AAE 450 – Senior Design

J. Darcey Kuhn

ERV Team – Communications

January 23, 2001

Parameters

• High Gain Antenna Sizes – Beamwidth and antenna gain

• Capacity (i.e. number of channels of each type) – or bandwidths and frequencies

• Uplink & Downlink signal strength and quality to Deep Space Network (DSN) – support communications, science data, voice, video, engineering

telemetry, and navigation

http://deepspace.jpl.nasa.gov/dsn/

High Gain Antenna

• Beamwidth: from an antenna pattern, the angle between the half-power (3 dB) points of the main lobe, when referenced to the peak effective radiated power of the main lobe

http://132.163.64.205/fs-1037/dir-004/_0572.htm

High Gain Antenna

A useful rule of thumb for calculating beamwidth is

3 dB beamwidth = 70λ / D (degrees)where λ is wavelength and D the antenna diameter

• Surveyor: 0.56 deg• Space Shuttle

Uplinking: 0.56 deg

Downlinking: 0.51 deg

High Gain Antenna

• Antenna Gain (Isotropic) – for a uniformly illuminated antenna with physical area A, the directive gain at the center of the main beam is given by:

http://web.bham.ac.uk/eee1roj8/wbe/wbe031.htm

High Gain Antenna

G = 4**A/λ2 A= d2/4

• Gain is normally expressed in dBs by taking 10*log(G)• Surveyor: 42.41 dB• Space Shuttle:

Uplinking: 42.39 dB

Downlinking: 43.14 dB

Bandwidths & Frequencies

• Bandwidth: Amount of data that can be transferred in a fixed amount of time

• Space Shuttle uses S-band (1,700 to 2,300 MHz) & Ku-band (15,250 to 17,250 MHz) to transfer information• Ku-band located in the payload bay

• Ku-band (12-18 GHz / λ = 2.5 to 1.67 cm) can handle higher quantities of data than the S-band systems (3 channels of data)

• All transmissions broadcasted by Surveyor utilized X-band radio signals near 8.4 GHz

Deep Space Network

• DSN is an international network of antennas that supports interplanetary spacecraft missions

• Currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world – CA, Spain, and Australia

Antenna Mounting

• High-gain antenna sits at the end of a long boom• Two rotating joints, called gimbals, hold antenna to

boom• Gimbals will allow the antenna to automatically track and

point at the Earth

Future Enhancements

http://deepspace.jpl.nasa.gov/dsn/array/index.html

Future Enhancements

• Cost Analysis• Power

• Consumption• Signal

• Signal-to-Noise Ratio• Weight

• Historically low

• Failure Probability • Low Gain Antenna as back-up

Related Skills

• Matlab, Fortran 77, UNIX, AutoCAD, C• Currently enrolled in 490E (Satellite Systems)• Two co-op tours with United Space Alliance at Johnson

Space Center – uplinking data from the MCC to ISS