This thread is to disband the myth that the SSME could act as an upper stage engine. While I think most of us are already in agreement on this, I would like to ensure that the "myth" of the second stage SSME goes no further. It might MIGHT be technically possible but the costs would be astronomical and your upper stage would be so overweight with extra equipment that it might not acheive orbit, and if it did preformance would be nil. CXP initially proposed air start SSME: This was yet another fundamental problem with the logic of CXP. Ares 1 was entirley dependent on the engine being convertable to air start. Once that went out the window so to did Ares 1. SSME requires complex, heavy, equipment to start properly. It is incapable of restarts. You cannot convert the engine to a restartable engine (and if somehow you had the money and managed to pull it off your preformance would be so bad that it wouldn't be worth it.)
Airstarts and restarts are two different things. the SSME can be used for an upperstage, just not one that does restarts.
Regrettably, FinalFrontier, I am unfamiliar with either your academic or industrial background leading to the technical expertise to make such definitive, sweeping statements. But I am greatly interested, and would be delighted to hear you describe in detail: <cut>I look forward to reading your numbers!
So here is the "new" question I would like to answer with this thread: If it can't restart, is there any way it could meet the qualifications of a given user to be an upper stage engine? Not sure about that, seems like most upper stages have to have restart capability.
I think that any useful upper stage engine developed for the future, especially if it is a high-energy cryogenic fuel engine, needs to be restartable. Being able to restart an engine makes it do more than one job, giving the possibility of reduced costs. An even bigger cost advantage would be provided by designing a rocket with only two stages - one big one to boost and a smaller one to both ascend to orbit and to restart for beyond LEO work. - Ed Kyle
Quote from: FinalFrontier on 07/02/2010 06:59 pmSo here is the "new" question I would like to answer with this thread: If it can't restart, is there any way it could meet the qualifications of a given user to be an upper stage engine? Not sure about that, seems like most upper stages have to have restart capability. Depends on the mission role; if LEO or below is the final destination of that stage, then restart unneeded -- see Shuttle and Soyuz, and most cases of solid upper stages. For GEO and higher-energy destinations, it seems to be typical to coast in LEO and await phasing before making a second burn. But Ariana V ECA does not -- the HM7B cryogenic engine isn't restartable, and burns for 15 minutes (WP). I presume they take some orbital geometry performance hit from that, but they're also launching nearly equatorially from Guyana. (BTW, thank you, FF, for constructively re-purposing the thread, and thanks also ChrisB for editing the title and setting policy precedent.)Quote from: edkyle99 on 07/02/2010 11:37 pmI think that any useful upper stage engine developed for the future, especially if it is a high-energy cryogenic fuel engine, needs to be restartable. Being able to restart an engine makes it do more than one job, giving the possibility of reduced costs. An even bigger cost advantage would be provided by designing a rocket with only two stages - one big one to boost and a smaller one to both ascend to orbit and to restart for beyond LEO work. - Ed Kyle Ed, are you alluding to Concept-103? I would assume (not having calculated it) that the heavy dual-J2X upper stage makes for a poor EDS. -Alex
Ed, are you alluding to Concept-103? I would assume (not having calculated it) that the heavy dual-J2X upper stage makes for a poor EDS. -Alex
Quote from: alexw on 07/03/2010 02:07 am Ed, are you alluding to Concept-103? I would assume (not having calculated it) that the heavy dual-J2X upper stage makes for a poor EDS. -AlexI thought so too, but was surprised when I did some calculations. It really should be able to do the claimed 45 tonnes to escape. The "heavy" is all relative. I figured a 260 tonne gross upper stage atop a nearly 3,100 tonne gross first stage. That is roughly (+/- 1%) the same ratio of Centaur to Atlas CCB gross mass - another rocket that can do escape with only two stages. - Ed Kyle
Quote from: edkyle99 on 07/03/2010 05:30 pmQuote from: alexw on 07/03/2010 02:07 am Ed, are you alluding to Concept-103? I would assume (not having calculated it) that the heavy dual-J2X upper stage makes for a poor EDS. -AlexI thought so too, but was surprised when I did some calculations. It really should be able to do the claimed 45 tonnes to escape. The "heavy" is all relative. I figured a 260 tonne gross upper stage atop a nearly 3,100 tonne gross first stage. That is roughly (+/- 1%) the same ratio of Centaur to Atlas CCB gross mass - another rocket that can do escape with only two stages. - Ed KyleHow does it stack up against a JUS (6 rl10b2) for TLI preformance?
Quote from: FinalFrontier on 07/03/2010 05:33 pmQuote from: edkyle99 on 07/03/2010 05:30 pmQuote from: alexw on 07/03/2010 02:07 am Ed, are you alluding to Concept-103? I would assume (not having calculated it) that the heavy dual-J2X upper stage makes for a poor EDS. -AlexI thought so too, but was surprised when I did some calculations. It really should be able to do the claimed 45 tonnes to escape. The "heavy" is all relative. I figured a 260 tonne gross upper stage atop a nearly 3,100 tonne gross first stage. That is roughly (+/- 1%) the same ratio of Centaur to Atlas CCB gross mass - another rocket that can do escape with only two stages. - Ed KyleHow does it stack up against a JUS (6 rl10b2) for TLI preformance? Not sure about "JUS", but the HLLV study compared Concept 103 to a 2x5SRB/5xSSME/4xRL10 in-line. The Shuttle-derived in-line could lift more to TLI/escape, but much less to LEO. It was projected to cost more, however, than 103, which makes sense because 103 only needs two stages versus the four propulsion units of SDV in-line. - Ed Kyle
It was interesting that Apollo 7 did not have the restart stuff on their S-IVB. That saves some weight, not sure how much.
I am not an expert, but a couple things come to mind when you talk about restart of a SSME:1. If you are using liquid hydrogen and oxygen, wouldn't you have a limited time to restart anyway based on the ability of the stage to keep the fuel at the correct temperature?2. I remember that the Saturn V third stage had to have small rocket engines that had to fire prior to the restart in order to push the fuel towards the engine. I would think you would need this same type of setup if using liquid hydrogen and oxygen on a stage that you wanted to use for other things beyond LEO.
Quote from: dks13827 on 07/03/2010 05:54 pm It was interesting that Apollo 7 did not have the restart stuff on their S-IVB. That saves some weight, not sure how much.1500 lbm.
Quote from: Jorge on 07/04/2010 02:30 amQuote from: dks13827 on 07/03/2010 05:54 pm It was interesting that Apollo 7 did not have the restart stuff on their S-IVB. That saves some weight, not sure how much.1500 lbm.IIRC, all the S-IVBs used on Saturn IBs were that way (no TLI, so no need to restart).
so what exactly is 103? A core with a second stage using 2 j2x (rs 68 first stage?) A bit confused, I though 103 was a proposal to use 2 j2xs on the EDS for ares v.......