Attachment_C_-_ACS3_Concept_of_Operations.pdf

Advanced Composite Solar Sail System (ACS3) Concept of Operations Document

ACS3 Project Concept of Operations

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Table of Contents

1.0 Introduction

2.0 Concept of Operations Diagram

3.0 Operations Timeline Diagram

4.0 Operations Phase Descriptions

4.1. Spacecraft Deployment and Commissioning (~ 1 week)

4.2. Sail Deployment (~ 1-3 days)

4.3. Data Downlink (~ 1-3 months)

4.4. Data Downlink and Orbit Raising (optional, ~ 1 month)

4.5. Data Downlink and Orbit Lowering (optional, ~ 1 month)

4.6. Extended Operations (optional)

4.7. End-of-Life Operations (~ 1 day)

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1.0 Introduction

The Advanced Composite Solar Sail System (ACS3) is a 12U CubeSat that will demonstrate and characterize solar sail structures technologies for future small spacecraft deep space missions requiring long-duration, low-thrust propulsion, and in particular, CubeSat-class missions that cannot be performed using solar electric or chemical propulsion. The deployable composite boom and solar sail technologies demonstrated with ACS3 will guide the development of a larger, mission-capable, CubeSat-class solar sail propulsion system to be demonstrated in the 2025 time-frame. Concepts for this mission include Sun-Earth sub-L1 space weather early warning sentinels, Asteroid 2016 HO3 rendezvous missions, and cislunar human exploration robotic support missions.

The primary objective of the ACS3 project is to deploy a solar sail with a minimum total area of 70 m2 using collapsible, tubular composite booms (Figure 1). The booms will support a metallized polymer film four-quadrant solar sail membrane. On-board cameras will record deployment of the solar sail.

Camera imagery will be downlinked and processed using photogrammetry techniques to characterize the deployed shape and uniformity of the sail.

Figure 1. Sail Planform (+x is sunward, +z is nadir).

A secondary objective of ACS3 will be to characterize the thrust characteristics of the deployed solar sail. This will be attempted by orienting the deployed sail to maximize solar radiation pressure-induced thrust in the direction of flight, resulting in a gradual change in the semi-major axis of the

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orbit. An altitude change of up to 1-2 km/day should be achievable with the ACS3 solar sail (depending on orbit altitude and final mass of the ACS3 spacecraft). Camera imagery data obtained and stored during the previous deployment and shape characterization operations will also be downlinked during this time.

A final objective of the ACS3 experiment will be to assess the fundamental structural dynamic properties of the deployed solar sail structure. This will be attempted through a combination of videogrammetry of low frame-rate camera data and analysis of attitude sensing and control data.

After completion of all mission success criteria, the sail will be oriented into an orbit-lowering attitude, which will be maintained until its final target orbit is achieved. At this stage the spacecraft will passivate and power-down in preparation for deorbiting.

The ACS3 mission is funded through NASA’s Small Spacecraft Technology Program (SSTP), whose primary objectives are to identify and support the development of new subsystem technologies to enhance or expand the capabilities of small spacecraft; support flight demonstrations of new technologies, capabilities, and applications for small spacecraft; and use small spacecraft as platforms for testing and demonstrating technologies and capabilities that might have more general applications in larger-scale spacecraft and systems. SSTP is one of nine programs within NASA’s Space Technology Mission Directorate (STMD).

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Event # Event Description

1 Dispenser Deployment

The spacecraft deploys from the dispenser on the launch vehicle into a 650-900 km dawn/dusk sun synchronous orbit.

2 Waiting Period The spacecraft bus enters a waiting period prior to power-on terminated by a timer.

3 Bus Power-On The spacecraft bus powers-on.

4 Null Rates The spacecraft bus attitude determination and control system (ADCS) nulls spacecraft rates to within pre-defined limits.

5 Deploy Solar Arrays The spacecraft bus deploys its solar arrays.

6 Power Positive State

The spacecraft bus reorients the spacecraft into a power positive state.

7 Enable Beacon The spacecraft bus powers on the payload’s UHF transmitter.

Note: this will most likely require powering-on the payload.

8 Enable Transceiver

The spacecraft bus powers on its transceiver and starts transmitting.

9 Wait for MOC Contact

The spacecraft waits for contact with the Mission Operations Center (MOC) to begin further operations.

10 MOC Contact MOC makes contact with the spacecraft.

11 H&S Check The spacecraft bus sends the MOC health and status (H&S).

12 Battery Charge The spacecraft remains in power positive state until its battery is fully charged.

13 Bus Commissioning

The spacecraft bus starts the commissioning process (e.g., ADCS, operational modes, comm data rates, thermal status, etc.).

14 Payload Power- On

The spacecraft bus powers on the payload.

Note: This may be OBE (see step 7).

15 Payload Commissioning

The payload starts payload commissioning process.

Note: This may include snapshots of stowed sail post solar array deployment.

16 Payload Stand- By

The payload enters stand-by mode until commanded by the

MOC.

4.2.Sail Deployment (~ 1-3 days)

Event # Event Description

1 Motor Heater Enabled The payload turns on its motor heater.

2 Test Imagery The payload turns on its cameras and commands test imagery to be taken. The spacecraft bus downlinks the imagery to the MOC.

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Motor Temp & Power State Verification

The payload verifies the motor temperature is above its operational temperature. The spacecraft bus verifies its power state.

Sail Deployment Attitude

The spacecraft bus reorients the spacecraft into its sail deployment attitude (sail parallel to the orbital plane), if necessary.

5 Imagery Start The payload commands its cameras to start recording.

6 Launch Lock Release

The payload commands a pair of frangibolts to disengage the deployment mechanism’s launch lock bar. The spacecraft bus will downlink data confirming the launch lock is disengaged.

Sail Deployment Start

The payload commands the sail to deploy.

Note 1: Target the beginning of a pass so the beginning of the deployment can be observed.

Note 2: Two ground stations may allow for both ends of the deployment to be observed.

Note 3: Deployment will continue even when out of comm line of sight (unless fault condition is triggered).

Note 4: 20-22 (TBR) hub rotations in up to 30 minutes for full deployment.

Note 5: The largest current draw is expected during the first few seconds as the motor overcomes start-up friction in the boom coils.

8 Deployment Data

The spacecraft bus downlinks payload limit switch (rotation counts), boom hub encoder, motor shaft encoder, and motor current draw data, as possible, to ensure proper deployment.

Deployment Motor Power- Off

The payload’s limit switches (end of travel) cut power to the deployment motor at full deployment.

Note: A large current pulse or spike is expected as the booms load the sail quadrants.

10 Launch Lock Reengagement

The payload commands a pair of frangibolts to reengage the deployment mechanism’s launch lock bar. The spacecraft bus will downlink data confirming the launch lock is reengaged.

11 Imagery Stop The payload commands its cameras to stop recording.

12 Sail Snapshots The payload commands its cameras to take a set of still images of the deployed sail, and the spacecraft bus downlinks the images to the MOC.

13 Imagery Downlink

The spacecraft bus starts downlinking the deployment imagery to the MOC (preferably during deployment, if possible).

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Note: It's estimated to take 85 days to downlink 3.1 GB of compressed data. This assumes four 30 minute videos at two frames per second during deployment (2.9 GB), and 800 post deployment images (160 MB) over 20 weeks, both with 10:1 lossy compression, a 1 Mbps downlink rate, and one ground station with an average daily time-in-view of 4.5 minutes.

4.3.Data Downlink (~ 1-3 months)

1 Imagery Downlink

The spacecraft bus continues downlinking the deployment imagery to the MOC.

Note: If the optional orbit raising/lowering maneuvers are executed, a subset of the deployment imagery (videos and/or still shots) needed to achieve mission success will be downlinked a priori.

2 Sail Snapshots

The payload commands its cameras to take a set of still images of the deployed sail.

Note: Images of the deployed sail are expected to be taken once every 8.5 minutes for the duration of a full orbit, and then repeated every week.

4.4.Data Downlink and Orbit Raising (optional, ~ 1 month)

1 Orbit Raising Attitude

The spacecraft bus reorients the spacecraft into its optimal orbit raising attitude [e.g., +25 deg rotation (TBR) about nadir-pointing z-axis at 675 km altitude].

Note: The exact angle of rotation depends on a handful of factors, including orbit altitude, and will be refined as the project matures. See ACS3-02-007, Attitude Control Supplement for additional details.

2 Imagery Downlink

The spacecraft bus continues downlinking the deployment imagery to the MOC.

3 Wheel Desaturation

The spacecraft bus reorients the spacecraft into its nominal attitude (i.e., minimal drag state) to allow for desaturation of its reaction wheels.

Note: This is only done if the wheels can’t be desaturated continuously in the orbit raising attitude.

4 Orbit Raising Attitude Return

The spacecraft bus reorients the spacecraft back into its orbit raising attitude.

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5 Sail Snapshots

The payload commands its cameras to take a set of still images of the deployed sail.

Note: Images of the deployed sail are expected to be taken once every 8.5 minutes for the duration of a full orbit, and then repeated every week.

6 Minimum Drag Attitude

The spacecraft bus reorients the spacecraft into its minimum drag attitude once the target altitude has been achieved.

Note: This event may not be needed if immediate transition to an orbit lowering attitude is desired.

4.5.Data Downlink and Orbit Lowering (optional, ~ 1 month)

Event # Event Description

1 Orbit Lowering Attitude

The spacecraft bus reorients the spacecraft into its orbit lowering attitude [-50 deg rotation (TBR) about nadir-pointing z-axis, for example, at 675 km altitude].

Note: The exact angle of rotation depends on a handful of factors, including orbit altitude, and will be refined as the project matures.

2 Imagery Downlink

The spacecraft bus continues downlinking the deployment imagery to the MOC.

3 Wheel Desaturation

The spacecraft bus reorients the spacecraft into its nominal attitude (i.e., minimal drag state) to allow for desaturation of its reaction wheels.

Note: This is only done if the wheels can’t be desaturated continuously in the orbit lowering attitude.

4 Orbit Lowering Attitude Return

The spacecraft bus reorients the spacecraft back into its orbit lowering attitude.

5 Sail Snapshots

The payload commands its cameras to take a set of still images of the deployed sail.

Note: Images of the deployed sail are expected to be taken once every 8.5 minutes for the duration of a full orbit, and then repeated every week.

6 Minimum Drag Attitude

The spacecraft bus reorients the spacecraft into its minimum drag attitude once the target altitude has been achieved.

Note: Ideally, the targeted altitude is low enough to guarantee reentry within one month (TBR) of passivation and power-down.

4.6.Extended Operations (optional)

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Extended operations beyond the optional orbit raising/lowering maneuvers are possible, including the possibility of fully transitioning operations to a third party. Further details regarding this option will be included as they are available.

4.7.End-of-Life Operations (~ 1 day)

1 Maximum Drag Orientation

The MOC commands the spacecraft to orient itself into its maximum drag configuration (sail normal approximately aligned with the spacecraft’s velocity vector).

2 Payload Power- Off The MOC commands the payload to power-off.

3 Bus Passivation The MOC commands the spacecraft bus to passivate all necessary subsystems (e.g., battery, reaction wheels, etc.).

4 Bus Power-Off

The MOC commands the spacecraft bus to power-down.

Note: The uncontrolled spacecraft is expected to begin tumbling within one orbit.

5 Reentry

The spacecraft reenters the Earth’s atmosphere and burns-up.

Note: Ideally, reentry will take no longer than one month (dependent on the altitude achieved post orbit lowering).