Specifications for the Attitude Dynamics and Control of the Group #1 CubeSAT

Transcription

1 Specifications for the Attitude Dynamics and Control of the Group #1 CubeSAT 1. SCOPE The attitude and determination and control system shall passively control and maintain the angular orientation of the Group #1 CubeSAT. 1.1 General. This specification establishes the design, construction, performance, development, and test requirements for the Attitude Determination and Control System for the Group #1 CubeSAT, herein referred to as the ADCS. 2. APPLICABLE DOCUMENTS This section is often poorly understood and poorly implemented. It is a list of documents that are a critical part of understanding the item or requirements imposed on the item. Every document listed must have a text reference in the body of the spec further describing and limiting how it is to be applied. Conversely, no document is to be referenced in the spec unless it is listed here. Don t put items here that are background information or of general interest. Always obtain and review all items listed here. Often has the following statement: The following documents of the exact issue shown shall form part of this specificaion to the extent specified herein. In the event of conflict between the requirements of this specification and any referenced document the order of precedence shall be 1. The contract, 2. This specification, 3. Referenced documents. 2.1 Government Documents. This is where to put MIL specs, MIL STDs, NASA specs and so forth. Be sure to include the revision level and date. 2.2 Industry Documents. This is where to put ANSI, ASTM, ASME, IEEE, Company specifications and so forth. Both this section and government documents can be divided up into logical subcategories. 3. REQUIREMENTS 3.1 Item definition. The ADCS will consist of an intra satellite tether, vibration dampers and a tether deployment actuator. Once deployed, the ADCS tether will provide passive stabilization Illustrations. Command and Data Handling J1 Power J2 Tether Release Actuator Table XX. The ADCS relationship with other subsystems. J1 = Commands to ADCS tether release actuator J2 = Power input to actuator Interface Definition.

2 The Functional Block Diagram (Table XX) indicates the ADCS relation to other subsystems for deployment. Deployment will be triggered by Command and Data Handling and Power; the information flow is one way Physical. The Group #1 CubeSAT ADCS shall have the following physical interfaces: The intra satellite tether shall be attached to the structures using TBD. Vibration dampers shall be attached to the structure using TBD. The deployment actuator shall be attached to the structure using TBD Electrical. The electrical interface shall be a power and data interface as per IEEE Power Connector Specification, IEEE Data Cable Specification, IEEE Power Cable Specification, and IEEE Data Connection Specification. The deployment actuators shall interface electrically with the power system using TBD Informational. The CubeSAT ADCS will receive communications from the Command and Data Handling system (CD&H) for deployment. This data will be a one way command to the deployment actuator to release the tether. After deployment, no further data transfer will be made. The electrical interface shall be a power and data interface as per IEEE Power Connector Specification, IEEE Data Cable Specification, IEEE Power Cable Specification, and IEEE Data Connection Specification. The CubeSAT ADCS tether deployment actuator shall interface with C&DH using TBD Characteristics. The CubeSAT ADCS will receive communications from the Command and Data Handling system (CD&H) for deployment and then no further commands will be sent. All attitude stabilization will be performed passively for the duration of the mission lifetime. Table XX+1. CubeSAT ADCS Operational Timeline Operational Mode Minimum Start Time of Operation Maximum Duration of Operation Off N/A Indefinite Deployment and PPOD Ejection 15 Days Stabilization + 60 seconds Passive Flight Mission Day 16 Indefinite Performance Characteristics. The CubeSat ADCS performance characteristics shall have the following specifications. Oscillation analyses were performed assuming the largest initial impulse derived from maximum applied torque from both P POD separation and free flight environments Deployment Oscillations

3 Specifications provided by the makers of the P POD launcher indicate that deployment from the P POD will be made with an unknown orientation and rotation. The CubeSAT ADCS must therefore be able to orient and settle the spacecraft within a maximum time and pointing requirement. Table XX+2. Initial Deployment Assumed Maximum Rotations Axis* Max Rotation (rad/sec) X π/2 Y π/2 Z π/2 *Axes are in the Master Satellite frame of reference Settling Time The maximum time to settle the CubeSAT within minimum pointing requirements is 15 days from P POD deployment Pointing The CubeSAT ADCS shall maintain pointing of the spacecraft to the limits imposed by the science mission sensors and the communications antenna. All spacecraft oscillations must be contained within these free flight mission requirements. Communications: The negative velocity direction within TBD accuracy. Science: Sensors must be aligned in the freestream velocity direction within +/ 30 accuracy Power The power consumption for the CubeSAT ADCS actuators during tether deployment shall not exceed 1W Physical characteristics. The CubeSAT ADCS shall have the following physical characteristics. Mass: Less than or equal to 200g Volume: TBD cm 3 Master Satellite Surface Area: TBD cm 2 Slave Satellite Surface Area: TBD cm Intra satellite Tether The intra satellite tether shall conform to the following physical characteristics. Length: Equal to 10m within +/ 1 cm Mass: Less than or equal to 150g Composition: Shall contain Power and Data Transfer wires as prescribed by Power and Command and Data Handling Subsystems Master Attachment Point: The intra satellite tether shall be attached at the X and Y co ordinates of the center of gravity of the Master satellite on surface?? within +/ 0.05 cm.

4 Slave Attachment Point: The intra satellite tether shall be attached at the X and Y co ordinates of the center of gravity of the Slave satellite on surface?? within +/ 0.05 cm. Strength: The intra satellite tether shall withstand a tension force equal to TBD Vibration Dampers The vibration dampers shall conform to the following physical characteristics. Mass: Less than or equal to 25g each Damping Coefficient: Greater than or equal to TBD Master Attachment Point: The vibration damper shall be located on the interior of the satellite at least TBD in the X direction from the Master satellite CG. Slave Attachment Point: The vibration damper shall be located on the interior of the satellite at least TBD in the X direction from the Slave satellite CG Reliability. The CubeSAT ADCS shall conform to the following reliability constraints. Lifetime: Minimum of 45 days Probability of Success: 99% Maintainability. No maintenance shall be required Environments. The CubeSAT ADCS shall withstand the following environmental effects Natural Environments. Temperature: 40 to +80 degrees Celsius Humidity: TBD Lightning: TBD Magnetic fields: TBD Radiation: TBD Pressure: 1 atmosphere to space vacuum Induced Environments. The CubeSAT ADCS shall meet the requirements of this specification during and after exposure to any logical combination of the following natural environments. Typical environments include (but not limited to): Mechanical Shock: TBD as specified in? Vibration: TBD as specified in? Acoustic Input: TBD as specified in? Load Factors and Acceleration: Launch conditions of 15 g as specified in?

5 Space Environment including Radiation,. Radiation is a specialty area that includes cosmic radiation, charged particles in the solar wind and Van Allen radiation in some orbits. Atomic oxygen is of concern for polymers and non metallic materials exposed on the front of the spacecraft (with reference to the velocity vector) in orbits under 500 km altitude. Spacecraft develop charges when moving through the earth s magnetic field in the continuous presence of charged particles. Increased solar wind can alter the magnitude of the charge. Design features may be needed to diminish charge separation within a spacecraft, make electronics less vulnerable to accumulated charge, and in the case of rendezvous and docking allow for harmless dissipation of accumulated charges between spacecraft. Other Possibilities include Transportability, Human Factors, 3.3 Design and construction Parts, materials, and processes Non destructive inspection. This section specifies the needs for dye penetrant, magnetic particle, x ray, ultrasound, microscopy, and other non destructive inspections Fasteners. This section is requirements for nuts and bolts (including strength, torque, head type, thread type), threaded inserts, rivets, and so forth Pneumatic, hydraulic and fluid parts. This section can define types of fittings, tubing and requirements for tube bending and forming, and requirements for tube supports. Component interfaces are usually on the envelope drawing Wiring, Cabling, and Connectors. This section can be used for requirement particular to cabling and connectors such as wire types and gages, insulation type, shielding, grounding of cables shield and connectors. Connector keying requirements are more often on the envelope drawing. Soldering requirements could be here. There may be requirements for insulation resistance and/or dielectric strength imposed here Plastics and polymers. This sections deals with special issues related to non metallic parts. Injection molding, adhesives, inserts, allowable stress margins, outgasing, UV or other exposure limits, and polymer selection and property data are some issues that might be covered Cleanliness. Cleanliness is, of course, next to Godliness, and that is even more true that you realize for spaceflight hardware. This section usually controls particulate and fiber cleanliness with tables of allowable count per range of particle size. Surface cleanliness is also controlled. The use and certification of cleanrooms is controlled in this section. Special issues such as propellant contacting surfaces, flushing fluid components, and electronic cleanliness are controlled here Electromagnetic interference (EMI). The unit shall met the EMI requirements for class xxx equipment as specified in MIL STD 461, except for yyy limits shall be modified as shown in Figure zzz. This is typical language, and MIL STD 461 is still commonly used. Emissions, refer to EMI that originates in the unit that can negatively affect other things. Susceptibility refers to unexpected negative effects on the unit that are caused by emissions from some other source. Self susceptibility is a special case when electrical noise created by the unit triggers and unexpected effect within the unit. EMI can be "conducted" along power or signal wires or "radiated". The MIL STD 461 limits have coded names like: CS01 = conducted susceptibility in the first frequency range, RE02 = radiated emissions in the second frequency range. Magnetic fields are still another category controlled by the MIL STD. Testing methods are usually defined by an associated methods document, MIL STD 462. Other parts or sub paragraphs in this section deal with electrical bonding (specified minimum resistance) between different subassemblies, EMI gasket and screen materials, grounding, lightning transients, and shielding Outgasing and venting. In space all materials emit gases that reduce the vacuum in closed volumes, coat nearby surfaces with condensable material, and increase the likelihood of and electrical arc in electronic hardware. Plastics, polymers, potting compounds and coatings are particularly sources of outgasing. Outgasing may be diminished by cyclical exposure to heat in a vacuum. Mass loss is one standard measure of outgasing.

6 3.3.5 Nameplates and Product Marking. Manufacturer s part number Manufacturer s name and trademark Serial number Workmanship. The unit shall be fabricated and finished in a thoroughly workmanlike manner. Particular attention shall be given to freedom from blemishes, defects, burrs, and sharp edges; accuracy of dimensions; radii of fillets; marking of parts; thoroughness of cleaning; quality of brazing, welding, riveting, painting, and wiring; alignment of parts; and tightness and torquing of fasteners Interchangeability and replaceability. Assemblies, components, and parts having identical part numbers shall meet the requirements for an interchangeable item that are two or more items that possess such functional and physical characteristics as to be equivalent in performance and durability and are capable of being exchanged one for another without alteration of the items themselves or of adjoining items except for adjustment, and without selection for fit or performance. Replaceable items are functionally interchangeable with another item, but differ physically from the original part in that the installation of the replaceable part requires operations such as drilling, reaming, cutting, filing, shimming, etc., in addition to the normal applications and methods of attachment Safety. The design of the unit shall be such that when the equipment is stored, transported, operated, or maintained in accordance with applicable procedures and precautions it will not cause damage to itself or to other equipment, or cause injury to or be detrimental to the health or safety of personnel. Hazardous conditions and or precautions to be observed shall be marked in a manner easily observed by personnel Hazardous materials. The materials utilized in the unit when subjected to specified environments and non operating conditions, shall not liberate fumes, vapors, gases, or dust in excess of the permissible exposure limits listed in OSHA In the event of conflicting standards the more stringent shall apply Pressurized systems. The unit shall comply with MIL STD The unit shall exhibit positive margin of safety at burst pressure Human performance/human engineering. The unit shall comply with the general requirements of MIL STD The unit shall be capable of being installed and operated by all personnel ranging from a fifth percentile female to a ninety fifth percentile male. 4. QUALITY ASSURANCE PROVISIONS 4.1 General. This section describes the requirements for the verification process during design, fabrication, development, acceptance, and qualification test programs. After this can be sub paragraphs that describe who is responsible for what test, what documents provide the source of the project quality requirements and so forth. 4.2 Quality conformance verification. The following are definitions that are pretty standard everywhere Quality conformance methods. The supplier shall verify all requirements of Section 3 by inspections, demonstrations, tests, or analyses as specified in Section 4 as follows: a. Inspection. Inspection is a method of verification consisting of investigation, without the use of special laboratory appliances or procedures, to determine compliance with requirements. Inspection is generally nondestructive and includes (but is not limited to) visual examination, manipulation, gauging, and measurement. b. Analysis. Analysis is a method of verification, taking the form of the processing of accumulated results and conclusions, intended to provide proof that verification of a requirement has been accomplished. The analytical results may be based on engineering

7 study, compilation or interpretation of existing information, similarity to previously verified requirements, or derived from lower level examinations, tests, demonstrations, or analyses.