Stratospheric Satellite Project for SHSSP16

Transcription

1 1.0 Introduction. Stratospheric Satellite Project for SHSSP16 High- altitude balloons reach near space (above 30km) and provide opportunities for testing small- satellite payloads. Adelaide is fortunate to host an experienced group of ballooning enthusiasts who have carried out many launches over the last several years, including a small number of pseudo cubesat missions. The aim of this SHSSP team project is to rapidly design, assemble, integrate and test a remote- sensing and communications payload suitable for high- altitude ballooning. This team project will complement the white- paper project of SHSSP- 16 by collecting visible and near IR images of local South Australian agricultural areas. In particular the main focus will involve viticulture, since it is an actively growing crop in January, whilst many other crops are harvested or dormant. While the products of the viticulture sector do not form a staple food that will feed humanity, from a horticultural perspective the cultivation of vineyards requires careful assessment of application of irrigation, fertilisers, herbicides and crop growth over intensively managed, small- area fields whose conditions can vary significantly. The use of airborne and high resolution satellite imaging is common practice in precision viticulture and forms and an analogue for similar practices used in the cultivation of rice and, at more regional scale, wheat and grains: crops which do impact on the food security of our planet. Given the relatively short time- scale of this team project, SHSSP students will be offered the use of various items for the payload. These items include a small number of electronic, sensing and imaging sub- systems, plus access to software packages, detailed below. The use of these components is not mandatory: any solution that fits within constrains outlines in Appendix A, plus takes into account procurement times suited to the launch schedule, is allowed. If students wish to buy additional hardware items, this will also be possible within a very limited budget. Given the schedule, it seems likely there will be greater scope for novel software components rather than hardware designs, but the latter are not precluded. Furthermore the specific outcomes of this project, including all project management issues, will not be prescribed but should be determined by the student team. The team will also be required to liaise with launch providers and staff at the ground- station, plan for contingencies, make a visual record of the project, undertake some analysis of the collected information and promote the project to the media. The rest of the document is organised as follows: Section 2 provides a brief description of the balloon operations and likely launch scenario. Section 3 provides a list of suggested items available for this project. 2. Launch and Operational Arrangements This ballooning project is run by AREG i who are located in Adelaide. Balloons are launched from Mt Barker in the Adelaide Hills (Appendix B). The procedure

2 involves filling a helium balloon with an amount of helium to achieve a particular ascent rate, assembling the client s payload (in this case the SHSSP experiment) plus various Horus hardware items onto a balloon train suspended below the balloon, then following the balloon s flight path and retrieving the equipment after landing. Many details and examples of previous flights are available on the Project Horus website. ii The SHSSP team will not need to deal with any of the tasks of balloon launching or retrieval as these functions are carried out by AREG members. However SHSSP will observe the launch and may assist with reception of balloon telemetry as described below. The flight is expected to last 3 or 4 hours. The primary role of the SHSSP team will be the preparation of the remote- sensing payload prior to launch, plus post launch data analysis. The launch day will include a field visit to a vine- growing area (Appendix B) for discussions with a local vigneron and viewing of previously acquired satellite imagery of the immediate area. In addition there will be an opportunity to acquire high resolution visible and possibly IR imagery from a small UAV which will be flown on the launch day at various altitudes over of sections of the vineyard. Individual frames and video will be available from this UAV camera. Launch day is scheduled as Jan 26 th but, in common with all aerospace projects, this is subject to meteorological conditions. High- altitude balloon trajectories can now be predicted with a reasonable degree of accuracy via detailed atmospheric models. Hence within 3 days of launch, if wind conditions are not suitable for the 26 th, the SHSSP activities on the 26 th may be swapped with those on Jan 30 th. As standard equipment on Horus launches, low- rate bi- directional communications are provided. The downlink carries data from a GPS receiver on the balloon train, allowing tracking. This information is relayed to an internet site for real- time display on a Google map. The Horus uplink provides a terminate ascent command, which severs the balloon from the equipment train and so initiates a parachute- controlled descent. This (usually) allows the recovery of the Horus payload with a soft landing. As part of the SHSSP payload it is envisaged the Horus launch will carry an additional telemetry system provided by ITR at UniSA. This is prototype equipment, designed for the forthcoming QB50 cubesat project, and is further described in Section 3. It will provide some options for real- time TT&C for the SHSSP payload. Note that this facility will probably carry limited or no downlink image data from the payload, but it could provide other telemetry plus uplink control options if the SHSSP team requires them. We envisage the primary payload image data will be captured on board the payload and retrieved after the balloon flight.

3 3: Payload Subsystems Available for the SHSSP Team The Australian organisation Launchbox provides various subsystems for cubesats, including whole assemblies that have been used in a number of Horus high- altitude balloon projects by local high schools iii. Dr Matt Tetlow, based in Adelaide and involved in SHSSP, is one of the founders of Launchbox. He will be available for consultation in this project. It is envisaged that the easiest approach for the SHSSP team will be to use Launchbox Mission 2 modules, plus the ITR communications system, and develop an augmented design. For example an extra camera could be included in the payload, possibly with some remote control options from ground via the TT&C link. Launchbox will make their existing source code available. Another camera option is outlined below. Brief details of this equipment follow: 1. ITR Communications Payload: This system resides on a small PCB of size about 50mm by 90mm of mass, including the antenna, of ~100 gms. It can provide can uplink or downlink communications at up to 9600 bit/s. Typically the payload operates with about 2 seconds in uplink mode (while it receives) and about 8 seconds in downlink mode (while it transmits to ground), but these periods may be adjusted to suit requirements. Power consumption in receive mode is < 100 mw and in transmit mode is < 700 mw. ITR will provide the ground station equipment to allow the other end of this communication link. 2. Launchbox power supply: This board carries two LiFePO4 1600mAh each. It includes a 5V 500mA capacity, with 1 x USB port for camera charging and support during flight, two 5V ports accessed via JST vertical XH type connector, plus one USB mini B connector for charging the batteries. The system weighs 130 to 150 gms. It may be possible to use larger batteries in this power supply, if required. 3. Mobius Camera: Launchbox has used the Mobius Wide Angle Lens C HD Action Camera, which includes 1080P HD Video or single image modes. The field of view is 131 degrees. The camera has its own micro SD storage capacity to 8Gb, plus its own internal battery. It includes an IR- cut filter, to remove IR wavelengths. According to some reports this filter can be removed, however Launchbox have not carried out that procedure. Note that image data is not available from the camera during flight; possibly shutter control will be possible although Launchbox have only employed this camera in a mode of taking pictures at a regular interval after turn- on. V 4. The Launchbox controller board (55 gms) uses an Arduino microcontroller with a GPS system, barometric sensor BMP180 and 3 axis accelerometer ADXL Structure. As shown on the Launchbox web pages, the Mission 2 kit includes a mechanical structure designed to suit the standard set of Mission 2 modules. We assume this could be modified fairly easily to

4 accommodate an extra camera or other components. 6. Optical filter: It is envisaged a small optical filter (e.g. of this type iv ) could be mounted in front of one (or more) cameras to provide some discrimination of near- IR/ visible bands. 7. RPI + camera: The raspberry pi is a small computer of credit- card size running Linux. This processor should be available with a 5M- pixel camera (either with or without IR cut filter). Power consumption is about 1.5 W. Use of this option would allow shutter control (e.g. via uplink command) and/or image processing, possibly with low- resolution download during flight. Appendix A: Payload Options and Constraints The overall constraints on the payload may be stated fairly simply: 1. Total Payload Mass: <1.5 kgm (TBC) 2. Serial Interface to ITR communications payload: I2C or UART 3. ITR max downlink rate: 9600 bit/s Nevertheless designing the payload needs to take many factors into consideration. First note there is no power budget above as the payload carries it s own battery supply, which is part of the total mass. The total power load needs to fit the capability of this payload power supply. This includes the ITR communications board whose power needs are also listed in Section 3. Of course the team might arrange suitable duty cycles for different sub- systems to better manage power consumption. Secondly, unlike a satellite payload, there is no specific volume constraint. In general, payload volume is not an issue on the balloon train. However if thermal insulation requires a foam box to be used, which is common, these packaging issues should be taken into account. On a related topic, the team may need to consider the possibility of overheating in near space due to the lack of normal convective cooling. AREG have experience in this area. At least one AREG member will be available for consultation with the SHSSP team on a date TBD and examples of previous Horus payloads will be available. Regarding imaging, ideally the sub- system will record both visible red (~ 650nm) and near IR ( nm) as these two EM wavelengths permit analysis of vegetation vigour, which is highly related to leaf structure and chlorophyll content. In the case of vines this is correlated with fruit crop yield (see Appendix C). The spatial resolution of the sensor(s) should be as high as possible, within budgetary and mass constraints, with the temporal cycle of image acquisition related to data storage, ascent rate, altitude and spatial coverage by each image.

5 SHSSP^216 Team Project Appendix B: Site Locations Launch site (Mt Barker school oval) and vine yard site (Lane Vineyard), which is 7.5 km NNW of the Launch site are shown in Figure 1derived from Google Earth. The red rectangle indicates the boundary of high resolution satellite imagery requested from AirBus hopefully to be acquired in early January. Figure 1: Launch site Appendix C: Vegetation Vigour and Spectral Imaging Leaf chlorophyll content and vegetation vigour can be assessed used spectral observations. The typical spectral reflectance curve for vegetation is shown in Figure 2. Draft v5

6 Figure 2: Typical reflectance curve for vegetation One of the many techniques for extracting information from these spectra is the use of the Normalised Difference Vegetation Index (NDVI which is defined as the difference between infrared and red energy divided by the sum of these values: NDVI = (IR R) / (IR + R) Red energy is absorbed by photosynthetically active leaves, whilst IR energy is strongly reflected. Thus one of the many analysis techniques which might be applied to the imagery collected at various altitudes might be NDVI. i Amateur Radio Experiments Group: ii Project Horus website ( ). iii Launchbox components: iv Optical filter example: filters/#f=categories_s *C87I* v Mobius ActionCam: actioncam.com/