New Second Stages

[spacester]

NASA's new soon-to-be-announced Rocketships - two of them! - will require extensive development of their second stages. My feeling is that our pal Mike Griffin wants some high-capability stages.<br /><br />The first stages will be STS-derived, but will the second stages be "clean sheet" designs?<br /><br />What are the requirements for this critical stage?<br /><br />Does it only have to loft an upper stage to near orbital velocity and then burn up, or do we move to an architecture that quits throwing this expensive hardware away?<br /><br />Many uses of an on-orbit second stage have been proposed - tugs ("orbital refueling") and habitats ("wet lab") being the two that immediately pop to mind.<br /><br /><font color="yellow">How much capability do these second stages need to have in order to optimize America's investment in space transportation infrastructure?</font><br /> <div class="Discussion_UserSignature"> </div>

 

[najab]

As I'm sure you know, the proposed engine for the upper stage is the J-2S - a pretty nifty piece of hardware which is certified for multiple on-orbit restarts. <img src="/images/icons/laugh.gif" />

 

[drwayne]

It can be hard to remember that when the J2 was being developed, there were serious concerns about the mechanics of doing multiple restarts in space.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vogon13]

IIRC, problem (one of many) with restart in orbit is the fuel may not be any where near the drain feed in the tank, just floating around in the tankage. Not good to start up high pressure turbo machinery and cavitate it. USSR had many problems with this too. <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>

 

[strandedonearth]

"IIRC, problem (one of many) with restart in orbit is the fuel may not be any where near the drain feed in the tank, just floating around in the tankage."<br /><br />I've always wondered how they solved this, with any liquid-fuel tanks in space, be it a Saturn S-IVB, or the STS Orbiter's RCS system.

 

[drwayne]

That is correct. The SIVB used a combination of tank venting and ullage motors for fuel settling.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[botch]

I think the saturn IV-B had little rockets on the side to push the fuel back into the bottom of the tank. I'm not sure how the SPS in apollo dealt with the problem.<br /><br />I wonder if you could have some sort of cap inside the tank that starts at the top but gets sucked down as the fuel level lowers, effectively reducing the volume of the tank as you use up propellant? I suppose you would have to inject a gas into the unused section of the tank to create the pressure gradient on either side of the cap. And it'd have to be a good seal aroung the rim to stop fuel leakage.<br />Now that I think about it, it sounds too complicated.

 

[lunatio_gordin]

Could they spin the propellant to get it to settle? it wouldn't take much force, would it?

 

[tap_sa]

<font color="yellow">"I wonder if you could have some sort of cap inside the tank that starts at the top but gets sucked down as the fuel level lowers, effectively reducing the volume of the tank as you use up propellant?"</font><br /><br />At least TRW has tried this in some military ground-to-ground test missile. But instead being sucked the cap was actually a sealed piston which pumped the fuel into reaction chamber. Pressure to drive the piston was generated by solid propellant gas generator.<br /><br />One way to ensure that the area near tank outlet is filled is to cover it with fine metal mesh. Because of surface tension liquids want to stick to such surfaces.<br /><br />Lunatio_Gordin, the idea of rotating tank is a good one, centrifugal force would keep a sidemounted outlet wet. Some additional baffles to partially compartmentalize the area near outlet would help.

 

[mikejz]

How about just an inflatable blatter? I'm thinking this would only work with room storable fuels, due to the gas from boil off...

 

[tap_sa]

That is the standard method for storable roomtemp propellants (usually nitrogen tetroxide and hydrazine) in comsats, deep space probes and spacecrafts. A rubber bladder wouldn freeze and crack in cryogenic temperatures.

 

[mikejz]

Maybe you could use a design somewhat like the Flowmeterics pistionless fuel pump.....<br /><br />

 

[tap_sa]

Flometrics pistonless pump looks quite promising. I'm hoping there will be a real test-vehicle using it soon. According to their site the pump has gone 'gold ie. they are confident enough to seek customers.

 

[gunsandrockets]

"I've always wondered how they solved this, with any liquid-fuel tanks in space, be it a Saturn S-IVB, or the STS Orbiter's RCS system. "<br /><br />From what I read the solution for the Saturn rocket was by briefly opening up only the fuel line to the rocket engine. The hydrogen gas puff venting out of the exhaust provided a gentle acceleration to the rocket thereby settling the propellents to the bottom of the tanks.<br />

 

[scottb50]

A simple piston in a cylinder would work very well. They call this an accumulator. The problem with a bladder, I would think, would be deterioration due to the temperatures, especially LH2. Helium would work to provide the push to the pistons and could be recycled for continuous use. <div class="Discussion_UserSignature"> </div>

 

[mikejz]

Well thining of it,<br /><br />You really only enough fuel to start the engine--so only small amount of the total fuel is needed. Small reserve tanks could do the job.

 

[spacester]

<font color="yellow">How much capability do these second stages need to have in order to optimize America's investment in space transportation infrastructure? </font><br /><br />The posts so far have determined that among the requirements for this new upper stage are that it be restartable. <img src="/images/icons/smile.gif" /> The difficulties of doing so are certainly worthy of discussion, but . . .<br /><br />I was kinda hoping for posts that address the questions I asked . . . <br /><br />Space Tugs?<br /><br />Wet Labs?<br /><br />Have we reached the point where folks are willing to talk about re-use of a second stage?<br /><br />Or are we forever doomed to either burn that valuable hardware up or create still more orbital debris?<br /><br /><font color="yellow">How much capability do these second stages need to have in order to optimize America's investment in space transportation infrastructure? </font><br /> <div class="Discussion_UserSignature"> </div>

 

[strandedonearth]

I'm certainly willing to talk about multi-functional upper stages. If they're saying the second stage of the Stick is to be restartable, then that means it will be in orbit. My next question is will the Stick upper-stage be big enough to function as a wet lab? Oh, wait, that's the SDHLV upper stage that needs to be restartable, I don't know if that's been said for the Stick.<br /><br />The best way to reuse hardware that is traveling at or near orbital velocity is to keep it in orbit, not to try to reenter it. We really need to take a page from Henry Ford's book. When Ford was ordering parts for his Model T's, he specified where the bolt holes had to be placed on the shipping crates. The baffled suppliers complied, and saw the light when Ford took the crates apart and used them for floorboards in his new auto-mobiles. We need to follow his lead in reusing the packaging.<br /><br />I've posted here before about my vision: an upper-stage that is made to be converted into a wet lab. It would already all the MMOD (space debris) protection and insulation wrapped around it. It would already have (or made to easily have) hatches installed, along with standardized fittings inside to mount standardized, modular equipment to (I envision parallel rails that plumbing and wiring could be laid into, then equipment mounted on top). It would need its own RCS, which could be removed when it becomes part of a larger vehicle if it was no longer necessary. There's many other details needed, but it would take too long to go into them all here. It would be heavier than the usual upper stage and therefore reduce the payload, but it would also BE payload, instead of just junk.<br /><br />For a really big wet lab, I started thinking of, say, wet-labbing a Delta 4 CBC. Nix the usual upper stage on the typical Delta 4, and surround the wet-lab version of the CBC with 4 or 6 regular CBC's. Use a smaller engine on the wet-lab to conserve fuel so it can burn all the way to orbit, or just air-light it

 

[gunsandrockets]

"No, that is not correct. Small rocket motors were used to provide a positive force to settle the propellants. "<br /><br />I read about the tank settling method for Saturn in the book "Chariots for Apollo" which was a pretty good book about the Moon Race and the Grumman Lunar Lander. The book credited Von Braun with the hydrogen gas venting method of tank settling. There was quite a bit of detail about it in the book.<br /><br />Can you post a link about the these small rocket motors you write about? It's the first I have heard of them.

 

[drwayne]

The venting maintained a small acceleration. It was one of several ways that the SIVB used to mimimize settling problems - another I recall was the use of a wire mesh. You are right though that the main method was the ullage motors.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[igorsboss]

Please pardon my ignorance, but if I might ask, what is a Wet Lab? I doubt it's a bird dog... Thanks...

 

[drwayne]

A wet lab was an idea in which you used a spent stage (i.e. that had fuel in it, i.e. was wet) and you convert it to a station. There are companies that have proposed using shuttle external tanks for this sort of thing.<br /><br />The contrast is Skylab, which was a dry lab, a dedicated vehicle.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>