The thread for space cadets!

[Cutlass]

Didn't they use a nuke core for electric power?

 

[hobbsyoyo]

I'm not sure if the US has ever launched a fully functional nuclear reactor. They do use RTG's, which use radioisotope decay to generate electricity, but they are far too weak to drive a large electric propulsion system. The Russians have used nuclear reactors in space and that has led to a handful of contamination events. One wound up smearing itself over most of Canada, for instance. Of course the amounts of pollution spread over huge areas is negligible but I just can't see NASA getting past the NIMBY/anti-nuclear cultural push to launch one.

Which is a pity because in-space nuclear reactors solve a lot of problems.

 

[red_elk]

Kosmos-954 accident...
Eventually USSR/Russia stopped using nuclear-powered satellites too. I think the risk of contamination was the main reason for that.

 

[uppi]

Though sls could loft really big solar arrays. Idk

They do use RTG's, which use radioisotope decay to generate electricity, but they are far too weak to drive a large electric propulsion system. \

At Neptune's orbit, a solar array would be much weaker than an RTG. I would say, if you are very good, you might be able to generate around 0.5 W/kg with solar arrays - but that is already pushing it. The RTG on Cassini had about 5W/kg power output. So that far out, there is no point taking solar arrays when you can bring RTGs.

 

[hobbsyoyo]

At Neptune's orbit, a solar array would be much weaker than an RTG. I would say, if you are very good, you might be able to generate around 0.5 W/kg with solar arrays - but that is already pushing it. The RTG on Cassini had about 5W/kg power output. So that far out, there is no point taking solar arrays when you can bring RTGs.

Oh boy you'd need an awful big RTG for that.

So I was doing some reading and I saw that there was a proposal for a non-electric orbiter with 3 (!!) landers that was intended to launch on an atlas or delta and still get to Neptune in 11.5 years. I find the proposal stretched credibility but it probably does put an extreme upper bound of what's possible just with the technology of this very minute. The landers were Huygens-style, 2 would have been crushed in Neptune's atmosphere and the third would've crashed on one of the moons.

https://en.wikipedia.org/wiki/Neptune_Orbiter

On the nuclear power issue I found that the US actually did launch a nuclear reactor but only once and it was a primitive design. No operational American reactor satellites followed it. NASA did also have a proposal for a stirling generator that ran on nuclear decay. It claimed to have about 5 times the power density of a conventional RTG and was earmarked for deep-space missions but ultimately canceled. I think a lot of the cancellation had to do with how expensive it was to restart plutonium processing, they don't want to waste any of it on untried designs. They only turn out a few grams I believe a year at great expense.

SNAP-10a, the only American in-space nuclear reactor.

Cut-away image of the advanced sterling radioisotope generator that was cancelled.

 

[hobbsyoyo]

The first SLS launch date has slipped again to no earlier than Dec 2019. This is basically another year-long delay. People talk crap about the unrealistic schedule for the first Falcon Heavy launch but the SLS has been in development longer and cost well over an order of magnitude more.

The second launch is also slipping a year as well (so it'll be in 2023 at the earliest) which is ridiculous. Apparently they are planning on upgrading the second stage after the first launch at a cost of a few billion more dollars. Ridiculous just doesn't describe this farce.

 

[Berzerker]

https://phys.org/news/2017-09-large-meteorite-impacts-drove-plate-tectonic.html

"Our results indicate that giant meteorite impacts in the past could have triggered events where the solid outer section of the Earth sinks into the deeper mantle at ocean trenches – a process known as subduction.<----->

"Large impact events may have also kick-started the Earth's magnetic field by triggering the planet's cold outer crust to suddenly move downward and interact with the Earth's outer core. This affects convection in the core, and thus the geodynamo – the process that creates the Earth's magnetic field,"

O'Neill also notes that while the magnetic field for much of Earth's ancient history has been quite low, but recent work has suggested field strengths up to present-day values existed between around 4.0-4.1 billion years ago.

"This is a really important age in the inner solar system. Impacting studies have suggested a big disturbance in the asteroid populations at this time, with perhaps a big upswing in impacts on the Earth. Our simulations show that larger amounts of meteorite collisions with the planet around this time could have driven the subduction process, explaining the formation of many zircons around this period, as well as the increase in magnetic field strength."

This world had a makeover just over 4 billion years ago followed by plate tectonics, but how do we know the magnetic field was weaker prior to this 'big disturbance'? Thats important... Large objects hit us ~4 bya creating plates (cracks in the cosmic egg), subduction (the start of continent-building), convection (strengthened magnetic field), and soon afterward, life... Or life was transferred to our world (panspermia) during this period of impacts. If our solar system was showered by material from nearby explosions, maybe life from another, older system made the journey too, albeit that seems less likely.

 

[Cutlass]

 

[hobbsyoyo]

So during a re-entry back in April a Soyuz capsule depressurized. They claim that a buckle on the parachute harness struck a weld seam and cracked it open. The astronauts/cosmonauts were in pressure suits so they weren't in immediate danger but it's still a really bad sign.

I feel like a broken record but Russian quality control in their aerospace industry is abysmal and they don't seem capable of fixing it. I just read the other day that the Proton suffered about a failure a year for like 7 years straight or something like that.

Elon Musk also gave details on his revamped BFR/BFS design. It's smaller now than the old version and he's claiming it will perform point-to-point launches to deliver people and packages around the globe in less than an hour which is neat but I don't think it will be practical. I just don't see their prices ever really getting low enough to enable that.

 

[Berzerker]

Uranus visible to the naked eye tonight

 

[Broken_Erika]

Uranus visible to the naked tonight

Did you put a spy cam in my bathroom?!?

 

[Berzerker]

eye


oops


lol

 

[red_elk]

Did you put a spy cam in my bathroom?!?

Uranus, the planet.
Ur anus is not visible, at least to the naked eye

 

[Berzerker]

the moon is

 

[Berzerker]

https://phys.org/news/2017-10-dawn-ancient-ocean-remnants-ceres.html

Ceres was covered by an ocean ~4 bya... How does that work?

 

[hobbsyoyo]

https://phys.org/news/2017-10-dawn-ancient-ocean-remnants-ceres.html

Ceres was covered by an ocean ~4 bya... How does that work?

Young planets would be outgassing a lot and would pretty much all have atmospheres. Most of them would be stripped away in time, depending on how far away they are from the sun. Ceres is in the belt (even farther than Mars which took billions of years to lose the bulk of its atmosphere) so it would have retained its atmosphere for a very long time. The presence of an atmosphere would have allowed liquid water to exist there for a long time as well. When the atmosphere got blown away it would have led to the oceans boiling off (and getting blown away) with a remnant remaining bound chemically to rocks or in buried ice.



---------


So they just announced the SLS is delayed until the end of 2019 but there is a news article out saying really it's going to be 2020 at the earliest before they launch. The original launch date was like 2015 for christ sakes.

People pick on Elon Musk/SpaceX for very long delays, especially for Falcon Heavy but NASA has had about a decade longer to get the SLS flying and tens, if not hundreds of billions of additional funding to do it.

I'm working on a lunar mission that's supposed to go up on the SLS and so it's personally frustrating for me. Plus, we don't have the luxury of slipping our dates in lockstep with NASA, we still have to meet delivery dates in part because NASA holds us to this rigid schedule that is not based on reality.

 

[Berzerker]

Young planets would be outgassing a lot and would pretty much all have atmospheres. Most of them would be stripped away in time, depending on how far away they are from the sun. Ceres is in the belt (even farther than Mars which took billions of years to lose the bulk of its atmosphere) so it would have retained its atmosphere for a very long time. The presence of an atmosphere would have allowed liquid water to exist there for a long time as well. When the atmosphere got blown away it would have led to the oceans boiling off (and getting blown away) with a remnant remaining bound chemically to rocks or in buried ice.

Then its possible Europa was covered by water - and other moons. The water was lost to space or became ice with liquid water deeper down where its still warmer - I'm sure we'll be tapping into those reservoirs. Now I'm wondering how large a body must be to retain an atmosphere, does it need to rotate and/or produce a magnetic field? Certainly a denser planet would keep more atmosphere.

 

[Michkov]

Then its possible Europa was covered by water - and other moons. The water was lost to space or became ice with liquid water deeper down where its still warmer - I'm sure we'll be tapping into those reservoirs. Now I'm wondering how large a body must be to retain an atmosphere, does it need to rotate and/or produce a magnetic field? Certainly a denser planet would keep more atmosphere.

Europa is mostly waterice on the surface with either a fluid layer underneath or ice all the way down to the a rocky core/mantle.

As for keeping an atmosphere that's a very good question. It's a bit odd that Venus has such a dense atmosphere without magnetic field, barely spins or any tectonic activity. It's dry but there is still plenty of gasses left, so size may play into it. On the smaller end of the scale you got Titan but it's so far away that there isn't much energy input from the sun. Also it hides in Saturns magnetosphere which helps.

 

[Berzerker]

thats true, gravity alone is enough with Venus as a great example - doesn't spin, no magnetic field, but a really thick atmosphere

 

[hobbsyoyo]

Then its possible Europa was covered by water - and other moons. The water was lost to space or became ice with liquid water deeper down where its still warmer - I'm sure we'll be tapping into those reservoirs. Now I'm wondering how large a body must be to retain an atmosphere, does it need to rotate and/or produce a magnetic field? Certainly a denser planet would keep more atmosphere.

It's possible these moons may have had a thick atmosphere and thus liquid water but probably more likely that they never did or that it was very brief. While the sun isn't blasting them, Jupiter certainly is. Europa is one of the most deadly radiation environments in the solar system and I imagine that doesn't help an atmosphere or an ocean as it will accelerate the breakdown of heavier chemicals (like water) which in turn makes them more likely to be lost.

Also, because they are so far from the Sun, the kind of chemistries and processes that happen in the inner solar system don't really apply. So water would be (and is on Titan) frozen hard as rock, CO2 is the same, and lots of other gases just can't be gases. Basically this means that while it's possible for a rocky planet to have a true atmosphere out in the outer solar system, it's still much less likely.

I read an article the other day that points out that it's very likely that the moon had a decent atmosphere for a long time given it was seeded for one since it came from such a rich planet (ours). Also because the moon is so small it's actually not that hard to give it an atmosphere that would take thousands or millions of years to dissipate.

I have a 1970's NASA design study on giant space stations built of lunar material and they did an analysis that showed that the exhaust gas from even a hundred big rockets a year off the surface of the moon would give it an appreciable atmosphere that would last thousands of years. Setting up any major industry on the moon will in fact result in enough out gassing through normal industrial processes and as byproduct of human habitation that an atmosphere would be unavoidable. You wouldn't want to breathe it but very plausibly you could walk outside with minimal space gear and the amount of radiation the surface sees would fall off a cliff.

The size of a planet really just affects the limits of a potential atmosphere. How close the planet can be from the sun, how thick the atmosphere will be, what types of chemicals it contains and so on are deeply affected by the mass of the planet.

I don't think the density of the planet has a big effect (especially compared to overall mass) though of course you could point out some oddball corner cases where it does.

Spin rate doesn't affect the ability to have an atmosphere that much I think.

Magnetic fields certainly help retain an atmosphere and modify the parameters of what kind of atmosphere a planet has and how close it can be to the sun and retain it but it isn't always necessary.