RS-68 Engines Considered for the (not so SD)HLV

[spacefire]

with 4 SRBs the HLV would look a lot like the Energia booster and have comparable performance (guessing).<br />It would have some potential to deliver a spaceplane piggyback, maybe a dumbed-down version of the Shuttle. Like taking an orbiter, removing the SSMEs, maybe upgrading the TPS, and putting a pressurized module in the bay, and you have a way to ferry 20 people or more to LEO. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[barrykirk]

Actually come to think of it. Doesn't the space shuttle throttle back it's SSME temporarily around the point of Max Q to keep it from getting to large.<br /><br />Actually, you would probably want to start with the RS-68's fired up and throttle them back slowly as the weight goes down.<br /><br />That serves two purposes.<br /><br />1) If you have a problem lighting the RS-68s, you can abort before lighting up the SRBs.<br /><br />2) We are trying to minimize max G's. At launch, the rocket is the heaviest and you need all the thrust you can get. You only need to throttle back as you burn off fuel and lighten up to prevent going to too many G's.

 

[frodo1008]

I didn't make a definitive statement. I said I THOUGHT that 4 SRB's were under consideration! I actually don't know that this is true, and I didn't say it was true!<br /><br />Now if NASA is going to go with two SRB's then I would suppose that the throw weight to LEO is going to be no more than lifting a fuly loaded orbiter to LEO (as this is the current shuttle configuration).<br /><br />Does this amount to what the SHLV is supposed to be lifting to LEO? Of course, some structure would still have to be dead weight to protect the payload at least, but it would still be a lot less that a fully loaded orbiter I would think!<br /><br />

 

[rfoshaug]

But the SRB's for the SDHLV are 5-segment compared to 4 on the shuttle.<br /><br />And it's got 5 SSME's (or a number of RS-68) compared to 3 SSME's on the shuttle<br /><br />So it's going to have more raw thrust than the shuttle. It's also going to be quite a bit heavier on the launch pad than the shuttle (= more fuel + more payload), so it should logically be able to lift more into LEO than the mass of a fully loaded shuttle. <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>

 

[barrykirk]

OK, I'm confused now.<br /><br />Are you saying that the Shuttle ( orbiter and cargo ) GLOW is 130 tons and the SDLV (payload + fairings ) is 130 tons?<br /><br />The Shuttle uses 3 SMSE and 2 ( 4 segment SRB )<br /><br />The SDLV uses 5 SMSE and 2 ( 5 segment SRB )<br /><br />Does the SDLV have a lot less LOX/LH2 on board?<br /><br />or is it capable of achieving a much higher orbit than the shuttle?

 

[strandedonearth]

Sorry, SG, but it doesn't quite compute here. 5-segment SRB's, more SSME's (or equivalent), stretched ET (er, tankage), second stage, and punching a smaller hole through the atmosphere (smaller frontal cross-section), and it's still the same total mass to orbit as the current STS stack? What are we missing from the equation?

 

[gofer]

I know, now this is a moot point, but has an F-1 like replica been considered for the first stage? Or any other Kerosene engine, for that matter. Of course, the tanks would begin to resemble the Saturn V, and do away with the ET tooling, but since now it seems it's really an all new rocket anyway (with dusting off the J-2 for the second stage, changing the tanks for the RS-68, and what not)

 

[frodo1008]

Also, I can see where if the amount of flights of such a booster reaches a truly reasonable level (say 10 or more per year) where it might even be possible to design and build a true Liquid Engine Fly Back Booster. Or at least a combination of recoverable SRB's and a liquid engine fly back. The point being total reusability!<br /><br />I can see where in the beginning an ELV is going to be the way to go, as it would actually be cheaper to develop initially. But if the flight rate eventually gets much greater, and a heavy build-up of not only moon infrastructure, but other projects between the moon and the Earth might just require a much larger amount of material being placed into LEO. Then the expense of designing and building a true lifting body type of reusable booster might be justified. <br /><br />Of course, by this time the pure private interests of the space tourism industry just might give us some kind of lifting body shape actually lifting at least some 20+ human beings at a time into LEO!<br /><br />While I agree that with NASA's limited funding the current designs are what is best. The future should be left relatively wide open! This should even make the lifting body advocates on this forum happy! And to be frank, so would I (if I am still among the living to see it!)<br />

 

[rfoshaug]

Shuttle_guy,<br /><br />Thanks for the invaluable info you bring to this forum! <img src="/images/icons/smile.gif" /><br /><br />If the SDLV will have about the same Gross Lift Off Weight as the shuttle system and about the same mass-to-orbit as the shuttle, then why does it need larger boosters and more engines?<br /><br />Is it to have some spare capability to be able to reach orbit even with an SSME out just after liftoff, due to the expensive nature of the launch+payload (and lack of capability to land in Spain if anything should break during launch)?<br /><br />Or is it to be able to lift heavier payloads (say 150 metric tonnes) at a later stage in the program, for example for future Mars missions or later-generation lunar missions?<br /><br />Or is it simply to save fuel by accelerating faster during the phases of the flight where you don't throttle down to limit G's? I'm thinking that the faster you can get some speed just after liftoff, the shorter time you "hover" above the launch pad and the less fuel you use. The most inefficient rocket would be one with a thrust-to-weight ratio at liftoff of 1.001 or something like that, using several minutes and hundreds of tonnes of fuel just to clear the tower.<br /><br />But still it seems strange that a rocket with the same liftoff weight and mass-to-orbit as the shuttle, but with less aerodynamic drag would need larger boosters and more engines than the shuttle (which itself jumps quite rapidly off the pad).<br /><br />Any comments? <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>

 

[gofer]

Personally, I do not favor paying my taxes for any "new technologies" like lifting bodies and scramjets and phantom space planes. If those 'new' technologies (quotation marks since they aren't really) are viable let the private interests prove it. I believe we have, and have had for some time (30+years), all the necessary tools to proceed with space exploration. <br /><br />I just think that since the (SD)HLV is beginning to resemble a crazy half-hearted mish-mash of SatrunV/STS/DeltaIV? , perhaps just doing a straight on Saturn -V reproduction would be simpler, cheaper and better? (well, bar state employment politics) F-1 was a relatively cheap, simple and robust (after being debugged) first stage engine with minimal plumbing, chamber pressure and serial production costs. <br />

 

[frodo1008]

Please note that I stated that I do fully support the SDLV as an ELV project at this time. It is going to be a long time before we need such a launch system to even come close to launching 12 launches per year (an average of one a month), so I don't think there is a problem here,<br /><br />However, after the rate reaches this amount (and I truly think it will eventually) then the advantages of developing a totally reuseable system start to come into play. If trade studies show that such a system would then save many billions over the years, then as a taxpayer I would hope that such a system would be adopted! Heck, it may even be true that long before this, the pure private efforts would have developed such a system to save large amounts of money not only for NASA, but for others as well!

 

[nacnud]

Thats one reason why keeping the SSME could be a nice idea, however remote, of making the core stage of aries-v reuseable without having to re-engin it. However it would probably require a couple of perminant Moon out posts and the beginnings of a Mars exploration to get to your 12 launches a year and thats a long way off yet.<br /><br /><br /><br />

 

[barrykirk]

Well, I always liked the Saturn V.... Since most of the mass was the first stage and that is the easiest stage to recover. How much would it have cost to equip it with parachutes and make it re-usable/ recoverable?

 

[barrykirk]

Fuel is the cheapest part of the rocket.<br />"Thrust to weight ratio of 1.001", that's not too far away from a Delta IV heavy launch.<br /><br />Now that is a rocket that would benefit greatly from a little extra thrust at liftoff.

 

[josh_simonson]

According to the chart of HLV options, the side mounted cargo HLV w/ 2 4 segment SRBs and 3 SSMEs (basically shuttle C) only yielded a 67Mt payload. Was the empty ET considered part of the 130 tons to orbit for the STS? That could explain the discrepancy.

 

[barrykirk]

Is that true?<br /><br />Does the ET tank weigh 63 tons?<br /><br />I had no idea it was that much.<br /><br />That is a lot of weight and since it goes all the way to orbit, it's friggin expensive to launch it!!<br /><br />As people who have been following my posts will know, I'm a big fan of LOX/RP-1.<br /><br />I know that a tank of LOX/LH2 goes a lot further than a tank of LOX/RP-1 because of the higher ISP.<br /><br />But the tank for LOX/RP-1 is smaller and lighter because of the higher density of RP-1 and because of the lower insulation requirements of RP-1.<br /><br />Since, in NASA's vision, you burn LOX/LH2 from ground to orbit and their are no drop tanks, how much of the that extra ISP efficiency are they burning by sending a big heavy expensive tank all the way to orbit?

 

[barrykirk]

According to Wikipedia, the most commonly used tank weighed 35 tons with a new verision used since Columbia weighing in at 30 tons.<br /><br />That's still a lot of mass going 95% of the way to orbit, but it's nowhere near the 67 tons from the last two posts.

 

[frodo1008]

Something sort of disturbs me a bit here then. If the new SDLV has a greater GLOW than the current shuttle stack does. Which is the only reason for the greater thrust, as it still only orbits the same throw weight to LEO. Then the only conclusion that we can come to is that the newer system is far less efficient than the 30 year old system? <br /><br />Is it then possible that our friend, the Italian fellow (gaet) might (as annoying as he was) still have had some degree of truth in some of his negative comments of the over all CEV system?<br /><br />Perhaps it has something to do with the upper stages of the SDLV? Perhaps they are not as powerful as running the 3 SSME's on the orbiter + ET for the full 8+ minutes that the current system runs them for? I am a bit confused!

 

[josh_simonson]

Perhaps we're confusing 'payload' with total weight to orbit. Maybe the 5 segment SRBs+5SSME provide 125 tons of payload (inside the fairing) to LEO, while the shuttle C look alike only got 67 tons up once you subtract the now useless fairing and 3 SSMEs. 10 Mt of SSME, and a fairing comparable in weight to the ET get you pretty close to 67 tons left.

 

[josh_simonson]

Here's the HLV section from the ESAS report. I'm pretty sure they're doing an apples to apples comparison. At least I hope so.<br /><br />(old ammo from the gaetanomarano bashing..)

 

[strandedonearth]

I think you're onto something josh. The Shuttle Orbiter includes the SSME's and the OMS engines and tanks. The question should be how much mass would be in orbit if the second stage of the SDHLV was included in the orbited mass (since it would also presumably make it into orbit, unless the payload also had an OMS).<br /><br />Hmm, that was awkward, let me simplify it: what's the mass of the SDHLV's empty second stage, and would the second stage make orbit?

 

[gunsandrockets]

"I've done some rough back-of-the-envelope calculations(!!): If the RS-68s were upgraded in ISP by 5%percent, thrust by 7-9%percent, and the corestage stretched (not fattened) by 5%percent, the CaLV you'd end up with would be 372 feet high. Also, by reducing the parking/assembly orbit to 150 nautical miles (instead of 160) the end LEO payload result should be in the range of 116 tons. Not 124.6 as outlined in ESAS. And this would be using 3x RS-68s, not four as some people suggest."<br /><br />Interesting.<br /><br />I believe the goal for the SDHLV is 125 tonnes only when using a third stage. With just two stages I think the SDHLV is only supposed to lift 109 tonnes or so.<br /><br />That said, your speculation inspired me to crunch some numbers myself. If RS-68 engines replace the SDHLV core-stage SSME on a one for one basis, such a modified vehicle could generate equal liftoff thrust by using the four-segment SRBs. The considerable weight saved from using the smaller SRB could be transferred to a stretched core stage, thereby compensating for the RS-68's lower ISP compared to the SSME.<br /><br />If the stretched core stage made the HLV too tall, maybe that could be countered by using a shorter third stage. The current plan is to use the J-2S with an ISP of about 430 in the third stage. Maybe the third stage could be smaller if it used an engine with a higher ISP than the J-2S. So I like the idea of using the RL-10b engine which has an ISP of 465 and a thrust of around 25,000 lbs. For a smaller third stage, a cluster of five or so RL-10b might do the trick.<br /><br />If a scheme of 4-segment SRB, RS-68, and RL-10b engines for the HLV is used, the greatest benefit is all of these engines are currently in service and in production and therefore no development would be needed.<br /><br />

 

[mattblack]

I think you'd find that the 4-second increased burntime of the 5-Segment SRBs and their better ISP with the HTPB propellant would handily offset the increased GLOW of using the 5-segments in the first place. <div class="Discussion_UserSignature"> <p> </p><p>One Percent of Federal Funding For Space: America <strong><em><u>CAN</u></em></strong> Afford it!!  LEO is a <strong><em>Prison</em></strong> -- It's time for a <em><strong>JAILBREAK</strong></em>!!</p> </div>

 

[propforce]

<font color="yellow">I think the performance increase would be very small and not worth the cost to do the modification. </font><br /><br />Hey S_G, do you know how much time is assumed in the current performance between SRB separation and the J-2X engine ignite? <br /><br /> <div class="Discussion_UserSignature"> </div>

 

[publiusr]

As long as it gets built. Throwing away 15-18 RS-68s with five to six three CBC Delta IV heavies is more expensive in the long run. Remember--the Boeing folks were thinking about new tooling for their own future concepts that would still loft less than SD HLLV.