My Fourteenth Lesson with Ms. Noor Azura

Date : 2^nd September 2009 (Wednesday)

Time : 11.00am-12.30pm

Place : DKG 3/9, UUM

Telecommunication to me is quite a strange thing. May be I rarely take the advantage on it. But today class exposes me to many new components in telecommunication. However, I think the one I used the most frequently is Wi-Fi.

Satellite is one among the new advanced technology device. RazakSAT is a Malaysian satellite carrying a high-resolution camera. It was launched into low earth orbit by a Falcon 1 rocket on July 12, 2009. It was placed into a unique near-equatorial orbit that presents many imaging opportunities for the equatorial region.

MACSAT (Medium-sized Aperture Camera Satellite) development project is a joint development program between Astronautic Technology (M) Sdn. Bhd. of Malaysia and Satrec Initiative, which started from end of 2001 and aimed to complete the development by the end of 2003. MACSAT has now been renamed RazakSAT.

The objectives of the project are to provide high-resolution images for Malaysia and build Malaysian space technology capabilities through ATSB^®. In order to meet the technology objective, a cost-effective high resolution imaging system for Earth observation specifically for a small satellite less than 200 kg was implemented. RazakSAT carries the Medium-sized Aperture Camera (MAC) that will provide 2.5m resolution panchromatic and 5.0m resolution multi-spectral images. This project involves the design, development, launch and operations of the satellite.

The RazakSAT satellite is planned to be launched near in the future on a USA launcher Falcon 1 owned and operated by the company Space Exploration Technologies (SpaceX). It will be a dedicated launch from kwajalein in the Republic of Marshall Islands which is situated very close to the equator to give the best orbital injection for RazakSAT, i.e. near equatorial orbit (NEqO). RazakSAT®s images would be applied to forestry, fishery, migration and other areas that will benefit the nation.

It carries an electro-optical payload, a Medium-sized Aperture Camera (MAC) a pushbroom camera with 5 linear detectors (1 panchromatic, 4 multi-spectral). The RazakSAT satellite will be operated through its ground segment in Malaysia, consisting of a Mission Control Station (MCS) and Image Receiving and Processing Station (IRPS). ATSB's engineers are operators at the MCS and they will execute the mission plan, command generation and telemetry receiving, archiving and analysis.

ATSB is also involved in Sg Lang Ground Station implementation project committee. ATSB has assisted in development of the system specification to support RazakSAT Mission Control Station (MCS) and Image Receiving and Processing Station (IRPS).

The MACSAT mission is to develop and validate technologies for a Near Equatorial Orbit (NEO) remote sensing mini-satellite system to acquire medium high resolution images. Due to its orbital and coverage characteristics, Malaysia and other countires in Equatorial region can have large benefit from NEO satellite operation. From the low Earth circular orbit of 685 km altitude with 9 degrees of inclination, geographical information and environment change over equatorial region can also be regularly observed with a unique revisit characteristic.

Nation	Malaysia
Type / Application	Earth observation
Contractors	Astronautic Technology (M) Sdn. Bhd, Satrec Initiative
Equipment	MAC
Configuration	SI-200 bus
Mass	200 kg
Orbit	675 x 695 km, 9°

Subsystems	Specifications
Altitude	685 km
Inclination	9 °
Payload (MAC)	GSD : 2.5 m (PAN), 5 m (MS) Swathwidth : 20 km @ 685 km
Attitude Determination & Control Subsystem (ADCS)	Three-axis stabilization based on four (reaction wheels) Pointing Accuracy : < style="">
Electrical Power Subsystem (EPS)	GaAs/Ge solar cells on honeycomb substrate NiCd batteries (18 Ahr) Peak Power Tracking (PPT) & constant current control Solar Power : >300 W @ EOL
Command & Data Handling Subsystem (C&DH)	Two on-board computers Telemetry and command interface modules Analog Telemetry channels : up to 90 Digital Telemetry channels : up to 120
Telecommunication Subsystem (TS)	9,600 bit/s / 1,200 bit/s S-brand TT&C uplink 38.4 kbs / 9,600 bit/s / 1,200 bit/s S-brand TT&C downlink
Payload Data Management	32 Gbit On-board solid-state memory 30 Mbit/s X band payload data downlink
Structure & Thermal	Ø1,200 x 1,200 mm Hexagonal shape Mass : 180 kg Modular structure Passive & Active thermal control
Mission Lifetime	> 3 Years

遗留

2009年9月2日

二零零九年的八月，就这样向我挥手说再见。

已经几天没有写文章了，虽然有许多话是想说的。

一个月回家两次，心情，确实是有点落差。

一直觉得自己很累，但是，我不知道为什么自己那么累。

星期五有统计学的考试，还没有准备好。

这个月得完成几份任务，却还没有动工。

我的脑袋，就是一直当机。

有点后悔今天说了一些不该告诉别人的话。

望着课本整晚，一段都读不完。

数学，曾经是我引以为傲的科目。

中六的洗礼，使我对自己完全失去信心。

我该怪谁？是自私的你吗？

感冒的病毒，在这时候悄悄盯上我，似乎有乘人之危之嫌。

我告诉自己，我一定要克服这次的难关。

朋友，我们一起努力，好吗？

只是，我害怕我将自己遗留在后头… …

二零零九年的九月，我告诉自己，我要活得更快乐！

My Thirteenth Lesson with Ms. Noor Azura

Date : 30th August 2009 (Sunday)

Time : 11.00am-12.30pm

Place : DKG 3/9, UUM

I am absent from this class. This is the very first time I skip class and go back to Penang. No choice, my friend get marry. I need to attend. Anyway, it’s a meaningful journey because I get the opportunity to meet with my dearest brother and sister in church.

Brother Jia Yang and Sister Chia Li, may God Father blesses your marriage with blossom of grace and happiness.

And, I would like to say sorry to my lecturer that I skip the class. This post is to memorize my experience. Nothing more than this.

My Twelfth Lesson with Ms. Noor Azura

Date : 26th August 2009 (Wednesday)

Time : 11.00am-12.30pm

Place : DKG 3/9, UUM

Oh no, the class is getting difficult and difficult. I’m exposed to so many new knowledge that I never knew before. It is a bit difficult for me, indeed. Luckily, my lecturer does explain it in simple yet easy for me to understand.

Today, I learn about data transmission. One of the sub topics is wired transmission media. There are three types, as I will explain them one by one.

Coaxial Cable

A coaxial cable is one that consists of two conductors that share a common axis. The inner conductor is typically a straight wire, either solid or stranded and the outer conductor is typically a shield that might be braided or a foil.

Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Coaxial cables exist because we can't run open-wire line near metallic objects (such as ducting) or bury it. We trade signal loss for convenience and flexibility. Coaxial cable consists of an insulated center conductor which is covered with a shield. The signal is carried between the cable shield and the center conductor. This arrangement give quite good shielding against noise from outside cable, keeps the signal well inside the cable and keeps cable characteristics stable.

The primary advantage of coaxial cable compared to twisted pair is the braided metal shield is very good at blocking electromagnetic signals from entering the cable and producing noise. And has also been used for long-distance telephone transmission, as the cabling within a local area network, and as a connector between a computer terminal and a mainframe computer.

Twisted Pairs

The twisting of wires reduces crosstalk because when electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Thus, the two magnetic fields cancel each other out. They also cancel out any outside magnetic fields. Twisting the wires can enhance this cancellation effect.

Twisted pair wire is placed inside a thin metallic shielding, similar to aluminum foil, and is then enclosed in an outer plastic casing. The shielding provides further electrical isolation of the signal-carrying pair of wires. Shielded twisted pair wires are less susceptible to electrical interference caused by nearby equipment or wires and, in turn, are less likely to cause interference themselves. Because it is electrically "cleaner," shielded twisted pair wire can carry data at a faster speed than unshielded twisted pair wire can

The disadvantage of shielded twisted pair wire is that it is physically larger and more expensive than twisted pair wire, and it is more difficult to connect to a terminating block.

Fiber Optic

A fiber optic cable transmits a signal using a wave of light, while copper wires transmit a signal using an electric current. (Palais, 1998). A typical fiber optic wire consists of a plastic sheath surrounding a glass tube. Inside the tube is a tiny core in which the light waves travel. Separating the core and the tube is a cladding that prevents the light waves from escaping. One wire design has a core diameter of 125 microns and a sheath diameter of 2.5 millimeters.

The wire’s small size provides an advantage over copper wires. Fiber optic cables weigh less than copper wires, which makes installation easier and allows the wires to be placed in smaller areas. (Palais, 1998). Although the wires are made of glass, they are extremely flexible therefore easing the problems involved with installation.

Although the core of a fiber optic cable is very small, large amounts of information can be transported at one time. In copper wires, only one signal can be sent across the wire at a single time but in a fiber optic cable, many light waves can be sent at once. This allows the wires to be more cost effective. Silicon oxide is the material used to make fiber optic wires. This material is less expensive than the copper used in coaxial cables making fiber optics less expensive to make. Also, fewer fiber optic cables are needed for mass communication.

Fiber optic cables also have disadvantages. Because they use light to transmit information they are incompatible with the old copper wires. This creates a problem because telephone companies cannot use the wire system that is already present. They must build a new system using fiber optics. Fiber optic cables are also very difficult to connect. In order to connect the wires, the glass tube must be broken and then melted together with the new wire. With copper wires, you simply cut away the plastic coating and join the wires. This also creates a problem when repairing fiber optic wires. A copper wire is much easier to repair than a fiber optic wire. Special tools and highly trained professionals are needed to repair the damaged fiber wires.

In a fiber optic cable, many light waves of information are transmitted at one time. Sometimes so much information comes in that the cable becomes jammed and the information slows down. This cannot occur in copper wires because only one signal is generated at a time. Often, at points in the cable where traffic is heavy, bottlenecks occur. A bottleneck is when so much information tries to squeeze through but is lost.

The comparison between among twisted pair, coaxial cable and optical fiber for the bandwidth and the attenuation

Twisted pair	Coaxial	Optical Fiber
The bandwidth is about 1 MHz. The attenuation is about 0.7 dB/km @ 1 kHz.	The bandwidth is about 500 MHz. The attenuation is about 7 dB/km @ 10 MHz.	The bandwidth is about 184 THz. The attenuation is about 0.2 to 0.5 dB/km.
Low attenuation from 0 to 1 MHz. The bandwidth in the low attenuation range is 1 MHz.	Low attenuation from 0 to 100 MHz. The bandwidth in the low attenuation range is 100 MHz.	Low attenuation from 800 to 1700 nm. The bandwidth in this is about 200 THz.