Cube satellite

8/7/2019 Cube satellite

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Cube satellite


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What is a cubesat???

type ofminiaturized satellite for space

research

usually has a volume of exactly one liter(10 cm cube),

weighs no more than one kilogram,

typically uses commercial off-the-s

helf

electronics components.


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List of CubeSats:

Name TypeOrganisatio

nMission

Launch Date

(GMT)Rocket Status

CanX-1 1U UTIAS Technology demonstration2003-06-30,

14:12Rockot Failed - no signal

DTUsat-1 1U DTU Tether research2003-06-30,

14:15Rockot Failed - no signal

AAU

CubeSat1U

Aalborg

UniversityImaging

2003-06-30,

14:15Rockot

Failed - battery

problems.

Deactivated on

22 September

2003

QuakeSat 3UStanford

UniversityEarthquake detection

2003-06-30,

14:15Rockot Active

CUTE-I

(Oscar 55)1U

Tokyo

Institute of

Technology

Amateur radio2003-06-30,

14:15Rockot Active


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Cubesat

XI-IV

(Osca

r 57)

1U

University

of

Tokyo


14:15Rockot Active

Cubesat

XI-V

(Osca

r 58)

1U

University

of

Tokyo


14:15

Kosmos-

3MActive

NCUBE-2 1U ARR/NSC Amateur radio2005-10-27,

14:15

Kosmos-

3MFailed - no signal

UWE-1 1U

University

of

Wrzb

urg

Technology/Communications2005-10-27,

14:15

Kosmos-

3M

Failed - contact

lost on 17

November

2005

GeneSat-1 3U

NASA/Santa

Clara

Univers

ity

Biological research

Technology

demonstration

2006-12-16,

12:00Minotaur

Active, primary

mission

complete

MAST 1U

Tethers

Unlimi

ted

Tether experiments2007-04-17,

06:46Dnepr Active


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PharmaSat 3U

NASA Ames

Resear

ch

Center,

Santa

Clara

Univer

sity,

UTMB

Measured the effect of

antifungal

countermeasures on

yeast strains in

microgravity. ~96 hour

experiment.

2009-05-19,

23:55 UTC

Minotaur

ISuccessful

ITUpSAT1 1U

Istanbul

Techni

cal

Univer

sity

Taking photos and creating

know how for future2009 September Successful

MaSat-1 1U BME

Technological demonstration

Will be the first

Hungarian satellite

2010 (planned) Successful

CHASQUI

- I1U UNI

Technological demonstration

Will be the first Peruvian

satellite

2010 (planned) Successful

COMPASS

-11U FH Aachen

Demonstration of commercial

off-the-shelf components

and taking photos

28-04-08, 03:53

(GMT)PSLV-C9 Successful/Active


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The COMPASS-1 CubeSat was designed and built bystudents from the Aachen University of AppliedSciences in Aachen, Germany.

More than four years were needed to realize this 1kilogram Picosatellite from scratch into a space-readyflight model.

The launch took place in April 2008 from the Indianspace port Sriharikota.

The mission received (and still receives) tremendoussupport by the radio amateur community, which

helped to collect a large amount of data and imagesfrom the satellite.


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System operation


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Control Mode

The control mode is necessary for the spacecraft tofulfill the mission requirements on the spacecraftsattitude, i.e. the pointing accuracy. Therefore it has to

secure a stabilization of the satellite shortly after itsdeployment from the P-POD. This phase is calleddetumbling

Regular Mode

here we will understand

how t

he spacecraft willoperate when it is in orbit and functions as it is

supposed to.


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When the satellite is in view of a user, the user can send a

command to the satellite to take a picture (1). In the next step the

OBC checks if the available power is above a minimum margin

and if so, it commands the payload to capture an image (2). Just

after that, the communication system downloads the taken picture

to the user (3).


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Operator Interaction:

For the operator the above mode is valid also. In addition theoperator is authorized to send commands concerning thehousekeeping and control of the spacecraft and furthermoreadvanced imaging commands

Emergency ModeIf for any reason, crucial components of the spacecraft do notwork in the expected way, and will therefore hinder the spacecraftto go into the regular operation mode the satellite will react withsending emergency signals. The system switches to theemergency mode and sends beacons periodically. In case thatthe problem resolves, the system switches back from emergencymode to regular mode.


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Launch and deployer


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The PSLV-

C9 was the

launch

vehicle. Thelaunch took

place in April

2008 from

the Indianspace port

Sriharikota.


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Deployer

CubeSats are typically launched and deployed from amechanism called a Poly-PicoSatelliteOrbital Deployer (P-POD),also developed and built by Cal Poly. P-PODs are mounted to alaunch vehicle

carry CubeSats into orbit and deploy them once the proper signal

is received from th

e launch

veh

icle. Since CubeSats are all 10x10 cm (regardless of length) they can

all be launched and deployed using a common deploymentsystem.


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For the design of the satellite we have to concentrate onthe requirements from the P-POD supplier. Thegeneral guidelines for a CubeSat are:

CubeSats must not present any danger to neighboring

CubeSats in the P-POD or to primary payloads, All satellites must be powered off during integration

and launch to prevent any electrical or RF interferencewith the launch vehicle and primary payloads

CubeSats must use designated space materialsapproved by NASA,to prevent contamination of otherCubeSats and primary payloads during integration,testing, and launch.


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Orbital Analysis


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Sunlight and Eclipse Times

In space the definition of day and night is completely

different to what we are used to on earth. Times of

direct sunlight and times of total darkness follow eac

hother in very short periods.


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payloads

Optical sensor

The sensor (a camera) will capture

images on request and th

eOB

C willstore them in the memory .

The mass will also be very little .

The sensor sits on t

he front side of t

hecube. The front side is maintained in a

nadir fixed position.


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Ka-band dish

The dish will also be in use only for a shorttime compared to the mission lifetime.

However, while in use it will probably consumea high amount of power. It has to be assured

by the power subsystem that thoserequirements are met.

The principle operation of the Ka-band

transmission is to continuously send thepayload information at a given time andduration.


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Data Format

The data from the camera is an array of bytes,in total 640x480 bytes for an VGA image.

To decrease data transfer rate t

he camerachip provides a solution, that is it can output

QVGA resolution image. This mode decreasespixel rate one half.

The resolution default value is 320x240 and

can be programmable. The digital video port also offer RGB RawData 16 Bit/8 Bit format.


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Attitude Determination and Control

The goal of the Attitude Determination

and Control System (ADCS) is to

stabilize the spacecraft against all

attitude disturbing influences resulting

from the environment in the earth orbit in

order to point the payload towards a

predetermined point on the earthssurface


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AD

CS layout


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The attitude acquisition will be performed by a combination of sunsensors and magnetometer.

The control of the attitude will be done using a magnetorquerwhich will be supported by the gravity gradient generated byradio-wave dipole antennas pointed towards the earth

The acquisition of the current position will be done by an on-board GPS receiver.

By using a simple lightweight GPS receiver the satellite willautonomously be informed about position and attitude without anyfurther intervention from the ground station

. A GPS antenna will be mounted into one of the side faces of thecube.


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ADCS operation mode


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Communication

A communication with the spacecraft takes place overtwo types of links.

The uplinkcarries commands from a ground station tothe spacecraft.

These commands are redirected to the OBC and theneither processed immediately or stored and executedat a specified time.

The downlinkcarries data, which consists of twodifferent types of information.

One are t

he data generated by t

he payload and t

hoseare in this case images.

The other data are information about the spacecraftsvital characteristics, so-called housekeeping data.


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Overview of communication system


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TNC

A TNC (Terminal Node Control) is a microprocessor,

previously also introduced as micro control unit (MCU),

whichhas the following functions for downlink:

- read the data to be transmitted and store them ifnecessary;

- pack the data into protocol format;

- send data to modem.

The other way around it works in the following manner:

- receive commands from modem;

- unpack commands;

- redirect commands to OBC.


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Command and Data Handling

The command and data handling subsystem providesthe main bus for the data exchange between all othersubsystems.

All data exchanged through the bus is in binary format

made up by zeros and ones. The system manages three digital data streams, each

critical to the spacecraft and each with distinctivecharacteristics. Those are:

- data from the payload

- housekeeping data

- Commands


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Hardware

Hardware is everything physical, e.g. the

PCB for the main bus and the electrical

ICs.

Main Bus The main bus assures the dataflow within the

spacecraft. Every subsystem is connected to the bus.

IC bus is used because of its suitable data rate andhigh flexibility.

The controllers of all subsystems have an inbuilt ICbus hardware module, making it easier to write thesoftware.


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OBC

It controls the spacecrafts operations in normal mode.

The OBC is the main data handling system.

It handles the exchange of data between payload, memory andcommunication.

Every command received from ground will be decoded by theOB

C andstored in the memory.

Because of its relatively high energy consumption, the OBC will be shutdown in case of entering the power saving emergency mode.

To prevent the OBC to hang up, an external WDT, watchdog timer, willalso be mounted on the PCB. It forces the MCU to restart and reboot, soit can go on doing its work.

Software The language used for programming will be C/C++ whereas some

routines, which need to be optimized for speed, might be written inAssembler code.


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Power

The spacecraft can only perform as long as it

has power

Functional breakdown of power subsystems


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Power source

Gallium Arsenid cells are better resistant to radiation than the

silicon cells

provide greater EOL (end-of-life) power for a given area.

they are more matured than the Indium Phosphid cells


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Energy Storage This system has to store the required power for eclipse times and

needs to be functional over the entire mission lifetime.

Li-Ion type batteries as they represent the best alternative for a CubeSat satellite


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PowerDistribution, Regulation & Control


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The input from the five with solar cells coveredsides needs to be converted to a stablevoltage level.

The charge controller manages the charging ofthe batteries and supplies the power. Whenthe kill switch is open, current flows throughthe power lines to the power board controllerand the communications system controlleralways.


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Thermal

All elements in the spacecraft have an influence on the thermalhousekeeping by either emitting or absorbing energy or bothrespectively.

Since the CubeSat is very limited in space and mass we cannotexpect to have the components insulated from each other.

Here th

e solution lies in th

e useful configuration of th

e elementsin order to protect vulnerable components with stringenttemperature boundaries.


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Thermal Control Components

The following components and devices are

used extensively in thermal control

subsystems of common satellites.


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Structure Elements and Interfaces

The model is based on the following simplifications:

- the thickness of each plate is 1mm

- the rails are made solid

The main frame consists of the following elements:

- rails

- beams- plates

It accommodates the following parts:

- main bus board

- subsystem boards

- antenna

- other elements (kill switches, etc.)


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Mission Operation

The mission operations really start when

the spacecraft is in orbit.

This section deals with three main issuesconcerning the mission operations

aspect.

Those are the communication

architecture, the ground station and the

user interface.


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Communications Architecture

Frequency band

Modulation Protocol

Bit ErrorRate

Polarization


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Ground station

The ground station is the counterpart to

th

e satellites communications system


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Results

Images of the Earth

The small camera on the bottom side of the satellite can be commandedfrom ground to take color pictures of the earth. Several images havebeen downloaded

The resolution is 640x480 pixels in 8bit resolution.

GPS Receiver

The GPS receiverhas already been activated several times. It initializesand operates without malfunction but fails to establish contact to anyGPS satellites. The problem is traced back to an improper integration ofthe patch antenna at the front panel

Three-Axis Attitude Control

The implementation of an attitude control system is highly complex,partly due to the fact that its proper operation cannot be fully verified onearth. It is therefore disappointing to report that due to a softwareproblem (bug) in the attitude determination software for reading andprocessing the analog sun sensors measurements correctly, the on-board process does not achieve a useful estimate of the satellite's actualattitude


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TechnologyDemonstration

Up to this very date, the satellite is still doing well in space and shows nosign of significant degradation.

The power system is constantly supplying energy to the on-boardselectronics

produces enough excessive power to charge the batteries for the eclipse

times. The communication system is also working just fine.

It is remarkable that the COMPASS-1 spacecraft comprises of a total ofnine (9) microcontrollers (one on EPS, COM, ADCS, and CDHS, andone on each sun sensor), all of whom apparently work very well inspace.

No single-point failure or malfunction appeared that resulted in a

significant degradation of the mission operation. This is particularly a great success, as most of the systems are

engineered with COTS components, which were designed for use interrestrial applications, most dominantly in industrial applications. Thefact that the satellite up to present still operates nominally, verifies thatthe spacecraft is well suitable for low earth orbit missions


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Other Applications Of CubeSats:

Earth remote sensing

Space tether

Biology


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StudSat

StudSat is a student satellite

conceptualized and currently beingdesigned by undergraduate students

across India. It is a picosatellite and first

of its kind in India.


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Organization-Studsat Consortium

Major contractor-ISRO(LSP)

Mission type-Remote sensing technology

Launch date-May 2010 Carrier rocket-PSLV-C15

Launch site-Satish dhawan space centre

Mass-950g

Regime-Sun synchronous circular orbit

Inclination-98


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The satellite itself is not much bigger than acup of tea, though the involved projectaspects (from project management tosystem engineering and qualification

testing) resemble very much any othersatellite mission, however on a lower scale.Through the combination of bright, novelideas of young engineers-to-be and the useof commercial off-the-self components, therealization of cheap and fast responsivepico- and nanosatellite missions becomenot only feasible, but also worthwhile!


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Thank you

Cube satellite

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