by randall cameron » Sat Jun 17, 2006 8:24 am
It is possible (now anyway) to perform mapping (either limited in area or limited in detail) with some modern types of radar on a single pass. An active electronic scanned array / phased array would allow collecting a lot of data in a short time frame, and offers weight and reliability advantages (no gimbals or other moving parts, component redundancy, ability of signal processor to compensate for individual transceiver failures).
However, a Cassini / Huygens or any deep space probe has several major limitations:
1. Size and weight - the smallest production model off-the-shelf radars with the synthetic aperture capability required are built for (15-ton plus) fighter aircraft. The radar alone probably weighs more than Huygens.
2. Power - existing AESA radars assume a large gas turbine to provide electrical power. Space probes have solar cells and tiny radio-isotope generators.
3. Budget - if a suitable production radar existed (it does not) it might cost a few million dollars. Space instruments are typically custom made and purpose designed because of the restricted weight and power available, increasing cost and engineering difficulties dramatically. Also, as puny as NASA's science budget is, ESA is an even lower budget operation.
4. Time - back when Cassini was launched, the only AESA radars were huge land- or ship-based systems -- the engineering experience with smaller units was not there yet.
5. Even if you collected the data, Cassini would still be busy transmitting it back because of bandwidth limitations.
Magellan had many major specific advantages related to its objectives and opportunity to orbit for years:
a. Even a simple doppler radar altimeter could provide detailed terrain mapping if you orbit enough times -- VOIR was simple, small and low-powered, and engineered for long term mapping;
b. The VOI radar was the primary scientific instrument and thus got a much bigger share of the Magellan financial, weight and power budgets;
c. Venus is close -- Magellan could be much heavier and still get their quicker and cheaper;
d. Venus is close to the sun -- solar panels provide loads of reliable power;
e. Data take per unit of time was modest, meaning no transmission backlog.
Of course, if you build a space probe that weighs as much as an F-15 and figure out a way to get it all the way to Saturn, you could have your radar map within weeks of arrival. But that won't happen while the Shuttle and ISS are sucking up all of NASA's budget. Things aren't likely to improve much while we try to get men to Mars.
A Titan orbiter could do the job using much simpler, low power technology. Then the question is one of science priorities.
I think Cassini/Huygens has done magnificently given the budget. Along with Galileo and Voyager 2, we have learned a ton about the outer solar system from these three (relatively) inexpensive missions. Bravo to ESA.
It is [i]possible [/i] (now anyway) to perform mapping (either limited in area or limited in detail) with some modern types of radar on a single pass. An active electronic scanned array / phased array would allow collecting a lot of data in a short time frame, and offers weight and reliability advantages (no gimbals or other moving parts, component redundancy, ability of signal processor to compensate for individual transceiver failures).
However, a Cassini / Huygens or any deep space probe has several major limitations:
1. Size and weight - the smallest production model off-the-shelf radars with the synthetic aperture capability required are built for (15-ton plus) fighter aircraft. The radar alone probably weighs more than Huygens.
2. Power - existing AESA radars assume a large gas turbine to provide electrical power. Space probes have solar cells and tiny radio-isotope generators.
3. Budget - if a suitable production radar existed (it does not) it might cost a few million dollars. Space instruments are typically custom made and purpose designed because of the restricted weight and power available, increasing cost and engineering difficulties dramatically. Also, as puny as NASA's science budget is, ESA is an even lower budget operation.
4. Time - back when Cassini was launched, the only AESA radars were huge land- or ship-based systems -- the engineering experience with smaller units was not there yet.
5. Even if you collected the data, Cassini would still be busy transmitting it back because of bandwidth limitations.
Magellan had many major specific advantages related to its objectives and opportunity to orbit for years:
a. Even a simple doppler radar altimeter could provide detailed terrain mapping if you orbit enough times -- VOIR was simple, small and low-powered, and engineered for long term mapping;
b. The VOI radar was the primary scientific instrument and thus got a much bigger share of the Magellan financial, weight and power budgets;
c. Venus is close -- Magellan could be much heavier and still get their quicker and cheaper;
d. Venus is close to the sun -- solar panels provide loads of reliable power;
e. Data take per unit of time was modest, meaning no transmission backlog.
Of course, if you build a space probe that weighs as much as an F-15 and figure out a way to get it all the way to Saturn, you could have your radar map within weeks of arrival. But that won't happen while the Shuttle and ISS are sucking up all of NASA's budget. Things aren't likely to improve much while we try to get men to Mars.
A Titan orbiter could do the job using much simpler, low power technology. Then the question is one of science priorities.
I think Cassini/Huygens has done magnificently given the budget. Along with Galileo and Voyager 2, we have learned a ton about the outer solar system from these three (relatively) inexpensive missions. Bravo to ESA.