What are the orbital elements for the spacecraft?
This contains more technical information than most people are interested in, so it's been placed in several separate files:
The maximum size of an image is roughly 5 megabits, or about 640 kilobytes (800x800 pixels x 8 bits/pixel); you could fit one or two full-size images on a floppy disk. Not all images are returned at this full size; a 2x2-pixel summation mode, for example, which uses about 1/4th the space of a full size image, is used to return many images.
At maximum possible downlink rate, with no compression or editing being used, it will take just under 9 hours to return a single full-size image. All images will be compressed or edited by at least a factor of 2 and will be returned in far less time (typically 1 to 2 hours).
An average of 2-3 images per day will be returned starting in late June of 1996.
Please see the Galileo Telecommunication Strategy fact sheet; in particular, the section titled Science Saved and Science Lost may be helpful.
The total cost of the Galileo mission, from the start of planning in 1977 through the end of mission in December 1997 is $1.354 billion. This value does not include launch costs, Deep Space Network tracking costs, and foreign contributions. (The latter is estimated at about $110 million, a very substantial international contribution indeed!) The total breaks down into $892 million in development costs (through about 30 days after launch, and $462 million in operating costs. Galileo has cost each citizen of the US only 27 cents a year during its 20 year life.
No, this is not the case for two reasons. First, several TCMs have been canceled: TCMs 3, 13, 18, and 21. Also, TCMs are not numbered consecutively - i.e., there was a TCM-4A and a TCM-4B, and a TCM-9A and a TCM- 9B, and there was also a TCM-22A.
The net effect of all this is that TCM-23 is the 22nd TCM since launch. Since TCM-24 was cancelled, TCM-25 (ODM) is either the 23rd TCM since launch, if one does not count the ODM wake-up burn as a TCM, or the 24th if one counts the wake-up burn.
If the probe was aimed at--and entered--the SL-9 impact site, it might not survive long enough to carry out its observations! When Mission Designers considered the probe's mission, they realized that the probe's speed relative to the atmosphere is minimized by having it enter near Jupiter's equator; entering at higher latitudes would raise this relative impact speed. A lower impact speed makes it easier to design the probe (rather like it being easier to design car bumpers that pass a bashing test of 3 miles per hour rather than 10 miles per hour). Thus, the probe was designed to allow it to enter within a few degrees of the equator, with an entry speed up to 47.8 km/sec (about 104,000 mph).
Regardless, it's impossible to retarget the probe at this stage. The probe, having been released, is on a purely ballistic trajectory. Also, retargetting the probe would have required a significant time-of- arrival change (hours), which would mean that the orbiter could not fly by Io as planned. Therefore, we would lose both the Io science and the required Io gravity-assist that reduces the size of the Jupiter Orbit Insertion maneuver by 175 m/s (which would cause a tremendous hit on the orbiter's propellent margin).
Ultracones are "listen only", that is, they receive the radio signal from Galileo but can't transmit a signal to it. Several times a week during Galileo's mission operations it is necessary to send commands to the spacecraft or collect what's called "two-way doppler" data, which allows the navigators to determine where the spacecraft has been and where it is going. Both of those activities are incompatible with using an ultracone, and so they are usually planned to be conducted at Goldstone or Madrid. Since Goldstone and Madrid have much shorter view periods of Galileo than Canberra, and since the ultracone would have to be bypassed frequently to allow for commanding and doppler collection, it was felt that the cost of installing ultracones at those sites outweighed the benefits.
There appears to be little hope that the ribs might come free, but, if they did, there would be a noticeable change in the spacecraft's wobble angle. The spacecraft's attitude control system detects a component of the wobble angle and sends it back to Earth. Analysts monitoring the spacecraft telemetry would see the change associated with rib release. Several steps would have to be completed before the HGA could be used, however. First, the antenna motors would have to be commanded to unfurl the antenna. Second, the spacecraft would have to be turned to point the narrow beam of the HGA at the Earth. This would allow testing of the HGA's performance. Third, this measured performance would have to be analyzed and subsequently incorporated into ground software to use in future sequence planning. Lastly, the already-built sequences would have to be updated to take advantage of the capability. Such a process would certainly take weeks to months to complete. Clearly a hig priority use of any HGA capability would be to increase the science downlink rate.
Lossy compression is to be used on imaging and plasma wave data. Let's focus on imaging data for now. Each picture is made up of an array of up to 800x800 picture elements, or pixels. Each pixel has 256 possible values, depending on the brightness of that part of the image. The lossy compression takes a group of these pixels and approximates their brightness values with a formula. On the ground this formula is reconverted into a set of data which is supposed to be close to the original data set. The fidelity of the reconstructed image depends on the selected compression factor, which will range from 3:1 to 80:1. Tests of the compression routine on Galileo and Voyager images demonstrated that pixel values were correctly reconstructed to within about one percent, which is considered excellent for most investigations.
Not all, but several are. Mars Pathfinder, Mars Global Surveyor, and Pluto Express have all expressed interest in the telemetry subsystem being developed for Galileo. The ultracone is usable by any spacecraft which transmits in S- band. It is also fair to say that Galileo's emphasis on data compression and encoding has spurred new research and development which is leading to the incorporation of sophisticated data compression schemes on projects under development.