Cooperative Data Reconstruction: Difference between revisions

From Despatch EN
Jump to navigation Jump to search
 
(129 intermediate revisions by 2 users not shown)
Line 1: Line 1:
[[File:CooperativeDiversityComm.png|400px|right|thumb|A schematic drawing of cooperative diversity communication]]
[[File:CooperativeDiversityComm.png|400px|right|thumb|A schematic drawing of cooperative diversity communication]]


As a main mission of DESPATCH, we are conducting an experiment in cooperative diversity communication.  
One important mission for DESPATCH is an experiment in what we call "cooperative diversity communication."
In the experiment, 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  
In this experiment, we attempt to collect signals from the spacecraft received not only at our own ground station in Tokyo, but also at many ham radio stations around the world, in order to reconstruct the original data from the spacecraft.  
to reconstruct them back into the original data from the spacecraft.  
In this page, the details of the experiment and how to join it are explained.
In this page, the details of the experiment and how to join it are explained.


Line 9: Line 8:
We are hereby providing a rare opportunity to receive radio signals transmitted by a spacecraft in deep space, and ask for your cooperation in this project.  
We are hereby providing a rare opportunity to receive radio signals transmitted by a spacecraft in deep space, and ask for your cooperation in this project.  


DESPATCH missions, subsystems, and trajectory are detailed in the Main Page.
DESPATCH design, subsystems, and trajectory are detailed in the Main Page.
*[[Main_Page|DESPATCH missions, subsystems, and trajectory]]
*[[Main_Page|DESPATCH design, subsystems, and trajectory]]




==Mission overview==
==Mission Overview==
[[File:DespatchFm_4.jpg|250px|right|thumb|DESPATCH flight model]]
[[File:DespatchFm_4.jpg|250px|right|thumb|DESPATCH flight model]]


"ARTSAT2: DESPATCH" is the second mission of the ARTSAT project.  
"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.
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) and moves away from Earth soon after launch.  
DESPATCH will be launched into an Earth escape trajectory at December 3, 2014 13:22:04, JST (UTC+9) and moves away from Earth soon after launch.  
The simulation shows that it reaches lunar distance (385,000 km) from Earth within 24 hours of separation from the launcher.
The simulation shows that it reaches lunar distance (385,000 km) from Earth within 24 hours of separation from the launcher.


The spacecraft, carrying a CW beacon in the 435 MHz band, will transmit the "generative poetry" created in deep space for only a week until it reaches a distance of 2.5 million km from Earth.  
The spacecraft, carrying a CW beacon in the 430MHz band, will transmit "generative poetry" created in deep space for only a week until it reaches a distance of 3 million km from Earth.  
However, the signals from DESPATCH are very weak and will be fading, because the spacecraft has no attitude control system and uses only a low-directivity antenna.  
The signals from DESPATCH are very weak and will be fading, because the spacecraft has no attitude control system and uses only a low-directivity antenna.  


The ARTSAT project asks that you attempt reception of these very weak signals at your radio stations.  
The ARTSAT project asks that you attempt to receive these very weak signals at your radio stations. DESPATCH's transmissions, decoded by volunteer ham-radio operators throughout the world, will be forwarded to our data server via the Internet, for reconstruction of the original poetry from the spacecraft.  
As a main mission of DESPATCH, we are conducting an experiment in cooperative diversity communication.
With this experiment, we would like to verify the practical effectiveness of cooperative diversity communication.
In the experiment, we hope 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.
The design is to have transmissions decoded by volunteer ham-radio operators throughout the world forwarded to our data server via the Internet for reconstruction back into the original poetry from the spacecraft.  
With this experiment (schematized in the Figure), we would like to verify the practical effectiveness of cooperative diversity communication.


==共同受信ミッションの実施期間==
==Mission Planning==
DESPATCHは2014年11月30日 13時24分48秒(日本標準時)にJAXA H-ⅡAロケット26号機により打ち上げられ、この打ち上げからおよそ2時間後に軌道投入がなされる予定である。
DESPATCH will be launched at
*[http://www.jaxa.jp/press/2014/09/20140930_h2af26_j.html H-ⅡAロケット26号機の打ち上げプレスリリース]
<span style="color:red">December 3, 2014 13:22:04, JST (UTC+9)</span>
along with the Hayabusa-2 asteroid probe, and injected into an earth escape trajectory about 2 hours later.
*[http://global.jaxa.jp/press/2014/11/20141130_h2af26.html Launch Postponement of Hayabusa2 by H-IIA Launch Vehicle No. 26]


DESPATCHが電波を送信するのは、この軌道投入直後から一週間のみである。
The spacecraft, carrying a CW beacon in the 430MHz band, will transmit the signals for only a week until it reaches a distance of 3 million km from Earth.
この一週間というミッション期間を、下の表のようにDESPATCHと地球との距離応じて3つのフェーズに分割し、「ハウスキーピングデータ」「宇宙生成詩」「アナログ温度情報(ビーコン)」という3種類のデータを地上で受信する。
We are hoping to receive three types of data — the generative poetry, housekeeping data, and a simple beacon.
共同受信実験の対象はフェーズ2の「宇宙生成詩」であるが、フェーズ1またはフェーズ3における受信協力・受信報告も歓迎する。
Accordingly, we have divided the 1 week mission period into three phases based on the spacecraft's distance from Earth, as shown in the table below.
In each of these phases, a different type of data will be transmitted by the spacecraft.


{|class="wikitable" style="width:50%"  
{|class="wikitable" style="width:50%"  
|+距離(フェーズ)と受信データの対応表
|+Types of data in each phase
!フェーズ !! 地球からの距離 !!地上で受信されるデータ
!Phase !! Distance from Earth !!Type of data received on Earth
|-
|-
|フェーズ1 || ~17万km || モールス信号によるハウスキーピングデータ
|Phase1 || ~ 180,000 km || Housekeeping data in Morse code
|-
|-
|フェーズ2 || 17万~160万km || 独自符号による宇宙生成詩
|Phase2 || 180,000 ~ 1,860,000 km || Generative poetry in Baudot code
|-
|-
|フェーズ3 || 160万km~ || アナログ温度情報(ビーコン)
|Phase3 || 1,860,000 km ~ || Spacecraft temperature in a simple beacon
|}
|}


The phase changes are shown in the figure below — the colors representing each phase.
The visibility times in five cities — Tokyo, Sydney, Berlin, Boston, and Buenos Aires — are shown in the figure as black bars.
Please note that the times in the figure are expressed in Coordinated Universal Time (UTC).
*[http://api.artsat.jp/pass/ Predict more accurate visibility period at your station]


下の図には、この3つのフェーズの期間を色で、世界の各地域における可視時間を黒い横棒で示している。
We conduct the experiment for the cooperative diversity communication only in the phase 2,
共同受信ミッションの実施期間であるフェーズ2は、日本における1回目の可視時間の後半から5回目の可視時間の最初までの約99時間である。
but we also appreciate your help and your reception reports in phase 1 or phase 3.
*[http://api.artsat.jp/pass/ より正確な可視時間の予測を行う(DESPATCHのトラッキングページ)]
Phase 2 runs for almost 100 hours as shown in the figure.  


[[File:VisiblityPeriods.png|600px|thumb|left|ミッションのフェーズと世界の各地域での可視時間]]
[[File:Despatch_PhaseAndPass.png|600px|thumb|left|Visibility times in five cities and three mission-phases]]
[[File:Distance7day.png|300px|thumb|none|DESPATCHの到達距離]]
[[File:Distance7day.png|300px|thumb|none|Transition in distance from Earth]]


==受信データ==
==Transmission Cycle==
DESPATCHには送信出力7W、送信周波数430MHz帯の送信機が搭載されており、地上で受信されるデータはすべてこの送信機によって送信されたものである。
To prevent overheating, the transmission is halted when the transmitter temperature is too high.
この送信機のアンテナにはモノポールアンテナを用いている。
The operation revealed that the transmitter repeats 50 minutes resting and 20 minutes sending, in phase 2 and phase3.
*[[メインページ#通信系|通信系の主要諸元]]


前述の通り、DESPATCHのミッション期間は地球との距離に応じて3つのフェーズに分割され、各フェーズで異なるデータが送信される。
The file below lists up the time when the transmission restarts.
以降では、この3種類のデータを地上で受信する目的とそのフォーマットについて説明する。
DESPATCH transmits CW for 20 minutes from the time listed up.


===ハウスキーピングデータ(モールス信号)===
*[https://drive.google.com/open?id=1_GuGQ96EHEEaZIl43IxujWdaMR5dRjnWMWvzARzKIP4&authuser=0 List of the time when the transmission restarts ver3.0](.xls)
フェーズ1では、モールス信号によるハウスキーピングデータを地上で受信し、宇宙機の健全性の確認を行う。
なお、このモールス信号の速度は6WPMである。


ハウスキーピングデータの送信はAS0, AS1, AS2, AS3という4つのセンテンスの繰り返しであり、各センテンスの間には10秒間のインターバル(電波を送信しない期間)が設けられている。
==Telemetry Format==
ハウスキーピングデータのフォーマットを以下のファイルに記載する。
  CallSign: JQ1ZNN
*[http://artsat.jp/wp-content/uploads/2014/11/Despatch_HKFormat_ver1.0.xls ハウスキーピングデータのフォーマット ver1.0](.xls)


===宇宙生成詩(独自符号)===
All of the signals from DESPATCH are transmitted by a CW transmitter in the 430MHz band.
フェーズ2では、宇宙生成詩の共同受信ミッションを行う。
The signals with 7W power are radiated from a monopole antenna.
この宇宙生成詩の受信は、宇宙機が地球から遠ざかるにつれて電波が弱くなり、信号がとぎれとぎれにしか聞こえない状況を想定している。
*[[Main_Page#Communication System|The communication system of DESPATCH]]
そこでARTSATプロジェクトの地上局だけでなく世界各地のアマチュア無線家に協力いただき、多数の受信局からの断片的な情報を地上で再結合する「協調ダイバーシティ通信」による詩の復元を試みる。
詩の復元方法としては下の図のように、各ビットごとデータが重複する部分については多数決によるエラー処理を行い、それ以外の部分ではORの処理を施すといったシンプルな手法を考えている。


[[File:DataReconstructionProcess.png|550px|thumb|none|各局で受信されたデータの統合プロセス]]
As mentioned above, the mission period is divided into 3 phases and different kinds of data are received in each phase.
Herein, the format of the data in each phase is explained.  


'''宇宙生成詩のフォーマット'''
===Housekeeping Data(Morse)===
In Phase 1, housekeeping data encoded in Morse, whose speed is 6 WPM, is received on Earth.
This data is used to monitor the health of the spacecraft mainly at our own station in Tokyo.
For this reason, this phase ends at the middle of the first visibility period in Tokyo.
This signal carrying housekeeping data, repeats 4 sentences named AS0, AS1, AS2, and AS4.
There are 10 second intervals, in which the transmission is off, between the sentences.
The data format of the housekeeping data is described in the file below.
*[http://artsat.jp/wp-content/uploads/2014/12/Despatch_HKFormat_ver1.4.xls Format of housekeeping data ver1.4](.xls)


宇宙生成詩の送信は、下の図に示すようなCP0 ~ CP7という8つのユニットの繰り返しである。
===Generative Poetry(Baudot code)===
各ユニットはヘッダー5ビット、フッター5ビット、その間に挟まれた40ビットで構成され、
Phase 2 is where we conduct our experiment on cooperative diversity communication.
これらは[http://ja.wikipedia.org/wiki/Baudot_Code Baudotコード]によって符号化されている。
In this phase, Baudot-encoded generative poetry will be transmitted for reception around the world.  
Baudotコードは5ビットで1文字を表現するため、各ユニットはBaudotコードでヘッダー1文字、フッター1文字、その間に挟まれた8文字の合計10文字で構成されている。
Reception will be limited to noisy and intermittent signals given the considerable distance between the spacecraft and Earth.  
ただし、CP1のヘッダーとフッターに挟まれた40ビット(下図の青い部分)については主要なセンサーの生データが格納されており、この部分はBaudotコードには従わない。
We expect it will be difficult (in some cases, impossible) for any lone ham operator to decode and interpret the signals.


[[File:CPformat.png|800px|thumb|none|宇宙詩のフォーマット]]
As such, we are attempting to gather all bit strings, received and decoded by ham operators around the world through the Internet, so that the bit strings can be patched together to reconstruct the original poetry.
The figure below shows the reconstruction process.
In the figure, the call-sign “JQ1ZNN” is reconstructed from data acquired by five ham operators.
Note that the red letters are those that were rejected by majority vote.  


搭載センサーのデータから生成された宇宙生成詩にあたるのは、CP2, CP3, CP4, CP5(下図の赤い部分)である。
[[File:ReceivedDataIntegration.png|550px|thumb|none|Process to integrate bit strings decoded by ham operators]]


CP2, CP3では、宇宙機の温度を4文字の「カラーコード」に変換する。
'''Format of generative poetry'''
このカラーコードは色を4文字で象徴したものであり、例えば「白」には "whit" が割り当てられる。
ちょうどサーモグラフィのように、宇宙機の温度が高いほど明るい色のカラーコードが受信される。
カラーコードから温度への変換は、以下の .xlsファイルを参照のこと。


また、CP4, CP5では、宇宙機の角速度および消費電流を4文字の「リズムフレーズ」に変換する。
The signal, carrying the generative poetry, repeats 8 units named CP0, CP1, ..., CP7.
リズムフレーズは、詩人[http://en.wikipedia.org/wiki/Hugo_Ball フーゴ・バル]の「Gadji beri bimba」のフレーズをカットアップしたものであり、
Every unit has a header in 5 bits, a footer in 5 bits, and 40 bits between them
[https://www.youtube.com/watch?v=b-RDJ4Z4XrQ 「I Zimbra」]という曲の歌詞にも使用されている。
(<span style="color:red">but CP7 does not have the header</span>),  
つまり、このリズムフレーズによって、宇宙機の回転や電流が奏でる一種の音響詩が受信される。
and they are encoded in [http://en.wikipedia.org/wiki/Baudot_code the Baudot code].
カラーコードから角速度(または消費電流)への変換は、以下の .xlsファイルを参照のこと。
Since the Baudot code represents a character in 5 bits,
every unit has the header in 1 character, the footer in 1 character, and 8 characters between them.  
Only the 40 bits in CP0, the blue part shown in the figure below, is not encoded and carries raw bits of some sensor readings.  


*[http://artsat.jp/wp-content/uploads/2014/11/Despatch_PoemFormat_ver1.0.xls 宇宙生成詩のフォーマット ver1.0](.xls)
[[File:PoetryFormat.png|800px|thumb|none|Structure of generative poetry]]  


'''宇宙生成詩の信号速度と符号化方式'''
4 units, CP2, CP3, CP4, and CP5, shown as red parts in the figure above, carries the generative poetry.


宇宙生成詩の信号速度は1bpsである。
CP2 and CP3 carry temperatures of the spacecraft represented in the "color-code."
前述の通り1ユニットは50ビットであるから、1ユニット送信するのに必要な時間は50秒である。
This color-code represents the color in 4 characters, e.g., white is represented as "WHIT."
ユニットとユニットの間には10秒のインターバルを設けているため、CP0~CP7全体を通して送信を行うのにかかる時間は、(8×(10+50)秒 =)8分である。
The higher the temperature is, the brighter color received on Earth, as if we see the spacecraft through a thermal imaging camera.
The rule to convert the color-code to the temperature is described in the xls file below.


注意点として、符号化方式に[http://en.wikipedia.org/wiki/Manchester_code マンチェスター符号化方式]を採用している。
CP4 and CP5 carry the consumption current and 3-axis angular velocities represented in the "rhythm phrase."
信号速度は前述の通り1bpsであるが、マンチェスター符号は1/0というバイナリデータを立ち上がりエッジ(CW OFF→ON)/立ち下がりエッジ(CW ON→OFF)によって表現するため、
This rhythm-phrase is a goup of phrases picked up from "Gadji beri bimba," a poem writted by [http://en.wikipedia.org/wiki/Hugo_Ball Hugo Ball],
CWのON/OFFは最短で0.5秒で切り替わる。
and it is used in a song, [https://www.youtube.com/watch?v=b-RDJ4Z4XrQ "I Zimbra."]
例えば、CP0が受信されるときの信号は下図("Received Signal")に示すようなものになる。
That is, this rhythm-phrase plays a kind of the acoustic poetry generated from sensor readings.  
The rule to convert the rhythm-phrase to the current or the angular velocity is described in the xls file below.


[[File:CP0.png|800px|thumb|none|マンチェスター符号により符号化された詩]]
*[http://artsat.jp/wp-content/uploads/2014/12/Despatch_PoemFormat_ver1.4.xls Format of generative poetry ver1.4](.xls)


参考として、このCP0の受信信号を音声に変換したもの(CW OFFのとき無音、CW ONのとき440Hzの可聴音)を以下からダウンロードできる。
'''Signal speed and encoding'''
*[http://artsat.jp/wp-content/uploads/2014/11/Despatch_CP0Sample_ver2.0.mp3 CP0のサンプル音声(音声は10秒後から始まる)](.mp3)


===アナログ温度情報(ビーコン)===
The speed of the signal carrying the poetry is 1 bps.
フェーズ3では、宇宙機の温度に応じて送信間隔が変化するようなビーコンを地上で受信する。
Since the size of every unit except for CP7 is 50 bits, it takes 50 seconds to transmit each of the units
宇宙機が遠く離れた後もこの信号の変化さえ捉えることができれば、その温度のおおよその値を知ることができる。
(<span style="color:red">45 seconds for CP7</span>).
このビーコンは、下図に示すように周期が3秒間で一定で、バッテリーの温度(''T'' = 0x00~0xFF)に応じてデューティ比が変化するような信号である。
Because there are 10-second intervals between them (<span style="color:red">15 seconds only between CP6 and CP7</span>),
[[File:BeaconFormat.png|550px|thumb|none|アナログ温度情報(ビーコン)の波形]]
it takes (7×(50+10) + (45+15) sec. =)8min. to transmit from CP0 through CP7.  


==受信の報告==
Please note that [http://en.wikipedia.org/wiki/Manchester_code the Manchester code] is used for encoding.
前述の通り、DESPATCHのミッション期間は3つのフェーズに分割されている。
Although the signal speed is 1 bps, the on/off of the CW can switch every 0.5 second in the best case
以降では、フェーズごとの受信報告方法を説明する。
since the Manchester code encodes each of the binary states
なお、受信報告は以下のページから受け付けている。
<span style="color:red">"1" and "0" as a falling edge (CW on→off) and a rising edge (CW off→on)</span>.
*[http://api.artsat.jp/report/ 受信報告ページ]
For example, the signal carrying CP0 is something like the "Received Signal" in the figure below.
<span style="color:red">Please note that the sequence of each character is little-endian.</span>


===ハウスキーピングデータ===
[[File:PoetryCP0_Signal.png|800px|thumb|none| Manchester-encoded signal, carrying CP0]]
モールス信号をデコードした結果を受信報告ページの "Comment" フォームに記入する。
もしくは、デコードした結果をテキストファイルなどに記入して受信報告ページからアップロードする。


===宇宙生成詩===
===Spacecraft Temperature (Simple beacon)===
共同受信ミッションにおいては、世界の各地域から寄せられた詩の一部分を、時刻同期をとることによって一つの詩として復元する。
Phase 3 is the reception of a radio beacon
このような復元を行うために、受信データだけではなく「受信時刻」も報告していただきたい。
whose duty-ratio is constantly 50% and tone-length (''t'' ) changes depending on temperature of the spacecraft batteries (''T'' = 0x00~0xFF), as shown in the figure below.
詩の受信報告の方法としては、次の3つの方法がある。
Spacecraft temperatures can be derived by simply detecting periodic changes in the faint signal.


'''1.専用のフォームに記入する'''
[[File:Despatch_Beacon.png|550px|thumb|none| Simple beacon carrying spacecraft temperature]]


受信報告ページの専用のフォーム("Received Data and Frequency with Time stamp")を利用して、データと受信時刻を一緒に報告することができる。
To convert the tone-length to the battery temperature, please refer to the following file.
専用フォームを使って報告する場合、以下の点に注意していただきたい。
*[http://artsat.jp/wp-content/uploads/2014/12/Despatch_BeaconFormat_ver1.0.xls Table to convert tone-length to battery temperature ver1.0](.xls)
*報告するデータは単なるCWのON/OFFではなく、それをマンチェスター符号でデコードした結果とする(下図の "Received Signal" ではなく、それをデコードした "Binary" を報告する)
*デコード結果(0/1)は1文字ごとにカンマ区切りで記入し、0/1の判断がつかない場合には"-"を記入する
*受信時刻として選択する時刻は、データの1文字目が受信された時刻を1秒の桁まで指定する
例えば、2014/11/30 20:00:33(JST)から下図 "Received Signal" に示すような信号が捕捉された場合、
左側のフォームから 2014/11/30 20:00:33(GMT +9:00) を選択して、
右側のフォームに "1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,0,1,1,1,1,1,1,1,1,1,0,0,0,1,0,1,1,0,0,0,1,1,0,0,0,0,0,0,0" と記入する
(中央の "Frequency" フォームについては後述するが、省略可能である)。
なお、複数の受信時刻で報告を行う場合は、フォーム右側の "Add a row" ボタンによって行を追加する。


[[File:CP0.png|800px|thumb|none|マンチェスター符号により符号化された詩]]
===Sample Sound===
The file below is MP3 sound data which is converted from the signal carrying the housekeeping data (from 00:00:00), generative poetry (from 01:00:34), and spacecraft temperature (from 02:37:16).
*[https://www.dropbox.com/s/1qat6twcawd172g/DESPATCH_TestSignal_2h_ver3.0.mp3?dl=0 Sample sound of DESPATCH signals ver3.0](.mp3)


'''2.テキストファイルをアップロードする'''
==Reception Report==
As mentioned above, the mission period is divided into 3 phases.  
Herein, how to report the data you received in each phase is explained.
Reception report is received at the web page below in every phase.
*[http://api.artsat.jp/report/ Reception report page]


受信したデータを受信時刻と一緒にテキストファイルに記入して、受信報告ページからアップロードしていただいても構わない。
===Housekeeping data===
テキストファイルにデータを記入する際の注意点は上で述べたものと同じであるが、
Please enter the strings decoded from the morse signal in the "Comment" form.
受信時刻の時刻系にはUTCを使うものとし、そのフォーマットとしては Java の SimpleDateFormat にしたがって "yyyy.MM.dd hh:mm:ss" のように記入するものとする。
Or, please upload the text file in which the decoded strings are written.
例えば、2014/11/30 11:00:33(UTC)から上図 "Received Signal" に示すような信号が捕捉された場合、テキストファイルに以下のように記入する。
 
なお、複数の受信時刻で報告を行う場合は、同じテキストファイル内に行を追加する。
===Generative poetry===
In the approach taken with this experiment in cooperative diversity communication,
we are attempting to gather all bit strings, received and decoded by ham operators around the world,
and synchronize them to reconstruct the original poetry from the spacecraft.
For this reason, we are asking every operator to send us not only the decoded bit strings but timestamps, which will tell us when each bit was received.
 
There are 3 types of methods to report the poetry with the timestamp.
 
'''1. Use the special forms'''
 
You can use the special forms, "Received Data and Frequency with Time stamp," in the reception report page to report the data (bit strings) with timestamps.
 
For examples, if you began to receive the signal carrying CP0 (like the "Received Signal" in the figure below) at December 4, 2014, 20:00:33 JST (GMT+9:00),
you should enter "12/04/2014 20:00:33 +0900" in the left form ("Date" form) and "1,1,1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,0,0,1,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0" in the right form ("Data" form).
The center form ("Frequency" form) may be omitted although there are additional explanations for it below this section.
 
To report using these forms, please note the following things:
*You should not report the CW state (on/off), but rather the bit strings decoded from CW state based on the Manchester encoding (NOT the "Received Signal", but rather the "Data," in the figure below)
*The strings should be split by commas (",") at each character ("0" or "1")
*If you cannot distinguish "0" or "1," replace it with a hyphen ("-")
*The timestamp should be specified as the moment when the first bit was received
 
And, using the "Add a row" button, you can report multiple bit strings received at different moments in the same submission.
 
[[File:PoetryCP0_Signal.png|800px|thumb|none| Manchester-encoded signal, carrying CP0]]
 
'''2. Upload a text file'''
 
You can upload a text file in which bit strings and timestamps are written in the reception report page.
Points to note are the same as those mentioned above, but you should use the UTC as the time standard for timestamps and write them in this form: "yyyy.MM.dd hh:mm:ss"  
 
For example, if you began to receive the signal carrying CP0 (like the "Received Signal" in the figure above) on December 4, 2014, 11:00:33 UTC,
you should write the text below in a text file you want to upload.
<pre>
<pre>
2014.11.30 11:00:33, 1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,0,1,1,1,1,1,1,1,1,1,0,0,0,1,0,1,1,0,0,0,1,1,0,0,0,0,0,0,0
2014.12.04 11:00:33, 1,1,1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,0,0,1,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0
</pre>
</pre>


'''3.音声ファイルをアップロードする'''
And, if you want to report multiple bit strings received at different moments in the same report, you can add new lines in the text file.
 
'''3. Upload a sound file'''


信号を録音したサウンドファイルを受信報告ページからアップロードする。
You can upload a sound file that records the signal, in the reception report page.
この場合、サウンドファイルの録音開始時刻(UTCで1秒の単位まで記入)を受信報告ページの "Comment" フォームに記載する。
In this case, you should enter the time when the recording started in the "Comment" form.
You should use UTC as the time standard of the time and write it in the form: "yyyy.MM.dd hh:mm:ss"


===アナログ温度情報===
===Spacecraft temperature===
受信された信号のデューティー比、信号の強度などを受信報告ページの "Comment" フォームから報告する。
Please access the reception report page and enter the strength and duty of the signal in the "Comment" form.


===受信周波数===
===Reception frequency===
DESPATCHのサブミッションとして、受信周波数を利用した軌道決定を行う。
As a secondary mission of DESPATCH, we are going to determine the spacecraft's orbit using the reception frequency reported by operators around the world.
電波の受信周波数に生じるドップラー効果は宇宙機の位置と速度(すなわち軌道)によって変化するため、
Since the degree of the Doppler effect changes depending on the spacecraft's position and velocity (i.e., the orbit), measurements of the Doppler frequency enable us to improve estimates of the orbit.
逆にドップラー効果の程度から宇宙機の軌道をより正確なものに更新(軌道を決定)することが可能である。
We use the [http://en.wikipedia.org/wiki/Kalman_filter Kalman filter] for orbit determination,
なお軌道決定の手法としては、宇宙機の位置と速度の6自由度を状態量とした
which has a state vector composed of spacecraft's position and velocity, and update the state vector using measurements of the Doppler frequency.
[http://ja.wikipedia.org/wiki/カルマンフィルター カルマンフィルタ]
を構成し、受信周波数を観測量として宇宙機の位置と速度を更新する。


このミッションのため、受信報告の際には受信周波数およびそのときの時刻を一緒に報告していただきたい。
For this mission, we are asking every operator to report the reception frequency with a timestamp.
受信報告のページに専用のフォーム("Received Data and Frequency with Time stamp")が用意されているので、
To report, you can use the special forms ("Received Data and Frequency with Time stamp") in the reception report page.
報告の際にはそこに記入をすればよいが、以下の点に注意していただきたい。
Please note the following things when you report:
*受信周波数は100Hzの桁まで記入する
*You should write the frequency down to hundred's digit in Hz (e.g., 435325500)
*受信時刻は(最低でも)1分の桁まで指定する
*You should specify the received date down to the minute (e.g., 12/05/2014 21:21:00 +0900)
なお、右側の"Data"フォームを空欄として周波数だけを報告することも可能である


この軌道決定の結果は後述するトラッキングページに反映し、より正確な宇宙機のトラッキングに役立てたいと考えている。
You can report the reception frequency even if the "Data" form is blank.
シミュレーションによると、この軌道決定によって受信周波数の予測精度が大幅に改善することがわかっている(下図を参照)。
報告される受信周波数の数が多いほど、軌道決定の精度は高くなる傾向にある。


[[File:OrbitDet.png|400px|thumb|none|軌道決定による周波数予測精度の改善(周波数を1時間ごとに計測した場合)]]
The updated orbit will be used for more accurate tracking.
A simulation shows that this orbit determination especially improves the accuracy of prediction of the reception frequency as shown in the figure below.
The more measurements we have, the more accurate the prediction is.  


==DESPATCHの電波を受信するには==
[[File:OrbitDet.png|400px|thumb|none| A simulation result showing that the orbit determination improves the prediction accuracy of the reception frequency]]


===必要な設備===
==What is needed to receive DESPATCH?==
まず、DESPATCHは430MHz帯のCWを送信するため、その電波を受信するためには430MHz帯CWモード対応の受信機が必要である。


次に、長期に渡って電波を受信するには、以下に示すようなアジマスおよびエレベーション方向に回転が可能なアンテナが必要である。
===Equipment for reception===
DESPATCHは地球から急激に遠ざかるため、ミッションの終盤まで電波を受信するためにはゲインの大きい受信アンテナを使用することが望ましい。
First of all, a receiver with CW mode is needed since DESPATCH transmits on 437.325MHz CW.
下図は、分離からの経過時間に対して、その時点で受信マージンがゼロとなるような受信ゲイン(必要ゲイン)をプロットしたものである。
この図から、自局のアンテナで電波を受信できる期間をおおよそ知ることができよう。


なお、DESPATCHの通信系の仕様および回線計算は、以下のページに記載されている。
Next, you need an antenna that is orientable in azimuth and elevation as in the picture below.
*[[メインページ#通信系|通信系の主要諸元]]
The receiving margin at every radio station will continue to decrease after the launch as the spacecraft moves away from Earth.
We calculated when the receiving margin will dip below zero for receiving antennas of different gains.
The result is shown in the figure below.
The graph takes time after separation from the rocket as the horizontal axis.
The receiving antenna gain whose receiving margin is zero at each point (we call this gain “required receiving-antenna gain”) is taken as the vertical axis.
This graph shows that you can receive signals only in periods during which the gain of your receiving antenna is higher than the curves in the graph.


[[File:TgsAntenna.jpg|500px|thumb|left|ARTSATプロジェクトの地上局の受信アンテナ]]
The communication system and link calculation of DESPATCH is detailed in the page below.  
[[File:RequiredReceivingGain.png|350px|thumb|none|時間(距離)と電波受信に必要な受信ゲイン]]
*[[Main_Page#Communication system|Communication system of DESPATCH]]


最後に、フェーズ2の共同受信ミッションに参加するには、受信したデータを処理するPCとその時刻調整が必要である。
[[File:TgsAntenna.jpg|500px|thumb|left|An antenna of the ARTSAT project]]
前述したように、共同受信ミッションにおいては、世界各地で受信されたデータをそれと一緒に報告された受信時刻を用いて統合し、一つの詩として復元する。
[[File:RequiredReceivingGain.png|350px|thumb|none|Required receiving antenna gain at each time period]]
CWのON/OFFが0.5秒で切り替わることを考えると、この統合処理を正確に行うためには受信時刻の計測精度が0.5秒以上に保たれていることがのぞましい。
このような理由から、NTP(Network Time Protocol)ツールを設定するなどして、受信に使用するPCのシステム時間をあらかじめ正しく調整しておいてほしい。


===アンテナのポインティング===
Finally, a PC whose system time is correctly adjusted is needed to process the data you received.
DESPATCHは地球脱出軌道に投入されるため、地球周回軌道を表現するTLE(二行軌道要素)はトラッキングに使用できない。
As mentioned above, in phase 2, we will attempt to gather all data received around the world,
そこで、以下のページからDESPATCHの軌道情報を配信する。
and synchronize them for reconstruction of the original poetry from the spacecraft.
*[http://api.artsat.jp/pass/ DESPATCHのトラッキングページ]
To perform this process correctly, the error of the system time should be less than 0.5 seconds, considering that on/off of the CW can switch every 0.5 second in the shortest case.
For this reason, you should adjust the system time in some way, e.g., by connecting the PC to the Internet and setting the NTP (Network Time Protocol) correctly.


このページのフォームに観測地点の緯度と経度(ほとんどの場合で、海抜は0で問題ない)を入力すると、観測地点から宇宙機がみえる時間帯(可視時間/パス)がいくつかリストアップされる。
===Antenna pointing===
また、その中で最も近い可視時間に関しては、宇宙機の方角および受信周波数などの情報が1分刻みでテーブルに出力される。
Since Despatch is injected into an Earth escape trajectory, no TLEs are unavailable.
Instead, we have made available a web-page for spacecraft tracking (both antenna-pointing and receiver-tuning).
*[http://api.artsat.jp/pass/ DESPATCH Tracking page]


DESPATCHの見かけの速度は、低軌道の衛星と比較して非常に遅いので、このテーブルをもとにアンテナを操作すれば十分な精度でトラッキングが行えると考えられる
Please go to the page and enter your geographic location, and you will get nearby passes and a table with 1 minute steps that gives you AZ, EL, Frequency, and so on. 
(受信設備にもよるが、操作の時間間隔は10分もあれば十分であろう)。
As the apparent movement and the change of the Doppler shift are slow, manual pointing of the antenna and tuning of the receiver every 10 minutes or so should suffice.


もしくは、ARTSAT APIを利用することで、自作のソフトウェアから上のページと同様の情報を取得することもできる。
Or, you can get the same information on the applications you developed using the ARTSAT API.
*[http://api.artsat.jp/web/despatch ARTSAT API 公式リファレンス]
*[http://api.artsat.jp/web/despatch ARTSAT API reference]
*[http://ji1izr.air-nifty.com/ham_satellite/2014/11/artsat2-despa-1.html ARTSAT API Visual C# からの利用例]
*[http://ji1izr.air-nifty.com/ham_satellite/2014/11/artsat2-despa-2.html An example of using ARTSAT API on Visual C#]


===受信機の調整===
===Receiver tuning===
DESPATCHの送信機の周波数は437.325MHzであるが、ドップラー効果による周波数のズレが生じる。
The receiver is to be tuned to the frequency of DESPATCH (437.325MHz) +/- the Doppler shift and your receiver's frequency error.
DESPATCHの周波数の変化は、低軌道の衛星と比較して非常に緩やかである(この周波数の変化のほとんどは地球の自転によるものである)。
The Doppler changes very slowly and is mainly due to the rotation of Earth.
前述のトラッキングページを利用することによって、ドップラー効果を加味した受信周波数を調べることができる。
In the tracking page above, you can pick up the reception frequency once a minute.
トラッキング中には適宜、このページを参考にして受信機のチューニングを行っていただきたい。


なお、ドップラー効果の程度は観測地の緯度によって異なる。
The degree of the Doppler shift depends on your latitude.
例えば、ARTSAプロジェクトの地上局(東京都、北緯35度)付近では、マイナス10kHzからマイナス5kHz 程度の範囲でドップラー効果が生じる(下図を参照)。
The following figure gives the expected Doppler frequency changes around Tokyo, Japan.


[[File:DopplerAtTokyo.png|400px|thumb|none|東京都における受信周波数の変化]]
[[File:DopplerAtTokyo.png|400px|thumb|none| doppler frequency changes around Tokyo, Japan]]


==リンク==
==Reception Results==
*最新情報・受信状況の配信
*[https://docs.google.com/spreadsheets/d/1pEr9FJ5Gk0QNB6yjZjR3qLncwLd7DwiBfZpc8KbENNQ/edit?usp=sharing Table of Reception Report]
**http://artsat.jp/news
[[File:Voyage-of-the-ARTSAT2DESPATCH 1214.png|400px|thumb|[https://docs.google.com/spreadsheets/d/1WP-FzXHe8axAzNy44SGbKpJqIRKWHAcIP9vXnaHMb6g/edit#gid=0 Table of Reception Report]]]
**https://www.facebook.com/artsat
*[https://github.com/ARTSAT/DespatchTelemetry Process of Data Analysis]
*受信状況の配信
*[https://docs.google.com/spreadsheets/d/1QPYDXtcQET225AAJusKgF9SgyG2wqcRSZIkzG7cRr0A/edit?usp=sharing Received Cosmic Poem from DESPATCH]
**https://twitter.com/DESPATCH_ARTSAT
[[file:DESPATCH Poem2.jpg|thumb|[https://docs.google.com/spreadsheets/d/1QPYDXtcQET225AAJusKgF9SgyG2wqcRSZIkzG7cRr0A/edit?usp=sharing Received Cosmic Poem from DESPATCH]]]


==Links==
*http://artsat.jp/news
*https://www.facebook.com/artsat
*https://twitter.com/DESPATCH_ARTSAT


==連絡先==
==Contact==
info@artsat.jp
info@artsat.jp

Latest revision as of 21:23, 2 March 2020

A schematic drawing of cooperative diversity communication

One important mission for DESPATCH is an experiment in what we call "cooperative diversity communication." In this experiment, we attempt to collect signals from the spacecraft received not only at our own ground station in Tokyo, but also at many ham radio stations around the world, in order to reconstruct the original data from the spacecraft. In this page, the details of the experiment and how to join it are explained.

Reception of such weak signals to reconstruct data from the spacecraft will require the expertise of exceptionally skilled ham operators. We are hereby providing a rare opportunity to receive radio signals transmitted by a spacecraft in deep space, and ask for your cooperation in this project.

DESPATCH design, subsystems, and trajectory are detailed in the Main Page.


Mission Overview

DESPATCH flight model

"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 December 3, 2014 13:22:04, JST (UTC+9) and moves away from Earth soon after launch. The simulation shows that it reaches lunar distance (385,000 km) from Earth within 24 hours of separation from the launcher.

The spacecraft, carrying a CW beacon in the 430MHz band, will transmit "generative poetry" created in deep space for only a week until it reaches a distance of 3 million km from Earth. The signals from DESPATCH are very weak and will be fading, because the spacecraft has no attitude control system and uses only a low-directivity antenna.

The ARTSAT project asks that you attempt to receive these very weak signals at your radio stations. DESPATCH's transmissions, decoded by volunteer ham-radio operators throughout the world, will be forwarded to our data server via the Internet, for reconstruction of the original poetry from the spacecraft. With this experiment, we would like to verify the practical effectiveness of cooperative diversity communication.

Mission Planning

DESPATCH will be launched at December 3, 2014 13:22:04, JST (UTC+9) along with the Hayabusa-2 asteroid probe, and injected into an earth escape trajectory about 2 hours later.

The spacecraft, carrying a CW beacon in the 430MHz band, will transmit the signals for only a week until it reaches a distance of 3 million km from Earth. We are hoping to receive three types of data — the generative poetry, housekeeping data, and a simple beacon. Accordingly, we have divided the 1 week mission period into three phases based on the spacecraft's distance from Earth, as shown in the table below. In each of these phases, a different type of data will be transmitted by the spacecraft.

Types of data in each phase
Phase Distance from Earth Type of data received on Earth
Phase1 ~ 180,000 km Housekeeping data in Morse code
Phase2 180,000 ~ 1,860,000 km Generative poetry in Baudot code
Phase3 1,860,000 km ~ Spacecraft temperature in a simple beacon

The phase changes are shown in the figure below — the colors representing each phase. The visibility times in five cities — Tokyo, Sydney, Berlin, Boston, and Buenos Aires — are shown in the figure as black bars. Please note that the times in the figure are expressed in Coordinated Universal Time (UTC).

We conduct the experiment for the cooperative diversity communication only in the phase 2, but we also appreciate your help and your reception reports in phase 1 or phase 3. Phase 2 runs for almost 100 hours as shown in the figure.

Visibility times in five cities and three mission-phases
Transition in distance from Earth

Transmission Cycle

To prevent overheating, the transmission is halted when the transmitter temperature is too high. The operation revealed that the transmitter repeats 50 minutes resting and 20 minutes sending, in phase 2 and phase3.

The file below lists up the time when the transmission restarts. DESPATCH transmits CW for 20 minutes from the time listed up.

Telemetry Format

 CallSign: JQ1ZNN

All of the signals from DESPATCH are transmitted by a CW transmitter in the 430MHz band. The signals with 7W power are radiated from a monopole antenna.

As mentioned above, the mission period is divided into 3 phases and different kinds of data are received in each phase. Herein, the format of the data in each phase is explained.

Housekeeping Data(Morse)

In Phase 1, housekeeping data encoded in Morse, whose speed is 6 WPM, is received on Earth. This data is used to monitor the health of the spacecraft mainly at our own station in Tokyo. For this reason, this phase ends at the middle of the first visibility period in Tokyo. This signal carrying housekeeping data, repeats 4 sentences named AS0, AS1, AS2, and AS4. There are 10 second intervals, in which the transmission is off, between the sentences. The data format of the housekeeping data is described in the file below.

Generative Poetry(Baudot code)

Phase 2 is where we conduct our experiment on cooperative diversity communication. In this phase, Baudot-encoded generative poetry will be transmitted for reception around the world. Reception will be limited to noisy and intermittent signals given the considerable distance between the spacecraft and Earth. We expect it will be difficult (in some cases, impossible) for any lone ham operator to decode and interpret the signals.

As such, we are attempting to gather all bit strings, received and decoded by ham operators around the world through the Internet, so that the bit strings can be patched together to reconstruct the original poetry. The figure below shows the reconstruction process. In the figure, the call-sign “JQ1ZNN” is reconstructed from data acquired by five ham operators. Note that the red letters are those that were rejected by majority vote.

Process to integrate bit strings decoded by ham operators

Format of generative poetry

The signal, carrying the generative poetry, repeats 8 units named CP0, CP1, ..., CP7. Every unit has a header in 5 bits, a footer in 5 bits, and 40 bits between them (but CP7 does not have the header), and they are encoded in the Baudot code. Since the Baudot code represents a character in 5 bits, every unit has the header in 1 character, the footer in 1 character, and 8 characters between them. Only the 40 bits in CP0, the blue part shown in the figure below, is not encoded and carries raw bits of some sensor readings.

Structure of generative poetry

4 units, CP2, CP3, CP4, and CP5, shown as red parts in the figure above, carries the generative poetry.

CP2 and CP3 carry temperatures of the spacecraft represented in the "color-code." This color-code represents the color in 4 characters, e.g., white is represented as "WHIT." The higher the temperature is, the brighter color received on Earth, as if we see the spacecraft through a thermal imaging camera. The rule to convert the color-code to the temperature is described in the xls file below.

CP4 and CP5 carry the consumption current and 3-axis angular velocities represented in the "rhythm phrase." This rhythm-phrase is a goup of phrases picked up from "Gadji beri bimba," a poem writted by Hugo Ball, and it is used in a song, "I Zimbra." That is, this rhythm-phrase plays a kind of the acoustic poetry generated from sensor readings. The rule to convert the rhythm-phrase to the current or the angular velocity is described in the xls file below.

Signal speed and encoding

The speed of the signal carrying the poetry is 1 bps. Since the size of every unit except for CP7 is 50 bits, it takes 50 seconds to transmit each of the units (45 seconds for CP7). Because there are 10-second intervals between them (15 seconds only between CP6 and CP7), it takes (7×(50+10) + (45+15) sec. =)8min. to transmit from CP0 through CP7.

Please note that the Manchester code is used for encoding. Although the signal speed is 1 bps, the on/off of the CW can switch every 0.5 second in the best case since the Manchester code encodes each of the binary states "1" and "0" as a falling edge (CW on→off) and a rising edge (CW off→on). For example, the signal carrying CP0 is something like the "Received Signal" in the figure below. Please note that the sequence of each character is little-endian.

Manchester-encoded signal, carrying CP0

Spacecraft Temperature (Simple beacon)

Phase 3 is the reception of a radio beacon whose duty-ratio is constantly 50% and tone-length (t ) changes depending on temperature of the spacecraft batteries (T = 0x00~0xFF), as shown in the figure below. Spacecraft temperatures can be derived by simply detecting periodic changes in the faint signal.

Simple beacon carrying spacecraft temperature

To convert the tone-length to the battery temperature, please refer to the following file.

Sample Sound

The file below is MP3 sound data which is converted from the signal carrying the housekeeping data (from 00:00:00), generative poetry (from 01:00:34), and spacecraft temperature (from 02:37:16).

Reception Report

As mentioned above, the mission period is divided into 3 phases. Herein, how to report the data you received in each phase is explained. Reception report is received at the web page below in every phase.

Housekeeping data

Please enter the strings decoded from the morse signal in the "Comment" form. Or, please upload the text file in which the decoded strings are written.

Generative poetry

In the approach taken with this experiment in cooperative diversity communication, we are attempting to gather all bit strings, received and decoded by ham operators around the world, and synchronize them to reconstruct the original poetry from the spacecraft. For this reason, we are asking every operator to send us not only the decoded bit strings but timestamps, which will tell us when each bit was received.

There are 3 types of methods to report the poetry with the timestamp.

1. Use the special forms

You can use the special forms, "Received Data and Frequency with Time stamp," in the reception report page to report the data (bit strings) with timestamps.

For examples, if you began to receive the signal carrying CP0 (like the "Received Signal" in the figure below) at December 4, 2014, 20:00:33 JST (GMT+9:00), you should enter "12/04/2014 20:00:33 +0900" in the left form ("Date" form) and "1,1,1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,0,0,1,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0" in the right form ("Data" form). The center form ("Frequency" form) may be omitted although there are additional explanations for it below this section.

To report using these forms, please note the following things:

  • You should not report the CW state (on/off), but rather the bit strings decoded from CW state based on the Manchester encoding (NOT the "Received Signal", but rather the "Data," in the figure below)
  • The strings should be split by commas (",") at each character ("0" or "1")
  • If you cannot distinguish "0" or "1," replace it with a hyphen ("-")
  • The timestamp should be specified as the moment when the first bit was received

And, using the "Add a row" button, you can report multiple bit strings received at different moments in the same submission.

Manchester-encoded signal, carrying CP0

2. Upload a text file

You can upload a text file in which bit strings and timestamps are written in the reception report page. Points to note are the same as those mentioned above, but you should use the UTC as the time standard for timestamps and write them in this form: "yyyy.MM.dd hh:mm:ss"

For example, if you began to receive the signal carrying CP0 (like the "Received Signal" in the figure above) on December 4, 2014, 11:00:33 UTC, you should write the text below in a text file you want to upload.

2014.12.04 11:00:33, 1,1,1,1,1,1,1,0,1,0,1,1,1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,0,0,1,0,0,1,1,0,0,0,1,1,0,0,0,0,0,0

And, if you want to report multiple bit strings received at different moments in the same report, you can add new lines in the text file.

3. Upload a sound file

You can upload a sound file that records the signal, in the reception report page. In this case, you should enter the time when the recording started in the "Comment" form. You should use UTC as the time standard of the time and write it in the form: "yyyy.MM.dd hh:mm:ss"

Spacecraft temperature

Please access the reception report page and enter the strength and duty of the signal in the "Comment" form.

Reception frequency

As a secondary mission of DESPATCH, we are going to determine the spacecraft's orbit using the reception frequency reported by operators around the world. Since the degree of the Doppler effect changes depending on the spacecraft's position and velocity (i.e., the orbit), measurements of the Doppler frequency enable us to improve estimates of the orbit. We use the Kalman filter for orbit determination, which has a state vector composed of spacecraft's position and velocity, and update the state vector using measurements of the Doppler frequency.

For this mission, we are asking every operator to report the reception frequency with a timestamp. To report, you can use the special forms ("Received Data and Frequency with Time stamp") in the reception report page. Please note the following things when you report:

  • You should write the frequency down to hundred's digit in Hz (e.g., 435325500)
  • You should specify the received date down to the minute (e.g., 12/05/2014 21:21:00 +0900)

You can report the reception frequency even if the "Data" form is blank.

The updated orbit will be used for more accurate tracking. A simulation shows that this orbit determination especially improves the accuracy of prediction of the reception frequency as shown in the figure below. The more measurements we have, the more accurate the prediction is.

A simulation result showing that the orbit determination improves the prediction accuracy of the reception frequency

What is needed to receive DESPATCH?

Equipment for reception

First of all, a receiver with CW mode is needed since DESPATCH transmits on 437.325MHz CW.

Next, you need an antenna that is orientable in azimuth and elevation as in the picture below. The receiving margin at every radio station will continue to decrease after the launch as the spacecraft moves away from Earth. We calculated when the receiving margin will dip below zero for receiving antennas of different gains. The result is shown in the figure below. The graph takes time after separation from the rocket as the horizontal axis. The receiving antenna gain whose receiving margin is zero at each point (we call this gain “required receiving-antenna gain”) is taken as the vertical axis. This graph shows that you can receive signals only in periods during which the gain of your receiving antenna is higher than the curves in the graph.

The communication system and link calculation of DESPATCH is detailed in the page below.

An antenna of the ARTSAT project
Required receiving antenna gain at each time period

Finally, a PC whose system time is correctly adjusted is needed to process the data you received. As mentioned above, in phase 2, we will attempt to gather all data received around the world, and synchronize them for reconstruction of the original poetry from the spacecraft. To perform this process correctly, the error of the system time should be less than 0.5 seconds, considering that on/off of the CW can switch every 0.5 second in the shortest case. For this reason, you should adjust the system time in some way, e.g., by connecting the PC to the Internet and setting the NTP (Network Time Protocol) correctly.

Antenna pointing

Since Despatch is injected into an Earth escape trajectory, no TLEs are unavailable. Instead, we have made available a web-page for spacecraft tracking (both antenna-pointing and receiver-tuning).

Please go to the page and enter your geographic location, and you will get nearby passes and a table with 1 minute steps that gives you AZ, EL, Frequency, and so on. As the apparent movement and the change of the Doppler shift are slow, manual pointing of the antenna and tuning of the receiver every 10 minutes or so should suffice.

Or, you can get the same information on the applications you developed using the ARTSAT API.

Receiver tuning

The receiver is to be tuned to the frequency of DESPATCH (437.325MHz) +/- the Doppler shift and your receiver's frequency error. The Doppler changes very slowly and is mainly due to the rotation of Earth. In the tracking page above, you can pick up the reception frequency once a minute.

The degree of the Doppler shift depends on your latitude. The following figure gives the expected Doppler frequency changes around Tokyo, Japan.

doppler frequency changes around Tokyo, Japan

Reception Results

Links

Contact

info@artsat.jp