Parabolic dishes are the most widely used antennas for high bandwidth communications for space applications. The technology is well understood and has proven very reliable. They provide high gains, enabling high bandwidth communication over long distances, and do not consume much power.

Verge HGA/LGA Background

The HGA used on the Verge, to transmit high-definition video and high-resolution imagery, is shown below¹. Similar in design to the Ulysses antenna, the Verge antenna provides a combination of a HGA and LGA in a single unit, providing the ability to design a lander of lighter mass. Slight differences between this antenna and the Ulysses antenna include that the Verge HGA/LGA would be approximately 1.2 m in diameter, as opposed to the Ulysses 1.65 m diameter, so as to fit more easily within the Falcon 1e payload unit. Simultaneously, gain statistics would not change by utilizing this antenna.

While preparing this proposal, EOSystems was in contact with a program manager at Harris Corp. regarding space-deployable antennas that Harris manufactures. Due to time constraints, and the fact that space-deployable antennas with our requirements are not simply manufactured as commercial-off-the-shelf units (COTS), EOSystems was unsuccessful in finding an antenna meeting our specifications. Given more time, we are confident that we would be able to determine an exact solution that fits our requirements.

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Specifications

Since specifications on the Ulysses antenna were not readily available, further assistance was provided by NASA - Jet Propulsion Laboratory engineer Daniel Presti. Mr. Presti gave EOSystems an educated estimate of 11 kg as the mass of the original Ulysses antenna. Assuming an even distribution of mass, the approximate mass for our 1.2 m diameter antenna would be:

(11 kg / (π * (1.65/2)^2)) * ((π * (1.2/2)^2)) ≈ 5.82 kg

The Verge HGA is a front-fed parabolic reflector dish, with both S-band and X-band feeds. The reflector is a carbon fiber dish reinforced with aluminium honeycomb (to insulate the HGA), interfacing with Verge through a support structure. The feed assembly is supported by three carbon fiber reinforced plastic (CFRP) struts.

The HGA has a transmit gain of 40.2 dB in the X-band at 8.495 GHz, which is the nominal downlink frequency. Uplink occurs in the S-band at 2.100 GHz, and the antenna has a receive gain of approximately 26.4 dB at this frequency. S-band downlink occurs at 2.25 GHz and the antenna gain is 25.8 dB at this frequency. The HGA operates in right-handed circular polarization (RHCP) in both the X and S bands. This information is contained below.

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Initially Considered: Planar Array Antenna

EOSystems initially considered implementing a planar array antenna, to be used as a HGA to transmit mooncasts to the ATA. EOSystems determined that this would not be feasible, due to its expensive implementation cost of at least $2 million (as told directly by Kenneth Perko, NASA GSFC).

As an example of one such antenna, Boeing Phantom Works, based in Seattle, WA, built a planar array antenna for NASA’s New Millenium Program’s Earth Observing-1 (EO-1) mission. The X-band phased array antenna is a high data rate, low-mass X-band antenna for downlinking images from the EO-1 solid-state recorder. This planar antenna eliminates the need for deployable structures and moving parts and eliminates torque disturbances that moving antennas impart to the spacecraft. Along with a 5.5 kg mass, the XPAA has an EIRP of 160 W and is able to transmit at 105 Mbps.

Other advantages include that this antenna is more efficient than similarly-specified parabolic antennas, its beam is controller electronically (not mechanically) by adjusting phases of individual transmitters, and it allows for extremely fast and precise communication-beam steering, which is important for high bandwidth communication since data rate decreases with increasing angular offset.

Additionally, the XPAA has the advantage that it is able to simultaneously capture-and-transmit data, while avoiding perturbations to spacecraft instruments. It can steer across wide beamwidths in milliseconds without imparting inertia to the spacecraft (especially while in route to the moon). For more information regarding this planar array antenna, email Kenneth Perko at NASA’s Goddard Space Flight Center.

Further developments in the area of phased planar array antennas will lend well to its implementation in private-industry spacecraft applications, such as later versions of the Verge. For more planar array antenna solutions, company literature can be attained from L-3 Communications, Matra Marconi, SPAR, Ball Aerospace, Westinghouse, Harris Corp., Malibau Research, or CV Engineering.

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[1]        http://ulysses-ops.jpl.esa.int/ulsfct/spacecraft/hga.html