Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!

 



Forgot your password?
typodupeerror
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. ×

Comment Re: Impressive spec (Score 1) 109

Well would you look at that indeed! I argued for a loss of 348-282=66 sec in Merlin, and said that Raptor would be somewhat less of a difference but not much, as "chamber pressure has a positive but fairly weak correlation with ISP". You said 384 - "360-370" = 14-24 sec difference.

And the reality is... drumroll... the envelope please...

384-334 = 50 sec

I hope this has been a learning experience for you.

Comment Re:Wat (Score 2) 90

This is not correct. Juno is planned to do some limited observation/a> of the Galilean moons. It's a side mission, not central to it's focus (and Juno is anything but optimized for it), but it's one of those cases where, if you're there and you have the hardware...

Concerning Europa (remember that this was before the recent news):

The most significant opportunity for Juno to do Europa science would be to follow up on the plumes possibly detected by Hubble Space Telescope. Confirming Hubble's detection would be very scientifically valuable. Any information on the source location would be valuable. This science goal just may not be possible with the large distances from Juno to Europa, but we will look.

JunoCam or ASC can only detect plumes if they contain fine particles. The Hubble discovery (if real) only shows the presence of water vapor. We can predict by analogy to Enceladus that water vapor plumes will also contain particles. However, it is important to remember that the Hubble discovery was of gas, not particles. If the putative Europa plumes are Enceladus-like and do contain particles, they would not be as tall as Enceladus', because of Europa's higher gravity. Scaling for Europa’s gravity gives a maximum plume height of under 140 kilometers. To detect plumes, we need at least two pixels, so the image spatial scale would need to be better than 70 kilometers, at a relatively high phase angle where the particles would forward-scatter light to JunoCam and ASC.

To achieve resolutions better than 70 kilometers per pixel, UVS needs to be within 40,000 kilometers of Europa; JunoCam, 100,000 kilometers; and ASC, 170,000 kilometers. For the cameras, given the low expected height of the plumes, there is not much flexibility.

There are just four orbits that have Europa flybys that are closer than 300,000 km. Juno reaches the best available geometry in September 2017 as the rotation of the line of apsides brings Juno’s orbit close to Europa’s orbit:

2017-03-08 253,118 km
2017-09-19 264,043 km
2017-10-03 92,267 km
2017-10-17 204,654 km

Comment Re:So how is it supposed to communicate? (Score 1) 90

It's pretty limited what you can gather from individual grains captured at hypersonic velocities and analyzed with spacecraft-sized instruments. Certainly there was no "clear evidence of life" from Enceladus - although it showed us some very promising things about the potential habitability of its oceans.

Personally, I'm not a believer in the theory that wherever there's liquid water, there's life. First off, it'd make the Fermi paradox even worse, as water is bloody everywhere. Secondly, I think it's incredibly naive. The argument goes, wherever we find water on Earth, we find life, and whereever we don't, we don't, so we should expect that with the universe. But that says nothing about how life came about. Sure, LAWKI requires hydrogen, and water is the most convenient source of hydrogen, so obviously that's going to form the boundaries of where life has spread to. But where it's spread to says nothing about where it originated, or what it looked like when it did. We have no reason to think that the entire wet surface of Earth just spontaneously erupted into life; we certainly don't see anything resembling this in laboratory abiogenesis experiments. So what were the specific conditions that brought life about? I think it's a safe bet that they were rare. Quite likely no longer present on Earth, as Earth was a radically different place back then. And quite possibly rare in the universe as a whole. Little bursts of luck separated by great relativistic distances.

Indeed, bodies like Europa (and the many other bodies confirmed to or believed to have subsurface water in our solar system) should help answer these questions. I'm also exceedingly curious about what's gone on with alternative solvents and polymeric compounds, such as at the surface of Titan (I find the cyanide chemistry there fascinating, it seems to be extremely flexible).

Comment Re:Wow (Score 2) 149

Yeah, landing the booster right next to the refueling tanker seems little,eh... optimistic

The video is clearly stylized and not meant to be taken that literally. Unless you think the arrival of the spacecraft is supposed to make Mars spin until it develops oceans ;)

That said, while there's much to like, there's one aspect of it that's really clawing at me... the fact that they plan to make it out of composites. Including the LOX tank. We've never succeeded (and failed multiple times) at making flight-intent LOX tanks for orbital rockets. And they want to make the first time be on what's by far the largest rocket ever built? Without a lining?

Is it worth mentioning that they just had an explosion somehow related to the only major carbon fiber component in the Falcon 9 in a LOX tank?

CF becomes brittle in LOX. It leaks. And most concerningly, it's impact / shock sensitive in LOX. At atmospheric pressure it usually won't do a self-sustained burn on impact, but it chars on impact, and even that alone would be bad. But they plan to have significant pressure as well. He mentions briefly that they expect this to be one of the biggest challenges, getting stable coatings and the like. I think that's an understatement.

I just don't want to see the largest rocket ever built turn into the largest flying fireball on Earth. I don't trust composites with LOX. Composite cryogenics tanks are an active research topic, and they're making progress, but it's not a solved problem.

Comment Re:Consumers (Score 1) 264

Try bandcamp.

Here, I'll start you off with some premium grade-A smokey music. Nope, that's not marijuana (though if that's your thing, it should still work out for you). Inhale again and you'll realize it's mesquite. I suppose the two are similar, because smelling this music gives me the munchies, except I don't wanna settle for anything less than slow-fuckin'-cooked brisket.

Comment Re: Impressive spec (Score 1) 109

Why compare apples with oranges?

Why show how much sea level and vacuum ISPs vary in other hydrocarbon engines? Because they vary that much in all engine, even non-hydrocarbons (same sort of difference in LOX/LH and solids). Methane is not some sort of magical exception to the rule.

The RD-0162 is the closest unit you can compare the Raptor with. It pushes all its propellant mass through the chamber. It uses the same propellant mixture. Therefore the real world vacuum performance of the sea-level version Raptor can be best guesstimated from the RD-0162 figures rather than by comparing it with dissimilar units.

No, they cannot. You have no clue whatsoever how the efficiency of the RD-0162 compares to Raptor. Not in the slightest. Which makes it a pointless comparison.

Slashdot Top Deals

"I think trash is the most important manifestation of culture we have in my lifetime." - Johnny Legend

Working...