RE: Phobos-Soil Project seeks observations of engine burns from South America

From: Ted Molczan (
Date: Fri Nov 04 2011 - 17:55:52 UTC

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    I offer the following suggestions for prospective observers of the engine firings.
    1. Plume Brightness
    I have been in contact with the project on the matter of expected plume brightness, and received the following guidance
    (which I have somewhat summarized), attributed to a professional in rocket engine development and test. Despite
    estimated exhaust gas temperature of about 500-600 K, which results in low gas brightness at visible wavelengths, a very
    bright plume is observed, due to very hot carbon particles generated in the engine chamber. It is predicted that it may
    be possible to observe the plume by binoculars, perhaps the naked eye.
    The reality is that we cannot be certain how bright the plume will be. If I were in a position to attempt to observe the
    engine firings, I would prepare for the worst case (a faint plume), and allow myself to be pleasantly surprised if it
    proves visible to the unaided eye. To enable precise astrometry of the spacecraft's trajectory, which is the primary
    objective, it will be required to observe a fairly faint star background, and the optical equipment that will detect
    such stars should do reasonably well on a faint engine plume.
    2. Observing Strategy
    When firing, the engine will be at the end of the spacecraft opposite the direction of travel. This means that during
    the first half of the pass, as the spacecraft approaches the observer, it will block the observer's view of the engine,
    and probably the brightest portion of the plume. After the point of closest approach, as the spacecraft recedes, the
    engine and brightest portion of the plume will be exposed to the observer, maximizing visibility and apparent
    So, if the plume proves faint, it will be more likely to be detected once the spacecraft is somewhat east of the
    observer. But that does not mean that observations should not be attempted earlier in the pass. For trajectory analysis,
    the longer the arc over which observations are available, the better; therefore, I would plan to intercept the
    spacecraft fairly early in the pass, but be prepared to rapidly re-aim to intercept it at several later points. 
    In the event it is spotted at the earliest intercept point, then I would track it as long as possible, and of course
    record data. In the event that it is not seen at the first intercept point, perhaps because it is faint, or obscured by
    a passing cloud, I would move to the next intercept point.
    In selecting intercept points, I would verify that a reasonable number of detectable stars will be in the field of view
    (to aid in the astrometry), and I would make certain to allow sufficient time between intercept points to re-aim the
    optics. This last point is an important consideration for everyone, but especially those closest to the ground track,
    who will experience angular velocity well over 1 deg/s.
    Since the spacecraft will move rapidly, and may not be visible to the unaided eye, observers need to quickly and
    reliably move from one intercept point to the next, without relying on easy visibility. If an automated pointing system
    is used, its mechanism be sufficiently fast to move to the next intercept point, to avoid missing the observation. If
    manual star-hopping is to be used, then that also will take time, that must be accounted for.
    The ephemeris is the most important tool for planning your strategy. Yesterday, I posted an example, computed for Carlos
    Bella, who is in a good location to observe part of burn #1:
    I will be pleased to provide the MS-Excel spreadsheet used to generate the ephemeris, on request. Not everyone uses
    Excel, so I would be pleased to produce the ephemeris. I need only the precise site coordinates, which should be
    accurate to within 100 m.
    Time permitting, I am also willing to assist in planning an observer's strategy. I will need information on the method
    of observing, the observer's experience, physical obstructions that may block the view of the track, etc.
    3. Near-Real-Time Data Requirement
    A significant challenge for observers is the requirement to report observed data in near-real-time, which practically
    means "as soon as possible".
    Prospective observers are requested to pre-register, and to report results via this page:
    An example of the required format is shown at the bottom of that page. I have reproduced it here, with my interpretation
    of the key information:
                 Date/time      R.A. and Dec (2000.0)   mag
             ---------------- ------------------------ ------
             yyyy mm dd.ddddd hh mm ss.sss+dd mm  
    Rosetta C2005 03 02.00860 11 05 08.545+02 24 23.95 16.1 V D0020557
    Elsewhere, the required format has been described as MPC 80-column. Since I concentrate on artificial satellites, I
    seldom encounter these formats, but my guess is that the above may be an abbreviated version.
    Observers should be prepared to reduce their observations quickly and reliably, to meet the near-time requirement.
    If there are observers who feel confident in their ability to obtain still or video imagery, but need assistance with
    data reduction, I am willing to assist, but please do not wait to the last minute to make your request. I need to know
    what form your data will take, so that I am prepared to handle it.
    4. Practice Makes Perfect
    If your astronomy specialty involves something other than observing artificial satellites, then you should consider
    practicing on a few satellites, to identify any problems in your proposed methodology and gain some efficiency and
    speed. The spacecraft will move rapidly, so planning and preparation are essential to success.
    Happy hunting!
    Ted Molczan
    Seesat-l mailing list

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