Experiment idea

[dj13]

I understand it isn't easy slowing an orbiting object enough for re-entry. I am wondering though what the effect of a parachute, deployed while still in orbit would have. <br /><br /> If an object with a parachute were to suddenly find itself relatively motionless in respect to the planet, what would happen? Gravity of course, and perhaps a loss of a controlled entry due to atmospheric uncertainties, but with a parachute would that object ever get to a speed before the parachute starts working where heat becames such a big problem. Or would the essentially zero atmosphere make the parachute just another object that gravity is yanking on? Or would the friction that built up on an unfilled parachute burn the fabric up before it could deploy?<br /><br /> So my experiment would be to drop something out of the space station, or the shuttle at orbital speeds which instantly opens a parachute. I propose it be GPS compliant, with radio capabilities so that its progress could be monitored by the public. <br /><br /> Oddly this experiment might have cost millions earlier in the space age, but now it could be set up and run almost as an afterthought. <br /><br /> If this experiment has already been done, in the early years of the space age, and not classified top secret, where might I find the results?

 

[henryhallam]

If the object + parachute is dropped from orbital altitude (up to 500km or so if not further) but without any tangential, i.e. forward, orbital velocity, then it will just parachute down quite easily without much heating load, as long as the parachute is designed to give a lot of drag quite early on.<br />Problem is that orbiting vehicles have tremendous tangential velocity and this is what needs to be gotten rid of in reentry. If you could use a rocket to get rid of this speed while still at altitude, reentry would be much easier - but this rocket would be the same size as a modern launch vehicle, which of course makes the rocket used to launch THAT ridiculously, impossibly big.<br /><br />There are however devices known as ballutes which, I think, use hydrogen to actually provide some lift. They can make a very slow, relatively uncontrolled re-entry over a whole orbit or more by keeping a low descent rate and staying in the very high upper atmosphere for most of the deceleration. Because the deceleration is spread over hours rather than a few minutes, peak heating loads are reduced and a considerably lighter TPS can be used.<br />I don't know if this has ever actually been tried from orbit proper, I think it has been demonstrated with suborbital velocities though IIRC.

 

[dj13]

Thanks for that reply, which gets this reply;<br /><br />Is there enough atmosphere at orbital heights to even 'inflate' or fully deploy a parachute. I know there is some as every satelite short of geosychronous tends to decay its orbit till it reenters. <br /><br />Or would a parachute deployed at such heights be destroyed by even the few molocules at those heights which the parachute would be attempting to use to slow the object. Perhaps the question becomes does modern materials science have a fabric capable of stopping a molocule travelling at something like 17,000 mph. Perhaps it would not need to stop (relatively) the molucule but be designed to allow the molocule to glance off an airfoil maybe. Each glancing molocule slowing the object ever so slowly. This is a modification of normal reentry, as rockets are used now to slow object enough so that gravity takes effect. Could a parchute slow that tangential energy enough to be all that would be needed, regardless of how many orbits it might take ?

 

[henryhallam]

The drag at proper LEO altitude is really very low, that's why thse "ballutes" are used - they are effectively an inflatable parachute since that is required to make it deploy fully.<br /><br />As far as I'm aware there is no problem with the fact that the molecules are moving very fast w.r.t. the ballute, it just feels like a very low drag, the same as if it were moving at a low speed in a higher pressure atmosphere. The molecules don't have enough K.E. to break chemical bonds, so a few molecular collisions at high speed have the same effect as lots of collisions at low speed. <br /><br /><font color="yellow"><br />This is a modification of normal reentry, as rockets are used now to slow object enough so that gravity takes effect.<br /></font><br />I think you would make a deorbit burn as normal except that the perigee would be lowered to perhaps 80 to 100km rather than the 40 or 30km that is usually used. This would require slightly <i>less</i> propellant, but not enough to make much of a mass saving - that would come from the lack of TPS.<br />It is worth noting that this ballute concept probably requires a relatively light reentry vehicle, if the ballute isn't to be absolutely enormous.<br /><br />I really don't know too much about these ballutes though, so please don't take what I'm saying as gospel!

 

[drwayne]

Tangentially related, but interesting:<br /><br />http://yarchive.net/space/launchers/personal_reentry.html<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[najab]

><i>Could a parchute slow that tangential energy enough to be all that would be needed, regardless of how many orbits it might take ?</i><p>No, because as the object slows, it's orbit will drop - it will fall into thick atmosphere before a significant amount of energy has been dissipated.</p>

 

[dj13]

OK, the ballute it is.<br /> <br />I just googled ballute and found a wealth of info, and the probable answer to my question. <br /><br />Thanks for your input, I think I have my answer!

 

[henryhallam]

I was thinking you could use a hydrogen balloon for lift to stay at altitude, but the highest balloon flight ever was about 54km (that was unmanned), and that's relatively thick atmosphere in re-entry terms, albeit higher than the 40-45km where the shuttle does most of its deceleration. But I think it is too thick for a balloon to survive in at that kind of velocity.

 

[dj13]

I read recently there were a couple of parachutists wanting to parachute from the ISS. The believed it would be the ultimate trip. After reading the tangentially speaking refernce from DRWAAYNE above, I got to thinking about the consumables, and having a picnic on the way down, visors open as soon as possible and a bottle of beer in hand. I do like this idea!

 

[vogon13]

Surprisingly enough, a relevant experiment has already been conducted. Echo 1 was a large mylar sphere inflated in orbit to reflect radio signals back down to earth. IIRC its diameter was over 100 ft. It was extremely light for it size and atmospheric drag must have been quite large. IIRC it remained in orbit for at least a couple of months. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[holmec]

So here is my question.<br /><br />With a balute, and I guess, the atmoshere slowing technique , can we have a reentry ship that does not need tiles or a traditional heat sheild? But maybe just a light heat sheild in the skin?<br /><br />And could it be done at a G level tolerable to the crew? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[mrmorris]

<font color="yellow">"Is there enough atmosphere at orbital heights to even 'inflate' or fully deploy a parachute. I know there is some as <b>every satelite short of geosychronous tends to decay its orbit till it reenters</b>. "</font><br /><br />Nope -- not that high. drwayne had a link he posted with orbital lifetimes on at least one occasion (probably many). IIRC -- above about 1000km, orbital decay due to atmospheric friction becomes essentially a non-issue (orbital lifetimes of 1000's of years). There's a lot of room between 1000km and GEO.

 

[gofer]

I think this is a great idea. If these can be used as personal emergency escape pods that'd would be great. Or as an extreme space sport. Imagine jumping from the Bigelow hotel and descending in these things. Adrenaline? You bet! I've been following one of the possible implementations. It's a very low-key low-budget (they use cheapest launchers that the military throws away) program that started in 2000, they've had 3 test suborbital flights called Demonstrator so far, but had some launcher problems on 2 of them and the first one they found on the 8th day after it had landed and it seems it was in good shape and gave good data. <br /><br />Reference: Not in English but there are some pictures and schematics of the planned ballute application (return of cargoes from ISS): http://www.laspace.ru/rus/ptu_future.php My understanding is that ballute deployment has been recently tested in a wind-tunnel and there are some commercial applications considered. There seems to be a commercial German-Russian enterprise to market these things. One detail is that it seems to be spun around the z-axis before ballute deployment. There also seems to be a version with its own OMS engines.

 

[dj13]

I would be happy with even one of those small plastic soldiers with a cheap vinyl parachute being tossed outside the shuttle to see what would happen. But it wouldn't tell me much unless I could somehow track it. It would not weigh much though.<br /><br />I think a small afterthought of an experiment still might shed enormous info. So I again propose the simple experiment.<br /><br />From an upcoming shuttle or other space platform, deploy at least one, perhaps several, signal generators (SG), each capable of modest environment readings; GPS, attitude, temps, etc. Several different designs could be housed in an experimental package only slightly heavier than the mass of the SG's. I'm thinking each might be about the size of a lunch pail, with most of that space being the parachute, ballute or whatever. Several would fit in a flight bag.<br /><br />My version would house the SG in something like a cardboard box (or with something akin to those fold up shields you might have in your car. The ones that help prevent the sun from overheating the car interior). It might have the SG on an interior gimbal, but a gimbal is getting a bit beyond simple. One side of this box could open to deploy a parachute, nothing fancy, but several times the diameter, which at ground level pressures would slow it to a speed where a raw egg would survive impact.<br /><br />The cardboard box might ignite shortly on exposure to a lot of air molecules, but I think it would start tumbling at first. Dissipating heat as it tumbled. As an aside would it tumble randomly, or to the left or right depending on hemisphere? Or end over end at the equator, (brings on a whole other silly thought)?<br /><br />At some point when the descent angle was sufficient or the box burned away the parachute would definitely have enough air to inflate. If the box didn't burn away then the parachute would be ejected and deployed. What would happen? For that matter without adequate oxygen, what would happen to something as simple