指派作業：畫一個狀態機（使用圓圈和箭頭符號）來描述HETE姿態控制系統（Attitude Control System，ACS）中模式轉換邏輯的需求：
Assignment: Draw the state machine (using the circles and arrows notation) that specifies the following requirements for the mode switching logic in the HETE Attitude Control System (ACS):
HETE航空器的一般描述
General Description of the HETE Spacecraft
高能瞬變爆發探測器（High-Energy Transient Explorer，HETE）任務的目的是研究珈瑪射線的爆發。珈瑪射線爆發是一種在天空中呈現等向分佈之電磁波中珈瑪射線部分的高能瞬變。這些能源瞬變爆發的持續時間可能從一個毫秒到好幾秒鐘，而且它們隱含了大量的能源。除了捕捉這些爆發的光譜資訊之外，當地面太空站與其它衛星出現時，航空器也會傳送關於這些爆發的位置資料好讓它們也可以研究這個現象。
The purpose of the High-Energy Transient Explorer (HETE) mission is to study gamma ray bursts. Gamma ray bursts are high-energy transients in the gamma ray portion of the elctromagnetic spectrum that seem to be isotropically distributd in the sky. These transient energy bursts range in duration anywhere from a millisecond to a few hundreds of seconds, and they involve a huge amount of energy. In addition to capturing spectral information about these bursts, the craft also relays position data about bursts as they occur to ground stations and other satellites so that they can also study the phenomena.
此衛星包含三個基本的元件：航空器主體、控制系統、以及科學酬載。控制系統包含了一些控制硬體、一組感測器、以及一組用來控制航空器的促動器。
The satellite consists of three basic components: the body of the craft, the control system, and the scientific payload. The control system consists of some controlling hardware, a set of sensors, and a set of actuators for controlling the spacecraft.
衛星的控制硬體包含了排列在控制匯流排上的四個運算節點。每一個節點有三個處理器（兩個Motorola DSP 56001可程式化數位訊號處理單元與一個INMOS T805傳算器）以及記憶體和輔助支援邏輯。
The control hardware for the satellite consists of four compute nodes arranged around a central bus. Each node has three processors (two Motorola DSP 56001 programmable digital signal processing units, and one INMOS T805 transputer) as well as some memory and auxiliary support logic.
控制器的每一個節點獨立運作並且負責其中數個衛星子系統。主要節點負責執行通訊子系統與姿態控制系統。其它三個節點則是負責操作酬載儀器。
Each node of the controller operates independently of the others and is responsible for operating a number of the many satellite subsystems. The primary node is responsible for running the communications subsystems and the attitude control system code. The other three nodes operate the payload instruments.
控制器的每一個節點獨立運作並且負責其中數個衛星子系統。主要節點負責執行通訊子系統與姿態控制系統。其它三個節點則是負責操作酬載儀器。
The Attitude Control Software
姿態控制系統（ACS）軟體負責維護航空器的姿態。除此之外，它也會在航空器移動到標稱姿態時執行一些部署操作。
The Attitude Control System (ACS) software is responsible for maintaining the attitude of the spacecraft. In addition, it also performs several deployment operations as the spacecraft moves into its nominal attitude.
在標稱操作中，控制系統將會從初始模式開始並在模式5、7、和8中達到穩定。這些模式是正常的操作模式，而且它們所對應的功能為姿態微量調整、白晝操作、以及夜間操作。所有其它模式不是以執行某特定動作為目的的暫態模式，就是透過姿態控制來將航空器的姿態調整到趨近於它的標稱姿態。模式4（部署轉輪）以及模式6（部署輪翼）只會被執行一次，模式4的目的是展開轉輪使得從航空器主體到轉輪的動量轉軸能夠趨於穩定，而模式6的目的是展開太陽能輪翼。模式0是一個延遲模式，讓航空器可以清除運載火箭，而沒有執行任何動作。模式1為姿態修正，也是讓航空器能夠進入一個安全狀態的關鍵模式。模式2將轉軸置於航空器的y軸，以幫助航空器能在xz平面上穩定其姿態。模式3執行在航空器上有關太陽的仰角與方位角的調整，好讓這些數值能在模式5時維持在容忍值之內。
In nominal operation, the control system will progress through the initial modes and stabilize in modes 5, 7, and 8. These are the normal operating modes, and they correspond to minor attitude correction, daytime operations, and nighttime operations. All other modes are either one-shot modes with the purpose of performing specific actions, or gross attitude control to adjust the attitude of the spacecraft into something approximating its nominal attitude. Mode 4 (deploy wheel) and Mode 6 (deploy paddles) are one-offs, mode 4 having the purpose of spinning up the wheel to shift the stabilizing momentum spin from the body of the craft to the wheel, and mode 6 having the purpose of deploying the solar paddles. Mode 0 is a delay mode, to allow the craft to clear the launch vehicle, and performs no action. Mode 1 is for gross attitude correction, and is the closest thing the craft has to a safe mode. Mode 2 applies spin on the y axis to the craft to help stabilize its attitude in the xz plane. Mode 3 performs gross adjustment to the elevation and azimuth of the craft with respect to the sun to place those vlaues within tolerances for mode 5.
在任何時間點，如果太陽仰角或是太陽方位角的錯誤或是動量向量的錯誤超過容忍度時，那麼ACS將會為了修正此問題而回到適當的模式。相同地，如果沒有關於姿態的資料，那麼ACS就會回復到模式2。
At any point, if the sun elevation or sun azimuth errors or the momentum vector error exceeds tolerances, the ACS will return to an appropriate mode in order to correct the problem. Also, in the absence of good data about the attitude, the ACS will revert to mode 2.
ACS在任何時間會處於這10種模式的哪一種是根據下列任一或全部因素：
Which of the 10 modes the ACS should be in at any time may depend on any or all of the following:
- 目前的模式。
The current mode.
- 軟體維持在目前模式的時間，也就是它執行了幾次完整的感測－命令－控制迴圈；
How long the software has been in the current mode, in terms of how many times it has run a complete sense-command-control loop;
- 輪翼是否已經部署完畢。
Whether or not the paddles have been deployed
- 目前轉輪的轉速。
The current rotational velocity of the wheel
- 目前所估計的陽光單位向量
The current estimated sun unit vector
- 目前經由修正轉矩線圈產生的磁場而估計到的正規化磁場方向。
The current estimated normalized magnetic field direction, corrected for the fields generated by the torque coils.
- 目前估計到的航空器主體速率向量。
The current estimated body rate vector
- 太陽感測器是否正在偵測太陽的存在。
Whether or not the sun sensors are detecting the sun's presence
HETE姿態控制系統（ACS）的模式轉換需求
Mode Switching Requirements for HETE Attitude Control System (ACS)
從透過火箭發射衛星到衛星可以在軌道上日／夜運行的標稱運作順序如下：第一個被呼叫的模式是模式0（等待），好讓感測器有時間取得一些資料並且讓過濾器可以初始化。經過當一段時間延遲後，ACS會離開模式0。在離開模式0時，因為沒有促動器被啟動，所以衛星仍然在旋轉。接下來ACS會從模式0轉換到模式1（旋轉減緩）。模式1會減緩三個座標軸的旋轉。當旋轉得到足夠的減緩時，也就是當動量向量的x與z元素低於某個門檻值時，ACS會離開模式1。接下來會有一個關於Y軸轉動剛度的計畫給航空器好讓仰角就可以很容易被控制。這也就是模式1之後的模式2所扮演的角色。離開模式2的條件也是動量向量：當衛星的動量向量夠接近目標動量向量時，航空器就準備好修正上升角度並轉換到模式3。模式3會處理動量向量。一旦高度錯誤在特定門檻值下穩定時，ACS會進入模式4來取消Y軸的旋轉。轉輪需要特定的延遲時間來達到它的速度。當此延遲時間過去之後，ACS會離開模式4。然後如果轉輪部署對於上升錯誤造成足夠的干擾討導致超過門檻值時，系統可能必須回到模式3。當高度又趨於穩定時，ACS會進入模式6來替衛星部署哪的太陽能輪翼。太陽能輪翼的釋放不能執行太久，所以ACS會在輪翼被釋放或是超過延遲時間之後離開模式6。在這個時機點，衛星已經進入最後的設定並且會透過修正方位角錯誤和仰角錯誤來達到最後的姿態。模式5、7、和8都是用來完成這個步驟，但是它們是在不同的狀況下被使用。模式5有較高的得益值，所以它只有在當進動序列結束、當方位角錯誤太大、或是當航空器受到干擾導致方位角錯誤超過門檻值時才會被使用。模式7是執行白晝運行任務的預設模式。模式8是在夜間運行任務中光學相機運作的預設模式。
The nominal sequence from the release of the satellite by the rocket to the orbit night/day cycle is as follows: The first mode to be called is mode 0 (wait), so that the sensors have time to acquire some data and the filters can initialize. The ACS exits mode 0 when a certain delay has elapsed. When leaving mode 0, the satellite is still tumbling because no actuators have been activated since the release. The ACS switches from mode 0 to mode 1 (detumble). Mode 1 will cancel most of the rotation about all three axes. The ACS exits mode 1 when the rotation has been dampened enough, that is, when the x and z components of the momentum vector drop below a certain threshold. Then the plan is to give the spacecraft some rotational stiffness about the Y axis so the elevation angle can be controlled easily. This is the role of mode 2, which comes after mode 1. The mode 2 exit criteria also concerns the momentum vector: when the satellite momentum vector is close enough to the target momentum vector, the spacecraft is ready to have its elevation angle error corrected and it switches to mode 3. Mode 3 precesses the momentum vector. Once the elevation error is stabilized under a certain threshold, the ACS enters mode 4 to cancel the rotation about Y. Mode 4 deploys the momentum wheel: the wheel spins up to a speed such that it completely dampens the rotation about Y. The wheel needs a certain delay to reach its speed. When this delay has elapsed, the ACS exists mode 4. Then the system may have to return to mode 3 if the wheel deployment has induced a disturbance strong enough for the elevation error to grow past the threshold. When the elevation is stabilized again, the ACS goes to mode 6 to have the satellite deploy its solar paddles. The solar paddle release must not be activated for too long, so the ACS leaves mode 6 either after the paddles are released or after the delay has elapsed. At this point, the satellite is in its final configuration and it will reach its final attitude by correcting the azimuth error as well as the elevation error. Modes 5, 7, and 8 all accomplish this, but they are used in different situations. Mode 5 has the higher gains, so it is used only at the end of the acquisition sequence, when the azimuth error can be big, or when the spacecraft has been subjected to disturbances that cause the azimuth error to go over its threshold. Mode 7 is the default mode during the mission at orbit-day. Mode 8 is the default mode when the optical cameras operate, that is during orbit-night.
上述規格所描述的是標稱行為，但是對於異常的狀況會有一些額外的需求。當模式7在處理方位角錯誤時無法同時維持較小的仰角錯誤時，ACS會從模式7轉換成模式3。當在夜間運行但是卻無法得到追蹤資料時（光學相機出現問題），ACS會從模式7轉換到模式2。在這種情況下，ACS無法使用太陽感測器而且也無法得到飄移速率，因此比較好的做法是退回到模式2（旋轉減緩）只利用磁力來保持衛星的穩定。當太陽升起時，衛星會再經由模式3、5、和7回復到正常的運作。當衛星在模式8（夜間運行）而且從相機而來的資料遺失或是當透過磁力取得的衛星轉速太大以致於讓ACS無法在追蹤模式中正確運作（在模式8中，轉速必須夠小，相機的影像才不會模糊）時，相同的流程會發生。在前面這些情況下，衛星接下來會進入模式2並等待太陽升起。
The above specification describes the nominal behavior, but there are some additional requirements that correspond to anomalous situations. The ACS switches from mode 7 to mode 3 when mode 7 is not able to maintain a small elevation error while dealing with the azimuth error at the same time. It switches from mode 7 to mode 2 when it is orbit night and no tracking data is provided (there is a problem with the optical cameras). In this case, the ACS cannot use the sun sensors and no drift rate is available, so the best compromise is to go back to mode 2 (detumble) where only the magnetometers are used to keep the satellite roughly stable. When the sun rises, the ACS will go again through modes 3, 5, and 7 to resume normal operations. The same process occurs when the satellite is in mode 8 (orbit-night) and the data from the cameras drops out or when the rotation of the satellite as determined by the magnetometers is too big for the ACS to cope with while in the tracking mode (in mode 8, the rotation rate must be small enough for the cameras not to blur). As in the previous case, the satellite will then enter mode 2 and wait for the sun to rise.
