0520 基礎設計メモ
作りやすい鋳物の形状設計
- 中空な鋳物は、壁の厚みを均一にする。
- 断面を均一にすると、重量材料、仕上費を抑えることができ、強い鋳物が得られる。
- 急な断面変化を避ける、角Rを大きくする
- 大きな隅肉を避ける。
- ボス周りの大きな断面変化、アンダーカットを避ける。
- 型の生成の自由度が下がってしまう。
- 鋳型の種類によって最小肉厚が異なるので注意
鍛造
目的
- 鍛造により粗大決勝を微細化し、材料の機械的性質を向上させる
- 成形することにより、材料および機械加工を節約する
特徴
- 高温に加熱して加工するため、材料の展延性が大きく、加工時間が短い
- 壁打ちへこみ部と盛り上がり凸部からなる。
- 盛り上がり部は正しい成形が困難。
鍛造に適した設計
- 壁ずれを防止する設計をする
- できるだけ左右対称にする
- 精度向上、熱処理ゆがみが出にくい
- 壁の制作が容易な形状にする
- できるだけ円形を採用
- 壁割面はなるべく平面とする
- 壁の制作用意、製品の精度向上
- 抜け勾配を考慮する
- 角、隅のRを大きくとる
- 面積の広い平面は避ける→材料の流れが悪い平面は少し角度を作る
- 急激な熱悪変化を避ける
- 仕上げ代を考慮する
- 最小肉厚を参照する
- 外角R標準を参照する
- 要求精度の高い部分を上か下の一方に集める
0531 ISDPメモ
Mission Elements: Propulsion
Requirements
- Delta-V Budget: Based on trajectory
- Performance:
- Thrust
- Specific Impulse
- Operational:
- Restart
- Control
- Throttling
- Gimballing: Change the directions of thrust vector -- attitude control
- Redundancy
- position of the thrusters is important
- Constraints
- Mass/ size (propellant margin: 5% - 20%)
- Power (Electric Propulsion)
- Environment (Temperature, Acceleration, Vibration)
- Structural loads on rocket
- Any combustion reaction generates heat
Components: Chemical Rockets
Liquid rockets
- High Thrust
- Active Control
- Intermediate Isp
- Complex
Solid Rockets
- Simple
- High Thrust
- Low Isp
- Combustion of oxidizer/fuel and other bonds create heavier molecules difficult to accelerate
- No Active Control
Hybrid Rockets
- High Thrust
- Active Control
- Safing Capability
- fuel coal apart from oxidizer -> less chance of explosion
- intermediate Isp
Cold Gas Thrusters
- Simple
- Good Reliability
- Low Thrust
- Low Isp
Liquid Rocket Power Cycles
Pressure-fed
- propellants are stored at high pressures
- Simple
- Requires strong (i.e. heavy) propellant tanks
Gas Generator
- Use a preburner + turbine to generate power, drive propellant pumps
- Powerful
- Wastes propellant (preburner exhaust)
- good Reliability
Expander:
- User propellants to cool the nozzle, then use the heated propellant to power a turbine, drive propellant pumps
- Efficient
- Self-contained
- Only works with certain propellants (near the triple point)
Staged combustion
- Use a preburner + turbine to generate power, drive propellant pumps
- Direct preburner exhaust into thrust chamber
- powerful & efficient
- complex
Electric
- Use electric motors to drive propellant pumps
- Simple
- Requires electrical power
Components: Electric Propulsion
High Isp, Low Thrust
Ion Thruster
- Ionize neutral gas
- Use electrostatic force (charged grids or plasma) to accelerate ions
- electrons fired into gas -> ionized gas
- positive ions are accelerated at very high speed
- there's no ground in space -> spacecraft gets negatively charged -> release some electrons in exhaust gas from neutralizing electron gun
Arcjet/Resistojet
- Use Electrical energy to heat propellant
- Convert internal energy to kinetic with a nozzle
- generally not very efficient
Plasma Propulsion
- Accelerate ionized plasma using an induced electromagnetic field
- require large amounts of power -> small amount of thrust
Laser Propulsion/Photonic Rocket
- Photonic pressure
- May require external source
- require large amounts of power -> small amount of thrust
Solar Sail
Infinite Isp, Very Low Thrust
220517 ISDP メモ
TT&C
Requirements
- Data transmission rate:
- Consider Uplink & Downlink
- generally downlink need more data than uplink
- limited power available -> constraints on the data transmission rate
- Dependent on mission operations (attitude), payload
- Consider Uplink & Downlink
- Link Margin:
- Near Earth: 6 dB
- Deep Space 3 dB
- Bit Error Rate:
- Uplink: to
- Downlink:
Uplink is more important (because commands you are sending to the satellites need to be sent accurately) , so it tends to be higher than downlink.
Link Budget
- Linke Budget:
SNR = Actual Signal-to-Noise Ratio (dB)
Signal-to-Noise Ratio: analogy) people talking around you. we are in a large room. the theater is quiet. we are standing far apart. I can talk in a normal voice. -> low noise
if the room is full of people, even if I talk to you normally as before, you can't hear my voice. I need to yell for you to hear me. -> more power to increase the signal-to-noise ratio.
-
- All calculation sin decibels
- Link Margin based on requirements
- Required SNR Method 1 (Shannon-Hartley Theorem):
C = Channel capacity (bit/s)
- Required SNR Method 2 (Bit Error Rate):
- Bit Error Rate (BER): how often your transmission signals contain errors
- Actual Signal-to-Noise Ratio (SNR):
EIRP: Effective Isotropic Radiated Power
G_R: Receiver Antenna Gain: direction of the antenna
Free Space Losses: radiated out signals are lost to free space
Atmospheric Losses: atmosphere, rain
Noise: inefficiency of noise
- Effective Isotropic Radiated Power:
P_Tx = Transmitter Power (dBW)
-
- not transmitter input power
G_Tx = Transmitting antenna gain (dB)
L_Tx = Transmitter & Antenna Losses (dB)
Isotropic: same to every directions
- Free Space Losses:
r = Transmission range : farther away higher losses
f = Transmission frequency: more frequency higher losses
c = speed of light
- Atmospheric Losses:
- Possible to consider atmospheric losses negligible
- Rain can increase antenna temperature (noise)
- Noise:
k = Boltsmann constant (J/K)
Ts = System temperature (K) : it's not the atmosphere temperature
Bn = Noise bandwidth (MHz)
Ts: based on hardware design (approximations are OK)
Antenna Design
Antenna Gain: How much an antenna can "focus" in one direction, expressed in decibels.
-
- Applicable to both transmitting and receiving signals
- general trade-off: range vs. flexibility
High gain can mean much less flexibility.
Link budget analysis process
1. Determine requirements (data rate, BER, etc.)
2. Determine frequency band
3. Determine hardware (antenna, transmitter/ receiver, etc.)
4. determine ground station
5. Calculate required SNR (Shannon channel capacity)
6. Calculate actual SNR
7. Calculate link margin
8. Adjust design accordingly
- Half-power Beam Width
- Width of beam at which signal strength is 50% of maximum (-3 dB)
- minimum of link margin (even if the signal get weaker by 50% still we can read)
- based on antenna design
- may affect ADCS requirements (pointing accuracy)
- one reason for Link Margin
e.g.) Hayabusa 2 has two antennas with different gains
Other Topics
- Modulation & Coding
- Varying signal characteristics
- Techniques: Phase Shift Keying (BPSK, QPSK), Frequency Shift Keying (FSK, MFSK)
- Amplitude Modulation not common
- Multiple Access Techniques
- "Sharing" a communication link between users
- Used for communication missions & relay satellites
- Diversity techniques
- Reduce risk by making signals redundant
- Methods: spatial diversity, time diversity, frequency diversity, etc.
- Optical/ Laser Communications
Ground Segment
- TT&C Interface
- Compatible frequency, modulation etc.
- Transmitter / Receiver Gain
- Visibility/ Line of Sight
- How often do you need a line-of-sight connection to your spacecraft?
- Can also use software tools (GMAT, STK, etc.)
- Availability
- Sharing of ground station resources between users
- Multiple ground stations may be required.
0506 基礎設計メモ
動力伝達要素
- シャフト:軸・・・ただまっすぐなだけでなく、途中で折れてもいいようになっている
- 軸受け:軸を受けるためのボールベアリングのようなものを入れる。
- 歯車、 チェーン:軸の間の動力伝達
- 継ぎ手:軸をつなぐ。動力源側と受動側の軸をつなぐものが必要。
軸の設計
回転のトルクと、振動的な曲げねじり応力を考える。
設計手順
1. 前提条件を決める
- 許容応力
- 軸は中空?
2. 電圧トルクを考慮し軸形状を検討
- パワーを回転数で割ったものが伝達トルク。
- ねじり応力は、トルクを断面二次モーメントで割ったもの
回転軸に査証する荷重の種類
静荷重:常に一定の大きさと方向で作用
動荷重:
- 変動荷重:時間とともに大きさや方向が変化
- 繰り返し荷重:一定の振幅と周期で繰り返し作用
- 交番荷重:大きさ、方向が繰り返し変化
- 衝撃荷重:大きな加速度により短時間に作用
軸受け選定のための検討事項
- 本当は構造よりも騒音対策の方が大変。
- 強度を上げようとして軸受けを太くすると振動の固有値が下がってくるため、低回転時の騒音が増えてくる。
- 振動を和らげる素材を使って振動を吸収する
- 速度が上がると許容速度が減少
ころがり軸受けの利点
- 動力損失、始動抵抗が少ない
- 潤滑油が少なく、保守がしやすい
欠点
- 振動・騒音
- 高速回転・重荷重
はめあいの種類
- すきまばめ:機能上大きな隙間が必要。回転や摺動するところ。
- 中間ばめ:部品を損傷しないで分解結合する。力の伝達は不可。手、木ハンマで組みつけ
- しまりばめ:分解時部品は損傷。力の伝達が可能。プレスで組みつけ
数字が大きいほど精度が低い。10などは隙間ばめにしか使わない
事故発生に対する備えで求められることは?
- 原因究明と解決力の向上
- 解明プロセスの明確化と風通しの良い調査体制
- 普段からの危機管理プロセスの訓練と整備
- 状況を合理的に社内外に一貫した論旨で説明すること
- 意思決定の迅速化、指揮命令系統の一本化
再度の発生を防ぐには?
- 顧客の期待値や市場実態に合わせた設計基準の見直し
- 重大事故につながる前の、初期のクレーム情報に対する重大さの感知能力向上
- 整備を含めたサービス体制の強化、その報告の一貫性、透明性
設計の要点
- 最低肉厚は強度より製造性で決まる。
220510 ISDPメモ
Mission Elements
Payload
diverse, difficult to teach
- Driven by Mission Objectives
- Communications
- Remote Sensing
- Navigation
- Military
- In-situ Science
- Resource utilization/Manufacturing
- Human spaceflight/Space tourism: life-support system
Communications Payloads
Broadcast vs. Duplex:
Broadcast: transmit signals only to end users (e.g. radio)
Duplex: transmit signals in two ways (e.g. network)
Typical Hardware:
- Antennas
- Transmitters
- Receivers
- Transceivers
Remote Sensing Payloads
Considerations:
- Passive vs. Active: just observing vs. does something to the target. e.g.) radar
- Noise, attenuation (loss in signal), scattering (signal bounce off in the atmosphere) etc.
- Resolution (spatial, temporal, spectral): how many pixel in images
→ spatial resolution: how many pixels per meter
→ temporal resolution: how often you can collect data: changed by the orbit/ the number of satellites (e.g. constellation)
→ spectral resolution: infrared? optical?
- Access to subject: distance, frequency : affected by velocity and orbit
Typical Hardware
- Cameras/ Imagers
- Lidar: radars that use optical light
- Radiometers
- Image Spectrometers: e.g.) exo-planets
- Radar/ SAR
Navigation Payloads
In-Situ Science
Considerations:
- in-situ analysis vs. sample return:
- sample return tends to yield the best data but is much more complex
- sample/data contamination
- contamination of bacteria from earth
- contamination of data (e.g. ice coal sample, melting can change the chemical structure)
Typical Hardware:
- Mechanical/ robotic systems
- Sample Cannisters
- Mass Spectrometers
- Environmental sensors (pressure, temperature, etc.)
- Seismometers
Payload Design Process
1. Select Payload Objectives
- based on mission objectives, constraints, mission concept, etc.
2. Conduct Subject Trades
- how does the payload interact with the subject?
- how is it going to do that?
- what are the performance thresholds?
- what sort of protection do you need for the sample?
- what are requirements?
- what sort of equipment can you use?
3. Develop Payload Operations Concept
- how does the payload connect the subject to the end user?
- how do you use the equipment
- how do you satisfy the need of the end user
4. Determine the required
- overlap with systems engineering: this is requirements definition
5. Identify Candidate Payloads
- what are the options for payload instruments and devices?
- what options do you have that will meet those requirement
6. Estimate Payload Characteristics
- what are the performance characteristics and interface requirements of the candidates from Step 5?
- how much power does it need?
- what it can do
- how frequently it can capture data
- what sort of data interface does it use?
7. Evaluate Candidates and Select a Baseline
- Compare the alternatives & make a preliminary selection
8. Asses Life Cycle Cost & Operability
- Consider trade-offs between cost and performance
- does it meet the budget
9. Define Payload-derived Requirements
- Other mission hardware must directly or indirectly support payload
- Consider functional interfaces & potential sources of interference
- This information will drive the design of other subsystems
- where does it need to be located?
10. Document and Iterate
- make sure your decisions and supporting information is traceable
- Don't be afraid to revisit this process.
C&DH
typically simple
Level of Autonomy
- E1 - Mission execution under ground control, limited onboard capability for safety issues e.g.) mars rover
- write codes for every moves
- E2 - Execution of pre-planned , ground-defined, mission operations on-board
- E3 - Execution of adaptive mission operations on-board
- spacecraft perform some tasks looking at environment
- e.g.) Hayabusa guidance system: reached so far with new propulsion system. long time delay to transmit signals to the spacecraft.
- E4 - Execution of goal-orientated mission operations on-board
- e.g.) Mars helicopter
- collect data itself
Mission Data Processing
- On-board processing - less data transmission (TT&C), more on-board processing (C&DH)
Design Considerations
- Encoding/Decoding
- Command Arbitration
- Input/ Output Channels
- Data Storage
- Buffer for mission & operational data
- Functional Allocation
Components
- Consider off-the shelf solution!
- think about the requirements/ the level of autonomy
Mission Operations
- Mission operations is your mission plan/schedule
- from launch to disposal
- Considerations:
- orbit/trajectory (cruise time, subject availability)
- attitude (payload, solar panels, TT&C)
- power (maximum load, duration, recharge rate)
→ what component are used at the same time?
→ discharge capacity is also a problem
-
- other environmental factors (heat, EM radiation, etc.)
- Use quantitative analysis
- Relate to subsystem requirements
- Main phases
1. Launch/Deployment
2. (Cruise)
3. Mission Phase (data collection)
4. End of Life
紹介された便利なサイト
www.cubesatshop.com
satsearch.co
220509 ISDP メモ
- atmosphere storage
- how much it covers? LEO? GEO?
- where it stands by?
- network / no blackout time
- pressurized section (habitable section)
- sure to have air circulation system
- expendable system (not too much CO2)
e.g.) oxygen candle: sort of like a stick. burns and hold close to their face -> use to breathe
- heat shield capsule
- detachable section
enough analysis
comparing with other capsules
ADCS: trade off b/w how mass efficient they are/ how power full they are
C&DH: human control computer
TT&C: how do you contact with earth
EPS: how much power does it need, solar panels/ battery? how to make it long-term
Bus/ Structure: not very detailed look at similarity with other similar missions, basically a capsule
Thermal Control: life-support system might need more technically complex system: more power, more weight
start thinking about right now
- propulsion
- electrical power: look at Dragon or other similar Soyuz (simple, reliable)
- payload (how many people?, how big it needs to be?)
- trajectory (service area)
basic idea about each system
different options for each category, then choose the best option.
論文メモ Lunar resources: A review
Potential lunar resources
Solar wind implanted volatiles
大気や磁場が存在しないため、太陽風が直接レゴリスに降り注ぐ。
太陽風は水素とヘリウムの原子核が大部分を占める。
300~900℃に温めることによって、これらの揮発性物質を取り出せることをアポロ計画のサンプルが示した。(700℃でほとんどの水素とヘリウムを取り出せる)
極地ほど太陽風が弱く、揮発性物質を蓄えることができる。
しかし、これらの揮発性物質を現地で取り出すのは容易なことではない。
レゴリスの温度は-20℃ほどで、それを700℃まで上げることを考える。レゴリスの比熱は平均X , 密度はであるから、レゴリスを720℃上げるために必要なエネルギーは、オーダーということになる。これは、月の赤道上で1平方メートルあたりに降り注ぐ太陽光のエネルギー9日分に等しい。
解決策
太陽光を集める。
マイクロ波で温める。
どちらにせよ、巨大なインフラが必要なのは明らか。
Water
月の水は将来の月を拠点とした経済という文脈で価値のあるものかもしれない。
自転軸が1.5°であるために、全く日の当たらない部分ができる。
彗星や含水隕石の衝突、太陽風とレゴリスの反応によって閉じ込められている可能性がある。
どれくらいの水があるかどうかはまだ不明。日陰は40Kぐらいしか温度がなくて非常に厳しい環境。
火砕ガラスの中には高い濃度で水が含まれている可能性がある。→太陽光に当たっている部分でも水を得ることができるかもしれない。
Oxygen
チタンが多い地域で、原子状態の水素を高温で反応させることによって還元反応を起こし、鉄と水と酸化チタンを得るという反応がある。
仮に極地で氷を見つけることができたとしても、今後の経済成長のためには、レゴリスから水や酸素を取り出す技術の開発は非常に重要である。
非常に寒いことと氷として水が保存されていることにはオフセットの関係がある。
また、レゴリスを還元する方法は酸素だけでなく金属を得ることにもつながり、これは極地の氷にはないメリット。
Metal
酸化物鉱物を還元するのには非常に大きなエネルギーが必要。
太陽風によって還元されたマイクロメートルオーダーの鉄の粒子を抽出するのはそもそも粒子が細かすぎて難しいと考えられている。
1平方メートル当たり、300gのニッケルと0.5グラムの白金族金属が得られるという。
月に衝突したアステロイドの残骸により多くの鉄とそれに付随するニッケルや白金族金属が得られる可能性があるが、詳しい量はまだ明らかになっていない。(磁場に不均質な部分が存在し、そこに通常以上の金属が含まれているといわれている)
将来の宇宙経済の文脈では、月が小惑星は、小惑星よりもTiの供給源として大きな優位性を持っている可能性がある。