IPB

Welcome Guest ( Log In | Register )

6 Pages V  « < 3 4 5 6 >  
Reply to this topicStart new topic
Sending Men To Venus
Guest_DonPMitchell_*
post Jul 1 2006, 10:10 AM
Post #61





Guests






I worked on the heavy-nuclei detector in HEAO-C. We actually calibrated it in space using iron nuclei, which are pretty abundant in cosmic rays. I've heard that astronauts occasionally see flashes of light, when one of these passes through their eye and generate Cherenkov radiation.

There has been some research on using strong magnetic fields to shield a craft from cosmic rays. I don't know if that is practical or not.

Perhaps research on suspended animation will open up better possibilities for dealing with multi-year interplanetary missions -- allowing a crew to be kept safe in small shielded areas, and eliminating the need for massive supplies. Some dogs have been maintained in a clinically dead state for many hours without ill effect. But it's far from perfected or safe at this point.
Go to the top of the page
 
+Quote Post
Bob Shaw
post Jul 1 2006, 11:34 AM
Post #62


Senior Member
****

Group: Members
Posts: 2488
Joined: 17-April 05
From: Glasgow, Scotland, UK
Member No.: 239



QUOTE (DonPMitchell @ Jul 1 2006, 11:10 AM) *
I worked on the heavy-nuclei detector in HEAO-C. We actually calibrated it in space using iron nuclei, which are pretty abundant in cosmic rays. I've heard that astronauts occasionally see flashes of light, when one of these passes through their eye and generate Cherenkov radiation.


Don:

I think the mechanism for 'seeing' cosmic rays actually involves direct stimulation of the optic nerve - the eyes aren't involved at all.

It's still scary!

Bob Shaw


--------------------
Remember: Time Flies like the wind - but Fruit Flies like bananas!
Go to the top of the page
 
+Quote Post
JRehling
post Jul 1 2006, 12:14 PM
Post #63


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
dvandorn
post Jul 1 2006, 12:26 PM
Post #64


Senior Member
****

Group: Members
Posts: 3227
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



QUOTE (Bob Shaw @ Jul 1 2006, 06:34 AM) *
Don:

I think the mechanism for 'seeing' cosmic rays actually involves direct stimulation of the optic nerve - the eyes aren't involved at all.

It's still scary!

Bob Shaw

Were there ever a set of results posted for the ALFMED experiments flown during Apollo lunar missions? They had a nice setup, with a head-enclosing box that contained film on five of six sides. The idea was that you'd be able to calibrate film hits against taped reports of light flashes reported by the test subjects.

One of the things this was supposed to settle was whether the crews were seeing real light generated inside their eyeballs, or whether the flashes were indeed the result of direct hits on the optic nerves of the brain.

I don't ever recall seeing any results that settled this question. Anyone have any more info about it?

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
dvandorn
post Jul 1 2006, 12:29 PM
Post #65


Senior Member
****

Group: Members
Posts: 3227
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



QUOTE (JRehling @ Jul 1 2006, 07:14 AM) *
This calls to mind the idea of having a large "dead" space station anywhere you want to revisit -- a shield that is heavy and needs to be put in place, but only once, for future missions to crawl inside it like a crab, then leave (or be pried out) when they're done. Incidentally, it could be done for robotic flights as well as manned, if you had a known orbital niche you wanted to revisit. For example, a Jupiter orbiter between Io and Europa. One dedicated launch to put the big shield/shell in place could create a home for many future missions. Sort of like the infrastructure effort in putting a comsat in place, except the shieldsat could conceivably last ~forever.

Why send such things, when you can use piles of rock and ice that Nature has provided? Assuming you can find piles of ice and rock in the orbits you want to use, of course.

Really, though -- just dig into a low-mass moon or asteroid, and you're all set. This would work for most of the worlds in our system, with the exceptions of Mercury and Venus...

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Guest_MarkG_*
post Jul 1 2006, 07:28 PM
Post #66





Guests






QUOTE
Why send such things, when you can use piles of rock and ice that Nature has provided? Assuming you can find piles of ice and rock in the orbits you want to use, of course.


Provided you can put a few tens of thousands of tons of hardware into orbit even that isn't an issue. Find a small near-Earth asteroid, land a mass-driver and some kind of decent power plant -- be it nuclear or solar -- on the asteroid and your 'home' also becomes your fuel supply. It won't get anywhere fast, but by throwing the rock out the back of the mass-driver you can take it to orbit pretty much any planet in the solar system.

Personally though I doubt people will ever land on another planet until they're doing it as a tourist trip. Venus is really kind of a no-hoper due to the atmosphere and surface conditions, where unmanned probes are clearly superior to humans (though obviously rovers controlled from orbit could move faster than rovers controlled from Earth), and while the Apollo astronauts probably achieved more in a few days in localised areas on the Moon than an unmanned probe would in months, for the cost of a manned trip to Mars with today's technology that could thorougly study one area you could 'pattern-bomb' Mars with a thousand or more unmanned rovers and get a good overview of the entire planet... I can't help but feel that the latter would be much better value for money.
Go to the top of the page
 
+Quote Post
Guest_DonPMitchell_*
post Jul 1 2006, 08:37 PM
Post #67





Guests






QUOTE (Bob Shaw @ Jul 1 2006, 04:34 AM) *
Don:

I think the mechanism for 'seeing' cosmic rays actually involves direct stimulation of the optic nerve - the eyes aren't involved at all.

It's still scary!

Bob Shaw


I think both effects exist. During the Apollo missions, flashes of light were seen, and these were explained as Cherenkov radiation in the vitreous humour. X-rays and gamma rays can also stimulate the optic nerve and brain.

Super energetic cosmic rays can cause the whole sky to flash. I don't believe the human eye can see this, but there are detectors that essentially use the night sky as a giant detector for these rare events.
Go to the top of the page
 
+Quote Post
dvandorn
post Jul 2 2006, 01:39 AM
Post #68


Senior Member
****

Group: Members
Posts: 3227
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



OK, here's a question that reveals an area of ignorance on my part...

We have a pretty decent idea of the energetic cosmic radiation levels outside of Earth's protective Van Allen belts. We also know we can see a certain number of these particles on Earth's surface itself (ever seen one of those nifty cloud scintillation chambers that were all the rage 40 years ago?), so we know that not all of these particles are shielded at the Earth's surface. (At least, when I saw one in grade school, they told me that the trails were energetic cosmic rays.)

The question is, what is the relative level of shielding provided by the Earth's magnetic field? I'm just looking for an order-of-magnitude feel for the thing -- is 1/10,000th of the unshielded flux coming through, or more, or less? That kind of thing.

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Guest_DonPMitchell_*
post Jul 2 2006, 04:30 AM
Post #69





Guests






Here is some information from Caltech's Space Radation Lab (where I was a grad student ages ago).

Interplanetary Dose

History

Radiation is also highly concentrated within the Earth's radation belt, so the most dangerous place to be is a few hundred miles above where ISS is orbiting. In the outer belt, you would get a lethal dose or radation in a couple days.

The Earth's magnetic field looks like it may collapse for a while and possibly reverse, sometime in the next thousand years or so. The field is already about half the strength that it was during the Roman era. The Earth's atmosphere is plenty of shielding against space radiation, but I've already heard people make bizarre and dire claims about what will happen then.
Go to the top of the page
 
+Quote Post
JRehling
post Jan 8 2008, 07:00 PM
Post #70


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
dvandorn
post Jan 10 2008, 07:54 AM
Post #71


Senior Member
****

Group: Members
Posts: 3227
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



It still occurs to me that surface sample return is beyond our capabilities at the moment. Venus has a gravity field very similar to that of Earth -- you would need something more powerful than a Delta II to get a sample off the surface and into an escape trajectory, I would think (especially when you consider how much more atmospheric drag it would encounter on the way up).

That's an awfully big rocket to land on Venus and to engineer such that it will survive any sort of surface stay long enough for teleoperations.

Here's a question, though: just how valuable would a sample of Venusian air, collected at, say, 50km altitude, be? We're still above a lot of the atmosphere at 50km, right? You could design an entry probe to pump a chamber full of Venusian air (complete with dust particles, etc.), or perhaps several chambers at different altitudes. Then, when the vehicle is still moving relatively fast (we're talking Mach 6 to Mach 10 operations, here) all you would really need to boost the sample chamber(s) back to an escape trajectory would be something like one of those air-to-orbit rockets.

I'd think the data on isotope abundances and elemental compositions of dust particles would make the samples worthwhile, and you could collect such samples and then rendezvous the collection chamber(s) with a manned flyby, just as John described.

What do y'all think?

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
JRehling
post Jan 10 2008, 08:21 AM
Post #72


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
ugordan
post Jan 10 2008, 08:43 AM
Post #73


Senior Member
****

Group: Members
Posts: 3562
Joined: 1-October 05
From: Croatia
Member No.: 523



QUOTE (JRehling @ Jan 10 2008, 09:21 AM) *
Launch from the surface of Venus is definitely a dicey proposition (imagine a Delta rocket descending by parachute into a 900F hell and the liquid propellant not exploding).

With the density of Venus' atmosphere, I think any rocket would have severe gravity loss penalties. You would need to avoid any significant dynamic pressure (easily builds up in Venus atmospheric density) and I think that'd actually imply subsonic velocities (and you still might have high losses due to air drag) for much of the atmospheric ride up.

How does this translate to gravity losses? If you're constrained to a velocity, your acceleration is even more constrained. The best (cheapest in terms of delta-V) way to get something into orbit is to send it up as fast as possible to minimize the time gravity decelerates you before you go on a ballistic trajectory with negligible further gravity losses. Fast accelerating rockets in other words. On Venus, your inertial acceleration would be limited to about 1 G (giving a total of about zero for early phases of flight) for a long time so the gravity losses would skyrocket. You'd need much more total delta-V imparted by the rocket than on Earth precisely because you're not allowed to accelerate fast enough in the lower atmosphere.

It begs the question if rockets can be even remotely feasible on Venus and that's even neglecting high surface temperatures and pressures and issues they cause with propellants.


--------------------
Go to the top of the page
 
+Quote Post
Doc
post Jan 10 2008, 11:15 AM
Post #74


Member
***

Group: Members
Posts: 276
Joined: 11-December 07
From: Dar es Salaam, Tanzania
Member No.: 3978



I don't know if this has already been considered but I think its worth mentioning.

Recently I had been examining atmospheric profiles of Venus and have noticed that if one were considering sending humans to the planet, it may be better to build some kind of floatable module that can hover at a certain height in the Venusian atmosphere with Terran air pressure and temperature. I can't recall how high exactly (17km?) but what I do know is that it is 'safe enough haven' for manned exploration.


--------------------
We talk of nothing but Curiosity here
Follow me on twitter or Google +
Go to the top of the page
 
+Quote Post
JRehling
post Jan 10 2008, 06:54 PM
Post #75


Senior Member
****

Group: Members
Posts: 1572
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post

6 Pages V  « < 3 4 5 6 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 2nd September 2014 - 09:22 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.