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==Avionics system==
==Avionics system==


==通信系==
==Communication system==
DESPATCHのメインミッションである共同受信ミッションを成功させるためには、なるべく多くのアマチュア無線家の受信協力が必要となる。
To conduct the experiment on cooperative data reconstruction,
そこで、送信電波の周波数としては、アマチュア衛星で最も一般的に使用され、より局数の多い430MHz帯を採用している。
we will need the cooperation of as many ham operators as possible.
For this reason, the 430 MHz band was selected, being the most commonly used frequency in amateur radio satellite communications.


変調方式としては最もシンプルな方式であるCW(搬送波のオン/オフで、1ビットを表現)を採用し、
CW was selected as the modulation mode — one of the simplest modulations each bit (1/0) represented as existence or non-existence of the carrier signal.
複雑な変調方式の電波を低出力で送るのではなく、できる限りシンプルな変調方式の電波をできる限り高出力で送ることによって受信の確実性を高めるという設計としている。
Transmitting high-power signals modulated in this simple manner is expected to raise the probability of the signals being received.
また、シンプルな変調方式を採用する副次的な効果として、なるべく多くの方に共同受信に参加していただけるようにするだけでなく、受信の際に各局で独自に工夫を凝らすことが比較的容易であるため、地上局の多様性を利用した異種冗長化を図れると考えている。
In addition, simple modulation will make it easier for ham operators to add their own “hacks” to their hardware — which should result in a heterogeneous redundant system for reception.


このような設計にしたがって、以下に示す諸元の送信機を宇宙機に搭載する。
The spacecraft is equipped with a transmitter specified in the following table.
この送信機は、[http://www.nishimusen.co.jp/eisei2013/eisei2013.htm 株式会社西無線研究所]によって設計・開発されたものである。
This transmitter was designed and developed by [http://www.nishimusen.co.jp/eisei2013/eisei2013.htm Nishi Musen Kenkyuusho co, Ltd].


{|class="wikitable" style="width:50%"  
{|class="wikitable" style="width:50%"  
|+DESPATCH搭載の送信機諸元
|+Specifications of the transmitter
|送信機出力 || 7 W
|RF power || 7W
|-
|-
|送信周波数 || 437.325 MHz
|Transmission frequency || 437.325MHz
|-
|-
|変調方式 || CW
|Modulation mode|| CW
|-
|-
|電源電圧 || +7V DC
|Power supply voltage || +7V DC
|-
|-
|消費電力 || 最大 24.5 W
|Power consumption || Max. 24.5 W
|-
|-
|周波数安定度 || 最大 ±0.3ppm (±130 Hz)  
|Carrier frequency stability || Max. ±0.3ppm (±130 Hz)  
|}
|}


この送信機は宇宙機搭載のタイマーICと計算機によって駆動され、およそ7Wの送信電力がモノポールアンテナから放射される。
This transmitter is controlled by an on-board computer and an integrated-circuit timer.
シミュレーションによって求めたアンテナパターンを図に示す。
Signals are transmitted using a monopole antenna.
なお、このアンテナは、造形部の中心に配置されたGFRP製の棒状部材に取り付けられており、
The following figures show the simulated antenna patterns.
棒状部材は造形部の先端と通信機等が格納されているアルミニウム製の容器とを接続している。
This antenna is attached to a support rod which is located at the center of the helix part.


<gallery caption="DESPATCHのアンテナパターンおよびそれを規定する座標系" widths="400px" heights="140px" perrow="2">
<gallery caption="Simulated antenna pattern of DESPATCH" widths="400px" heights="140px" perrow="2">
File:AntennaGain_1.jpg
File:AntennaGain_1.jpg
File:AntennaGain_2.jpg
File:AntennaGain_2.jpg
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</gallery>
</gallery>


参考として、この送信系とARTSATプロジェクトの地上局での回線計算の結果を、以下のファイルに記載した。
The result of the link calculation at our radio station can be downloaded here:
*[http://artsat.jp/wp-content/uploads/2014/11/Despatch_LinkMargin_ver1.0.xls ARTSAT地上局における回線計算 ver1.0]
*[http://artsat.jp/wp-content/uploads/2014/11/Despatch_LinkMargin_ver1.0.xls Link margin calculation ver1.1] (.xls)


なお、このCW送信機によって送信するデータの具体的な形式については、以下のページを参照されたい。
If you want to know the format of the data which is sent to Earth by this transmitter, please see the following page.
*[[共同受信ミッション|共同受信ミッションの詳細]]
*[[共同受信ミッション|共同受信ミッションの詳細]]



Revision as of 01:26, 19 November 2014

DESPATCH flight model

"DESPATCH" (DEep SPace Amateur Troubadour’s CHallenge) is the second spacecraft in the ARTSAT series. This spacecraft will be launched into an Earth escape trajectory November 2014, along with the Hayabusa-2 asteroid probe. In this page, DESPATCH design, subsystems, and trajectory are detailed.

As a main mission of DESPATCH, we attempt to collect signals from the spacecraft received not only at our own radio station in Tokyo, but at many ham radio stations around the world to reconstruct them back into the original data from the spacecraft. In the following page, the details of the experiment and how to join it are explained.


ARTSAT project

The “ARTSAT: Art and Satellite Project” utilizes a satellite orbiting Earth as a “medium that connects everyday life to the space.” In the course of the project, a variety of interactive works of media art and other artworks are being created. The project is carried out in a collaborative effort around a core team of over 70 members from Tama Art University and The University of Tokyo. The latter team designs and develops satellites and spacecrafts for artistic missions, while the team from Tama Art University is in charge of producing works based on data from the satellite, operating a ground station, and distributing data.

ARTSAT2: DESPATCH

A full-scale prototype (engineering model) of DESPATCH

"ARTSAT2: DESPATCH" is the second mission of the ARTSAT project. This spacecraft, 50x50x45 cm in size with a mass of 32 kg has a helix-shaped segment making it a beautiful sculpture. DESPATCH will be launched into an Earth escape trajectory at November 30, 2014 13:24:48, JST (UTC+9).

Missions

DESPATCH has both artistic and technical missions, as described below.

  • Artistic missions:
    • To create a "deep-space sculpture” by launching the spacecraft into an Earth escape trajectory
    • To create “generative poetry" in the deep space and transmit the poetry from the spacecraft for reception on Earth
  • Technical missions:
    • To experiment with the possibilities of receiving very weak signals using a "cooperative diversity communication" approach, in which fragmented transmissions sent from the spacecraft are received around the world, gathered, and reconstructed
    • To test the use of 3D-printed parts for spacecraft


One of the artistic missions, ”generative poetry,” is a broadcast of sentences in English. They are automatically generated by software running on the spacecraft’s on-board computer (OBC). The poetry generator is “seeded” using sensor readings such as temperature, angular velocity of the spacecraft, etc. For details of the "generative poetry" and "cooperative diversity communication," please see the following page.

Features

To complete these missions, DESPATCH will be operating under three unusual parameters:

  • The spacecraft will transmit the signals for only a week until it reaches a distance of 2.5 million km from Earth
  • It is battery-powered (rather than solar-powered) enabling a highly flexible design
  • No uplink command will be sent to the spacecraft — the unit being designed to operate autonomously

Structure and Design

Appearance design

Structure and components layout

Structure/Components layout of DESPATCH
Six-view drawing of DESPATCH


Avionics system

Communication system

To conduct the experiment on cooperative data reconstruction, we will need the cooperation of as many ham operators as possible. For this reason, the 430 MHz band was selected, being the most commonly used frequency in amateur radio satellite communications.

CW was selected as the modulation mode — one of the simplest modulations each bit (1/0) represented as existence or non-existence of the carrier signal. Transmitting high-power signals modulated in this simple manner is expected to raise the probability of the signals being received. In addition, simple modulation will make it easier for ham operators to add their own “hacks” to their hardware — which should result in a heterogeneous redundant system for reception.

The spacecraft is equipped with a transmitter specified in the following table. This transmitter was designed and developed by Nishi Musen Kenkyuusho co, Ltd.

Specifications of the transmitter
RF power 7W
Transmission frequency 437.325MHz
Modulation mode CW
Power supply voltage +7V DC
Power consumption Max. 24.5 W
Carrier frequency stability Max. ±0.3ppm (±130 Hz)

This transmitter is controlled by an on-board computer and an integrated-circuit timer. Signals are transmitted using a monopole antenna. The following figures show the simulated antenna patterns. This antenna is attached to a support rod which is located at the center of the helix part.

The result of the link calculation at our radio station can be downloaded here:

If you want to know the format of the data which is sent to Earth by this transmitter, please see the following page.

投入軌道

DESPATCHは地球脱出軌道に投入され、ちょうど地球の横を並走するような人工小惑星となる。 その軌道は下図に示すとおりであり、打ち上げからおよそ1年ごとに地球に最接近する。 なお、図に示した緑色の軌道は、DESPATCHが相乗りする小惑星探査機はやぶさ2の目標天体(小惑星1999JU3)の軌道である。

DESPATCHの軌道
DESPATCHと地球との距離の推移


地上から観測するとき、DESPATCHは他の惑星と同様に数時間かけてゆっくりと天球上を移動する。 以下のウェブページにて、地上の任意の地点からDESPATCHがみえる時間と方角を予測することができる。

リンク


連絡先

info@artsat.jp