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#1
Old 08-30-2004, 03:10 PM
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how much does a satelite weigh?

I was thinking along the lines of the type of satelite used for satelite TV.
I'm specifically looking for the weight without all the bits that keep it in orbit (such as shielding, thrusters and fuel, etc), but just the bits that receive and send the signals (along with whatever support structures hold it in place of course).
#2
Old 08-30-2004, 03:28 PM
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A couple thousand pounds, give or take.

The Australians made one that weighs 3,652 lb.

Boeing makes one that is described, sadly enough, as weighing 1438 lb. while in orbit.
#3
Old 08-30-2004, 03:34 PM
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Out of curiosity I looked up some facts on Sputnik. It weighed only about 180 pounds but of course it didn't have to do much besides beep.
#4
Old 08-30-2004, 04:06 PM
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That's an ugly question! "The bits that keep it on-orbit" are not a discreet set of items. A modern satellite like NPOESS is comprised of a "bus" and its "payload(s)". The bus contains the thrusters for orbit maintenance, the fuel tanks for those thrusters, the reaction wheels that keep the sensor from tumbling, the solar panels and batteries that keep the sensors working, the heaters that keep sensors from freezing when they're on the dark side of the satellite, and the command antenna that relays information back and forth from the sensors to the ground. Here's a simple list of all the things a spacecraft bus provides for its payload.

The payload consists of the sensors, any reaction wheels they have internally, any radiators those payloads need to stay cool, and of course, the cables and vibration mounts required to attach them to the bus. One payload on NPOESS is so vibration sensitive that it's actually going to fly "in formation" with the bus -- the spacecraft will actually release it so that it floats a centimeter above the surface of the bus, attached only by its data and power cabling.

Add to all of those concerns that NPOESS is only one type of satellite, and that communications satellites (normally geosynchronous) are sized differently and carry different payloads altogether. To make an analogy, your question is like asking what a modern PC would weigh without the case or power supply -- there's an answer, but calculating it is really tough.

Give me more details -- name the satellite -- and I could probably begin to help you figure out the payload mass, but you're not likely to get an answer that doesn't include fuel or thrusters. Here's a NASA communications satellite. Notice that they still use pounds and the word "weight", and have a giggle at their expense.

In deference to Ethilrist's absolutely dead-on pedantry, I'll point out that weight is an earthbound notion, and is often used in America interchangeably with mass. When you work with a satellite, someone saying "weight" is assumed to mean "mass," and kilograms are the unit of choice.
#5
Old 08-30-2004, 05:03 PM
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Yup, def. not a "clear' question (which is of course why I'm asking it here. )
As an example of the satellite "type" I'm trying to get info on there is the Direct TV DBS-1 or D4-S. In other words satellites used for digital media transmission. I'm trying to get the land based weight of the components themselves (rather than the whole), as they aren't intended for space.
#6
Old 08-30-2004, 05:23 PM
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Quote:
Originally Posted by rabbit
I was thinking along the lines of the type of satelite used for satelite TV. I'm specifically looking for the weight without all the bits that keep it in orbit (such as shielding, thrusters and fuel, etc), but just the bits that receive and send the signals (along with whatever support structures hold it in place of course).
According to this description of the HS-702 satellite, this satellite has a launch mass of 5200 kg, of which 1200 kg is the "payload." The payload consists of up to 118 transponders; I'm not sure if it also includes the antennas, but I'd guess not. This is one of the largest communications satellites available today.
#7
Old 08-30-2004, 05:46 PM
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Quote:
Originally Posted by Ethilrist
Boeing makes one that is described, sadly enough, as weighing 1438 lb. while in orbit.
It could weigh that much in orbit. It'd just be ridiculously massive. Actually, I'm curious, how massive would an object have to be to weigh 1438 lbs. in orbit?
#8
Old 08-30-2004, 05:58 PM
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Depends on what exactly you mean by "weight." If you use dictionary.com's 2nd definition:
Quote:
The force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity.
Then in low earth orbit, things weigh almost the same as it does on the ground. That is, it's still attracted towards the earth with the same force; it's just that there's another force keeping it from falling (i.e. centrifugal force).
#9
Old 08-30-2004, 06:10 PM
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I work on a weather satellite (DMSP). We made the main sensor. It weighs about 50lbs. The electronics boxes weigh prolly another 200lbs. Other sensors on the same bus add maybe 700lbs. The satellite weighs just over 4,500lbs total.
#10
Old 08-30-2004, 09:34 PM
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Actually, its weight in orbit is 0. It's in free fall. Stick a bathroom scale under it and you'll see.
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