Temperature of satellite

[DaveHein]

Batteries do OK on high altitude balloons that go up to 100k feet. The pressure at that altitude is about 1 percent of sea level pressure, so it's pretty close to a vacuum. I suspect most batteries are sealed well enough where they can witstand an internal pressure of 14 PSI without bursting.

[rick m]

[DaveHein]

A single reception isn't enough to determine the orbital path. Of course, if you receive it 2 days after the launch then it probably executed more than 9 orbits. However, it's possible that it was in something like a highly elliptical 12-hour orbit, and it had only done 4 orbits in 2 days, and it might re-enter the atmosphere before it completes its ninth orbit. I think you need at least 2 or 3 measurements to determine the orbital elements.

It would probably be better to transmit at a high rate during the first orbit so that there will be many receptions. The orbital elements could then be calculated, and it would be possible to predict whether the satellite could do nine orbits even if the transmitter quit after the first orbit.

I think the safest approach would be to transmit a short burst at least once every 15 seconds. The burst should be high enough power to produce a good chance of reception. A one-half second beep every 15 seconds is a duty cycle of 3.3 percent. If the average power use is 50 mW this would correspond to a 1.5 Watt spike in power every 15 seconds. If the transmitter has an efficiency of 25%, that would be a 375 mW transmitted signal.

[lavalamp]

[DaveHein]

You wouldn't even need to fly rockets to fake the N-Prize. Someone could mail transmitters to friends around the world, and they could each send out a signal at the appropriate time to simulate an orbital path. Verification of the N-Prize will require many radio receptions from many radio operators around the world.

[rick m]

Someone planning on faking the orbits with bogus radio transmissions would at least need to launch a rocket or balloon that travels out of site, they could then transmit some beeps from an existing LEO satellite they have access to.

A secondary objective of the exSS is to refurbish the sub-orbital rocket to be flight ready in 14 days but we are not planning to orbit anything with that project. Everything about it, success and failures are posted with detailed documentation on our web site for anyone to see.

[pyramids]

[lavalamp]

[pyramids]

Sorry for the late reply, lavalamp ... I stopped watching the thread!

With inbound vs. outbound I just meant the received heat (both solar and from earth) vs. what's radiated away from the satellite.

You're right that there's a reduction factor because the night side of earth radiates.

[lavalamp]

Well in that case, I did calculate the inward and outward heat separately.

More specifically I calculated the amount of energy absorbed due to the sun and the earth separately, taking account of the fact that the intensity of radiation from the earth varies, and for nearly half the orbit the earth blocks out the sun completely.

I then calculated how much energy is radiated by the satellite at it's specific temperature. With these two values, energy in and out, it's just a subtraction to find the total energy change, and then I recalculated the temperature of the satellite based on that. I did this for every time slice of the simulation, and the time slice was 1 ms (so a full simulation of 9 orbits took nearly 50 million steps).

I also used several values for the emissivity of the surface of the satellite which affects the amount of energy absorbed AND emitted.