The Great Ongoing Space Exploration Thread

That is amazing. The power of the signal arriving here on earth from Voyager 2 is, “10^-16 watts (1 part in 10 quadrillion). A modern-day electronic digital watch operates at a power level 20 billion times greater than this feeble level.” SOURCE

It is nothing short of astonishing that we can do that.

Speaking of poignant:

Using receivers located in the middle of the electronic din we call 21st Century Earth civilization. Truly amazing.

Ok that made me feel sad.

You’re not alone. Back when the xkcd forums were alive, the thread dedicated to that episode was … choked up.

It should have been titled “How to Make a Grown Engineer Cry”.

But hey, Spirit and the other rovers are about to get a new friend! Just over 5 days to go. Kinda remarkable how many Mars-related missions are happening at once. Well, it’s largely a function of orbital mechanics, but missions from three different organizations is new, I think.

Comparing it to the power of a watch isn’t really useful.

A better comparison would be the signal that your TV receives, and that can be as low as -65 to -75 dBm, which is equivalent to 10^-9 to 10^-10.

Still impressive, in that it’s a million times fainter than the signal that your TV can pick up, but the 20 billion times lower than what a watch uses doesn’t really mean much.

You should write the people at NASA. That’s where I got that from (see link in my post). I have no idea why they chose that comparison (probably some intern working on the website who phoned some guy/gal during lunch and he ballparked it to a digital watch off-hand while between bites of his/her sandwich).

I saw where you got your info, and I wasn’t criticizing you, I was criticising it, as well as informing anyone who wished to read about it. It was certainly not an engineer who wrote that, but someone in the PR department.

I would assume because it sounds more impressive. But it really is comparing apples and orange trees.

It’s not very informative, as you don’t try to run your watch off of radio waves, and it is not as though people are unfamiliar with other forms of radio receivers in their daily lives.

If they compared it to cellphones, then it loses quite a bit of its impressiveness. A cell phone can go down to -85dBm, which is on the order of 3x10^-12. So your cellphone can pick up a signal only about 10,000 times stronger.

At least they didn’t go the other way, and claim that the Voyager signal was trillions of times weaker than your microwave oven.

Stuff like this makes me think we are missing something here.

IIRC Voyager 2’s transmitter is 20 watts. Voyager 2 is 11.6 billion miles form earth. They just upgraded radio telescopes to be able to hear it yet my cell phone isn’t too far off at picking up such weak signals?

I mean, 10,000x less sensitive seems big until you think that is my cell phone going from 1 mile from a transmitter to 10,000 miles from a transmitter (maybe a lot less…does the inverse square law work here?).

Voyager 2 is 11.6 billion miles away. My cell phone getting within 1/10,000 of that puts it at 1.16 million miles to get a signal. Pretty sure my cell phone cannot do that.

Again, doubtless I am missing something. Not sure what it is though.

I’m not sure where they got that number. Voyager 2 is 1.9e13 meters away and has an X-band power output of 21.3 W. The gain on the antenna is 48 dB, or a factor of 63,100. Taking these together we get a power density on Earth of 2.96e-22 W/m^2.

NASA receives the signals using Deep Space Station 43, which has a diameter of 70 m. So the amount of power it gets is 1.14e-18 W.

So a couple orders of magnitude different from the claim above, and that’s with the giant receiving dish.

All that said, cell phones are extremely impressive. In fact the whole reason they are so impressive is that they use coding schemes which come close to the Shannon limit. Space transmission drove much of the early development of high performance codes. Voyager 2 is too old to use the most advanced schemes (Turbo codes, LDPC), but the state of the art generally showed up on space probes first, and consumer devices later.

That makes sense, we were talking about the signal at the receiver, not in space. The W/m2 of a cell signal is going to be much, much higher than that of Voyager, as the cell antenna is much smaller (but bigger than one would think, with its fractal shape) than the dish to pick up Voyager’s signal.

I can’t find a good reference for what the W/m2 of a cell signal is, but I assume it is many orders of magnitude higher.

Anyway, I just didn’t like the analogy that NASA used here, comparing the strength of a radio signal to that of a battery powered device.

The inevitable result of the previous decision about the Europa Clipper (EC) and SLS:

In January, Congress decided that NASA was no longer obligated to fly EC on SLS. Now, the SLS is categorically excluded from flying EC.

Ironically, one of the significant factors in the decision is also one of the only reasons for SLS’s existence in the first place: the solid rocket boosters. SLS got support from Utah’s Orrin Hatch due to its use of solid boosters, effectively continuing their use from the Shuttle program. And it’s those same solid boosters that make SLS unsuitable for launching EC: the probe is too delicate to survive the extreme vibration environment caused by solid rockets.

All that remains to be see is which commercial provider they choose. The Delta IV Heavy could launch it, but there are no vehicles available. New Glenn or Vulcan could also launch it, but these vehicles do not yet exist and may not have many (or any) flights under their belts by the time EC launches. Non-American launchers are out. Falcon Heavy is the only vehicle that exists now and could launch EC, so it’s clearly the favorite even if NASA won’t say so.

And now NASA’s rover has landed.

Discussion here: Mars lander set for Feb 18th landing


I’ll just leave this here:

Huge static fire test right now by NASA - firing up the SLS which will take humans back to the moon.

Just finished. Finally, a clean win for SLS. They got through not just the minimum requirements, but completed a full 8-minute cycle (running the propellant to depletion). I’m not exactly a fan of SLS, but it’s still nice to see a successful test.

And now SpaceX are stacking their Super Heavy rocket for the first time which is going to be another historic rocket. Exciting times!

Meanwhile the astronomers refuse to be left behind: