For Questions That Don't Merit Their Own Thread

[Bill Phil]

It's a lower mass than ethane, but a higher mass than methane. I wouldn't say so.

[K^2]

Disregarding the price (for now), is there any sense in using acetylene (C2H2) as rocket propellant, either plain or in a mix?

No. While it generates a lot of extra heat, thanks to its high enthalpy, which makes it great for burners, it only has the two hydrogens, and water vapor is going to give you the bulk of your I_SP. CO2 is just too heavy in comparison, meaning ecetylene exhaust is going to be much slower.

[Kryten]

DARPA's ALASA is intended to use an acetylene/NOX propellant combination.

[shynung]

No. While it generates a lot of extra heat, thanks to its high enthalpy, which makes it great for burners, it only has the two hydrogens, and water vapor is going to give you the bulk of your I_SP. CO2 is just too heavy in comparison, meaning ecetylene exhaust is going to be much slower.

What about fuel mixes? As in, acetylene with some hydrogen mixed in? It has a higher flame temperature, though just by a few hundred degrees.

[K^2]

I_SP of a mixture of two fuels will always be worse than I_SP of the better of the two fuels. There can be other advantages to mixing fuels, such as getting higher net density, or changing some other physical properties. But I_SP will always be worse.

[Robotengineer]

How much electric charge does HST's solar panels produce? I'm making an RO config for for the CactEye mod.

[K^2]

Real electric power is not measured in charge. Charge at known voltage gives you total energy stored. So charge per second only becomes power once you establish voltage.

That said, HST is about 2.8kW.

[xenomorph555]

I have been told that when giving small children vaccines for virus's like Polio the dead virus from the vaccine is converted into live virus through the liver and can cause contamination when peeing, etc.

My question is how the dead virus is converted to live virus in the liver?

/I ain't a biologist :P/

[Iskierka]

It isn't, as virii aren't even technically "alive" - they're little protein balls that contain a bit of injectable DNA that takes over a cell they attach to. Vaccines are typically the protein ball shell, or a similar clone, that is enough to trigger the immune system response, but with the DNA removed, or replaced with non-harmful dud DNA samples. The liver can't re-add the DNA - it doesn't even know what DNA it would be - so it's physically impossible for the virus to be "re-activated".

[K^2]

I am not a biologist either, so this is just an educated guess. Poliovirus is a very simple virus consisting of a single RNA strand and a protein shell. Proteins on virus' surface bind to a receptor on host cell's wall, allowing RNA into cytoplasm. There, RNA is transcribed to produce proteins required to build copies of the virus.

Oral Polio Vaccine (OPV) is produced via heat-induced mutations. It is meant to be a non-virulent form of poliovirus. My best guess is that OPV virus can still get into cells, where it is partially transcribed despite mutations. Depending on RNA replication scheme, it is possible that segments of the RNA are swapped out. Given that each dose will contain millions of deactivated viruses, and each cell will make tens of thousands of copies, it is possible that some recombination of mutated strands can make a virulent version of poliovirus RNA.

Again, this is a guess, but all I can think of.

It is worth noting that injected form of the vaccine is supposed to be free of this risk.

Edit: Iskierka, I was surprised to learn this, bu OPV really can revert to virulent form. It has to do with RNA not being fully denatured, as with most vaccines. But I could not find details, hence filling in blanks with guesses.

Edited February 23, 2015 by K^2

[xenomorph555]

I am not a biologist either, so this is just an educated guess. Poliovirus is a very simple virus consisting of a single RNA strand and a protein shell. Proteins on virus' surface bind to a receptor on host cell's wall, allowing RNA into cytoplasm. There, RNA is transcribed to produce proteins required to build copies of the virus.

Oral Polio Vaccine (OPV) is produced via heat-induced mutations. It is meant to be a non-virulent form of poliovirus. My best guess is that OPV virus can still get into cells, where it is partially transcribed despite mutations. Depending on RNA replication scheme, it is possible that segments of the RNA are swapped out. Given that each dose will contain millions of deactivated viruses, and each cell will make tens of thousands of copies, it is possible that some recombination of mutated strands can make a virulent version of poliovirus RNA.

Again, this is a guess, but all I can think of.

It is worth noting that injected form of the vaccine is supposed to be free of this risk.

Edit: Iskierka, I was surprised to learn this, bu OPV really can revert to virulent form. It has to do with RNA not being fully denatured, as with most vaccines. But I could not find details, hence filling in blanks with guesses.

That was a really good explanation thanks

[Sirrobert]

I am not a biologist either, so this is just an educated guess. Poliovirus is a very simple virus consisting of a single RNA strand and a protein shell. Proteins on virus' surface bind to a receptor on host cell's wall, allowing RNA into cytoplasm. There, RNA is transcribed to produce proteins required to build copies of the virus.

Oral Polio Vaccine (OPV) is produced via heat-induced mutations. It is meant to be a non-virulent form of poliovirus. My best guess is that OPV virus can still get into cells, where it is partially transcribed despite mutations. Depending on RNA replication scheme, it is possible that segments of the RNA are swapped out. Given that each dose will contain millions of deactivated viruses, and each cell will make tens of thousands of copies, it is possible that some recombination of mutated strands can make a virulent version of poliovirus RNA.

Again, this is a guess, but all I can think of.

It is worth noting that injected form of the vaccine is supposed to be free of this risk.

Edit: Iskierka, I was surprised to learn this, bu OPV really can revert to virulent form. It has to do with RNA not being fully denatured, as with most vaccines. But I could not find details, hence filling in blanks with guesses.

That is interesting. My first reaction was 'probably just another baseless point from anti vaccination people'

After doing some digging on NCBI though, this is indeed a very real condition. It's called "vaccine-associated paralytic poliomyelitis". It is however a very rare condition, the numbers I found range from 1 in 1.4million to 1 in 2.5million doses administered. Note that this is doses, not people.(http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2486585/)

It also apears that VAPP is ONLY a concern for OPV (oral vaccin) and does not occur in IPV (Inactivated Polio Vaccin. The version with a needle). It seems OPV are only really used in regions where regular Polio is active. Regions without normal Polio (like west Europe) use primarely IPV.

Aparently, OPV uses a weakend (through mutation) live strain of Polio, while IPV uses an inactivated strain

It seems that VAPP happends more often in immunodeficient childred (with a weaker immune system).

OPV seems to work by actually infecting the guts with this weakened strain, while it is unable to infect the nerves (where it actually does damage). [speculation] It seems that, in the event of a significantly weakened immune system, the body is unable to stop the infection as normal, and the virus has a chance to mutate back to it's original version, which can infect nerves [/speculation]

The wikipedia page explains it all very well: http://en.wikipedia.org/wiki/Polio_vaccine

For more sciencey details, try here: http://www.ncbi.nlm.nih.gov/pmc/?term=vaccine-associated+paralytic%20poliomyelitis (warning: High density of science speak. Large risk of confusion)

Edited February 23, 2015 by Sirrobert

[K^2]

Yes, it is only the mechanism of mutation back to paralytic and virulent form that is not clear from any of this.

[RainDreamer]

Why are thermal soak heat shields (the non ablative ones like on the space shuttle) composed of small tiles of heat resistant materials, instead of one full segment, or at least bigger plates?

[K^2]

On the Shuttle, main reason is that they are replaceable. I have no idea if any of the tiles were actually reused from one flight to the next, but even if not, it's still far easier to take the shield off and put it back on if it is made up of tiles.

For non-reusable craft, similar considerations are still valid. Servicing and testing the tiles prior to flight is going to be easier than working with a solid shield. And if you discover a crack or another flaw, you only need to replace a tile, not the whole thing. So it's going to be a choice between simplicity of solid shield vs versatility of tiles. I would imagine Solid shield to win out for smaller capsules and tiles for larger ones. But I'm not familiar with enough pure soak designs out there to really test this hypothesis against the real world.

[Kryten]

Why are thermal soak heat shields (the non ablative ones like on the space shuttle) composed of small tiles of heat resistant materials, instead of one full segment, or at least bigger plates?

Three main reasons;

-it frequently gets chunks knocked out of it, and the material can't be repaired safely. Replacing a few damaged tiles is a lot cheaper than having to whip out an entire heatshield every mission

- so uneven expansion through heating doesn't crack it

- producing a single-piece unit would require a gigantic (i.e. expensive) kiln

EDIT:

On the Shuttle, main reason is that they are replaceable. I have no idea if any of the tiles were actually reused from one flight to the next, but even if not, it's still far easier to take the shield off and put it back on if it is made up of tiles.

Tiles were inspected, and only damaged/missing ones replaced.

Edited February 24, 2015 by Kryten

[K^2]

- so uneven expansion through heating doesn't crack it

Good call. But this applies to ablative shields as well. Of course, so do some of my reasons. I wonder if it's really the difference between ablative making more sense for small capsules and soak making more sense for large ships?

[Kryten]

Good call. But this applies to ablative shields as well. Of course, so do some of my reasons. I wonder if it's really the difference between ablative making more sense for small capsules and soak making more sense for large ships?

Partially, but there's also the factor that the materials used in these tiles are simply much brittler than most ablatives.

[YNM]

Does anyone here know about what PIDM (Partially Interacting Dark Matter) is actually (least are, as envisioned by the proposer) ? Why would it be "partially" interacting ? Because I read somewhere they talk about symmetries for these things... Least are, if you can tell me what this paper want to tell people : http://arxiv.org/abs/1405.7708v3

[Robotengineer]

What is the scientific benefit of a Mars Sample Return Mission? What can we do on Earth that we couldn't do with a rover/lander?

[magnemoe]

What is the scientific benefit of a Mars Sample Return Mission? What can we do on Earth that we couldn't do with a rover/lander?

Far better instruments in an fully equipped laboratory than the stuff you can put on an rover. Better you can easy do other experiments based on the findings.

This would be true even if you did an manned landing and established an base.

To maximize return from an sample return mission it would make sense to send some rovers fist to collect samples then load them on the return rocket.

[Mazon Del]

The new President of Worcester Polytechnic Institute gave a pretty great presentation on what we could do with material brought back from Mars. If we were able to bring back a single grain of sand, we have the tech to slice it into about 30 pieces which could be sent to various labs around the world to tell us pretty much every bit of information we could possibly learn about that grain of sand, and thus a load about Mars itself.

[MartGonzo]

I see lots of screenshots of craft with Kerbals in the external command chair, how do you guys do that?

I found a mod that allows you to man those chairs in the VAB but it was well out of date and didn't work for me, so how do you launch a craft with manned external seats?

[RainDreamer]

Spawn craft on launch pad, get another vehicle carrying the kerbal from the runway over to the launch pad? Or vice versa. Can also do it with a crewed part which gets ejected after the kerbal gets to the seat.

[magnemoe]

Spawn craft on launch pad, get another vehicle carrying the kerbal from the runway over to the launch pad? Or vice versa. Can also do it with a crewed part which gets ejected after the kerbal gets to the seat.

Launch an simple rover with kerbal in a pod fists, an plane cocpit with wheels and batteries works well. Drive off the launchpad area or runway.

Return to spaceport, load second ship on launchpad, drive rover up to it and board the seat, You will need ladders to get into seat so put on your second craft or rover