Use of Shuttle External Tank in orbit

[spd405]

Plans for converting the shuttle's ET for use in orbit have been floating around for some time.<br /><br />What has stopped these plans from being attempted and how effective would they be?

 

[chriscdc]

Unlike Skylab the tank has to be filled with fuel to get off the ground. The extra weight of any airlocks fitted to the tanks, would severly limit performance.<br />Overall it would be far easier to build a specially built module like the 'can' version of the ISS.

 

[lunatio_gordin]

I believe for a while they had an offer of three ETs into orbit for anyone who could make use of them. I don't know if that still stands... I read a book about it, maybe three years ago. No one could really figure out how to conver them to livable space once they were in orbit.

 

[najab]

It's actually 5 tanks...and the Presidential Executive Order still stands.

 

[lunatio_gordin]

Now that i think about it, it's definitely five, because they had a picture with them linked together forming a ring that would spin...

 

[le3119]

The trouble is, the EFT would have to be modified in LEO, which would require an advanced "workshop" akin to the one on the good 'ol Space Station Freedom configuration. But EFTs, since they're a dime a dozen would be great structures in which to practice space construction, if you screw up, just send 'em in reentry. It is sad that Island One's concept never was realized, I could find SOMETHING to do with five EFTs....<br /><br />An in-depth presentation by David R. Hunt (thanks for the great link!)<br /><br />http://members.tripod.com/~AeroMaster/paper1.htm

 

[spd405]

Would it cost in payload to get it into orbit for possible use at a later date - some reports I've seen say yes, others say no??

 

[lunatio_gordin]

I beleive there's always some extra fuel in the tank, so all they would have to do then is use that extra fuel to pull it into orbit. there *shouldn't* be any payload cost, but don't quote me on that <img src="/images/icons/tongue.gif" />

 

[tomnackid]

I once read that it actually takes MORE propellant to insure that the tanks are on a reentry trajectory into the Indian ocean than it would to take them all the way into orbit.<br /><br />The main thing stopping tanks from being used as building materials in orbit is an advanced space infrastructure. NASA will only release the tanks to organizations that can insure that they will be maintained in stable orbits. So far no one has been able to make that kind of commitment.

 

[lunatio_gordin]

guess that's why they shut down, huh <img src="/images/icons/wink.gif" /><br />Why did they change the location for dumping the ET? is it because there was too many islands to hit in the Indian ocean, or because of going to the Space Stations? or is it just easier to send it into the pacific?

 

[nacnud]

Given that the pacific is almost 1/3 of the globe it must be hard not to target the pacific <img src="/images/icons/laugh.gif" />

 

[strandedonearth]

The main showstoppers, I believe, have been:<br /><br />1: The foam insulation would disintegrate in the space environment, creating a big cloud of orange dust around the tank.<br /><br />2: Thin aluminum-alloy skin offers little radiation or MMOD protection<br /><br />3: The huge size and comparatively low mass would allow drag to slow it out of orbit quickly, unless re-boosted.<br /><br />I've been saying the best way to re-use tankage in orbit is to design them to be re-used as a wet lab. Make a big tank that has adequate MMOD shielding, standardized euiqpment mounts, and can have hatches easily installed. It would also need some sort of RCS/OMS package. All this wolud cost payload, but that shouldn't be a big deal, because the tank would also BE payload.<br /><br />I keep thinking the ultimate woud be to re-design a Delta-4 CBC as a wet-lab, using a smaller engine that could burn all the way to orbit, and surround it with 4-6 standard CBC's as a stage zero to get it off the ground.<br /><br />Question for SG: How much (if any) extra MMOD and/or radiation shielding had to be added to the S-IVB to make Skylab habitable, mass-wise?<br /><br />

 

[chriscdc]

Could you use an ET as a dry workshop if it was launched by an inline SDHLV? Would there be any advantage for this, over developing a specialy built module?

 

[lunatio_gordin]

Yeah, as i thought about it, (and mentioned in an M&L thread) i realized the foam would probably keep breaking off once it's in orbit. Which is really not good. That's a lot of debris flying around in an are where delicate docking operations wiould be taking place...

 

[publiusr]

See here:<br />http://www.spaceislandgroup.com

 

[mlorrey]

Actually, this is untrue. As the shuttle passes maxQ, thermal effects melt the outer surface of the foam which solidifies to form a rather hard shell that contains the unmelted foam. Supposed "popcorning" is a fictitious supposition unsupported by any facts.

 

[rocketman5000]

Does the foam retain it thermal properties after this melting process? If so wouldn't it be a viable fix for NASA?

 

[vogon13]

I have seen test footage from a high altitude aircraft carrying a foam covered plate to demonstrate popcorning.<br /><br />Seems like that would be a fact, Jack.<br /><br /> <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>

 

[mlorrey]

Such high altitude aircraft operate far below the speed and thermal conditions of Max Q, so your 'popcorning' is unrepresentative of true flight conditions.

 

[mlorrey]

the popcorning happens BEFORE Max Q. Hypersonics causes a rind to form on the foam, which is why the tank looks very dark after it reaches orbit (as seen in the attached picture) rather than the bright/light orange seen at launch... Once this rind forms, popcorning does not happen.

 

[qso1]

You asked and pretty much answered your own question. The use of ETs for structures in space has some very attractive advantages. Mainly sheer size. But that also means expense. Expense in the form of airlocks to access the internal portions of the tank. An airlock and/or passageway between the LH2 and LOX tank since both would be useful as cabin space. Radiation sheilding would be required which would be one reason for removing the tank foam.<br /><br />ETs to orbit and being utilized there have been proposed since very nearly the beginning of the shuttle program. The fact that nobody has actually been able to get it going (Several companies have proposed this idea) is an indication that the cost still outweighs the benefits of its size. <br /><br />One reason is outfitting the tanks on orbit. This would be an expensive undertaking when compared to the process of building and checking payloads out on the ground before launching them. <br /><br />As for foam. That should be a moot issue because if an SDHLV is used to put them into orbit. The tank insulation foam would not be required. Its primary reason for being on ETs is to protect the shuttle from ice chunks during ascent. <br /><br />The ET does not reach orbit at separation from the shuttle because its velocity is still below orbital velocity by around 1,000 mph.<br /><br />If I understood the original question, it being used as part of an inline SDHLV, and being atop of the LV, it would require major modifications. Mods such as an interface to replace the bottom end which is somewhat bowl shaped. The tank atop an SDHLV would probably not be a propellant tank unless it had engines on the bottom and thus served as an upper stage. To put the engines on the bottom just so it can be a wet tank, plus removal of shuttle orbiter attach points etc. Basically means you may as well start with a clean slate.<br /><br />If an ET is sent up atop an SDHLV dry, one still has to do something about the bowl shaped bottom end. The tank stil <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[qso1]

From a size standpoint, an ET outfitted as a lab or whatever is an attractive proposition on the surface. It has not been done because of cost.<br /><br />It is still less expensive to build modules that are ground processed and checked out than to outfit one in orbit. For one thing, experiment racks, stowage lockers, etc would have to be sent up for installation on later missions.<br /><br />The early ideas consisted of getting the tank to orbit on a shuttle mission. This would be the least expensive method of getting an ET to orbit however. Modifications would be required to get the ET to a stable orbit. Currently, the ET is jettisoned just below orbital velocity.<br /><br />Orbital velocity being 17,500 mph, ET jettisoned at around 16,500 mph.<br /><br />To send an ET to orbit via SDHLV would require the ET to be atop the LV if its launched wet. There would be no reason to do this unless the ET served as an upper stage which would require mods to the bottom bowl shaped end and the top. The bottom mods to allow an economical interface to the stage the ET sits upon and engines. The top because the wet ET would be wet in order to loft some useful payload sitting on top of it to orbit.<br /><br />The foam could be done away with because like the Saturn rocket, an ET atop an SDHLV would not require foam insulation. Other mods as shown on my crude graphic include eliminating the installation of shuttle attaching hardware and SSME plumbing. The tank itself would require an airlock to gain access to the inside. A passageway would have to be provided between the LH2 and LOX tanks to make use of both.<br /><br />Because there is always residual propellant in the tanks, safety precautions would be required, especially for welding operations within the tank.<br /><br />There is really no logical reason to send up a dry ET atop an inline LV. It would actually be more economical to gear up ET production lines to build ETs as payload carriers rather than propellant tanks. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[nacnud]

<font color="yellow">The foam could be done away with because like the Saturn rocket, an ET atop an SDHLV would not require foam insulation. <br /><br /><font color="white">Sure about that? Boil off rates on the pad could be horrendous.</font></font>

 

[qso1]

It wasn't a significant problem for the Saturn V which had upper stages loaded with LH2 and LOX and the first stage with LOX. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[mcs_seattle]

How is such a precise pre-OMS burn speed managed when the payload weight for the shuttle can vary so much? Are the SRB's loaded with essentially the same amount of fuel each launch? Is the ET jettisoned with varying amounts of fuel left in it?