University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

Mission Parameters

D.S.W Gray, V. Masteika

Date Updated Reference Number change

30/10/2007 PLM-MAN-MissionParam-508-1 first version issued

PLUME is a high payload density random tumbling pico-satellite mounting a nano-meteoroid detector, RadFET and camera, following the Cubesat concept of a 10x10x10cm satellite with a 1 kg mass. The nano-meteoroid detector will characterise the flux of orbital dust with masses greater than 2x10-18 kg [1], while a RadFET will analyses the radiation environment. A camera will also be flown for outreach purposes.

Current mission assumptions are as follows:

Orbit- The launch vehicle, expected to be a Dnepr from Kazakhstan, Vega or Ariane from French Guiana, will restrict the available orbit depending on the main rocket payload. The most likely scenarios are a circular Low Earth Orbit (defined as between 200-2000km) at around 300km altitude and of inclination up to ~70 degrees, or Ariane Geosynchronous-Transfer Orbit (24,582 km [3]) of low inclination (~5 degrees). It is assumed that the cubesat will pass through the South Atlantic Anomaly (SAA), and the ‘power save mode’ of the spacecraft should be hardened against SAA effects, especially as the launch inclination is not fixed at this time.

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University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

Above: From left to right, Ariane 5, Vega and Dnepr launch vehicles.

Payload- The main nano-meteoroid detector payload will use a side mounting of ~2cm2. There will be three detectors for multi-axis pointing. A RadFET and an unspecified colour CMOS camera chip will also be flown. The payloads should not draw more than 1-1.5 W. This is assuming that the camera and nano-meteoroid detector are not used at the same time.

Power- Power is provided by 5-6 solar panels fixed in orientation on side mountings and storage batteries. The power out is estimated at 1 W per panel during operation, when they will not be orthogonal to the incoming light. Lithium Ion batteries will provide spaceship power during deployment and eclipse. Such batteries have an energy density of 100Wh/kg. The mass per cell is assumed to be around 60g per battery, and the battery lifetime must be not less than 300 minutes. Total power consumption will be no greater than 3W. In ‘power saving’ mode consumption should be…?

Comms- The deployable antenna will be sprung loaded and released by wire electric burn through system or by memory metal irradiation. All transmitted data will be received by the National Space Centre ground station, Leicester, England. Although it is hoped that collaborations with other institutes will lead to several ground stations serving the mission, it is not critical. The antenna will emit an isotropic signal so that no pointing is required. When visible a download time of 5 minutes or less must be considered. There will be long periods of time when the satellite is not in contact with the ground station. Consideration should be given to collaboration with other world wide ground station download sites, possibly as part of esa’s GENSO programme presented at the Vega maiden flight cubesat conference in January 2008.

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University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

ADCS- Attitude detection will be provided by 3 axis magneto-resistors. The nano-meteoroid payload is not direction critical. The tumbling rate is assumed to be less than 0.1 rad/s. This is the spin expected following deployment from the PPOD. The magneto-resistors will determine the direction of the Earth’s magnetic field relative to the cubesat for science reference to an accuracy of within 1 degree. The camera will double as a sun/moon/limb detector along with a dedicated sun sensor under consideration.

Structure- Pumpkin Inc and ISIS can both provide the structural kit require for mounting of the bus and sub-systems. The Pumpkin cost around US$ 6000, and has a mass of 170g. All internal structures are to be made in house, and must with stand a general resonance of 400 Hz. The cubesat will be deployable from any payload delivery system provided it is specified in sufficient time. The preferred launch adapter is currently…

The skeletal Pumpkin Inc kit.

OBDH- Pumpkin kit hardware will be used for on-board-data-handling. The time frame of the project limits the amount of electrical engineering that can be completed. The aim must be to have sufficient data storage space for an autonomous cubesat operational flight time of around 3 months. Will there really? All subsystems must be compatible with the Pumpkin Inc computer kit interfaces. The science data output of the payload is negligible relative to the camera and so no problems are expected due to insufficient data storage. Flash memory will be used, as radiation hard as possible. This means a memory space to the order of between 10 and 100Mb.

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University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

Launch Environment-

The Ariane 5 has a value of 4.55g for general acceleration. The longitude acceleration is between -7.5 and +5.5g, and the lateral acceleration is between + or – 6g. Ground airflow through payload bay does not exceed 2 m s-1, and the decompression rate of payload bay is normally around 2 kPa s-1. This can reach 5 kPa s-1 for a single payload launch.

Ariane 5 decompression rate.

The Dnepr Quasi Static Load has a maximum value of 8.3g longitudinal, and 1g lateral.

Dnepr decompression rate.

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University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

Vega launch vehicle’s peak longitudinal load is 5.5g, and the peak lateral load is 0.9g including wind gust effects. Ground airflow through the payload bay will not exceed 2 m s-1. The decompression rate will be less than 5.0 kPa s-1. The erratic nature of the decompression rate is due to the launch strategy of Vega. The rocket cannot throttle back to reduce dynamic pressure from the atmosphere (max Q).

Space Environment-

The Cubesat must resist the effects of impacting particles in the near Earth environment. The main populations of stationary particles impacting at 7.5 x 103

m/sec are oxygen 1+, atomic oxygen, oxygen 2 molecules, and nitrogen 2 molecules. The sum of the power deposited on the Cubesat from these particles will be around 1.2Wm-2, so heating effects from these species can be ignored. The power from the Sun is 1360Wm-2 in LEO. This results in a surface temperature of 394K of a black body. In eclipse the external temperature is 2.7K plus 234Wm-2 IR radiation is emitted from the Earth’s dark side. The charge build-up on the craft is considered negligible due to populations of both free protons and electrons. The proton distribution may be greater closer into the planet.

References

[1] J. D. Carpenter, T. S. Stevenson, G. W. Fraser, J. C. Bridges, A. T. Kearsley, R. J. Chater and S. V. Hainsworth: Nanometer Hypervelocity Dust Impacts In Low Earth Orbit

[2] P. Molyneux Payload Science Requirements Document http://cubesat.wikidot.com.

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University of Leicester PLUME Ref: PLM-MAN-MissionParam-508-1Date: 30/10/2007

[3] http://en.wikipedia.org/wiki/Geostationary_transfer_orbit

[4] http://www.ll.mit.edu/ST/sbv/saa.html

[5] http://snebulos.mit.edu/projects/crm/DNEPR/Dnepr_User_Guide.pdf

[6] http://www.arianespace.com/site/documents/main_docs.html

[7] http://www.grc.nasa.gov/WWW/K-12/Numbers/Math/Mathematical_Thinking/estimating_the_temperature.htm

[8] http://klabs.org/DEI/References/design_guidelines/design_series/1258jsc.pdf

Not used but may be useful for thermal design.

[9] http://www.tak2000.com/data/planets/earth.htm

May be useful for thermal design.

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