Observer's Frequently Asked Questions
Last modified: January 2002

Frequently Asked Questions about VSOP observations.

Q: When is the next AO due to be released?
A: The sixth Announcement of Opportunity (AO) was released on 7 May 2001 with a proposal deadline of Friday 1 June 2001 -- see the AO page for details. It is not anticiapted that another AO will be released: with the withdrawal of NASA-funded mission elements, the mission has changed focus and has placed the emphasis on completing the VSOP Survey Program of 289 active galactic nuclei at 5 GHz.

Q: Where can I find up-to-date HALCA orbital elements?
A: The Simulation Software page was updated in August 2000.

Q: When will my observation be scheduled?
A: Look at the Observing page for details of upcoming observations. The Principal Investigator (or nominated contact person) on each proposal will be contacted 2--4 weeks before each observation and given a chance to comment on the ground radio telescope schedule files.

Q: How can I find the status of my observation?
A: An Observation Status page has been added to the WWW site. Work is continuing on bringing this page up to date.

Q: I see an observation code v330 -- were there that many proposals for the first AO period??
A: No -- see the Observation Code explanation page for details.

Q: Where is my data?
A: Once correlation is completed and the correlated data checked it will be sent to the address given on the proposal sheets and included in the ground radio telescope schedule files. When checking these files make sure this address is correct!

Q: Why is there no data from the satellite for three minutes mid-way through a Ku band tracking pass?
A: Occasionally during a tracking pass HALCA's K-u band antenna reaches its azimuth limit, and it takes three minutes to `unwrap' the antenna.

Q: Where is the calibration data?
A: Calibration data for the ground radio telescopes is available from the usual regional FTP sites. HALCA calibration data is now described on the HALCA calibration page. Files are (or will be!) available for each observation, and nominal system temperature values, which have found to work well in practice, are also given. HALCA gain information is also provided.

Q: What's the story with 22 GHz?
A: The detection of 22GHz fringes to HALCA is good news, however few sources are are strong as Orion-KL during outburst! It is likely that only the very strongest sources in the sky can be detected at 22 GHz, and that any successful 22 GHz observations will require considerable effort on the part of mission personnel. Any 22 GHz observations carried out in the foreseeable future will be made as In-Orbit Checkout observations.

Q: What happens if my observation fails?
A: It depends on what fails. If one ground radio telescope or tracking station fails but the data is still sufficient to meet the scientific goals of the proposal, the observation will not be rescheduled. If HALCA does not observe or the majority of ground telescopes or tracking stations fail, the observation will be re-scheduled.

Q: How do I analyze my data?
A: Fringe-fitting should be carried out in AIPS. The recently revised Chapter 9 of the AIPS CookBook `Reducing VLBI Data in AIPS' has the relevant details.
The AIPS FAQ also contains useful information for those not familiar with this software package. You will need the most recent version of AIPS (00DEC31 version) in order to successfully reduce your VSOP data. The use of the regularly updated development version of AIPS, which is available at the regional user-support facilities and data-reduction centers, is recommended where possible.
Imaging can be carried out with either AIPS or Difmap both of which have been upgraded to handle space VLBI data.

There is now an updated DIFMAP cookbook, with a new section (section 11) on using DIFMAP to process space VLBI data. Note that the 2.3c release of DIFMAP is required for space VLBI data.

Q: How can I find when HALCA was at apogee or perigee?
A: Fringe finding may be easier closer to perigee (but not too close, as HALCA is moving fastest, and orbital uncertainty is largest, at perigee). Check the List of HALCA's apogee and perigee times. Apogee and perigee times given in this file are expected to be accurate to within a minute or so. This information is also available on an observation by observation basis for most observations from the files linked to the Observation Status page.

Q: Are all of these really Frequently Asked Questions?
A: No, we made some up.