External Tanks in Orbit

Hi all,

Does anyone have any data on what would be required for a shuttle to pull an External Tank all the way into orbit? Assuming modifications were made to allow either a cargo-bay based fuel source to provide the extra boost or a redesigned ET (w/ greater capacity but a similiar weight distribution), what type of obstacles would need to be overcome to get them all the way up?

It seems to me that the ETs (especially the lighter, newer generation) could potentially make extremely valuable living/storage/hydroponics space. Heck, it's already pre-insulated (for holding the fuel)!

Ideas?

Well NASA were complete idiots weren't they?

They could have made provisions for additional boosters to put the external tank into orbit instead of throwing away all that hardware once it gets near space!!

It wouldn't take any extra hardware at all to put the External Tank into orbit. IIRC, it gets to 98% of orbital velocity before the tank is dumped. On the trajectory the first shuttles used, it actually COST energy to make the pitch-up maneuver and ump the tank.

NASA did look at using the ETs for stations early on, but decided they didn't need such a large volume and didn't want to tackle problems like venting residual propellants, controlling such large structures in LEO, etc. In hindsight, it would seem the problems involved should be child's play compared to the struggles to design, build, launch, and assemble the ISS.

At least one nonprofit and one private entity also tried to work out ways to use the tanks in orbit, but were unable to attract funding.

Matt Bille (MattWriter@AOL.com) OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

True. That was with the old "standard insertion" trajectory. The newer "direct insertion" doesn't do this, so there's no energy cost to dump the tank. There is an energy cost to keep it: the propellant required for OMS-2 goes up by about 25% if the ET is still attached. Depending on the insertion altitude, this increases the propellant requirements by 700-3500 lbm. Most ISS assembly flights won't have that much OMS margin to spare, but Columbia's flights, and ISS utilization flights, may.

--

JRF

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: for OMS-2 goes up by about 25% if the ET is still attached. Depending ^^^ : on the insertion altitude, this increases the propellant requirements by : 700-3500 lbm. Most ISS assembly flights won't have that much OMS margin

But, what about cryogenic propellant remaining in the ET?

-- Filip De Vos FilipPC.DeVos@rug.ac.be

There are plenty of ways to empty a solar system. -- John S. Lewis --

OMS-2 is supposed to be performed at the apogee of the post-MECO orbit, to raise the perigee above the atmosphere. Since the orbiter is not at apogee at MECO, this would require the SSMEs to be shut down, and restarted at the OMS-2 time of ignition. However, the SSMEs cannot be restarted after MECO. Simply burning the SSMEs longer at MECO would not do the job; it would raise the apogee further while leaving the perigee within the atmosphere.

--

JRF

Reply-to address spam-proofed - to reply by E-mail, check "Organization" and think one step ahead of IBM.

I confess to not knowing what it would take to make the SSME restartable. You may not want to do that anyway, though locating an extra small hydrogen engine (like an RL-10) at the Shuttle's back-end would be problematic.

: do the job; it would raise the apogee further while leaving the perigee : within the atmosphere.

I thought that the ET-reuse partizans also had plans recovering remaining propellant...

-- Filip De Vos FilipPC.DeVos@rug.ac.be

There are plenty of ways to empty a solar system. -- John S. Lewis --

Joseph Michael (joe99@stellar.dkuzn.co.uk) wrote: : They could have made provisions for additional boosters to put : the external tank into orbit instead of throwing away all that hardware : once it gets near space!!

Actually, throwing away the E.T. just before it reaches orbit is not such a bad idea. It is a very large structure, and almost empty, very light. In a low orbit (the only one reacheable with E.T.), atmospheric drag would quickly force a re-entry. The area were that happened would be unpredictable for more than a day or two in advance. Remember Skylab?

To avoid re-entry and uncontrolled spinning, a large OMS and RCS would be needed, with its own problems as to replenishment and supply (let alone installation).

The problem is exacerbated if every E.T. for every launch is orbited. Orbital parking space or junkyards have been proposed, but for these, the problems of keeping the orbit (and attitude of the stack) would be even more severe. First you would need at least two of them, one in high-inclination flights (51 deg) one for launches due east (28 deg). There your costs are allready doubled.

Undoubtedly it would be possible to bring along one or two E.T.'s into orbit and keep it/them safely in orbit, vent it, convert it into living space etc. ... after a couple of years of engineering and training, provided stable funding etc. In other words never.

Tough Tom Abbott and some others on the NG want otherwise, orbital E.T.'s, like other Shuttle derived stuff (Liquid Fly Back boosters, Shuttle-C, Ares etc), will not ever get off the drawing board.

Additional boosters like you propose would mean re-engineering the whole Shuttle stack. Not trivial (read billions).

Billions better spend funding the next generation of re-useables Unfortunately this means V*, with its own problems. This is still better than trying to stretch basic, marginally capable, late Sixties technologies into the next century.

Could you get your fractal cubes to work for a billion or two?

-- Filip De Vos FilipPC.DeVos@rug.ac.be

There are plenty of ways to empty a solar system. -- John S. Lewis --

Filip De Vos wrote:
> The problem is exacerbated if every E.T. for every launch is orbited.

It's even worse than that. The insertion altitude (where the ETs would be deposited) is considerably lower than the altitude of ISS. Since nodal regression is a function of altitude, an ET deposited at 51.6 deg during an ISS rendezvous would drift out of plane with respect to ISS prior to the next shuttle launch to ISS. This would make it very difficult for the second tank to meet with the first. The stationkeeping costs to keep the ET park co-planar with ISS would be enormous.

The problem is even worse for 28.5 deg because of the lack of a common target for launches at that inclination. You can safely say that all launches at 51.6 deg will go to ISS, but 28.5 deg launches could be doing anything, and their launch windows will be dictated by payload requirements. The ETs will wind up in pretty much random planes with respect to each other.

--

JRF

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For those interested in the background of the ET in Orbit idea, in the June 1991 issue of Ad Astra is an article I wrote summarizing the plans and challenges involved in ET re-use at that time. (The editors chopped it up horribly, but the information is still there.) Unfortunately, I no longer have it in electronic form, but I can Xerox it if someone really wants it and doesn't have access to that magazine.

Matt Bille (MattWriter@AOL.com) OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

Ben:

There have been numerous proposals by aerospace engineers over the past 20 years in treating the ET as a resource for space. Yes, it is quite possible to take an empty shuttle and ET to orbit. It is even possible to build an additional propulsion unit that attaches to the ET and uses an onboard guidance computer to raise that orbit so it won't decay quickly. This is preferable to, and cheaper than, modifying the shuttle fleet.

The ET is released nearly on orbit anyway. There is the OMS propulsion system onboard the shuttle that raises its orbit after the ET is released. The ET also has spare oygen and hydrogen at the time of release. The ET is also filled with moderately pressurized gaseous hydrogen and oxygen. For a tank the size of an ET small ullages can impart measurable delta vees.

I have examined the possibility of placing a propulsion pack that uses spare ET fuel. This pack would be placed inline with the transfer lines connecting the ET with the SSME cluster. The pack consists of two RL10A3 engines, one on each side of the shuttle. When the ET is released, LOX/LH is directed through the RL10 engines and they are ignited. The extra ET propellant is burnt off in these engines while raising the delta vee of the ET.

In fact, if the Shuttle OMS tanks are allowed to remain empty, and the extra mass put in as ET fuel, you can have a mode of operation that permits the ET to attain a permanent orbit as the Shuttle glides back to the launch center. When ET separates in this scenario you're at MECO, and this is perigee of a low Earth orbit. Both Shuttle and ET rise to a low apogee, and there the ET propulsion pack is lit to raise ETs perigee - to a point where the old apogee is now the perigee. Meanwhile the Shuttle continues on its descent to the old perigee where it re-enters and glides back to the launch center. The ET meanwhile reaches its new apogee, circularizes its orbit with its final gasp of propellant. And now you have a rather massive gas tight assembly in orbit.

This assembly could have attached to it a small quantity of hardware to build out the ET into a space habitat or some other structure. Another shuttle flight could bring crew and additional hardware to create a space hotel, or some other large piloted structure. It could also be used as a propellant tank - accumulating propellant for a return to the moon, or a return to Mars.

Some studies have shown that you could build for less than the cost of three Shuttle launches, a rather large habitable structure based around a recovered ET. This would be similar to the old skylab process where we took an SIVB and made the LH tank into a habitable structure. This would be easy to do with the ET.

In fact, NASA and others have done detailed studies of using 'recovered' ETs as space habitats and for piloted mars missions.

I have even designed a rather large vehicle around ET and SSME hardware. A single fully loaded ET can be lifted by 7 SSME. Imagine an ET with a capsule beneath it. This capsule houses 7 SSME. The capsule can be recovered. The ETs cannot. In this design.

Now imagine 7 of these ET/SSME capsule assemblies connected together. From above looking down they look like this:

All 49 engines fire at launch, but the 7 ETs are connected so that they draw propellant from 1,2,6,7 only. The system lifts off, and accelerates. When these 4 ET empty, they are released. The four engine capsules are recovered downrange. Now, the propellant flows from 3 and 5 only, to feed 3,4,5 which are still firing. When 3,5 empty they are released and recovered downrange. Now only 4 remains, and it continues to orbit.

This 7 up assembly could put over 1 million lbs into LEO. In fact, a fully loaded ET with engines, etc., could form the payload of this huge vehicle, and an empty ET could be made into a massive piloted structure and placed atop *that*! So, you'd have a huge ship with 7 ETs clustered around the base, and another modified ET/SSME assembly sitting atop that, and attached to that would be an empty, piloted ET. The ship would be over 500 feet tall, and be capable of carrying large piloted module to the moon's surface or a smaller module to mars' surface.

If the orbital assembly were propelled by nuclear thermal rockets (we have an active program in this area, but we have never flown any of those engines - only test fired them) - if we use NTR we replace the LOX in the orbiting ET, stretch it to double its LH capacity, and still increase the mass again in the piloted structure. This would allow round trips to Mars complete with space station sized accomodations, as well as landings on the moon with the same assets.

The cool part about all of this is that for about half the money already spent on the space station -- this vehicle could be built, and in two launches could place sufficient propellant to maintain a permanent presence on Mars or the moon.

Of course doing this makes good use of existing infrastructure, but it doesn't make good use of NASA labs which Congress has turned into a politically charged pork barrel system. This pork barrelling steals money from programs of steady technical growth and gradual real achievement and spends it on flashy programs that have high political value of high technical risk. So, we have NASP which never flew, ISS, and SSTO, at many multiples of the programs described here.

-William Mook

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Ben Hallert <hallert@mediaone.net> wrote:
> Does anyone have any data on what would be required for a shuttle to
> pull an External Tank all the way into orbit?

Check out http://www.personal.isat.com/fitch/text/et_orbit.htm

TFR

kyfho at firecloud dot com

>Does anyone have any data on what would be required for a shuttle to pull an
>External Tank all the way into orbit?

All it takes is the will to do so (by the appropriate authorities, of course).

>Ideas?

The space shuttle can presently take the ET right into orbit with it, if that's what NASA wants to do.

See this url for more on External Tank's and their potential uses:

http://www.vswap.com/fitch/text/et_orbit.htm

TA

Do you have a cost figure for NASA re: modifying the current setup to haul the ET's all the way to orbit?

-- Chuck Stewart

"Anime-style catgirls: Threat? Menace? Or just studying algebra?"

Just hauling the ET to orbit, NASA would not have to modify the current setup, all they have to do is release the ET a little later than normal. Handling the ET once it separates from the shuttle would require spending some money. To get an idea of how much, two private companies who won bids to outfit ET's in orbit (1989) predicted $100 million and $200 million respectively as the cost to outfit an ET in orbit. These figures were totals to turn the ET into a commercial facility and the guidance and control costs were only part of the total (I don't have a detailed breakdown).

TA

Say, all you want to do is get one ET to a higher orbit, so high that it's drag will not deorbit it for say 10 years. This would need to be higher than 400 miles, perhaps 600 miles would be high enough. If you limit your objective you will lower the cost of your operation, and if you meet your objective you can leverage your "asset" to get a more complex use from your ET- whatever that may be.

Launch a "tug" which will be in orbit prior to the Shuttle launch and be "waiting about 20 miles away" from the Shuttle when it comes up and leaves the ET. The Tug then docks to the ET, uses the ET's fuel, and boosts it to a higher orbit.

Tug needs: A communication system capable of handling teleoperation. One or more good cameras A propulsion system capable of boosting and docking. A way of docking- could be very simple. A refueling capablity.

The excess fuel in the ET should be enough to get it to a higher orbit and still have extra fuel- allowing the tug to do other missions- another ET brought up, etc... The cameras needed for teleoperations could also have other uses- pictures of Earth, ISS operations, or other space missions.

Financing: First this tug doesn't need to be very big, therefore a small launcher could get it into space, and you could use mostly off-the shelf: Roughly a communicate satellite, that uses LH&LOX engine- finding a small enough one might be a problem. If you want to reuse (get another ET) you would need a fuel tank big enough to get back to a lower orbit- you also could brake using the Earth atmosphere. If you put the ET in a eliptical orbit above ISS and say 800 mile, you would reduce this fuel tank requirement.

The camera(s) doesn't have to be too good- good picture up close & some resolution at 50 miles (to see the ET) and the ability point at something independently say 90 degree arc. You could also do this piecemeal by "sponsorship"- communicate and camera components could be paid for. You could sell the ET once it's in a stable orbit, etc...

-gb

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Could the ET's be attached to the finished ISS infrastructure, instead of being placed into a separate orbit ? This would make it a lot easier to refurbish the ET's in orbit, rather than having to go out after them. Would it be possible to add a layer of foam inside the ET, once in orbit. Sort of the reverse of the current design, where the soft layers on the outside protect the hull in the center. If the tank was compromised, The foam would provide a reasonable measure of protection by absorbing the energy. I know that poly urea foam is not well liked by the EPA, But it does make a great insulator and is easy to install.

Special arrangements would have to be made, but yes, the ET could be attached to the space station. It is highly unlikely these "arrangements" will be made anytime soon because NASA has enough to do just getting ISS in orbit.

> Would it be possible to add a layer of foam inside the ET?

Outgassing would be a big problem, and the foam will not provide much protectiion. You would be as safe in an ET and you would be in a space station module, as far as impacts are concerned.

TA

Incorrect. Don't confuse the thickness of the shielding with effectiveness. ISS modules have two layers of shielding, separated by several inches of dead space. The first layer disperses the energy of the strike before it hits the inner layer. The ET provides no such protection. Even if the impact did not completely penetrate the ET, spalling would cause secondary debris to fly across the interior.

--

JRF

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Can't you put the secondary layer inside the pressure vessel? Would the gas not help with slowing down the incoming impact?

Something like take a couple of sheets of Ti, maybe a meter square, and a milimeter thick, take one, stick it on the inside with self-activating glue of some sort, and then it springs out so it's got a half-meter or so between them, along with a little beeper that goes off if it gets hit with spall. Most of the inside is covered with these plates, little is attatched to the surface directly, so the hull is easy to get to.

Get clever, and you might even be able to make the plates collapse onto the hull, under the flow from a puncture, sealing it.

From: "Jorge R. Frank" <jrfrank@ibm-pc.org>
Date: Sun, 01 Aug 1999 17:05:51 -0500

> Can't you put the secondary layer inside the pressure vessel?

You certainly could, but you wouldn't want to put the second layer in prior to launch because of the performance loss you'd take. So you'd have to install it in orbit. It doesn't make Tom's statement valid, since he's comparing ISS modules with the *current* ET.

--

JRF

Reply-to address spam-proofed - to reply by E-mail, check "Organization" and think one step ahead of IBM.

Could you install an Inflatable like a recent Mars Hab proposal, as the inner hull. Then surround that with foam out the the tank of the ET. The foam might absorb the energy of impact, though it probably have to be several feet thick. You would then have secondary hull that was very light. This would eliminate the problem of out gassing, from the foam.

Sure, you can use inflatables, but then what would you need the ET for? NASA tests on TransHab show that it has better impact resistance than aluminum already. You might as well launch your inflatable structure standalone. --

JRF

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Safety, more between you and the elements is always a good thing. Besides how would you move the Hab without deflating it ? Wire the balloon to something solid, just to keep it from rolling around the docking port ?

I imagine you'd do the same thing as TransHab: build the inflatable structure around a rigid core. The core could be a telescoping structure so you could launch it using a smaller launcher. --

JRF

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While prying the lemmings from hir ankles, <edward@shore.net> wrote:
> Safety, more between you and the elements is always a good thing.
>Besides how would you move the Hab without deflating it ? Wire the
>balloon to something solid, just to keep it from rolling around the
>docking port ?

TransHab has a framed metal core. Also, the bag is 18 inches thick, IIRC. It's not like it's a water balloon. :)

-- pixelATshoreDOTnet - http://www.shore.net/~pixel Assistant Forum Manager, MSN IE forums (pix posts a patch prying proximity pitfalls ...um... out of the hedge maze) --William Tanksley, on alt.games.omega

>You certainly could, but you wouldn't want to put the second layer in
>prior to launch because of the performance loss you'd take. So you'd
>have to install it in orbit. It doesn't make Tom's statement valid,
>since he's comparing ISS modules with the *current* ET.

I'm comparing bare-metal space station modules against the bare-metal ET.

TA

>Incorrect. Don't confuse the thickness of the shielding with
>effectiveness.

I don't.

> ISS modules have two layers of shielding, separated by
>several inches of dead space. The first layer disperses the energy of
>the strike before it hits the inner layer. The ET provides no such
>protection. Even if the impact did not completely penetrate the ET,
>spalling would cause secondary debris to fly across the interior.

The space station modules use "blankets" as this added "first layer" of protection. The ET can have "blankets" added to it just as easily. The bare-metal space station module and the bare-metal ET are comparable in impact protection.

TA

>Problem 1: The ET is single-wall Aluminum and is very prone to particle
>impact damage. Worst-case, a hit at the wrong place would cause it to
>pop like a balloon.

An ET won't "pop like a balloon" any more than a space station module would. Compare the wall thickness of the ET to the wall thickness of an international space station module (the ET is thicker). Consider the stress placed on an ET. Also, similar punctures to an ISS module and an ET would be more dangerous for the smaller ISS module because it would take less time for the atmosphere to leak to space.

>Problem 2: The insulation can't tolerate solar UV and would shred into a
>horrible particle ring wreaking havoc with anything (including other
>shuttles) at the same or lower orbital altitude (because the particles
>would slowly decay).

The insulation is stable for the most part, and can be covered or removed without much trouble. A commercially-available defocused electronbeam gun could remove all the insulation in a matter of a few days, and the debris would deorbit in a matter of days also.

>Problem 3: Even if it were pointed into the orbit vector, it's so huge
>that the large amount of drag on it would either greatly overtax a
>chemical orbit-boosting system and deplete it's fuel or require many
>tens of kilowatts to drive an ion system with enough thrust.

One ET would require about seven tons of propellant per year to keep it in orbit. That's less than the international space station will require, and hardly "greatly overtaxing" of a chemical orbit-boosting system.

>You might be able to put the ET into a really high orbit this way:
>
>1. Keep the ET attached for the entire ISS mission.
>
>2. Instead of lowering the ET/OV from 225 x 225 nmi to 225 x 25 nmi, it
>raises itself and the ET to 225 x 425 nmi (keeping enough OMS propellant
>for a deorbit from 425 nmi by OMS-use only).
>
>3. Put the ET out on a 100 nmi tether. At this point the OV is at 205
>nmi and the ET is suspended above it at 305 nmi.
>
>4. Cut the ET loose at apogee. The shuttle is put into a 405 x 25 nmi
>deorbit, and the ET is put into a 405 x 605 nmi storage orbit.
>
>This would work with later resupply flights not carrying major modules.
>You'd also have to either take the insulation off or put some kind of
>huge anti-shred ET-condom on the ET.

TA

Ok, so let me see if I can sum up the recent discussions: