To: Panel Members

From: Joel Smith

Subject: Minutes - IACG Panel-3 on Space VLBI, August 21, 1999, Toronto,

Canada

Copy: Marc Allen, Valery Altunin, Chuck Holmes, Vittorio Manno, Adriana

Ocampo, Carl Pilcher, Guenter Riegler, Gael Squibb, Rick Wietfeldt,

VLBI/IACG, Dave Jauncey, Wayne Cannon, Peter Dewdney, Jon Romney, Alan Whitney

LOGISTICS:

The IACG Panel-3 on Space VLBI met Saturday, August 21, 1999, from 10:30 am
to 12:00 noon, in room 134, McLennan Physics Building, University of
Toronto, in conjunction with the Toronto International Union of Radio
Science (URSI) meeting.

Panel members included: Leonid Gurvits and Richard Schilizzi (ESA), Hisashi
Hirabayashi and Makoto Inoue (ISAS), and Bob Preston, Joel Smith, and Jim
Ulvestad (NASA).

Also in attendance: Ron Ekers and David Jauncey (Australia), Wayne Cannon,
Sean Dougherty, and George Feil (Canada), Anton Zensus (Germany), Phil
Edwards (Japan), and Phil Diamond, David Murphy, Jon Romney, and Alan
Whitney (U.S.)

INTERFACE STANDARDS:

Alan Whitney, Haystack Observatory, reported on the status of the VLBI
Standards Interface committee (jointly with the Global VLBI Working Group
whose meeting preceded the panel 3 meeting). A proposal has been drafted
and circulated for comment for a VLBI Hardware Standard Interface. The
standard is to allow agencies (including Space VLBI mission designers) to
cope with existing and projected incompatibilities among wide band VLBI
data transmissions and/or recordings. If fully implemented such a standard
would remove many of the operational constraints which are now imposed on
the VSOP mission, and allow lower costs of operation for future missions.

FUTURE MISSIONS:

The review of future missions was cursory since so many of the missions had
been described elsewhere within URSI. However, the number of potential
Space VLBI missions continues to grow.
Within Japan, the VSOP-2 mission is still under study within ISAS with
international workshops in Tokyo last July and next January. VSOP-2 plans
on observations to 43 GHz from a 10-to-15-meter telescope with down-link
rates of 1 Gbps (500 MHz observing bandwidth) from apogees of 30,000 Km.

Also, as a follow-on, VSOP-3, with even greater sensitivity and resolution
than VSOP-2, is envisioned, possibly with two spacecraft in orbit
simultaneously for fuller coverage.

Within Europe, the ISS VLBI-2 Project, with its large (30-m) antenna to be
constructed on-board the Space Station, will report out their
pre-assessment study in September. The ISS VLBI-2 (once launched from the

Space Station) would observe to 87 GHz from a 30-meter telescope with
down-link rates to 8 Gbps (2000 MHz observing bandwidth) from apogees of
80,000 Km.

Within Russia, a Space VLBI mission to follow on after RadioAstron is under
consideration: Millemetron with observations to 1500 GHz from a 12-meter
telescope in lunar-perturbed elliptical orbits (apogee of 300,000 Km) would
extend the angular resolution of observations orders of magnitude over
current missions.

Within the U.S., the ARISE mission has completed their study. They have
presented their findings to NASA's Structure and Evolution of the Universe
(SEU) Sub-committee for consideration in NASA's Space Science strategic
plan. They have also submitted their report to NASA's Decadal Committee.

ARISE is designed for observations to 86 GHz from a 25-meter telescope with
down-link rates to 8 Gbps (2000 MHz observing bandwidth) from apogees of
40,000 Km.

The ALFA proposal, for a mission designed to make high resolution radio
images below the Earth's ionosphere with an array of small low-data-rate
Space VLBI spacecraft in a distant retrograde Earth orbit, was rejected as
a MIDEX mission on cost grounds but generated good interest in both the SEU
and Sun-Earth Connection Sub-committees, and will be re-submitted next year.

TECHNOLOGIES:

The major technology issues for Space VLBI missions tend to be "ultra"
low-noise front ends, large antennas capable of high frequency observations
(from 43 to 1500 GHz), data rates(1 to 8 Gbps) for down-links, recording,
and correlation, spectrum allocations for the high down-link rates, and
cost. Reports were given on data rates and spectrum allocation.

Reports from Canada, Europe, Japan, and the U.S. confirm that the VLBI
community can achieve 1 Gbps data rates for recording and correlation in
the immediate future and sustain it (albeit marginally) with existing and
planned programs and technologies. Capabilities to support data rates of 2
Gbps are more difficult, with some agencies (Canada, Japan) able to project
some capabilities, but generally most would accommodate the doubled rates
with doubled tapes and/or doubled operating time. No agency had much to
offer for data rates of 4 Gbps, except for one (Canada) and that was fairly
fuzzy. No one had anything to offer at data rates of 8 Gbps except for
extreme options such as "bent-pipes" (direct transmission from telescopes
to correlators).

Higher data rates beyond the current VLBI maximum of 128 Mbps reflect
broader observing bands beyond the current 32 MHz, and pose problems of how
to organize channels of data within the band. Space and ground telescopes
are generally built for multiples of 16 MHz channels, but these will
proliferate wildly as rates climb to 1 to 8 Gbps, and, eventually, wider
channels will be required world-wide to accommodate the higher rates. An
international study group is needed to develop an orderly progression of
channelization for Space and ground VLBI.

Frequency allocation of the space-to-Earth link also is an increasing
problem as data rates increase from the current 128 Mbps to 1 to 8 Gbps.
However, a trade-off exists among various (nearly) constant-envelope
modulation techniques to allow high rate data to fit existing and proposed
bands, albeit with sometimes secondary allocations. These modulation
techniques range from standard quadrature-phase-shift-keying (QPSK) to
spectrally-shaped QPSK, dual-polarized QPSK, or constant-envelope analog
modulation. It is believed that increasingly advanced modulation techniques
would allow data-rates as high as 4 Gbps to remain in the existing Space
VLBI allocation at Ku-band (14.0-14.7 GHz), but that higher rates or less
advanced modulation techniques would necessitate moving the down-links to
Ka-band (37.0-38.0) or W-band (above 70 GHz).

FUTURE PANEL MEETINGS:

There may be a small IACG Panel 3 meeting in Moscow in October during the
meeting for the RadioAstron International Science Council, primarily to
involve the Russians (who were not at URSI) and to learn more about

Millimetron and other Russian concepts.
There will be a Panel 3 meeting on Okinawa on November 16 on the first day
of the IACG. A Panel 3 report to the IACG will be given on November 17 or
18 during the plenary sessions.