Space walk and other astronaut questions

[cacho]

I read that most space shuttle missions occur in low orbit... low enough that if the space shuttle lost all power, and couldn't occasionally correct it's orbit, that it would eventually fall back to earth and burn up, after 8 hours or so.<br /><br />Let's say that something catastrophic happens, and a space shuttle blowsup/breaks apart while in orbit. An astronaut who was doing a space walk is pushed away by the blast towards earth. He is now abandoned in space.<br /><br />1. would the astronaut eventually fall back to earth and burn up? if so how long would that take?<br /><br />2. are there suicide pills (as seen in movies) or some other method for the astronoaut to kill himself knowing he'll either die from oxygen running out or burning up?<br /><br />3. would it be possible for the astronaut to catch a satellite, then have ground controllers maneuver the satellite to rendevous with the INT'l Space Station? <br /><br />4. what does an explosion in space look like? If the space shuttle some how exploded in space, would you see a fire ball? If so, does the fireball expand quickly as the air that fuels it expands into space?

 

[ve7rkt]

<font color="yellow">2. are there suicide pills (as seen in movies) or some other method for the astronoaut to kill himself knowing he'll either die from oxygen running out or burning up?</font><br /><br />Space is not a forgiving place. In space, you have to work very hard NOT to die. If you decide that you want to end things sooner, just stop trying.<br /><br /><font color="yellow">4. what does an explosion in space look like?</font><br /><br />We'll find that out real soon now. On July 4, look up...

 

[CalliArcale]

[bI read that most space shuttle missions occur in low orbit... low enough that if the space shuttle lost all power, and couldn't occasionally correct it's orbit, that it would eventually fall back to earth and burn up, after 8 hours or so.<br /><br />Yes, it's a fundamentally unstable orbit. This is partly because it is low in the gravity well (far below the Roche limit, which is the lower limit for indefinintely stable orbits; Saturn's rings are actually below its Roche limit and will someday be gone) but mostly because there is still an extremely tenuous atmosphere up there. It's far too thin to be useful for steering or attitude control for most shuttle operations, but it does produce a noticeable drag. However, it would take a lot longer than eight hours for the Shuttle to deorbit. How long would depend on what its orbit was and how active the Sun was, as that affects the density of the upper atmosphere. It would probably take somewhere between weeks and years.<br /><br /><b>1. would the astronaut eventually fall back to earth and burn up? if so how long would that take?</b><br /><br />Yes, the astronaut would eventually reenter. How long would depend on orbit, atmospheric density, etc. Occasionally, tools are lost during spacewalks. US Space Command (located under Cheyenne Mountain) tracks them; it can track pretty small stuff. Not long ago, I recall a foot restraint getting lost. They tracked it for several weeks at least before it reentered. It was almost certainly consumed during reentry. I don't want to speculate about the condition of an astronaut after reentry; there are those on this forum who were involved with the Columbia recovery and, well, it's just not something I want to speculate about right now.<br /><br />The astronaut would not be killed by reentry, though. They'd die when the life support systems failed. They only last a few hours before they need recharging. (The typical eight-hour spacewalks include breaks to recharge the PLSS - <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[henryhallam]

<font color="yellow"><br />This is partly because it is low in the gravity well (far below the Roche limit, which is the lower limit for indefinintely stable orbits; Saturn's rings are actually below its Roche limit and will someday be gone) but mostly because there is still an extremely tenuous atmosphere up there. <br /></font><br />I thought the Roche limit only applied to moons, i.e. objects held together primarily by their own gravity (as opposed to structural integrity of the materials). Tidal forces cause moons to break up into rings if they get too close to the planet - and even then they don't deorbit (although the ring material may eventually fall in due to collisions). This effect doesn't apply to spacecraft held together by bolts and welds. I suppose ignoring atmospheric drag, perturbations from the moon and masscons in the Earth might eventually make the orbit eccentric enough to intersect the Earth's surface, but that would take a LONG time and is only tangentially related to the Roche effect.<br />In reality I think that drag is the ONLY cause of orbit decay for anything in LEO. Please do correct me if I'm wrong about this.

 

[CalliArcale]

I'm no expert on orbital mechanics, but my understanding was that tidal forces will slowly bring an object down (and if it's big enough, tear it apart) if it's below a certain average altitude. The laws of physics do apply to spacecraft held together with nuts and bolts. But yes, it will take a heck of a long time. Thousands of years, most likely. I would assume that the smaller the object is, the longer it will take. (Saturn's rings are expected to persist for millions of years. This is remarkable mainly because Saturn is billions of years old, so they can't possibly be original features of the Saturn system.) <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>