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KaTE

KaTE (Ka-band TTC Experiment) is proposed as a Technology Experiment onboard the SMART-1 spacecraft.

Overview of the KaTE Technology Experiment

KaTE (Ka-band TTC Experiment) shall demonstrate the advantages of the X/Ka-band TTC system for future science missions, in particular for Deep Space. The demonstration will include high rate telemetry in Ka-band, Radio Science, Turbo Encoding and the high performance of the Deep Space Transponder.

Objectives of KaTE Technology Experiment

The general objective of the experiment is the demonstration of the X/Ka-band TTC system, mainly developed under Agency contracts and intended for Agency missions, under realistic and relevant conditions as a key spacecraft technology for future deep space missions.
The proposed KaTE experiment comprises the DST (deep space transponder), spacecraft antennae (combined X-band transmit and receive horn, separate Ka-band horn) and turbo encoder on the spacecraft and the turbo decoder and ground-station upgrade options.

The need to change from the traditional S-band links to X/Ka-band links is substantiated by

  • the increasing interference problems with terrestrial and mobile SATCOM systems,
  • enhanced requirements of future missions and scientific programmes (threshold, data rate, accuracy, dimension, mass, etc.)
  • reduction of mission and spacecraft costs
  • compatibility to future NASA/JPL programmes
  • enhanced radio science capabilities

It is important that a demonstration of the KaTE X/Ka-band TTC system is performed to allow for sufficient maturity and experience of the techniques required relevant to the ESA Horizon 2000 cornerstone Deep Space applications. It should be noted that the Ka-band link has a unique advantage for missions such as the Mercury Mission as it suffers negligible signal-to-noise degradations due to radio-frequency scintillation in the solar plasma.

Elements of the KaTE Experiment

KaTE is an end-to-end TTC technology and science experiment covering the use of Ka-band and X-band. These bands are the only feasible bands for future deep space missions. In particular the future Cornerstone Mission to Mercury would have to use X/Ka-band.

Deep Space Transponder

An Engineering Model of the Deep Space Transponder is currently under development within the frame of a GSTP-2 contract. Under this proposal a flight model will be developed and flown on Smart-1 as a technology demonstration and used for Radio Science and high rate telemetry in Ka-band.

Horn Antennas

To ensure a complete onboard RF system a set of horn antennas will be designed and procured to enable X-band reception and transmission and Ka-band transmission

XKaT (X-band Ka-band Testbed)

XKaT is the ESTEC laboratory testbed with experimental antenna which will be used to support all the end-to-end experiments listed below.

Perth 35m Antenna

The new 35m large aperture antenna in the Southern Hemisphere near Perth will have an X-band uplink capability. The mechanical design for a Ka-band downlink will also be implemented but the electronics will be subject to further investment. The KaTE experiment will validate the antenna and provide increased TC/TM capability, and provide the operations experience with Ka-band.

RSIS

The RSIS scientific and technological goals are achieved primarily by means of precision tracking of the SMART-1 spacecraft. Some measurements (moon librations and, just in case of an extended mission, asteroid mass ) require also image acquisition from the high resolution camera and accurate attitude reconstruction from star sensor data.

In the transfer and lunar phase the two-way coherent radio link shall be used to

  • Monitor the performances of the electric propulsion system (opportunity experiment).
  • Measure the rotational state of the moon (in particular the physical librations in latitude) from orbit, by combining accurate orbit determination, attitude reconstruction and imaging of the surface by the AMIE camera.
  • Perform a thorough analysis of the capabilities of the new, advanced X/Ka microwave link for precision Doppler and ranging measurements. This assessment is essential for the planning of future, high precision geodesy and relativity experiments proposed for the planetary missions of the next decades, in particular Mercury Orbiter.

RSIS experiment fits quite well the SMART-1 mission concept to offer a breadboard for novel technologies to be used in next space missions, and to provide at the same time some scientific opportunities for lunar and space research. On the technology side, the RSIS will assess the capabilities of the X/Ka radio link, crucial to future European deep space missions. Moreover, the same tracking experiment will offer a monitoring of the performances of the electric propulsion subsystem, which is one of the main SMART-1 mission drivers. From the scientific point of view, the RSIS can provide the first measurement of librations of a celestial body carried out from orbit. This technique, which will be used in the planned Mercury mission, will be tested by SMART-1 and validated with respect to a known benchmark (the Moon librations have been measured with a very good precision from laser-ranging data.

Turbo Encoder

For future missions and especially for deep space missions the requirements on the link performance becomes most severe. The concept of Turbo coding has recently been introduced to provide telemetry close to the Shannon limit.

Turbo coding has a better performance than the convolutional codes with high constraint length. The potential gain is of the order of about 2 to 3dB. Additionally the Turbo code decoder on the receiver side is less complex than an equivalent performance Viterbi decoder. Furthermore the onboard encoder is very simple and could be readily implemented on a FPGA. An experimental Turbo encoder including PN-generator will be implemented on-board the spacecraft in the KaTE transponder. In this way by a simple command a Turbo encoded pseudo-random data stream may be sent or a Turbo encoded TM data stream may be transmitted by the KaTE TT&C system to ground.

Within the CCSDS there is a draft standard supported by ESA and NASA for Turbo codes thus ensuring cross-agency support, the KaTE Turbo encoder will be the first demonstration of these CCSDS codes.

Experiment Objectives and Description

Experiment Objectives

The aims of the proposed experiment are:

Validate the onboard deep space transponder as a technology experiment in X/Ka-band demonstrating

  • Extremely low threshold levels (adaptable to mission criterion, note: the expected performance of KaTE is 6 to 9dB better than the stringent spec placed on the Rosetta transponder - this would imply emergency communication possible from Perth out to Mars and Mercury i.e. to an LGA)
  • Low phase noise (at least 20dB better than the S-band transponder)
  • VLBI signal transmission
  • TC demodulation (with possible extension to onboard decoding)
  • X/Ka-coherent transmission
  • Turbo encoding (near Shannon limit communication )
  • High rate telemetry additional to Smart-1 baseline via the CAN bus or by direct connection
  • Possible extension to spacecraft status signalling for autonomous operation by subcarrier switching.

Science experiment

  • A system experiment preparing for the measurement of the Libration of Mercury
  • Propagation experiments through earth's ionosphere

Electric Propulsion Monitoring

  • Accurate acceleration determination by improved spacecraft tracking in X/Ka bands

Ground Segment Experiment

  • In orbit source used for calibration/test of upgraded Perth Ground Station (X/Ka) and/or additionally the ASI Sardinia Ground Station