spacewalks and Perseid meteor shower

[flatboat]

I wish there had been some discussion of doing spacewalks during the Perseid Meteor shower. It seemed a strange time for a shuttle mission, much less extended space walks to replace a gyroscope. If there was a specific evaluation for the Perseid environment instead of relying on one year exposure averages, I wish it had been addressed in a briefing since spacewalks and the Perseid shower were sided-by-side in the news. It seems like one hour exposure while the earth goes through the Perseid environment is equivalent to (some big number) hours of exposure at other times. Will the glove damage and the space suits be inspected for potential meteoroid damage? What is the equivalence? are their special precautions that the astronauts took? Do we need any more data? should their have been witness panels exposed for 3 days during Perseid for comparison to 3 month panels at other times? Enquiring minds and even me, would like to know. Anybody have any links that I should visit? I understand that the space station is well protected for meteoroid and debris impacts but is a separate meteoroid shower risk calculation made? Are the new suits so robust they can stay outside with impunity?<br />

 

[3488]

Welcome to SDC flatboat. <br /><br />A great first post.<br /><br />This is a good one for MeteorWayne. <img src="/images/icons/laugh.gif" /> <img src="/images/icons/laugh.gif" /><br /><br />IMO, NASA would have weighed up the risks asscociated with the Persieds<br />& space walking astronauts outside the ISS.<br /><br />Clearly they thought the risk was low enough to allow the space walkers to carry out that task.<br /><br />MeteorWayne & shuttle_guy will know for sure.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[billslugg]

Welcome to SDC. My guess is that NASA weighed the risk as in: "Chance of collision with man made debris is X. Chance of micrometeorite strike is X divided by one million, chance of Perseid micrometeorite strike is X divided by 500,000.<br /><br />Our risk goes from X + .000001 up to X + .000002 <br /><br />No problem. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[MeteorWayne]

That is correct billslugg (I was going to abbreviate it, but that dog won't hunt <img src="/images/icons/smile.gif" /> )<br /><br />The risk from manmade debris is far greater than the risk from meteoroids.<br /><br />I've been meaning to dig up density stats for meteor showers, and actually have some time today, so will pursue that.<br /><br />MW <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bobblebob]

Has any serious damage ever occured on the ISS due to MMOD? With it being alot bigger the odds must be alot shorter

 

[MeteorWayne]

OK, just some very consevative back of the envelope calculations.<br /><br />For the Perseids, the peak rate is ~ 100/Hr.<br />When you are watching, you are examining a part of the sky greater than 500 km in all directions. So lets use 500 km as a ballpark figure.<br /><br />That makes the area PI*D or roughly 3142 sq km.<br /><br />That's 3,142,000,000 square meters.<br /><br />Lets assume an astronaut is 1 sq meter.<br /><br />So the odds of a Perseid impacting that space is 1 per<br /><br />31,420,000 hours of peak activity.<br /><br />The Perseid peak FWHM (full width half maximum), i.e. rate /> 50/hour is about 48 hours. see here <br /><br />So the odds of a perseid hitting that sq meter is about 1 in 650,000, if an astronaut were outside for the full 48 hours.<br /><br />Since they were only outside about 1/8 of that time, the odds are <br />about 1 in 5 1/4 million. The odds of a fatal hit are many times higher still.<br /><br />The risk from manmade debris is far higher.<br /><br />MW<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[henryhallam]

Is that 1 in 2200 a per-EVA figure? A best estimate or a conservative upper bound?

 

[erioladastra]

<br />It was analyzed before the flight and was not a significant increase of risk. The ISS also is very effective at shielding. The HST repair missions have had greater risks. There is a risk on any space walk. There is an increased risk during the Perseids. The increase is not that great compared to other risks.

 

[flatboat]

thanks for the responses! <br /><br />Let me preface the following with the fact that I usually get the "Ask Marilyn" (Sunday Parade magazine in the newspapaer) questions on probablity wrong!<br /><br />MeteorWayne, is your number of 100 per hour the number visible from the ground? How does that compare to the rest of the year when not in a "meteor shower"? (Based on your link I'm guessing only 10x larger, I would have previously guessed much more, hence my concern.) My inclination is to use that ratio as a multiplier for the much smaller meteoroid particles that could cause a leak in a spacesuit (without making a visible meteor). <br /><br />Shuttle_guy, I'm glad the subject came up in a briefing. thanks for passing it on: "Actually the chance of a fatal MMOD hit to a EVA crewman was quoted last night (By John Shannon the MMT manager) to be 1 in 2200. (I think I heard him correctly) He was talking about how risky EVAs are. " I didn't see it in the mainstream news, but since the spacewalk and Perseids were next to each other in the headlines it was time for the question to come out. If the Perseid environment is only a factor of 10 higher than the normal background, then that doesn't seem like much increase in risk.<br /><br />Maybe "Ask Marilyn" will get the details on relative flux and overall risk vs risk at a given time, and spell it out for me somethime (cause I never understood the probablities of winning when the gameshow host asking me if I want to switch doors...) <br /><br />thanks!

 

[MeteorWayne]

You've got it about right..<br />Sporadic meteor levels range from about 6 per hour in the spring to 15 or so in the fall (in the northern hemisphere, roughly reversed for the southern hemisphere. so say 10-15 per hour is a very rough average.<br />There's almost always one or several meteor showers active at any given time so most times the rate is higher.<br />In fact, the night of the Perseids there's 4 other active showers adding another 5 or more per hour.<br /><br />So 10X the flux on this night is about right.<br /><br />Even during the Leonid storms, when rates can reach />40,000 per hour (wow!) if you plug those numbers in, the risk still very small, much smaller than the impact risk from man made debris in orbit, although with some showers the velocity is much greater, giving the particle 25 times the energy.<br /><br />In fact during the Leonid storms of 1996-2002 satellite operators did take some precautions, such as protecting sensitive areas, aligning solar panels so minimum areas faces the stream, shutting the cover of the HST etc, but they were precautionary.<br /><br />As newsartist said (and my calculations showed) you are actually<br />sampling a huge area, over 3000 sq km, 100 an hour isn't very much over that area.<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[MeteorWayne]

I did forget to mention the thickness of the disk (or more correctly, the meniscus, since it is curved like the earth's surface.)<br />Most meteors occur between 100 and 60 km above the surface (60 and 40 miles) and ones you see near the horizon can be over 400 miles away. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>