RD-0120 for SDHLV?

[propforce]

<font color="yellow">"... The big issue is always reliability. The RS-25 is going to have to be essentially a new engine..... However, they also make the far less expensive (and in some ways the even more robust, and therefore more reliable engine) RS68 engine...."</font><br /><br />I must point out that, if one considers using the RS-68 replacing the SSME for the CaLV, there will be a few "upgrades" on the RS-68 as well, some of which are on-going already. <br /><br />It should be no suprise, to those who're in this industry, to know that each engine is so tailor designed to a specific launch vehicle such that, when one consider its use for another launch vehicle, some "upgrades" are inevitable. We do this as we constantly struggle with weight in any launch vehicles. Payload in most cases, are merely 3~4% of the gross lift off weight of a launch vehicle. <br /><br />Also, while reliability is always important in any space launch. In this case, however; the reliability requirement should be much more relaxed for the CaLV as oppose to the CLV. The CaLV is afterall, an <i>unmanned cargo launch vehicle</i>, therefore the most severe failure mode would be the Loss of Mission (and loss of cargo in this case) but not the Loss of Crew reliability. <div class="Discussion_UserSignature"> </div>

 

[propforce]

<font color="yellow">The scorching part is the worry, particularly as it pertains to man-rating and safety for the SRM skirts: Do we really want to wrap lots of insulation round the base of those 5-Segment monsters? </font><br /><br />The spectacular "hydrogen burn off" on the Delta IV Heavy has to do with how its launch pad was constructed, e.g., an enclosed exhause duct. The "fuel lead" start of RS-68 does pump out quite a bit of hydrogen, but the "enclosed duct" design actually encourage the hydrogen to rise directly up toward top of the vehicle. It would have been much less spectacular if it was launch on "open exhaust" pad such as the Shuttle pad. <br /><br />BTW, I do not believe the CaLV will be required to be "man-rated" as it is an <i>unmanned cargo launch vehicle</i>. But any case, I do not believe these hydrogen burn off will impair the safety and the operation of 5-seqment SRB. The aftskirt of the FSB is made of steel so no insulation will be required. <div class="Discussion_UserSignature"> </div>

 

[mattblack]

Sounds more promising. If the budget squeeze really comes on, I'd say go for a trio of Regeneratively-cooled RS-68s. <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>

 

[frodo1008]

That does sound like what NASA is thinking of. But remember that the Heavy Lift Launch Vehicle is still a long way off! So these are just preliminary parameters at this time!

 

[propforce]

The RS-68 nozzle exit internal diameter (ID) is 89 inches. It is much bigger than the SSME because it only has 50% of chamber pressure (Pc) as the SSME, but has 70% more thrust at Sea Level than the SSME.<br /><br />Keep in mind that the RS-68 has both the HEX exhaust duct as well as the Roll Control Nozzle duct extending down to around the chamber area. The widest part of the engine is around 157 inches (HEX exhaust duct to the RCN exhaust). One has to consider how to 'clock' the engine positions for a multiple engine installation. <br /><br />You can see what I mean about the RS-68 width clearance from this link below. You'll have to do some geometry calculation with the nozzle length and gimbal angle.<br /><br />http://www.boeing.com/defense-space/space/propul/RS68.html <div class="Discussion_UserSignature"> </div>

 

[rfoshaug]

Regarding the possibility for a bigger diameter on the launch vehicle and the need for new tools - it's clear that the ET part of the SDHLV would need substantial redesign anyway because the current ET isn't designed to have 125 tonnes of payload and an upper stage stacked on top of it. So it would need to be considerably stronger than today's ET.<br /><br />How would this affect the tools involved in the manufacturing process compared to if the diameter increases as well? <div class="Discussion_UserSignature"> <p><font color="#ff9900">----------------------------------</font></p><p><font color="#ff9900">My minds have many opinions</font></p> </div>

 

[propforce]

<font color="yellow"><i>"The exit diameter of the SSME I could find, at some 94 inches (just two inches shy of 8 feet), " </i><br /><br />Actually I thought this sounded to big but I did not check it until I got to my office. The SSME exit diameter is only 62 inches. </font><br /><br />The number I have for the SSME exit diameter is around 95 inches. <div class="Discussion_UserSignature"> </div>

 

[propforce]

Interesting. Thanks for the link. <br /><br />I got exit <i>internal</i> diameter (ID) at 90 inches, but thought the OD would be wider. <div class="Discussion_UserSignature"> </div>