorporate mechanical constraints (weight & dimension)

• Availability of components (Detector & Optics)

• Space qualification requirements

• Time bound development

• Low cost

iCubeSat 2016, Oxford25-05-2016 10

Instrument Specifications

Instrument UV Wide Field Imager

Telescope Lens System

Field of View 10.8 ° (~ 100 degree square)

Aperture 70 mm

Focal length 209.08 mm

Detector MCP based UV detector

Sensor format 40 mm MCP Dia.

Resolution 30”

Band of operation 280-340 nm

Weight ~ 4 kg

Dimension 180 mm x 160 x 90mm (LxWxH)

Power < 5 W

Limiting Magnitude 20 with S/N: 3

Spacecraft 6U CubeSat in LEO


Instrument Overview

UV OpticsUV

Detector

Electro-

nics

module

Power

Supply

S

A

T

E

L

L

I

T

E

I

N

T

E

R

F

A

C

E

UV

Detector

UV

Detector


Optics Design Considerations

• Dimensional constraints

• Minimum no. of components

• Weight of the optics

• Length of the instrument

• Wide FOV

• Sensitivity and Resolution

• Spherical components

• Low manufacturing time, cost effective


Optical Layout


Optics Properties

• Aperture: 70 mm

• Focal Length: 209.08 mm

• FOV: 10.8° circular field

• Resolution: 30”

• Materials

Lenses: Fused Silica and CaF2

Mount: Invar

• UV Band pass filter

Band: 280 – 340 nm

Transmission: 80 %


Encircled Energy


PSF


UV Detector


• Normal CCD/CMOS have less sensitivity in UV

• Micro Channel Plate detector

- has better QE in UV band

- Low noise

- Less data storage requirement in photon counting mode

MCP based UV Detector


MCP 340

MCP Operation

MCP detector block diagram

Photon counting imaging


Electronics Module

CMOS PCB FPGA

MemoryVoltage

Regulator

PCB

Sensor i/f

Image Processing Card

Data Bus i/f


MCP HVPS

photons

Electronics

Image Sensor PCB

Voltage Regulator PCB

Image Processing PCB

- FPGA (Spartan 6)

• Centroiding

• Memory Interface

• On board compression

• Data bus interface (RS 422/ 1553)


6U CubeSat


Credit: Pumpkins 6U SUPERNOVA

6U Configuration


UV Imager in 6U CubeSat


Operation

• Low-Earth Orbit mission

• Observations while in Earth shadow

• Communication and solar panel charging while on

day side

• Return to same fields in every 100 min for 2 months

and then switch field

• Data downlink ~ 3-4 times per day (depends on

downlink availability)


Mission Comparison


Mission parameter GALEX UVIT CUWI

A (cm^2) 1950 880 39

Detector size 4 K×4 K 512×512 40 mm Dia.

Pixel scale (arcsec/pix) 1.5 3 30’’ resolution

FOV (deg^2) 1.1 0.7 100

FOV degree) 1.2 0.5 10.8

UV bandpass (nm) 40 50 60

Λ (nm) 151.6 151.4 300

Effective Area


Field of View


Status

• Opto - mechanical components are under procurement

• Realized the MCP based photon counting detector

• Implemented an FPGA based electronic readout and on

board data processing

• Launch with ISRO PSLV by 2018


Conclusion

• UV wide field imager can play a vital role in the field of time domain astronomy

• CubeSat based UV imager is designed, which can be fit in a

6 U CubeSat for a LEO (Low Earth Orbit) mission

• The transient survey with the proposed imager will have an overlap in time with other ongoing and planned astronomical facilities for transient studies, such as LSST, LIGO etc.


Thank You


Documents

An Ultraviolet imager on a CubeSat for astronomical ... · PDF fileAn Ultraviolet imager on a CubeSat for astronomical transient studies Joice Mathew Indian Institute of Astrophysics,